In Situ Determination of Siderophile Trace Elements in Metals and Sulfides in Enstatite Achondrites

NASA Technical Reports Server (NTRS)

vanAcken, D.; Humayun, M.; Brandon, A. D.; Peslier, A.

2010-01-01

Enstatite meteorites are identified by their extremely reduced mineralogy (1) and similar oxygen isotope composition (2). The enstatite meteorite clan incorporates both EH and EL chondrites, as well as a wide variety of enstatite achondrites, such as aubrites or anomalous enstatite meteorites (e.g. Mt. Egerton, Shallowater, Zaklodzie, NWA 2526). The role of nebular versus planetary processes in the formation of enstatite meteorites is still under debate (e.g. 3-5). Past studies showed a significant influence of metal segregation in the formation of enstatite achondrites. Casanova et al. (6) suggested incomplete metal-silicate segregation during core formation and attributed the unfractionated siderophile element patterns in aubrites metals to a lack of fractional crystallization in a planetary core. Recent studies suggest a significant role of impact melting in the formation of primitive enstatite chondrites (7) and identified NWA 2526 as a partial melt residue of an enstatite chondrite (8). To understand the nature of siderophile element-bearing phases in enstatite achondrites, establish links between enstatite achondrites and enstatite chondrites (9), and constrain planetary differentiation on their respective parent bodies and their petrogenetic histories, we present laser ablation ICP-MS measurements of metal and sulfide phases in Shallowater, Mt. Egerton, and the aubrites Aubres, Cumberland Falls, and Mayo Belwa.

Planetary population synthesis coupled with atmospheric escape: a statistical view of evaporation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, Sheng; Ji, Jianghui; Mordasini, Christoph

2014-11-01

We apply hydrodynamic evaporation models to different synthetic planet populations that were obtained from a planet formation code based on the core-accretion paradigm. We investigated the evolution of the planet populations using several evaporation models, which are distinguished by the driving force of the escape flow (X-ray or EUV), the heating efficiency in energy-limited evaporation regimes, or both. Although the mass distribution of the planet populations is barely affected by evaporation, the radius distribution clearly shows a break at approximately 2 R {sub ⊕}. We find that evaporation can lead to a bimodal distribution of planetary sizes and to anmore » 'evaporation valley' running diagonally downward in the orbital distance—planetary radius plane, separating bare cores from low-mass planets that have kept some primordial H/He. Furthermore, this bimodal distribution is related to the initial characteristics of the planetary populations because low-mass planetary cores can only accrete small primordial H/He envelopes and their envelope masses are proportional to their core masses. We also find that the population-wide effect of evaporation is not sensitive to the heating efficiency of energy-limited description. However, in two extreme cases, namely without evaporation or with a 100% heating efficiency in an evaporation model, the final size distributions show significant differences; these two scenarios can be ruled out from the size distribution of Kepler candidates.« less

Osmium Stable Isotope Composition of Chondrites and Iron Meteorites: Implications for Planetary Core Formation

NASA Astrophysics Data System (ADS)

Nanne, J. A. M.; Millet, M. A.; Burton, K. W.; Dale, C. W.; Nowell, G. M.; Williams, H. M.

2016-12-01

Mass-dependent Os stable isotope fractionation is expected to occur during metal-silicate segregation as well as during crystallization of metal alloys due to the different bonding environment between silicate and metals. As such, Os stable isotopes have the potential to resolve questions pertaining to planetary accretion and differentiation. Here, we present stable Os isotope data for a set of chondrites and iron meteorites to examine the processes associated with core solidification. Carbonaceous, ordinary, and enstatite chondrites show no detectable stable isotope variation with a δ190Os weighted average of +0.12±0.04 (n=37). The uniform composition observed for chondrites implies Os stable isotope homogeneity of the bulk solar nebula. Contrary to chondrites, iron meteorites display a large range in Os stable isotope compositions from δ190Os of +0.05 up to +0.49‰. Variation is only observed in the IIAB and IIIAB irons. Type IVB irons display values similar to chondrites (+0.107±0.047 [n=3]) and IVA compositions are slightly different +0.187±0.004 (n=2). The type IIAB and IIIAB groups show values both within the chondritic range and up to heavier values extending up to +0.49‰. Since core formation in small planetary bodies is expected to quantitatively sequester Os in metal phases, bulk planetary cores are expected to display chondritic δ190Os values. Conversely, samples of the IIAB and IIIAB group display significant variation, possibly indicating that stable isotope fractionation occurred during solidification of the parent-body core. However, no covariation is observed between δ190Os and either Os abundance or radiogenic Os isotope ratios. Instead, liquid immiscibility during core crystallization, where the liquid metal splits into separate S- and P-rich liquids, may be a source of Os stable isotope fractionation.

Formation and Detection of Planetary Systems

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; DeVincenzi, Donald (Technical Monitor)

1999-01-01

Modern theories of star and planet formation and of the orbital stability of planetary systems are described and used to discuss possible characteristics of undiscovered planetary systems. The most detailed models of planetary growth are based upon observations of planets and smaller bodies within our own Solar System and of young stars and their environments. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth as do terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. These models predict that rocky planets should form in orbit about most single stars. It is uncertain whether or not gas giant planet formation is common, because most protoplanetary disks may dissipate before solid planetary cores can grow large enough to gravitationally trap substantial quantities of gas. A potential hazard to planetary systems is radial decay of planetary orbits resulting from interactions with material within the disk. Planets more massive than Earth have the potential to decay the fastest, and may be able to sweep up smaller planets in their path. The implications of the giant planets found in recent radial velocity searches for the abundances of habitable planets are discussed, and the methods that are being used and planned for detecting and characterizing extrasolar planets are reviewed.

Implications of pebble accretion on the composition of hot and cold Jupiters

NASA Astrophysics Data System (ADS)

Bitsch, Bertram; Johansen, Anders; Madhusudhan, Nikku

2016-10-01

The formation of the planetary cores of gas giants via the accretion of planetesimals takes very long and is not compatible with the lifetime of protoplanetary discs (Levison et al. 2010). This time-scale problem can be solved through the accretion of pebbles onto a planetary seed. Contrary to planetesimals, pebbles feel the headwind from the gas which robs them of angular momentum allowing an efficient growth from the entire Hill sphere, which reduces the growth time-scale by several orders of magnitude (Lambrechts & Johansen, 2012; 2014). However, pebble accretion self-terminates when the planets start to open a partial gap in the disc, which accelerates the gas outside of the planets orbit to super-Keplerian speeds and thus stops the flow of pebbles onto the planetary core (Lambrechts et al. 2014). Typically this mass is of the order of 10-20 Earth masses, depending on the local disc properties. The planet can then start to accrete a gaseous envelope without a pollution of pebbles. During its growth, the planet migrates through the disc, which evolves in time (Bitsch et al. 2015a,b).Different volatile species like CO2 or H2O have different condensation temperatures and are thus present in either solid or gaseous form at different locations in the disc. A pebble accreting planet can thus only accrete volatiles that are in solid form, while a gas accreting planet will only accrete volatiles which are in gaseous form. Therefore the final chemical composition of the planetary atmosphere of a giant planet is strongly influenced by the formation location of the initial planetary seed and its subsequent migration path through the disc. Additionally, the envelope can be enriched through the erosion of the planetary core.I will discuss the implications of the formation of planets via pebble accretion and their subsequent migration through the disc on the composition of gas giants. In particular I will focus on the carbon to oxygen ratio of hot Jupiters around other stars and on the carbon to oxygen ratio of Jupiter in our own solar system.

Thermal evolution of trans-Neptunian objects, icy satellites, and minor icy planets in the early solar system

NASA Astrophysics Data System (ADS)

Bhatia, Gurpreet Kaur; Sahijpal, Sandeep

2017-12-01

Numerical simulations are performed to understand the early thermal evolution and planetary scale differentiation of icy bodies with the radii in the range of 100-2500 km. These icy bodies include trans-Neptunian objects, minor icy planets (e.g., Ceres, Pluto); the icy satellites of Jupiter, Saturn, Uranus, and Neptune; and probably the icy-rocky cores of these planets. The decay energy of the radionuclides, 26Al, 60Fe, 40K, 235U, 238U, and 232Th, along with the impact-induced heating during the accretion of icy bodies were taken into account to thermally evolve these planetary bodies. The simulations were performed for a wide range of initial ice and rock (dust) mass fractions of the icy bodies. Three distinct accretion scenarios were used. The sinking of the rock mass fraction in primitive water oceans produced by the substantial melting of ice could lead to planetary scale differentiation with the formation of a rocky core that is surrounded by a water ocean and an icy crust within the initial tens of millions of years of the solar system in case the planetary bodies accreted prior to the substantial decay of 26Al. However, over the course of billions of years, the heat produced due to 40K, 235U, 238U, and 232Th could have raised the temperature of the interiors of the icy bodies to the melting point of iron and silicates, thereby leading to the formation of an iron core. Our simulations indicate the presence of an iron core even at the center of icy bodies with radii ≥500 km for different ice mass fractions.

Natural fracture systems on planetary surfaces: Genetic classification and pattern randomness

NASA Technical Reports Server (NTRS)

Rossbacher, Lisa A.

1987-01-01

One method for classifying natural fracture systems is by fracture genesis. This approach involves the physics of the formation process, and it has been used most frequently in attempts to predict subsurface fractures and petroleum reservoir productivity. This classification system can also be applied to larger fracture systems on any planetary surface. One problem in applying this classification system to planetary surfaces is that it was developed for ralatively small-scale fractures that would influence porosity, particularly as observed in a core sample. Planetary studies also require consideration of large-scale fractures. Nevertheless, this system offers some valuable perspectives on fracture systems of any size.

Planet Formation

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; Fonda, Mark (Technical Monitor)

2002-01-01

Modern theories of star and planet formation and of the orbital stability of planetary systems are described and used to discuss possible characteristics of undiscovered planetary systems. The most detailed models of planetary growth are based upon observations of planets and smaller bodies within our own Solar System and of young stars and their environments. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth as do terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. These models predict that rocky planets should form in orbit about most single stars. It is uncertain whether or not gas giant planet formation is common, because most protoplanetary disks may dissipate before solid planetary cores can grow large enough to gravitationally trap substantial quantities of gas. A potential hazard to planetary systems is radial decay of planetary orbits resulting from interactions with material within the disk. Planets more massive than Earth have the potential to decay the fastest, and may be able to sweep up smaller planets in their path. The implications of the giant planets found in recent radial velocity searches for the abundances of habitable planets are discussed, and the methods that are being used and planned for detecting and characterizing extrasolar planets are reviewed.

The diversity of planetary system architectures: contrasting theory with observations

NASA Astrophysics Data System (ADS)

Miguel, Y.; Guilera, O. M.; Brunini, A.

2011-10-01

In order to explain the observed diversity of planetary system architectures and relate this primordial diversity to the initial properties of the discs where they were born, we develop a semi-analytical model for computing planetary system formation. The model is based on the core instability model for the gas accretion of the embryos and the oligarchic growth regime for the accretion of the solid cores. Two regimes of planetary migration are also included. With this model, we consider different initial conditions based on recent results of protoplanetary disc observations to generate a variety of planetary systems. These systems are analysed statistically, exploring the importance of several factors that define the planetary system birth environment. We explore the relevance of the mass and size of the disc, metallicity, mass of the central star and time-scale of gaseous disc dissipation in defining the architecture of the planetary system. We also test different values of some key parameters of our model to find out which factors best reproduce the diverse sample of observed planetary systems. We assume different migration rates and initial disc profiles, in the context of a surface density profile motivated by similarity solutions. According to this, and based on recent protoplanetary disc observational data, we predict which systems are the most common in the solar neighbourhood. We intend to unveil whether our Solar system is a rarity or whether more planetary systems like our own are expected to be found in the near future. We also analyse which is the more favourable environment for the formation of habitable planets. Our results show that planetary systems with only terrestrial planets are the most common, being the only planetary systems formed when considering low-metallicity discs, which also represent the best environment for the development of rocky, potentially habitable planets. We also found that planetary systems like our own are not rare in the solar neighbourhood, its formation being favoured in massive discs where there is not a large accumulation of solids in the inner region of the disc. Regarding the planetary systems that harbour hot and warm Jupiter planets, we found that these systems are born in very massive, metal-rich discs. Also a fast migration rate is required in order to form these systems. According to our results, most of the hot and warm Jupiter systems are composed of only one giant planet, which is also shown by the current observational data.

On the formation of planetary systems in photoevaporating transition discs

NASA Astrophysics Data System (ADS)

Terquem, Caroline

2017-01-01

In protoplanetary discs, planetary cores must be at least 0.1 M⊕ at 1 au for migration to be significant; this mass rises to 1 M⊕ at 5 au. Planet formation models indicate that these cores form on million year time-scales. We report here a study of the evolution of 0.1 and 1 M⊕ cores, migrating from about 2 and 5 au, respectively, in million year old photoevaporating discs. In such a disc, a gap opens up at around 2 au after a few million years. The inner region subsequently accrete on to the star on a smaller time-scale. We find that, typically, the smallest cores form systems of non-resonant planets beyond 0.5 au with masses up to about 1.5 M⊕. In low-mass discs, the same cores may evolve in situ. More massive cores form systems of a few Earth-mass planets. They migrate within the inner edge of the disc gap only in the most massive discs. Delivery of material to the inner parts of the disc ceases with opening of the gap. Interestingly, when the heavy cores do not migrate significantly, the type of systems that are produced resembles our Solar system. This study suggests that low-mm flux transition discs may not form systems of planets on short orbits but may instead harbour Earth-mass planets in the habitable zone.

Planet Formation - Overview

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.

2005-01-01

Modern theories of star and planet formation are based upon observations of planets and smaller bodies within our own Solar System, exoplanets &round normal stars and of young stars and their environments. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth as do terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. These models predict that rocky planets should form in orbit about most single stars. It is uncertain whether or not gas giant planet formation is common, because most protoplanetary disks may dissipate before solid planetary cores can grow large enough to gravitationally trap substantial quantities of gas. A potential hazard to planetary systems is radial decay of planetary orbits resulting from interactions with material within the disk. Planets more massive than Earth have the potential to decay the fastest, and may be able to sweep up smaller planets in their path.

Iron Isotope Constraints on Planetesimal Core Formation

NASA Astrophysics Data System (ADS)

Jordan, M.; Young, E. D.

2016-12-01

The prevalence of iron in both planetary cores and silicate mantles renders the element a valuable tool for understanding core formation. Magmatic iron meteorites exhibit an enrichment in 57Fe/54Fe relative to chondrites and HED meteorites. This is suggestive of heavy Fe partitioning into the cores of differentiated bodies. If iron isotope fractionation accompanies core formation, we can elucidate details about the history of accretion for planetary bodies as well as their compositions and relative core sizes. The equilibrium 57Fe/54Fe between metal and silicate is necessary for understanding observed iron isotope compositions and placing constraints on core formation. We measure this fractionation in two Aubrite meteorites, Norton County and Mount Egerton, which have known temperatures of equilibration and equilibrated silicon isotopes. Iron was purified using ion-exchange chromatography. Data were collected on a ThermoFinnigan NeptuneTM multiple-collector inductively coupled plasma-source mass spectrometer (MC-ICP-MS) run in wet plasma mode. The measured fractionation Δ57Femetal-silicate is 0.08‰ ± 0.039 (2 SE) for Norton County and 0.09‰ ± 0.019 (2 SE) for Mount Egerton, indicating that the heavy isotopes of Fe partition into the metallic phase. These rocks are in isotopic equilibrium at a temperature of 1130 K and 1200 K ± 80 K, respectively. The concentration of the heavy isotopes of iron in the metallic phase is consistent with recent experimental studies. Using our measured metal-silicate Fe isotope fractionation and the resulting temperature calibration, while taking into account impurities in the metallic phase and temperatures of equilibration, determine that core formation could explain the observed difference between magmatic iron meteorites and chondrites if parent bodies have small cores. In order to verify that Rayleigh distillation during fractional crystallization was not a cause of iron isotope fractionation in iron meteorites, we measured iron isotope ratios in a suite of iron meteorites representing a large range of degrees of fractional crystallization. We find no clear variation in 57Fe/54Fe among these samples.

Platinum Partitioning at Low Oxygen Fugacity: Implications for Core Formation Processes

NASA Technical Reports Server (NTRS)

Medard, E.; Martin, A. M.; Righter, K.; Lanziroti, A.; Newville, M.

2016-01-01

Highly siderophile elements (HSE = Au, Re, and the Pt-group elements) are tracers of silicate / metal interactions during planetary processes. Since most core-formation models involve some state of equilibrium between liquid silicate and liquid metal, understanding the partioning of highly siderophile elements (HSE) between silicate and metallic melts is a key issue for models of core / mantle equilibria and for core formation scenarios. However, partitioning models for HSE are still inaccurate due to the lack of sufficient experimental constraints to describe the variations of partitioning with key variable like temperature, pressure, and oxygen fugacity. In this abstract, we describe a self-consistent set of experiments aimed at determining the valence of platinum, one of the HSE, in silicate melts. This is a key information required to parameterize the evolution of platinum partitioning with oxygen fugacity.

Formation of CaS-MgS in Enstatite Chondrites and Achondrites as a Function of Redox Conditions and Temperature: Constraints on Their Evolution in a Planetesimal and in a Proto-planet

NASA Technical Reports Server (NTRS)

Malavergne, Valerie; Berthet, S.; Righter, K.

2007-01-01

The cubic monosulfide series with the general formula (Mg,Mn,Ca,Fe)S are common phases in the enstatite chondrite (EH) and aubrite meteorite groups. In the Earth s mantle, sulfide minerals are associated with peridotites and eclogites. Study of these sulfide mineral systems is of interest for the mineralogy and petrology of planetary mantles. For example, MgS could occur in the primitive Earth and because it remains a low density phase compared to metal, would stay a separate phase during the core formation process, and thus not segregate to the core. (Mg,Ca,Mn,Fe)S sulphides might thus be important phases even in planetary differentiation processes. The importance of such minerals, and their formation, composition and textural relationships for understanding the genesis of enstatite chondrites and aubrites, has long been recognized. The main objective of this experimental study is to understand the formation and evolution of (Mg,Ca,Mn,Fe)S sulphides, particularly the oldhamite CaS and ningerite MgS, with pressure, temperature but also with redox conditions because EH and aubrites are meteorites that formed under reduced conditions. Piston-cylinder (PC) and multi-anvil (MA) experiments at high pressure (HP) and high temperature (HT) have been performed in order to simulate the evolution of these phases in a small planetary body from a planetesimal (with PC experiments) up to a proto-planet (with MA experiments).

A NEW HYBRID N-BODY-COAGULATION CODE FOR THE FORMATION OF GAS GIANT PLANETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bromley, Benjamin C.; Kenyon, Scott J., E-mail: bromley@physics.utah.edu, E-mail: skenyon@cfa.harvard.edu

2011-04-20

We describe an updated version of our hybrid N-body-coagulation code for planet formation. In addition to the features of our 2006-2008 code, our treatment now includes algorithms for the one-dimensional evolution of the viscous disk, the accretion of small particles in planetary atmospheres, gas accretion onto massive cores, and the response of N-bodies to the gravitational potential of the gaseous disk and the swarm of planetesimals. To validate the N-body portion of the algorithm, we use a battery of tests in planetary dynamics. As a first application of the complete code, we consider the evolution of Pluto-mass planetesimals in amore » swarm of 0.1-1 cm pebbles. In a typical evolution time of 1-3 Myr, our calculations transform 0.01-0.1 M{sub sun} disks of gas and dust into planetary systems containing super-Earths, Saturns, and Jupiters. Low-mass planets form more often than massive planets; disks with smaller {alpha} form more massive planets than disks with larger {alpha}. For Jupiter-mass planets, masses of solid cores are 10-100 M{sub +}.« less

Torques Induced by Scattered Pebble-flow in Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Benítez-Llambay, Pablo; Pessah, Martin E.

2018-03-01

Fast inward migration of planetary cores is a common problem in the current planet formation paradigm. Even though dust is ubiquitous in protoplanetary disks, its dynamical role in the migration history of planetary embryos has not been assessed. In this Letter, we show that the scattered pebble-flow induced by a low-mass planetary embryo leads to an asymmetric dust-density distribution that is able to exert a net torque. By analyzing a large suite of multifluid hydrodynamical simulations addressing the interaction between the disk and a low-mass planet on a fixed circular orbit, and neglecting dust feedback onto the gas, we identify two different regimes, gas- and gravity-dominated, where the scattered pebble-flow results in almost all cases in positive torques. We collect our measurements in a first torque map for dusty disks, which will enable the incorporation of the effect of dust dynamics on migration into population synthesis models. Depending on the dust drift speed, the dust-to-gas mass ratio/distribution, and the embryo mass, the dust-induced torque has the potential to halt inward migration or even induce fast outward migration of planetary cores. We thus anticipate that dust-driven migration could play a dominant role during the formation history of planets. Because dust torques scale with disk metallicity, we propose that dust-driven outward migration may enhance the occurrence of distant giant planets in higher-metallicity systems.

New Clues to the Mysterious Origin of Wide-Separation Planetary-Mass Companions

NASA Astrophysics Data System (ADS)

Bryan, Marta

2018-01-01

Over the past decade, direct imaging searches for young gas giant planets have revealed a new population of young planetary-mass companions with extremely wide orbital separations (>50 AU) and masses near or at the deuterium-burning limit. These companions pose significant challenges to standard formation models, including core accretion, disk instability, and turbulent fragmentation. In my talk I will discuss new results from high-contrast imaging and high-resolution infrared spectroscopy of a sample of directly imaged wide-separation companions that can be used to directly test these three competing formation mechanisms. First, I use high-contrast imaging to strongly discount scattering as a hypothesis for the origin of wide-separation companions. Second, I measure rotation rates of a subset of these companions using their near-IR spectra, and place the first constraints on the angular momentum evolution of young planetary-mass objects. Finally, I explore the ability of high-resolution spectroscopy to constrain the atmospheric C/O ratios of these companions, providing a complementary test of competing formation scenarios.

Implications of the giant planets for the formation and evolution of planetary systems

NASA Technical Reports Server (NTRS)

Stevenson, David J.

1989-01-01

The giant planet region in the solar system appears to be bounded inside by the limit of water condensation, suggesting that the most abundant astrophysical condensate plays an important role in giant planet formation. Indeed, Jupiter and Saturn exhibit evidence for rock and/or ice cores or central concentrations that probably accumulated first, acting as nuclei for subsequent gas accumulation. This is a 'planetary' accumulation process, distinct from the stellar formation process, even though most of Jupiter has a similar composition to the primordial sun. Uranus and Neptune appear to exhibit evidence of an important role for giant impacts in their structure and evolution. No simple picture emerges for the temperature structure of the solar nebula from observations alone. However, it seems likely that Jupiter is the key to the planetary system, and a similar planet could be expected for other systems. The data and inferences from these data are summarized for the entire known solar system beyond the asteroid belt.

Formation and Internal Structure of Terrestrial Planets, and Atmospheric Escape

NASA Astrophysics Data System (ADS)

Jin, S.

2014-11-01

As of 2014 April 21, over 1490 confirmed exoplanets and 3705 Kepler candidates have been detected. This implies that exoplanets may be ubiquitous in the universe. In this paper, we focus on the formation, evolution, and internal structure of terrestrial planets, and the atmospheric escape of close-in planets. In chapter 2, we investigate the dynamical evolution of planetary system after the protoplanetary disk has dissipated. We find that in the final assembly stage, the occurrence of terrestrial planets is quite common and in 40% of our simulations finally at least one planet is formed in the habitable zone. We also find that if there is a highly-inclined giant planet in the system, a great many bodies will be either driven out of the system, or collide with the giant planet or the central star. This will lead to the difficulty in planetary accretion. Moreover, our results show that planetary migration can lead to the formation of close-in planets. Besides migration, close-in terrestrial planets can also be formed by a collision-merger mechanism, which means that planetary embryos can kick terrestrial planets directly into orbits that are extremely close to their parent stars. In chapter 3, we construct numerically an internal structure model for terrestrial planets, and provide three kinds of possible internal structures of Europa (Jupiter's moon) based on this model. Then, we calculate the radii of low-mass exoplanets for various mass combinations of core and mantle, and find that some of them are inconsistent with the observed radius of rocky planets. This phenomenon can be explained only if there exists a large amount of water in the core, or they own gaseous envelopes. In chapter 4, we improve our planetary evolution codes using the semi-gray model of Guillot (2010), which includes the incident flux from the host star as a heating source in planetary atmosphere. The updated codes can solve the structure of the top radiative zone of intensely irradiated planets, and thus can simulate the atmospheric escape of close-in planets driven by strong stellar X-ray or EUV emissions. We find that low-mass planets are sensitive to the atmospheric escape, and they could lose all their initial H/He envelopes during the evolution. On the other hand, gas giant can only lose a small fraction of their initial envelopes. We then carry out a parameter study of atmospheric escape at the planetary core mass, envelope mass fraction, and semi-major axis space. We find that the most intense phase of evaporation occurs within the early 100 Myr. Afterwards, atmospheric escape only has a small impact on the planetary evolution. In chapter 5, we apply our new planetary evolution model to different synthetic planet populations that are directly produced by the core-accretion paradigm (Mordasini et al. 2012a,b). We show that although the mass distribution of the planet populations is hardly affected by evaporation, the radius distribution clearly shows a break around 2 R_{⊕}. This break leads to a bimodal distribution in planet sizes (Owen & Wu 2013). Furthermore, the bimodal distribution is related to the initial characteristics of the planetary populations. We find that in two extreme cases, namely without any evaporation or with a 100% heating efficiency in the evaporation model, the final radius distributions show significant differences compared to the radius distribution of Kepler candidates. In chapter 6, we introduce a radiative transfer model that can calculate the radiation spectrum of close-in exoplanets.

Extended halos and intracluster light using Planetary Nebulae as tracers in nearby clusters

NASA Astrophysics Data System (ADS)

Arnaboldi, Magda

Since the first detection of intracluster planetary nebulae in 1996, imaging and spectroscopic surveys identified such stars to trace the radial extent and the kinematics of diffuse light in clusters. This topic of research is tightly linked with the studies of galaxy formation and evolution in dense environment, as the spatial distribution and kinematics of planetary nebulae in the outermost regions of galaxies and in the cluster cores is relevant for setting constraints on cosmological simulations. In this sense, extragalactic planetary nebulae play a very important role in the near-field cosmology, in order to measure the integrated mass as function of radius and the orbital distribution of stars in structures placed in the densest regions of the nearby universe.

From Disks to Planets: The Making of Planets and Their Early Atmospheres. An Introduction

NASA Astrophysics Data System (ADS)

Lammer, Helmut; Blanc, Michel

2018-03-01

This paper is an introduction to volume 56 of the Space Science Series of ISSI, "From disks to planets—the making of planets and their proto-atmospheres", a key subject in our quest for the origins and evolutionary paths of planets, and for the causes of their diversity. Indeed, as exoplanet discoveries progressively accumulated and their characterization made spectacular progress, it became evident that the diversity of observed exoplanets can in no way be reduced to the two classes of planets that we are used to identify in the solar system, namely terrestrial planets and gas or ice giants: the exoplanet reality is just much broader. This fact is no doubt the result of the exceptional diversity of the evolutionary paths linking planetary systems as a whole as well as individual exoplanets and their proto-atmospheres to their parent circumstellar disks: this diversity and its causes are exactly what this paper explores. For each of the main phases of the formation and evolution of planetary systems and of individual planets, we summarize what we believe we understand and what are the important open questions needing further in-depth examination, and offer some suggestions on ways towards solutions. We start with the formation mechanisms of circumstellar disks, with their gas and disk components in which chemical composition plays a very important role in planet formation. We summarize how dust accretion within the disk generates planet cores, while gas accretion on these cores can lead to the diversity of their fluid envelopes. The temporal evolution of the parent disk itself, and its final dissipation, put strong constraints on how and how far planetary formation can proceed. The radiation output of the central star also plays an important role in this whole story. This early phase of planet evolution, from disk formation to dissipation, is characterized by a co-evolution of the disk and its daughter planets. During this co-evolution, planets and their protoatmospheres not only grow, but they also migrate radially as a result of their interaction with the disk, thus moving progressively from their distance of formation to their final location. The formation of planetary fluid envelopes (proto-atmospheres and oceans), is an essential product of this planet formation scenario which strongly constrains their possible evolution towards habitability. We discuss the effects of the initial conditions in the disk, of the location, size and mass of the planetary core, of the disk lifetime and of the radiation output and activity of the central star, on the formation of these envelopes and on their relative extensions with respect to the planet core. Overall, a fraction of the planets retain the primary proto-atmosphere they initially accreted from the gas disk. For those which lose it in this early evolution, outgassing of volatiles from the planetary core and mantle, together with some contributions of volatiles from colliding bodies, give them a chance to form a "secondary" atmosphere, like that of our own Earth. When the disk finally dissipates, usually before 10 Million years of age, it leaves us with the combination of a planetary system and a debris disk, each with a specific radial distribution with respect to their parent star(s). Whereas the dynamics of protoplanetary disks is dominated by gas-solid dynamical coupling, debris disks are dominated by gravitational dynamics acting on diverse families of planetesimals. Solid-body collisions between them and giant impacts on young planetary surfaces generate a new population of gas and dust in those disks. Synergies between solar system and exoplanet studies are particularly fruitful and need to be stimulated even more, because they give access to different and complementary components of debris disks: whereas the different families of planetesimals can be extensively studied in the solar system, they remain unobserved in exoplanet systems. But, in those systems, long-wavelength telescopic observations of dust provide a wealth of indirect information about the unobserved population of planetesimals. Promising progress is being currently made to observe the gas component as well, using millimetre and sub-millimetre giant radio interferometers. Within planetary systems themselves, individual planets are the assembly of a solid body and a fluid envelope, including their planetary atmosphere when there is one. Their characteristics range from terrestrial planets through sub-Neptunes and Neptunes and to gas giants, each type covering most of the orbital distances probed by present-day techniques. With the continuous progress in detection and characterization techniques and the advent of major providers of new data like the Kepler mission, the architecture of these planetary systems can be studied more and more accurately in a statistically meaningful sense and compared to the one of our own solar system, which does not appear to be an exceptional case. Finally, our understanding of exoplanets atmospheres has made spectacular advances recently using the occultation spectroscopy techniques implemented on the currently operating space and ground-based observing facilities. The powerful new observing facilities planned for the near and more distant future will make it possible to address many of the most challenging current questions of the science of exoplanets and their systems. There is little doubt that, using this new generation of facilities, we will be able to reconstruct more and more accurately the complex evolutionary paths which link stellar genesis to the possible emergence of habitable worlds.

Models of the Earth's Core.

PubMed

Stevenson, D J

1981-11-06

Combined inferences from seismology, high-pressure experiment and theory, geomagnetism, fluid dynamics, and current views of terrestrial planetary evolution lead to models of the earth's core with the following properties. Core formation was contemporaneous with earth accretion; the core is not in chemical equilibrium with the mantle; the outer core is a fluid iron alloy containing significant quantities of lighter elements and is probably almost adiabatic and compositionally uniform; the more iron-rich inner solid core is a consequence of partial freezing of the outer core, and the energy release from this process sustains the earth's magnetic field; and the thermodynamic properties of the core are well constrained by the application of liquid-state theory to seismic and laboratory data.

Formation of Giant Planets and Brown Dwarves

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.

2003-01-01

According to the prevailing core instability model, giant planets begin their growth by the accumulation of small solid bodies, as do terrestrial planets. However, unlike terrestrial planets, the growing giant planet cores become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. Models predict that rocky planets should form in orbit about most stars. It is uncertain whether or not gas giant planet formation is common, because most protoplanetary disks may dissipate before solid planetary cores can grow large enough to gravitationally trap substantial quantities of gas. Ongoing theoretical modeling of accretion of giant planet atmospheres, as well as observations of protoplanetary disks, will help decide this issue. Observations of extrasolar planets around main sequence stars can only provide a lower limit on giant planet formation frequency . This is because after giant planets form, gravitational interactions with material within the protoplanetary disk may cause them to migrat inwards and be lost to the central star. The core instability model can only produce planets greater than a few jovian masses within protoplanetary disks that are more viscous than most such disks are believed to be. Thus, few brown dwarves (objects massive enough to undergo substantial deuterium fusion, estimated to occur above approximately 13 jovian masses) are likely to be formed in this manner. Most brown dwarves, as well as an unknown number of free-floating objects of planetary mass, are probably formed as are stars, by the collapse of extended gas/dust clouds into more compact objects.

Core formation, wet early mantle, and H2O degassing on early Mars

NASA Technical Reports Server (NTRS)

Kuramoto, K.; Matsui, T.

1993-01-01

Geophysical and geochemical observations strongly suggest a 'hot origin of Mars,' i.e., the early formation of both the core and the crust-mantle system either during or just after planetary accretion. To consider the behavior of H2O in the planetary interior it is specifically important to determine by what mechanism the planet is heated enough to cause melting. For Mars, the main heat source is probably accretional heating. Because Mars is small, the accretion energy needs to be effectively retained in its interior. Therefore, the three candidates of heat retention mechanism are discussed first: (1) the blanketing effect of the primordial H2-He atmosphere; (2) the blanketing effect of the impact-induced H2O-CO2 atmosphere; and (3) the higher deposition efficiency of impact energy due to larger impacts. It was concluded that (3) the is the most plausible mechanism for Mars. Then, its possible consequence on how wet the early martian mantle was is discussed.

Planetary Nebulae and their parent stellar populations. Tracing the mass assembly of M87 and Intracluster light in the Virgo cluster core

NASA Astrophysics Data System (ADS)

Arnaboldi, Magda; Longobardi, Alessia; Gerhard, Ortwin

2016-08-01

The diffuse extended outer regions of galaxies are hard to study because they are faint, with typical surface brightness of 1% of the dark night sky. We can tackle this problem by using resolved star tracers which remain visible at large distances from the galaxy centers. This article describes the use of Planetary Nebulae as tracers and the calibration of their properties as indicators of the star formation history, mean age and metallicity of the parent stars in the Milky Way and Local Group galaxies. We then report on the results from a deep, extended, planetary nebulae survey in a 0.5 deg2 region centered on the brightest cluster galaxy NGC 4486 (M87) in the Virgo cluster core, carried out with SuprimeCam@Subaru and FLAMES-GIRAFFE@VLT. Two planetary nebulae populations are identified out to 150 kpc distance from the center of M87. One population is associated with the M87 halo and the second one with the intracluster light in the Virgo cluster core. They have different line-of-sight velocity and spatial distributions, as well as different planetary nebulae specific frequencies and luminosity functions. The intracluster planetary nebulae in the surveyed region correspond to a luminosity of four times the luminosity of the Large Magellanic Cloud. The M87 halo planetary nebulae trace an older, more metal-rich, parent stellar population. A substructure detected in the projected phase-space of the line-of-sight velocity vs. major axis distance for the M87 halo planetary nebulae provides evidence for the recent accretion event of a satellite galaxy with luminosity twice that of M33. The satellite stars were tidally stripped about 1 Gyr ago, and reached apocenter at a major axis distance of 60-90 kpc from the center of M87. The M87 halo is still growing significantly at the distances where the substructure is detected.

Chondritic Mn/Na ratio and limited post-nebular volatile loss of the Earth

NASA Astrophysics Data System (ADS)

Siebert, Julien; Sossi, Paolo A.; Blanchard, Ingrid; Mahan, Brandon; Badro, James; Moynier, Frédéric

2018-03-01

The depletion pattern of volatile elements on Earth and other differentiated terrestrial bodies provides a unique insight as to the nature and origin of planetary building blocks. The processes responsible for the depletion of volatile elements range from the early incomplete condensation in the solar nebula to the late de-volatilization induced by heating and impacting during planetary accretion after the dispersion of the H2-rich nebular gas. Furthermore, as many volatile elements are also siderophile (metal-loving), it is often difficult to deconvolve the effect of volatility from core formation. With the notable exception of the Earth, all the differentiated terrestrial bodies for which we have samples have non-chondritic Mn/Na ratios, taken as a signature of post-nebular volatilization. The bulk silicate Earth (BSE) is unique in that its Mn/Na ratio is chondritic, which points to a nebular origin for the depletion; unless the Mn/Na in the BSE is not that of the bulk Earth (BE), and has been affected by core formation through the partitioning of Mn in Earth's core. Here we quantify the metal-silicate partitioning behavior of Mn at deep magma ocean pressure and temperature conditions directly applicable to core formation. The experiments show that Mn becomes more siderophile with increasing pressure and temperature. Modeling the partitioning of Mn during core formation by combining our results with previous data at lower P-T conditions, we show that the core likely contains a significant fraction (20 to 35%) of Earth's Mn budget. However, we show that the derived Mn/Na value of the bulk Earth still lies on the volatile-depleted end of a trend defined by chondritic meteorites in a Mn/Na vs Mn/Mg plot, which tend to higher Mn/Na with increasing volatile depletion. This suggests that the material that formed the Earth recorded similar chemical fractionation processes for moderately volatile elements as chondrites in the solar nebula, and experienced limited post nebular volatilization.

Redox Variations in Early Solar System Materials and Implications for Late Stage Planetary Accretion and Planet Formation

NASA Technical Reports Server (NTRS)

Righter, K.

2017-01-01

Oxygen fugacity plays an important role in determining the detailed physical and chemical aspects of planets and their building blocks. Basic chemical properties such as the amount of oxidized Fe in a mantle (as FeO), the nature of alloying elements in the core (S, C, H, O, Si), and the solubility of various volatile elements in the silicate and metallic portions of embryos and planets can influence physical properties such as the size of the core, the liquidus and solidus of the mantle and core, and the speciation of volatile compounds contributing to atmospheres. This paper will provide an overview of the range of fO2 variation observed in primitive and differentiated materials that may have participated in accretion (cosmic dust, Star-dust and meteorites), a comparison to observations of planetary fO2 (Mercury, Mars and Earth), and a discus-sion of timing of variation of fO2 within both early and later accreted materials. This overview is meant to promote discussion and interaction between students of these two stages of planet formation to identify areas where more work is needed.

Timing of the formation and migration of giant planets as constrained by CB chondrites

PubMed Central

Johnson, Brandon C.; Walsh, Kevin J.; Minton, David A.; Krot, Alexander N.; Levison, Harold F.

2016-01-01

The presence, formation, and migration of giant planets fundamentally shape planetary systems. However, the timing of the formation and migration of giant planets in our solar system remains largely unconstrained. Simulating planetary accretion, we find that giant planet migration produces a relatively short-lived spike in impact velocities lasting ~0.5 My. These high-impact velocities are required to vaporize a significant fraction of Fe,Ni metal and silicates and produce the CB (Bencubbin-like) metal-rich carbonaceous chondrites, a unique class of meteorites that were created in an impact vapor-melt plume ~5 My after the first solar system solids. This indicates that the region where the CB chondrites formed was dynamically excited at this early time by the direct interference of the giant planets. Furthermore, this suggests that the formation of the giant planet cores was protracted and the solar nebula persisted until ~5 My. PMID:27957541

Timing of the formation and migration of giant planets as constrained by CB chondrites.

PubMed

Johnson, Brandon C; Walsh, Kevin J; Minton, David A; Krot, Alexander N; Levison, Harold F

2016-12-01

The presence, formation, and migration of giant planets fundamentally shape planetary systems. However, the timing of the formation and migration of giant planets in our solar system remains largely unconstrained. Simulating planetary accretion, we find that giant planet migration produces a relatively short-lived spike in impact velocities lasting ~0.5 My. These high-impact velocities are required to vaporize a significant fraction of Fe,Ni metal and silicates and produce the CB (Bencubbin-like) metal-rich carbonaceous chondrites, a unique class of meteorites that were created in an impact vapor-melt plume ~5 My after the first solar system solids. This indicates that the region where the CB chondrites formed was dynamically excited at this early time by the direct interference of the giant planets. Furthermore, this suggests that the formation of the giant planet cores was protracted and the solar nebula persisted until ~5 My.

Defining the Core Archive Data Standards of the International Planetary Data Alliance (IPDA)

NASA Technical Reports Server (NTRS)

Hughes, J. Steven; Crichton, Dan; Beebe, Reta; Guinness, Ed; Heather, David; Zender, Joe

2007-01-01

A goal of the International Planetary Data Alliance (lPDA) is to develop a set of archive data standards that enable the sharing of scientific data across international agencies and missions. To help achieve this goal, the IPDA steering committee initiated a six month proj ect to write requirements for and draft an information model based on the Planetary Data System (PDS) archive data standards. The project had a special emphasis on data formats. A set of use case scenarios were first developed from which a set of requirements were derived for the IPDA archive data standards. The special emphasis on data formats was addressed by identifying data formats that have been used by PDS nodes and other agencies in the creation of successful data sets for the Planetary Data System (PDS). The dependency of the IPDA information model on the PDS archive standards required the compilation of a formal specification of the archive standards currently in use by the PDS. An ontology modelling tool was chosen to capture the information model from various sources including the Planetary Science Data Dictionary [I] and the PDS Standards Reference [2]. Exports of the modelling information from the tool database were used to produce the information model document using an object-oriented notation for presenting the model. The tool exports can also be used for software development and are directly accessible by semantic web applications.

Formation of Jupiter and Saturn

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; Young, Richard E. (Technical Monitor)

1998-01-01

An overview of current theories of the formation of our Solar System, with emphasis on giant planets, is presented. The most detailed models are based upon observations of planets and smaller bodies within our own Solar System and of young stars and their environments. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth as do terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. Larger disk mass allows for faster growth of solid planetary bodies. The ability of a solid planet to trap gas from the protoplanetary disk increases rapidly as its mass increases (because the depth of its gravitational potential well increases), but decreases as the planetesimal accretion rate is increased (as it becomes hotter). The net effect of increasing disk mass is that gas giant planets form more rapidly, but with larger core masses. Observations of circumstellar disks suggest an upper bound on the time available prior to dissipation of the gas, and planetary models place upper limits on core sizes. Together, these constraints suggest that Jupiter and Saturn formed in 1-10 million years, and the density of solids in the region of their formation was a few times as large as the lower bound provided by the traditional minimum mass nebula.

Formation of Jupiter and Saturn

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; DeVincenzi, Donald L. (Technical Monitor)

1998-01-01

An overview of current theories of the formation of our Solar System, with emphasis on giant planets, is presented. The most detailed models are based upon observations of planets and smaller bodies within our own Solar System and of young stars and their environments. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth as do terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. Larger disk mass allows for faster growth of solid planetary bodies. The ability of a solid planet to trap gas from the protoplanetary disk increases rapidly as its mass increases (because the depth of its gravitational potential well increases), but decreases as the planetesimal accretion rate is increased (as it becomes hotter). The net effect of increasing disk mass is that gas giant planets form more rapidly, but with larger core masses. Observations of circumstellar disks suggest an upper bound on the time available prior to dissipation of the gas, and planetary models place upper limits on core sizes. Together, these constraints suggest that Jupiter and Saturn formed in 1 - 10 million years, and the density of solids in the region of their formation was a few times as large as the lower bound provided by the traditional minimum mass nebula.

Models of the earth's core

NASA Technical Reports Server (NTRS)

Stevenson, D. J.

1981-01-01

Combined inferences from seismology, high-pressure experiment and theory, geomagnetism, fluid dynamics, and current views of terrestrial planetary evolution lead to models of the earth's core with five basic properties. These are that core formation was contemporaneous with earth accretion; the core is not in chemical equilibrium with the mantle; the outer core is a fluid iron alloy containing significant quantities of lighter elements and is probably almost adiabatic and compositionally uniform; the more iron-rich inner solid core is a consequence of partial freezing of the outer core, and the energy release from this process sustains the earth's magnetic field; and the thermodynamic properties of the core are well constrained by the application of liquid-state theory to seismic and labroatory data.

Depletion of Vandium in Planetary Mantles: Controlled by Metal, Oxide, or Silicate?

NASA Technical Reports Server (NTRS)

Righter, Kevin

2006-01-01

Vanadium concentrations in planetary mantles can provide information about the conditions during early accretion and differentiation. Because V is a slightly siderophile element, it is usually assumed that any depletion would be due to core formation and metal-silicate equilibrium. However, V is typically more compatible in phases such as spinel, magnesiowuestite and garnet. Fractionation of all of these phases would cause depletions more marked than those from metal. In this paper consideration of depletions due to metal, oxide and silicate are critically evaluated.

Phase Equilibrium Investigations of Planetary Materials

NASA Technical Reports Server (NTRS)

Grove, T. L.

1997-01-01

This grant provided funds to carry out experimental studies designed to illuminate the conditions of melting and chemical differentiation that has occurred in planetary interiors. Studies focused on the conditions of mare basalt generation in the moon's interior and on processes that led to core formation in the Shergottite Parent Body (Mars). Studies also examined physical processes that could lead to the segregation of metal-rich sulfide melts in an olivine-rich solid matrix. The major results of each paper are discussed below and copies of the papers are attached as Appendix I.

Silver contents and Cu/Ag ratios in Martian meteorites and the implications for planetary differentiation

NASA Astrophysics Data System (ADS)

Wang, Zaicong; Becker, Harry

2017-11-01

Silver and Cu show very similar partitioning behavior in sulfide melt-silicate melt and metal-silicate systems at low and high pressure-temperature (P-T) experimental conditions, implying that mantle melting, fractional crystallization and core-mantle differentiation have at most modest (within a factor of 3) effects on Cu/Ag ratios. For this reason, it is likely that Cu/Ag ratios in mantle-derived magmatic products of planetary bodies reflect that of the mantle and, in some circumstances, also the bulk planet composition. To test this hypothesis, new Ag mass fractions and Cu/Ag ratios in different groups of Martian meteorites are presented and compared with data from chondrites and samples from the Earth's mantle. Silver contents in lherzolitic, olivine-phyric and basaltic shergottites and nakhlites range between 1.9 and 12.3 ng/g. The data display a negative trend with MgO content and correlate positively with Cu contents. In spite of displaying variable initial Ɛ143Nd values and representing a diverse spectrum of magmatic evolution and physiochemical conditions, shergottites and nakhlites display limited variations of Cu/Ag ratios (1080 ± 320, 1 s, n = 14). The relatively constant Cu/Ag suggests limited fractionation of Ag from Cu during the formation and evolution of the parent magmas, irrespectively of whether sulfide saturation was attained or not. The mean Cu/Ag ratio of Martian meteorites thus reflects that of the Martian mantle and constrains its Ag content to 1.9 ± 0.7 ng/g (1 s). Carbonaceous and enstatite chondrites display a limited range of Cu/Ag ratios of mostly 500-2400. Ordinary chondrites show a larger scatter of Cu/Ag up to 4500, which may have been caused by Ag redistribution during parent body metamorphism. The majority of chondrites have Cu/Ag ratios indistinguishable from the Martian mantle value, indicating that Martian core formation strongly depleted Cu and Ag contents, but probably did not significantly change the Cu/Ag ratio of the mantle compared to bulk Mars. Bulk Mars is richer in moderately volatile elements than Earth, however, the Martian mantle displays a much stronger depletion of the moderately volatile elements Cu and Ag, e.g., by a factor of 15 for Cu. This observation is consistent with experimental studies suggesting that core formation at low P-T conditions on Mars led to more siderophile behavior of Cu and Ag than at high P-T conditions as proposed for Earth. In contrast, Cu/Ag ratios of the mantles of Mars and Earth (Cu/AgEarth = 3500 ± 1000) display only a difference by a factor of 3, which implies restricted fractionation of Cu and Ag even at high P-T conditions. The concentration data support the notion that siderophile element partitioning during planetary core formation scales with the size of the planetary body, which is particularly important for the differentiation of large terrestrial planets such as Earth. Collectively, the Ag and Cu data on magmatic products from the mantles of Mars and Earth and the data on chondrites confirm experimental predictions and support the limited fractionation of Cu and Ag during planetary core formation and high-temperature magmatic evolution, and probably also in early solar nebular processes.

New Indivisible Planetary Science Paradigm: Consequence of Questioning Popular Paradigms

NASA Astrophysics Data System (ADS)

Marvin Herndon, J.

2014-05-01

Progress in science involves replacing less precise understanding with more precise understanding. In science and in science education one should always question popular ideas; ask "What's wrong with this picture?" Finding limitations, conflicts or circumstances that require special ad hoc consideration sometimes is the key to making important discoveries. For example, from thermodynamic considerations, I found that the 'standard model of solar system formation' leads to insufficiently massive planetary cores. That understanding led me to discover a new indivisible planetary science paradigm. Massive-core planets formed by condensing and raining-out from within giant gaseous protoplanets at high pressures and high temperatures, accumulating heterogeneously on the basis of volatility with liquid core-formation preceding mantle-formation; the interior states of oxidation resemble that of the Abee enstatite chondrite. Core-composition was established during condensation based upon the relative solubilities of elements, including uranium, in liquid iron in equilibrium with an atmosphere of solar composition at high pressures and high temperatures. Uranium settled to the central region and formed planetary nuclear fission reactors, producing heat and planetary magnetic fields. Earth's complete condensation included a ~300 Earth-mass gigantic gas/ice shell that compressed the rocky kernel to about 66% of Earth's present diameter. T-Tauri eruptions, associated with the thermonuclear ignition of the Sun, stripped the gases away from the Earth and the inner planets. The T-Tauri outbursts stripped a portion of Mercury's incompletely condensed protoplanet and transported it to the region between Mars and Jupiter where it fused with in-falling oxidized condensate from the outer regions of the Solar System, forming the parent matter of ordinary chondrite meteorites, the main-Belt asteroids, and veneer for the inner planets, especially Mars. With its massive gas/ice shell removed, pressure began to build in the compressed rocky kernel of Earth and eventually the rigid crust began to crack. The major energy source for planetary decompression and for heat emplacement at the base of the crust is the stored energy of protoplanetary compression. In response to decompression-driven volume increases, cracks form to increase surface area and fold-mountain ranges form to accommodate changes in curvature. One of the most profound mysteries of modern planetary science is this: As the terrestrial planets are more-or-less of common chondritic composition, how does one account for the marked differences in their surface dynamics? Differences among the inner planets are principally due to the degree of compression experienced. Planetocentric georeactor nuclear fission, responsible for magnetic field generation and concomitant heat production, is applicable to compressed and non-compressed planets and large moons. The internal composition of Mercury is calculated based upon an analogy with the deep-Earth mass ratio relationships. The origin and implication of Mercurian hydrogen geysers is described. Besides Earth, only Venus appears to have sustained protoplanetary compression; the degree of which might eventually be estimated from understanding Venetian surface geology. A basis is provided for understanding that Mars essentially lacks a 'geothermal gradient' which implies potentially greater subsurface water reservoir capacity than previously expected. Resources at NuclearPlanet.com .

Core layering

NASA Astrophysics Data System (ADS)

Jacobson, S. A.; Rubie, D. C.; Hernlund, J. W.; Morbidelli, A.

2015-12-01

We have created a planetary accretion and differentiation model that self-consistently builds and evolves Earth's core. From this model, we show that the core grows stably stratified as the result of rising metal-silicate equilibration temperatures and pressures, which increases the concentrations of light element impurities into each newer core addition. This stable stratification would naturally resist convection and frustrate the onset of a geodynamo, however, late giant impacts could mechanically mix the distinct accreted core layers creating large homogenous regions. Within these regions, a geodynamo may operate. From this model, we interpret the difference between the planetary magnetic fields of Earth and Venus as a difference in giant impact histories. Our planetary accretion model is a numerical N-body integration of the Grand Tack scenario [1]—the most successful terrestrial planet formation model to date [2,3]. Then, we take the accretion histories of Earth-like and Venus-like planets from this model and post-process the growth of each terrestrial planet according to a well-tested planetary differentiation model [4,5]. This model fits Earth's mantle by modifying the oxygen content of the pre-cursor planetesimals and embryos as well as the conditions of metal-silicate equilibration. Other non-volatile major, minor and trace elements included in the model are assumed to be in CI chondrite proportions. The results from this model across many simulated terrestrial planet growth histories are robust. If the kinetic energy delivered by larger impacts is neglected, the core of each planet grows with a strong stable stratification that would significantly impede convection. However, if giant impact mixing is very efficient or if the impact history delivers large impacts late, than the stable stratification can be removed. [1] Walsh et al. Nature 475 (2011) [2] O'Brien et al. Icarus 223 (2014) [3] Jacobson & Morbidelli PTRSA 372 (2014) [4] Rubie et al. EPSL 301 (2011) [5] Rubie et al. Icarus 248 (2015)

Lunar and Planetary Science XXXV: Terrestrial Planets: Building Blocks and Differentiation

NASA Technical Reports Server (NTRS)

2004-01-01

The session "Terrestrial Planets: Building Blocks and Differentiation: included the following topics:Magnesium Isotopes in the Earth, Moon, Mars, and Pallasite Parent Body: High-Precision Analysis of Olivine by Laser-Ablation Multi-Collector ICPMS; Meteoritic Constraints on Collision Rates in the Primordial Asteroid Belt and Its Origin; New Constraints on the Origin of the Highly Siderophile Elements in the Earth's Upper Mantle; Further Lu-Hf and Sm-Nd Isotopic Data on Planetary Materials and Consequences for Planetary Differentiation; A Deep Lunar Magma Ocean Based on Neodymium, Strontium and Hafnium Isotope Mass Balance Partial Resetting on Hf-W System by Giant Impacts; On the Problem of Metal-Silicate Equilibration During Planet Formation: Significance for Hf-W Chronometry ; Solid Metal-Liquid Metal Partitioning of Pt, Re, and Os: The Effect of Carbon; Siderophile Element Abundances in Fe-S-Ni-O Melts Segregated from Partially Molten Ordinary Chondrite Under Dynamic Conditions; Activity Coefficients of Silicon in Iron-Nickel Alloys: Experimental Determination and Relevance for Planetary Differentiation; Reinvestigation of the Ni and Co Metal-Silicate Partitioning; Metal/Silicate Paritioning of P, Ga, and W at High Pressures and Temperatures: Dependence on Silicate Melt Composition; and Closure of the Fe-S-Si Liquid Miscibility Gap at High Pressure and Its Implications for Planetary Core Formation.

Fossil Cores In The Kepler Data

NASA Astrophysics Data System (ADS)

Jackson, Brian

Most gas giant exoplanets with orbital periods < few days are unstable against tidal decay and may be tidally disrupted before their host stars leave the main sequence. These gas giants probably contain rocky/icy cores, and so their cores will be stranded near their progenitor's Roche limit (few hours orbital period). These fossil cores will evade the Kepler mission's transit search because it is focused on periods > 0.5 days, but finding these fossil cores would provide unprecedented insights into planetary interiors and formation ? e.g., they would be a smoking gun favoring formation of gas giants via core accretion. We propose to search for and characterize fossil cores in the Kepler dataset. We will vet candidates using the Kepler photometry and auxiliary data, collect ground-based spectra of the host stars and radial-velocity (RV) and adaptive optics (AO) data to corroborate candidates. We will also constrain stellar tidal dissipation efficiencies (parameterized by Q) by determining our survey's completeness, elucidating dynamical origins and evolution of exoplanets even if we find no fossil cores. Our preliminary search has already found several dozen candidates, so the proposed survey has a high likelihood of success.

Carbon and sulfur budget of the silicate Earth explained by accretion of differentiated planetary embryos

NASA Astrophysics Data System (ADS)

Li, Yuan; Dasgupta, Rajdeep; Tsuno, Kyusei; Monteleone, Brian; Shimizu, Nobumichi

2016-10-01

The abundances of volatile elements in the Earth's mantle have been attributed to the delivery of volatile-rich material after the main phase of accretion. However, no known meteorites could deliver the volatile elements, such as carbon, nitrogen, hydrogen and sulfur, at the relative abundances observed for the silicate Earth. Alternatively, Earth could have acquired its volatile inventory during accretion and differentiation, but the fate of volatile elements during core formation is known only for a limited set of conditions. Here we present constraints from laboratory experiments on the partitioning of carbon and sulfur between metallic cores and silicate mantles under conditions relevant for rocky planetary bodies. We find that carbon remains more siderophile than sulfur over a range of oxygen fugacities; however, our experiments suggest that in reduced or sulfur-rich bodies, carbon is expelled from the segregating core. Combined with previous constraints, we propose that the ratio of carbon to sulfur in the silicate Earth could have been established by differentiation of a planetary embryo that was then accreted to the proto-Earth. We suggest that the accretion of a Mercury-like (reduced) or a sulfur-rich (oxidized) differentiated body--in which carbon has been preferentially partitioned into the mantle--may explain the Earth's carbon and sulfur budgets.

The Effects of Core Composition on Iron Isotope Fractionation During Planetary Differentiation

NASA Astrophysics Data System (ADS)

Elardo, S. M.; Shahar, A.; Caracas, R.; Mock, T. D.; Sio, C. K. I.

2018-05-01

High pressure and temperature isotope exchange experiments and density functional theory calculations show how the composition of planetary cores affects the fractionation of iron isotopes during planetary differentiation.

Complex organic molecules and star formation

NASA Astrophysics Data System (ADS)

Bacmann, A.; Faure, A.

2014-12-01

Star forming regions are characterised by the presence of a wealth of chemical species. For the past two to three decades, ever more complex organic species have been detected in the hot cores of protostars. The evolution of these molecules in the course of the star forming process is still uncertain, but it is likely that they are partially incorporated into protoplanetary disks and then into planetesimals and the small bodies of planetary systems. The complex organic molecules seen in star forming regions are particularly interesting since they probably make up building blocks for prebiotic chemistry. Recently we showed that these species were also present in the cold gas in prestellar cores, which represent the very first stages of star formation. These detections question the models which were until now accepted to account for the presence of complex organic molecules in star forming regions. In this article, we shortly review our current understanding of complex organic molecule formation in the early stages of star formation, in hot and cold cores alike and present new results on the formation of their likely precursor radicals.

Iron isotopic fractionation between silicate mantle and metallic core at high pressure

PubMed Central

Liu, Jin; Dauphas, Nicolas; Roskosz, Mathieu; Hu, Michael Y.; Yang, Hong; Bi, Wenli; Zhao, Jiyong; Alp, Esen E.; Hu, Justin Y.; Lin, Jung-Fu

2017-01-01

The +0.1‰ elevated 56Fe/54Fe ratio of terrestrial basalts relative to chondrites was proposed to be a fingerprint of core-mantle segregation. However, the extent of iron isotopic fractionation between molten metal and silicate under high pressure–temperature conditions is poorly known. Here we show that iron forms chemical bonds of similar strengths in basaltic glasses and iron-rich alloys, even at high pressure. From the measured mean force constants of iron bonds, we calculate an equilibrium iron isotope fractionation between silicate and iron under core formation conditions in Earth of ∼0–0.02‰, which is small relative to the +0.1‰ shift of terrestrial basalts. This result is unaffected by small amounts of nickel and candidate core-forming light elements, as the isotopic shifts associated with such alloying are small. This study suggests that the variability in iron isotopic composition in planetary objects cannot be due to core formation. PMID:28216664

Planet traps and first planets: The critical metallicity for gas giant formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hasegawa, Yasuhiro; Hirashita, Hiroyuki, E-mail: yasu@asiaa.sinica.edu.tw, E-mail: hirashita@asiaa.sinica.edu.tw

2014-06-10

The ubiquity of planets poses an interesting question: when are first planets formed in galaxies? We investigate this by adopting a theoretical model where planet traps are combined with the standard core accretion scenario in which the efficiency of forming planetary cores directly relates to the metallicity ([Fe/H]) in disks. Three characteristic exoplanetary populations are examined: hot Jupiters, exo-Jupiters around 1 AU, and low-mass planets in tight orbits, such as super-Earths. We statistically compute planet formation frequencies (PFFs), as well as the orbital radius (〈R{sub rapid}〉) within which gas accretion becomes efficient enough to form Jovian planets, as a functionmore » of metallicity (–2 ≤ [Fe/H] ≤–0.6). We show that the total PFFs for these three populations increase steadily with metallicity. This is the direct outcome of the core accretion picture. For the metallicity range considered here, the population of low-mass planets dominates Jovian planets. The Jovian planets contribute to the PFFs above [Fe/H] ≅ –1. We find that the hot Jupiters form more efficiently than the exo-Jupiters at [Fe/H] ≲ –0.7. This arises from the slower growth of planetary cores and their more efficient radial inward transport by the host traps in lower metallicity disks. We show that the critical metallicity for forming Jovian planets is [Fe/H] ≅ –1.2 by comparing 〈R{sub rapid}〉 of hot Jupiters and low-mass planets. The comparison intrinsically links to the different gas accretion efficiency between these two types of planets. Therefore, this study implies that important physical processes in planet formation may be tested by exoplanet observations around metal-poor stars.« less

Simulation of the planetary interior differentiation processes in the laboratory.

PubMed

Fei, Yingwei

2013-11-15

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to that layered structure, (1) percolation of liquid metal in a solid silicate matrix by planet differentiation, and (2) inner core crystallization by subsequent planet cooling. We conduct high-pressure and high-temperature experiments to simulate both processes in the laboratory. Formation of percolative planetary core depends on the efficiency of melt percolation, which is controlled by the dihedral (wetting) angle. The percolation simulation includes heating the sample at high pressure to a target temperature at which iron-sulfur alloy is molten while the silicate remains solid, and then determining the true dihedral angle to evaluate the style of liquid migration in a crystalline matrix by 3D visualization. The 3D volume rendering is achieved by slicing the recovered sample with a focused ion beam (FIB) and taking SEM image of each slice with a FIB/SEM crossbeam instrument. The second set of experiments is designed to understand the inner core crystallization and element distribution between the liquid outer core and solid inner core by determining the melting temperature and element partitioning at high pressure. The melting experiments are conducted in the multi-anvil apparatus up to 27 GPa and extended to higher pressure in the diamond-anvil cell with laser-heating. We have developed techniques to recover small heated samples by precision FIB milling and obtain high-resolution images of the laser-heated spot that show melting texture at high pressure. By analyzing the chemical compositions of the coexisting liquid and solid phases, we precisely determine the liquidus curve, providing necessary data to understand the inner core crystallization process.

Simulation of the Planetary Interior Differentiation Processes in the Laboratory

PubMed Central

Fei, Yingwei

2013-01-01

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to that layered structure, (1) percolation of liquid metal in a solid silicate matrix by planet differentiation, and (2) inner core crystallization by subsequent planet cooling. We conduct high-pressure and high-temperature experiments to simulate both processes in the laboratory. Formation of percolative planetary core depends on the efficiency of melt percolation, which is controlled by the dihedral (wetting) angle. The percolation simulation includes heating the sample at high pressure to a target temperature at which iron-sulfur alloy is molten while the silicate remains solid, and then determining the true dihedral angle to evaluate the style of liquid migration in a crystalline matrix by 3D visualization. The 3D volume rendering is achieved by slicing the recovered sample with a focused ion beam (FIB) and taking SEM image of each slice with a FIB/SEM crossbeam instrument. The second set of experiments is designed to understand the inner core crystallization and element distribution between the liquid outer core and solid inner core by determining the melting temperature and element partitioning at high pressure. The melting experiments are conducted in the multi-anvil apparatus up to 27 GPa and extended to higher pressure in the diamond-anvil cell with laser-heating. We have developed techniques to recover small heated samples by precision FIB milling and obtain high-resolution images of the laser-heated spot that show melting texture at high pressure. By analyzing the chemical compositions of the coexisting liquid and solid phases, we precisely determine the liquidus curve, providing necessary data to understand the inner core crystallization process. PMID:24326245

Planetary exploration through year 2000: A core Program, part 1

NASA Technical Reports Server (NTRS)

1983-01-01

The Core Program, goals for planetary exploration, continuity and expansion, core program missions, mission implementation, anticipated accomplishments, resource requirements, and near term budget decisions are discussed.

Low hydrogen contents in the cores of terrestrial planets.

PubMed

Clesi, Vincent; Bouhifd, Mohamed Ali; Bolfan-Casanova, Nathalie; Manthilake, Geeth; Schiavi, Federica; Raepsaet, Caroline; Bureau, Hélène; Khodja, Hicham; Andrault, Denis

2018-03-01

Hydrogen has been thought to be an important light element in Earth's core due to possible siderophile behavior during core-mantle segregation. We reproduced planetary differentiation conditions using hydrogen contents of 450 to 1500 parts per million (ppm) in the silicate phase, pressures of 5 to 20 GPa, oxygen fugacity varying within IW-3.7 and IW-0.2 (0.2 to 3.7 log units lower than iron-wüstite buffer), and Fe alloys typical of planetary cores. We report hydrogen metal-silicate partition coefficients of ~2 × 10 -1 , up to two orders of magnitude lower than reported previously, and indicative of lithophile behavior. Our results imply H contents of ~60 ppm in the Earth and Martian cores. A simple water budget suggests that 90% of the water initially present in planetary building blocks was lost during planetary accretion. The retained water segregated preferentially into planetary mantles.

The Chesapeake Bay Impact Crater: An Educational Investigation for Students into the Planetary Impact Process and its Environmental Consequences

NASA Technical Reports Server (NTRS)

Levine, Arlene S.

2008-01-01

Planetary impact craters are a common surface feature of many planetary bodies, including the Earth, the Moon, Mars, Mercury, Venus, and Jupiter s moons, Ganymede and Callisto. The NASA Langley Research Center in Hampton, VA, is located about 5 km inside the outer rim of the Chesapeake Bay Impact Crater. The Chesapeake Bay Impact Crater, with a diameter of 85 km is the sixth largest impact crater on our planet. The U.S. Geological Survey (USGS), in collaboration with the NASA Langley Research Center, the Virginia Department of Environmental Quality (VDEQ), the Hampton Roads Planning District Commission (HRPDC), and the Department of Geology of the College of William and Mary (WM) drilled into and through the crater at the NASA Langley Research Center and obtained a continuous core to a depth of 2075.9 ft (632.73 meters) from the Chesapeake Bay Impact Crater. At the NASA Langley location, the granite basement depth was at 2046 ft (623.87 meters). This collaborative drilling activity provided a unique educational opportunity and ongoing educational partnership between USGS, NASA Langley and the other collaborators. NASA Langley has a decade-long, ongoing educational partnership with the Colonial Coast Council of the Girl Scouts. The core drilling and on site analysis and cataloguing of the core segments provided a unique opportunity for the Girl Scouts to learn how geologists work in the field, their tools for scientific investigation and evaluation, how they perform geological analyses of the cores in an on-site tent and learn about the formation of impact craters and the impact of impacting bodies on the sub-surface, the surface, the oceans and atmosphere of the target body. This was accomplished with a two-part activity. Girl Scout day camps and local Girl Scout troops were invited to Langley Research Center Conference Center, where more than 300 Girl Scouts, their leaders and adult personnel were given briefings by scientists and educators from the USGS, NASA, VDEQ, HRPDC and WM on the principles of geology, the formation of impact craters, the consequences of the impacting body on the atmosphere, ocean, surface and sub-surface, the geological, chemical and biological analyses of the core and the cataloguing and storage of the core segments, etc. After the briefings, the Girl Scouts visited the drilling site where they inspected the core drilling rig, examined the core samples and discussed the drilling procedures, cores and interpretation of the cores with scientists and educators from the organizations conducting the core drilling. Demonstrations at the drilling site included demonstrations of impacting objects hitting multi-colored layered mud targets at different angles of entry. The multi-colored layers of mud were instructive in mapping out the distribution of impact-ejected material around the impact crater. The presentation will include a series of photographs of the Girl Scout participating in activities at the Chesapeake Bay Impact Crater drill site, including retrieving cores from the drilling rig, inspecting the core samples and participating in the impact-crater formation demonstrations.

Giant Planet Formation

NASA Astrophysics Data System (ADS)

D'Angelo, G.; Durisen, R. H.; Lissauer, J. J.

2010-12-01

Gas giant planets play a fundamental role in shaping the orbital architecture of planetary systems and in affecting the delivery of volatile materials to terrestrial planets in the habitable zones. Current theories of gas giant planet formation rely on either of two mechanisms: the core accretion model and the disk instability model. In this chapter, we describe the essential principles upon which these models are built and discuss the successes and limitations of each model in explaining observational data of giant planets orbiting the Sun and other stars.

Pebble-isolation mass: Scaling law and implications for the formation of super-Earths and gas giants

NASA Astrophysics Data System (ADS)

Bitsch, Bertram; Morbidelli, Alessandro; Johansen, Anders; Lega, Elena; Lambrechts, Michiel; Crida, Aurélien

2018-04-01

The growth of a planetary core by pebble accretion stops at the so-called pebble isolation mass, when the core generates a pressure bump that traps drifting pebbles outside its orbit. The value of the pebble isolation mass is crucial in determining the final planet mass. If the isolation mass is very low, gas accretion is protracted and the planet remains at a few Earth masses with a mainly solid composition. For higher values of the pebble isolation mass, the planet might be able to accrete gas from the protoplanetary disc and grow into a gas giant. Previous works have determined a scaling of the pebble isolation mass with cube of the disc aspect ratio. Here, we expand on previous measurements and explore the dependency of the pebble isolation mass on all relevant parameters of the protoplanetary disc. We use 3D hydrodynamical simulations to measure the pebble isolation mass and derive a simple scaling law that captures the dependence on the local disc structure and the turbulent viscosity parameter α. We find that small pebbles, coupled to the gas, with Stokes number τf < 0.005 can drift through the partial gap at pebble isolation mass. However, as the planetary mass increases, particles must be decreasingly smaller to penetrate the pressure bump. Turbulent diffusion of particles, however, can lead to an increase of the pebble isolation mass by a factor of two, depending on the strength of the background viscosity and on the pebble size. We finally explore the implications of the new scaling law of the pebble isolation mass on the formation of planetary systems by numerically integrating the growth and migration pathways of planets in evolving protoplanetary discs. Compared to models neglecting the dependence of the pebble isolation mass on the α-viscosity, our models including this effect result in higher core masses for giant planets. These higher core masses are more similar to the core masses of the giant planets in the solar system.

Sensitivities of Earth's core and mantle compositions to accretion and differentiation processes

NASA Astrophysics Data System (ADS)

Fischer, Rebecca A.; Campbell, Andrew J.; Ciesla, Fred J.

2017-01-01

The Earth and other terrestrial planets formed through the accretion of smaller bodies, with their core and mantle compositions primarily set by metal-silicate interactions during accretion. The conditions of these interactions are poorly understood, but could provide insight into the mechanisms of planetary core formation and the composition of Earth's core. Here we present modeling of Earth's core formation, combining results of 100 N-body accretion simulations with high pressure-temperature metal-silicate partitioning experiments. We explored how various aspects of accretion and core formation influence the resulting core and mantle chemistry: depth of equilibration, amounts of metal and silicate that equilibrate, initial distribution of oxidation states in the disk, temperature distribution in the planet, and target:impactor ratio of equilibrating silicate. Virtually all sets of model parameters that are able to reproduce the Earth's mantle composition result in at least several weight percent of both silicon and oxygen in the core, with more silicon than oxygen. This implies that the core's light element budget may be dominated by these elements, and is consistent with ≤1-2 wt% of other light elements. Reproducing geochemical and geophysical constraints requires that Earth formed from reduced materials that equilibrated at temperatures near or slightly above the mantle liquidus during accretion. The results indicate a strong tradeoff between the compositional effects of the depth of equilibration and the amounts of metal and silicate that equilibrate, so these aspects should be targeted in future studies aiming to better understand core formation conditions. Over the range of allowed parameter space, core and mantle compositions are most sensitive to these factors as well as stochastic variations in what the planet accreted as a function of time, so tighter constraints on these parameters will lead to an improved understanding of Earth's core composition.

On the Terminal Rotation Rates of Giant Planets

NASA Astrophysics Data System (ADS)

Batygin, Konstantin

2018-04-01

Within the general framework of the core-nucleated accretion theory of giant planet formation, the conglomeration of massive gaseous envelopes is facilitated by a transient period of rapid accumulation of nebular material. While the concurrent build-up of angular momentum is expected to leave newly formed planets spinning at near-breakup velocities, Jupiter and Saturn, as well as super-Jovian long-period extrasolar planets, are observed to rotate well below criticality. In this work, we demonstrate that the large luminosity of a young giant planet simultaneously leads to the generation of a strong planetary magnetic field, as well as thermal ionization of the circumplanetary disk. The ensuing magnetic coupling between the planetary interior and the quasi-Keplerian motion of the disk results in efficient braking of planetary rotation, with hydrodynamic circulation of gas within the Hill sphere playing the key role of expelling spin angular momentum to the circumstellar nebula. Our results place early-stage giant planet and stellar rotation within the same evolutionary framework, and motivate further exploration of magnetohydrodynamic phenomena in the context of the final stages of giant planet formation.

Oxygen isotope variation in stony-iron meteorites.

PubMed

Greenwood, R C; Franchi, I A; Jambon, A; Barrat, J A; Burbine, T H

2006-09-22

Asteroidal material, delivered to Earth as meteorites, preserves a record of the earliest stages of planetary formation. High-precision oxygen isotope analyses for the two major groups of stony-iron meteorites (main-group pallasites and mesosiderites) demonstrate that each group is from a distinct asteroidal source. Mesosiderites are isotopically identical to the howardite-eucrite-diogenite clan and, like them, are probably derived from the asteroid 4 Vesta. Main-group pallasites represent intermixed core-mantle material from a single disrupted asteroid and have no known equivalents among the basaltic meteorites. The stony-iron meteorites demonstrate that intense asteroidal deformation accompanied planetary accretion in the early Solar System.

Structure of exoplanets

PubMed Central

Spiegel, David S.; Fortney, Jonathan J.; Sotin, Christophe

2014-01-01

The hundreds of exoplanets that have been discovered in the past two decades offer a new perspective on planetary structure. Instead of being the archetypal examples of planets, those of our solar system are merely possible outcomes of planetary system formation and evolution, and conceivably not even especially common outcomes (although this remains an open question). Here, we review the diverse range of interior structures that are both known and speculated to exist in exoplanetary systems—from mostly degenerate objects that are more than 10× as massive as Jupiter, to intermediate-mass Neptune-like objects with large cores and moderate hydrogen/helium envelopes, to rocky objects with roughly the mass of Earth. PMID:24379369

Structure of exoplanets.

PubMed

Spiegel, David S; Fortney, Jonathan J; Sotin, Christophe

2014-09-02

The hundreds of exoplanets that have been discovered in the past two decades offer a new perspective on planetary structure. Instead of being the archetypal examples of planets, those of our solar system are merely possible outcomes of planetary system formation and evolution, and conceivably not even especially common outcomes (although this remains an open question). Here, we review the diverse range of interior structures that are both known and speculated to exist in exoplanetary systems--from mostly degenerate objects that are more than 10× as massive as Jupiter, to intermediate-mass Neptune-like objects with large cores and moderate hydrogen/helium envelopes, to rocky objects with roughly the mass of Earth.

Core segregation mechanism and compositional evolution of terretrial planets

NASA Astrophysics Data System (ADS)

Petford, N.; Rushmer, T.

2009-04-01

A singular event in the formation of the earth and terrestrial planets was the separation iron-rich melt from mantle silicate to form planetary cores. On Earth, and by implication other rocky planets, this process induced profound internal chemical fractionation, with siderophile elements (Ni, Co, Au, Pt, W, Re) following Fe into the core, leaving the silicate crust and mantle with strong depletions of these elements relative to primitive planetary material. Recent measurements of radiogenic 182W anomalies in the silicate Earth, Mars and differentiated meteorites imply that planetesimals segregated metallic cores within a few Myr of the origin of the solar system. Various models have been put forward to explain the physical nature of the segregation mechanism (Fe-diapirs, ‘raining' through a magma ocean), and more recently melt flow via fractures. In this contribution we present the initial results of a numerical study into Fe segregation in a deforming silicate matrix that captures the temperature-dependent effect of liquid metal viscosity on the transport rate. Flow is driven by pressure gradients associated with impact deformation in a growing planetesimal and the fracture geometry is constrained by experimental data on naturally deformed H6 chondrite. Early results suggest that under dynamic conditions, fracture-driven melt flow can in principle be extremely rapid, leading to a significant draining of the Fe-liquid metal and siderophile trace element component on a timescale of hours to days. Fluid transport in planetesimals where deformation is the driving force provides an attractive and simple way of segregating Fe from host silicate as both precursor and primary agent of core formation. The potential for flow of metal-rich melt to induce local magnetic anomalies will also be addressed.

DYNAMICAL ACCRETION OF PRIMORDIAL ATMOSPHERES AROUND PLANETS WITH MASSES BETWEEN 0.1 AND 5 M {sub ⊕} IN THE HABITABLE ZONE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stökl, Alexander; Dorfi, Ernst A.; Johnstone, Colin P.

2016-07-10

In the early, disk-embedded phase of evolution of terrestrial planets, a protoplanetary core can accumulate gas from the circumstellar disk into a planetary envelope. In order to relate the accumulation and structure of this primordial atmosphere to the thermal evolution of the planetary core, we calculated atmosphere models characterized by the surface temperature of the core. We considered cores with masses between 0.1 and 5 M {sub ⊕} situated in the habitable zone around a solar-like star. The time-dependent simulations in 1D-spherical symmetry include the hydrodynamics equations, gray radiative transport, and convective energy transport. Using an implicit time integration scheme,more » we can use large time steps and and thus efficiently cover evolutionary timescales. Our results show that planetary atmospheres, when considered with reference to a fixed core temperature, are not necessarily stable, and multiple solutions may exist for one core temperature. As the structure and properties of nebula-embedded planetary atmospheres are an inherently time-dependent problem, we calculated estimates for the amount of primordial atmosphere by simulating the accretion process of disk gas onto planetary cores and the subsequent evolution of the embedded atmospheres. The temperature of the planetary core is thereby determined from the computation of the internal energy budget of the core. For cores more massive than about one Earth mass, we obtain that a comparatively short duration of the disk-embedded phase (∼10{sup 5} years) is sufficient for the accumulation of significant amounts of hydrogen atmosphere that are unlikely to be removed by later atmospheric escape processes.« less

Planetary Formation: From the Earth and Moon to Extrasolar Giant Planets

NASA Technical Reports Server (NTRS)

Lissauer, Jack; DeVincenzi, Donald (Technical Monitor)

1999-01-01

An overview of current theories of star and planet formation is presented. These models are based upon observations of the Solar System and of young stars and their environments. They predict that rocky planets should form around most single stars, although it is possible that in some cases such planets are lost to orbital decay within the protoplanetary disk. The frequency of formation of gas giant planets is more difficult to predict theoretically. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth like terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. Specific issues to be discussed include: (1) how large a solid core is needed to initiate rapid accumulation of gas? (2) can giant planets form very close to stars? (3) could a giant impact leading to lunar formation have occurred approximately 100 million years after the condensation of the oldest meteorites?

Planetary Formation: From the Earth and Moon to Extrasolar Giant Planets

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; DeVincenzi, Donald (Technical Monitor)

1999-01-01

An overview of current theories of star and planet formation is presented. These models are based upon observations of the Solar System and of young stars and their environments. They predict that rocky planets should form around most single stars, although it is possible that in some cases-such planets are lost to orbital decay within the protoplanetary disk. The frequency of formation of gas giant planets is more difficult to predict theoretically. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth like terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. Specific issues to be discussed include: (1) how large a solid core is needed to initiate rapid accumulation of gas? (2) can giant planets form very close to stars? (3) could a giant impact leading to lunar formation have occurred approx. 100 million years after the condensation of the oldest meteorites?

Planet Formation Imager (PFI): science vision and key requirements

NASA Astrophysics Data System (ADS)

Kraus, Stefan; Monnier, John D.; Ireland, Michael J.; Duchêne, Gaspard; Espaillat, Catherine; Hönig, Sebastian; Juhasz, Attila; Mordasini, Chris; Olofsson, Johan; Paladini, Claudia; Stassun, Keivan; Turner, Neal; Vasisht, Gautam; Harries, Tim J.; Bate, Matthew R.; Gonzalez, Jean-François; Matter, Alexis; Zhu, Zhaohuan; Panic, Olja; Regaly, Zsolt; Morbidelli, Alessandro; Meru, Farzana; Wolf, Sebastian; Ilee, John; Berger, Jean-Philippe; Zhao, Ming; Kral, Quentin; Morlok, Andreas; Bonsor, Amy; Ciardi, David; Kane, Stephen R.; Kratter, Kaitlin; Laughlin, Greg; Pepper, Joshua; Raymond, Sean; Labadie, Lucas; Nelson, Richard P.; Weigelt, Gerd; ten Brummelaar, Theo; Pierens, Arnaud; Oudmaijer, Rene; Kley, Wilhelm; Pope, Benjamin; Jensen, Eric L. N.; Bayo, Amelia; Smith, Michael; Boyajian, Tabetha; Quiroga-Nuñez, Luis Henry; Millan-Gabet, Rafael; Chiavassa, Andrea; Gallenne, Alexandre; Reynolds, Mark; de Wit, Willem-Jan; Wittkowski, Markus; Millour, Florentin; Gandhi, Poshak; Ramos Almeida, Cristina; Alonso Herrero, Almudena; Packham, Chris; Kishimoto, Makoto; Tristram, Konrad R. W.; Pott, Jörg-Uwe; Surdej, Jean; Buscher, David; Haniff, Chris; Lacour, Sylvestre; Petrov, Romain; Ridgway, Steve; Tuthill, Peter; van Belle, Gerard; Armitage, Phil; Baruteau, Clement; Benisty, Myriam; Bitsch, Bertram; Paardekooper, Sijme-Jan; Pinte, Christophe; Masset, Frederic; Rosotti, Giovanni

2016-08-01

The Planet Formation Imager (PFI) project aims to provide a strong scientific vision for ground-based optical astronomy beyond the upcoming generation of Extremely Large Telescopes. We make the case that a breakthrough in angular resolution imaging capabilities is required in order to unravel the processes involved in planet formation. PFI will be optimised to provide a complete census of the protoplanet population at all stellocentric radii and over the age range from 0.1 to 100 Myr. Within this age period, planetary systems undergo dramatic changes and the final architecture of planetary systems is determined. Our goal is to study the planetary birth on the natural spatial scale where the material is assembled, which is the "Hill Sphere" of the forming planet, and to characterise the protoplanetary cores by measuring their masses and physical properties. Our science working group has investigated the observational characteristics of these young protoplanets as well as the migration mechanisms that might alter the system architecture. We simulated the imprints that the planets leave in the disk and study how PFI could revolutionise areas ranging from exoplanet to extragalactic science. In this contribution we outline the key science drivers of PFI and discuss the requirements that will guide the technology choices, the site selection, and potential science/technology tradeoffs.

Scientific objectives of the primitive body sample return missions: An approach from the light-induced effect on water vapor

NASA Technical Reports Server (NTRS)

Shimizu, Mikio

1994-01-01

Water is undoubtedly one of the most crucial components of the solar nebula for determining planetary composition: planets were formed from the accretion of the dust particles in the nebula, and the redox state of Fe in the particles can be determined by the reaction of Fe with water vapor diffused into the interior of the particle in the early stage of solar system formation. It has been discussed from various observations that the cores of Mercury, Venus, and the Earth might be metallic Fe, although the core of the Earth may be somewhat oxidized by the high pressure and temperature reaction of liquid Fe with perovskite at the boundary of the mantle and the core, whereas the core of Mars may be highly oxidized, as suggested by its low density. Isotopic anomalies of various elements have frequently been observed in the solar system (in planetary atmospheres and in meteorites) and some of them can be attributed to the injection of exotic particles formed in other stars into the solar nebula. Hydrogen and D anomalies in planetary atmospheres were frequently believed to correlate with the differential escape of H and D from the exospheres of Venus and Mars, although no one knows the primordial D/H ratios before thermal escape. This paper explains the decrease of the observed D/H ratios with distance from the sun by considering the light-induced drift effect to displace H2(16)O alone to the outside in the solar nebula.

Lightweight Low Force Rotary Percussive Coring Tool for Planetary Applications

NASA Technical Reports Server (NTRS)

Hironaka, Ross; Stanley, Scott

2010-01-01

A prototype low-force rotary-percussive rock coring tool for use in acquiring samples for geological surveys in future planetary missions was developed. The coring tool could eventually enable a lightweight robotic system to operate from a relatively small (less than 200 kg) mobile or fixed platform to acquire and cache Mars or other planetary rock samples for eventual return to Earth for analysis. To gain insight needed to design an integrated coring tool, the coring ability of commercially available coring bits was evaluated for effectiveness of varying key parameters: weight-on-bit, rotation speed, percussive rate and force. Trade studies were performed for different methods of breaking a core at its base and for retaining the core in a sleeve to facilitate sample transfer. This led to a custom coring tool design which incorporated coring, core breakage, core retention, and core extraction functions. The coring tool was tested on several types of rock and demonstrated the overall feasibility of this approach for robotic rock sample acquisition.

Simultaneous alloy-silicate fractionation of carbon, nitrogen, and sulfur at high pressures and temperatures: Implications for establishing the volatile budget of the Earth

NASA Astrophysics Data System (ADS)

Grewal, D. S.; Dasgupta, R.; Sun, C.; Tsuno, K.

2017-12-01

Constraining the origin, distribution and evolution of volatiles such as carbon (C), nitrogen (N) and sulfur (S) in terrestrial planets is essential to understand planetary differentiation, habitability and comparative planetology [1]. C/N ratio of Bulk Silicate Earth (BSE) is superchondritic (40 ± 8), while C/S ratio is nearly chondritic (0.49 ± 0.14) [2]. Accretion, core formation, and magma ocean (MO) crystallization are the key processes that could have set the relative budgets of C, N and S in different planetary reservoirs [3]. However, experiments using either C-N or C-S-bearing systems have shown that C is more siderophile than N and S, consequently core formation would have left behind subchondritic C/N and C/S ratios in BSE [4-6]. Accretion of extremely C-rich bodies during core formation or/and as a late veneer along with an early atmospheric blow-off are amongst the scenarios that have been suggested to explain C/N ratio while the addition of a differentiated body with a C-rich mantle has been suggested to explain C/S ratio in BSE [4-6]. However, no internally consistent explanations exist on the origin of all the volatile elements. We performed piston cylinder and multi-anvil experiments, using Fe-Ni-N-C±S alloy with variable amounts of S and mafic-ultramafic silicate mixtures in graphite saturated conditions at 1-7 GPa, 1600-1800 °C, and fO2 ranging from ΔIW of -1.1 to -0.3. EPMA and SIMS were used to determine major elements and volatile abundances in the coexisting alloy and silicate melt phases, while the speciation of the volatiles was determined using Raman spectroscopy. Our experimental data reveals that C becomes less siderophile in the presence of N and S during core-mantle differentiation involving an S-rich alloy. Using a set of inverse Monte-Carlo simulations, we propose that a disequilibrium merger of a Mars-sized planetary embryo with a C-saturated, S-rich core to a volatile-depleted proto-Earth during the main stage of accretion could have simultaneously satisfied C-N-S abundances and ratios in BSE along with setting up the stage of for the presence of NH3 and HCN in the Earth's early atmosphere via MO degassing. [1] Zahnle et al. (2007) Space Sci. Rev. [2] Marty (2012) EPSL. [3] Dasgupta et al. (2013) GCA. [4] Hirschmann (2016) AM. [5] Dalou et al. (2017) EPSL. [6] Li et al. (2016) Nat. Geosci.

Planetary populations in the mass-period diagram: A statistical treatment of exoplanet formation and the role of planet traps

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hasegawa, Yasuhiro; Pudritz, Ralph E., E-mail: yasu@asiaa.sinica.edu.tw, E-mail: pudritz@physics.mcmaster.ca

2013-11-20

The rapid growth of observed exoplanets has revealed the existence of several distinct planetary populations in the mass-period diagram. Two of the most surprising are (1) the concentration of gas giants around 1 AU and (2) the accumulation of a large number of low-mass planets with tight orbits, also known as super-Earths and hot Neptunes. We have recently shown that protoplanetary disks have multiple planet traps that are characterized by orbital radii in the disks and halt rapid type I planetary migration. By coupling planet traps with the standard core accretion scenario, we showed that one can account for themore » positions of planets in the mass-period diagram. In this paper, we demonstrate quantitatively that most gas giants formed at planet traps tend to end up around 1 AU, with most of these being contributed by dead zones and ice lines. We also show that a large fraction of super-Earths and hot Neptunes are formed as 'failed' cores of gas giants—this population being constituted by comparable contributions from dead zone and heat transition traps. Our results are based on the evolution of forming planets in an ensemble of disks where we vary only the lifetimes of disks and their mass accretion rates onto the host star. We show that a statistical treatment of the evolution of a large population of planetary cores caught in planet traps accounts for the existence of three distinct exoplanetary populations—the hot Jupiters, the more massive planets around r = 1 AU, and the short-period super-Earths and hot Neptunes. There are very few populations that feed into the large orbital radii characteristic of the imaged Jovian planet, which agrees with recent surveys. Finally, we find that low-mass planets in tight orbits become the dominant planetary population for low-mass stars (M {sub *} ≤ 0.7 M {sub ☉}).« less

Protostars and Disks

NASA Technical Reports Server (NTRS)

Ho, Paul

1997-01-01

The research concentrated on high angular resolution (arc-second scale) studies of molecular cloud cores associated with very young star formation. New ways to study disks and protoplanetary systems were explored. Findings from the areas studied are briefly summarized: (1) molecular clouds; (2) gravitational contraction; (3) jets, winds, and outflows; (4) Circumstellar Disks (5) Extrasolar Planetary Systems. A bibliography of publications and submitted papers produced during the grant period is included.

Planetary Origin Evolution and Structure

NASA Technical Reports Server (NTRS)

Stevenson, David J.

2005-01-01

This wide-ranging grant supported theoretical modeling on many aspects of the formation, evolution and structure of planets and satellites. Many topics were studied during this grant period, including the evolution of icy bodies; the origin of magnetic fields in Ganymede; the thermal histories of terrestrial planets; the nature of flow inside giant planets (especially the coupling to the magnetic field) and the dynamics of silicate/iron mixing during giant impacts and terrestrial planet core formation. Many of these activities are ongoing and have not reached completion. This is the nature of this kind of research.

Anionic Pt in Silicate Melts at Low Oxygen Fugacity: Speciation, Partitioning and Implications for Core Formation Processes on Asteroids

NASA Technical Reports Server (NTRS)

Medard, E.; Martin, A. M.; Righter, K.; Malouta, A.; Lee, C.-T.

2017-01-01

Most siderophile element concentrations in planetary mantles can be explained by metal/ silicate equilibration at high temperature and pressure during core formation. Highly siderophile elements (HSE = Au, Re, and the Pt-group elements), however, usually have higher mantle abundances than predicted by partitioning models, suggesting that their concentrations have been set by late accretion of material that did not equilibrate with the core. The partitioning of HSE at the low oxygen fugacities relevant for core formation is however poorly constrained due to the lack of sufficient experimental constraints to describe the variations of partitioning with key variables like temperature, pressure, and oxygen fugacity. To better understand the relative roles of metal/silicate partitioning and late accretion, we performed a self-consistent set of experiments that parameterizes the influence of oxygen fugacity, temperature and melt composition on the partitioning of Pt, one of the HSE, between metal and silicate melts. The major outcome of this project is the fact that Pt dissolves in an anionic form in silicate melts, causing a dependence of partitioning on oxygen fugacity opposite to that reported in previous studies.

Planet Formation

NASA Astrophysics Data System (ADS)

Podolak, Morris

2018-04-01

Modern observational techniques are still not powerful enough to directly view planet formation, and so it is necessary to rely on theory. However, observations do give two important clues to the formation process. The first is that the most primitive form of material in interstellar space exists as a dilute gas. Some of this gas is unstable against gravitational collapse, and begins to contract. Because the angular momentum of the gas is not zero, it contracts along the spin axis, but remains extended in the plane perpendicular to that axis, so that a disk is formed. Viscous processes in the disk carry most of the mass into the center where a star eventually forms. In the process, almost as a by-product, a planetary system is formed as well. The second clue is the time required. Young stars are indeed observed to have gas disks, composed mostly of hydrogen and helium, surrounding them, and observations tell us that these disks dissipate after about 5 to 10 million years. If planets like Jupiter and Saturn, which are very rich in hydrogen and helium, are to form in such a disk, they must accrete their gas within 5 million years of the time of the formation of the disk. Any formation scenario one proposes must produce Jupiter in that time, although the terrestrial planets, which don't contain significant amounts of hydrogen and helium, could have taken longer to build. Modern estimates for the formation time of the Earth are of the order of 100 million years. To date there are two main candidate theories for producing Jupiter-like planets. The core accretion (CA) scenario supposes that any solid materials in the disk slowly coagulate into protoplanetary cores with progressively larger masses. If the core remains small enough it won't have a strong enough gravitational force to attract gas from the surrounding disk, and the result will be a terrestrial planet. If the core grows large enough (of the order of ten Earth masses), and the disk has not yet dissipated, then the planetary embryo can attract gas from the surrounding disk and grow to be a gas giant. If the disk dissipates before the process is complete, the result will be an object like Uranus or Neptune, which has a small, but significant, complement of hydrogen and helium. The main question is whether the protoplanetary core can grow large enough before the disk dissipates. A second scenario is the disk instability (DI) scenario. This scenario posits that the disk itself is unstable and tends to develop regions of higher than normal density. Such regions collapse under their own gravity to form Jupiter-mass protoplanets. In the DI scenario a Jupiter-mass clump of gas can form—in several hundred years which will eventually contract into a gas giant planet. The difficulty here is to bring the disk to a condition where such instabilities will form. Now that we have discovered nearly 3000 planetary systems, there will be numerous examples against which to test these scenarios.

Experiments pertaining to the formation and equilibration of planetary cores

NASA Technical Reports Server (NTRS)

Jeanloz, Raymond; Knittle, Elise; Williams, Quentin

1987-01-01

The phase diagram of FeO was experimentally determined to pressures of 155 GPa and temperatures of 4000 K using shock wave and diamond-cell techniques. Researchers discovered a metallic phase of FeO at pressures greater than 70 GPa and temperatures exceeding 1000 K. The metallization of FeO at high pressures implies that oxygen can be present as the light alloying element of the Earth's outer core, in accord with the geochemical predictions of Ringwood. The high pressures necessry for this metallization suggest that the core has acquired its composition well after the initial stages of the Earth's accretion. The core forming alloy can react chemically with oxides such as those forming the mantle. The core and mantle may never have reached complete chemical equilibrium, however. If this is the case, the core-mantle boundary is likely to be a zone of active chemical reactions.

Planetesimal and Protoplanet Dynamics in a Turbulent Protoplanetary Disk

NASA Astrophysics Data System (ADS)

Yang, Chao-Chin; Mac Low, M.; Menou, K.

2010-01-01

In core accretion scenario of planet formation, kilometer-sized planetesimals are the building blocks toward planetary cores. Their dynamics, however, are strongly influenced by their natal protoplanetary gas disks. It is generally believed that these disks are turbulent, most likely due to magnetorotational instability. The resulting density perturbations in the gas render the movement of the particles a random process. Depending on its strength, this process might cause several interesting consequences in the course of planet formation, specifically the survivability of objects under rapid inward type-I migration and/or collisional destruction. Using the local-shearing-box approximation, we conduct numerical simulations of planetesimals moving in a turbulent, magnetized gas disk, either unstratified or vertically stratified. We produce a fiducial disk model with turbulent accretion of Shakura-Sunyaev alpha about 10-2 and root-mean-square density perturbation of about 10% and statistically characterize the evolution of the orbital properties of the particles moving in the disk. These measurements result in accurate calibration of the random process of particle orbital change, indicating noticeably smaller magnitudes than predicted by global simulations, although the results may depend on the size of the shearing box. We apply these results to revisit the survivability of planetesimals under collisional destruction or protoplanets under type-I migration. Planetesimals are probably secure from collisional destruction, except for kilometer-sized objects situated in the outer regions of a young protoplanetary disk. On the other hand, we confirm earlier studies of local models in that type-I migration probably dominates diffusive migration due to stochastic torques for most planetary cores and terrestrial planets. Discrepancies in the derived magnitude of turbulence between local and global simulations of magnetorotationally unstable disks remains an open issue, with important consequences for planet formation scenarios.

Distortion of Magnetic Fields in a Starless Core: Near-infrared Polarimetry of FeSt 1–457

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kandori, Ryo; Tamura, Motohide; Kusakabe, Nobuhiko

Magnetic fields are believed to play an important role in controlling the stability and contraction of the dense condensations of gas and dust that lead to the formation of stars and planetary systems. In the present study, the magnetic field of FeSt 1–457, a cold starless molecular cloud core, was mapped on the basis of the polarized near-infrared light from 185 background stars after being dichroically absorbed by dust aligned with the magnetic field in the core. A distinct “hourglass-shaped” magnetic field was identified in the region of the core, and was interpreted as the first evidence of a magneticmore » field structure distorted by mass condensation in a starless core. The steep curvature of the magnetic field lines obtained in the present study indicates that the distortion was mainly created during the formation phase of the dense core. The derived mass-to-magnetic flux ratio indicates that the core is in a magnetically supercritical state. However, the stability of the core can be considered to be in a nearly critical state if the additional contributions from the thermal and turbulent support are included. Further diffusion of the magnetic field and/or turbulent dissipation would cause the onset of the dynamical collapse of the core. The geometrical relationship between the direction of the magnetic field lines and the elongation of the core was found to be in good agreement with theoretical predictions for the formation of Sun-like stars under the influence of a magnetic field.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kikuchi, Akihiro; Higuchi, Arika; Ida, Shigeru, E-mail: kikuchi.a@geo.titech.ac.jp, E-mail: higuchia@geo.titech.ac.jp, E-mail: ida@elsi.jp

Recently, gas giant planets in nearly circular orbits with large semimajor axes (a ∼ 30-1000 AU) have been detected by direct imaging. We have investigated orbital evolution in a formation scenario for such planets, based on a core accretion model. (1) Icy cores accrete from planetesimals at ≲ 30 AU, (2) they are scattered outward by an emerging nearby gas giant to acquire highly eccentric orbits, and (3) their orbits are circularized through the accretion of disk gas in outer regions, where they spend most of their time. We analytically derived equations to describe the orbital circularization through gas accretion.more » Numerical integrations of these equations show that the eccentricity decreases by a factor of more than 5 while the planetary mass increases by a factor of 10. Because runaway gas accretion increases planetary mass by ∼10-300, the orbits are sufficiently circularized. On the other hand, a is reduced at most only by a factor of two, leaving the planets in the outer regions. If the relative velocity damping by shock is considered, the circularization slows down, but is still efficient enough. Therefore, this scenario potentially accounts for the formation of observed distant jupiters in nearly circular orbits. If the apocenter distances of the scattered cores are larger than the disk sizes, their a shrink to a quarter of the disk sizes; the a-distribution of distant giants could reflect the outer edges of the disks in a similar way that those of hot jupiters may reflect inner edges.« less

The early thermal evolution of Mars

NASA Astrophysics Data System (ADS)

Bhatia, G. K.; Sahijpal, S.

2016-01-01

Hf-W isotopic systematics of Martian meteorites have provided evidence for the early accretion and rapid core formation of Mars. We present the results of numerical simulations performed to study the early thermal evolution and planetary scale differentiation of Mars. The simulations are confined to the initial 50 Myr (Ma) of the formation of solar system. The accretion energy produced during the growth of Mars and the decay energy due to the short-lived radio-nuclides 26Al, 60Fe, and the long-lived nuclides, 40K, 235U, 238U, and 232Th are incorporated as the heat sources for the thermal evolution of Mars. During the core-mantle differentiation of Mars, the molten metallic blobs were numerically moved using Stoke's law toward the center with descent velocity that depends on the local acceleration due to gravity. Apart from the accretion and the radioactive heat energies, the gravitational energy produced during the differentiation of Mars and the associated heat transfer is also parametrically incorporated in the present work to make an assessment of its contribution to the early thermal evolution of Mars. We conclude that the accretion energy alone cannot produce widespread melting and differentiation of Mars even with an efficient consumption of the accretion energy. This makes 26Al the prime source for the heating and planetary scale differentiation of Mars. We demonstrate a rapid accretion and core-mantle differentiation of Mars within the initial ~1.5 Myr. This is consistent with the chronological records of Martian meteorites.

Core formation in the shergottite parent body and comparison with the earth

NASA Technical Reports Server (NTRS)

Treiman, Allan H.; Jones, John H.; Drake, Michael J.

1987-01-01

Abundances of elements in shergottite, nakhlite, and Chassigny meteorites which originated on a single planet, the shergottite parent body (SPB), were examined with the aim of elucidating the chemical conditions of metal separation and core formation in the SPB and of testing present models of planetary core formation. Using partition coefficients and the SPB mantle composition determined in earlier studies, the abundances of Ag, Au, Co, Ga, Mo, Ni, P, Re, S, and W were modeled, with free parameters being oxygen fugacity, proportion of solid metal formed, proportion of metallic liquid formed, and proportion of silicate that is molten. It is shown that the abundances of all elements (except Mo) could be reproduced using models with these four free parameters. In contrast to the SPB, an equivalent model used to predict element abundances in the earth's mantle was shown by Jones and Drake (1986) to be inadequate; there is at present no hypothesis capable of quantitatively reproducing the elemental abundances of the earth's mantle. The contrast suggests that these two terrestrial planets (assuming that the SPB is Mars) may have accreted or differentiated differently.

High-pressure behavior of iron-nickel-cobalt phosphides and its implications for meteorites and planetary cores

NASA Astrophysics Data System (ADS)

Dera, P.; Lavina, B.; Borkowski, L. A.; Downs, R. T.; Prewitt, C. T.; Prakapenka, V.; Rivers, M. L.; Sutton, S.; Boctor, N.

2008-12-01

Minerals with composition (Fe,Ni)xP, are rare, but important accessory phases present in iron and chondrite meteorites. The occurrence of these minerals in meteoritic samples is believed to originate either from the equilibrium condensation of protoplanetary materials taking place in solar nebulae or from crystallization processes in the cores of parent bodies. Fe-Ni phosphides are considered an important candidate for a minor phase present in Earth's core, and at least partially responsible for the observed core density deficit with respect to pure Fe. We report results of high-pressure high-temperature single-crystal X- ray diffraction experiments with end-members belonging to the (Fe,Ni,Co)2P family, including Fe2P, Ni2P and Co2P. A new phase transition to the Co2Si-type structure (allabogdanite) has been found in Fe2P barringerite at 8.0 GPa, upon heating. The high-pressure phase can be quenched metastably to ambient conditions and then, if heated again, it transforms back to barringerite. Ni2P barringerite does not undergo transformation to allabogdanite structure up to 50 GPa, but instead exhibits incongruent melting with formation of pyrite-type NiP2 and Ni-P glass. Our results indicate that the presence of allabogdanite in meteoritic samples places two important constraints on the thermodynamic history of the meteorite. First, it imposes a minimum pressure and temperature for the formation of the Fe2P, and additionally rules out any higher temperature low pressure alterations. If present in the Earth's core, Fe2P will have the allabogdanite rather than the barringerite structure. Crystal chemical trends in the compressibility of (Fe,Ni,Co)2P minerals, as well as polymorphic transition paths are analyzed in the context of Earth and planetary core composition and properties.

The Formation and Evolution of the Solar System

NASA Astrophysics Data System (ADS)

Marov, Mikhail

2018-05-01

The formation and evolution of our solar system (and planetary systems around other stars) are among the most challenging and intriguing fields of modern science. As the product of a long history of cosmic matter evolution, this important branch of astrophysics is referred to as stellar-planetary cosmogony. Interdisciplinary by way of its content, it is based on fundamental theoretical concepts and available observational data on the processes of star formation. Modern observational data on stellar evolution, disc formation, and the discovery of extrasolar planets, as well as mechanical and cosmochemical properties of the solar system, place important constraints on the different scenarios developed, each supporting the basic cosmogony concept (as rooted in the Kant-Laplace hypothesis). Basically, the sequence of events includes fragmentation of an original interstellar molecular cloud, emergence of a primordial nebula, and accretion of a protoplanetary gas-dust disk around a parent star, followed by disk instability and break-up into primary solid bodies (planetesimals) and their collisional interactions, eventually forming a planet. Recent decades have seen major advances in the field, due to in-depth theoretical and experimental studies. Such advances have clarified a new scenario, which largely supports simultaneous stellar-planetary formation. Here, the collapse of a protosolar nebula's inner core gives rise to fusion ignition and star birth with an accretion disc left behind: its continuing evolution resulting ultimately in protoplanets and planetary formation. Astronomical observations have allowed us to resolve in great detail the turbulent structure of gas-dust disks and their dynamics in regard to solar system origin. Indeed radio isotope dating of chondrite meteorite samples has charted the age and the chronology of key processes in the formation of the solar system. Significant progress also has been made in the theoretical study and computer modeling of protoplanetary accretion disk thermal regimes; evaporation/condensation of primordial particles depending on their radial distance, mechanisms of clustering, collisions, and dynamics. However, these breakthroughs are yet insufficient to resolve many problems intrinsically related to planetary cosmogony. Significant new questions also have been posed, which require answers. Of great importance are questions on how contemporary natural conditions appeared on solar system planets: specifically, why the three neighbor inner planets—Earth, Venus, and Mars—reveal different evolutionary paths.

Effects of Earth's rotation on the early differentiation of a terrestrial magma ocean

NASA Astrophysics Data System (ADS)

Maas, Christian; Hansen, Ulrich

2015-11-01

Similar to other terrestrial planets like Moon and Mars, Earth experienced a magma ocean period about 4.5 billion years ago. On Earth differentiation processes in the magma ocean set the initial conditions for core formation and mantle evolution. During the magma ocean period Earth was rotating significantly faster than today. Further, the viscosity of the magma was low, thus that planetary rotation potentially played an important role for differentiation. However, nearly all previous studies neglect rotational effects. All in all, our results suggest that planetary rotation plays an important role for magma ocean crystallization. We employ a 3-D numerical model to study crystal settling in a rotating and vigorously convecting early magma ocean. We show that crystal settling in a terrestrial magma ocean is crucially affected by latitude as well as by rotational strength and crystal density. Due to rotation an inhomogeneous accumulation of crystals during magma ocean solidification with a distinct crystal settling between pole and equator could occur. One could speculate that this may have potentially strong effects on the magma ocean solidification time and the early mantle composition. It could support the development of a basal magma ocean and the formation of anomalies at the core-mantle boundary in the equatorial region, reaching back to the time of magma ocean solidification.

Magnesium isotope evidence that accretional vapour loss shapes planetary compositions

PubMed Central

Hin, Remco C.; Coath, Christopher D.; Carter, Philip J.; Nimmo, Francis; Lai, Yi-Jen; Pogge von Strandmann, Philip A.E.; Willbold, Matthias; Leinhardt, Zoë M.; Walter, Michael J.; Elliott, Tim

2017-01-01

It has long been recognised that Earth and other differentiated planetary bodies are chemically fractionated compared to primitive, chondritic meteorites and by inference the primordial disk from which they formed. An important question has been whether the notable volatile depletions of planetary bodies are a consequence of accretion1, or inherited from prior nebular fractionation2. The isotopic compositions of the main constituents of planetary bodies can contribute to this debate3–6. Using a new analytical approach to address key issues of accuracy inherent in conventional methods, we show that all differentiated bodies have isotopically heavier magnesium compositions than chondritic meteorites. We argue that possible magnesium isotope fractionation during condensation of the solar nebula, core formation and silicate differentiation cannot explain these observations. However, isotopic fractionation between liquid and vapour followed by vapour escape during accretionary growth of planetesimals generates appropriate residual compositions. Our modelling implies that the isotopic compositions of Mg, Si and Fe and the relative abundances of the major elements of Earth, and other planetary bodies, are a natural consequence of substantial (~40% by mass) vapour loss from growing planetesimals by this mechanism. PMID:28959965

Core to Atmosphere Exploration of Ice Giants: A Uranus Mission Concept Study

NASA Astrophysics Data System (ADS)

Jensema, R. J.; Arias-Young, T. M.; Wilkins, A. N.; Ermakov, A.; Bennett, C.; Dietrich, A.; Hemingway, D.; Klein, V.; Mane, P.; Marr, K. D.; Masterson, J.; Siegel, V.; Stober, K. J.; Talpe, M.; Vines, S. K.; Wetteland, C. J.

2014-12-01

Ice giants remain largely unexplored, as their large distance from the Sun limits both Earth-based observations and spacecraft visits. The significant occurrence of ice giant-sized planets among detected exoplanets presents an impetus to study Uranus to understand planetary formation, dynamics, and evolution. In addition, Uranus is also uniquely interesting, given the large inclination of its rotation axis and magnetospheric configuration. In this work, we design a mission concept that aims to maximize scientific return by measuring Uranus' chemical composition, internal structure, and magnetosphere, the first two being primary indicators of ice giant formation mechanisms. For this study, we analyze the trade space for a Uranus mission constrained by a cost cap of $1B. We discuss the decision making processes behind our choices of the science priorities, instrument suite and orbital configuration. Trade space decisions include a strong onboard instrument suite in lieu of a descent probe, an orbiter instead of a flyby mission, and design constraints on the power and propulsion systems. The mission, CAELUS (Core and Atmospheric Evolution Laboratory for Uranus Science), is designed for an August 2023 launch. Following a 14-year cruise with multiple planetary gravity assists, the spacecraft would begin its science mission, which consists of a series of ten 30-day near-polar orbits around Uranus. The instrument suite would consist of a microwave radiometer, Doppler seismometer, magnetometer, and UV spectrometer. These four instruments, along with a high-gain antenna capable of gravity science, would provide a comprehensive science return that meets the bulk of the scientific objectives of the 2013 NRC Planetary Science Decadal Survey for ice giants, most notably those regarding the chemical composition, interior structure, and dynamo of Uranus. This mission concept was created as part of an educational exercise for the 2014 Planetary Science Summer School at the Jet Propulsion Laboratory.

Compositional Imprints in Density–Distance–Time: A Rocky Composition for Close-in Low-mass Exoplanets from the Location of the Valley of Evaporation

NASA Astrophysics Data System (ADS)

Jin, Sheng; Mordasini, Christoph

2018-02-01

We use an end-to-end model of planet formation, thermodynamic evolution, and atmospheric escape to investigate how the statistical imprints of evaporation depend on the bulk composition of planetary cores (rocky versus icy). We find that the population-wide imprints like the location of the “evaporation valley” in the distance–radius plane and the corresponding bimodal radius distribution clearly differ depending on the bulk composition of the cores. Comparison with the observed position of the valley suggests that close-in low-mass Kepler planets have a predominantly Earth-like rocky composition. Combined with the excess of period ratios outside of MMR, this suggests that low-mass Kepler planets formed inside of the water iceline but were still undergoing orbital migration. The core radius becomes visible for planets losing all primordial H/He. For planets in this “triangle of evaporation” in the distance–radius plane, the degeneracy in composition is reduced. In the observed planetary mass–mean density diagram, we identify a trend to more volatile-rich compositions with an increasing radius (R/R ⊕ ≲ 1.6 rocky; 1.6–3.0 ices, and/or H/He ≳3: H/He). The mass–density diagram contains important information about formation and evolution. Its characteristic broken V-shape reveals the transitions from solid planets to low-mass core-dominated planets with H/He and finally to gas-dominated giants. Evaporation causes the density and orbital distance to be anticorrelated for low-mass planets in contrast to giants, where closer-in planets are less dense, likely due to inflation. The temporal evolution of the statistical properties reported here will be of interest for the PLATO 2.0 mission, which will observe the temporal dimension.

Formation of Authigenic Sulfates in Cold Dry Glaciers: Terrestrial and Planetary Implications of Sublimites

NASA Astrophysics Data System (ADS)

Massé, M.; Rondeau, B.; Ginot, P.; Schmitt, B.; Bourgeois, O.; Mitri, G.

2015-12-01

Salts are common on planetary surfaces, and sulfates have been widely observed on Earth, Mars (Gendrin et al., 2005) and on some of Jupiter's and Saturn's icy moons like Europa (Dalton et al., 2007). These minerals can form under a wide range of conditions, and the determination of sulfate formation processes can provide key elements for deciphering past planetary surface conditions. Most terrestrial sulfates form as evaporites in warm environments with high water/rock ratios, but these conditions are rarely encountered on other planets. Here we describe the formation of cryogenic sulfates in an extreme cold and dry environment: the Guanaco glacier located in the Chilean Andes (Fig.1a, Rabatel et al., 2011). Field analyses reveal that it is a cold-based glacier, its surface temperature remains below 0°C throughout the year, and ablation occurs mostly by sublimation. Ablation creates ice cliffs punctuated of pluricentimetric whitish, tapered crystals embedded in the ice (Fig.1b, c). By Raman and chemistry, they proved to be gypsum, covered by micrometric crystals of jarosite, halotrichite and native sulfur. The euhedral morphology of these soft minerals indicates that they are neoformed and have not been transported in the ice. This is supported by the absence of gypsum crystals in ice cores drilled through the glacier. We infer that the crystallization thus occurred at the glacier surface during ice sublimation and does not involve liquid water. To distinguish this original salt formation process from the more common evaporites, we name these minerals "sublimites". Though this formation process is uncommon and generates minor quantities of sulfates on Earth, it may be dominant on other bodies in the Solar System where sublimation is effective. Examples of planetary sublimites may include gypsum on the North Polar Cap of Mars (Massé et al., 2012), and other sulfates on icy moons where sublimation has been observed (Howard et al., 2008).

N-body simulations of planet formation: understanding exoplanet system architectures

NASA Astrophysics Data System (ADS)

Coleman, Gavin; Nelson, Richard

2015-12-01

Observations have demonstrated the existence of a significant population of compact systems comprised of super-Earths and Neptune-mass planets, and a population of gas giants that appear to occur primarily in either short-period (<10 days) or longer period (>100 days) orbits. The broad diversity of system architectures raises the question of whether or not the same formation processes operating in standard disc models can explain these planets, or if different scenarios are required instead to explain the widely differing architectures. To explore this issue, we present the results from a comprehensive suite of N-body simulations of planetary system formation that include the following physical processes: gravitational interactions and collisions between planetary embryos and planetesimals; type I and II migration; gas accretion onto planetary cores; self-consistent viscous disc evolution and disc removal through photo-evaporation. Our results indicate that the formation and survival of compact systems of super-Earths and Neptune-mass planets occur commonly in disc models where a simple prescription for the disc viscosity is assumed, but such models never lead to the formation and survival of gas giant planets due to migration into the star. Inspired in part by the ALMA observations of HL Tau, and by MHD simulations that display the formation of long-lived zonal flows, we have explored the consequences of assuming that the disc viscosity varies in both time and space. We find that the radial structuring of the disc leads to conditions in which systems of giant planets are able to form and survive. Furthermore, these giants generally occupy those regions of the mass-period diagram that are densely populated by the observed gas giants, suggesting that the planet traps generated by radial structuring of protoplanetary discs may be a necessary ingredient for forming giant planets.

An Interconnected Network of Core-Forming Melts Produced by Shear Deformation

NASA Technical Reports Server (NTRS)

Bruhn, D.; Groebner, N.; Kohlstedt, D. L.

2000-01-01

The formation mechanism of terrestrial planetary is still poorly understood, and has been the subject of numerous experimental studies. Several mechanisms have been proposed by which metal-mainly iron with some nickel-could have been extracted from a silicate mantle to form the core. Most recent models involve gravitational sinking of molten metal or metal sulphide through a partially or fully molten mantle that is often referred to as a'magma ocean. Alternative models invoke percolation of molten metal along an interconnected network (that is, porous flow) through a solid silicate matrix. But experimental studies performed at high pressures have shown that, under hydrostatic conditions, these melts do not form an interconnected network, leading to the widespread assumption that formation of metallic cores requires a magma ocean. In contrast, here we present experiments which demonstrate that shear deformation to large strains can interconnect a significant fraction of initially isolated pockets of metal and metal sulphide melts in a solid matrix of polycrystalline olivine. Therefore, in a dynamic (nonhydrostatic) environment, percolation remains a viable mechanism for the segregation and migration of core-forming melts in a solid silicate mantle.

The composition of Earth's core from equations of state, metal-silicate partitioning, and core formation modeling

NASA Astrophysics Data System (ADS)

Fischer, Rebecca; Campbell, Andrew; Ciesla, Fred

2016-04-01

The Earth accreted in a series of increasingly large and violent collisions. Simultaneously, the metallic core segregated from the silicate mantle, acquiring its modern composition through high pressure (P), high temperature (T) partitioning reactions. Here we present a model that couples these aspects of early planetary evolution, building on recent accretion simulations and metal-silicate partitioning experiments, constrained by density measurements of Fe-rich alloys. Previously, the equations of state of FeO, Fe-9Si, Fe-16Si, and FeSi were measured to megabar pressures and several thousand K using a laser-heated diamond anvil cell. With these equations of state, we determined that the core's density can be reproduced through the addition of 11.3 +/- 0.6 wt% silicon or 8.1 +/- 1.1 wt% oxygen to an Fe-Ni alloy (Fischer et al., 2011, 2014). Metal-silicate partitioning experiments of Ni, Co, V, Cr, Si, and O have been performed in a diamond anvil cell to 100 GPa and 5700 K, allowing the effects of P, T, and composition on the partitioning behaviors of these elements to be parameterized (Fischer et al., 2015; Siebert et al., 2012). Here we apply those experimental results to model Earth's core formation, using N-body simulations to describe the delivery, masses, and original locations of planetary building blocks (Fischer and Ciesla, 2014). As planets accrete, their core and mantle compositions are modified by high P-T reactions with each collision (Rubie et al., 2011). For partial equilibration of the mantle at 55% of the evolving core-mantle boundary pressure and the liquidus temperature, we find that the core contains 5.4 wt% Si and 1.9 wt% O. This composition is consistent with the seismologically-inferred density of Earth's core, based on comparisons to our equations of state, and indicate that the core cannot contain more than ~2 wt% S or C. Earth analogues experience 1.2 +/- 0.2 log units of oxidation during accretion, due to both the effects of high P-T partitioning and the temporal evolution of the Earth's feeding zone. This modeling can reveal the relative importance of various accretion and differentiation processes to core composition, highlighting targets for future experimental and numerical studies.

Stable Nd isotope variations in the inner Solar System: The effect of sulfide during differentiation?

NASA Astrophysics Data System (ADS)

McCoy-West, A.

2017-12-01

Radiogenic neodymium isotopes have been widely used in studies of planetary accretion to constrain the timescales of early planetary differention [1]. Whereas stable isotope varitaions potentially provide information on the the processes that occur during planet formation. Experimental work suggests that the Earth's core contains a significant proportion of sulfide [2], and recent experimental work shows that under reducing conditions sulfide can incorporate substantial quantities of refractory lithophile elements [including Nd; 3]. If planetary embroyos also contain sulfide-rich cores, Nd stable isotopes have the potential to trace this sulfide segregation event in highly reduced environments, because there is a significant contrast in bonding environment between sulfide and silicate, where heavy isotopes should be preferentially incorporated into high force-constant bonds involving REE3+ (i.e. the silicate mantle). Here we present 146Nd/144Nd data, obtained using a double spike TIMS technique, for a range of planetary bodies formed at variable oxidation states including samples from the Moon, Mars, the asteriod 4Vesta and the Angrite and Aubrite parent bodies. Analyses of chondritic meteorites and terrestrial igneous rocks indicate that the Earth has a Nd stable isotope composition that is indistinguishable from that of chondrites [4]. Eucrites and martian meteorites also have compositons within error of the chondritic average. Significantly more variabilty is observed in the low concentration lunar samples and diogienite meteorites with Δ146Nd = 0.16‰. Preliminary results suggest that the Nd stable isotope composition of oxidised planetary bodies are homogeneous and modifications are the result of subordinate magmatic processes. [1] Boyet & Carlson, Science 309, 576 (2005) [2] Labidi et al. Nature 501, 208 (2013); [3] Wohlers &Wood, Nature 520, 337 (2015); [4] McCoy-West et al. Goldschmidt Ab. 429 (2017).

An interconnected network of core-forming melts produced by shear deformation

PubMed

Bruhn; Groebner; Kohlstedt

2000-02-24

The formation mechanism of terrestrial planetary cores is still poorly understood, and has been the subject of numerous experimental studies. Several mechanisms have been proposed by which metal--mainly iron with some nickel--could have been extracted from a silicate mantle to form the core. Most recent models involve gravitational sinking of molten metal or metal sulphide through a partially or fully molten mantle that is often referred to as a 'magma ocean'. Alternative models invoke percolation of molten metal along an interconnected network (that is, porous flow) through a solid silicate matrix. But experimental studies performed at high pressures have shown that, under hydrostatic conditions, these melts do not form an interconnected network, leading to the widespread assumption that formation of metallic cores requires a magma ocean. In contrast, here we present experiments which demonstrate that shear deformation to large strains can interconnect a significant fraction of initially isolated pockets of metal and metal sulphide melts in a solid matrix of polycrystalline olivine. Therefore, in a dynamic (non-hydrostatic) environment, percolation remains a viable mechanism for the segregation and migration of core-forming melts in a solid silicate mantle.

Large-Scale Flows and Magnetic Fields Produced by Rotating Convection in a Quasi-Geostrophic Model of Planetary Cores

NASA Astrophysics Data System (ADS)

Guervilly, C.; Cardin, P.

2017-12-01

Convection is the main heat transport process in the liquid cores of planets. The convective flows are thought to be turbulent and constrained by rotation (corresponding to high Reynolds numbers Re and low Rossby numbers Ro). Under these conditions, and in the absence of magnetic fields, the convective flows can produce coherent Reynolds stresses that drive persistent large-scale zonal flows. The formation of large-scale flows has crucial implications for the thermal evolution of planets and the generation of large-scale magnetic fields. In this work, we explore this problem with numerical simulations using a quasi-geostrophic approximation to model convective and zonal flows at Re 104 and Ro 10-4 for Prandtl numbers relevant for liquid metals (Pr 0.1). The formation of intense multiple zonal jets strongly affects the convective heat transport, leading to the formation of a mean temperature staircase. We also study the generation of magnetic fields by the quasi-geostrophic flows at low magnetic Prandtl numbers.

Planetary exploration through year 2000, a core program: Mission operations

NASA Technical Reports Server (NTRS)

1986-01-01

In 1980 the NASA Advisory Council created the Solar System Exploratory Committee (SSEC) to formulate a long-range program of planetary missions that was consistent with likely fiscal constraints on total program cost. The SSEC had as its primary goal the establishment of a scientifically valid, affordable program that would preserve the nation's leading role in solar system exploration, capitalize on two decades of investment, and be consistent with the coordinated set of scientific stategies developed earlier by the Committe on Planetary and Lunar Exploration (COMPLEX). The result of the SSEC effort was the design of a Core Program of planetary missions to be launched by the year 2000, together with a realistic and responsible funding plan. The Core Program Missions, subcommittee activities, science issues, transition period assumptions, and recommendations are discussed.

Antarctic Testing of the European Ultrasonic Planetary Core Drill (UPCD)

NASA Astrophysics Data System (ADS)

Timoney, R.; Worrall, K.; Li, X.; Firstbrook, D.; Harkness, P.

2018-04-01

An overview of a series of field testing in Antarctica where the Ultrasonic Planetary Core Drill (UPCD) architecture was tested. The UPCD system is the product an EC FP7 award to develop a Mars Sample Return architecture based around the ultrasonic technique.

Planetary Nebulae: Reviews and Previews of a Rapidly Evolving Field

NASA Astrophysics Data System (ADS)

Balick, Bruce

2015-01-01

Observational results from the ground and space in the past decade and covering the entire spectrum have jolted and energized research into the nature, the formation, and the evolution of planetary nebulae (PNs). The 101-level bubble structure of PNs turned out to be a pleasant but misleading fantasy as observations by HST and ALMA revealed basic details of their infancy. Some combination of close geriatric binary stars (the precusrors of SN Ia's) and magnetic fields dredged into the dusty winds appear to play vital roles in the ejection and collimation of AGB atmospheres. As a result, PNe and their antecedents, AGB stars and prePNs, are providing an array of new opportunities to study asymmetric wind formation, complex gas dynamics, CNO production rates in various galactic environments, and galaxy structure and evolution. I shall review the highlights of recent results, summarize their interpretations, and show some of the observational opportunities to monitor in the next decade, many of which couple strongly to research to related fields.This talk is dedicated to the career of Olivier Chesneau (1972-2014) who pioneered new high-resolution imaging methods that peered into the deep inner cores of nascent planetary nebulae. We remember Olivier as everyone's enthusiastic friend and colleague whose career ended in full stride.

The effects of mass and metallicity upon planetary nebula formation

NASA Astrophysics Data System (ADS)

Papp, K. A.; Purton, C. R.; Kwok, S.

1983-05-01

A parameterized function is constructed which describes the possible dependence of planetary nebula formation upon metal abundance and stellar mass. Data on galaxies in the Local Group compared with predictions made from the parameterized function indicate that heavy element abundance is the principal agent influencing the formation of planetary nebulae; stars which are rich in heavy elements are the progenitors of planetary nebulae. This analysis, when compared with the observations, argues for a modest degree of pre-enrichment in a few of the sample galaxies. The heavy element dependence of planetary nebula formation also accounts for the deficit of planetary nebulae in the nuclei of NGC 221 and NGC 224, and in the bulge of our Galaxy.

Planetary environments and the conditions of life.

PubMed

Chang, S

1988-01-01

Life arose on Earth within a billion years (1 Ga) after planetary accretion and core formation. The geological record, which begins 3.8 Ga BP, indicates environmental conditions much like today's, except for the absence of oxygen. By 3.5 Ga BP microbial ecosystems were already colonizing shallow marine hydrothermal environments along shorelines of volcanic islands. Although similar environments could have existed more than 3.8 Ga BP, they may not have been the spawning grounds of life. Geophysical models of the first 600 Ma of Earth history following accretion and core formation point to a period of great environmental disequilibrium. In such an environment the passage of energy from Earth's interior and from the Sun through gas-liquid-solid domains and their boundaries with each other generated a dynamically interacting, complex hierarchy of self-organized structures, ranging from bubbles at the sea-air interface to tectonic plates. Nested within this hierarchy were the precursors of living systems. The ability of a planet to produce such a hierarchy is speculated to be a prerequisite for the origin and sustenance of life. Application of this criterion to Mars, which apparently experienced no plate tectonism, argues against the origin of martian life. Because only further geological and biogeochemical exploration of the planet can place these qualitative speculations on firm ground, the search for evidence of extinct life on Mars continues to be of highest scientific priority.

Single rotating stars and the formation of bipolar planetary nebula

DOE Office of Scientific and Technical Information (OSTI.GOV)

García-Segura, G.; Villaver, E.; Langer, N.

2014-03-10

We have computed new stellar evolution models that include the effects of rotation and magnetic torques under different hypotheses. The goal is to test whether a single star can sustain the rotational velocities needed in the envelope for magnetohydrodynamical(MHD) simulations to shape bipolar planetary nebulae (PNe) when high mass-loss rates take place. Stellar evolution models with main sequence masses of 2.5 and 5 M {sub ☉} and initial rotational velocities of 250 km s{sup –1} have been followed through the PNe formation phase. We find that stellar cores have to be spun down using magnetic torques in order to reproducemore » the rotation rates observed for white dwarfs. During the asymptotic giant branch phase and beyond, the magnetic braking of the core has a practically null effect on increasing the rotational velocity of the envelope since the stellar angular momentum is efficiently removed by the wind. We have also tested the best possible case scenarios in rather non-physical contexts to give enough angular momentum to the envelope. We find that we cannot get the envelope of a single star to rotate at the speeds needed for MHD simulations to form bipolar PNe. We conclude that single stellar rotators are unlikely to be the progenitors of bipolar PNe under the current MHD model paradigm.« less

Water in the Earth's Interior: Distribution and Origin

NASA Astrophysics Data System (ADS)

Peslier, Anne H.; Schönbächler, Maria; Busemann, Henner; Karato, Shun-Ichiro

2017-10-01

The concentration and distribution of water in the Earth has influenced its evolution throughout its history. Even at the trace levels contained in the planet's deep interior (mantle and core), water affects Earth's thermal, deformational, melting, electrical and seismic properties, that control differentiation, plate tectonics and volcanism. These in turn influenced the development of Earth's atmosphere, oceans, and life. In addition to the ubiquitous presence of water in the hydrosphere, most of Earth's "water" actually occurs as trace amounts of hydrogen incorporated in the rock-forming silicate minerals that constitute the planet's crust and mantle, and may also be stored in the metallic core. The heterogeneous distribution of water in the Earth is the result of early planetary differentiation into crust, mantle and core, followed by remixing of lithosphere into the mantle after plate-tectonics started. The Earth's total water content is estimated at 18_{-15}^{+81} times the equivalent mass of the oceans (or a concentration of 3900_{-3300}^{+32700} ppm weight H2O). Uncertainties in this estimate arise primarily from the less-well-known concentrations for the lower mantle and core, since samples for water analyses are only available from the crust, the upper mantle and very rarely from the mantle transition zone (410-670 km depth). For the lower mantle (670-2900 km) and core (2900-4500 km), the estimates rely on laboratory experiments and indirect geophysical techniques (electrical conductivity and seismology). The Earth's accretion likely started relatively dry because it mainly acquired material from the inner part of the proto-planetary disk, where temperatures were too high for the formation and accretion of water ice. Combined evidence from several radionuclide systems (Pd-Ag, Mn-Cr, Rb-Sr, U-Pb) suggests that water was not incorporated in the Earth in significant quantities until the planet had grown to ˜60-90% of its current size, while core formation was still on-going. Dynamic models of planet formation provide additional evidence for water delivery to the Earth during the same period by water-rich planetesimals originating from the asteroid belt and possibly beyond. This early delivered water may have been partly lost during giant impacts, including the Moon forming event: magma oceans can form in their aftermath, degas and be followed by atmospheric loss. More water may have been delivered and/or lost after core formation during late accretion of extraterrestrial material ("late-veneer"). Stable isotopes of hydrogen, carbon, nitrogen and some noble gases in Earth's materials show similar compositions to those in carbonaceous chondrites, implying a common origin for their water, and only allowing for minor water inputs from comets.

Molybdenum Valence in Basaltic Silicate Melts

NASA Technical Reports Server (NTRS)

Danielson, L. R.; Righter, K.; Newville, M.; Sutton, S.; Pando, K.

2010-01-01

The moderately siderophile element molybdenum has been used as an indicator in planetary differentiation processes, and is particularly relevant to core formation [for example, 1-6]. However, models that apply experimental data to an equilibrium differentiation scenario infer the oxidation state of molybdenum from solubility data or from multivariable coefficients from metal-silicate partitioning data [1,3,7]. Partitioning behavior of molybdenum, a multivalent element with a transition near the J02 of interest for core formation (IW-2) will be sensitive to changes in JO2 of the system and silicate melt structure. In a silicate melt, Mo can occur in either 4+ or 6+ valence state, and Mo6+ can be either octahedrally or tetrahedrally coordinated. Here we present first XANES measurements of Mo valence in basaltic run products at a range of P, T, and JO2 and further quantify the valence transition of Mo.

A simple 3-D numerical model of thermal convection in Earth's growing inner core: on the possibility of the formation of the degree-one structure with lateral viscosity variations

NASA Astrophysics Data System (ADS)

Yoshida, M.

2015-12-01

An east-west hemispherically asymmetric structure for Earth's inner core has been suggested by various seismological evidence, but its origin is not clearly understood. Here, to investigate the possibility of an "endogenic origin" for the degree-one thermal/mechanical structure of the inner core, I performed new numerical simulations of thermal convection in the growing inner core. A setup value that controls the viscosity contrast between the inner core boundary and the interior of the inner core, ΔηT, was taken as a free parameter. Results show that the degree-one structure only appeared for a limited range of ΔηT; such a scenario may be possible but is not considered probable for the real Earth. The degree-one structure may have been realized by an "exogenous factor" due to the planetary-scale thermal coupling among the lower mantle, the outer core, and the inner core, not by an endogenic factor due to the internal rheological heterogeneity.

Does the Momentum Flux Generated by Gravitational Contraction Drive Asymptotic Giant Branch Mass Loss?

NASA Astrophysics Data System (ADS)

Lewis, B. M.

1997-12-01

Gravitational contraction always generates a radially directed momentum flow. A particularly simple example occurs in the electron-degenerate cores of asymptotic giant branch (AGB) stars, which contract steadily under the addition of helium ashes from shell hydrogen burning. The resulting momentum flux is quantified here. And since the cores of AGB stars lack efficient momentum-cancellation mechanisms, they can maintain equilibrium by exporting their excess momentum flux to the stellar envelope, which disposes of much of it in a low velocity wind. Gravitational contraction easily accounts for the momentum flux in the solar wind, as well as the flux required to lift mass into the dust formation zone of every AGB star, whereon radiation pressure continues its ejection as a low-velocity wind. This mechanism explains the dependence of the AGB mass-loss rate on core mass; its generalization to objects with angular momentum and/or strong magnetic fields suggests a novel explanation as to why most planetary nebulae and proto-planetary nebulae exhibit axial symmetry. Quasi-static contraction is inherently biased to the generation of the maximum possible momentum flux. Its formalism is, therefore, readily adapted to providing an upper limit to the momentum flux needed to sustain mass loss when this begins from a semicontinuous rather than an impulsive process.

Gravitational mechanism of active life of the Earth, planets and satellites

NASA Astrophysics Data System (ADS)

Barkin, Yury

2010-05-01

From positions of geodynamic model of the forced gravitational swing, wobble and displacements of shells of a planet are studied and fundamental problems of geodynamics, geology, geophysics, planetary sciences are solved etc.: 1) The mechanism of cyclic variations of activity of natural processes in various time scales. 2) The power of endogenous activity of planetary natural processes on planets and satellites. 3) The phenomenon of polar inversion of natural processes on planets and satellites. 4) Spasmodic and catastrophic changes of activity of natural processes. 5) The phenomenon of twisting of hemispheres (latitude zones or belts) of celestial bodies. 6) Formation of the pear-shaped form of celestial bodies and the mechanism of its change. 7) The ordered planetary structures of geological formations. 8) The phenomena of bipolarity of celestial bodies and antipodality of geology formations. Mechanism. The fundamental feature of a structure of celestial bodies is their shell structure. The most investigated is the internal structure of the Earth. For the Moon and wide set of other bodies of solar system models of an internal structure have been constructed on the basis of the data of observations obtained at studying of their gravitational fields as a result of realization of the appropriate space missions. The basic components for the majority of celestial bodies are the core, the mantle and the crust. To other shells we concern atmospheres (for example, at Venus, Mars, the Titan etc.) and oceanic shells (the Titan, the Earth, Enceladus etc.). Shells are the complex (composite) formations. Planets and satellites are not spherical celestial bodies. The centers of mass of shells of the given planet (or the satellite) and their appropriate principal axes of inertia do not coincide. Accordingly, all their shells are characterized by the certain dynamic oblatenesses. Differences of dynamical oblatenesses results in various forced influences of external celestial bodies on shells of the given body. Dynamical oblatenesses of shells, thus, characterize the endogenous activity of a planet by external celestial bodies. Other important factor of endogenous activity of a planet is a eccentric position of the centers of mass of the shells (for example, of the core and the mantle). The eccentricity of the shells is inherited during geological evolution of a planet as system of shells (Barkin, 2002). Consequences of exitation of the Earth system. The new tides (Barkin, 2005) are caused by relative displacements of the core and mantle. These displacements are reflected in variations of many natural processes due to gravitational action of the core. The displacing core causes deformations of all layers of viscous-elastic mantle. In the given work from more general positions the mechanisms of excitation of a system of shells of the Earth under action of a gravitational attraction of the Sun, the Moon and planets, the phenomena of their relative swings, translational displacements and turns relatively from each other, and the wide list geodynamical consequences of the specified excitation of the Earth are studied. At once we shall emphasize, that the developed geodynamic model has allowed to carry out the important dynamic researches of displacements of shells of the Earth, their deformations and changes, and variations of its natural processes and for the first time to explain the nature of such fundamental phenomena and processes in geodynamics, geology and geophysics as: cyclicity of natural processes and its mechanism; power of processes in various time scales; unity of cyclic processes and universality of their frequency bases; synchronism of geodynamic, geophysical, biophysical and social events; inversion, contrast and opposite directed changes of activity of natural processes in opposite hemispheres of the Earth; step-by-step variations of natural processes, sawtooth course of activity of natural processes in various time scales; orderliness in an distribution of geological formations on the Earth, planets and satellites; existence of antipodal formations on planets and satellites; the phenomenon of twisting of hemispheres of bodies of solar system, twisting of layers and latitudinal zones of shells of celestial bodies including inner layers and shells, etc. All the specified phenomena from the resulted list to some extent are discussed in the given work and illustrated on the basis of modern researches in Earth's sciences and the researches executed by means of space missions. In a complex, the executed researches have shown universality of discussed mechanisms and their important role in dynamics and geoevolution of planets and satellites in other planetary systems, and also stars and pulsars with the systems of planets (Barkin, 2009). Cyclicity. The excitation on the part of external celestial bodies of the system core-mantle depends from relative positions of external celestial bodies, from particularities of their perturbed orbital motions and from rotary motion of the planet. The specified motions have a cyclic nature which is shown in various time scales. Hence, and excitation of shells and their layers will have also cyclic character and to be shown in various time scales. Hence, cyclic variations of all planetary natural processes in all the variety widely should be observed, as takes place in reality. The periods of variations are characterized by extremely wide range - from hours up to tens and hundreds millions years. If the core makes slow secular drift relatively to the mantle all layers and shells of the Earth test secular deformation, thermodynamic and other changes. The cavity of the core and its flows are changed slowly that results in secular variations of a magnetic field (Barkin, 2002, 2009). Inversion and asymmetry of cyclic and secular variations of natural processes. The essence of it rather wide distributed phenomena is, that activity of natural processes varies in an antiphase in opposite hemispheres of the Earth (first of all in northern and southern hemispheres). Told concerns to all geodynamic and geophysical processes, to variations of physical fields, to tectonic and geodetic reorganizations of layers of the Earth, to redistributions of atmospheric, oceanic and other fluid masses of the Earth. The certain asymmetry of displays of processes in northern and southern hemispheres on the other hand is marked. So secular trends of some processes are contrast in northern and southern hemispheres, i.e. velocities of secular changes are essentially different. All described phenomena are caused first of all by cyclic oscillations and secular drift of the core to the north (in present epoch). In longer time scales the similar phenomena of inversion, dissymmetry also have place and determine a nature and style of displacements of continents and lithospheric plates, planetary magmatic activity and plume tectonics as a whole, formation of mountains, elevations and depressions, systems of lineaments and cracks, regressions and transgressions of sea level (Barkin, 2002). Synchronous steps of activity of natural processes. 'For an explanation of observably step-by-step variations of geodynamic and geophysical processes the mechanism of sharp sporadic relative displacements of the core and the mantle and deformations of the mantle in the certain periods of time (the phenomenon of "galloping of the core') is offered.

Condensed matter physics of planets - Puzzles, progress and predictions

NASA Technical Reports Server (NTRS)

Stevenson, D. J.

1984-01-01

Attention is given to some of the major unresolved issues concerned with the physics of planetary interiors. The important advances in observations, and experimental and theoretical investigations are briefly reviewed, and some areas for further study are identified, including: the characteristics of atomic and electronic degrees of freedom at the high pressures and temperatures typical of a condensed planetary core; the behavior of water at megabar pressures; and the nature of the core-alloy in the earth and in the core mantle phase boundary. Consideration is also given to the behavior of carbon at high pressures and temperatures in the presence of oxygen and hydrogen; the behavior of the volatile ice assemblage in Titan at pressures of 2-40 kbar; and the electrical conductivities of matter under planetary core conditions.

ON THE NATURE OF THE TERTIARY COMPANION TO FW TAU: ALMA CO OBSERVATIONS AND SED MODELING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Caceres, Claudio; Hardy, Adam; Schreiber, Matthias R.

2015-06-20

It is thought that planetary mass companions may form through gravitational disk instabilities or core accretion. Identifying such objects in the process of formation would provide the most direct test for the competing formation theories. One of the most promising candidates for a planetary mass object still in formation is the third object in the FW Tau system. We present here ALMA cycle 1 observations confirming the recently published 1.3 mm detection of a dust disk around this third object and present for the first time a clear detection of a single peak {sup 12}CO (2–1) line, providing direct evidencemore » for the simultaneous existence of a gas disk. We perform radiative transfer modeling of the third object in FW Tau and find that current observations are consistent with either a brown dwarf embedded in an edge-on disk or a planet embedded in a low inclination disk, which is externally irradiated by the binary companion. Further observations with ALMA, aiming for high SNR detections of non-contaminated gas lines, are required to conclusively unveil the nature of the third object in FW Tau.« less

Early Earth differentiation [rapid communication

NASA Astrophysics Data System (ADS)

Walter, Michael J.; Trønnes, Reidar G.

2004-09-01

The birth and infancy of Earth was a time of profound differentiation involving massive internal reorganization into core, mantle and proto-crust, all within a few hundred million years of solar system formation ( t0). Physical and isotopic evidence indicate that the formation of iron-rich cores generally occurred very early in planetesimals, the building blocks of proto-Earth, within about 3 million years of t0. The final stages of terrestrial planetary accretion involved violent and tremendously energetic giant impacts among core-segregated Mercury- to Mars-sized objects and planetary embryos. As a consequence of impact heating, the early Earth was at times partially or wholly molten, increasing the likelihood for high-pressure and high-temperature equilibration among core- and mantle-forming materials. The Earth's silicate mantle harmoniously possesses abundance levels of the siderophile elements Ni and Co that can be reconciled by equilibration between iron alloy and silicate at conditions comparable to those expected for a deep magma ocean. Solidification of a deep magma ocean possibly involved crystal-melt segregation at high pressures, but subsequent convective stirring of the mantle could have largely erased nascent layering. However, primitive upper mantle rocks apparently have some nonchondritic major and trace element refractory lithophile element ratios that can be plausibly linked to early mantle differentiation of ultra-high-pressure mantle phases. The geochemical effects of crystal fractionation in a deep magma ocean are partly constrained by high-pressure experimentation. Comparison between compositional models for the primitive convecting mantle and bulk silicate Earth generally allows, and possibly favors, 10-15% total fractionation of a deep mantle assemblage comprised predominantly of Mg-perovskite and with minor but geochemically important amounts of Ca-perovskite and ferropericlase. Long-term isolation of such a crystal pile is generally consistent with isotopic constraints for time-integrated Sm/Nd and Lu/Hf ratios in the modern upper mantle and might account for the characteristics of some mantle isotope reservoirs. Although much remains to be learned about the earliest formative period in the Earth's development, a convergence of theoretical, physical, isotopic and geochemical arguments is beginning to yield a self-consistent portrait of the infant Earth.

Siderophile Element Constraints on the Conditions of Core Formation in Mars

NASA Technical Reports Server (NTRS)

Righter, K.; Humayun, M.

2012-01-01

Siderophile element concentrations in planetary basalts and mantle samples have been used to estimate conditions of core formation for many years and have included applications to Earth, Moon, Mars and asteroid 4 Vesta [1]. For Earth, we have samples of mantle and a diverse collection of mantle melts which have provided a mature understanding of the how to reconstruct the concentration of siderophile elements in mantle materials, from only concentrations in surficial basalt (e.g., [2]). This approach has led to the consensus views that Earth underwent an early magma ocean stage to pressures of 40-50 GPa (e.g., [3,4]), Moon melted extensively and formed a small (approx. 2 mass %) metallic core [5], and 4 Vesta contains a metallic core that is approximately 18 mass % [6,7]. Based on new data from newly found meteorites, robotic spacecraft, and experimental partitioning studies, [8] showed that eight siderophile elements (Ni, Co, Mo, W, Ga, P, V and Cr) are consistent with equilibration of a 20 mass% S-rich metallic core with the mantle at pressures of 14 +/- 3 GPa. We aim to test this rather simple scenario with additional analyses of meteorites for a wide range of siderophile elements, and application of new experimental data for the volatile siderophile and highly siderophile elements.

Molecular Composition and Chemistry of Isolated Dense Cores

NASA Astrophysics Data System (ADS)

Cook, Amanda; Boogert, A.

2009-01-01

The composition of molecular clouds and the envelopes and disks surrounding low mass protostars within them is still poorly known. There is little doubt that a large fraction of the molecules is frozen on grains, but the abundance of several crucial species (e.g. ammonia, methanol, ions) in the ices is still uncertain. In addition, prominent spectral features discovered decades ago are still not securely identified (e.g. the 6.85-micron absorption band). Gas phase and grain surface chemistry play pivotal roles in molecule formation, but numerous other processes could have significant impacts as well: shocks, thermal heating, irradiation of ices by ultraviolet photons and cosmic rays. Complex species could be formed this way, profoundly influencing cloud, disk and planetary/cometary chemistry. We have obtained Spitzer/IRS spectra of an unprecedented sample of sight-lines tracing 25 dense isolated cores. These cores physically differ from the large, cluster-forming molecular clouds (e.g. Ophiuchus, Perseus) that are commonly studied: they are less turbulent, colder, less dense, and likely longer lived. These IRS spectra of isolated cores thus provide unique information on ice formation and destruction mechanisms. Toward the same cores, we observed 33 highly extincted background stars as well, tracing the quiescent cloud medium against which the ices around protostars can be contrasted.

Fracture-induced flow and liquid metal transport during core formation

NASA Astrophysics Data System (ADS)

Jones, V.; Petford, N.; Rushmer, T.; Wertheim, D.

2008-12-01

The most important event in the early history of the earth was the separation of its iron-rich core. Core formation induced profound chemical fractionations and extracted into the core most of Earth's iron and siderophile elements (Ni, Co, Au, Pt, W, Re), leaving the silicate crust and mantle with strong depletions of these elements relative to primitive planetary material. Recent measurements of radiogenic 182W anomalies in the silicate Earth, Mars and differentiated meteorites imply that planetesimals segregated metallic cores within a few Myr of the origin of the solar system. Various models have been put forward to explain the physical nature of the segregation mechanism (Fe-diapirs, 'raining' through a magma ocean), and more recently melt flow via fractures. In this contribution we present the initial results of a numerical study into Fe segregation in a deforming silicate matrix that captures the temperature-dependent effect of liquid metal viscosity on the transport rate. Flow is driven by pressure gradients associated with impact deformation in a growing planetesimal and the fracture geometry is constrained by experimental data on naturally deformed H6 chondrite. Early results suggest that under dynamic conditions, fracture-driven melt flow can in principle be extremely rapid, leading to a significant draining of the Fe-liquid metal and siderophile trace element component on a timescale of hours to days. Fluid transport in planetesimals where deformation is the driving force provides an attractive and simple way of segregating Fe from host silicate as both precursor and primary agent of core formation

The Initial Physical Conditions of Kepler-36 b and c

NASA Astrophysics Data System (ADS)

Owen, James E.; Morton, Timothy. D.

2016-03-01

The Kepler-36 planetary system consists of two exoplanets at similar separations (0.115 and 0.128 au), which have dramatically different densities. The inner planet has a density consistent with an Earth-like composition, while the outer planet is extremely low density, such that it must contain a voluminous H/He envelope. Such a density difference would pose a problem for any formation mechanism if their current densities were representative of their composition at formation. However, both planets are at close enough separations to have undergone significant evaporation in the past. We constrain the core mass, core composition, initial envelope mass, and initial cooling time of each planet using evaporation models conditioned on their present-day masses and radii, as inferred from Kepler photometry and transit timing analysis. The inner planet is consistent with being an evaporatively stripped core, while the outer planet has retained some of its initial envelope due to its higher core mass. Therefore, both planets could have had a similar formation pathway, with the inner planet having an initial envelope-mass fraction of ≲10% and core mass of ˜4.4 M⊕, while the outer had an initial envelope-mass fraction of the order of 15%-30% and core mass ˜7.3 M⊕. Finally, our results indicate that the outer planet had a long (≳30 Myr) initial cooling time, much longer than would naively be predicted from simple timescale arguments. The long initial cooling time could be evidence for a dramatic early cooling episode such as the recently proposed “boil-off” process.

Fictitious Supercontinent Cycles

NASA Astrophysics Data System (ADS)

Marvin Herndon, J.

2014-05-01

"Supercontinent cycles" or "Wilson cycles" is the idea that before Pangaea there were a series of supercontinents that each formed and then broke apart and separated before colliding again, re-aggregating, and suturing into a new supercontinent in a continuing sequence. I suggest that "supercontinent cycles" are artificial constructs, like planetary orbit epicycles, attempts to describe geological phenomena within the framework of problematic paradigms, namely, planetesimal Earth formation and plate tectonics' mantle convection. The so-called 'standard model of solar system formation' is problematic as it would lead to insufficiently massive planetary cores and necessitates additional ad hoc hypotheses such as the 'frost line' between Mars and Jupiter to explain planetary differences and whole-planet melting to explain core formation from essentially undifferentiated matter. The assumption of mantle convection is crucial for plate tectonics, not only for seafloor spreading, but also for continental movement; continent masses are assumed to ride atop convection cells. In plate tectonics, plate collisions are thought to be the sole mechanism for fold-mountain formation. Indeed, the occurrence of mountain chains characterized by folding which significantly predate the breakup of Pangaea is the primary basis for assuming the existence of supercontinent cycles with their respective periods of ancient mountain-forming plate collisions. Mantle convection is physically impossible. Rayleigh Number justification has been misapplied. The mantle bottom is too dense to float to the surface by thermal expansion. Sometimes attempts are made to obviate the 'bottom heavy' prohibition by adopting the tacit assumption that the mantle behaves as an ideal gas with no viscous losses, i.e., 'adiabatic'. But the mantle is a solid that does not behave as an ideal gas as evidenced by earthquakes occurring at depths as great as 660 km. Absent mantle convection, plate tectonics is not valid and there is no motive force for driving supercontinent cycles. The reasonable conclusion one must draw, as in the case of epicycles, is there must exist a new and fundamentally different geoscience paradigm which obviates the problems inherent in plate tectonics and in planetesimal Earth formation and yet better explains geological features. I have disclosed a new indivisible geoscience paradigm, called Whole-Earth Decompression Dynamics (WEDD), that begins with and is the consequence of our planet's early formation as a Jupiter-like gas giant and which permits deduction of: (1) Earth's internal composition and highly-reduced oxidation state; (2) Core formation without whole-planet melting; (3) Powerful new internal energy sources, protoplanetary energy of compression and georeactor nuclear fission energy; (4) Mechanism for heat emplacement at the base of the crust; (5) Georeactor geomagnetic field generation; (6) Decompression-driven geodynamics that accounts for the myriad of observations attributed to plate tectonics without requiring physically-impossible mantle convection, and; (7) A mechanism for fold-mountain formation that does not necessarily require plate collision. The latter obviates the necessity to assume supercontinent cycles. The fundamental basis of geodynamics is this: In response to decompression-driven Earth volume increases, cracks form to increase surface area and mountain ranges characterized by folding form to accommodate changes in curvature. Resources at NuclearPlanet.com .

Ordinary planetary systems - Architecture and formation

NASA Technical Reports Server (NTRS)

Levy, E. H.

1993-01-01

Today we believe ordinary planetary systems to be an unremarkable consequence of star formation. The solar system, so far the only confidently known example in the universe of a planetary system, displays a set of striking structural regularities. These structural regularities provide fossil clues about the conditions and mechanisms that gave rise to the planets. The formation of our planetary system, as well as its general characteristics, resulted from the physical environment in the disk-shaped nebula that accompanied the birth of the sun. Observations of contemporary star formation indicate that the very conditions and mechanisms thought to have produced our own planetary system are widely associated with the birth of stars elsewhere. Consequently, it is reasonable to believe that planetary systems occur commonly, at least in association with single, sunlike stars. Moreover, it is reasonable to believe that many planetary systems have gross characteristics resembling those of our own solar system.

Visualizing Earth's Core-Mantle Interactions using Nanoscale X-ray Tomography

NASA Astrophysics Data System (ADS)

Mao, W. L.; Wang, J.; Yang, W.; Hayter, J.; Pianetta, P.; Zhang, L.; Fei, Y.; Mao, H.; Hustoft, J. W.; Kohlstedt, D. L.

2010-12-01

Early-stage, core-mantle differentiation and core formation represent a pivotal geological event which defined the major geochemical signatures. However current hypotheses of the potential mechanism for core-mantle separation and interaction need more experimental input which has been awaiting technological breakthroughs. Nanoscale x-ray computed tomography (nanoXCT) within a laser-heated diamond anvil cell has exciting potential as a powerful 3D petrographic probe for non-destructive, nanoscale (<40nm) resolution of multiple minerals and amorphous phases (including melts) which are synthesized under the high pressure-temperature conditions found deep within the Earth and planetary interiors. Results from high pressure-temperature experiments which illustrate the potential for this technique will be presented. By extending measurements of the texture, shape, porosity, tortuosity, dihedral angle, and other characteristics of molten Fe-rich alloys in relation to silicates and oxides, along with the fracture systems of rocks under deformation by high pressure-temperature conditions, potential mechanisms of core formation can be tested. NanoXCT can also be used to investigate grain shape, intergrowth, orientation, and foliation -- as well as mineral chemistry and crystallography at core-mantle boundary conditions -- to understand whether shape-preferred orientation is a primary source of the observed seismic anisotropy in Earth’s D” layer and to determine the textures and shapes of the melt pockets and channels which would form putative partial melt which may exist in ultralow velocity zones.

OGLE-2008-BLG-355Lb: A massive planet around a late-type star

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koshimoto, N.; Sumi, T.; Fukagawa, M.

2014-06-20

We report the discovery of a massive planet, OGLE-2008-BLG-355Lb. The light curve analysis indicates a planet:host mass ratio of q = 0.0118 ± 0.0006 at a separation of 0.877 ± 0.010 Einstein radii. We do not measure a significant microlensing parallax signal and do not have high angular resolution images that could detect the planetary host star. Therefore, we do not have a direct measurement of the host star mass. A Bayesian analysis, assuming that all host stars have equal probability to host a planet with the measured mass ratio, implies a host star mass of M{sub h}=0.37{sub −0.17}{sup +0.30}more » M{sub ⊙} and a companion of mass M{sub P}=4.6{sub −2.2}{sup +3.7}M{sub J}, at a projected separation of r{sub ⊥}=1.70{sub −0.30}{sup +0.29} AU. The implied distance to the planetary system is D {sub L} = 6.8 ± 1.1 kpc. A planetary system with the properties preferred by the Bayesian analysis may be a challenge to the core accretion model of planet formation, as the core accretion model predicts that massive planets are far more likely to form around more massive host stars. This core accretion model prediction is not consistent with our Bayesian prior of an equal probability of host stars of all masses to host a planet with the measured mass ratio. Thus, if the core accretion model prediction is right, we should expect that follow-up high angular resolution observations will detect a host star with a mass in the upper part of the range allowed by the Bayesian analysis. That is, the host would probably be a K or G dwarf.« less

Partitioning experiments in the laser-heated diamond anvil cell: volatile content in the Earth's core.

PubMed

Jephcoat, Andrew P; Bouhifd, M Ali; Porcelli, Don

2008-11-28

The present state of the Earth evolved from energetic events that were determined early in the history of the Solar System. A key process in reconciling this state and the observable mantle composition with models of the original formation relies on understanding the planetary processing that has taken place over the past 4.5Ga. Planetary size plays a key role and ultimately determines the pressure and temperature conditions at which the materials of the early solar nebular segregated. We summarize recent developments with the laser-heated diamond anvil cell that have made possible extension of the conventional pressure limit for partitioning experiments as well as the study of volatile trace elements. In particular, we discuss liquid-liquid, metal-silicate (M-Sil) partitioning results for several elements in a synthetic chondritic mixture, spanning a wide range of atomic number-helium to iodine. We examine the role of the core as a possible host of both siderophile and trace elements and the implications that early segregation processes at deep magma ocean conditions have for current mantle signatures, both compositional and isotopic. The results provide some of the first experimental evidence that the core is the obvious replacement for the long-sought, deep mantle reservoir. If so, they also indicate the need to understand the detailed nature and scale of core-mantle exchange processes, from atomic to macroscopic, throughout the age of the Earth to the present day.

Planetary and meteoritic Mg/Si and δ30 Si variations inherited from solar nebula chemistry

NASA Astrophysics Data System (ADS)

Dauphas, Nicolas; Poitrasson, Franck; Burkhardt, Christoph; Kobayashi, Hiroshi; Kurosawa, Kosuke

2015-10-01

The bulk chemical compositions of planets are uncertain, even for major elements such as Mg and Si. This is due to the fact that the samples available for study all originate from relatively shallow depths. Comparison of the stable isotope compositions of planets and meteorites can help overcome this limitation. Specifically, the non-chondritic Si isotope composition of the Earth's mantle was interpreted to reflect the presence of Si in the core, which can also explain its low density relative to pure Fe-Ni alloy. However, we have found that angrite meteorites display a heavy Si isotope composition similar to the lunar and terrestrial mantles. Because core formation in the angrite parent-body (APB) occurred under oxidizing conditions at relatively low pressure and temperature, significant incorporation of Si in the core is ruled out as an explanation for this heavy Si isotope signature. Instead, we show that equilibrium isotopic fractionation between gaseous SiO and solid forsterite at ∼1370 K in the solar nebula could have produced the observed Si isotope variations. Nebular fractionation of forsterite should be accompanied by correlated variations between the Si isotopic composition and Mg/Si ratio following a slope of ∼1, which is observed in meteorites. Consideration of this nebular process leads to a revised Si concentration in the Earth's core of 3.6 (+ 6.0 / - 3.6) wt% and provides estimates of Mg/Si ratios of bulk planetary bodies.

Statistical Constraints from Siderophile Elements on Earth's Accretion, Differentiation, and Initial Core Stratification

NASA Astrophysics Data System (ADS)

O'Rourke, J. G.; Stevenson, D. J.

2015-12-01

Abundances of siderophile elements in the primitive mantle constrain the conditions of Earth's core/mantle differentiation. Core growth occurred as Earth accreted from collisions between planetesimals and larger embryos of unknown original provenance, so geochemistry is directly related to the overall dynamics of Solar System formation. Recent studies claim that only certain conditions of equilibration (pressure, temperature, and oxygen fugacity) during core formation can reproduce the available data. Typical analyses, however, only consider the effects of varying a few out of tens of free parameters in continuous core formation models. Here we describe the Markov chain Monte Carlo method, which simultaneously incorporates the large uncertainties on Earth's composition and the parameterizations that describe elemental partitioning between metal and silicate. This Bayesian technique is vastly more computationally efficient than a simple grid search and is well suited to models of planetary accretion that involve a plethora of variables. In contrast to previous work, we find that analyses of siderophile elements alone cannot yield a unique scenario for Earth's accretion. Our models predict a wide range of possible light element contents for the core, encompassing all combinations permitted by seismology and mineral physics. Specifically, we are agnostic between silicon and oxygen as the dominant light element, and the addition of carbon or sulfur is also permissible but not well constrained. Redox conditions may have remained roughly constant during Earth's accretion or relatively oxygen-rich material could have been incorporated before reduced embryos. Pressures and temperatures of equilibration, likewise, may only increase slowly throughout accretion. Therefore, we do not necessarily expect a thick (>500 km), compositionally stratified layer that is stable against convection to develop at the top of the core of Earth (or, by analogy, Venus). A thinner stable layer might inhibit the initialization of the dynamo.

Terrestrial Planet Formation in Binary Star Systems

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; Quintana, Elisa V.; Chambers, John; Duncan, Martin J.; Adams, Fred

2003-01-01

Most stars reside in multiple star systems; however, virtually all models of planetary growth have assumed an isolated single star. Numerical simulations of the collapse of molecular cloud cores to form binary stars suggest that disks will form within such systems. Observations indirectly suggest disk material around one or both components within young binary star systems. If planets form at the right places within such circumstellar disks, they can remain in stable orbits within the binary star systems for eons. We are simulating the late stages of growth of terrestrial planets within binary star systems, using a new, ultrafast, symplectic integrator that we have developed for this purpose. We show that the late stages of terrestrial planet formation can indeed take place in a wide variety of binary systems and we have begun to delineate the range of parameter space for which this statement is true. Results of our initial simulations of planetary growth around each star in the alpha Centauri system and other 'wide' binary systems, as well as around both stars in very close binary systems, will be presented.

Towards combined modeling of planetary accretion and differentiation

NASA Astrophysics Data System (ADS)

Golabek, G. J.; Gerya, T. V.; Morishima, R.; Tackley, P. J.; Labrosse, S.

2012-09-01

accretion yield an onion-like thermal structure with very high internal temperatures due to powerful short-lived radiogenic heating in the planetesimals. These lead to extensive silicate melting in the parent bodies. Yet, magma ocean and impact processes are not considered in these models and core formation is, if taken into account, assumed to be instantaneous with no feedback on the mantle evolution. It was pointed out that impacts can not only deposit heat deep into the target body, which is later buried by ejecta of further impacts [1], but also that impacts expose in the crater region originally deep-seated layers, thus cooling the interior [2]. This combination of impact effects becomes even more important when we consider that planetesimals of all masses contribute to planetary accretion. This leads occasionally to collisions between bodies with large ratios between impactor and target mass. Thus, all these processes can be expected to have a profound effect on the thermal evolution during the epoch of planetary accretion and may have implications for the onset of mantle convection and cannot be described properly in 1D geometry. Here we present a new methodology, which can be used to simulate the internal evolution of a planetary body during accretion and differentiation: Using the N-body code PKDGRAV[3] we simulate the accretion of planetary embryos from an initial annulus of several thousand planetesimals. The growth history of the largest resulting planetary embryo is used as an input for the thermomechanical 2D code I2ELVIS [4]. The thermomechanical model takes recent parametrizations of impact processes like impact heating and crater excavation [5] into account. The model also includes both long- and short-lived radiogenic isotopes and a more realistic treatment of largely molten silicates [6]. Results show that late-formed planetesimals do not experience silicate melting and avoid thermal alteration, whereas in early-formed bodies accretion and iron core growth occur almost simultaneously and magma oceans develop in the interior of these bodies. These tend to form first close to the coremantle boundary and migrate upwards with growing internal pressure.

Efficiency of planetesimal ablation in giant planetary envelopes

NASA Astrophysics Data System (ADS)

Pinhas, Arazi; Madhusudhan, Nikku; Clarke, Cathie

2016-12-01

Observations of exoplanetary spectra are leading to unprecedented constraints on their atmospheric elemental abundances, particularly O/H, C/H, and C/O ratios. Recent studies suggest that elemental ratios could provide important constraints on formation and migration mechanisms of giant exoplanets. A fundamental assumption in such studies is that the chemical composition of the planetary envelope represents the sum-total of compositions of the accreted gas and solids during the formation history of the planet. We investigate the efficiency with which accreted planetesimals ablate in a giant planetary envelope thereby contributing to its composition rather than sinking to the core. From considerations of aerodynamic drag causing `frictional ablation' and the envelope temperature structure causing `thermal ablation', we compute mass ablations for impacting planetesimals of radii 30 m to 1 km for different compositions (ice to iron) and a wide range of velocities and impact angles, assuming spherical symmetry. Icy impactors are fully ablated in the outer envelope for a wide range of parameters. Even for Fe impactors substantial ablation occurs in the envelope for a wide range of sizes and velocities. For example, iron impactors of sizes below ˜0.5 km and velocities above ˜30 km s-1 are found to ablate by ˜60-80 per cent within the outer envelope at pressures below 103 bar due to frictional ablation alone. For deeper pressures (˜107 bar), substantial ablation happens over a wider range of parameters. Therefore, our exploratory study suggests that atmospheric abundances of volatile elements in giant planets reflect their accretion history during formation.

Disentangling hot Jupiters formation location from their chemical composition

NASA Astrophysics Data System (ADS)

Ali-Dib, Mohamad

2017-05-01

We use a population synthesis model that includes pebbles and gas accretion, planetary migration and a simplified chemistry scheme to study the formation of hot Jupiters. Models have been proposed that these planets can either originate beyond the snowline and then move inwards via disc migration, or form 'in situ' inside the snowline. The goal of this work is to verify which of these two scenarios is more compatible with pebble accretion, and whether we can distinguish observationally between them via the resulting planetary C/O ratios and core masses. Our results show that for Solar system composition, the C/O ratios will vary but moderately between the two populations, since a significant amount of carbon and oxygen is locked up in refractories. In this case, we find a strong correlation between the carbon and oxygen abundances and core mass. The C/O ratio variations are more pronounced in the case where we assume that all carbon and oxygen are in volatiles. On average, hot Jupiters forming 'in situ' inside the snowline will have higher C/O ratios because they accrete less water ice. However, only hot Jupiters forming in situ around stars with C/O = 0.8 can have a C/O ratio higher than unity. We finally find that even with fast pebble accretion, it is significantly easier to form hot Jupiters outside of the snowline, even if forming these 'in situ' is not impossible in the limit of the simplifying assumptions made.

Evidence for Reduced, Carbon-rich Regions in the Solar Nebula from an Unusual Cometary Dust Particle

NASA Astrophysics Data System (ADS)

De Gregorio, Bradley T.; Stroud, Rhonda M.; Nittler, Larry R.; Kilcoyne, A. L. David

2017-10-01

Geochemical indicators in meteorites imply that most formed under relatively oxidizing conditions. However, some planetary materials, such as the enstatite chondrites, aubrite achondrites, and Mercury, were produced in reduced nebular environments. Because of large-scale radial nebular mixing, comets and other Kuiper Belt objects likely contain some primitive material related to these reduced planetary bodies. Here, we describe an unusual assemblage in a dust particle from comet 81P/Wild 2 captured in silica aerogel by the NASA Stardust spacecraft. The bulk of this ˜20 μm particle is comprised of an aggregate of nanoparticulate Cr-rich magnetite, containing opaque sub-domains composed of poorly graphitized carbon (PGC). The PGC forms conformal shells around tiny 5-15 nm core grains of Fe carbide. The C, N, and O isotopic compositions of these components are identical within errors to terrestrial standards, indicating a formation inside the solar system. Magnetite compositions are consistent with oxidation of reduced metal, similar to that seen in enstatite chondrites. Similarly, the core-shell structure of the carbide + PGC inclusions suggests a formation via FTT reactions on the surface of metal or carbide grains in warm, reduced regions of the solar nebula. Together, the nanoscale assemblage in the cometary particle is most consistent with the alteration of primary solids condensed from a C-rich, reduced nebular gas. The nanoparticulate components in the cometary particle provide the first direct evidence from comets of reduced, carbon-rich regions that were present in the solar nebula.

Phase Equilibrium Investigations of Planetary Materials

NASA Technical Reports Server (NTRS)

Grove, T. L.

2005-01-01

This grant provided funds to carry out phase equilibrium studies on the processes of chemical differentiation of the moon and the meteorite parent bodies, during their early evolutionary history. Several experimental studies examined processes that led to the formation of lunar ultramafic glasses. Phase equilibrium studies were carried out on selected low-Ti and high-Ti lunar ultramafic glass compositions to provide constraints on the depth range, temperature and processes of melt generation and/or assimilation. A second set of experiments examined the role of sulfide melts in core formation processes in the earth and terrestrial planets. The major results of each paper are discussed, and copies of the papers are attached as Appendix I.

The Fuzziness of Giant Planets’ Cores

DOE Office of Scientific and Technical Information (OSTI.GOV)

Helled, Ravit; Stevenson, David

2017-05-01

Giant planets are thought to have cores in their deep interiors, and the division into a heavy-element core and hydrogen–helium envelope is applied in both formation and structure models. We show that the primordial internal structure depends on the planetary growth rate, in particular, the ratio of heavy elements accretion to gas accretion. For a wide range of likely conditions, this ratio is in one-to-one correspondence with the resulting post-accretion profile of heavy elements within the planet. This flux ratio depends sensitively on the assumed solid-surface density in the surrounding nebula. We suggest that giant planets’ cores might not bemore » distinct from the envelope and includes some hydrogen and helium, and the deep interior can have a gradual heavy-element structure. Accordingly, Jupiter’s core may not be well defined. Accurate measurements of Jupiter’s gravitational field by Juno could put constraints on Jupiter’s core mass. However, as we suggest here, the definition of Jupiter’s core is complex, and the core’s physical properties (mass, density) depend on the actual definition of the core and on the planet’s growth history.« less

Siderophile Element Constraints on the Origin of the Moon

NASA Astrophysics Data System (ADS)

Walker, R. J.; Day, J. M.

2016-12-01

Siderophile elements provide important clues to the origin of the Moon. One key feature of the Earth-Moon system is the estimated 20X lower abundances of highly siderophile elements (HSE) in the accessible lunar mantle, compared to the bulk silicate Earth. This has been attributed to the disproportional addition of materials with chondritic bulk compositions to the mantles of each body by stochastic late accretion. When corrected for late accretionary differences, the two bodies appear to have 182W compositions that are identical to within a few ppm. This observation follows other evidence for isotopic similarity between the two bodies (e.g., O, Ti and Cr) which record the genetic signatures of planetary building blocks. Giant impact models have been sought to account for the isotopic similarities between the Moon and Earth, given the outcomes of some scenarios that the Moon is composed mainly of impactor materials. This may indicate the proto-Earth and giant impactor formed from genetically similar materials. The similarity in 182W is more problematic because the 182Hf-182W system is radiogenic (t½ = 8.9 Ma), and the proportion of 182W present in each body reflects the average timing of core formation, combined with the Hf/W. The collision of two planetary bodies with essentially identical 182W is improbable, so the isotopic match provides strong evidence of isotopic mixing between the Earth's mantle and proto-lunar disk. The identical 182W for the Earth and Moon at the time of formation also argues for formation of the Moon >60 Ma after solar system formation, as previously suggested, although this constraint is relaxed if the Hf/W of the mantles of both bodies are the same to within a few percent. The homogeneity of 182W in disparate products of the lunar magma ocean also argues for system closure occurring >60 Ma after solar system formation. If the interpretation of disproportional late accretion is correct, then the late accretionary accumulation clocks for both the Moon and Earth began at the time of the giant impact, which must have been a clearinghouse event for any HSE that were present in the terrestrial mantle prior to the impact. This means that at least some of the metal from the core of the impactor efficiently extracted HSE from the silicate Earth while en route to merge with Earth's core.

Neutron capture on Pt isotopes in iron meteorites and the Hf-W chronology of core formation in planetesimals

NASA Astrophysics Data System (ADS)

Kruijer, Thomas S.; Fischer-Gödde, Mario; Kleine, Thorsten; Sprung, Peter; Leya, Ingo; Wieler, Rainer

2013-01-01

The short-lived 182Hf-182W isotope system can provide powerful constraints on the timescales of planetary core formation, but its application to iron meteorites is hampered by neutron capture reactions on W isotopes resulting from exposure to galactic cosmic rays. Here we show that Pt isotopes in magmatic iron meteorites are also affected by capture of (epi)thermal neutrons and that the Pt isotope variations are correlated with variations in 182W/184W. This makes Pt isotopes a sensitive neutron dosimeter for correcting cosmic ray-induced W isotope shifts. The pre-exposure 182W/184W derived from the Pt-W isotope correlations of the IID, IVA and IVB iron meteorites are higher than most previous estimates and are more radiogenic than the initial 182W/184W of Ca-Al-rich inclusions (CAI). The Hf-W model ages for core formation range from +1.6±1.0 million years (Ma; for the IVA irons) to +2.7±1.3 Ma after CAI formation (for the IID irons), indicating that there was a time gap of at least ˜1 Ma between CAI formation and metal segregation in the parent bodies of some iron meteorites. From the Hf-W ages a time limit of <1.5-2 Ma after CAI formation can be inferred for the accretion of the IID, IVA and IVB iron meteorite parent bodies, consistent with earlier conclusions that the accretion of differentiated planetesimals predated that of most chondrite parent bodies.

Studies of hydrodynamic events in stellar evolution. 3: Ejection of planetary nebulae

NASA Technical Reports Server (NTRS)

Sparks, W. M.; Kutter, G. S.

1973-01-01

The dynamic behavior of the H-rich envelope (0.101 solar mass) of an evolved star (1.1 solar mass) as the luminosity rises to 19000 solar luminosity during the second ascent of the red giant branch. For luminosities in the range 3100 L 19000 solar luminosity the H-rich envelope pulsates like a long-period variable (LPV) with periods of the order of a year. As L reaches 19000 solar luminosity, the entire H-rich envelope is ejected as a shell with speeds of a few 10 km/s. The ejection occurs on a timescale of a few LPV pulsation periods. This ejection is associated with the formation of a planetary nebula. The computations are based on an implicit hydrodynamic computer code. T- and RHO-dependent opacities and excitation and ionization energies are included. As the H-rich envelope is accelerated off the stellar core, the gap between envelope and core is approximated by a vacuum, filled with radiation. Across the vacuum, the luminosity is conserved and the anisotropy of the radiation is considered as well as the solid angle subtended by the remnant star at the inner surface of the H-rich envelope. Spherical symmetry and the diffusion approximation are assumed.

Jupiter Formation, Life in the Slow Lane?

NASA Astrophysics Data System (ADS)

Hamilton, D. P.; Kortenkamp, S. J.; Fleming, H. J.

2000-10-01

The growth of Jupiter, as predicted by the favored core-accretion model of planetary formation, is a two-stage process. First an ≈ 10 Earth mass core is formed by runaway growth of an icy protoplanet, after which the protoplanet gravitationally captures over 300 Earth masses of gas directly from the Solar Nebula. The process is thought to take ≈ 107 years. An alternate possibility, the mass-instability hypothesis, has recently experienced a resurgence of interest due to the increasingly rapid discoveries of unusual jovian-mass extrasolar planets. A sufficiently massive gas disk can become unstable and form an azimuthally asymmetric blob destined to become a giant planet in as short as 102 years. Which process actually formed Jupiter? Trojan asteroids, very numerous and with close dynamical links to Jupiter, are ideally suited to provide critical clues about Jupiter's formation. A number of processes could potentially capture objects into 1:1 resonance with Jupiter including radial migration, gas drag, mass accretion, collisional emplacement, disk tides, and gravitational scattering by massive protoplanetary embryos. We are currently undertaking a systematic study of each of these processes. The mass-instability scenario, in its simplest form, posits a fully-formed Jupiter with L4 and L5 points clear of gas and unpopulated with Trojans. By contrast, in the core-accretion model, precursor material is already trapped in 1:1 resonance with the jovian core. Furthermore, subsequent mass accretion and gas drag systematically concentrate matter toward the L4 and L5 points. The emerging theme is that a populous Trojan region is more easily achieved by the slower core-accretion model.

Fragmentation and Thermochemical Exchanges during Planetary Core Formation - an Experimental Approach

NASA Astrophysics Data System (ADS)

Le Bars, M.; Wacheul, J. B.

2015-12-01

Telluric planet formation involved the settling of large amounts of liquid iron coming from impacting planetesimals into an ambient viscous magma ocean. The initial state of planets was mostly determined by exchanges of heat and elements during this iron rain. Up to now, most models of planet formation simply assume that the metal rapidly equilibrated with the whole mantle. Other models account for simplified dynamics of the iron rain, involving the settling of single size drops at the Stokes velocity. But the fluid dynamics of iron sedimentation is much more complex, and influenced by the large viscosity ratio between the metal and the ambient fluid, as shown in studies of rising gas bubbles (e.g. Bonometti and Magnaudet 2006). We aim at developing a global understanding of the iron rain dynamics. Our study relies on a model experiment, consisting in popping a balloon of heated metal liquid at the top of a tank filled with viscous liquid. The experiments reach the relevant turbulent planetary regime, and tackle the whole range of expected viscosity ratios. High-speed videos allow determining the dynamics of drop clouds, as well as the statistics of drop sizes, shapes, and velocities. We also develop an analytical model of turbulent diffusion during settling, validated by measuring the temperature decrease of the metal blob. We finally present consequences for models of planet formation.

Toward a mineral physics reference model for the Moon's core.

PubMed

Antonangeli, Daniele; Morard, Guillaume; Schmerr, Nicholas C; Komabayashi, Tetsuya; Krisch, Michael; Fiquet, Guillaume; Fei, Yingwei

2015-03-31

The physical properties of iron (Fe) at high pressure and high temperature are crucial for understanding the chemical composition, evolution, and dynamics of planetary interiors. Indeed, the inner structures of the telluric planets all share a similar layered nature: a central metallic core composed mostly of iron, surrounded by a silicate mantle, and a thin, chemically differentiated crust. To date, most studies of iron have focused on the hexagonal closed packed (hcp, or ε) phase, as ε-Fe is likely stable across the pressure and temperature conditions of Earth's core. However, at the more moderate pressures characteristic of the cores of smaller planetary bodies, such as the Moon, Mercury, or Mars, iron takes on a face-centered cubic (fcc, or γ) structure. Here we present compressional and shear wave sound velocity and density measurements of γ-Fe at high pressures and high temperatures, which are needed to develop accurate seismic models of planetary interiors. Our results indicate that the seismic velocities proposed for the Moon's inner core by a recent reanalysis of Apollo seismic data are well below those of γ-Fe. Our dataset thus provides strong constraints to seismic models of the lunar core and cores of small telluric planets. This allows us to propose a direct compositional and velocity model for the Moon's core.

Disk tides and accretion runaway

NASA Technical Reports Server (NTRS)

Ward, William R.; Hahn, Joseph M.

1995-01-01

It is suggested that tidal interaction of an accreting planetary embryo with the gaseous preplanetary disk may provide a mechanism to breach the so-called runaway limit during the formation of the giant planet cores. The disk tidal torque converts a would-be shepherding object into a 'predator,' which can continue to cannibalize the planetesimal disk. This is more likely to occur in the giant planet region than in the terrestrial zone, providing a natural cause for Jupiter to predate the inner planets and form within the O(10(exp 7) yr) lifetime of the nebula.

Collisional and Dynamical Evolution of Planetary Systems

NASA Technical Reports Server (NTRS)

Weidenschilling, Stuart J.

2004-01-01

Senior Scientst S. J. Weidenschilling presents his final administrative report in the research program entitled "Collisional and Dynamical Evolution of Planetary Systems," on which he was the Principal Investigator. This research program produced the following publications: 1) "Jumping Jupiters" in binary star systems. F. Marzari, S. J. Weidenschilling, M. Barbieri and V. Granata. Astrophys. J., in press, 2005; 2) Formation of the cores of the outer planets. To appear in "The Outer Planets" (R. Kallenbach, ED), ISSI Conference Proceedings (Space Sci. Rev.), in press, 2005; 3) Accretion dynamics and timescales: Relation to chondrites. S. J. Weidenschilling and J. Cuzzi. In Meteorites and the Early Solar System LI (D. Lauretta et al., Eds.), Univ. of Arizona Press, 2005; 4) Asteroidal heating and thermal stratification of the asteroid belt. A. Ghosh, S. J.Weidenschilling, H. Y. McSween, Jr. and A. Rubin. In Meteorites and the Early Solar System I1 (D. Lauretta et al., Eds.), Univ. of Arizona Press, 2005.

Disk-Planet Torques from Radiation-Hydrodynamics Calculations with Spatially-Resolved Planetary Envelopes Undergoing Solids' Accretion

NASA Astrophysics Data System (ADS)

D'Angelo, G.

2016-12-01

D'Angelo & Bodenheimer (2013, ApJ, 778, 77) performed global 3D radiation-hydrodynamics disk-planet simulations aimed at studying envelope formation around planetary cores, during the phase of sustained planetesimal accretion. The calculations modeled cores of 5, 10, and 15 Earth masses orbiting a sun-like star in a protoplanetary disk extending from ap/2 to 2ap in radius, ap=5 or 10 AU being the core's orbital radius. The gas equation of state - for a solar mixture of H2, H, He - accounted for translational, rotational, and vibrational states, for molecular dissociation and atomic ionization, and for radiation energy. Dust opacity calculations applied the Mie theory to multiple grain species whose size distributions ranged from 5e-6 to 1 mm. Mesh refinement via grid nesting allowed the planets' envelopes to be resolved at the core-radius length scale. Passive tracers were used to determine the volume of gas bound to a core, defining the envelope, and resulting in planet radii comparable to the Bondi radius. The energy budjet included contributions from the accretion of solids on the cores, whose rates were self-consistently computed with a 1D planet formation code. At this stage of the planet's growth, gravitational energy released in the envelope by solids' accretion far exceeds that released by gas accretion. These models are used to determine the gravitational torques exerted by the disk's gas on the planet and the resulting orbital migration rates. Since the envelope radius is a direct product of the models, they allow for a non-ambiguous assessment of the torques exerted by gas not bound to the planet. Additionally, since planets' envelopes are fully resolved, thermal and dynamical effects on the surrounding disk's gas are accurately taken into account. The computed migration rates are compared to those obtained from existing semi-analytical formulations for planets orbiting in isothermal and adiabatic disks. Because these formulations do not account for thermodynamical interactions between the planet's envelope and the disk's gas, the numerical models are also used to quanitfy the impact of short-scale tidal interactions on the total torque acting on the planet. Computing resources were provided by the NASA High-End Computing Program through the NASA Advanced Supercomputing Division at Ames Research Center.

HUBBLE PROBES THE VIOLENT BIRTH OF STARS IN GALAXY NGC 253 [Left

NASA Technical Reports Server (NTRS)

2002-01-01

An image of the spiral galaxy NGC 253, taken with a ground-based telescope. The galaxy is located about 8 million light-years away in the constellation Sculptor. Credit: Jay Gallagher (University of Wisconsin-Madison), Alan Watson (Lowell Observatory, Flagstaff, AZ), and NASA [Right] This NASA Hubble Space Telescope image of the core of the nearest starburst spiral galaxy, NGC 253, reveals violent star formation within a region 1,000 light-years across. A starburst galaxy has an exceptionally high rate of star birth, first identified by its excess of infrared radiation from warm dust. Hubble's high resolution allows astronomers to quantify complex structures in the starburst core of the galaxy for the first time, including luminous star clusters, dust lanes which trace regions of dense gas and filaments of glowing gas. Hubble identifies several regions of intense star formation, which include a bright, super-compact star cluster. These observations confirm that stars are often born in dense clusters within starbursts, and that dense gas coexists with and obscures the starburst core. This image was taken with Hubble's Wide Field Planetary Camera 2 (in PC mode). Credit: Carnegie Institution of Washington

Paleomagnetic evidence for dynamo activity driven by inward crystallisation of a metallic asteroid

NASA Astrophysics Data System (ADS)

Bryson, James F. J.; Weiss, Benjamin P.; Harrison, Richard J.; Herrero-Albillos, Julia; Kronast, Florian

2017-08-01

The direction in which a planetary core solidifies has fundamental implications for the feasibility and nature of dynamo generation. Although Earth's core is outwardly solidifying, the cores of certain smaller planetary bodies have been proposed to inwardly solidify due to their lower central pressures. However, there have been no unambiguous observations of inwardly solidified cores or the relationship between this solidification regime and planetary magnetic activity. To address this gap, we present the results of complimentary paleomagnetic techniques applied to the matrix metal and silicate inclusions within the IVA iron meteorites. This family of meteorites has been suggested to originate from a planetary core that had its overlaying silicate mantle removed by collisions during the early solar system. This process is thought to have produced a molten ball of metal that cooled rapidly and has been proposed to have inwardly solidified. Recent thermal evolution models of such a body predict that it should have generated an intense, multipolar and time-varying dynamo field. This field could have been recorded as a remanent magnetisation in the outer, cool layers of a solid crust on the IVA parent core. We find that the different components in the IVA iron meteorites display a range of paleomagnetic fidelities, depending crucially on the cooling rate of the meteorite. In particular, silicate inclusions in the quickly cooled São João Nepomuceno meteorite are poor paleomagnetic recorders. On the other hand, the matrix metal and some silicate subsamples from the relatively slowly cooled Steinbach meteorite are far better paleomagnetic recorders and provide evidence of an intense (≳100 μT) and directionally varying (exhibiting significant changes on a timescale ≲200 kyr) magnetic field. This is the first demonstration that some iron meteorites record ancient planetary magnetic fields. Furthermore, the observed field intensity, temporal variability and dynamo lifetime are consistent with thermal evolution models of the IVA parent core. Because the acquisition of remanent magnetisation by some IVA iron meteorites require that they cooled below their Curie temperature during the period of dynamo activity, the magnetisation carried by Steinbach also provides strong evidence favouring the inward solidification of its parent core.

In-situ Density and Thermal Expansion Measurements of Fe and Fe-S Alloying Liquids Under Planetary Core Conditions

NASA Astrophysics Data System (ADS)

Jing, Z.; Chantel, J.; Yu, T.; Sakamaki, T.; Wang, Y.

2015-12-01

Liquid iron is likely the dominant constituent in the cores of terrestrial planets and icy satellites such as Earth, Mars, Mercury, the Moon, Ganymede, and Io. Suggested by geophysical and geochemical observations, light elements such as S, C, Si, etc., are likely present in planetary cores. These light elements can significantly reduce the density and melting temperature of the Fe cores, and hence their abundances are crucial to our understanding of the structure and thermal history of planetary cores, as well as the generation of intrinsic magnetic fields. Knowledge on the density of Fe-light element alloying liquids at high pressures is critical to place constraints on the composition of planetary cores. However, density data on liquid Fe-light element alloys at core pressures are very limited in pressure and composition and are sometimes controversial. In this study, we extend the density dataset for Fe-rich liquids by measuring the density of Fe, Fe-10wt%S, Fe-20wt%S, Fe-27wt%S, and FeS liquids using the X-ray absorption technique in a DIA-type multianvil apparatus up to 7 GPa and 2173 K. An ion chamber (1D-detector) and a CCD camera (2D-detector) were used to measure intensities of transmitted monochromatic X-rays through molten samples, with the photon energy optimized at 40 keV. The densities were then determined from the Beer-Lambert law using the mass absorption coefficients, calibrated by solid standards using X-ray diffraction. At each pressure, density measurements were conducted at a range of temperatures above the liquidus of the samples, enabling the determination of thermal expansion. Combined with our previous results on the sound velocity of Fe and Fe-S liquids at high pressures (Jing et al., 2014, Earth Planet. Sci. Lett. 396, 78-87), these data provide tight constraints on the equation of state and thermodynamic properties such as the adiabatic temperature gradient for Fe-S liquids. We will discuss these results with implications to planetary cores.

Evidence of an Upper Bound on the Masses of Planets and Its Implications for Giant Planet Formation

NASA Astrophysics Data System (ADS)

Schlaufman, Kevin C.

2018-01-01

Celestial bodies with a mass of M≈ 10 {M}{Jup} have been found orbiting nearby stars. It is unknown whether these objects formed like gas-giant planets through core accretion or like stars through gravitational instability. I show that objects with M≲ 4 {M}{Jup} orbit metal-rich solar-type dwarf stars, a property associated with core accretion. Objects with M≳ 10 {M}{Jup} do not share this property. This transition is coincident with a minimum in the occurrence rate of such objects, suggesting that the maximum mass of a celestial body formed through core accretion like a planet is less than 10 {M}{Jup}. Consequently, objects with M≳ 10 {M}{Jup} orbiting solar-type dwarf stars likely formed through gravitational instability and should not be thought of as planets. Theoretical models of giant planet formation in scaled minimum-mass solar nebula Shakura–Sunyaev disks with standard parameters tuned to produce giant planets predict a maximum mass nearly an order of magnitude larger. To prevent newly formed giant planets from growing larger than 10 {M}{Jup}, protoplanetary disks must therefore be significantly less viscous or of lower mass than typically assumed during the runaway gas accretion stage of giant planet formation. Either effect would act to slow the Type I/II migration of planetary embryos/giant planets and promote their survival. These inferences are insensitive to the host star mass, planet formation location, or characteristic disk dissipation time.

Kepler Planet Formation

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.

2015-01-01

Kepler has vastly increased our knowledge of planets and planetary systems located close to stars. The new data shows surprising results for planetary abundances, planetary spacings and the distribution of planets on a mass-radius diagram. The implications of these results for theories of planet formation will be discussed.

The Formation of a Planetary Nebula.

ERIC Educational Resources Information Center

Harpaz, Amos

1991-01-01

Proposes a scenario to describe the formation of a planetary nebula, a cloud of gas surrounding a very hot compact star. Describes the nature of a planetary nebula, the number observed to date in the Milky Way Galaxy, and the results of research on a specific nebula. (MDH)

The postcollapse core of M15 imaged with the HST planetary camera

NASA Technical Reports Server (NTRS)

Lauer, Tod R.; Holtzman, Jon A.; Faber, S. M.; Baum, William A.; Currie, Douglas G.; Ewald, S. P.; Groth, Edward J.; Hester, J. Jeff; Kelsall, T.

1991-01-01

It is shown here that, despite the severe spherical aberration present in the HST, the Wide Field/Planetary Camera (WFPC) images still present useful high-resolution information on M15, the classic candidate for a cluster with a collapsed core. The stars in M15 have been resolved down to the main-sequence turnoff and have been subtracted from the images. The remaining faint, unresolved stars form a diffuse background with a surprisingly large core with r(c) = 0.13 pc. The existence of a large core interior to the power-law cusp may imply that M15 has evolved well past maximum core collapse and may rule out the presence of a massive central black hole as well.

The effects of sulfur on carbon partitioning and solubility in high pressure-temperature alloy-silicate systems: Implications for fractionation of carbon and sulfur during accretion and core formation of Earth and Mars

NASA Astrophysics Data System (ADS)

Tsuno, K.; Dasgupta, R.; Grewal, D. S.

2017-12-01

Constraining the carbon (C) fractionation between the silicate magma ocean (MO) and core-forming alloy liquid is required to determine the origin and evolution of C between reservoirs such as atmosphere, crust, mantle, and core of terrestrial planets. [1]. Alloy-silicate partitioning experiments of C have shown that preferential fractionation of C into the alloy liquid would have left the bulk silicate Earth (BSE) devoid of C [2-4]. Merger of a sulfur (S)-rich differentiated planetary embryo into the proto-Earth could have supplied almost the entire C budget of the present-day BSE [5], however, experimental data on the systematic effect of S on C solubility in Fe-Ni alloy liquid and its partitioning between the alloy liquid and silicate melt are lacking. We have performed multi anvil experiments with alloy-silicate±glassy carbon mixtures at 6-13 GPa and 1800-2000 °C, fO2 of ΔIW of -0.4 to -2.3, using graphite or MgO capsules and varying alloy S content from 10 to 36 wt.%. We find that C content of the alloy liquid decreases from 4.6 to 0.2 wt.% with increasing alloy S content of 10 to 36 wt.%. Temperature has a small positive effect and pressure has little effect on alloy C solubility. Alloy-silicate partition coefficient of C also decreases with increasing alloy S content at a given P-T-fO2. We used the data to quantify the distribution of C between the silicate MO and core-forming alloy liquid of an S-rich planetary embryo. The model calculations using our data suggest that the addition of a relatively oxidized, C-poor ( 0.3 wt.%) and S-rich ( 3 wt.%) large embryo (6-20% of the present-day Earth mass) to a volatile-poor growing Earth can establish the C and S contents [6, 7] and C/S ratio [8] in BSE. The resulting core composition after the accretion and core formation process is estimated to be C- and S-poor ( 0.05 wt.% and 0.6 wt.%, respectively). On the other hand, a single stage core formation on Mars that results in a core with 8-10 wt.% S can yield a mantle with terrestrial-mantle like carbon abundance if the bulk Mars contains 0.6 wt.% C and 1.5-1.7 wt.% S. [1] Dasgupta (2013) RiMG. [2] Dasgupta et al. (2013) GCA. [3] Chi et al. (2014) GCA. [4] Li et al. (2015) EPSL. [5] Li et al. (2016) Nat. Geo. [6] Dasgupta & Hirschmann (2010) EPSL. [7] Palme & O'Neill (2013), Treat. Geochem. [8] Hirschmann (2016) Am Min.

Toward a mineral physics reference model for the Moon’s core

PubMed Central

Antonangeli, Daniele; Morard, Guillaume; Schmerr, Nicholas C.; Komabayashi, Tetsuya; Krisch, Michael; Fiquet, Guillaume; Fei, Yingwei

2015-01-01

The physical properties of iron (Fe) at high pressure and high temperature are crucial for understanding the chemical composition, evolution, and dynamics of planetary interiors. Indeed, the inner structures of the telluric planets all share a similar layered nature: a central metallic core composed mostly of iron, surrounded by a silicate mantle, and a thin, chemically differentiated crust. To date, most studies of iron have focused on the hexagonal closed packed (hcp, or ε) phase, as ε-Fe is likely stable across the pressure and temperature conditions of Earth’s core. However, at the more moderate pressures characteristic of the cores of smaller planetary bodies, such as the Moon, Mercury, or Mars, iron takes on a face-centered cubic (fcc, or γ) structure. Here we present compressional and shear wave sound velocity and density measurements of γ-Fe at high pressures and high temperatures, which are needed to develop accurate seismic models of planetary interiors. Our results indicate that the seismic velocities proposed for the Moon’s inner core by a recent reanalysis of Apollo seismic data are well below those of γ-Fe. Our dataset thus provides strong constraints to seismic models of the lunar core and cores of small telluric planets. This allows us to propose a direct compositional and velocity model for the Moon’s core. PMID:25775531

Search for Wide Planetary-Mass Companions in Young Star-Forming Regions with UKIDSS and Pan-STARRS

NASA Astrophysics Data System (ADS)

Aller, Kimberly M.; Kraus, A. L.; Liu, M. C.; Bowler, B. P.

2013-01-01

Over the past decade, planetary-mass (<15 MJup) companions have been discovered in very wide orbits (>100 AU) around young stars. It is unclear whether these objects formed like planets or like stars. If these are planets, then modifications to core accretion or disk instability models are needed to allow formation at such wide orbits, or planet scattering must be an important mechanism. On the other hand, if these objects formed like stars, we need to understand the frequency of these extremely low mass ratio binary companions which challenge brown dwarf formation models. Regardless of their origins, these wide companions are easier to observe than close-in planets and can be used as benchmarks to understand the properties of young planets. We have combined optical and NIR photometry from UKIDSS and Pan-STARRS-1 to search the young star-forming region of Upper Scorpius and Taurus for new planetary-mass objects, going ≈3 mag deeper than previous work with 2MASS. We identified several candidates with very wide separations (≈400-4000 AU) from known members using a combination of color selection and spectral energy distribution (SED) fitting to templates of known low-mass stars and brown dwarfs. Furthermore, we have obtained followup NIR spectra of several Upper Scorpius candidates to spectroscopically identify three new wide very low-mass companions (≈15-25 MJup spectral type of M8-L0).

Phase Transitions of MgO Along the Hugoniot (Invited)

NASA Astrophysics Data System (ADS)

Root, S.; Shulenburger, L.; Lemke, R. W.; Cochrane, K. R.; Mattsson, T. R.

2013-12-01

The formation of terrestrial planets and planetary structure has become of great interest because of recent exoplanet discoveries of super earths. MgO is a major constituent of Earth's mantle, the rocky cores of gas giants such as Jupiter, and likely constitutes the interiors of many exoplanets. The high pressure - high temperature behavior of MgO directly affects equation of state models for planetary structure and formation. In this work, we examine single crystal MgO under shock compression utilizing experimental and density functional theory (DFT) methods to determine phase transformations along the Hugoniot. We perform plate impact experiments using Sandia's Z - facility on MgO up to 11.6 Mbar. The plate impact experiments generate highly accurate Hugoniot state data. The experimental results show the B1 - B2 solid - solid phase transition occurs near 4 Mbar on the Hugoniot. The solid - liquid transition is determined to be near 7 Mbar with a large region of B2-liquid coexistence. Using DFT methods, we also determine melt along the B1 and B2 solid phase boundaries as well as along the Hugoniot. The combined experimental and DFT results have determined the phase boundaries along the Hugoniot, which can be implemented into new planetary and EOS models. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Securities Administration under Contract No. DE-AC04-94AL85000.

Enhancement of the Accretion of Jupiters Core by a Voluminous Low-Mass Envelope

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; D'angelo, Gennaro; Weidenschilling, Stuart John; Bodenheimer, Peter; Hubickyj, Olenka

2013-01-01

We present calculations of the early stages of the formation of Jupiter via core nucleated accretion and gas capture. The core begins as a seed body of about 350 kilometers in radius and orbits in a swarm of planetesimals whose initial radii range from 15 meters to 100 kilometers. We follow the evolution of the swarm by accounting for growth and fragmentation, viscous and gravitational stirring, and for drag-induced migration and velocity damping. Gas capture by the core substantially enhances the cross-section of the planet for accretion of small planetesimals. The dust opacity within the atmosphere surrounding the planetary core is computed self-consistently, accounting for coagulation and sedimentation of dust particles released in the envelope as passing planetesimals are ablated. The calculation is carried out at an orbital semi-major axis of 5.2 AU and an initial solids' surface density of 10/g/cm^2 at that distance. The results give a core mass of 7 Earth masses and an envelope mass of approximately 0.1 Earth mass after 500,000 years, at which point the envelope growth rate surpasses that of the core. The same calculation without the envelope gives a core mass of only 4 Earth masses.

Significant achievements in the Planetary Geology Program. [geologic processes, comparative planetology, and solar system evolution

NASA Technical Reports Server (NTRS)

Head, J. W. (Editor)

1978-01-01

Developments reported at a meeting of principal investigators for NASA's planetology geology program are summarized. Topics covered include: constraints on solar system formation; asteriods, comets, and satellites; constraints on planetary interiors; volatiles and regoliths; instrument development techniques; planetary cartography; geological and geochemical constraints on planetary evolution; fluvial processes and channel formation; volcanic processes; Eolian processes; radar studies of planetary surfaces; cratering as a process, landform, and dating method; and the Tharsis region of Mars. Activities at a planetary geology field conference on Eolian processes are reported and techniques recommended for the presentation and analysis of crater size-frequency data are included.

Broad Halpha Wing Formation in the Planetary Nebula IC 4997.

PubMed

Lee; Hyung

2000-02-10

The young and compact planetary nebula IC 4997 is known to exhibit very broad wings with a width exceeding 5000 km s-1 around Halpha. We propose that the broad wings are formed through Rayleigh-Raman scattering that involves atomic hydrogen, by which Lybeta photons with a velocity width of a few 102 km s-1 are converted to optical photons and fill the Halpha broad wing region. The conversion efficiency reaches 0.6 near the line center, where the scattering optical depth is much larger than 1, and rapidly decreases in the far wings. Assuming that close to the central star there exists an unresolved inner compact core of high density, nH approximately 109-1010 cm-3, we use the photoionization code "CLOUDY" to show that sufficient Lybeta photons for scattering are produced. Using a top-hat-incident profile for the Lybeta flux and a scattering region with a H i column density NHi=2x1020 cm-2 and a substantial covering factor, we perform a profile-fitting analysis in order to obtain a satisfactory fit to the observed flux. We briefly discuss the astrophysical implications of the Rayleigh-Raman processes in planetary nebulae and other emission objects.

From Core to Solar Wind: Studying the Space Environment of Planets

NASA Astrophysics Data System (ADS)

Bagenal, F.

2004-05-01

Space physics permeates studies of the planets - from the magnetic field generated in a planetary core, through the charged particle bombardment of surfaces, the heating, excitation and ionization of an atmosphere or corona, to the acceleration of ions and electrons trapped in a planet's magnetosphere. This presentation provides an introductory overview of the space environment of planetary objects - from giant planets to tiny comets. The talk highlights three cases that illustrate the range of issues and applications of planetary space physics. (1) How has the solar wind interaction with Mars' strong, patchy remnant magnetization affected the loss of water? (2) How does the activity of volcanoes on Io trigger dynamics of the vast magnetosphere of Jupiter? (3) How could measurements of particles and fields by the Galileo spacecraft as it flew past Ganymede and Europa tell us that former has a liquid iron core and the latter a layer of liquid water?

Evaluating Core Quality for a Mars Sample Return Mission

NASA Technical Reports Server (NTRS)

Weiss, D. K.; Budney, C.; Shiraishi, L.; Klein, K.

2012-01-01

Sample return missions, including the proposed Mars Sample Return (MSR) mission, propose to collect core samples from scientifically valuable sites on Mars. These core samples would undergo extreme forces during the drilling process, and during the reentry process if the EEV (Earth Entry Vehicle) performed a hard landing on Earth. Because of the foreseen damage to the stratigraphy of the cores, it is important to evaluate each core for rock quality. However, because no core sample return mission has yet been conducted to another planetary body, it remains unclear as to how to assess the cores for rock quality. In this report, we describe the development of a metric designed to quantitatively assess the mechanical quality of any rock cores returned from Mars (or other planetary bodies). We report on the process by which we tested the metric on core samples of Mars analogue materials, and the effectiveness of the core assessment metric (CAM) in assessing rock core quality before and after the cores were subjected to shocking (g forces representative of an EEV landing).

Toward a Deterministic Model of Planetary Formation. II. The Formation and Retention of Gas Giant Planets around Stars with a Range of Metallicities

NASA Astrophysics Data System (ADS)

Ida, Shigeru; Lin, D. N. C.

2004-11-01

The apparent dependence of detection frequency of extrasolar planets on the metallicity of their host stars is investigated with Monte Carlo simulations using a deterministic core-accretion planet formation model. According to this model, gas giants formed and acquired their mass Mp through planetesimal coagulation followed by the emergence of cores onto which gas is accreted. These protoplanets migrate and attain their asymptotic semimajor axis a through tidal interaction with their nascent disk. Based on the observed properties of protostellar disks, we generate an Mp-a distribution. Our results reproduce the observed lack of planets with intermediate mass Mp=10-100 M⊕ and a<~3 AU and with large mass Mp>~103 M⊕ and a<~0.2 AU. Based on the simulated Mp-a distributions, we also evaluate the metallicity dependence of the fraction of stars harboring planets that are detectable with current radial velocity surveys. If protostellar disks attain the same fraction of heavy elements as contained in their host stars, the detection probability around metal-rich stars would be greatly enhanced because protoplanetary cores formed in them can grow to several Earth masses prior to their depletion. These large masses are required for the cores to initiate rapid gas accretion and to transform into giant planets. The theoretically extrapolated metallicity dependence is consistent with the observations. This correlation does not arise naturally in the gravitational-instability scenario. We also suggest other metallicity dependences of the planet distributions that can be tested by ongoing observations.

Possible consequences of absence of "Jupiters" in planetary systems.

PubMed

Wetherill, G W

1994-01-01

The formation of the gas giant planets Jupiter and Saturn probably required the growth of massive approximately 15 Earth-mass cores on a time scale shorter than the approximately 10(7) time scale for removal of nebular gas. Relatively minor variations in nebular parameters could preclude the growth of full-size gas giants even in systems in which the terrestrial planet region is similar to our own. Systems containing "failed Jupiters," resembling Uranus and Neptune in their failure to capture much nebular gas, would be expected to contain more densely populated cometary source regions. They will also eject a smaller number of comets into interstellar space. If systems of this kind were the norm, observation of hyperbolic comets would be unexpected. Monte Carlo calculations of the orbital evolution of region of such systems (the Kuiper belt) indicate that throughout Earth history the cometary impact flux in their terrestrial planet regions would be approximately 1000 times greater than in our Solar System. It may be speculated that this could frustrate the evolution of organisms that observe and seek to understand their planetary system. For this reason our observation of these planets in our Solar System may tell us nothing about the probability of similar gas giants occurring in other planetary systems. This situation can be corrected by observation of an unbiased sample of planetary systems.

High Pressure/Temperature Metal Silicate Partitioning of Tungsten

NASA Technical Reports Server (NTRS)

Shofner, G. A.; Danielson, L.; Righter, K.; Campbell, A. J.

2010-01-01

The behavior of chemical elements during metal/silicate segregation and their resulting distribution in Earth's mantle and core provide insight into core formation processes. Experimental determination of partition coefficients allows calculations of element distributions that can be compared to accepted values of element abundances in the silicate (mantle) and metallic (core) portions of the Earth. Tungsten (W) is a moderately siderophile element and thus preferentially partitions into metal versus silicate under many planetary conditions. The partitioning behavior has been shown to vary with temperature, silicate composition, oxygen fugacity, and pressure. Most of the previous work on W partitioning has been conducted at 1-bar conditions or at relatively low pressures, i.e. <10 GPa, and in two cases at or near 20 GPa. According to those data, the stronger influences on the distribution coefficient of W are temperature, composition, and oxygen fugacity with a relatively slight influence in pressure. Predictions based on extrapolation of existing data and parameterizations suggest an increased pressured dependence on metal/ silicate partitioning of W at higher pressures 5. However, the dependence on pressure is not as well constrained as T, fO2, and silicate composition. This poses a problem because proposed equilibration pressures for core formation range from 27 to 50 GPa, falling well outside the experimental range, therefore requiring exptrapolation of a parametereized model. Higher pressure data are needed to improve our understanding of W partitioning at these more extreme conditions.

Pebble Accretion in Turbulent Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Xu, Ziyan; Bai, Xue-Ning; Murray-Clay, Ruth A.

2017-09-01

It has been realized in recent years that the accretion of pebble-sized dust particles onto planetary cores is an important mode of core growth, which enables the formation of giant planets at large distances and assists planet formation in general. The pebble accretion theory is built upon the orbit theory of dust particles in a laminar protoplanetary disk (PPD). For sufficiently large core mass (in the “Hill regime”), essentially all particles of appropriate sizes entering the Hill sphere can be captured. However, the outer regions of PPDs are expected to be weakly turbulent due to the magnetorotational instability (MRI), where turbulent stirring of particle orbits may affect the efficiency of pebble accretion. We conduct shearing-box simulations of pebble accretion with different levels of MRI turbulence (strongly turbulent assuming ideal magnetohydrodynamics, weakly turbulent in the presence of ambipolar diffusion, and laminar) and different core masses to test the efficiency of pebble accretion at a microphysical level. We find that accretion remains efficient for marginally coupled particles (dimensionless stopping time {τ }s˜ 0.1{--}1) even in the presence of strong MRI turbulence. Though more dust particles are brought toward the core by the turbulence, this effect is largely canceled by a reduction in accretion probability. As a result, the overall effect of turbulence on the accretion rate is mainly reflected in the changes in the thickness of the dust layer. On the other hand, we find that the efficiency of pebble accretion for strongly coupled particles (down to {τ }s˜ 0.01) can be modestly reduced by strong turbulence for low-mass cores.

The influence of carbon, sulfur, and silicon on trace element partitioning in iron alloys

NASA Astrophysics Data System (ADS)

Han, J.; Van Orman, J. A.; Crispin, K. L.; Ash, R. D.

2014-12-01

Non-metallic light elements are important constituents of planetary cores and have a strong influence on the partitioning behavior of trace elements. Planetary cores may contain a wide range of non-metallic light elements, including H, N, S, P, Si, and C. Under highly reducing conditions, such as those that are thought to have pertained during the formation of Mercury's core, Si and C, in addition to sulfur, may be particularly important constituents. Each of these elements may strongly effect and have a different impact on the partitioning behavior of trace elements but their combined effects on trace element partitioning have not been quantified. We investigated the partitioning behavior of more than 25 siderophile trace elements within the Fe-S-C-Si system with varying concentrations of C, S, and Si. The experiments were performed under pressures varying from 1 atm to 2 GPa and temperatures ranging from 1200˚C to 1450˚C. All experiments produced immiscible liquids, one enriched in Si and C, and the other predominantly FeS. We found some highly siderophile elements including Os, Ru, Ir, and Re are much more enriched in Fe-Si-C phase than in Fe-S phase, whereas other trace elements like V, Co, Ag, Hf, and Pb are enriched in S-rich phase. However, not all the trace elements enriched in Fe-Si-C phase are repelled by sulfur. Elements like Re and Ru could have different partitioning trends if sulfur concentration in S-rich phase rises. The partitioning behavior of these trace elements could enhance our understanding of the differentiation of Mercury's core under oxygen-poor conditions.

Planetary and Primitive Object Strength Measurement and Sampling Apparatus

NASA Technical Reports Server (NTRS)

Ahrens, Thomas J.

1995-01-01

Support is requested for continuation of a program of dynamic impact (harpoon) coring of planetary, comet, or asteroid surface materials. We have previously demonstrated that good quality cores are obtainable for planetary materials with compressive strengths less than 200 MPa. Since the dynamics of penetration are observable on a Discovery class spacecraft, which images the sampling operation, these data can be used with a model developed under this project, to measure in-situ strength and frictional strength of the crust of the object. During the last year we have developed a detailed analytic model of penetrator mechanics. Progress is reported for the solid penetrators experiments, the CIT penetrator model, and the impact spall sampling apparatus.

Constraining Mercury's interior structure with geodesy data and its present thermal state

NASA Astrophysics Data System (ADS)

Rivoldini, Attilio; Van Hoolst, Tim; Noack, Lena

2015-04-01

Recent measurements of Mercury's spin state and gravitational field supplemented by the assumption that the planet's core is made of iron and sulfur give strong constraints on its interior structure. In particular, they allow a precise determination of Mercury's core size and average mantle density. Present geodesy data do, however, almost not constrain the size of the inner core. Interior structure models with a fully molten liquid core as well as models with an inner core almost as large as the core agree with the observations. Additionally, the observed internally generated magnetic field of Mercury does not preclude the absence of an inner core, since remelting of iron snow inside the core could produce a sufficient buoyancy flux to drive magnetic field generation by compositional convection. Although sulfur is ubiquitously invoked as being the principal candidate light element in terrestrial planet's cores its abundance in the core depends on the redox conditions during planetary formation. Remote sensing data of Mercury's surface by MESSENGER indicate that Mercury formed under reducing conditions. As a consequence, substantial amounts of other light elements like for example silicon and carbon could be present together with sulfur inside Mercury's core. Compared to sulfur, which does almost not partition into solid iron at Mercury's core conditions, silicon partitions almost equally well between solid and liquid iron whereas a few percent of carbon can partition into solid iron. Therefore, compared to a pure iron-sulfur core, if silicon and carbon are present in the core the density jump at the inner-core outer-core boundary could be smaller and induce a large enough change in the inner-core flattening to alter Mercury's libration amplitude. Moreover, the presence of carbon together with sulfur further reduces the core solidus temperature, potentially delaying the onset of inner core formation. Finally, if both silicon and sulfur are present in sufficient quantities a thin layer much enriched in sulfur and depleted in silicon could form at the top of the core as a consequence of a large immiscibility region in liquid Fe-S-Si at Mercury's core conditions. The present radius of an inner core depends mainly on Mercury's thermal state and concentration of light elements inside the core. Because of the secular cooling of the planet, at a time in Mercury's evolution the temperature inside the core drops below the core liquidus temperature somewhere in the core, which can lead to the formation of an inner core and to the global contraction of the planet. The amount of contraction depends mainly on the temperature decrease, on the thermal expansion of the materials inside the planet, on the volume of crystallized iron-rich core liquid, and on the volume of crystallized crust. In this study we use geodesy data (88 day libration amplitude, polar moment of inertia, and tidal Love number), the recent estimate about the radial contraction of Mercury, and thermo-chemical evolution calculations taking into account the formation of the crust, a growing inner core, and modeling the formation of iron-rich snow in the core in order to improve our knowledge about Mercury's inner core radius and thermal state. Since data from remote sensing of Mercury's surface indicate that Mercury formed under reducing conditions we consider models that have sulfur, silicon, and carbon as light elements inside their core.

A volatile-rich Earth's core inferred from melting temperature of core materials

NASA Astrophysics Data System (ADS)

Morard, G.; Andrault, D.; Antonangeli, D.; Nakajima, Y.; Auzende, A. L.; Boulard, E.; Clark, A. N.; Lord, O. T.; Cervera, S.; Siebert, J.; Garbarino, G.; Svitlyk, V.; Mezouar, M.

2016-12-01

Planetary cores are mainly constituted of iron and nickel, alloyed with lighter elements (Si, O, C, S or H). Understanding how these elements affect the physical and chemical properties of solid and liquid iron provides stringent constraints on the composition of the Earth's core. In particular, melting curves of iron alloys are key parameter to establish the temperature profile in the Earth's core, and to asses the potential occurrence of partial melting at the Core-Mantle Boundary. Core formation models based on metal-silicate equilibration suggest that Si and O are the major light element components1-4, while the abundance of other elements such as S, C and H is constrained by arguments based on their volatility during planetary accretion5,6. Each compositional model implies a specific thermal state for the core, due to the different effect that light elements have on the melting behaviour of Fe. We recently measured melting temperatures in Fe-C and Fe-O systems at high pressures, which complete the data sets available both for pure Fe7 and other binary alloys8. Compositional models with an O- and Si-rich outer core are suggested to be compatible with seismological constraints on density and sound velocity9. However, their crystallization temperatures of 3650-4050 K at the CMB pressure of 136 GPa are very close to, if not higher than the melting temperature of the silicate mantle and yet mantle melting above the CMB is not a ubiquitous feature. This observation requires significant amounts of volatile elements (S, C or H) in the outer core to further reduce the crystallisation temperature of the core alloy below that of the lower mantle. References 1. Wood, B. J., et al Nature 441, 825-833 (2006). 2. Siebert, J., et al Science 339, 1194-7 (2013). 3. Corgne, A., et al Earth Planet. Sc. Lett. 288, 108-114 (2009). 4. Fischer, R. a. et al. Geochim. Cosmochim. Acta 167, 177-194 (2015). 5. Dreibus, G. & Palme, H. Geochim. Cosmochim. Acta 60, 1125-1130 (1995). 6. McDonough, W. F. Treatise in Geochemistry 2, 547-568 (2003). 7. Anzellini, S., et al Science 340, 464-6 (2013). 8. Morard, G. et al. Phys. Chem. Miner. 38, 767-776 (2011). 9. Badro, J., et al Proc. Natl. Acad. Sci. U. S. A. 111, 7542-5 (2014).

Petrographic studies of refractory inclusions from the Murchison meteorite

NASA Technical Reports Server (NTRS)

Macpherson, G. J.; Grossman, L.; Hashimoto, A.; Bar-Matthews, M.; Tanaka, T.

1984-01-01

Textural and mineral-chemical data on freeze-thaw disaggregated refractory inclusions from the Murchison meteorite are reported. The data were obtained with neutron activation analysis, SEM, and spectroscopy, the study revealed corundum-bearing inclusions, spinel-hibonite aggregates and spherules, and spinel-pyroxene and elivine-pyroxene inclusions. One of the three spinel-, pyroxene-, forsterite-rich inclusions had an amoeba-shaped spinel-pyroxene core, implying vapor-to-solid condensation and therefore crystallization from a melt. It is concluded that the meteorite formation encompassed diverse nebular materials, and that further studies of the meteorite will enhance the data base on the planetary nebular processes.

MIGRATION AND GROWTH OF PROTOPLANETARY EMBRYOS. II. EMERGENCE OF PROTO-GAS-GIANT CORES VERSUS SUPER EARTH PROGENITORS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Beibei; Zhang, Xiaojia; Lin, Douglas N. C.

2015-01-01

Nearly 15%-20% of solar type stars contain one or more gas giant planets. According to the core-accretion scenario, the acquisition of their gaseous envelope must be preceded by the formation of super-critical cores with masses 10 times or larger than that of the Earth. It is natural to link the formation probability of gas giant planets with the supply of gases and solids in their natal disks. However, a much richer population of super Earths suggests that (1) there is no shortage of planetary building block material, (2) a gas giant's growth barrier is probably associated with whether it can mergemore » into super-critical cores, and (3) super Earths are probably failed cores that did not attain sufficient mass to initiate efficient accretion of gas before it is severely depleted. Here we construct a model based on the hypothesis that protoplanetary embryos migrated extensively before they were assembled into bona fide planets. We construct a Hermite-Embryo code based on a unified viscous-irradiation disk model and a prescription for the embryo-disk tidal interaction. This code is used to simulate the convergent migration of embryos, and their close encounters and coagulation. Around the progenitors of solar-type stars, the progenitor super-critical-mass cores of gas giant planets primarily form in protostellar disks with relatively high (≳ 10{sup –7} M {sub ☉} yr{sup –1}) mass accretion rates, whereas systems of super Earths (failed cores) are more likely to emerge out of natal disks with modest mass accretion rates, due to the mean motion resonance barrier and retention efficiency.« less

Subcritical Thermal Convection of Liquid Metals in a Rapidly Rotating Sphere

NASA Astrophysics Data System (ADS)

Kaplan, E. J.; Schaeffer, N.; Vidal, J.; Cardin, P.

2017-09-01

Planetary cores consist of liquid metals (low Prandtl number Pr) that convect as the core cools. Here, we study nonlinear convection in a rotating (low Ekman number Ek) planetary core using a fully 3D direct numerical simulation. Near the critical thermal forcing (Rayleigh number Ra), convection onsets as thermal Rossby waves, but as Ra increases, this state is superseded by one dominated by advection. At moderate rotation, these states (here called the weak branch and strong branch, respectively) are smoothly connected. As the planetary core rotates faster, the smooth transition is replaced by hysteresis cycles and subcriticality until the weak branch disappears entirely and the strong branch onsets in a turbulent state at Ek <10-6. Here, the strong branch persists even as the thermal forcing drops well below the linear onset of convection (Ra =0.7 Racrit in this study). We highlight the importance of the Reynolds stress, which is required for convection to subsist below the linear onset. In addition, the Péclet number is consistently above 10 in the strong branch. We further note the presence of a strong zonal flow that is nonetheless unimportant to the convective state. Our study suggests that, in the asymptotic regime of rapid rotation relevant for planetary interiors, thermal convection of liquid metals in a sphere onsets through a subcritical bifurcation.

Plastic deformation of FeSi at high pressures: implications for planetary cores

NASA Astrophysics Data System (ADS)

Kupenko, Ilya; Merkel, Sébastien; Achorner, Melissa; Plückthun, Christian; Liermann, Hanns-Peter; Sanchez-Valle, Carmen

2017-04-01

The cores of terrestrial planets is mostly comprised of a Fe-Ni alloy, but it should additionally contain some light element(s) in order to explain the observed core density. Silicon has long been considered as a likely candidate because of geochemical and cosmochemical arguments: the Mg/Si and Fe/Si ratios of the Earth does not match those of the chondrites. Since silicon preferentially partition into iron-nickel metal, having 'missing' silicon in the core would solve this problem. Moreover, the evidence of present (e.g. Mercury) or ancient (e.g. Mars) magnetic fields on the terrestrial planets is a good indicator of (at least partially) liquid cores. The estimated temperature profiles of these planets, however, lay below iron melting curve. The addition of light elements in their metal cores could allow reducing their core-alloy melting temperature and, hence, the generation of a magnetic field. Although the effect of light elements on the stability and elasticity of Fe-Ni alloys has been widely investigated, their effect on the plasticity of core materials remains largely unknown. Yet, this information is crucial for understanding how planetary cores deform. Here we investigate the plastic deformation of ɛ-FeSi up to 50 GPa at room temperature employing a technique of radial x-ray diffraction in diamond anvil cells. Stoichiometric FeSi endmember is a good first-order approximation of the Fe-FeSi system and a good starting material to develop new experimental perspectives. In this work, we focused on the low-pressure polymorph of FeSi that would be the stable phase in the cores of small terrestrial planets. We will present the analysis of measured data and discuss their potential application to constrain plastic deformation in planetary cores.

Concept for a research project in early crustal genesis

NASA Technical Reports Server (NTRS)

Phillips, R. J. (Compiler); Ashwal, L. (Compiler)

1983-01-01

Planetary volatiles, physical and chemical planetary evolution, surface processes, planetary formation, metallogenesis, crustal features and their development, tectonics, and paleobiology are discussed.

Possible Role of Hydrogen in the Earth Core

NASA Astrophysics Data System (ADS)

Takahashi, E.; Imai, T.

2011-12-01

Possible role of hydrogen in the Earth core has been discussed by Stevenson (1977) and demonstrated experimentally by Fukai (1984), Okuchi (1997) and others. Planetary theory proposes a possibility of hydrogen incorporation in Earth's magma ocean from ambient solar nebula gas (Ikoma & Genda 2005, Genda & Ikoma 2008). More recently, migration of snow line during planet formation was examined (Min et al., 2010; Oka et al, 2011) and it was proposed that the Earth building material originally contained abundant water as ice and hydrous minerals. Therefore, it is very important to investigate the fate of water in the planet building process and clarify the role of hydrogen in the planetary core. Using SPring-8 synchrotron (NaCl capsule, LiAlH4 as hydrogen source), we determined the melting curve of FeH up to 20 GPa under hydrogen saturated conditions (Sakamaki, Takahashi et al, 2009). Observed melting point is below 1300C and has a very small dT/dP slope. By extrapolating the melting curve using Lindeman's law, we proposed that hydrogen could lower the melting temperature of the Earth core by more than 1500K than current estimate. Here we report our new experiments using SPring-8 synchrotron (single crystal diamond capsule, water as hydrogen source). Hydrogen concentration and melting temperature of FeHx that coexists with hydrous mantle minerals were determined at 15-20GPa and 1000-1600C. We show that 1) hydrogen concentration in FeHx at 1000C, coexisting with hydrous-B and ringwoodite is approximately X=0.6. 2) Upon heating, hydrous-B decomposes and hydrogen strongly partitions into FeHx (X=0.8~1.0) than ringwoodite. 3) FeHx that coexists with ringwoodite melts between ~1300C (solidus) and ~1600C (liquidus). Combined our new experiments with those by Sakamaki et al (2009) and Shibazaki et al (2009), partitioning of hydrogen between proto-core and primitive mantle is discussed. We propose that >90% of water in the source material may have entered the Earth core. Given large hydrogen concentration in the Earth core, temperature of the outermost core could be as low as that of lower mantle adiabat. Presence of the light element-rich layer at the top 300km layer of the outer core (Helffrich & Kaneshima, 2010) may be easily understood if there is no temperature gap between the core and the lower mantle.

The Pressure Dependence of Thermal Expansion of Core-Forming Alloys: A Key Parameter in Determining the Convective Style of Planetary Cores

NASA Astrophysics Data System (ADS)

Williams, Q. C.; Manghnani, M. H.

2017-12-01

The convective style of planetary cores is critically dependent on the thermal properties of iron alloys. In particular, the relation between the adiabatic gradient and the melting curve governs whether planetary cores solidify from their top down (when the adiabat is steeper than the melting curve) or the bottom up (the converse). Molten iron alloys, in general, have large, ambient pressure thermal expansions: values in excess of 1.2 x 10^-4/K are dictated by data derived from levitated and sessile drop techniques. These high values of the thermal expansion imply that the adiabatic gradients within early planetesimals and present day moons that have comparatively low-pressure, iron-rich cores are steep (typically greater than 35 K/GPa at low pressures): values, at low pressures, that are greater than the slope of the melting curve, and hence show that the cores of small solar system objects probably crystallize from the top-down. Here, we deploy a different manifestation of these large values of thermal expansion to determine the pressure dependence of thermal expansion in iron-rich liquids: a difficult parameter to experimentally measure, and critical for determining the size range of cores in which top-down core solidification predominates. In particular, the difference between the adiabatic and isothermal bulk moduli of iron liquids is in the 20-30% range at the melting temperature, and scales as the product of the thermal expansion, the Grüneisen parameter, and the temperature. Hence, ultrasonic (and adiabatic) moduli of iron alloy liquids, when coupled with isothermal sink-float measurements, can yield quantitative constraints on the pressure dependence of thermal expansion. For liquid iron alloys containing 17 wt% Si, we find that the thermal expansion is reduced by 50% over the first 8 GPa of compression. This "squeezing out" of the anomalously high low-pressure thermal expansion of iron-rich alloys at relatively modest conditions likely limits the size range over which top-down crystallizing cores are anticipated within planetary bodies.

Synthesizing Planetary Nebulae for Large Scale Surveys: Predictions for LSST

NASA Astrophysics Data System (ADS)

Vejar, George; Montez, Rodolfo; Morris, Margaret; Stassun, Keivan G.

2017-01-01

The short-lived planetary nebula (PN) phase of stellar evolution is characterized by a hot central star and a bright, ionized, nebula. The PN phase forms after a low- to intermediate-mass star stops burning hydrogen in its core, ascends the asymptotic giant branch, and expels its outer layers of material into space. The exposed hot core produces ionizing UV photons and a fast stellar wind that sweeps up the surrounding material into a dense shell of ionized gas known as the PN. This fleeting stage of stellar evolution provides insight into rare atomic processes and the nucleosynthesis of elements in stars. The inherent brightness of the PNe allow them to be used to obtain distances to nearby stellar systems via the PN luminosity function and as kinematic tracers in other galaxies. However, the prevalence of non-spherical morphologies of PNe challenge the current paradigm of PN formation. The role of binarity in the shaping of the PN has recently gained traction ultimately suggesting single stars might not form PN. Searches for binary central stars have increased the binary fraction but the current PN sample is incomplete. Future wide-field, multi-epoch surveys like the Large Synoptic Survey Telescope (LSST) can impact studies of PNe and improve our understanding of their origin and formation. Using a suite of Cloudy radiative transfer calculations, we study the detectability of PNe in the proposed LSST multiband observations. We compare our synthetic PNe to common sources (stars, galaxies, quasars) and establish discrimination techniques. Finally, we discuss follow-up strategies to verify new LSST-discovered PNe and use limiting distances to estimate the potential sample of PNe enabled by LSST.

A Model for Siderophile Element Distribution in Planetary Differentiation

NASA Technical Reports Server (NTRS)

Humayun, M.; Rushmer, T.; Rankenburg, K.; Brandon, A. D.

2005-01-01

Planetary differentiation begins with partial melting of small planetesimals. At low degrees of partial melting, a sulfur-rich liquid segregates by physical mechanisms including deformation-assisted porous flow. Experimental studies of the physical mechanisms by which Fe-S melts segregate from the silicate matrix of a molten H chondrite are part of a companion paper. Geochemical studies of these experimental products revealed that metallic liquids were in equilibrium with residual metal in the H chondrite matrix. This contribution explores the geochemical signatures produced by early stages of core formation. Particularly, low-degree partial melt segregation of Fe-S liquids leaves residual metal in the silicate matrix. Some achondrites appear to be residues of partial melting, e.g., ureilites, which are known to contain metal. The metal in these achondrites may show a distinct elemental signature. To quantify the effect of sulfur on siderophile element contents of residual metal we have developed a model based on recent parametrizations of equilibrium solid metal-liquid metal partitioning experiments.

Coupled 142Nd-143Nd evidence for a protracted magma ocean in Mars.

PubMed

Debaille, V; Brandon, A D; Yin, Q Z; Jacobsen, B

2007-11-22

Resolving early silicate differentiation timescales is crucial for understanding the chemical evolution and thermal histories of terrestrial planets. Planetary-scale magma oceans are thought to have formed during early stages of differentiation, but the longevity of such magma oceans is poorly constrained. In Mars, the absence of vigorous convection and plate tectonics has limited the scale of compositional mixing within its interior, thus preserving the early stages of planetary differentiation. The SNC (Shergotty-Nakhla-Chassigny) meteorites from Mars retain 'memory' of these events. Here we apply the short-lived 146Sm-142Nd and the long-lived 147Sm-143Nd chronometers to a suite of shergottites to unravel the history of early silicate differentiation in Mars. Our data are best explained by progressive crystallization of a magma ocean with a duration of approximately 100 million years after core formation. This prolonged solidification requires the existence of a primitive thick atmosphere on Mars that reduces the cooling rate of the interior.

Preliminary results of sulfide melt/silicate wetting experiments in a partially melted ordinary chondrite

NASA Technical Reports Server (NTRS)

Jurewicz, Stephen R.; Jones, John H.

1994-01-01

Recently, mechanisms for core formation in planetary bodies have received considerable attention. Most current theories emphasize the need for large degrees of silicate partial melting to facilitate the coalescence and sinking of sulfide-metal liquid blebs through a low strength semi-crystalline silicate mush. This scenario is based upon observations that sulfide-metal liquid tends to form circular blebs in partially molten meteorites during laboratory experiments. However, recent experimental work by Herpfer and Larimer indicates that some sulfide-Fe liquids have wetting angles at and slightly below 60 deg in an olivine aggregate, implying an interconnected melt structure at any melt fraction. Such melt interconnectivity provides a means for gravitational compaction and extraction of the majority of a sulfide liquid phase in small planetary bodies without invoking large degrees of silicate partial melting. Because of the important ramifications of these results, we conducted a series of experiments using H-chondrite starting material in order to evaluate sulfide-liquid/silicate wetting behavior in a more complex natural system.

The problem of iron partition between Earth and Moon during simultaneous formation as a double planet system

NASA Technical Reports Server (NTRS)

Cassidy, W. A.

1984-01-01

A planetary model is described which requires fractional vapor/liquid condensation, planet accumulation during condensation, a late start for accumulation of the Moon, and volatile accretion to the surfaces of each planet only near the end of the accumulation process. In the model, initial accumulation of small objects is helped if the agglomerating particles are somewhat sticky. Assuming that growth proceeds through this range, agglomeration continues. If the reservoir of vapor is being preferentially depleted in iron by fractional condensation, an iron-rich planetary core forms. As the temperature decreases, condensing material becomes progressively richer in silicates and poorer in iron, forming the silicate-rich mantle of an already differentiated Earth. A second center of agglomeration successfully forms near the growing Earth after most of the iron in the reservoir has been used up. The bulk composition of the Moon then is similar to the outer mantle of the accumulating Earth.

Astrobiological benefits of human space exploration.

PubMed

Crawford, Ian A

2010-01-01

An ambitious program of human space exploration, such as that envisaged in the Global Exploration Strategy and considered in the Augustine Commission report, will help advance the core aims of astrobiology in multiple ways. In particular, a human exploration program will confer significant benefits in the following areas: (i) the exploitation of the lunar geological record to elucidate conditions on early Earth; (ii) the detailed study of near-Earth objects for clues relating to the formation of the Solar System; (iii) the search for evidence of past or present life on Mars; (iv) the provision of a heavy-lift launch capacity that will facilitate exploration of the outer Solar System; and (v) the construction and maintenance of sophisticated space-based astronomical tools for the study of extrasolar planetary systems. In all these areas a human presence in space, and especially on planetary surfaces, will yield a net scientific benefit over what can plausibly be achieved by autonomous robotic systems. A number of policy implications follow from these conclusions, which are also briefly considered.

A nonmagnetic differentiated early planetary body

DOE PAGES

Weiss, Benjamin P.; Wang, Huapei; Sharp, Thomas G.; ...

2017-06-19

Paleomagnetic studies of meteorites have shown that the solar nebula was likely magnetized and that many early planetary bodies generated dynamo magnetic fields in their advecting metallic cores. The surface fields on these bodies were recorded by a diversity of chondrites and achondrites, ranging in intensity from several μT to several hundred μT. In fact, an achondrite parent body without evidence for paleomagnetic fields has yet to be confidently identified, hinting that early solar system field generation and the dynamo process in particular may have been common. Here we present paleomagnetic measurements of the ungrouped achondrite NWA 7325 indicating thatmore » it last cooled in a near-zero field (<~1.7μT), estimated to have occurred at 4563.09 ± 0.26 million years ago (Ma) from Al–Mg chronometry. Because NWA 7325 is highly depleted in siderophile elements, its parent body nevertheless underwent large-scale metal-silicate differentiation and likely formed a metallic core. This makes NWA 7325 the first recognized example of an essentially unmagnetized igneous rock from a differentiated early solar system body. These results indicate that all magnetic fields, including those from any core dynamo on the NWA 7325 parent body, the solar nebula, young Sun, and solar wind, were <1.7 μT at the location of NWA 7325 at 4563 Ma. Finally, this supports a recent conclusion that the solar nebula had dissipated by ~4 million years after solar system formation. NWA 7325 also serves as an experimental control that gives greater confidence in the positive identification of remanent magnetization in other achondrites.« less

A nonmagnetic differentiated early planetary body

NASA Astrophysics Data System (ADS)

Weiss, Benjamin P.; Wang, Huapei; Sharp, Thomas G.; Gattacceca, Jérôme; Shuster, David L.; Downey, Brynna; Hu, Jinping; Fu, Roger R.; Kuan, Aaron T.; Suavet, Clément; Irving, Anthony J.; Wang, Jun; Wang, Jiajun

2017-06-01

Paleomagnetic studies of meteorites have shown that the solar nebula was likely magnetized and that many early planetary bodies generated dynamo magnetic fields in their advecting metallic cores. The surface fields on these bodies were recorded by a diversity of chondrites and achondrites, ranging in intensity from several μT to several hundred μT. In fact, an achondrite parent body without evidence for paleomagnetic fields has yet to be confidently identified, hinting that early solar system field generation and the dynamo process in particular may have been common. Here we present paleomagnetic measurements of the ungrouped achondrite NWA 7325 indicating that it last cooled in a near-zero field (<∼1.7 μT), estimated to have occurred at 4563.09 ± 0.26 million years ago (Ma) from Al-Mg chronometry. Because NWA 7325 is highly depleted in siderophile elements, its parent body nevertheless underwent large-scale metal-silicate differentiation and likely formed a metallic core. This makes NWA 7325 the first recognized example of an essentially unmagnetized igneous rock from a differentiated early solar system body. These results indicate that all magnetic fields, including those from any core dynamo on the NWA 7325 parent body, the solar nebula, young Sun, and solar wind, were <1.7 μT at the location of NWA 7325 at 4563 Ma. This supports a recent conclusion that the solar nebula had dissipated by ∼4 million years after solar system formation. NWA 7325 also serves as an experimental control that gives greater confidence in the positive identification of remanent magnetization in other achondrites.

Convective Differentiation of the Earth's Mantle

NASA Astrophysics Data System (ADS)

Hansen, U.; Schmalzl, J.; Stemmer, K.

2007-05-01

The differentiation of the Earth is likely to be influenced by convective motions within the early mantle. Double- diffusive convection (d.d.c), driven by thermally and compositionally induced density differences is considered as a vital mechanism behind the dynamic differentiation of the early mantle.. We demonstrate that d.d.c can lead to layer formation on a planetary scale in the diffusive regime where composition stabilizes the system whil heat provides the destabilizing force. Choosing initial conditions in which a stable compositional gradient overlies a hot reservoir we mimic the situation of a planet in a phase after core formation. Differently from earlier studies we fixed the temperature rather than the heat flux at the lower boundary, resembling a more realistic condition for the core-mantle boundary. We have carried out extended series of numerical experiments, ranging from 2D calculations in constant viscosity fluids to fully 3D experiments in spherical geometry with strongly temperature dependent viscosity. The buoyancy ratio R and the Lewis number Le are the important dynamical parameters. In all scenarios we could identify a parameter regime where the non-layered initial structure developed into a state consisting of several, mostly two layers. Initially plumes from the bottom boundary homogenize a first layer which subsequently thickens. The bottom layer heats up and then convection is initiated in the top layer. This creates dynamically (i.e. without jump in the material behavior) a stack of separately convecting layers. The bottom layer is significantly thicker than the top layer. Strongly temperature dependent viscosity leads to a more complex evolution The formation of the bottom layer is followed by the generation of several layers on top. Finally the uppermost layer starts to convect. In general, the multilayer structure collapses into a two layer system. We employed a numerical technique, allowing for a diffusion free treatment of the compositional field. In each case a similar evolution has been observed. This indicates that a temporary formation of layered structures in planetary interiors is a typical phenomenon. Moreover, in this scenario, plate tectonics appears only in later stages of the evolution.

Gondola for High Altitude Planetary Science (GHAPS)

NASA Technical Reports Server (NTRS)

Hoffmann, Monica

2017-01-01

Description of the NASA Gondola for High Altitude Planetary Science (GHAPS) balloon project and its planetary science capabilities provided in a poster or fact sheet format as needed. The ability of GHAPS to provide a re-useable platform to collect planetary information is described.

Deformation of a crystalline olivine aggregate containing two immiscible liquids: Implications for early core-mantle differentiation

NASA Astrophysics Data System (ADS)

Cerantola, V.; Walte, N. P.; Rubie, D. C.

2015-05-01

Deformation-assisted segregation of metallic and sulphidic liquid from a solid peridotitic matrix is a process that may contribute to the early differentiation of small planetesimals into a metallic core and a silicate mantle. Here we present results of an experimental study using a simplified system consisting of a polycrystalline Fo90-olivine matrix containing a small percentage of iron sulphide and a synthetic primitive MORB melt, in order to investigate whether the silicate melt enhances the interconnection and segregation of FeS liquid under deformation conditions at varying strain rates. The experiments have been performed at 2 GPa, 1450 °C and strain rates between 1 ×10-3s-1 to 1 ×10-5s-1. Our results show that the presence of silicate melt actually hinders the migration and segregation of sulphide liquid by reducing its interconnectivity. At low to moderate strain rates the sulphide liquid pockets preserved a roundish shape, showing the liquid behavior is governed mainly by surface tension rather than by differential stress. Even at the highest strain rates, insignificant FeS segregation and interconnection were observed. On the other hand the basaltic melt was very mobile during deformation, accommodating part of the strain, which led to its segregation from the matrix at high bulk strains leaving the sulphide liquid stranded in the olivine matrix. Hence, we conclude that deformation-induced percolation of sulphide liquid does not contribute to the formation of planetary cores after the silicate solidus is overstepped. A possible early deformation enhanced core-mantle differentiation after overstepping the Fe-S solidus is not possible between the initial formation of silicate melt and the formation of a widespread magma ocean.

Implications of the Homogeneous Nucleation Barrier for Top-Down Crystallization in Mercury's Core

NASA Astrophysics Data System (ADS)

Huguet, L.; Hauck, S. A.; Van Orman, J. A.; Jing, Z.

2018-05-01

Crystallization of solids in planetary cores depends both on ambient temperatures falling below the liquidus and on the ability to nucleate crystal growth. We discuss the implications of the nucleation barrier for thermal evolution of Mercury's core.

Aftermath of early Hit-and-Run collisions in the Inner Solar System

NASA Astrophysics Data System (ADS)

Sarid, Gal; Stewart, Sarah T.; Leinhardt, zoe M.

2015-08-01

Planet formation epoch, in the terrestrial planet region and the asteroid belt, was characterized by a vigorous dynamical environment that was conducive to giant impacts among planetary embryos and asteroidal parent bodies, leading to diverse outcomes. Among these the greatest potential for producing diverse end-members lies is the erosive Hit-and-Run regime (small mass ratios, off-axis oblique impacts and non-negligible ejected mass), which is also more probable in terms of the early dynamical encounter configuration in the inner solar system. This collision regime has been invoked to explain outstanding issues, such as planetary volatile loss records, origin of the Moon and mantle stripping from Mercury and some of the larger asteroids (Vesta, Psyche).We performed and analyzed a set of simulations of Hit-and-Run events, covering a large range of mass ratios (1-20), impact parameters (0.25-0.96, for near head-on to barely grazing) and impact velocities (~1.5-5 times the mutual escape velocity, as dependent on the mass ratio). We used an SPH code with tabulated EOS and a nominal simlated time >1 day, to track the collisional shock processing and the provenance of material components. of collision debris. Prior to impact runs, all bodies were allowed to initially settle to negligible particle velocities in isolation, within ~20 simulated hrs. The total number of particles involved in each of our collision simulations was between (1-3 x 105). Resulting configurations include stripped mantles, melting/vaporization of rock and/or iron cores and strong variations of asteroid parent bodies fromcanonical chondritic composition.In the context of large planetary formation simulations, velocity and impact angle distributions are necessary to asses impact probabilities. The mass distribution and interaction within planetary embryo and asteroid swarms depends both on gravitational dynamics and the applied fragmentation mechanism. We will present results pertaining to general projectile remnant scaling relations, constitution of ejected unbound material and the composition of variedcollision remnants, which become available to seed the asteroid belt.

Subcritical thermal convection of liquid metals in a rapidly rotating sphere

NASA Astrophysics Data System (ADS)

Cardin, P.; Schaeffer, N.; Guervilly, C.; Kaplan, E.

2017-12-01

Planetary cores consist of liquid metals (low Prandtl number Pr) that convect as the core cools. Here we study nonlinear convection in a rotating (low Ekman number Ek) planetary core using a fully 3D direct (down to Ek=10-7) and a quasi geostrophic (down to Ek=10-10) numerical simulations. Near the critical thermal forcing (Rayleigh number Ra), convection onsets as thermal Rossby waves, but as Ra increases, this state is superceded by one dominated by advection. At moderate rotation, these states (here called the weak branch and strong branch, respectively) are continuously connected. As the planetary core rotates faster, the continuous transition is replaced by hysteresis cycles and subcriticality until the weak branch disappears entirely and the strong branch onsets in a turbulent state at Ek<10-6 when Pr=0.01. Here the strong branch persists even as the thermal forcing decreases well below the linear onset of convection (Ra 0.4Racrit in this study for Ek=10-10 and Pr=0.01). We highlight the importance of the Reynolds stress, which is required for convection to persist below the linear onset. We further note the presence of a strong zonal flow that is nonetheless unimportant to the convective subcritical state. Our study suggests that, in the asymptotic regime of rapid rotation relevant for planetary interiors, thermal convection of liquid metals in a sphere onsets and shuts down through a subcritical bifurcation. This scenario may be relevant to explain the lunar and martian dynamo extinctions.

Thermopyhsical conditions for the onset of a core dynamo in Vesta

NASA Astrophysics Data System (ADS)

Formisano, Michelangelo; Federico, Costanzo; De Angelis, Simone; De Sanctis, Maria Cristina; Magni, Gianfranco

2016-04-01

Recently, a study on the magnetization of the eucrite meteorite Allan Hills A81001 [1] has suggested the possibility that, in its primordial history, Vesta had an active core dynamo. The magnetic field associated could have preserved Vesta from the space-weathering. In this work, using a parametrized thermal convection method, we verified the thermophysical conditions for the onset of a core dynamo. The starting point is a post-differentiated structure [2,3,4], made of a metallic core, silicate mantle and rocky crust. We explored four different fully differentiated configurations of Vesta [5], characterized by different chondritic composition, with the constraints on the core size and density provided by [6]. We also explored three different scaling laws for the core velocity (mixing-length theory, MAC and an intermediate case). Core and mantle have both a temperature-dependent viscosity, which is the parameter that largely influences the magnetic Reynolds number and the dynamo duration. Our results suggest that Vesta had an active dynamo, whose duration lies in the range 150-500 Myr and the more appropriate scaling law for the core velocity is that given by the mixing-length theory. The maximum strength of the primordial core magnetic field is compatible with the estimations provided by [1]. [1] Fu, R. et al, 2012, Science 338, 238 [2] Ghosh, A. and McSween, H.Y., 1998, Icarus, 134, 187 [3] Formisano, M. et al., 2013, Meteoritics and Planetary Science, 48, 2316 [4] Neumann, W., et al., 2014, Earth and Planetary Science Letters, 395, 267 [5] Toplis, M.J., et al., 2013, Meteoritics and Planetary Science, 48, 2300 [6] Ermakov, A.I., et al.2014, Icarus, 240, 146

Geology, geochemistry, and geophysics of the Moon: Status of current understanding

NASA Astrophysics Data System (ADS)

Jaumann, R.; Hiesinger, H.; Anand, M.; Crawford, I. A.; Wagner, R.; Sohl, F.; Jolliff, B. L.; Scholten, F.; Knapmeyer, M.; Hoffmann, H.; Hussmann, H.; Grott, M.; Hempel, S.; Köhler, U.; Krohn, K.; Schmitz, N.; Carpenter, J.; Wieczorek, M.; Spohn, T.; Robinson, M. S.; Oberst, J.

2012-12-01

The Moon is key to understanding both Earth and our Solar System in terms of planetary processes and has been a witness of the Solar System history for more than 4.5 Ga. Building on earlier telescopic observations, our knowledge about the Moon was transformed by the wealth of information provided by Apollo and other space missions. These demonstrated the value of the Moon for understanding the fundamental processes that drive planetary formation and evolution. The Moon was understood as an inert body with its geology mainly restricted to impact and volcanism with associated tectonics, and a relative simple composition. Unlike Earth, an absence of plate tectonics has preserved a well-defined accretion and geological evolution record. However recent missions to the Moon show that this traditional view of the lunar surface is certainly an over simplification. For example, although it has long been suspected that ice might be preserved in cold traps at the lunar poles, recent results also indicate the formation and retention of OH- and H2O outside of polar regions. These volatiles are likely to be formed as a result of hydration processes operating at the lunar surface including the production of H2O and OH by solar wind protons interacting with oxygen-rich rock surfaces produced during micrometeorite impact on lunar soil particles. Moreover, on the basis of Lunar Prospector gamma-ray data, the lunar crust and underlying mantle has been found to be divided into distinct terranes that possess unique geochemical, geophysical, and geological characteristics. The concentration of heat producing elements on the nearside hemisphere of the Moon in the Procellarum KREEP Terrane has apparently led to the nearside being more volcanically active than the farside. Recent dating of basalts has shown that lunar volcanism was active for almost 3 Ga, starting at about 3.9-4.0 Ga and ceasing at ˜1.2 Ga. A recent re-processing of the seismic data supports the presence of a partially molten layer at the base of the mantle and shows not only the presence of a 330 km liquid core, but also a small solid inner core. Today, the Moon does not have a dynamo-generated magnetic field like that of the Earth. However, remnant magnetization of the lunar crust and the paleomagnetic record of some lunar samples suggest that magnetization was acquired, possibly from an intrinsic magnetic field caused by an early lunar core dynamo. In summary, the Moon is a complex differentiated planetary object and much remains to be explored and discovered, especially regarding the origin of the Moon, the history of the Earth-Moon system, and processes that have operated in the inner Solar System over the last 4.5 Ga. Returning to the Moon is therefore the critical next stepping-stone to further exploration and understanding of our planetary neighborhood.

Drilling systems for extraterrestrial subsurface exploration.

PubMed

Zacny, K; Bar-Cohen, Y; Brennan, M; Briggs, G; Cooper, G; Davis, K; Dolgin, B; Glaser, D; Glass, B; Gorevan, S; Guerrero, J; McKay, C; Paulsen, G; Stanley, S; Stoker, C

2008-06-01

Drilling consists of 2 processes: breaking the formation with a bit and removing the drilled cuttings. In rotary drilling, rotational speed and weight on bit are used to control drilling, and the optimization of these parameters can markedly improve drilling performance. Although fluids are used for cuttings removal in terrestrial drilling, most planetary drilling systems conduct dry drilling with an auger. Chip removal via water-ice sublimation (when excavating water-ice-bound formations at pressure below the triple point of water) and pneumatic systems are also possible. Pneumatic systems use the gas or vaporization products of a high-density liquid brought from Earth, gas provided by an in situ compressor, or combustion products of a monopropellant. Drill bits can be divided into coring bits, which excavate an annular shaped hole, and full-faced bits. While cylindrical cores are generally superior as scientific samples, and coring drills have better performance characteristics, full-faced bits are simpler systems because the handling of a core requires a very complex robotic mechanism. The greatest constraints to extraterrestrial drilling are (1) the extreme environmental conditions, such as temperature, dust, and pressure; (2) the light-time communications delay, which necessitates highly autonomous systems; and (3) the mission and science constraints, such as mass and power budgets and the types of drilled samples needed for scientific analysis. A classification scheme based on drilling depth is proposed. Each of the 4 depth categories (surface drills, 1-meter class drills, 10-meter class drills, and deep drills) has distinct technological profiles and scientific ramifications.

The core of the nearby S0 galaxy NGC 7457 imaged with the HST planetary camera

NASA Technical Reports Server (NTRS)

Lauer, Tod R.; Faber, S. M.; Holtzman, Jon A.; Baum, William A.; Currie, Douglas G.; Ewald, S. P.; Groth, Edward J.; Hester, J. Jeff; Kelsall, T.

1991-01-01

A brief analysis is presented of images of the nearby S0 galaxy NGC 7457 obtained with the HST Planetary Camera. While the galaxy remains unresolved with the HST, the images reveal that any core most likely has r(c) less than 0.052 arcsec. The light distribution is consistent with a gamma = -1.0 power law inward to the resolution limit, with a possible stellar nucleus with luminosity of 10 million solar. This result represents the first observation outside the Local Group of a galaxy nucleus at this spatial resolution, and it suggests that such small, high surface brightness cores may be common.

Planetary science: Iron fog of accretion

DOE PAGES

Anderson, William W.

2015-03-02

Here, pinpointing when Earth's core formed depends on the extent of metal–silicate equilibration in the mantle. Vaporization and recondensation of impacting planetesimal cores during accretion may reconcile disparate lines of evidence.

The double-degenerate, super-Chandrasekhar nucleus of the planetary nebula Henize 2-428.

PubMed

Santander-García, M; Rodríguez-Gil, P; Corradi, R L M; Jones, D; Miszalski, B; Boffin, H M J; Rubio-Díez, M M; Kotze, M M

2015-03-05

The planetary nebula stage is the ultimate fate of stars with masses one to eight times that of the Sun (M(⊙)). The origin of their complex morphologies is poorly understood, although several mechanisms involving binary interaction have been proposed. In close binary systems, the orbital separation is short enough for the primary star to overfill its Roche lobe as the star expands during the asymptotic giant branch phase. The excess gas eventually forms a common envelope surrounding both stars. Drag forces then result in the envelope being ejected into a bipolar planetary nebula whose equator is coincident with the orbital plane of the system. Systems in which both stars have ejected their envelopes and are evolving towards the white dwarf stage are said to be double degenerate. Here we report that Henize 2-428 has a double-degenerate core with a combined mass of ∼1.76M(⊙), which is above the Chandrasekhar limit (the maximum mass of a stable white dwarf) of 1.4M(⊙). This, together with its short orbital period (4.2 hours), suggests that the system should merge in 700 million years, triggering a type Ia supernova event. This supports the hypothesis of the double-degenerate, super-Chandrasekhar evolutionary pathway for the formation of type Ia supernovae.

Planetary environments and the conditions of life

NASA Technical Reports Server (NTRS)

Chang, S.

1988-01-01

Geophysical models of the first 600 Ma ofthe earth's history following accretion and core formation point to a period of great environmental disequilibrium. In such an environment, the passage of energy from the earth's interior and from the sun through gas-liquid-solid domains and their boundaries with each other generated a dynamically interacting, complex hierarchy of self-organized structures ranging from bubbles at the sea-air interface to tectonic plates. The ability of a planet to produce such a hierarchy is speculated to be a prerequisite to the origin and sustenance of life. The application of this criterion to Mars argues against the origin of Martian life.

Planets around pulsars - Implications for planetary formation

NASA Technical Reports Server (NTRS)

Bodenheimer, Peter

1993-01-01

Data on planets around pulsars are summarized, and different models intended to explain the formation mechanism are described. Both theoretical and observational evidence suggest that very special circumstances are required for the formation of planetary systems around pulsars, namely, the prior presence of a millisecond pulsar with a close binary companion, probably a low mass main-sequence star. It is concluded that the discovery of two planets around PSR 1257+12 is important for better understanding the problems of dynamics and stellar evolution. The process of planetary formation should be learned through intensive studies of the properties of disks near young objects and application of techniques for detection of planets around main-sequence solar-type stars.

Architectures of planetary systems and implications for their formation.

PubMed

Ford, Eric B

2014-09-02

Doppler planet searches revealed that many giant planets orbit close to their host star or in highly eccentric orbits. These and subsequent observations inspired new theories of planet formation that invoke gravitation interactions in multiple planet systems to explain the excitation of orbital eccentricities and even short-period giant planets. Recently, NASA's Kepler mission has identified over 300 systems with multiple transiting planet candidates, including many potentially rocky planets. Most of these systems include multiple planets with closely spaced orbits and sizes between that of Earth and Neptune. These systems represent yet another new and unexpected class of planetary systems and provide an opportunity to test the theories developed to explain the properties of giant exoplanets. Presently, we have limited knowledge about such planetary systems, mostly about their sizes and orbital periods. With the advent of long-term, nearly continuous monitoring by Kepler, the method of transit timing variations (TTVs) has blossomed as a new technique for characterizing the gravitational effects of mutual planetary perturbations for hundreds of planets. TTVs can provide precise, but complex, constraints on planetary masses, densities, and orbits, even for planetary systems with faint host stars. In the coming years, astronomers will translate TTV observations into increasingly powerful constraints on the formation and orbital evolution of planetary systems with low-mass planets. Between TTVs, improved Doppler surveys, high-contrast imaging campaigns, and microlensing surveys, astronomers can look forward to a much better understanding of planet formation in the coming decade.

Architectures of planetary systems and implications for their formation

PubMed Central

Ford, Eric B.

2014-01-01

Doppler planet searches revealed that many giant planets orbit close to their host star or in highly eccentric orbits. These and subsequent observations inspired new theories of planet formation that invoke gravitation interactions in multiple planet systems to explain the excitation of orbital eccentricities and even short-period giant planets. Recently, NASA’s Kepler mission has identified over 300 systems with multiple transiting planet candidates, including many potentially rocky planets. Most of these systems include multiple planets with closely spaced orbits and sizes between that of Earth and Neptune. These systems represent yet another new and unexpected class of planetary systems and provide an opportunity to test the theories developed to explain the properties of giant exoplanets. Presently, we have limited knowledge about such planetary systems, mostly about their sizes and orbital periods. With the advent of long-term, nearly continuous monitoring by Kepler, the method of transit timing variations (TTVs) has blossomed as a new technique for characterizing the gravitational effects of mutual planetary perturbations for hundreds of planets. TTVs can provide precise, but complex, constraints on planetary masses, densities, and orbits, even for planetary systems with faint host stars. In the coming years, astronomers will translate TTV observations into increasingly powerful constraints on the formation and orbital evolution of planetary systems with low-mass planets. Between TTVs, improved Doppler surveys, high-contrast imaging campaigns, and microlensing surveys, astronomers can look forward to a much better understanding of planet formation in the coming decade. PMID:24778212

X-ray photoevaporation's limited success in the formation of planetesimals by the streaming instability

NASA Astrophysics Data System (ADS)

Ercolano, Barbara; Jennings, Jeff; Rosotti, Giovanni; Birnstiel, Tilman

2017-12-01

The streaming instability is often invoked as solution to the fragmentation and drift barriers in planetesimal formation, catalysing the aggregation of dust on kyr time-scales to grow km-sized cores. However, there remains a lack of consensus on the physical mechanism(s) responsible for initiating it. One potential avenue is disc photoevaporation, wherein the preferential removal of relatively dust-free gas increases the disc metallicity. Late in the disc lifetime, photoevaporation dominates viscous accretion, creating a gradient in the depleted gas surface density near the location of the gap. This induces a local pressure maximum that collects drifting dust particles, which may then become susceptible to the streaming instability. Using a one-dimensional viscous evolution model of a disc subject to internal X-ray photoevaporation, we explore the efficacy of this process to build planetesimals. Over a range of parameters, we find that the amount of dust mass converted into planetesimals is often <1 M⊕ and at most a few M⊕ spread across tens of au. We conclude that photoevaporation may at best be relevant for the formation of debris discs, rather than a common mechanism for the formation of planetary cores. Our results are in contrast to a recent, similar investigation that considered an far-ultra-violet (FUV)-driven photoevaporation model and reported the formation of tens of M⊕ at large (>100 au) disc radii. The discrepancies are primarily a consequence of the different photoevaporation profiles assumed. Until observations more tightly constrain photoevaporation models, the relevance of this process to the formation of planets remains uncertain.

The fate of moderately volatile elements during planetary formation in the inner Solar System

NASA Astrophysics Data System (ADS)

Pringle, E. A.; Moynier, F.

2017-12-01

Moderately volatile element abundances are variable among inner Solar System bodies, with differing degrees of depletion compared to chondrites. These variations are a consequence of the processes of planetary formation. The conditions and the specific mechanisms of planetary accretion and differentiation can be investigated by analyzing the stable isotope compositions of terrestrial and extraterrestrial samples. The moderately volatile lithophile elements are particularly useful to distinguish between the effects of accretion and those of core formation. Recent work has shown isotope variations in inner Solar System bodies for the moderately volatile elements Zn and K. The purely lithophile nature of Rb (in contrast to Zn) and the higher volatility of Rb compared to K make Rb an ideal element with which to further study moderately volatile element depletion. We have developed a new method for the high-precision measurement of Rb isotope ratios by MC-ICP-MS. Terrestrial rocks define a narrow range in Rb isotope composition, indicating that Rb isotope fractionation during igneous differentiation is limited (<30 ppm/amu). Larger Rb isotope variations are observed in extraterrestrial materials. Carbonaceous chondrites display a trend toward lighter Rb isotope composition coupled with decreasing Rb/Sr, opposite to the effect expected if their volatile element variations were caused by evaporative loss of Rb. This relationship indicates that the volatile element abundance variations in carbonaceous chondrites are not due to evaporation or condensation, but rather are due to the mixing of chemically and isotopically distinct primordial reservoirs. In contrast, there is a clear signature of Rb loss during evaporation in volatile-depleted achondrites and lunar rocks. Significant heavy isotope enrichments (up to several per mil for 87Rb/85Rb) are found for volatile-depleted planetesimals, including eucrites. In addition, lunar rocks also display heavy Rb isotope enrichments compared to the BSE. The most likely cause of these variations is Rb isotope fractionation due to evaporation during accretion.

Origin of the solar system

NASA Technical Reports Server (NTRS)

Cameron, A. G. W.

1988-01-01

The current status of the classical model of solar-system formation is surveyed, reviewing the results of recent observational and theoretical investigations. Topics addressed include interstellar clouds, the collapse of interstellar gas, the primitive solar nebula, the formation of the sun, planetesimal accumulation, planetary accumulation, major planetary collisions, the development of planetary atmospheres, and comets. The relative merits of conflicting theories on many key problems are indicated, with reference to more detailed reviews in the literature.

The Interiors of Jupiter and Saturn

NASA Astrophysics Data System (ADS)

Helled, Ravit

2018-05-01

Probing the interiors of the giant planets in our Solar System is not an easy task. This requires a set of observations combined with theoretical models that are used to infer the planetary composition and its depth dependence. The masses of Jupiter and Saturn are 318 and 96 Earth masses, respectively, and since a few decades, we know that they mostly consist of hydrogen and helium. It is the mass of heavy elements (all elements heavier than helium) that is not well determined, as well as its distribution within the planets. While the heavy elements are not the dominating materials in Jupiter and Saturn, they are the key for our understanding of their formation and evolution histories. The planetary internal structure is inferred to fit the available observational constraints including the planetary masses, radii, 1-bar temperatures, rotation rates, and gravitational fields. Then, using theoretical equations of states (EOSs) for hydrogen, helium, their mixtures, and heavier elements (typically rocks and/or ices), a structure model is developed. However, there is no unique solution for the planetary structure, and the results depend on the used EOSs and the model assumptions imposed by the modeler. Standard interior models of Jupiter and Saturn include three main regions: (1) the central region (core) that consists of heavy elements, (2) an inner metallic hydrogen envelope that is helium rich, and (3) an outer molecular hydrogen envelope depleted with helium. The distribution of heavy elements can be either homogenous or discontinuous between the two envelopes. Major model assumptions that can affect the derived internal structure include the number of layers, the heat transport mechanism within the planet (and its entropy), the nature of the core (compact vs. diluted), and the location/pressure where the envelopes are divided. Alternative structure models assume a less distinct division between the layers and/or a less non-homogenous distribution of the heavy elements. The fact that the behavior of hydrogen at high pressures and temperatures in not perfectly known, and that helium separates from hydrogen at the deep interior add sources of uncertainties to the interior model. Today, with accurate measurements of the gravitational fields of Jupiter and Saturn from the Juno and Cassini missions, structure models can be further constrained. At the same time, these measurements introduce new challenges and open question for planetary modelers.

Iron snow in the Martian Core?

NASA Astrophysics Data System (ADS)

Davies, C. J.; Pommier, A.

2017-12-01

The decline of Mars' global magnetic field some 3.8-4.1 billion years ago is thought to reflect the demise of the dynamo that operated in its liquid core. The termination of the dynamo is intimately tied to the thermochemical evolution of the core-mantle system and therefore to the present-day physical state of the Martian core. The standard model predicts that the Martian dynamo failed because thermal convection stopped and the core remained entirely liquid until the present. Here we consider an alternative hypothesis that the Martian core crystallized from the top down in the so-called iron snow regime. We derive energy-entropy equations describing the long-timescale thermal and magnetic evolution of the core that incorporate the self-consistent formation of a snow layer that freezes out pure iron and is assumed to be on the liquidus; the iron sinks and remelts in the deeper core, acting as a possible source for magnetic field generation. Compositions are in the FeS system, with a sulfur content up to 16 wt%. The values of the different parameters (core radius, density and CMB pressure) are varied within bounds set by recent internal structure models that satisfy existing geodetic constraints (planetary mass, moment of inertia and tidal Love number). The melting curve and adiabat, CMB heat flow and thermal conductivity were also varied, based on previous experimental and numerical works. We observe that the formation of snow zones occurs for a wide range of interior and thermal structure properties and depends critically on the initial sulfur concentration. Gravitational energy release and latent heat effects arising during growth of the snow zone do not generate sufficient entropy to restart the dynamo unless the snow zone occupies a significant fraction of the core. Our results suggest that snow zones can be 1.5-2 Gyrs old, though thermal stratification of the uppermost core, not included in our model, likely delays onset. Models that match the available magnetic and geodetic constraints have an initial S concentration of about 10wt.% and snow zones that occupy approximately the top 100 km of the present-day Martian core.

An Ontology-Based Archive Information Model for the Planetary Science Community

NASA Technical Reports Server (NTRS)

Hughes, J. Steven; Crichton, Daniel J.; Mattmann, Chris

2008-01-01

The Planetary Data System (PDS) information model is a mature but complex model that has been used to capture over 30 years of planetary science data for the PDS archive. As the de-facto information model for the planetary science data archive, it is being adopted by the International Planetary Data Alliance (IPDA) as their archive data standard. However, after seventeen years of evolutionary change the model needs refinement. First a formal specification is needed to explicitly capture the model in a commonly accepted data engineering notation. Second, the core and essential elements of the model need to be identified to help simplify the overall archive process. A team of PDS technical staff members have captured the PDS information model in an ontology modeling tool. Using the resulting knowledge-base, work continues to identify the core elements, identify problems and issues, and then test proposed modifications to the model. The final deliverables of this work will include specifications for the next generation PDS information model and the initial set of IPDA archive data standards. Having the information model captured in an ontology modeling tool also makes the model suitable for use by Semantic Web applications.

Dynamos in asymptotic-giant-branch stars as the origin of magnetic fields shaping planetary nebulae.

PubMed

Blackman, E G; Frank, A; Markiel, J A; Thomas, J H; Van Horn, H M

2001-01-25

Planetary nebulae are thought to be formed when a slow wind from the progenitor giant star is overtaken by a subsequent fast wind generated as the star enters its white dwarf stage. A shock forms near the boundary between the winds, creating the relatively dense shell characteristic of a planetary nebula. A spherically symmetric wind will produce a spherically symmetric shell, yet over half of known planetary nebulae are not spherical; rather, they are elliptical or bipolar in shape. A magnetic field could launch and collimate a bipolar outflow, but the origin of such a field has hitherto been unclear, and some previous work has even suggested that a field could not be generated. Here we show that an asymptotic-giant-branch (AGB) star can indeed generate a strong magnetic field, having as its origin a dynamo at the interface between the rapidly rotating core and the more slowly rotating envelope of the star. The fields are strong enough to shape the bipolar outflows that produce the observed bipolar planetary nebulae. Magnetic braking of the stellar core during this process may also explain the puzzlingly slow rotation of most white dwarf stars.

A bibliography of planetary geology principal investigators and their associates, 1976-1978

NASA Technical Reports Server (NTRS)

1978-01-01

This bibliography cites publications submitted by 484 principal investigators and their associates who were supported through NASA's Office of Space Sciences Planetary Geology Program. Subject classifications include: solar system formation, comets, and asteroids; planetary satellites, planetary interiors, geological and geochemical constraints on planetary evolution; impact crater studies, volcanism, eolian studies, fluvian studies, Mars geological mapping; Mercury geological mapping; planetary cartography; and instrument development and techniques. An author/editor index is provided.

The formation of Uranus and Neptune in the Jupiter-Saturn region of the Solar System.

PubMed

Thommes, E W; Duncan, M J; Levison, H F

1999-12-09

Planets are believed to have formed through the accumulation of a large number of small bodies. In the case of the gas-giant planets Jupiter and Saturn, they accreted a significant amount of gas directly from the protosolar nebula after accumulating solid cores of about 5-15 Earth masses. Such models, however, have been unable to produce the smaller ice giants Uranus and Neptune at their present locations, because in that region of the Solar System the small planetary bodies will have been more widely spaced, and less tightly bound gravitationally to the Sun. When applied to the current Jupiter-Saturn zone, a recent theory predicts that, in addition to the solid cores of Jupiter and Saturn, two or three other solid bodies of comparable mass are likely to have formed. Here we report the results of model calculations that demonstrate that such cores will have been gravitationally scattered outwards as Jupiter, and perhaps Saturn, accreted nebular gas. The orbits of these cores then evolve into orbits that resemble those of Uranus and Neptune, as a result of gravitational interactions with the small bodies in the outer disk of the protosolar nebula.

Implications of (Less) Accurate Mass-Radius-Measurements for the Habitability of Extrasolar Terrestrial Planets: Why Do We Need PLATO?

NASA Astrophysics Data System (ADS)

Noack, L.; Wagner, F. W.; Plesa, A.-C.; Höning, D.; Sohl, F.; Breuer, D.; Rauer, H.

2012-04-01

Several space missions (CoRoT, Kepler and others) already provided promising candidates for terrestrial exoplanets (i.e. with masses less than about 10 Earth masses) and thereby triggered an exciting new research branch of planetary modelling to investigate the possible habitability of such planets. Earth analogues (low-mass planets with an Earth-like structure and composition) are likely to be found in the near future with new missions such as the proposed M3 mission PLATO. Planets may be more diverse in the universe than they are in the solar system. Our neighbouring planets in the habitable zone are all terrestrial by the means of being differentiated into an iron core, a silicate mantle and a crust. To reliably determine the interior structure of an exoplanet, measurements of mass and radius have to be sufficiently accurate (around +/-2% error allowed for the radius and +/-5% for the mass). An Earth-size planet with an Earth-like mass but an expected error of ~15% in mass for example may have either a Mercury-like, an Earth-like or a Moon-like (i.e. small iron core) structure [1,2]. Even though the atmospheric escape is not strongly influenced by the interior structure, the outgassing of volatiles and the likeliness of plate tectonics and an ongoing carbon-cycle may be very different. Our investigations show, that a planet with a small silicate mantle is less likely to shift into the plate-tectonics regime, cools faster (which may lead to the loss of a magnetic field after a short time) and outgasses less volatiles than a planet with the same mass but a large silicate mantle and small iron core. To be able to address the habitability of exoplanets, space missions such as PLATO, which can lead up to 2% accuracy in radius [3], are extremely important. Moreover, information about the occurrence of different planetary types helps us to better understand the formation of planetary systems and to further constrain the Drake's equation, which gives an estimate of the expected number of potentially habitable exoplanets in the universe.

Palaeointensity, core thermal conductivity and the unknown age of the inner core

NASA Astrophysics Data System (ADS)

Smirnov, Aleksey V.; Tarduno, John A.; Kulakov, Evgeniy V.; McEnroe, Suzanne A.; Bono, Richard K.

2016-05-01

Data on the evolution of Earth's magnetic field intensity are important for understanding the geodynamo and planetary evolution. However, the paleomagnetic record in rocks may be adversely affected by many physical processes, which must be taken into account when analysing the palaeointensity database. This is especially important in the light of an ongoing debate regarding core thermal conductivity values, and how these relate to the Precambrian geodynamo. Here, we demonstrate that several data sets in the Precambrian palaeointensity database overestimate the true paleofield strength due to the presence of non-ideal carriers of palaeointensity signals and/or viscous re-magnetizations. When the palaeointensity overestimates are removed, the Precambrian database does not indicate a robust change in geomagnetic field intensity during the Mesoproterozoic. These findings call into question the recent claim that the solid inner core formed in the Mesoproterozoic, hence constraining the thermal conductivity in the core to `moderate' values. Instead, our analyses indicate that the presently available palaeointensity data are insufficient in number and quality to constrain the timing of solid inner core formation, or the outstanding problem of core thermal conductivity. Very young or very old inner core ages (and attendant high or low core thermal conductivity values) are consistent with the presently known history of Earth's field strength. More promising available data sets that reflect long-term core structure are geomagnetic reversal rate and field morphology. The latter suggests changes that may reflect differences in Archean to Proterozoic core stratification, whereas the former suggest an interval of geodynamo hyperactivity at ca. 550 Ma.

A metallicity recipe for rocky planets

NASA Astrophysics Data System (ADS)

Dawson, Rebekah I.; Chiang, Eugene; Lee, Eve J.

2015-10-01

Planets with sizes between those of Earth and Neptune divide into two populations: purely rocky bodies whose atmospheres contribute negligibly to their sizes, and larger gas-enveloped planets possessing voluminous and optically thick atmospheres. We show that whether a planet forms rocky or gas-enveloped depends on the solid surface density of its parent disc. Assembly times for rocky cores are sensitive to disc solid surface density. Lower surface densities spawn smaller planetary embryos; to assemble a core of given mass, smaller embryos require more mergers between bodies farther apart and therefore exponentially longer formation times. Gas accretion simulations yield a rule of thumb that a rocky core must be at least 2M⊕ before it can acquire a volumetrically significant atmosphere from its parent nebula. In discs of low solid surface density, cores of such mass appear only after the gas disc has dissipated, and so remain purely rocky. Higher surface density discs breed massive cores more quickly, within the gas disc lifetime, and so produce gas-enveloped planets. We test model predictions against observations, using planet radius as an observational proxy for gas-to-rock content and host star metallicity as a proxy for disc solid surface density. Theory can explain the observation that metal-rich stars host predominantly gas-enveloped planets.

Melting in super-earths.

PubMed

Stixrude, Lars

2014-04-28

We examine the possible extent of melting in rock-iron super-earths, focusing on those in the habitable zone. We consider the energetics of accretion and core formation, the timescale of cooling and its dependence on viscosity and partial melting, thermal regulation via the temperature dependence of viscosity, and the melting curves of rock and iron components at the ultra-high pressures characteristic of super-earths. We find that the efficiency of kinetic energy deposition during accretion increases with planetary mass; considering the likely role of giant impacts and core formation, we find that super-earths probably complete their accretionary phase in an entirely molten state. Considerations of thermal regulation lead us to propose model temperature profiles of super-earths that are controlled by silicate melting. We estimate melting curves of iron and rock components up to the extreme pressures characteristic of super-earth interiors based on existing experimental and ab initio results and scaling laws. We construct super-earth thermal models by solving the equations of mass conservation and hydrostatic equilibrium, together with equations of state of rock and iron components. We set the potential temperature at the core-mantle boundary and at the surface to the local silicate melting temperature. We find that ancient (∼4 Gyr) super-earths may be partially molten at the top and bottom of their mantles, and that mantle convection is sufficiently vigorous to sustain dynamo action over the whole range of super-earth masses.

The Formation of Nucleobases from the Irradiation of Purine in Astophysical Ices and Comparisons with Meteorites.

NASA Technical Reports Server (NTRS)

Sandford, S. A.; Materese, C. K.; Nuevo, M.

2016-01-01

N-heterocycles have been identified in meteorites and their extraterrestrial origins are suggested by isotopic ratio measurements. Although small N- heterocycles have not been detected in the interstellar medium (ISM), recent experiments in our lab have shown that the irradiation of the aromatic molecules like benzene (C6H6) and naphthalene (C10H8) in mixed molecular ices leads to the formation of O- and N-heterocyclic molecules. Among the class of N-heterocycles are the nucleobases, which are of astrobiological interest because they are the information bearing units of DNA and RNA. Nucleobases have been detected in meteorites [3-5], with isotopic signatures that are also consistent with an extraterrestrial origin. Three of the biologically relevant nucleobases (uracil, cytosine, and guanine) have a pyrimidine core structure while the remaining two (adenine and guanine) possess a purine core. Previous experiments in our lab have demonstrated that all of the bio-logical nucleobases (and numerous other molecules) with a pyrimidine core structure can be produced by irradiating pyrimidine in mixed molecular ices of several compositions [6-8]. In this work, we study the formation of purine-based molecules, including the nucleobases adenine, and guanine, from the ultraviolet (UV) irradiation of purine in ices consisting mixtures of H2O and NH3 at low temperature. The experiments are designed to simulate the astrophysical conditions under which these species may be formed in dense molecular clouds, protoplanetary disks, or on the surfaces of icy bodies in planetary systems.

Istoriya al'ternativnykh techenij v planetnoj kosmogonii (gomogennaya ili geterogennaya akkretsiya) %t The history of two alternative concepts in planetary cosmogony (homogeneous of heterogeneous accretion)

NASA Astrophysics Data System (ADS)

Rezanov, I. A.

Initially the hypotheses of Kant, Laplace, and other authors implied homogeneous accretion of planets from uniform material. O. Yu. Schmidt shared this idea. The idea of heterogeneous accretion was proposed in the mid-1940s by V. G. Fesenkov, who demonstrated that the iron cores of planets started to form prior to their silicate mantles. The obvious increase in average planet density with decreasing distance from the Sun suggests that the protoplanetary nebula was also heterogeneous - iron concentrated closer to the Sun, probably under the effect of its magnetic field. In the second half of the 20th century, planetary cosmogony developed against the background of continuous dispute between the adherents of homogeneous and heterogeneous planetary accretion. The confrontation still exists, although arguments in favour of heterogeneous accretion increase in weight. The dilemma under discussion is directly related to modern tectonic concepts, because it is necessary to find an answer to the question whether the core originated from the differentiation of the Earth's material or our planet had a core from the beginning.

Variety in planetary systems

NASA Technical Reports Server (NTRS)

Wetherill, George W.

1993-01-01

Observation of circumstellar disks, regular satellite systems of outer planets, and planet-size objects orbiting pulsars support the supposition that formation of planetary systems is a robust, rather than a fragile, byproduct of the formation and evolution of stars. The extent to which these systems may be expected to resemble one another and our Solar System, either in overall structure or in detail remains uncertain. When the full range of possible stellar masses, disk masses, and initial specific angular momenta are considered, the possible variety of planetary configurations is very large. Numerical modeling indicates a difference between the formation of small, inner, terrestrial planets and the outer planets.

New isotopic clues to solar system formation

NASA Technical Reports Server (NTRS)

Lee, T.

1979-01-01

The presence of two new extinct nuclides Al-26 and Pd-107 with half lives of approximately one million years in the early solar system implies that there were nucleosynthetic activities involving a great many elements almost at the instant of solar system formation. Rate gas and oxygen isotopic abundance variations ('anomalies') relative to the 'cosmic' composition were observed in a variety of planetary objects, which indicates that isotopic heterogeneities caused by the incomplete mixing of distinct nucleosynthesis components permeate the entire solar system. These new results have major implications for cosmochronology, nucleosynthesis theory, star formation, planetary heating, and the genetic relationship between different planetary bodies

A Nonmagnetic Differentiated Early Planetary Body

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weiss, Benjamin P.; Wang, Jun

2017-06-15

Paleomagnetic studies of meteorites have shown that the solar nebula was likely magnetized and that many early planetary bodies generated dynamo magnetic fields in their advecting metallic cores. The surface fields on these bodies were recorded by a diversity of chondrites and achondrites, ranging in intensity from several μT to several hundred μT. In fact, an achondrite parent body without evidence for paleomagnetic fields has yet to be confidently identified, hinting that early solar system field generation and the dynamo process in particular may have been common. Here we present paleomagnetic measurements of the ungrouped achondrite NWA 7325 indicating thatmore » it last cooled in a near-zero field (<∼1.7μT), estimated to have occurred at 4563.09 ± 0.26 million years ago (Ma) from Al–Mg chronometry. Because NWA 7325 is highly depleted in siderophile elements, its parent body nevertheless underwent large-scale metal-silicate differentiation and likely formed a metallic core. This makes NWA 7325 the first recognized example of an essentially unmagnetized igneous rock from a differentiated early solar system body. These results indicate that all magnetic fields, including those from any core dynamo on the NWA 7325 parent body, the solar nebula, young Sun, and solar wind, were <1.7 μT at the location of NWA 7325 at 4563 Ma. This supports a recent conclusion that the solar nebula had dissipated by ∼4 million years after solar system formation. NWA 7325 also serves as an experimental control that gives greater confidence in the positive identification of remanent magnetization in other achondrites.« less

The nuclear regions of NGC 3311 and NGC 7768 imaged with the Hubble Space Telescope Planetary Camera

NASA Technical Reports Server (NTRS)

Grillmair, Carl J.; Faber, S.M.; Lauer, Tod R.; Baum, William A.; Lynds, Roger C.; O'Neil, Earl J., Jr.; Shaya, Edward J.

1994-01-01

We present high-resolution, V band images of the central regions of the brightest cluster ellipticals NGC 3311 and NGC 7768 taken with the Planetary Camera of the Hubble Space Telescope. The nuclei of both galaxies are found to be obscured by dust, though the morphology of the dust is quite different in the two cases. The dust cloud which obscures the central 3 arcsec of NGC 3311 is complex and irregular, while the central region of NGC 7768 contains a disk of material similar in appearance and scale to that recently observed in HST images of NGC 4261. The bright, relatively blue source detected in ground-based studies of NGC 3311 is marginally resolved and is likely to be a site of ongoing star formation. We examine the distribution of globular clusters in the central regions of NGC 3311. The gradient in the surface density profile of the cluster system is significantly shallower than that found by previous investigators at larger radii. We find a core radius for the cluster distribution of 12 plus or minus 3 kpc, which is even larger than the core radius of the globular cluster system surrounding M87. It is also an order of magnitude larger than the upper limit on the core radius of NGC 3311's stellar light and suggests that the central field-star population and the globular cluster system are dynamically distinct. We briefly discuss possible sources for the cold/warm interstellar material in early-type galaxies. While the issue has not been resolved, models which involve galactic wind failure appear to be mo st naturally consistent with the observations.

The Virgo Cluster of Galaxies in the Making

NASA Astrophysics Data System (ADS)

2004-10-01

VLT Observations of Planetary Nebulae Confirm the Dynamical Youth of Virgo [1] Summary An international team of astronomers [2] has succeeded in measuring with high precision the velocities of a large number of planetary nebulae [3] in the intergalactic space within the Virgo Cluster of galaxies. For this they used the highly efficient FLAMES spectrograph [4] on the ESO Very Large Telescope at the Paranal Observatory (Chile). These planetary nebulae stars free floating in the otherwise seemingly empty space between the galaxies of large clusters can be used as "probes" of the gravitational forces acting within these clusters. They trace the masses, visible as well as invisible, within these regions. This, in turn, allows astronomers to study the formation history of these large bound structures in the universe. The accurate velocity measurements of 40 of these stars confirm the view that Virgo is a highly non-uniform galaxy cluster, consisting of several subunits that have not yet had time to come to equilibrium. These new data clearly show that the Virgo Cluster of galaxies is still in its making. They also prove for the first time that one of the bright galaxies in the region scrutinized, Messier 87, has a very extended halo of stars, reaching out to at least 65 kpc. This is more than twice the size of our own galaxy, the Milky Way. PR Photo 29a/04: Velocity Measurements of Forty Intracluster Planetary Nebulae (FLAMES/VLT) PR Photo 29b/04: Intracluster Planetary Nebulae in the SUC field in the Virgo Cluster (Digital Sky Survey) A young cluster At a distance of approximately 50 million light-years, the Virgo Cluster is the nearest galaxy cluster. It is located in the zodiacal constellation Virgo (The Virgin) and contains many hundreds of galaxies, ranging from giant and massive elliptical galaxies and spirals like our own Milky Way, to dwarf galaxies, hundreds of times smaller than their big brethren. French astronomer Charles Messier entered 16 members of the Virgo cluster in his famous catalogue of nebulae. An image of the core of the cluster obtained with the Wide Field Imager camera at the ESO La Silla Observatory was published last year as PR Photo 04a/03. Clusters of galaxies are believed to have formed over a long period of time by the assembly of smaller entities, through the strong gravitational pull from dark and luminous matter. The Virgo cluster is considered to be a relatively young cluster because previous studies have revealed small "sub-clusters of galaxies" around the major galaxies Messier 87, Messier 86 and Messier 49. These sub-clusters have yet to merge to form a denser and smoother galaxy cluster. Recent observations have shown that the so-called "intracluster" space, the region between galaxies in a cluster, is permeated by a sparse "intracluster population of stars", which can be used to study in detail the structure of the cluster. Cosmic wanderers The first discoveries of intracluster stars in the Virgo cluster were made serendipitously by Italian astronomer, Magda Arnaboldi (Torino Observatory, Italy) and her colleagues, in 1996. In order to study the extended halos of galaxies in the Virgo cluster, with the ESO New Technology Telescope at La Silla, they searched for objects known as "planetary nebulae" [3]. Planetary nebulae (PNe) can be detected out to large distances from their strong emission lines. These narrow emission lines also allow for a precise measure of their radial velocities. Planetary Nebulae can thus serve to investigate the motions of stars in the halo regions of distant galaxies. In their study, the astronomers found several planetary nebulae apparently not related to any galaxies but moving in the gravity field of the whole cluster. These "wanderers" belonged to a newly discovered intracluster population of stars. Since these first observations, several hundreds of these wanderers have been discovered. They must represent the tip of the iceberg of a huge population of stars swarming among the galaxies in these enormous clusters. Indeed, as planetary nebulae are the final stage of common low mass stars - like our Sun - they are representative of the stellar population in general. And as planetary nebulae are rather short-lived (a few tens of thousand years - a blitz on astronomical timescales), astronomers can estimate that one star in about 8,000 million of solar-type stars is visible as a planetary nebula at any given moment. There must thus be a comparable number of stars in between galaxies as in the galaxies themselves. But because they are diluted in such a huge volume, they are barely detectable. Because these stars are predominantly old, the most likely explanation for their presence in the intracluster space is that they formed within individual galaxies, which were subsequently stripped of many of their stars during close encounters with other galaxies during the initial stages of cluster formation. These "lost" stars were then dispersed into intracluster space where we now find them. Thus planetary nebulae can provide a unique handle on the number, type of stars and motions in regions that may harbour a substantial amount of mass. Their motions contain the fossil record of the history of galaxy interaction and the formation of the galaxy cluster. Measuring the speed of dying stars ESO PR Photo 29a/04 ESO PR Photo 29a/04 Velocity Measurements of Forty Intracluster Planetary Nebulae [Preview - JPEG: 400 x 502 pix - 50k] [Normal - JPEG: 800 x 1004 pix - 330k] [Full Res - JPEG: 2321 x 2912 pix - 1.2M] Caption: ESO PR Photo 29a/04 shows the intracluster planetary nebulae radial velocity distributions in three different regions of the sky (identified with the following labels: FCJ, CORE and SUC) in the Virgo cluster core region. The central panel shows the image of the VIRGO cluster core obtained from the Digital Sky Survey. The four brighter galaxies in the field are on the left Messier 87 near the FCJ field, and Messier 86, Messier 84 and NGC 4388 in the SUC field. In the FCJ panel, the blue dashed line shows a Gaussian curve with a mean velocity, vrad= 1276 km/s, and a dispersion, σrad= 247 km/s. In CORE, the green dashed line shows a Gaussian curve with vrad= 1436 km/s and σrad= 538 km/s for Virgo Cluster dwarf ellipticals and lenticular galaxies within 2 degrees of Messier 87. In the SUC panel, the dashed red line shows a Gaussian curve with vrad= 1079 km/s and σrad= 286 km/s, associated to the Messier 84 (M84) peak. The overplotted dash-dotted lines show the SUC-FLAMES spectra of intracluster HII regions, which have radial velocities in the M84 and NGC 4388 velocity ranges. The international team of astronomers [2] went on further to make a detailed study of the motions of the planetary nebulae in the Virgo cluster in order to determine its dynamical structure and compare it with numerical simulations. To this aim, they carried out a challenging research programme, aimed at confirming intracluster planetary nebula candidates they found earlier and measuring their radial velocities in three different regions ("survey fields") in the Virgo cluster core. This is far from an easy task. The emission in the main Oxygen emission line from a planetary nebula in Virgo is comparable to that of a 60-Watt light bulb at a distance of about 6.6 million kilometres, about 17 times the average distance to the Moon. Furthermore intracluster planetary nebula samples are sparse, with only a few tens of planetary nebulae in a quarter of a degree square sky field - about the size of the Moon. Spectroscopic observations thus require 8 metre class telescopes and spectrographs with a large field of view. The astronomers had therefore to rely on the FLAMES-GIRAFFE spectrograph on the VLT [4], with its relatively high spectral resolution, its field of view of 25 arcmin and the possibility to take up to 130 spectra at a time. The astronomers studied a total of 107 stars, among which 71 were believed to be genuine intracluster planetary candidates. They observed between 21 and 49 objects simultaneously for about 2 hours per field. The three parts of the Virgo core surveyed contain several bright galaxies (Messier 84, 86, 87, and NGC 4388) and a large number of smaller galaxies. They were chosen to represent different entities of the cluster. The spectroscopic measurements could confirm the intracluster nature of 40 of the planetary nebulae studied. They also provided a wealth of knowledge on the structure of this part of the Virgo cluster. In The Making ESO PR Photo 29b/04 ESO PR Photo 29b/04 Intracluster Planetary Nebulae in the SUC field in the Virgo Cluster. (Digital Sky Survey) [Preview - JPEG: 400 x 471 pix - 55k] [Normal - JPEG: 800 x 942 pix - 512k] [Full Res - JPEG: 2189 x 2580 pix - 2.3M] Caption: ESO PR Photo 29b/04: Zoomed in view of the pointing relative to the SUC field. The image shows a 30 x 30 arcminute field centred on the Messier 86/ Messier 84 region of the Virgo cluster. The brighter galaxies in the field are (clockwise from the left) M86, M84 and NGC 4388. Their systemic velocities are -244, 1060 and 2524 km/s, respectively. Here the envelopes of bright galaxies are subtracted as much as possible for the detection of planetary nebulae embedded there. The larges circle indicates the FLAMES field-of-view. Intracluster planetary nebula candidates are marked by circles and show a highly non-uniform distribution in this field. The numbers near each circle indicate the measured line-of-sight velocity for that intracluster planetary nebula. The colour code used is blue for velocities smaller than the M84 systemic velocity (1060 km/s), red for larger velocities. In the first field near Messier 87 (M87), the astronomers measured a mean velocity close to 1250 km/s and a rather small dispersion around this value. Most stars in this field are thus physically bound to the bright galaxy M87, in the same way as the Earth is bound to the Sun. Magda Arnaboldi explains: "This study has led to the remarkable discovery that Messier 87 has a stellar halo in approximate dynamical equilibrium out to at least 65 kpc, or more than 200,000 light-years. This is more than twice the size of our own galaxy, the Milky Way, and was not known before." The velocity dispersion observed in the second field, which is far away from bright galaxies, is larger than in the first one by a factor four. This very large dispersion, indicating stars moving in very disparate directions at different speeds, also tells us that this field most probably contains many intracluster stars whose motions are barely influenced by large galaxies. The new data suggest as a tantalizing possibility that this intracluster population of stars could be the leftover from the disruption of small galaxies as they orbit M87. The velocity distribution in the third field, as deduced from FLAMES spectra, is again different. The velocities show substructures related to the large galaxies Messier 86, Messier 84 and NGC 4388. Most likely, the large majority of all these planetary nebulae belong to a very extended halo around Messier 84. Ortwin Gerhard (University of Basel, Switzerland), member of the team, is thrilled: "Taken together these velocity measurements confirm the view that the Virgo Cluster is a highly non-uniform and unrelaxed galaxy cluster, consisting of several subunits. With the FLAMES spectrograph, we have thus been able to watch the motions in the Virgo Cluster, at a moment when its subunits are still coming together. And it is certainly a view worth seeing!" More information The results presented in this ESO Press Release are based on a research paper ("The Line-of-Sight Velocity Distributions of Intracluster Planetary Nebulae in the Virgo Cluster Core" by M. Arnaboldi et al.) that has just appeared in the research journal Astrophysical Journal Letters Vol. 614, p. 33. Notes [1]: The University of Basel Press Release on this topic is available at http://www.zuv.unibas.ch/uni_media/2004/20041022virgo.html. [2]: The members of the team are Magda Arnaboldi (INAF, Osservatorio di Pino Torinese, Italy), Ortwin Gerhard (Astronomisches Institut, Universität Basel, Switzerland), Alfonso Aguerri (Instituto de Astrofisica de Canarias, Spain), Kenneth C. Freeman (Mount Stromlo Observatory, ACT, Australia), Nicola Napolitano (Kapteyn Astronomical Institute, The Netherlands), Sadanori Okamura (Dept. of Astronomy, University of Tokyo, Japan), and Naoki Yasuda (Institute for Cosmic Ray Research, University of Tokyo, Japan). [3]: Planetary nebulae are Sun-like stars in their final dying phase during which they eject their outer layers into surrounding space. At the same time, they unveil their small and hot stellar core which appears as a "white dwarf star". The ejected envelope is illuminated and heated by the stellar core and emits strongly in characteristic emission lines of several elements, notably oxygen (at wavelengths 495.9 and 500.7 nm). Their name stems from the fact that some of these nearby objects, such as the "Dumbbell Nebula" (see ESO PR Photo 38a/98) resemble the discs of the giant planets in the solar system when viewed with small telescopes. [4]: FLAMES, the Fibre Large Array Multi-Element Spectrograph, is installed at the 8.2-m VLT KUEYEN Unit Telescope. It is able to observe the spectra of a large number of individual, faint objects (or small sky areas) simultaneously and covers a sky field of no less than 25 arcmin in diameter, i.e., almost as large as the full Moon. It is the result of a collaboration between ESO, the Observatoire de Paris-Meudon, the Observatoire de Genève-Lausanne, and the Anglo Australian Observatory (AAO).

The formation of planetary systems during the evolution of close binary stars

NASA Astrophysics Data System (ADS)

Tutukov, A. V.

1991-08-01

Modern scenarios of the formation of planetary systems around single stars and products of merging close binaries are described. The frequencies of the realization of different scenarios in the Galaxy are estimated. It is concluded that the modern theory of the early stages of the evolution of single stars and the theory of the evolution of close binaries offer several possible versions for the origin of planetary systems, while the scenario dating back to Kant and Laplace remains the likeliest.

Proceedings of the 38th Lunar and Planetary Science Conference

NASA Technical Reports Server (NTRS)

2007-01-01

The sessions in the conference include: Titan, Mars Volcanism, Mars Polar Layered Deposits, Early Solar System Isotopes, SPECIAL SESSION: Mars Reconnaissance Orbiter: New Ways of Studying the Red Planet, Achondrites: Exploring Oxygen Isotopes and Parent-Body Processes, Solar System Formation and Evolution, SPECIAL SESSION: SMART-1, . Impact Cratering: Observations and Experiments, SPECIAL SESSION: Volcanism and Tectonism on Saturnian Satellites, Solar Nebula Composition, Mars Fluvial Geomorphology, Asteroid Observations: Spectra, Mostly, Mars Sediments and Geochemistry: View from the Surface, Mars Tectonics and Crustal Dichotomy, Stardust: Wild-2 Revealed, Impact Cratering from Observations and Interpretations, Mars Sediments and Geochemistry: The Map View, Chondrules and Their Formation, Enceladus, Asteroids and Deep Impact: Structure, Dynamics, and Experiments, Mars Surface Process and Evolution, Martian Meteorites: Nakhlites, Experiments, and the Great Shergottite Age Debate, Stardust: Mainly Mineralogy, Astrobiology, Wind-Surface Interactions on Mars and Earth, Icy Satellite Surfaces, Venus, Lunar Remote Sensing, Space Weathering, and Impact Effects, Interplanetary Dust/Genesis, Mars Cratering: Counts and Catastrophes?, Chondrites: Secondary Processes, Mars Sediments and Geochemistry: Atmosphere, Soils, Brines, and Minerals, Lunar Interior and Differentiation, Mars Magnetics and Atmosphere: Core to Ionosphere, Metal-rich Chondrites, Organics in Chondrites, Lunar Impacts and Meteorites, Presolar/Solar Grains, Topics for Print Only papers are: Outer Planets/Satellites, Early Solar System, Interplanetary Dust, Comets and Kuiper Belt Objects, Asteroids and Meteoroids, Chondrites, Achondrites, Meteorite Related, Mars Reconnaissance Orbiter, Mars, Astrobiology, Planetary Differentiation, Impacts, Mercury, Lunar Samples and Modeling, Venus, Missions and Instruments, Global Warming, Education and Public Outreach, Poster sessions are: Asteroids/Kuiper Belt Objects, Galilean Satellites: Geology and Mapping, Titan, Volcanism and Tectonism on Saturnian Satellites, Early Solar System, Achondrite Hodgepodge, Ordinary Chondrites, Carbonaceous Chondrites, Impact Cratering from Observations and Interpretations, Impact Cratering from Experiments and Modeling, SMART-1, Planetary Differentiation, Mars Geology, Mars Volcanism, Mars Tectonics, Mars: Polar, Glacial, and Near-Surface Ice, Mars Valley Networks, Mars Gullies, Mars Outflow Channels, Mars Sediments and Geochemistry: Spirit and Opportunity, Mars Reconnaissance Orbiter: New Ways of Studying the Red Planet, Mars Reconnaissance Orbiter: Geology, Layers, and Landforms, Oh, My!, Mars Reconnaissance Orbiter: Viewing Mars Through Multicolored Glasses; Mars Science Laboratory, Phoenix, and ExoMars: Science, Instruments, and Landing Sites; Planetary Analogs: Chemical and Mineral, Planetary Analogs: Physical, Planetary Analogs: Operations, Future Mission Concepts, Planetary Data, Imaging, and Cartography, Outer Solar System, Presolar/Solar Grains, Stardust Mission; Interplanetary Dust, Genesis, Asteroids and Comets: Models, Dynamics, and Experiments, Venus, Mercury, Laboratory Instruments, Methods, and Techniques to Support Planetary Exploration; Instruments, Techniques, and Enabling Techologies for Planetary Exploration; Lunar Missions and Instruments, Living and Working on the Moon, Meteoroid Impacts on the Moon, Lunar Remote Sensing, Lunar Samples and Experiments, Lunar Atmosphere, Moon: Soils, Poles, and Volatiles, Lunar Topography and Geophysics, Lunar Meteorites, Chondrites: Secondary Processes, Chondrites, Martian Meteorites, Mars Cratering, Mars Surface Processes and Evolution, Mars Sediments and Geochemistry: Regolith, Spectroscopy, and Imaging, Mars Sediments and Geochemistry: Analogs and Mineralogy, Mars: Magnetics and Atmosphere, Mars Aeolian Geomorphology, Mars Data Processing and Analyses, Astrobiology, Engaging Student Educators and the Public in Planetary Science,

A TREND BETWEEN COLD DEBRIS DISK TEMPERATURE AND STELLAR TYPE: IMPLICATIONS FOR THE FORMATION AND EVOLUTION OF WIDE-ORBIT PLANETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ballering, Nicholas P.; Rieke, George H.; Su, Kate Y. L.

2013-09-20

Cold debris disks trace the limits of planet formation or migration in the outer regions of planetary systems, and thus have the potential to answer many of the outstanding questions in wide-orbit planet formation and evolution. We characterized the infrared excess spectral energy distributions of 174 cold debris disks around 546 main-sequence stars observed by both the Spitzer Infrared Spectrograph and the Multiband Imaging Photometer for Spitzer. We found a trend between the temperature of the inner edges of cold debris disks and the stellar type of the stars they orbit. This argues against the importance of strictly temperature-dependent processesmore » (e.g., non-water ice lines) in setting the dimensions of cold debris disks. Also, we found no evidence that delayed stirring causes the trend. The trend may result from outward planet migration that traces the extent of the primordial protoplanetary disk, or it may result from planet formation that halts at an orbital radius limited by the efficiency of core accretion.« less

View planetary differentiation process through high-resolution 3D imaging

NASA Astrophysics Data System (ADS)

Fei, Y.

2011-12-01

Core-mantle separation is one of the most important processes in planetary evolution, defining the structure and chemical distribution in the planets. Iron-dominated core materials could migrate through silicate mantle to the core by efficient liquid-liquid separation and/or by percolation of liquid metal through solid silicate matrix. We can experimentally simulate these processes to examine the efficiency and time of core formation and its geochemical signatures. The quantitative measure of the efficiency of percolation is usually the dihedral angle, related to the interfacial energies of the liquid and solid phases. To determine the true dihedral angle at high pressure and temperatures, it is necessary to measure the relative frequency distributions of apparent dihedral angles between the quenched liquid metal and silicate grains for each experiment. Here I present a new imaging technique to visualize the distribution of liquid metal in silicate matrix in 3D by combination of focus ion beam (FIB) milling and high-resolution SEM image. The 3D volume rendering provides precise determination of the dihedral angle and quantitative measure of volume fraction and connectivity. I have conducted a series of experiments using mixtures of San Carlos olivine and Fe-S (10wt%S) metal with different metal-silicate ratios, up to 25 GPa and at temperatures above 1800C. High-quality 3D volume renderings were reconstructed from FIB serial sectioning and imaging with 10-nm slice thickness and 14-nm image resolution for each quenched sample. The unprecedented spatial resolution at nano scale allows detailed examination of textural features and precise determination of the dihedral angle as a function of pressure, temperature and composition. The 3D reconstruction also allows direct assessment of connectivity in multi-phase matrix, providing a new way to investigate the efficiency of metal percolation in a real silicate mantle.

Reports of planetary geology program, 1976 - 1977. [abstracts

NASA Technical Reports Server (NTRS)

Arvidson, R. (Compiler); Wahmann, R. (Compiler); Howard, J. H., III

1977-01-01

One hundred seventeen investigations undertaken in the NASA Planetary Geology Program in 1976-1977 are reported in abstract form. Topics discussed include solar system formation; planetary interiors; planetary evolution; asteroids, comets and moons; cratering; volcanic, eolian, fluvial and mass wasting processes; volatiles and the Martian regolith; mapping; and instrument development and techniques. An author index is provided.

Accretion timescale and impact history of Mars deduced from the isotopic systematics of martian meteorites

DOE PAGES

Borg, Lars E.; Brennecka, Gregory A.; Symes, Steven J. K.

2015-12-12

High precision Sm-Nd isotopic analyses have been completed on a suite of 11 martian basaltic meteorites in order to better constrain the age of silicate differentiation on Mars associated with the formation of their mantle sources. Our data is used to evaluate the merits and disadvantages of various mathematical approaches that have been employed in previous work on this topic. Ages determined from the Sm-Nd isotopic systematics of individual samples are strongly dependent on the assumed Nd isotopic composition of the bulk planet. This assumption is problematic given differences observed between the Nd isotopic composition of Earth and chondritic meteoritesmore » and the fact that these materials are both commonly used to represent bulk planetary Nd isotopic compositions. Ages determined from the slope of Sm-146-Nd-142 whole rock isochrons are not dependent on the assumed Nd-142/Nd-144 ratio of the planet, but require the sample suite to be derived from complementary, contemporaneously-formed reservoirs. In this work, we present a mathematical expression that defines the age of formation of the source regions of such a suite of samples that is based solely on the slope of a Nd-143-Nd-142 whole rock isochron and is also independent of any a priori assumptions regarding the bulk isotopic composition of the planet. This expression is also applicable to mineral isochrons and has been used to successfully calculate Nd-143-Nd-142 model crystallization ages of early refractory solids as well as lunar samples. This permits ages to be obtained using only Nd isotopic measurements without the need for Sm-147/Nd-144 isotope dilution determinations. When used in conjunction with high-precision Nd isotopic measurements completed on martian meteorites this expression yields an age of formation of the martian basaltic meteorite source regions of 4504 +/- 6 Ma. Because the Sm-Nd model ages for the formation of martian source regions are commonly interpreted to record the age at which large scale mantle reservoirs formed during planetary differentiation associated with magma ocean solidification, the age determined here implies that magma ocean solidification occurred several tens of millions of years after the beginning of the Solar System. Recent thermal models, however, suggest that Mars-sized bodies cool rapidly in less than similar to 5 Ma after accretion ceases, even in the presence of a thick atmosphere. In assuming these models are correct, an extended period of accretion is necessary to provide a mechanism to keep portions of the martian mantle partially molten until 4504 Ma. Late accretional heating of Mars could either be associated with protracted accretion occurring at a quasi-steady state or alternatively be associated with a late giant impact. If this scenario is correct, then accretion of Mars-sized bodies takes up to 60 Ma and is likely to be contemporaneous with the core formation and possibly the onset of silicate differentiation. This further challenges the concept that isotopic equilibrium is attained during primordial evolution of planets, and may help to account for geochemical evidence implying addition of material into planetary interiors after core formation was completed.« less

Accretion timescale and impact history of Mars deduced from the isotopic systematics of martian meteorites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borg, Lars E.; Brennecka, Gregory A.; Symes, Steven J. K.

High precision Sm-Nd isotopic analyses have been completed on a suite of 11 martian basaltic meteorites in order to better constrain the age of silicate differentiation on Mars associated with the formation of their mantle sources. Our data is used to evaluate the merits and disadvantages of various mathematical approaches that have been employed in previous work on this topic. Ages determined from the Sm-Nd isotopic systematics of individual samples are strongly dependent on the assumed Nd isotopic composition of the bulk planet. This assumption is problematic given differences observed between the Nd isotopic composition of Earth and chondritic meteoritesmore » and the fact that these materials are both commonly used to represent bulk planetary Nd isotopic compositions. Ages determined from the slope of Sm-146-Nd-142 whole rock isochrons are not dependent on the assumed Nd-142/Nd-144 ratio of the planet, but require the sample suite to be derived from complementary, contemporaneously-formed reservoirs. In this work, we present a mathematical expression that defines the age of formation of the source regions of such a suite of samples that is based solely on the slope of a Nd-143-Nd-142 whole rock isochron and is also independent of any a priori assumptions regarding the bulk isotopic composition of the planet. This expression is also applicable to mineral isochrons and has been used to successfully calculate Nd-143-Nd-142 model crystallization ages of early refractory solids as well as lunar samples. This permits ages to be obtained using only Nd isotopic measurements without the need for Sm-147/Nd-144 isotope dilution determinations. When used in conjunction with high-precision Nd isotopic measurements completed on martian meteorites this expression yields an age of formation of the martian basaltic meteorite source regions of 4504 +/- 6 Ma. Because the Sm-Nd model ages for the formation of martian source regions are commonly interpreted to record the age at which large scale mantle reservoirs formed during planetary differentiation associated with magma ocean solidification, the age determined here implies that magma ocean solidification occurred several tens of millions of years after the beginning of the Solar System. Recent thermal models, however, suggest that Mars-sized bodies cool rapidly in less than similar to 5 Ma after accretion ceases, even in the presence of a thick atmosphere. In assuming these models are correct, an extended period of accretion is necessary to provide a mechanism to keep portions of the martian mantle partially molten until 4504 Ma. Late accretional heating of Mars could either be associated with protracted accretion occurring at a quasi-steady state or alternatively be associated with a late giant impact. If this scenario is correct, then accretion of Mars-sized bodies takes up to 60 Ma and is likely to be contemporaneous with the core formation and possibly the onset of silicate differentiation. This further challenges the concept that isotopic equilibrium is attained during primordial evolution of planets, and may help to account for geochemical evidence implying addition of material into planetary interiors after core formation was completed.« less

Planet population synthesis driven by pebble accretion in cluster environments

NASA Astrophysics Data System (ADS)

Ndugu, N.; Bitsch, B.; Jurua, E.

2018-02-01

The evolution of protoplanetary discs embedded in stellar clusters depends on the age and the stellar density in which they are embedded. Stellar clusters of young age and high stellar surface density destroy protoplanetary discs by external photoevaporation and stellar encounters. Here, we consider the effect of background heating from newly formed stellar clusters on the structure of protoplanetary discs and how it affects the formation of planets in these discs. Our planet formation model is built on the core accretion scenario, where we take the reduction of the core growth time-scale due to pebble accretion into account. We synthesize planet populations that we compare to observations obtained by radial velocity measurements. The giant planets in our simulations migrate over large distances due to the fast type-II migration regime induced by a high disc viscosity (α = 5.4 × 10-3). Cold Jupiters (rp > 1 au) originate preferably from the outer disc, due to the large-scale planetary migration, while hot Jupiters (rp < 0.1 au) preferably form in the inner disc. We find that the formation of gas giants via pebble accretion is in agreement with the metallicity correlation, meaning that more gas giants are formed at larger metallicity. However, our synthetic population of isolated stars host a significant amount of giant planets even at low metallicity, in contradiction to observations where giant planets are preferably found around high metallicity stars, indicating that pebble accretion is very efficient in the standard pebble accretion framework. On the other hand, discs around stars embedded in cluster environments hardly form any giant planets at low metallicity in agreement with observations, where these changes originate from the increased temperature in the outer parts of the disc, which prolongs the core accretion time-scale of the planet. We therefore conclude that the outer disc structure and the planet's formation location determines the giant planet occurrence rate and the formation efficiency of cold and hot Jupiters.

Lunar and Planetary Science Conference, 9th, Houston, Tex., March 13-17, 1978, Proceedings. Volume 2 - Lunar and planetary surfaces

NASA Technical Reports Server (NTRS)

Merrill, R. B.

1978-01-01

Regolith studies are summarized with attention given to isotope and solar wind effects, core studies, and soil maturation and agglutinates. Consideration is also given to radiometric, cosmic-ray and track chronologies for meteorites and lunar samples and to lunar impact phenomena.

Mercury

NASA Technical Reports Server (NTRS)

Vilas, Faith (Editor); Chapman, Clark R. (Editor); Matthews, Mildred Shapley (Editor)

1988-01-01

Papers are presented on future observations of and missions to Mercury, the photometry and polarimetry of Mercury, the surface composition of Mercury from reflectance spectrophotometry, the Goldstone radar observations of Mercury, the radar observations of Mercury, the stratigraphy and geologic history of Mercury, the geomorphology of impact craters on Mercury, and the cratering record on Mercury and the origin of impacting objects. Consideration is also given to the tectonics of Mercury, the tectonic history of Mercury, Mercury's thermal history and the generation of its magnetic field, the rotational dynamics of Mercury and the state of its core, Mercury's magnetic field and interior, the magnetosphere of Mercury, and the Mercury atmosphere. Other papers are on the present bounds on the bulk composition of Mercury and the implications for planetary formation processes, the building stones of the planets, the origin and composition of Mercury, the formation of Mercury from planetesimals, and theoretical considerations on the strange density of Mercury.

Lunar and Planetary Science XXXV: Origin of Planetary Systems

NASA Technical Reports Server (NTRS)

2004-01-01

The session titled Origin of Planetary Systems" included the following reports:Convective Cooling of Protoplanetary Disks and Rapid Giant Planet Formation; When Push Comes to Shove: Gap-opening, Disk Clearing and the In Situ Formation of Giant Planets; Late Injection of Radionuclides into Solar Nebula Analogs in Orion; Growth of Dust Particles and Accumulation of Centimeter-sized Objects in the Vicinity of a Pressure enhanced Region of a Solar Nebula; Fast, Repeatable Clumping of Solid Particles in Microgravity ; Chondrule Formation by Current Sheets in Protoplanetary Disks; Radial Migration of Phyllosilicates in the Solar Nebula; Accretion of the Outer Planets: Oligarchy or Monarchy?; Resonant Capture of Irregular Satellites by a Protoplanet ; On the Final Mass of Giant Planets ; Predicting the Atmospheric Composition of Extrasolar Giant Planets; Overturn of Unstably Stratified Fluids: Implications for the Early Evolution of Planetary Mantles; and The Evolution of an Impact-generated Partially-vaporized Circumplanetary Disk.

Mars geoscience/climatology orbiter low cost mission operations

NASA Technical Reports Server (NTRS)

Erickson, K. D.

1984-01-01

It will not be possible to support the multiple planetary missions of the magnitude and order of previous missions on the basis of foreseeable NASA funding. It is, therefore, necessary to seek innovative means for accomplishing the goals of planetary exploration with modestly allocated resources. In this connection, a Core Program set of planetary exploration missions has been recommended. Attention is given to a Mission Operations design overview which is based on the Mars Geoscience/Climatology Orbiter Phase-A study performed during spring of 1983.

The role of phosphorus in chemical evolution.

PubMed

Maciá, Enrique

2005-08-01

In this tutorial review we consider the role of phosphorus and its compounds within the context of chemical evolution in galaxies. Following an interdisciplinary approach we first discuss the position of P among the main biogenic elements by considering its relevance in most essential biochemical functions as well as its peculiar chemistry under different physicochemical conditions. Then we review the phosphorus distribution in different cosmic sites, such as terrestrial planets, interplanetary dust particles, cometary dust, planetary atmospheres and the interstellar medium (ISM). In this way we realize that this element is both scarce and ubiquitous in the universe. These features can be related to the complex nucleosynthesis of P nuclide in the cores of massive stars under explosive conditions favouring a wide distribution of this element through the ISM, where it would be ready to react with other available atoms. A general tendency towards more oxidized phosphorus compounds is clearly appreciated as chemical evolution proceeds from circumstellar and ISM materials to protoplanetary and planetary condensed matter phases. To conclude we discuss some possible routes allowing for the incorporation of phosphorus compounds of prebiotic interest during the earlier stages of solar system formation.

Meteoritic basalts: the nakhlites, their parental magmas, cooling rates, and equivalents on Earth. Final technical report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Treiman, A.H.

1987-07-01

Proposed one-bar phase equilibrium experiments, designed to determine the compositions of the nakhlites' parental magmas, are in progress. Proposed field studies on Earth, designed to find occurrences of rocks like the nakhlites, were extraordinarily successful. Other work supported in the past year included: attendance at the 1986 national meeting of the Geological Society of America; attendance at the 18th Lunar and Planetary Science Conference; completion and publication of a study of core formation in the SNC parent body; initiation of a study of the flux of SNC meteorites onto the Earth; and initiation of petrologic study of the Angra dosmore » Reis achondrite.« less

Experimental determination of the Mo isotope fractionation factor between metal and silicate liquids

NASA Astrophysics Data System (ADS)

Hin, R. C.; Burkhardt, C.; Schmidt, M. W.; Bourdon, B.

2011-12-01

The conditions and chemical consequences of core formation have mainly been reconstructed from experimentally determined element partition coefficients between metal and silicate liquids. However, first order questions such as the mode of core formation or the nature of the light element(s) in the Earth's core are still debated [1]. In addition, the geocentric design of most experimental studies leaves the conditions of core formation on other terrestrial planets and asteroids even more uncertain than for Earth. Through mass spectrometry, records of mass-dependent stable isotope fractionation during high-temperature processes such as metal-silicate segregation are detectable. Stable isotope fractionation may thus yield additional constrains on core formation conditions and its consequences for the chemical evolution of planetary objects. Experimental investigations of equilibrium mass-dependent stable isotope fractionation have shown that Si isotopes fractionate between metal and silicate liquids at temperatures of 1800°C and pressures of 1 GPa, while Fe isotopes leave no resolvable traces of core formation processes [2,3]. Molybdenum is a refractory and siderophile trace element in the Earth, and thus much less prone to complications arising from mass balancing core and mantle and from potential volatile behaviour than other elements. To determine equilibrium mass-dependent Mo isotope fractionation during metal-silicate segregation, we have designed piston cylinder experiments with a basaltic silicate composition and an iron based metal with ~8 wt% Mo, using both graphite and MgO capsules. Metal and silicate phases are completely segregated by the use of a centrifuging piston cylinder at ETH Zurich, thus preventing analysis of mixed metal and silicate signatures. Molybdenum isotope compositions were measured using a Nu Instruments 1700 MC-ICP-MS at ETH Zurich. To ensure an accurate correction of analytical mass fractionation a 100Mo-97Mo double spike was admixed before chemical purification. Initial results provide an equilibrium 98Mo/95Mo isotope fractionation factor between metal and silicate liquids of -0.18±0.10% (2σ) at 1400°C and 1 GPa. Although the relative mass difference of these Mo isotopes is smaller than for Fe isotopes, this result implies that metal-silicate segregation may have led to mass-dependent stable Mo isotope fractionation, as opposed to Fe isotopes. A possible explanation is that the bonding environment of Mo may counterbalance its relatively small mass separation. At reducing conditions, Mo occurs in 4+ valence state in silicates [4] and thus its bond strength difference between metal and silicate may be more similar to that of Si than Fe. Stable Mo isotopes may thus become an important tool for constraining the conditions of core formation in asteroids and terrestrial planets. [1] Rubie et al. (2011) EPSL 301, 31-42. [2] Shahar et al. (2009) EPSL 288, 228-234. [3] Poitrasson et al. (2009) EPSL 278, 376-385. [4] Farges et al. (2006) Can. Min. 44, 731-753.

Release of Nitrogen during Planetary Accretion Explains Missing Nitrogen in Earth's Mantle

NASA Astrophysics Data System (ADS)

Liu, J.; Dorfman, S.; Lv, M.; Li, J.; Kono, Y.

2017-12-01

Nitrogen and carbon are essential elements for life on Earth, and their relative abundances in planetary bodies (C/N ratios) are important for understanding planetary evolution and habitability1,2. However, the high C/N ratio in the bulk silicate Earth relative to CI chondrites and other volatile-rich chondrites is difficult to explain with partitioning behavior between silicate and metallic liquid or solubility in silicate melt, and has thus been a major unsolved problem in geochemistry1-5. Because core formation does not explain nitrogen depletion in the mantle, another process is required to match the observed BSE C/N ratio, such as devolatilization of metallic liquid. Previous studies have examined the Fe-C phase diagram extensively (e.g. ref. 6), but very limited melting data is available for the Fe-N system7. Here we examine melting relations for four Fe-N-C compositions with 1-7 wt% nitrogen up to 7 GPa and 2200 K in the Paris-Edinburgh press by a combination of in-situ X-ray radiography, X-ray diffraction and ex-situ electron microprobe techniques. In striking contrast to the Fe-C system, near-surface melting in all compositions in the Fe-N-C system entails release of nitrogen fluid and depletion of nitrogen from the liquid alloy. This could provide a pathway for nitrogen to escape the magma ocean in the accretion stage while carbon is retained. On the basis of our experimental results, we propose a new quantitative model of mantle nitrogen evolution during the core formation stage to explain the high BSE C/N ratios and resolve the paradox of missing mantle nitrogen1-5. Although nitrogen itself is not a greenhouse gas, the nitrogen released to the atmosphere from metallic melt early in Earth's history could amplify the greenhouse effect through collision-enhanced absorption8,9, which may help to explain warm surface temperatures during the Hadean and Archean eras on Earth when the solar luminosity was 25-30% lower than the present10. References1. Bergin et al., PNAS (2015). 2. Hirschmann, Am. Mineral. (2016). 3. Marty, EPSL (2012). 4. Halliday, GCA (2013). 5. Dalou et al., EPSL (2017). 6. Walker et al., Contrib. Mineral. Petrol. (2013). 7. Guillermet et al., Z. Metallkd. (1994). 8. Wordsworth et al., Science (2013). 9. Goldblatt et al. Nat. Geosci. (2009). 10. Gough. Sol. Phys. (1981)

Planetary science. Shock compression of stishovite and melting of silica at planetary interior conditions.

PubMed

Millot, M; Dubrovinskaia, N; Černok, A; Blaha, S; Dubrovinsky, L; Braun, D G; Celliers, P M; Collins, G W; Eggert, J H; Jeanloz, R

2015-01-23

Deep inside planets, extreme density, pressure, and temperature strongly modify the properties of the constituent materials. In particular, how much heat solids can sustain before melting under pressure is key to determining a planet's internal structure and evolution. We report laser-driven shock experiments on fused silica, α-quartz, and stishovite yielding equation-of-state and electronic conductivity data at unprecedented conditions and showing that the melting temperature of SiO2 rises to 8300 K at a pressure of 500 gigapascals, comparable to the core-mantle boundary conditions for a 5-Earth mass super-Earth. We show that mantle silicates and core metal have comparable melting temperatures above 500 to 700 gigapascals, which could favor long-lived magma oceans for large terrestrial planets with implications for planetary magnetic-field generation in silicate magma layers deep inside such planets. Copyright © 2015, American Association for the Advancement of Science.

Na, Rb and Cs partitioning between metal, silicate and sulfide: Implications for volatile depletion in terrestrial planets

NASA Astrophysics Data System (ADS)

Boujibar, A.; Fei, Y.; Du, Z.; Righter, K.; Bullock, E. S.

2017-12-01

Inner Solar System materials are known for their depletion in volatile elements, including the moderately volatile alkalis: Na, K, Rb, and Cs. The origin of this depletion is still uncertain, as several processes could have been involved, during the nebular condensation or planetary accretion. Volatile depletion is commonly estimated through comparison of alkali concentrations relatively to those of chondrites, assuming they remain in planetary mantles during core segregation. However, experimental studies show that substantial K can partition into metals that are enriched in sulfur and oxygen. Several models have also suggested that sulfides may have played an important role during episodes of sulfide segregation from a crystallizing magma ocean (sulfide matte) or accretion of S-rich planetary embryos. For Mercury, a sulfide layer could be present between core and mantle, due to immiscibility between Si-rich and S-rich metals. Therefore, here we investigate whether alkali elements (Na, Cs and Rb) could be partly sequestered in planetary cores during their differentiation. We conducted experiments at high pressure and temperature (1 to 5 GPa and up to 1900 °C) to determine partition coefficients of Na, Rb and Cs between metal and silicate. Our results show that pressure, temperature, sulfur and oxygen in metals enhance the partitioning of Na, Rb and Cs into metals, as previously found for K. For all three investigated alkalis (Na, Rb and Cs), we found a maximum partition coefficient of 1 between sulfides containing 13 wt% O and silicate melt. Therefore, S-rich cores or sulfide layers formed due to immiscibility in Fe-S-O systems could have acted as important geochemical reservoirs for alkali elements. Using our experimental data and different assumptions on initial bulk abundances, we evaluate volatile depletion in terrestrial planets, by comparing resulting mantle alkali concentrations after core segregation, with actual concentrations in the Earth's mantle.

Formation of solar system analogues - I. Looking for initial conditions through a population synthesis analysis

NASA Astrophysics Data System (ADS)

Ronco, M. P.; Guilera, O. M.; de Elía, G. C.

2017-11-01

Population synthesis models of planetary systems developed during the last ˜15 yr could reproduce several of the observables of the exoplanet population, and also allowed us to constrain planetary formation models. We present our planet formation model, which calculates the evolution of a planetary system during the gaseous phase. The code incorporates relevant physical phenomena for the formation of a planetary system, like photoevaporation, planet migration, gas accretion, water delivery in embryos and planetesimals, a detailed study of the orbital evolution of the planetesimal population, and the treatment of the fusion between embryos, considering their atmospheres. The main goal of this work, unlike other works of planetary population synthesis, is to find suitable scenarios and physical parameters of the disc to form Solar system analogues. We are specially interested in the final planet distributions, and in the final surface density, eccentricity and inclination profiles for the planetesimal population. These final distributions will be used as initial conditions for N-body simulations to study the post-oligarchic formation in a second work. We then consider different formation scenarios, with different planetesimal sizes and different type I migration rates. We find that Solar system analogues are favoured in massive discs, with low type I migration rates, and small planetesimal sizes. Besides, those rocky planets within their habitables zones are dry when discs dissipate. At last, the final configurations of Solar system analogues include information about the mass and semimajor axis of the planets, water contents, and the properties of the planetesimal remnants.

Formation of Planetary Satellites and Prospects for Exomoons

NASA Astrophysics Data System (ADS)

Barr, A.

2014-04-01

The formation of planetary satellites is thought to be a natural by-product of terrestrial and giant planet formation. I will discuss the proposed methods of satellite formation including fission, co-accretion, giant impact, and capture and where these modes of formation might operate in extrasolar planetary systems. Giant impacts like the event that formed Earth's Moon are thought to be common during the late stages of terrestrial planet formation; it is currently thought that Mercury, Mars, and the Earth were hit by objects of planetary size during their early history. I will discuss the effects that large impacts may have on rocky exoplanets, including moon formation and compositional changes, which can affect prospects for habitability on these worlds. The giant planets in our solar system harbor dozens of planet-size rocky and icy moons, some of which have habitats that may be dissimilar to Earth but could still be suitable for life. Because the accretion of regular satellites is thought to be a by-product of gas inflow to growing gas giants, it seems likely that many extrasolar planets may have created regular satellite systems as well. I will discuss the types of satellite systems we have in our solar system and whether those are likely to occur elsewhere. I will also discuss the conditions on the "front-runners" for habitable giant planet moons in our solar system including Europa, Enceladus, and Titan.

Viscous dissipation of energy at the stage of accumulation of the Earth

NASA Astrophysics Data System (ADS)

Yurie Khachay, Professor; Olga Hachay, Professor; Antipin, Alexandr

2017-04-01

In the papers [1,2] it is published the differentiation model of the proto planet cloud during the accumulation of the Earth's group planets. In [2] it was shown that the energy released during the decay of short-lived radioactive elements in the small size more than 50 km, it is enough that the temperature inside of the protoplanet becomes larger than the temperature of iron melting. It provides a realization of the matter differentiation process and convection development inside the inner envelopes. With increasing of the Earth, the forming region of the outer core remains in a molten state, although the power and viscosity of the layer changed. In [3] it is shown that during the sequence of growth changes of accumulated protoplanets, the main contribution of heat is provided first by radioactive sources, and then heated from above by converting the kinetic energy during the growing impact inside the Earth, and finally heated from below. That provides three types of driving mechanisms of convection: internal heat sources; heated top; heated from bottom and chemical-thermal convection. At all stages of proto Earth's development the convective heat-mass transfer becomes a most significant factor in the dynamics of the planet. However, the heat release due to friction in the viscous liquid of the outer core up to now was not still considered, or it was considered only for the formed planetary envelopes with a constant radius. In this paper we present the first results of thermal evolution numerical modeling of 3D spherical segment for a protoplanet with increasing radius and accounting random falling of bodies and particles. To describe the planetary accumulation Safronov equation is used [4]. For the quantitative account of the released heat by viscous friction a system of hydro dynamic equations for a viscous liquid is used. The obtained results show that the heat input due to viscous friction heat release at the early stage of planetary accumulation was very significant. That influence is defined by a set of factors. It was changed the width of the formed outer core. It was changed the distribution of the temperature and hydrostatic pressure inside the core and reciprocally the viscosity of the matter. It had been changed the orbit parameters of the system Earth-Moon. The received results depend from the parameters, the values of which are known with large degree of uncertainty. They have to be specified during next researchers. This work was supported by grant RFBRI №16-05-00540 References. 1. V.Anfilogov,Y. Khachay ,2005, Possible variant of matter differentiation on the initial stage of Earth's forming //DAN, 2005, V. 403, № 6, p. 803-806. 2.V.Anfilogov,Y.Khachay ,2015, Some Aspects of the Solar System Formation. Springer Briefs of the Earth Sciences. -75p 3.Khachay Yu.V., Hachay O.A. Heat production by the viscous dissipation of energy at the stage of accumulation of the Earth. Geophysical Research AbstractsVol. 18, EGU2016-2825, 2016 4. Khachay Yu. Realization of thermal Convection into the initial Earth's Core on the Stage of planetary Accumulation // Geophysical Research Abstracts, Vol. 17, EGU2015-2211, 2015.

Pulsed Laser Techniques to Determine Lattice and Radiative Thermal Conductivity of Deep Planetary Materials at Extreme Pressure-Temperature Conditions

NASA Astrophysics Data System (ADS)

Lobanov, S.; Goncharov, A. F.; Holtgrewe, N.; Konopkova, Z.; McWilliams, R. S.

2017-12-01

Thermal conductivity of deep planetary materials determines the planetary heat transport mode and properties (e.g. magnetic field) and can be used to decipher the planetary thermal history. Due to the lack of direct measurements of the lattice and radiative conductivity of the relevant materials at the planetary conditions, the current geodynamical models use theoretical calculations and extrapolations of the available experimental data. Here we describe our pulsed laser techniques that enable direct measurements of the lattice and radiative lattice conductivity of the Earth's mantle and core materials and also of noble gases and simple molecules present in the interiors of giant planets (e.g. hydrogen). Flash heating laser techniques working in a pump-probe mode that include time resolved two-side radiative and thermoreflection temperature probes employ various laser and photo-detector configurations, which provide a measure of the thermal fluxes propagating through the samples confined in the diamond anvil cell cavity. A supercontinuum ultra-bright broadband laser source empower accurate measurements of the optical properties of planetary materials used to extract the radiative conductivity. Finite element calculations serve to extract the temperature and pressure dependent thermal conductivity and temperature gradients across the sample. We report thermal conductivity measurements of the Earth's minerals (postperovskite, bridgmanite, ferropericlase) and their assemblies (pyrolite) and core materials (Fe and alloys with Si and O) at the realistic deep Earth's pressure temperature conditions. We thank J.-F.Lin, M. Murakami, J. Badro for contributing to this work.

European Workshop on Planetary Sciences, Rome, Italy, April 23-27, 1979, Proceedings. Part 1

NASA Astrophysics Data System (ADS)

1980-02-01

Papers are presented on the dynamics and evolution of the solar system and its components. Specific topics include the dynamic stability of the solar system, the tidal friction theory of the earth moon system, the stability and irregularity of extrasolar planetary systems, angular momentum and magnetic braking during star formation, the collisional growth of planetesimals, the dynamics, interrelations and evolution of the asteroids and comets, the formation and stability of Saturn's rings, and the importance of nearly tangent orbits in planetary close encounters.

Geochemical Constraints on Core-Mantle Interaction from Fe/Mn Ratios

NASA Astrophysics Data System (ADS)

Humayun, M.; Qin, L.

2003-12-01

The greater density of liquid iron alloy, and its immiscibility with silicate, maintains the physical separation of the core from the mantle. There are no a priori reasons, however, why the Earth's mantle should be chemically isolated from the core. Osmium isotopic variations in mantle plumes have been interpreted in terms of interaction between outer core and the source regions of deep mantle plumes. If chemical transport occurs across the core-mantle boundary its mechanism remains to be established. The Os isotope evidence has also been interpreted as the signatures of subducted Mn-sediments, which are known to have relatively high Pt/Os. In the mantle, Fe occurs mainly as the divalent ferrous ion, and Mn occurs solely as a divalent ion, and both behave in a geochemically coherent manner because of similarity in ionic charge and radius. Thus, the Fe/Mn ratio is a planetary constant insensitive to processes of mantle differentiation by partial melting. Two processes may perturb the ambient mantle Fe/Mn of 60: a) the subduction of Mn-sediments should decrease the Fe/Mn ratio in plume sources, while b) chemical transport from the outer core may increase the Fe/Mn ratio. The differentiation of the liquid outer core to form the solid inner core may increase abundances of the light element constituents (FeS, FeO, etc.) to the point of exsolution from the core at the CMB. The exact rate of this process is determined by the rate of inner core growth. Two end-member models include 1) inner core formation mainly prior to 3.5 Ga with heat release dominated by radioactive sources, or 2) inner core formation occurring mainly in the last 1.5 Ga with heat release dominated by latent heat. This latter model would imply large fluxes of Fe into the sources of modern mantle plumes. Existing Fe/Mn data for Gorgona and Hawaiian samples place limits on both these processes. We describe a new procedure for the precise determination of the Fe/Mn ratio in magmatic rocks by ICP-MS. This high-resolution study of the Fe/Mn of mantle-derived samples offers a new set of chemical constraints on the rates of inner core differentiation and the viability of Os isotope interpretations.

The Kepler Dichotomy in Planetary Disks: Linking Kepler Observables to Simulations of Late-stage Planet Formation

NASA Astrophysics Data System (ADS)

Moriarty, John; Ballard, Sarah

2016-11-01

NASA’s Kepler Mission uncovered a wealth of planetary systems, many with planets on short-period orbits. These short-period systems reside around 50% of Sun-like stars and are similarly prevalent around M dwarfs. Their formation and subsequent evolution is the subject of active debate. In this paper, we simulate late-stage, in situ planet formation across a grid of planetesimal disks with varying surface density profiles and total mass. We compare simulation results with observable characteristics of the Kepler sample. We identify mixture models with different primordial planetesimal disk properties that self-consistently recover the multiplicity, radius, period and period ratio, and duration ratio distributions of the Kepler planets. We draw three main conclusions. (1) We favor a “frozen-in” narrative for systems of short-period planets, in which they are stable over long timescales, as opposed to metastable. (2) The “Kepler dichotomy,” an observed phenomenon of the Kepler sample wherein the architectures of planetary systems appear to either vary significantly or have multiple modes, can naturally be explained by formation within planetesimal disks with varying surface density profiles. Finally, (3) we quantify the nature of the “Kepler dichotomy” for both GK stars and M dwarfs, and find that it varies with stellar type. While the mode of planet formation that accounts for high multiplicity systems occurs in 24% ± 7% of planetary systems orbiting GK stars, it occurs in 63% ± 16% of planetary systems orbiting M dwarfs.

Onset of a planetesimal dynamo

NASA Astrophysics Data System (ADS)

Wang, H.; Weiss, B. P.; Wang, J.; Chen-Wiegart, Y. C. K.; Downey, B. G.; Suavet, C. R.; Andrade Lima, E.; Zucolotto, M. E.

2014-12-01

The paleomagnetism of achondritic meteorites provides evidence for advecting metallic core dynamos and large-scale differentiation on their parent planetesimals. The small sizes of these bodies (~102 km) enable a new opportunity to understand the physics of dynamo generation in a size regime with distinct thermal evolution parameters that are more accessible to model than planets. One key unknown about planetesimal dynamos is their onset time. Theoretical studies have suggested that it might occur instantaneously after large-scale melting (Weiss et al. 2008, Elkins-Tanton et al. 2011) while others have argued that a dynamo could be delayed by ~6 My (Sterenborg and Crowley 2013) or longer. Here we present the first paleomagnetic study that has constrained the onset time of a planetesimal dynamo, which has key implications for the physics of core formation, planetary thermal evolution and dynamo generation mechanisms. Our study focused on angrites, a group of ancient basaltic achondrites from near the surface of an early differentiated planetesimal. With unshocked, unbrecciated textures and Pb/Pb ages ranging from only ~3-10 My younger than the formation of calcium aluminum inclusions (CAIs), they are among the oldest known and best preserved planetary igneous rocks. We used a new CO2 + H2 gas mixture system (Suavet et al. 2014) for controlled oxygen fugacity thermal paleointensity experiments on two of the oldest angrites (D'Orbigny and SAH 99555; 4564.4 Ma) and a younger angrite (Angra dos Reis; 4557.7 Ma). For D'Orbigny and SAH 99555, we found that the natural remanence (NRM) demagnetizes at much lower temperatures than lab-applied thermoremanence (TRM), indicating that their NRMs are dominantly overprints from the Earth's field and hand magnets. In contrast, the NRM of Angra dos Reis behaves similarly to a TRM, confirming its thermal origin. We estimate the paleointensities to be < 0.2 µT for D'Orbigny and SAH 99555 and ~10 µT for Angra dos Reis. This indicates that the angrite parent body dynamo originated between 3 and 10 My after CAI formation. Our results are consistent with planetesimal evolution models calling for dynamos delayed by mantle heating due to radiogenic 26Al. Furthermore, these data suggest that external nebular fields in the angrite parent body region had declined to < 0.2 μT at 3 My after CAI formation.

Thermal evolution and core formation of planetesimals

NASA Astrophysics Data System (ADS)

Suwa, Taichi; Nagahara, Hiroko

2017-04-01

Planetesimals did not get an adequate thermal energy by accretion to form large scale magma ocean because of smaller radii, masses, gravity and accretion energy, however, there are various evidences for the presence of core in planetesimals: 4-Vesta has a core and non-magmatic iron meteorites were segregated metal in bodies that did not experience silicate melting. It has been pointed out that accretion time of planetesimals controls melting and differentiation, because short lived nuclides are plausible heat source. Other factors such as radiative cooling from the surface and thermal conductivity, would also affect thermal evolution of planetesimals. Furthermore, percolation of Fe-S melt through silicate matrix is controlled by the porosity and grain size of silicates and dihedral angle between the melt and silicates. Therefore, the interior structure of planetesimals should be considered by taking the accretion, growth, and thermal evolution of the interior simultaneously. We make a numerical simulation with a spherical 1D model on the basis of the model by Neuman, which is a non-stationary heat conduction equation. We specifically pay attention to the process at temperatures between eutectic temperature Fe-FeS (1213K) and silicate solidus (1425K) and the surface tension of the melt that governs percolation. The model contains three free parameters, formation time, accretion duration, and final size of the planetesimals. The results show that the interior structure can be divided to four types: Type A is undifferentiated, Type B is differentiated to core and mantle of which core was formed by Fe-S melt percolation, Type C is partially differentiated to FeS core and mantle, where mantle retains residual Fe metal, and Type D is differentiated to core and mantle by metal separation in silicate magma. Type A would correspond to the parent bodies of chondrites, and Type B (and Type C?) core would be the source of non-magmatic iron meteorites. Type D would be parent bodies for 4 Vesta and angrites. The conditions for the four types of planetesimals are throuly investigated as a function of the three parameters, accretion time, accreting duration, and palnetesimal size. We found that the planetesimal interior is strongly controlled by the formation time: planetesimals formed after 3 Ma after CAIs would be undifferentiated (Type A) regardless of the planetary size, whereas most of them formed within 1 Ma are Type D (differentiated bodies with magmatically formed core). Types B and C bodies are preferentially formed between 1 and 3 Ma after CAIs. Longer accretion duration tends to be resulted in formation of Types A, B and C. The present work predicts the planetesimal interior structure if we know the formation age with the isotopic measurements of samples and the size of the body, which would be a very powerful tool for future explorations of small bodies except for very small (< 20 km) bodies.

Planetary Citizenship and the Ecology of Knowledges in Brazilian Universities

ERIC Educational Resources Information Center

Moraes, Silvia Elisabeth; de Almeida Freire, Ludmila

2017-01-01

This article discusses the formation of a "planetary citizenship" based on the "ecology of knowledges" perspective in Brazilian universities. It is informed by the authors' experiences and the partial results from a research project entitled "Planetary citizenship and the ecology of knowledges: Interdisciplinarity,…

Tracing the ingredients for a habitable earth from interstellar space through planet formation

PubMed Central

Bergin, Edwin A.; Blake, Geoffrey A.; Ciesla, Fred; Hirschmann, Marc M.; Li, Jie

2015-01-01

We use the C/N ratio as a monitor of the delivery of key ingredients of life to nascent terrestrial worlds. Total elemental C and N contents, and their ratio, are examined for the interstellar medium, comets, chondritic meteorites, and terrestrial planets; we include an updated estimate for the bulk silicate Earth (C/N = 49.0 ± 9.3). Using a kinetic model of disk chemistry, and the sublimation/condensation temperatures of primitive molecules, we suggest that organic ices and macromolecular (refractory or carbonaceous dust) organic material are the likely initial C and N carriers. Chemical reactions in the disk can produce nebular C/N ratios of ∼1–12, comparable to those of comets and the low end estimated for planetesimals. An increase of the C/N ratio is traced between volatile-rich pristine bodies and larger volatile-depleted objects subjected to thermal/accretional metamorphism. The C/N ratios of the dominant materials accreted to terrestrial planets should therefore be higher than those seen in carbonaceous chondrites or comets. During planetary formation, we explore scenarios leading to further volatile loss and associated C/N variations owing to core formation and atmospheric escape. Key processes include relative enrichment of nitrogen in the atmosphere and preferential sequestration of carbon by the core. The high C/N bulk silicate Earth ratio therefore is best satisfied by accretion of thermally processed objects followed by large-scale atmospheric loss. These two effects must be more profound if volatile sequestration in the core is effective. The stochastic nature of these processes hints that the surface/atmospheric abundances of biosphere-essential materials will likely be variable. PMID:26150527

Tracing the ingredients for a habitable earth from interstellar space through planet formation.

PubMed

Bergin, Edwin A; Blake, Geoffrey A; Ciesla, Fred; Hirschmann, Marc M; Li, Jie

2015-07-21

We use the C/N ratio as a monitor of the delivery of key ingredients of life to nascent terrestrial worlds. Total elemental C and N contents, and their ratio, are examined for the interstellar medium, comets, chondritic meteorites, and terrestrial planets; we include an updated estimate for the bulk silicate Earth (C/N = 49.0 ± 9.3). Using a kinetic model of disk chemistry, and the sublimation/condensation temperatures of primitive molecules, we suggest that organic ices and macromolecular (refractory or carbonaceous dust) organic material are the likely initial C and N carriers. Chemical reactions in the disk can produce nebular C/N ratios of ∼1-12, comparable to those of comets and the low end estimated for planetesimals. An increase of the C/N ratio is traced between volatile-rich pristine bodies and larger volatile-depleted objects subjected to thermal/accretional metamorphism. The C/N ratios of the dominant materials accreted to terrestrial planets should therefore be higher than those seen in carbonaceous chondrites or comets. During planetary formation, we explore scenarios leading to further volatile loss and associated C/N variations owing to core formation and atmospheric escape. Key processes include relative enrichment of nitrogen in the atmosphere and preferential sequestration of carbon by the core. The high C/N bulk silicate Earth ratio therefore is best satisfied by accretion of thermally processed objects followed by large-scale atmospheric loss. These two effects must be more profound if volatile sequestration in the core is effective. The stochastic nature of these processes hints that the surface/atmospheric abundances of biosphere-essential materials will likely be variable.

Dynamical Evolution of Planetary Embryos

NASA Technical Reports Server (NTRS)

Wetherill, George W.

2002-01-01

During the past decade, progress has been made by relating the 'standard model' for the formation of planetary systems to computational and observational advances. A significant contribution to this has been provided by this grant. The consequence of this is that the rigor of the physical modeling has improved considerably. This has identified discrepancies between the predictions of the standard model and recent observations of extrasolar planets. In some cases, the discrepancies can be resolved by recognition of the stochastic nature of the planetary formation process, leading to variations in the final state of a planetary system. In other cases, it seems more likely that there are major deficiencies in the standard model, requiring our identifying variations to the model that are not so strongly constrained to our Solar System.

New Extra-Solar Planet - thermal state and structure

NASA Astrophysics Data System (ADS)

Valencia, D.; O'Connell, R. J.; Sasselov, D.

2005-12-01

For the last decade astronomers have found more than 160 planets orbiting stars other than our sun. All but three of them are gaseous planets. The variety of characteristics of these newly discovered planets opens a new field with questions about planetary formation, structure and evolution, as well as the possibility of existence of life beyond our solar system. Planetary formation models suggested the existence of terrestrial extra-solar planets with masses up to 10 times the mass of the Earth. In June of 2005 the first Super-Earth was discovered orbiting a star 15 light years away with a mass that is about 7.5 times the mass of the Earth and a period of 1.94 days. The composition of this planet is unknown but probably has an Earth-like composition. Astronomers believe the surface temperature ranges between ~500 K and ~700 K. Liquid water can exist at temperatures above T=400K at high pressures (above 10 MPa) allowing for the possibility of a water layer on top of a rocky core. Our work focuses on determining scaling relationships with mass, internal structure parameters and thermal state. We explore the effects of a water/icy layer above a rocky core as well as other types of compositions in determining the internal structure. This water layer may convect causing the planet to have two layer convection. We explore the effects of a layer convection mode versus whole mantle convection for a Super-Earth. Due to the closeness of this planet to its parent star we can expect substantial tidal heating that can affect the thermal state of this planet. We explore the effects of tidal heating in the internal structure of a planet. Differences in composition have much larger effects in the mass-radius relationship than the uncertainties in thermodynamic parameters of the minerals composing the planet.

Experimental evidence for Mo isotope fractionation between metal and silicate liquids

NASA Astrophysics Data System (ADS)

Hin, Remco C.; Burkhardt, Christoph; Schmidt, Max W.; Bourdon, Bernard; Kleine, Thorsten

2013-10-01

Stable isotope fractionation of siderophile elements may inform on the conditions and chemical consequences of core-mantle differentiation in planetary objects. The extent to which Mo isotopes fractionate during such metal-silicate segregation, however, is so far unexplored. We have therefore investigated equilibrium fractionation of Mo isotopes between liquid metal and liquid silicate to evaluate the potential of Mo isotopes as a new tool to study core formation. We have performed experiments at 1400 and 1600 °C in a centrifuging piston cylinder. Tin was used to lower the melting temperature of the Fe-based metal alloys to <1400 °C, while variable Fe-oxide contents were used to vary oxygen fugacity in graphite and MgO capsules. Isotopic analyses were performed using a double spike technique. In experiments performed at 1400 °C, the 98Mo/95Mo ratio of silicate is 0.19±0.03‰ (95% confidence interval) heavier than that of metal. This fractionation is not significantly affected by the presence or absence of carbon. Molybdenum isotope fractionation is furthermore independent of oxygen fugacity in the range IW -1.79 to IW +0.47, which are plausible values for core formation. Experiments at 1600 °C show that, at equilibrium, the 98Mo/95Mo ratio of silicate is 0.12±0.02‰ heavier than that of metal and that the presence or absence of Sn does not affect this fractionation. Equilibrium Mo isotope fractionation between liquid metal and liquid silicate as a function of temperature can therefore be described as ΔMoMetal-Silicate98/95=-4.70(±0.59)×105/T2. Our experiments show that Mo isotope fractionation may be resolvable up to metal-silicate equilibration temperatures of about 2500 °C, rendering Mo isotopes a novel tool to investigate the conditions of core formation in objects ranging from planetesimals to Earth sized bodies.

An Earth-sized exoplanet with a Mercury-like composition

NASA Astrophysics Data System (ADS)

Santerne, A.; Brugger, B.; Armstrong, D. J.; Adibekyan, V.; Lillo-Box, J.; Gosselin, H.; Aguichine, A.; Almenara, J.-M.; Barrado, D.; Barros, S. C. C.; Bayliss, D.; Boisse, I.; Bonomo, A. S.; Bouchy, F.; Brown, D. J. A.; Deleuil, M.; Delgado Mena, E.; Demangeon, O.; Díaz, R. F.; Doyle, A.; Dumusque, X.; Faedi, F.; Faria, J. P.; Figueira, P.; Foxell, E.; Giles, H.; Hébrard, G.; Hojjatpanah, S.; Hobson, M.; Jackman, J.; King, G.; Kirk, J.; Lam, K. W. F.; Ligi, R.; Lovis, C.; Louden, T.; McCormac, J.; Mousis, O.; Neal, J. J.; Osborn, H. P.; Pepe, F.; Pollacco, D.; Santos, N. C.; Sousa, S. G.; Udry, S.; Vigan, A.

2018-05-01

Earth, Venus, Mars and some extrasolar terrestrial planets1 have a mass and radius that is consistent with a mass fraction of about 30% metallic core and 70% silicate mantle2. At the inner frontier of the Solar System, Mercury has a completely different composition, with a mass fraction of about 70% metallic core and 30% silicate mantle3. Several formation or evolution scenarios are proposed to explain this metal-rich composition, such as a giant impact4, mantle evaporation5 or the depletion of silicate at the inner edge of the protoplanetary disk6. These scenarios are still strongly debated. Here, we report the discovery of a multiple transiting planetary system (K2-229) in which the inner planet has a radius of 1.165 ± 0.066 Earth radii and a mass of 2.59 ± 0.43 Earth masses. This Earth-sized planet thus has a core-mass fraction that is compatible with that of Mercury, although it was expected to be similar to that of Earth based on host-star chemistry7. This larger Mercury analogue either formed with a very peculiar composition or has evolved, for example, by losing part of its mantle. Further characterization of Mercury-like exoplanets such as K2-229 b will help to put the detailed in situ observations of Mercury (with MESSENGER and BepiColombo8) into the global context of the formation and evolution of solar and extrasolar terrestrial planets.

Comets - Mementos of creation

NASA Astrophysics Data System (ADS)

Sagan, C.; Druyan, A.

1989-04-01

Consideration is given to the Kant-Laplace hypothesis that the sun once had a ring system from which the planets condensed. It is suggested that the theory is supported by the IRAS observation of an accretion disk around Vega, which implies that ordinary stars are surrounded by a disk during and immediately after formation. A model for planetary formation from a disk is presented. The possibility that cometary bodies may have been ejected into the Oort Cloud during planetary formation is examined.

The nature of cometary materials

NASA Technical Reports Server (NTRS)

Stephens, James

1989-01-01

Because cometary surfaces are likely to be far colder and of a different composition than planetary surfaces, there are some new considerations that must be examined in regards to placing instrumented packages or sample return devices on their surfaces. The qualitative analysis of the problem of attaching hardware to a comet and not being ejected back into space can be divided into two parts. The first problem is to pierce the mantle and obtain access to the icy core. Drilling through the mantle requires that the drilling forces be reacted. Reacting such forces probably requires attachment to the icy core below. Therefore, some kinetic impact piercing device is likely to be required as the first act of attachment. The second problem for a piercing device to overcome is the force produced by the impact kinetic energy that tries to eject the piercing device back into space. The mantle and icy core can absorb some of the impact kinetic energy in the form of fracture formation and friction energy. The energy that is not absorbed in these two ways is stored by the core as elastic deformation of the mantle and icy core. It is concluded that because the cometary materials are almost certainly brittle and the icy core is likely to be self lubricating, the elastic rebound and gas pressure expulsion forces must be counteracted by forces greater than those that may be provided by a piercing device or its capture devices (barbs).

Did 26Al and impact-induced heating differentiate Mercury?

NASA Astrophysics Data System (ADS)

Bhatia, G. K.; Sahijpal, S.

2017-02-01

Numerical models dealing with the planetary scale differentiation of Mercury are presented with the short-lived nuclide, 26Al, as the major heat source along with the impact-induced heating during the accretion of planets. These two heat sources are considered to have caused differentiation of Mars, a planet with size comparable to Mercury. The chronological records and the thermal modeling of Mars indicate an early differentiation during the initial 1 million years (Ma) of the formation of the solar system. We theorize that in case Mercury also accreted over an identical time scale, the two heat sources could have differentiated the planets. Although unlike Mars there is no chronological record of Mercury's differentiation, the proposed mechanism is worth investigation. We demonstrate distinct viable scenarios for a wide range of planetary compositions that could have produced the internal structure of Mercury as deduced by the MESSENGER mission, with a metallic iron (Fe-Ni-FeS) core of radius 2000 km and a silicate mantle thickness of 400 km. The initial compositions were derived from the enstatite and CB (Bencubbin) chondrites that were formed in the reducing environments of the early solar system. We have also considered distinct planetary accretion scenarios to understand their influence on thermal processing. The majority of our models would require impact-induced mantle stripping of Mercury by hit and run mechanism with a protoplanet subsequent to its differentiation in order to produce the right size of mantle. However, this can be avoided if we increase the Fe-Ni-FeS contents to 71% by weight. Finally, the models presented here can be used to understand the differentiation of Mercury-like exoplanets and the planetary embryos of Venus and Earth.

Toward a Deterministic Model of Planetary Formation. I. A Desert in the Mass and Semimajor Axis Distributions of Extrasolar Planets

NASA Astrophysics Data System (ADS)

Ida, S.; Lin, D. N. C.

2004-03-01

In an attempt to develop a deterministic theory for planet formation, we examine the accretion of cores of giant planets from planetesimals, gas accretion onto the cores, and their orbital migration. We adopt a working model for nascent protostellar disks with a wide variety of surface density distributions in order to explore the range of diversity among extrasolar planetary systems. We evaluate the cores' mass growth rate Mc through runaway planetesimal accretion and oligarchic growth. The accretion rate of cores is estimated with a two-body approximation. In the inner regions of disks, the cores' eccentricity is effectively damped by their tidal interaction with the ambient disk gas and their early growth is stalled by ``isolation.'' In the outer regions, the cores' growth rate is much smaller. If some cores can acquire more mass than a critical value of several Earth masses during the persistence of the disk gas, they would be able to rapidly accrete gas and evolve into gas giant planets. The gas accretion process is initially regulated by the Kelvin-Helmholtz contraction of the planets' gas envelope. Based on the assumption that the exponential decay of the disk gas mass occurs on the timescales ~106-107 yr and that the disk mass distribution is comparable to those inferred from the observations of circumstellar disks of T Tauri stars, we carry out simulations to predict the distributions of masses and semimajor axes of extrasolar planets. In disks as massive as the minimum-mass disk for the solar system, gas giants can form only slightly outside the ``ice boundary'' at a few AU. However, cores can rapidly grow above the critical mass inside the ice boundary in protostellar disks with 5 times more heavy elements than those of the minimum-mass disk. Thereafter, these massive cores accrete gas prior to its depletion and evolve into gas giants. The limited persistence of the disk gas and the decline in the stellar gravity prevent the formation of cores capable of efficient gas accretion outside 20-30 AU. Unimpeded dynamical accretion of gas is a runaway process that is terminated when the residual gas is depleted either globally or locally in the form of a gap in the vicinity of their orbits. Since planets' masses grow rapidly from 10 to 100 M⊕, the gas giant planets rarely form with asymptotic masses in this intermediate range. Our model predicts a paucity of extrasolar planets with mass in the range 10-100 M⊕ and semimajor axis less than 3 AU. We refer to this deficit as a ``planet desert.'' We also examine the dynamical evolution of protoplanets by considering the effect of orbital migration of giant planets due to their tidal interactions with the gas disks, after they have opened up gaps in the disks. The effect of migration is to sharpen the boundaries and to enhance the contrast of the planet desert. It also clarifies the separation between the three populations of rocky, gas giant, and ice giant planets. Based on our results, we suggest that the planets' mass versus semimajor axes diagram can provide strong constraints on the dominant formation processes of planets analogous to the implications of the color-magnitude diagram on the paths of stellar evolution. We show that the mass and semimajor axis distributions generated in our simulations for the gas giants are consistent with those of the known extrasolar planets. Our results also indicate that a large fraction (90%-95%) of the planets that have migrated to within 0.05 AU must have perished. Future observations can determine the existence and the boundaries of the planet desert in this diagram, which can be used to extrapolate the ubiquity of rocky planets around nearby stars. Finally, the long-term dynamical interaction between planets of various masses can lead to both eccentricity excitation and scattering of planets to large semimajor axes. These effects are to be included in future models.

Obtaining and Using Planetary Spatial Data into the Future: The Role of the Mapping and Planetary Spatial Infrastructure Team (MAPSIT)

NASA Technical Reports Server (NTRS)

Radebaugh, J.; Thomson, B. J.; Archinal, B.; Hagerty, J.; Gaddis, L.; Lawrence, S. J.; Sutton, S.

2017-01-01

Planetary spatial data, which include any remote sensing data or derived products with sufficient positional information such that they can be projected onto a planetary body, continue to rapidly increase in volume and complexity. These data are the hard-earned fruits of decades of planetary exploration, and are the end result of mission planning and execution. Maintaining these data using accessible formats and standards for all scientists has been necessary for the success of past, present, and future planetary missions. The Mapping and Planetary Spatial Infrastructure Team (MAPSIT) is a group of planetary community members tasked by NASA Headquarters to work with the planetary science community to identify and prioritize their planetary spatial data needs to help determine the best pathways for new data acquisition, usable product derivation, and tools/capability development that supports NASA's planetary science missions.

Orbits and Interiors of Planets

NASA Astrophysics Data System (ADS)

Batygin, Konstantin

2012-05-01

The focus of this thesis is a collection of problems of timely interest in orbital dynamics and interior structure of planetary bodies. The first three chapters are dedicated to understanding the interior structure of close-in, gaseous extrasolar planets (hot Jupiters). In order to resolve a long-standing problem of anomalously large hot Jupiter radii, we proposed a novel magnetohydrodynamic mechanism responsible for inflation. The mechanism relies on the electro-magnetic interactions between fast atmospheric flows and the planetary magnetic field in a thermally ionized atmosphere, to induce electrical currents that flow throughout the planet. The resulting Ohmic dissipation acts to maintain the interior entropies, and by extension the radii of hot Jupiters at an enhanced level. Using self-consistent calculations of thermal evolution of hot Jupiters under Ohmic dissipation, we demonstrated a clear tendency towards inflated radii for effective temperatures that give rise to significant ionization of K and Na in the atmosphere, a trend fully consistent with the observational data. Furthermore, we found that in absence of massive cores, low-mass hot Jupiters can over-flow their Roche-lobes and evaporate on Gyr time-scales, possibly leaving behind small rocky cores. Chapters four through six focus on the improvement and implications of a model for orbital evolution of the solar system, driven by dynamical instability (termed the "Nice" model). Hydrodynamical studies of the orbital evolution of planets embedded in protoplanetary disks suggest that giant planets have a tendency to assemble into multi-resonant configurations. Following this argument, we used analytical methods as well as self-consistent numerical N-body simulations to identify fully-resonant primordial states of the outer solar system, whose dynamical evolutions give rise to orbital architectures that resemble the current solar system. We found a total of only eight such initial conditions, providing independent constraints for the solar system's birth environment. Next, we addressed a significant drawback of the original Nice model, namely its inability to create the physically unique, cold classical population of the Kuiper Belt. Specifically, we showed that a locally-formed cold belt can survive the transient instability, and its relatively calm dynamical structure can be reproduced. The last four chapters of this thesis address various aspects and consequences of dynamical relaxation of planetary orbits through dissipative effects as well as the formation of planets in binary stellar systems. Using octopole-order secular perturbation theory, we demonstrated that in multi-planet systems, tidal dissipation often drives orbits onto dynamical "fixed points," characterized by apsidal alignment and lack of periodic variations in eccentricities. We applied this formalism towards investigating the possibility that the large orbital eccentricity of the transiting Neptune-mass planet Gliese 436b is maintained in the face of tidal dissipation by a second planet in the system and computed a locus of possible orbits for the putative perturber. Following up along similar lines, we used various permutations of secular theory to show that when applied specifically to close-in low-mass planetary systems, various terms in the perturbation equations become separable, and the true masses of the planets can be solved for algebraically. In practice, this means that precise knowledge of the system's orbital state can resolve the sin( i) degeneracy inherent to non-transiting planets. Subsequently, we investigated the onset of chaotic motion in dissipative planetary systems. We worked in the context of classical secular perturbation theory, and showed that planetary systems approach chaos via the so-called period-doubling route. Furthermore, we demonstrated that chaotic strange attractors can exist in mildly damped systems, such as photo-evaporating nebulae that host multiple planets. Finally, we considered planetary formation in highly inclined binary systems, where orbital excitation due to the Kozai resonance apparently implies destructive collisions among planetesimals. Through a proper account of gravitational interactions within the protoplanetary disk, we showed that fast apsidal recession induced by disk self-gravity tends to erase the Kozai effect, and ensure that the disk's unwarped, rigid structure is maintained, resolving the difficulty in planet-formation. (Abstract shortened by UMI.)

Advances in Planetary Geology

NASA Technical Reports Server (NTRS)

Woronow, A. (Editor)

1982-01-01

Advances in Planetary Geology is a new series intended to serve the planetary geology community with a form for quick and thorough communications. There are no set lists of acceptable topics or formats, and submitted manuscripts will not undergo a formal review. All submissions should be in a camera ready form, preferably spaced, and submitted to the editor.

Photochemical Formation of Aerosol in Planetary Atmospheres: Photon and Water Mediated Chemistry of SO_2

NASA Astrophysics Data System (ADS)

Kroll, Jay A.; Donaldson, D. J.; Vaida, Veronica

2016-06-01

Sulfur compounds have been observed in a number of planetary atmospheres throughout our solar system. Our current understanding of sulfur chemistry explains much of what we observe in Earth's atmosphere. However, several discrepancies between modeling and observations of the Venusian atmosphere show there are still problems in our fundamental understanding of sulfur chemistry. This is of particular concern due to the important role sulfur compounds play in the formation of aerosols, which have a direct impact on planetary climates, including Earth's. We investigate the role of water complexes in the hydration of sulfur oxides and dehydration of sulfur acids and will present spectroscopic studies to document such effects. I will present recent work investigating mixtures of SO_2 and water that generate large quantities of aerosol when irradiated with solar UV light, even in the absence of traditional OH chemistry. I will discuss a proposed mechanism for the formation of sulfurous acid (H_2SO_3) and present recent experimental work that supports this proposed mechanism. Additionally, the implications that photon-induced hydration of SO_2 has for aerosol formation in the atmosphere of earth as well as other planetary atmospheres will be discussed.

Arsine in Saturn and Jupiter

NASA Technical Reports Server (NTRS)

Noll, Keith S.; Geballe, T. R.; Knacke, R. F.

1989-01-01

New spectra of Saturn and Jupiter are reported that show a prominent, heretofore unidentified absorption near 2126/cm. The observation is interpreted as unambiguous evidence for the presence of arsine, AsH3. The abundance of AsH3 appears to be almost a factor of two higher in Saturn than in Jupiter. The observed enrichments are consistent with the core instability model for the formation of giant planets. Models of arsenic chemistry that predict strong depletions of AsH3 at temperatures below 370 K are not consistent with the observations, suggesting that vertical convection or perhaps some other mechanism inhibits depletion. Arsenic is the first new element identified in a planetary atmosphere since germanium was found in Jupiter a decade ago.

Spectroscopic Studies of Pre-Biotic Carbon Chemistry

NASA Technical Reports Server (NTRS)

Blake, Geoffrey A.

2002-01-01

As described in the original proposal and in our progress reports, research in the Blake group supported by the Exobiology program seeks to understand the pre-biotic chemistry of carbon along with that of other first- and second-row elements from the earliest stages of star formation through the development of planetary systems. The major tool used is spectroscopy, and the program has observational, laboratory, and theoretical components. The observational and theoretical programs are concerned primarily with a quantitative assessment of the chemical budgets of the biogenic elements in star-forming molecular cloud cores, while the laboratory work is focused on the complex species that characterize the prebiotic chemistry of carbon. We outline below our results over the past two years acquired, in part, with Exobiology support.

Observed properties of extrasolar planets.

PubMed

Howard, Andrew W

2013-05-03

Observational surveys for extrasolar planets probe the diverse outcomes of planet formation and evolution. These surveys measure the frequency of planets with different masses, sizes, orbital characteristics, and host star properties. Small planets between the sizes of Earth and Neptune substantially outnumber Jupiter-sized planets. The survey measurements support the core accretion model, in which planets form by the accumulation of solids and then gas in protoplanetary disks. The diversity of exoplanetary characteristics demonstrates that most of the gross features of the solar system are one outcome in a continuum of possibilities. The most common class of planetary system detectable today consists of one or more planets approximately one to three times Earth's size orbiting within a fraction of the Earth-Sun distance.

Types of Information Expected from a Photometric Search for Extra-Solar Planets

NASA Technical Reports Server (NTRS)

Borucki, William; Koch, David; Bell, James, III; Cuzzi, Jeffrey N. (Technical Monitor)

1994-01-01

The current theory postulates that planets are a consequence of the formation of stars from viscous accretion disks. Condensation from the hotter, inner portion of the accretion disk favors the formation of small rocky planets in the inner portion and the formation of gas giants in the cuter, cooler part. Consequently, terrestrial-type planets in inner orbits must be commonplace (Wetheril 1991). From the geometry of the situation (Borucki and Summers 1984), it can be shown that 1% of those planetary systems that resemble our solar system should show transits for Earth-sized (or larger) planets. Thus a photometric satellite that uses a wide field of view telescope and a large CCD array to simultaneously monitor 5000 target stars should detect 50 planetary systems. To verify that regularly recurring transits are occurring rather than statistical fluctuations of the stellar flux, demands observations that extend over several orbital periods so that the constancy of the orbital period, signal amplitude, and duration can be measured. Therefore, to examine the region from Mercury's orbit to that of the Earth requires a duration of three years whereas a search out to the orbit of mars requires about six years. The results of the observations should provide estimates of the distributions of planetary size and orbital radius, and the frequency of planetary systems that have Earth-sized planets in inner orbits. Because approximately one half of the star systems observed will be binary systems, the frequency of planetary systems orbit ' ing either one or both of the stars can also be determined. Furthermore, the complexity of the photometric signature of a planet transiting a pair of stars provides enough information to estimate the eccentricities of the planetary orbits. In summary, the statistical evidence from a photometric search of solar-like stars should be able to either confirm or deny the applicability of the current theory of planet formation and provide new information about the stability of planetary orbits in binary star systems.

Planetary and synoptic-scale interactions during the life cycle of a mid-latitude blocking anticyclone over the North Atlantic

NASA Technical Reports Server (NTRS)

Smith, Phillip J.

1995-01-01

The formation of a blocking anticyclone over the North Atlantic has been examined over its entire life-CyCle using the Zwack-Okossi (Z-O) equation as the diagnostic tool. This blocking anticyclone occurred in late October and early November of 1985. The data used were provided by the NASA Goddard Laboratory for Atmospheres on a global 2.O degree latitude by 2.5 degree longitudinal grid. The horizontal distribution of the atmospheric forcing mechanisms that were important to 500 mb block formation, maintenance and decay were examined. A scale-partitioned form of the Z-O equation was then used to examine the relative importance of forcing on the planetary and synoptic scales, and their interactions. As seen in previous studies, the results presented here show that upper tropospheric anticyclonic vorticity advection was the most important contributor to block formation and maintenance. However, adiabatic warming, and vorticity tilting were also important at various times during the block lifetime. In association with precursor surface cyclogenesis, the 300 mb jet streak in the downstream (upstream) from a long-wave trough (ridge) amplified significantly. This strengthening of the jet streak enhanced the anti-cyclonic vorticity advection field that aided the amplification of a 500 mb short-wave ridge. Tile partitioned height tendency results demonstrate that the interactions between the planetary and sn,noptic-scale through vorticity advection was the most important contributor to block formation. Planetary-scale, synoptic-scale. and their interactions contributed weakly to the maintenance of the blocking anticyclone with the advection of synoptic-scale vorticity by the planetary-scale flow playing a more important role. Planetary-scale decay ofthe long-wave ridge contributed to the demise of this blocking event.

Contrasting Effects of Carbon and Sulfur on Fe-Isotope Fractionation between Metal and Silicate Melt during Planetary Core Formation

NASA Astrophysics Data System (ADS)

Elardo, S. M.; Shahar, A.

2015-12-01

There are numerous studies that show well-resolved Fe isotope fractionations in igneous materials from different planetary bodies. Potential explanations for these fractionations include a non-chondritic bulk planetary Fe isotopic composition, and equilibrium fractionation between Fe-alloys or minerals and silicate melts during planetary differentiation, mantle melting, or fractional crystallization. This is further complicated by the fact that these processes are not mutually exclusive, making the interpretation of Fe isotope data a complex task. Here we present new experimental results investigating the effect of C on Fe isotope fractionation between molten peridotite and an Fe-alloy. Experiments were conducted at 1 GPa and 1850° C for 0.5 - 3 hours on a mixture of an 54Fe-spiked peridotite and Fe-metal with and without Ni metal in an end-loaded piston cylinder at the Geophysical Laboratory. Carbon saturation was achieved with a graphite capsule, and resulted in C contents of the Fe-alloy in our experiments ranging from 3.8 - 4.9 wt. %. The metal and silicate phases from half of each experiment were separated manually and dissolved in concentrated acids. Iron was separated from matrix elements by anion exchange chromatagraphy. Iron-isotopic compositions were determined with the Nu Plasma II MC-ICP-MS at GL. The other half of each experiment was used for quantitative microbeam analysis. Equilibrium was assessed with a time series and the three-isotope exchange method. The Ni-free experiments resulted in no resolvable Fe isotope fractionation between the Fe-C-alloy and molten silicate. This is in contrast to the results of Shahar et al. (2015) which showed a fractionation for Δ57Fe of ~0.18 ‰ between a peridotite and an Fe-alloy with a similar S abundance to C in these experiments. The one experiment thus far that contained Ni (~4 wt. % in the alloy) showed a resolvable fractionation between the Fe-Ni-C alloy and silicate of ~0.10 ‰. Shahar et al. found a similar magnitude fractionation to our Ni bearing experiment in experiments with no C or S. The difference in temperature (1650° C in Shahar et al. vs. 1850° C here) may be partially responsible for these discrepancies. Ongoing experiments will further investigate the effects of C and other light elements on Fe isotope fractionation during core segregation.

Ultrasonic Drilling and Coring

NASA Technical Reports Server (NTRS)

Bar-Cohen, Yoseph

1998-01-01

A novel drilling and coring device, driven by a combination, of sonic and ultrasonic vibration, was developed. The device is applicable to soft and hard objects using low axial load and potentially operational under extreme conditions. The device has numerous potential planetary applications. Significant potential for commercialization in construction, demining, drilling and medical technologies.

Terrestrial Planet Formation Around Close Binary Stars

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; Quintana, Elisa V.

2003-01-01

Most stars reside in multiple star systems; however, virtually all models of planetary growth have assumed an isolated single star. Numerical simulations of the collapse of molecular cloud cores to form binary stars suggest that disks will form within such systems. Observations indirectly suggest disk material around one or both components within young binary star systems. If planets form at the right places within such circumstellar disks, they can remain in stable orbits within the binary star systems for eons. We are simulating the late stages of growth of terrestrial planets around close binary stars, using a new, ultrafast, symplectic integrator that we have developed for this purpose. The sum of the masses of the two stars is one solar mass, and the initial disk of planetary embryos is the same as that used for simulating the late stages of terrestrial planet growth within our Solar System and in the Alpha Centauri wide binary star system. Giant planets &are included in the simulations, as they are in most simulations of the late stages of terrestrial planet accumulation in our Solar System. When the stars travel on a circular orbit with semimajor axis of up to 0.1 AU about their mutual center of mass, the planetary embryos grow into a system of terrestrial planets that is statistically identical to those formed about single stars, but a larger semimajor axis and/or a significantly eccentric binary orbit can lead to significantly more dynamically hot terrestrial planet systems.

Autonomous Sample Acquisition for Planetary and Small Body Explorations

NASA Technical Reports Server (NTRS)

Ghavimi, Ali R.; Serricchio, Frederick; Dolgin, Ben; Hadaegh, Fred Y.

2000-01-01

Robotic drilling and autonomous sample acquisition are considered as the key technology requirements in future planetary or small body exploration missions. Core sampling or subsurface drilling operation is envisioned to be off rovers or landers. These supporting platforms are inherently flexible, light, and can withstand only limited amount of reaction forces and torques. This, together with unknown properties of sampled materials, makes the sampling operation a tedious task and quite challenging. This paper highlights the recent advancements in the sample acquisition control system design and development for the in situ scientific exploration of planetary and small interplanetary missions.

On the Role of Dissolved Gases in the Atmosphere Retention of Low-mass Low-density Planets

NASA Astrophysics Data System (ADS)

Chachan, Yayaati; Stevenson, David J.

2018-02-01

Low-mass low-density planets discovered by Kepler in the super-Earth mass regime typically have large radii for their inferred masses, implying the presence of H2–He atmospheres. These planets are vulnerable to atmospheric mass loss due to heating by the parent star’s XUV flux. Models coupling atmospheric mass loss with thermal evolution predicted a bimodal distribution of planetary radii, which has gained observational support. However, a key component that has been ignored in previous studies is the dissolution of these gases into the molten core of rock and iron that constitute most of their mass. Such planets have high temperatures (>2000 K) and pressures (∼kbars) at the core-envelope boundary, ensuring a molten surface and a subsurface reservoir of hydrogen that can be 5–10 times larger than the atmosphere. This study bridges this gap by coupling the thermal evolution of the planet and the mass loss of the atmosphere with the thermodynamic equilibrium between the dissolved H2 and the atmospheric H2 (Henry’s law). Dissolution in the interior allows a planet to build a larger hydrogen repository during the planet formation stage. We show that the dissolved hydrogen outgasses to buffer atmospheric mass loss. The slow cooling of the planet also leads to outgassing because solubility decreases with decreasing temperature. Dissolution of hydrogen in the interior therefore increases the atmosphere retention ability of super-Earths. The study highlights the importance of including the temperature- and pressure-dependent solubility of gases in magma oceans and coupling outgassing to planetary evolution models.

Application of high explosion cratering data to planetary problems

NASA Technical Reports Server (NTRS)

Oberbeck, V. R.

1977-01-01

The present paper deals with the conditions of explosion or nuclear cratering required to simulate impact crater formation. Some planetary problems associated with three different aspects of crater formation are discussed, and solutions based on high-explosion data are proposed. Structures of impact craters and some selected explosion craters formed in layered media are examined and are related to the structure of lunar basins. The mode of ejection of material from impact craters is identified using explosion analogs. The ejection mode is shown to have important implications for the origin of material in crater and basin deposits. Equally important are the populations of secondary craters on lunar and planetary surfaces.

Ways that our Solar System helps us understand the formation of other planetary systems and ways that it doesn't

NASA Technical Reports Server (NTRS)

Wetherill, G. W.

1996-01-01

Models of planetary formation can be tested by comparison of their ability to predict features of our Solar System in a consistent way, and then extrapolated to other hypothetical planetary systems by different choice of parameters. When this is done, it is found that the resulting systems are insensitive to direct effects of the mass of the star, but do strongly depend on the properties of the disk, principally its surface density. Major uncertainty results from lack of an adequate theoretical model that predicts the existence, size, and distribution of analogs of our Solar System, particularly the gas giants Jupiter and Saturn. Nevertheless, reasons can be found for expecting that planetary systems, including those containing biologically habitable planets similar to Earth, may be abundant in the Galaxy and Universe.

Ways that our Solar System helps us understand the formation of other planetary systems and ways that it doesn't.

PubMed

Wetherill, G W

1996-01-01

Models of planetary formation can be tested by comparison of their ability to predict features of our Solar System in a consistent way, and then extrapolated to other hypothetical planetary systems by different choice of parameters. When this is done, it is found that the resulting systems are insensitive to direct effects of the mass of the star, but do strongly depend on the properties of the disk, principally its surface density. Major uncertainty results from lack of an adequate theoretical model that predicts the existence, size, and distribution of analogs of our Solar System, particularly the gas giants Jupiter and Saturn. Nevertheless, reasons can be found for expecting that planetary systems, including those containing biologically habitable planets similar to Earth, may be abundant in the Galaxy and Universe.

Development of a Linear Ion Trap Mass Spectrometer (LITMS) Investigation for Future Planetary Surface Missions

NASA Technical Reports Server (NTRS)

Brinckerhoff, W.; Danell, R.; Van Ameron, F.; Pinnick, V.; Li, X.; Arevalo, R.; Glavin, D.; Getty, S.; Mahaffy, P.; Chu, P.;

Herschel Planetary Nebula Survey (HerPlaNS). hydrogen recombination laser lines in Mz 3

NASA Astrophysics Data System (ADS)

Aleman, Isabel; Exter, Katrina; Ueta, Toshiya; Walton, Samuel; Tielens, A. G. G. M.; Zijlstra, Albert; Montez, Rodolfo; Abraham, Zulema; Otsuka, Masaaki; Beaklini, Pedro P. B.; van Hoof, Peter A. M.; Villaver, Eva; Leal-Ferreira, Marcelo L.; Mendoza, Edgar; Lépine, Jacques D. R.

2018-07-01

The bipolar nebula Menzel 3 (Mz 3) was observed as part of the Herschel Planetary Nebula Survey (HerPlaNS), which used the PACS and SPIRE instruments aboard the Herschel Space Observatory to study a sample of planetary nebulae (PNe). In this paper, one of the series describing HerPlaNS results, we report the detection of H I recombination lines (HRLs) in the spectrum of Mz 3. Inspection of the spectrum reveals the presence of 12 HRLs in the 55-680 µm range covered by the PACS and SPIRE instruments (H11α to H21α and H14β). The presence of HRLs in this range is unusual for PNe and has not been reported in Mz 3 before. Our analysis indicates that the HRLs we observed are enhanced by laser effect occurring in the core of Mz 3. Our arguments for this are (i) the available Mz 3 optical to submillimetre HRL α line intensity ratios are not well reproduced by the spontaneous emission of optically thin ionized gas, as would be typical for nebular gas in PNe; (ii) the compact core of Mz 3 is responsible for a large fraction of the Herschel HRLs emission; (iii) the line intensity ratios for Mz 3 are very similar to those in the core emission of the well known star MWC 349A, where laser effect is responsible for the enhancement of HRLs in the Herschel wavelength range; (iv) the physical characteristics relevant to cause laser effect in the core of MWC 349A are very similar to those in the core of Mz 3.

Bunte Breccia of the Ries - Continuous deposits of large impact craters

NASA Technical Reports Server (NTRS)

Horz, F.; Ostertag, R.; Rainey, D. A.

1983-01-01

The 26-km-diameter Ries impact crater in south Germany and the mechanism of ejection and emplacement associated with its formation about 15 Myr ago are discussed in detail, and the implications of the findings for models of crater formation on earth, moon, and planets are considered. Field observations and laboratory tests on 560-m core materials from nine locations are reported. The continuous deposits (Bunte Breccia) are found to be a chaotic mixture resulting from deposition at ambient temperatures in a highly turbulent environment, probably in the ballistic scenario proposed by Oberbeck et al. (1975), with an emplacement time of only about 5 min. Further impact parameters are estimated using the 'Z model' of Maxwell (1977): initial radius = 6.5 km, excavation depth = 1650 m, excavation volume = 136 cu km, and transient cavity volume = 230 cu km. The interpretation of lunar and planetary remote-sensing and in situ evidence from impact craters is reviewed in the light of the Ries findings. Numerous photographs, maps, diagrams, and tables illustrate the investigation.

Iron snow in the Martian core?

NASA Astrophysics Data System (ADS)

Davies, Christopher J.; Pommier, Anne

2018-01-01

The decline of Mars' global magnetic field some 3.8-4.1 billion years ago is thought to reflect the demise of the dynamo that operated in its liquid core. The dynamo was probably powered by planetary cooling and so its termination is intimately tied to the thermochemical evolution and present-day physical state of the Martian core. Bottom-up growth of a solid inner core, the crystallization regime for Earth's core, has been found to produce a long-lived dynamo leading to the suggestion that the Martian core remains entirely liquid to this day. Motivated by the experimentally-determined increase in the Fe-S liquidus temperature with decreasing pressure at Martian core conditions, we investigate whether Mars' core could crystallize from the top down. We focus on the "iron snow" regime, where newly-formed solid consists of pure Fe and is therefore heavier than the liquid. We derive global energy and entropy equations that describe the long-timescale thermal and magnetic history of the core from a general theory for two-phase, two-component liquid mixtures, assuming that the snow zone is in phase equilibrium and that all solid falls out of the layer and remelts at each timestep. Formation of snow zones occurs for a wide range of interior and thermal properties and depends critically on the initial sulfur concentration, ξ0. Release of gravitational energy and latent heat during growth of the snow zone do not generate sufficient entropy to restart the dynamo unless the snow zone occupies at least 400 km of the core. Snow zones can be 1.5-2 Gyrs old, though thermal stratification of the uppermost core, not included in our model, likely delays onset. Models that match the available magnetic and geodetic constraints have ξ0 ≈ 10% and snow zones that occupy approximately the top 100 km of the present-day Martian core.

Observational Research on Star and Planetary System Formation

NASA Technical Reports Server (NTRS)

Simpson, Janet P.

1998-01-01

Institute scientists collaborate with a number of NASA Ames scientists on observational studies of star and planetary system formation to their mutual benefit. As part of this collaboration, SETI scientists have, from 1988 to the present: (1) contributed to the technical studies at NASA Ames of the Stratospheric Observatory for Infrared Astronomy (SOFIA), an infrared 2.5 meter telescope in a Boeing 747, which will replace the Kuiper Airborne Observatory (KAO), a 0.9 meter telescope in a Lockheed C-141. SOFIA will be an important facility for the future exploration of the formation of stars and planetary systems, and the origins of life, and as such will be an important future facility to SETI scientists; (2) worked with the Laboratory Astrophysics Group at Ames, carrying out laboratory studies of the spectroscopic properties of ices and pre-biotic organics, which could be formed in the interstellar or interplanetary media; (3) helped develop a photometric approach for determining the Frequency of Earth-Sized Inner Planets (FRESIP) around solar-like stars, a project (now called Kepler) which complements the current efforts of the SETI Institute to find evidence for extraterrestrial intelligence; and (4) carried out independent observational research, in particular research on the formation of stars and planetary systems using both ground-based telescopes as well as the KAO.

Observational Research on Star and Planetary System Formation

NASA Astrophysics Data System (ADS)

Simpson, Janet P.

1998-07-01

Institute scientists collaborate with a number of NASA Ames scientists on observational studies of star and planetary system formation to their mutual benefit. As part of this collaboration, SETI scientists have, from 1988 to the present: (1) contributed to the technical studies at NASA Ames of the Stratospheric Observatory for Infrared Astronomy (SOFIA), an infrared 2.5 meter telescope in a Boeing 747, which will replace the Kuiper Airborne Observatory (KAO), a 0.9 meter telescope in a Lockheed C-141. SOFIA will be an important facility for the future exploration of the formation of stars and planetary systems, and the origins of life, and as such will be an important future facility to SETI scientists; (2) worked with the Laboratory Astrophysics Group at Ames, carrying out laboratory studies of the spectroscopic properties of ices and pre-biotic organics, which could be formed in the interstellar or interplanetary media; (3) helped develop a photometric approach for determining the Frequency of Earth-Sized Inner Planets (FRESIP) around solar-like stars, a project (now called Kepler) which complements the current efforts of the SETI Institute to find evidence for extraterrestrial intelligence; and (4) carried out independent observational research, in particular research on the formation of stars and planetary systems using both ground-based telescopes as well as the KAO.

Planetary Formation: From The Earth And Moon To Extrasolar Planets

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; DeVincenzi, Donald (Technical Monitor)

1999-01-01

An overview of current theories of planetary growth, emphasizing the formation of habitable planets, is presented. These models are based upon observations of the Solar System and of young stars and their environments. They predict that rocky planets should form around most single stars, although it is possible that in some cases such planets are lost - to orbital decay within the protoplanetary disk. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth like terrestrial planets, but if they become massive enough before the protoplanetary disk dissipates, then they are able to accumulate substantial amounts of gas. Specific issues to be discussed include: (1) how do giant planets influence the formation and habitability of terrestrial planets? (2) could a giant impact leading to lunar formation have occurred - 100 million years after the condensation of the oldest meteorites?

Theory of Planetary System Formation

NASA Technical Reports Server (NTRS)

Cassen, Patrick

1996-01-01

Observations and theoretical considerations support the idea that the Solar System formed by the collapse of tenuous interstellar matter to a disk of gas and dust (the primitive solar nebula), from which the Sun and other components separated under the action of dissipative forces and by the coagulation of solid material. Thus, planets are understood to be contemporaneous byproducts of star formation. Because the circumstellar disks of new stars are easier to observe than mature planetary systems, the possibility arises that the nature and variety of planets might be studied from observations of the conditions of their birth. A useful theory of planetary system formation would therefore relate the properties of circumstellar disks both to the initial conditions of star formation and to the consequent properties of planets to those of the disk. Although the broad outlines of such a theory are in place, many aspects are either untested, controversial, or otherwise unresolved; even the degree to which such a comprehensive theory is possible remains unknown.

A non-ideal MHD model for structure formation

NASA Astrophysics Data System (ADS)

Karmakar, Pralay Kumar; Sarma, Pankaj

2018-02-01

The evolutionary initiation dynamics of triggered planetary structure formation is indeed a complex process yet to be well understood. We herein develop a theoretical classical model to see the gravitational fragmentation kinetics of the viscoelastic non-ideal magneto-hydro-dynamic (MHD) fabric. The inhomogeneous planetary disk is primarily composed of heavier dust grains (strongly correlated) together with relatively lighter electrons, ions and neutrals (weakly correlated) in a mean-fluidic approximation. A normal harmonic mode analysis results in a quadratic dispersion relation of a unique shape. It is demonstrated that the growth rate of the MHD fluctuations (magnetosonic) contributing to the planet formation rate, apart from the wave vector and its projection orientation, has a pure explicit dependency on the viscoelastic parameters. The analysis specifically shows that the effective generalized viscosity (χ) , viscoelastic relaxation time (τm) , and K-orientation (θ) play as destabilizing agencies against the non-local gravitational disk collapse. The relevancy is briefly indicated in the real astronomical context of bounded planetary structure formation and evolution.

NanoRocks: A Long-Term Microgravity Experiment to Stydy Planet Formation and Planetary Ring Particles

NASA Astrophysics Data System (ADS)

Brisset, J.; Colwell, J. E.; Dove, A.; Maukonen, D.; Brown, N.; Lai, K.; Hoover, B.

2015-12-01

We report on the results of the NanoRocks experiment on the International Space Station (ISS), which simulates collisions that occur in protoplanetary disks and planetary ring systems. A critical stage of the process of early planet formation is the growth of solid bodies from mm-sized chondrules and aggregates to km-sized planetesimals. To characterize the collision behavior of dust in protoplanetary conditions, experimental data is required, working hand in hand with models and numerical simulations. In addition, the collisional evolution of planetary rings takes place in the same collisional regime. The objective of the NanoRocks experiment is to study low-energy collisions of mm-sized particles of different shapes and materials. An aluminum tray (~8x8x2cm) divided into eight sample cells holding different types of particles gets shaken every 60 s providing particles with initial velocities of a few cm/s. In September 2014, NanoRocks reached ISS and 220 video files, each covering one shaking cycle, have already been downloaded from Station. The data analysis is focused on the dynamical evolution of the multi-particle systems and on the formation of cluster. We track the particles down to mean relative velocities less than 1 mm/s where we observe cluster formation. The mean velocity evolution after each shaking event allows for a determination of the mean coefficient of restitution for each particle set. These values can be used as input into protoplanetary disk and planetary rings simulations. In addition, the cluster analysis allows for a determination of the mean final cluster size and the average particle velocity of clustering onset. The size and shape of these particle clumps is crucial to understand the first stages of planet formation inside protoplanetary disks as well as many a feature of Saturn's rings. We report on the results from the ensemble of these collision experiments and discuss applications to planetesimal formation and planetary ring evolution.

IUE observations of the 'Butterfly' Nebula M2-9

NASA Technical Reports Server (NTRS)

Feibelman, W. A.

1984-01-01

IUE observations of the peculiar 'Butterfy' nebula M2-9 indicate that it is not a normal planetary nebula. The ultraviolet spectrum is characterized by few emission lines and a weak continuum. Mg II 2800 A is the strongest emission line present and may be indicative of a binary nucleus. Lines of N v, Q I, N III, N IV, Si III, and C III are seen, but C IV and O III are conspicuous by their absence. T(e) = 10,250 + or - 400 K was determined for the core. Nitrogen in the core is found to be overabundant by about a factor of 5 over the solar value. M2-9 may be an object in the early stages of becoming a planetary nebula.

Planet Formation Instrument for the Thirty Meter Telescope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Macintosh, B; Troy, M; Graham, J

2006-02-22

In the closing years of the 20th Century humankind began its exploration of the planetary systems in the solar neighborhood. Precision radial velocity measurements have now yielded the discovery of over 160 planets. Direct imaging of these planets, as opposed to detection of the effects of orbital motion on their parent star, is now feasible, and the first young planet in a wide orbit may have been detected using adaptive optics systems. Gemini and the VLT are building the first generation of high contrast adaptive optics systems, which deliver planet-imaging performance within few Airy rings of the host star. Thesemore » systems will make the first surveys of the outer regions of solar systems by detecting the self-luminous radiation of young planets. These instruments will establish whether Jovian planets form predominantly through 'top-down' (global gravitational instability) or 'bottom-up' (core accretion) processes. The 8-m 'extreme' AO systems cannot see close enough to the host stars to image Doppler planets, and they cannot reach the relatively distant, young clusters and associations where planets are forming. The Planet Formation Instrument will use the nearly four-fold improved angular resolution of TMT to peer into the inner solar systems of Doppler-planet bearing stars to yield a unified sample of planets with known Keplerian orbital elements and atmospheric properties. In star formation regions, where T Tauri stars (young solar type stars) are found in abundance, PFI can see into the snow line, where the icy cores of planets like Jupiter must have formed. Thus, TMT will be the first facility to witness the formation of new planets.« less

The Geology of the Terrestrial Planets

NASA Technical Reports Server (NTRS)

Carr, M. H. (Editor); Saunders, R. S.; Strom, R. G.; Wilhelms, D. E.

1984-01-01

The geologic history of the terrestrial planets is outlined in light of recent exploration and the revolution in geologic thinking. Among the topics considered are planet formation; planetary craters, basins, and general surface characteristics; tectonics; planetary atmospheres; and volcanism.

A large planetary body inferred from diamond inclusions in a ureilite meteorite.

PubMed

Nabiei, Farhang; Badro, James; Dennenwaldt, Teresa; Oveisi, Emad; Cantoni, Marco; Hébert, Cécile; El Goresy, Ahmed; Barrat, Jean-Alix; Gillet, Philippe

2018-04-17

Planetary formation models show that terrestrial planets are formed by the accretion of tens of Moon- to Mars-sized planetary embryos through energetic giant impacts. However, relics of these large proto-planets are yet to be found. Ureilites are one of the main families of achondritic meteorites and their parent body is believed to have been catastrophically disrupted by an impact during the first 10 million years of the solar system. Here we studied a section of the Almahata Sitta ureilite using transmission electron microscopy, where large diamonds were formed at high pressure inside the parent body. We discovered chromite, phosphate, and (Fe,Ni)-sulfide inclusions embedded in diamond. The composition and morphology of the inclusions can only be explained if the formation pressure was higher than 20 GPa. Such pressures suggest that the ureilite parent body was a Mercury- to Mars-sized planetary embryo.

Photochemical Formation of Sulfur-Containing Aerosols

NASA Astrophysics Data System (ADS)

Kroll, Jay A.; Vaida, Veronica

2017-06-01

In order to understand planetary climate systems, modeling the properties of atmospheric aerosols is vital. Aerosol formation plays an important role in planetary climates and is tied to feedback loops that can either warm or cool a planet. Sulfur compounds are known to play an important role in new particle aerosol formation and have been observed in a number of planetary atmospheres throughout our solar system. Our current understanding of sulfur chemistry explains much of what we observe in Earth's atmosphere; however, several discrepancies arise when comparing observations of the Venusian atmosphere with model predictions. This suggests that there are still problems in our fundamental understanding of sulfur chemistry. This is concerning given recent renewed interest in sulfate injections in the stratosphere for solar radiation management geo-engineering schemes. We investigate the role of sunlight as a potential driver of the formation of sulfur-containing aerosols. I will present recent work investigating the generation of large quantities of aerosol from the irradiation of mixtures of SO_2 with water and organic species, using a solar simulator that mimics the light that is available in the Earth's troposphere and the Venusian middle atmosphere. I will present on recent work done in our lab suggesting the formation of sulfurous acid, H_2SO_3, and describe experimental work that supports this proposed mechanism. Additionally I will present on new work showing the highly reactive nature of electronically excited SO_2 with saturated alkane species. The implications of this photochemically induced sulfur aerosol formation in the atmosphere of Earth and other planetary atmospheres will be discussed.

Stochastic late accretion to Earth, the Moon, and Mars.

PubMed

Bottke, William F; Walker, Richard J; Day, James M D; Nesvorny, David; Elkins-Tanton, Linda

2010-12-10

Core formation should have stripped the terrestrial, lunar, and martian mantles of highly siderophile elements (HSEs). Instead, each world has disparate, yet elevated HSE abundances. Late accretion may offer a solution, provided that ≥0.5% Earth masses of broadly chondritic planetesimals reach Earth's mantle and that ~10 and ~1200 times less mass goes to Mars and the Moon, respectively. We show that leftover planetesimal populations dominated by massive projectiles can explain these additions, with our inferred size distribution matching those derived from the inner asteroid belt, ancient martian impact basins, and planetary accretion models. The largest late terrestrial impactors, at 2500 to 3000 kilometers in diameter, potentially modified Earth's obliquity by ~10°, whereas those for the Moon, at ~250 to 300 kilometers, may have delivered water to its mantle.

Research in astrophysical processes

NASA Technical Reports Server (NTRS)

Ruderman, Malvin A.

1994-01-01

Work completed under this grant is summarized in the following areas:(1) radio pulsar turn on and evaporation of companions in very low mass x-ray binaries and in binary radio pulsar systems; (2) effects of magnetospheric pair production on the radiation from gamma-ray pulsars; (3) radiation transfer in the atmosphere of an illuminated companion star; (4) evaporation of millisecond pulsar companions;(5) formation of planets around pulsars; (6) gamma-ray bursts; (7) quasi-periodic oscillations in low mass x-ray binaries; (8) origin of high mass x-ray binaries, runaway OB stars, and the lower mass cutoff for core collapse supernovae; (9) dynamics of planetary atmospheres; (10) two point closure modeling of stationary, forced turbulence; (11) models for the general circulation of Saturn; and (12) compressible convection in stellar interiors.

Preface: New challenges for planetary protection

NASA Astrophysics Data System (ADS)

Kminek, Gerhard

2016-05-01

Planetary protection as a discipline goes back to the advent of the space age and the formation of the Committee on Space Research (COSPAR). Planetary protection constraints are in place to ensure that scientific investigations related to the search for extraterrestrial life are not compromised and that the Earth is protected from the potential hazard posed by extraterrestrial matter carried by a spacecraft returning from an interplanetary mission.

Formation of spectral lines in planetary atmospheres. I - Theory for cloudy atmospheres: Application to Venus.

NASA Technical Reports Server (NTRS)

Hunt, G. E.

1972-01-01

The theory of the formation of spectral lines in a cloudy planetary atmosphere is studied in detail. It is shown that models based upon homogeneous, isotropically scattering atmospheres cannot be used to reproduce observed spectroscopic features of phase effect and the shape of spectral lines for weak and strong bands. The theory must, therefore, be developed using an inhomogeneous (gravitational) model of a planetary atmosphere, accurately incorporating all the physical processes of radiative transfer. Such a model of the lower Venus atmosphere, consistent with our present knowledge, is constructed. The results discussed in this article demonstrate the effects of the parameters that describe the atmospheric model on the spectroscopic features of spectral line profile and phase effect, at visible and near infrared wavelengths. This information enables us to develop a comprehensive theory of line formation in a Venus atmosphere.

Chondrule Formation in Bow Shocks around Eccentric Planetary Embryos

NASA Astrophysics Data System (ADS)

Morris, Melissa A.; Boley, Aaron C.; Desch, Steven J.; Athanassiadou, Themis

2012-06-01

Recent isotopic studies of Martian meteorites by Dauphas & Pourmand have established that large (~3000 km radius) planetary embryos existed in the solar nebula at the same time that chondrules—millimeter-sized igneous inclusions found in meteorites—were forming. We model the formation of chondrules by passage through bow shocks around such a planetary embryo on an eccentric orbit. We numerically model the hydrodynamics of the flow and find that such large bodies retain an atmosphere with Kelvin-Helmholtz instabilities allowing mixing of this atmosphere with the gas and particles flowing past the embryo. We calculate the trajectories of chondrules flowing past the body and find that they are not accreted by the protoplanet, but may instead flow through volatiles outgassed from the planet's magma ocean. In contrast, chondrules are accreted onto smaller planetesimals. We calculate the thermal histories of chondrules passing through the bow shock. We find that peak temperatures and cooling rates are consistent with the formation of the dominant, porphyritic texture of most chondrules, assuming a modest enhancement above the likely solar nebula average value of chondrule densities (by a factor of 10), attributable to settling of chondrule precursors to the midplane of the disk or turbulent concentration. We calculate the rate at which a planetary embryo's eccentricity is damped and conclude that a single planetary embryo scattered into an eccentric orbit can, over ~105 years, produce ~1024 g of chondrules. In principle, a small number (1-10) of eccentric planetary embryos can melt the observed mass of chondrules in a manner consistent with all known constraints.

Insights into Mercury's interior structure from geodesy measurements

NASA Astrophysics Data System (ADS)

Rivoldini, A.; Van Hoolst, T.; Trinh, A.

2013-09-01

The measurements of the gravitational field of Mercury by MESSENGER [1] and improved measurements of the spin state of Mercury [2] provide important constraints on the interior structure of Mercury. In particular, these data give strong constraints on the radius and density of Mercury's core and on the core's concentration of sulfur if sulfur is the only light element in the core [3]. Although sulfur is ubiquitously invoked as being the principal candidate light element in terrestrial planet's cores its abundance in the core depends on the redox conditions during planetary formation. MESSENGER data from remote sensing of Mercury's surface [4] indicate a high abundance of sulfur and confirm the low abundance in FeO supporting the hypotheses that Mercury formed under reducing conditions [5]. Therefore, substantial amounts of other light elements like for instance silicon could be present together with sulfur inside Mercury's core. Unlike sulfur, which does almost not partition into solid iron under Mercury's core pressure and temperature conditions, silicon partitions virtually equally between solid and liquid iron. Thus, if silicon is the only light element inside the core, the density jump at the inner-core outer-core boundary is significantly smaller if compared to an Fe - FeS core. If both silicon and sulfur are present inside Mercury's core then as a consequence of a large immiscibility region in liquid Fe - Si - S at Mercury's core conditions and for specific concentrations of light elements [6] a thin layer much enriched in sulfur and depleted in silicon could form at the top of the core. In this study we analyze interior structure models with silicon as the only light element in the core and with both silicon and sulfur in the core. Compared to models with Fe - FeS both settings have different mass distributions within their cores and will likely deform differently due to different elastic properties. Consequently their libration and tides will be different. Here we will use the measured 88 day libration amplitude and polar moment of inertia of Mercury in order to constrain the interior structure of both settings and calculate their tides.

Migration-induced architectures of planetary systems.

PubMed

Szuszkiewicz, Ewa; Podlewska-Gaca, Edyta

2012-06-01

The recent increase in number of known multi-planet systems gives a unique opportunity to study the processes responsible for planetary formation and evolution. Special attention is given to the occurrence of mean-motion resonances, because they carry important information about the history of the planetary systems. At the early stages of the evolution, when planets are still embedded in a gaseous disc, the tidal interactions between the disc and planets cause the planetary orbital migration. The convergent differential migration of two planets embedded in a gaseous disc may result in the capture into a mean-motion resonance. The orbital migration taking place during the early phases of the planetary system formation may play an important role in shaping stable planetary configurations. An understanding of this stage of the evolution will provide insight on the most frequently formed architectures, which in turn are relevant for determining the planet habitability. The aim of this paper is to present the observational properties of these planetary systems which contain confirmed or suspected resonant configurations. A complete list of known systems with such configurations is given. This list will be kept by us updated from now on and it will be a valuable reference for studying the dynamics of extrasolar systems and testing theoretical predictions concerned with the origin and the evolution of planets, which are the most plausible places for existence and development of life.

Walking on Exoplanets: Is Star Wars Right?

PubMed

Ballesteros, Fernando J; Luque, B

2016-05-01

As the number of detected extrasolar planets increases, exoplanet databases become a valuable resource, confirming some details about planetary formation but also challenging our theories with new, unexpected properties. Exoplanets-Gravity-Planetary habitability and biosignatures. Astrobiology 16, 325-327.

Questions about Mercury's role in comparative planetary geophysics

NASA Technical Reports Server (NTRS)

Chapman, C. R.; Weidenschilling, S. J.; Davis, D. R.; Greenberg, R.; Leake, M. A.

1985-01-01

Problems which have arisen in formulating a mutually consistent picture of Mercury's evolution are outlined. It appears that one or more of the following widely adopted assumptions are wrong about Mercury: (1) its original composition at least approximately resulted from equilibrium condensation; (2) its magnetic field arises from a still-active dynamo; (3) its thermal evolution should have yielded early core formation followed by cooling and a global contraction approaching 20 km in the planet's radius; (4) Mercury's surface is basaltic and the intercrater plains are of volcanic origin. It is suggested that Mercury's role in comparative planetology be reevaluated in the context of an alternative timescale based on the possibility that Mercury was subjected to a continuing source of cratering projectiles over recent aeons, which have not impacted the other terrestrial planets. Although such vulcanoids have not yet been discovered, the evolution of Mercury's orbit due to secular perturbations could well have led to a prolonged period of sweeping out any intra-Mercurian planetesimals that were originally present. Mercury's surface could be younger than previously believed, which explains why Mercury's core is still molten.

Planetary Drilling and Resources at the Moon and Mars

NASA Technical Reports Server (NTRS)

George, Jeffrey A.

2012-01-01

Drilling on the Moon and Mars is an important capability for both scientific and resource exploration. The unique requirements of spaceflight and planetary environments drive drills to different design approaches than established terrestrial technologies. A partnership between NASA and Baker Hughes Inc. developed a novel approach for a dry rotary coring wireline drill capable of acquiring continuous core samples at multi-meter depths for low power and mass. The 8.5 kg Bottom Hole Assembly operated at 100 We and without need for traditional drilling mud or pipe. The technology was field tested in the Canadian Arctic in sandstone, ice and frozen gumbo. Planetary resources could play an important role in future space exploration. Lunar regolith contains oxygen and metals, and water ice has recently been confirmed in a shadowed crater at the Moon.s south pole. Mars possesses a CO2 atmosphere, frozen water ice at the poles, and indications of subsurface aquifers. Such resources could provide water, oxygen and propellants that could greatly simplify the cost and complexity of exploration and survival. NASA/JSC/EP/JAG

Effect of Silicon on the Activity Coefficient of Rhenium in Fe-Si Liquids: Implications for HSE and Os Isotopes in Planetary Mantles

NASA Technical Reports Server (NTRS)

Righter, K.; Pando, K.; Yang, S.; Humayun, M.

2018-01-01

Metallic cores contain light alloying elements that can be a combination of S, C, Si, and O, all of which have important chemical and physical influences. For Earth, Si may be the most abundant light element in the core. Si dissolved into Fe liquids can have a large effect on the magnitude of the activity coefficient of siderophile elements (SE), and thus the partitioning behavior of those elements between core and mantle. The effect of Si on the highly siderophile elements is only beginning to be studied and the effects on Au, Pd and Pt are significant. Here we report new experiments designed to quantify the effect of Si on the partitioning of Re between metal and silicate melt. A solid understanding of Re partitioning is required for a complete understanding of the Re-Os isotopic systems. The results will be applied to understanding the HSEs and Os isotopic data for planetary mantles, and especially Earth.

Fault Mitigation Schemes for Future Spaceflight Multicore Processors

NASA Technical Reports Server (NTRS)

Alexander, James W.; Clement, Bradley J.; Gostelow, Kim P.; Lai, John Y.

2012-01-01

Future planetary exploration missions demand significant advances in on-board computing capabilities over current avionics architectures based on a single-core processing element. The state-of-the-art multi-core processor provides much promise in meeting such challenges while introducing new fault tolerance problems when applied to space missions. Software-based schemes are being presented in this paper that can achieve system-level fault mitigation beyond that provided by radiation-hard-by-design (RHBD). For mission and time critical applications such as the Terrain Relative Navigation (TRN) for planetary or small body navigation, and landing, a range of fault tolerance methods can be adapted by the application. The software methods being investigated include Error Correction Code (ECC) for data packet routing between cores, virtual network routing, Triple Modular Redundancy (TMR), and Algorithm-Based Fault Tolerance (ABFT). A robust fault tolerance framework that provides fail-operational behavior under hard real-time constraints and graceful degradation will be demonstrated using TRN executing on a commercial Tilera(R) processor with simulated fault injections.

Magnetic and microstructural characterisation of FeNi: Insight into the formation and impact history of the IAB parent body

NASA Astrophysics Data System (ADS)

Nichols, C. I. O.; Krakow, R.; Herrero-Albillos, J.; Kronast, F.; Northwood-Smith, G.; Harrison, R. J.

2017-12-01

The IABs represent one of only two groups of iron meteorites that did not form by fractional crystallization of liquid Fe-Ni in the core of a differentiated planetesimal. Instead, they are believed to originate from a partially differentiated body that was severely disrupted by one or more impacts during its early history. Paleomagnetic signals from two IABs, Toluca and Odessa, were investigated using X-ray magnetic circular dichroism (XMCD) and X-ray photoemission electron microscopy (X-PEEM) to image the magnetisation of the cloudy zone. The IABs do not appear to have experienced a magnetic field, consistent with the lack of a metallic core on the parent body. We also present a detailed microstructural and magnetic study of the observed FeNi microstructures, characterising their properties using XMCD and X-PEEM. The crystallographic architecture of the microstructures was analysed using electron backscatter diffraction (EBSD). Odessa and Toluca both exhibit a complex series of microstructures, requiring an unusual evolution during slow cooling. A conventional Widmanstätten sequence of kamacite, tetrataenite rim and cloudy zone developed via slow cooling to temperatures below 400 ºC. Subsequent modification of the microstructures resulted in the formation of pearlitic plessite and spheroidized plessite. Compositional and crystallographic analysis suggests that pearlitic and spheroidized plessite formed by impact modification of the cloudy zone and martensite, respectively. This study highlights the importance of characterising microstructures in order to corroborate paleomagnetic observations, as well as improving our understanding of the processes effecting planetary formation and evolution.

Cosmic rays and other rpace phenomena influenced on the Earth's climate

NASA Astrophysics Data System (ADS)

Lev, Dorman

2016-07-01

We consider effects of cosmic rays (CR) and some other space phenomena on the Earth's climate change. It is well known that the system of internal and external factors formatting the Earth's climate is very unstable: decreasing of planetary average annual temperature leads to an increase of planetary snow surface, and decreasing of the total annual solar energy input into the system decreases the planetary temperature even more. And inverse: increasing planetary temperature leads to an decrease of snow surface, and increasing of the total solar energy input into the system increases the planetary temperature even more. From this follows that even energetically small factors acted long time in one direction may have a big influence on climate change. In our opinion, the most important of these factors are CR (mostly through its influence on planetary cloudiness) and space dust (SD) through their influence on the flux of solar irradiation and on formation of clouds (these actions are in one direction). It is important that CR and SD influenced on global climate change in the same direction. Increasing of CR planetary intensity leads to increasing of formation clouds (especially low clouds on altitudes smaller than 3 km), increasing annual average of raining and decreasing of annual average planetary temperature. Increasing of SD decreases of solar irradiation and increases cloudiness what leads also to decreasing of annual average planetary temperature. Moreover, interactions of CR particles with dust granules decreases their dimensions what increased effectiveness of their actions on clouds. We consider data great variations of planetary temperature much before the beginning of the Earth's technological civilization (mostly caused by moving of the solar system around our Galaxy centre and collisions with molecular-dust clouds). We consider in details not only situation during the last hundred years, but also situation in the last one thousand years (and especially situation during Maunder minimum of solar activity), during many thousand and many millions years. It is shown that very big changes in climate were caused also by some rarely phenomena as impacts of asteroids and nearby supernova explosions with great influence on biosphere. We discuss also the problem on forecasting of global climate change what is especially important for saving present civilization from great climate catastrophes.

An analytical theory of planetary rotation rates

NASA Technical Reports Server (NTRS)

Harris, A. W.

1977-01-01

An approximate analytical theory is derived for the rate of rotation acquired by a planet as it grows from the solar nebula. This theory was motivated by a numerical study by Giuli, and yields fair agreement with his results. The periods of planetary rotation obtained are proportional to planetesimal encounter velocity, and appear to suggest lower values of this velocity than are commonly assumed to have existed during planetary formation.

Radial velocity detection of extra-solar planetary systems

NASA Technical Reports Server (NTRS)

Cochran, William D.

1991-01-01

The goal of this program was to detect planetary systems in orbit around other stars through the ultra high precision measurement of the orbital motion of the star around the star-planet barycenter. The survey of 33 nearby solar-type stars is the essential first step in understanding the overall problem of planet formation. The program will accumulate the necessary statistics to determine the frequency of planet formation as a function of stellar mass, age, and composition.

Comets, impacts, and atmospheres

NASA Astrophysics Data System (ADS)

Owen, Tobias; Bar-Nun, Akiva

Studies of element abundances and values of D/H in the atmospheres of the giant planets and Titan have emphasized the important role of icy planetesimals in the formation of these bodies. In these atmospheres, C/H and D/H increase as the relative masses of the 'cores' of the planets increase. N/H appears to deviate from this trend in an interesting way. In the inner solar system, the traditional approach of using carbonaceous chondrites as the source of planetary volatiles is in serious trouble because of the depletion of xenon and the unusual pattern of xenon isotopes found in the atmospheres of Earth and Mars, and because of the solar-type abundance ratios of argon, krypton and xenon and the large amounts of neon and argon on Venus. Recent studies of elemental abundances in comets, especially P/Halley, coupled with laboratory studies of the trapping of gas in ice formed at low temperatures by A. Bar-Nun et al. provide a consistent interpretation of all of these results. This interpretation emphasizes the fundamental importance of icy planetesimals (comets) and the randomness of early impacts in the formation of planetary systems. Cometary delivery by itself will not explain the noble gas abundances on the inner planets. There is good evidence for at least one additional source, which presumably consists of the rocky material making up the bulk of the planets. The existence of this rocky reservoir is manifested in the nucleogenic isotopes and in the neon which is found in all these atmospheres and is also present in the Earth's mantle. This neon may well be a relic of the planets' earliest, accretional atmospheres.

Towards a population synthesis model of self-gravitating disc fragmentation and tidal downsizing II: the effect of fragment-fragment interactions

NASA Astrophysics Data System (ADS)

Forgan, D. H.; Hall, C.; Meru, F.; Rice, W. K. M.

2018-03-01

It is likely that most protostellar systems undergo a brief phase where the protostellar disc is self-gravitating. If these discs are prone to fragmentation, then they are able to rapidly form objects that are initially of several Jupiter masses and larger. The fate of these disc fragments (and the fate of planetary bodies formed afterwards via core accretion) depends sensitively not only on the fragment's interaction with the disc, but also with its neighbouring fragments. We return to and revise our population synthesis model of self-gravitating disc fragmentation and tidal downsizing. Amongst other improvements, the model now directly incorporates fragment-fragment interactions while the disc is still present. We find that fragment-fragment scattering dominates the orbital evolution, even when we enforce rapid migration and inefficient gap formation. Compared to our previous model, we see a small increase in the number of terrestrial-type objects being formed, although their survival under tidal evolution is at best unclear. We also see evidence for disrupted fragments with evolved grain populations - this is circumstantial evidence for the formation of planetesimal belts, a phenomenon not seen in runs where fragment-fragment interactions are ignored. In spite of intense dynamical evolution, our population is dominated by massive giant planets and brown dwarfs at large semimajor axis, which direct imaging surveys should, but only rarely, detect. Finally, disc fragmentation is shown to be an efficient manufacturer of free-floating planetary mass objects, and the typical multiplicity of systems formed via gravitational instability will be low.

Evidence for Reduced, Carbon-rich Regions in the Solar Nebula from an Unusual Cometary Dust Particle

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Gregorio, Bradley T.; Stroud, Rhonda M.; Nittler, Larry R.

Geochemical indicators in meteorites imply that most formed under relatively oxidizing conditions. However, some planetary materials, such as the enstatite chondrites, aubrite achondrites, and Mercury, were produced in reduced nebular environments. Because of large-scale radial nebular mixing, comets and other Kuiper Belt objects likely contain some primitive material related to these reduced planetary bodies. Here, we describe an unusual assemblage in a dust particle from comet 81P/Wild 2 captured in silica aerogel by the NASA Stardust spacecraft. The bulk of this ∼20 μ m particle is comprised of an aggregate of nanoparticulate Cr-rich magnetite, containing opaque sub-domains composed of poorlymore » graphitized carbon (PGC). The PGC forms conformal shells around tiny 5–15 nm core grains of Fe carbide. The C, N, and O isotopic compositions of these components are identical within errors to terrestrial standards, indicating a formation inside the solar system. Magnetite compositions are consistent with oxidation of reduced metal, similar to that seen in enstatite chondrites. Similarly, the core–shell structure of the carbide + PGC inclusions suggests a formation via FTT reactions on the surface of metal or carbide grains in warm, reduced regions of the solar nebula. Together, the nanoscale assemblage in the cometary particle is most consistent with the alteration of primary solids condensed from a C-rich, reduced nebular gas. The nanoparticulate components in the cometary particle provide the first direct evidence from comets of reduced, carbon-rich regions that were present in the solar nebula.« less

Exterior Companions to Hot Jupiters Orbiting Cool Stars Are Coplanar

NASA Astrophysics Data System (ADS)

Becker, Juliette C.; Vanderburg, Andrew; Adams, Fred C.; Khain, Tali; Bryan, Marta

2017-12-01

The existence of hot Jupiters has challenged theories of planetary formation since the first extrasolar planets were detected. Giant planets are generally believed to form far from their host stars, where volatile materials like water exist in their solid phase, making it easier for giant planet cores to accumulate. Several mechanisms have been proposed to explain how giant planets can migrate inward from their birth sites to short-period orbits. One such mechanism, called Kozai-Lidov migration, requires the presence of distant companions in orbits inclined by more than ˜40° with respect to the plane of the hot Jupiter’s orbit. The high occurrence rate of wide companions in hot-Jupiter systems lends support to this theory for migration. However, the exact orbital inclinations of these detected planetary and stellar companions is not known, so it is not clear whether the mutual inclination of these companions is large enough for the Kozai-Lidov process to operate. This paper shows that in systems orbiting cool stars with convective outer layers, the orbits of most wide planetary companions to hot Jupiters must be well aligned with the orbits of the hot Jupiters and the spins of the host stars. For a variety of possible distributions for the inclination of the companion, the width of the distribution must be less than ˜20° to recreate the observations with good fidelity. As a result, the companion orbits are likely well aligned with those of the hot Jupiters, and the Kozai-Lidov mechanism does not enforce migration in these systems.

The Dynamics of Planet Formation

NASA Astrophysics Data System (ADS)

Chambers, J. E.

2005-05-01

The transformation of a protoplanetary disk of gas and dust into a system of planets is a mysterious business that is frustratingly difficult to observe in detail. For this reason, studies of planet formation are largely based on theoretical models with only a few anchor points where precious observations are available. In this talk I will give an overview of some of these theoretical models, indicating areas of uncertainty and places where the models are on firmer ground. For convenience, theorists usually divide planet formation into a series of stages: formation of solid bodies from dust, aggregation of solid bodies into protoplanets, late-stage growth and the formation of giant planets, and planetary migration. Here I will concentrate mostly on the second and third of these stages (understanding of the first and last stages is rather limited, and the author's understanding is especially so). The intermediate stages involve interplay between several physical processes: physical collisions, gravitational scattering, dynamical friction, gas drag, and the capture and collapse of atmospheres. I will describe these processes in some detail, and show using analytical models how these effects can lead to a variety of planetary outcomes. This work was supported by NASA's Planetary Geology and Geophysics and TPF Foundation Science Mission programmes.

Boundary pressure of inter-connection of Fe-Ni-S melt in olivine based on in-situ X-ray tomography: Implication to core formation in asteroids

NASA Astrophysics Data System (ADS)

Terasaki, H.; Urakawa, S.; Uesugi, K.; Nakatsuka, A.; Funakoshi, K.; Ohtani, E.

2011-12-01

Interconnectivity of Fe-alloy melt in crystalline silicates is important property for the core formation mechanism in planetary interior. In previous studies, the interconnectivity of Fe-alloy melt has been studied based on textural observation of recovered samples from high pressure and temperature. However, there is no observation under high pressure and temperature. We have developed 80-ton uni-axial press for X-ray computed micro-tomography (X-CT) and performed X-CT measurement under high pressure (Urakawa et al. 2010). Here we report X-CT measurement of Fe-Ni-S melt in crystalline olivine and interconnectivity of the melt up to 3.5 GPa and 1273 K. X-CT measurements were carried out at BL20B2 beamline, SPring-8 synchrotron facility. The sample was powder mixture of Fe-Ni-S and olivine, which was enclosed in graphite capsule. Heating was performed using a cylindrical graphite furnace. Pressure was generated using opposed toroidal-shape WC anvil. The uni-axial press was set on the rotational stage and X-ray radiography image of the sample was collected using CCD camera from 0°to 180°with 0.3° step. 3-D image of the sample was obtained by reconstructing the 2-D radiography image. The 3-D CT image shows that the size of the Fe-Ni-S melt increased significantly compared to that before melting below 2.5 GPa, suggesting that the melt was interconnected in olivine crystals. On the other hand, 3-D texture of the sample at 3.5 GPa did not show difference from that before melting. Therefore, the boundary of inter-connection of Fe-Ni-S melt is likely to locate between 2.5 and 3.5 GPa. This result is important application for the core formation mechanism especially in small bodies, such as differentiated asteroids.

Planetary Volcanism

NASA Technical Reports Server (NTRS)

Antonenko, I.; Head, J. W.; Pieters, C. W.

1998-01-01

The final report consists of 10 journal articles concerning Planetary Volcanism. The articles discuss the following topics: (1) lunar stratigraphy; (2) cryptomare thickness measurements; (3) spherical harmonic spectra; (4) late stage activity of volcanoes on Venus; (5) stresses and calderas on Mars; (6) magma reservoir failure; (7) lunar mare basalt volcanism; (8) impact and volcanic glasses in the 79001/2 Core; (9) geology of the lunar regional dark mantle deposits; and (10) factors controlling the depths and sizes of magma reservoirs in Martian volcanoes.

Impact-Basin Formation on Mercury: Current Observations and Outstanding Questions

NASA Astrophysics Data System (ADS)

Baker, D. M. H.; Head, J. W.; Fassett, C. I.

2018-05-01

Mercury provides an important laboratory for understanding impact-basin formation on planetary bodies. MESSENGER observations improved our understanding, but much is still unknown about the formation and evolution of basin features.

Alloying effects of Ni, Si, and S on the phase diagram and sound velocities of Fe under high pressures and high temperatures

NASA Astrophysics Data System (ADS)

Lin, J.; Fei, Y.; Sturhahn, W.; Zhao, J.; Mao, H.; Hemley, R.

2004-05-01

Iron-nickel is the most abundant constituent of the Earth's core. The amount of Ni in the core is about 5.5 wt%. Geophysical and cosmochemical studies suggest that the Earth's outer core also contains approximately 10% of light element(s) and a certain amount of light element(s) may be present in the inner core. Si and S are believed to be alloying light elements in the iron-rich planetary cores such as the Earth and Mars. Therefore, understanding the alloying effects of Ni, Si, and S on the phase diagram and physical properties of Fe under core conditions is crucial for geophysical and geochemical models of planetary interiors. The addition of Ni and Si does not appreciably change the compressibility of hcp-Fe under high pressures. Studies of the phase relations of Fe and Fe-Ni alloys indicate that Fe with up to 10 wt% Ni is likely to be in the hcp structure under inner core conditions. On the other hand, adding Si into Fe strongly stabilizes the bcc structure to much higher pressures and temperatures (Lin et al., 2002). We have also studied the sound velocities and magnetic properties of Fe0.92Ni0.08, Fe0.85Si0.15, and Fe3S alloys with nuclear resonant inelastic x-ray scattering and nuclear forward scattering up to 106 GPa, 70 GPa, and 57 GPa, respectively. The sound velocities of the alloys are obtained from the measured partial phonon density of states for 57Fe incorporated in the alloys. Addition of Ni slightly decreases the VP and VS of Fe under high pressures (Lin et al., 2003). Si or S alloyed with Fe increases the VP and VS under high pressures, which provides a better match to seismological data of the Earth's core. We note that the increase in the VP and VS of Fe0.85Si0.15 and Fe3S is mainly contributed from the density decrease of adding Si and S in iron. Time spectra of the nuclear forward scattering reveal that the most iron rich sulfide, Fe3S, undergoes a magnetic to non-magnetic transition at approximately 18 GPa from a low-pressure magnetically ordered state to a high-pressure non-magnetic ordered state. The magnetic transition significantly affects the elastic, thermodynamic, and vibrational properties of Fe3S. It is conceivable that the magnetic collapse of Fe3S may also affect the binary phase diagram of the iron-sulfur system, changing the solubility of sulfur in iron under higher pressures. Study of the non-magnetic phase is more relevant to understand the properties of the Fe3S under planetary core conditions where high pressures and high temperature ensure the non-magnetic ordering state, affecting the interpretation of the amount and properties of sulfur being in the planetary cores. If the Martian core is in the solid state containing 14.2 wt% sulfur, it is likely that the non-magnetic Fe3S phase is a dominant component and that our measured sound velocities of Fe3S can be used to understand the velocity profile in the Martian core.

Urey prize lecture: On the diversity of plausible planetary systems

NASA Technical Reports Server (NTRS)

Lissauer, J. J.

1995-01-01

Models of planet formation and of the orbital stability of planetary systems are used to predict the variety of planetary and satellite systems that may be present within our galaxy. A new approximate global criterion for orbital stability of planetary systems based on an extension of the local resonance overlap criterion is proposed. This criterion implies that at least some of Uranus' small inner moons are significantly less massive than predicted by estimates based on Voyager volumes and densities assumed to equal that of Miranda. Simple calculations (neglecting planetary gravity) suggest that giant planets which acrete substantial amounts of gas while their envelopes are extremely distended ultimately rotate rapidly in the prgrade direction.

Post-main-sequence planetary system evolution.

PubMed

Veras, Dimitri

2016-02-01

The fates of planetary systems provide unassailable insights into their formation and represent rich cross-disciplinary dynamical laboratories. Mounting observations of post-main-sequence planetary systems necessitate a complementary level of theoretical scrutiny. Here, I review the diverse dynamical processes which affect planets, asteroids, comets and pebbles as their parent stars evolve into giant branch, white dwarf and neutron stars. This reference provides a foundation for the interpretation and modelling of currently known systems and upcoming discoveries.

Planetary rings and astrophysical discs

NASA Astrophysics Data System (ADS)

Latter, Henrik

2016-05-01

Disks are ubiquitous in astrophysics and participate in some of its most important processes. Of special interest is their role in star, planet and moon formation, the growth of supermassive black holes, and the launching of jets. Although astrophysical disks can be up to ten orders of magnitude larger than planetary rings and differ hugely in composition, all disks share to some extent the same basic dynamics and many physical phenomena. This review explores these areas of overlap. Topics covered include disk formation, accretion, collisions, instabilities, and satellite-disk interactions.

Extrasolar planets: constraints for planet formation models.

PubMed

Santos, Nuno C; Benz, Willy; Mayor, Michel

2005-10-14

Since 1995, more than 150 extrasolar planets have been discovered, most of them in orbits quite different from those of the giant planets in our own solar system. The number of discovered extrasolar planets demonstrates that planetary systems are common but also that they may possess a large variety of properties. As the number of detections grows, statistical studies of the properties of exoplanets and their host stars can be conducted to unravel some of the key physical and chemical processes leading to the formation of planetary systems.

Adjustment of Jacobs' formulation to the case of Mercury

NASA Astrophysics Data System (ADS)

Chiappini, M.; de Santis, A.

1991-04-01

Magnetic investigations play an important role in studies on the constitution of planetary interiors. One of these techniques (the so-called Jacobs' formulation), appropriately modified, has been applied to the case of Mercury. According to the results found, the planet, supposed to be divided internally as the earth (crust-mantle-core), would have a core/planet volume ratio of 28 percent, much greater than the earth's core percentage (16 percent). This result is in agreement with previous work which used other independent methods.

Migration & Extra-solar Terrestrial Planets: Watering the Planets

NASA Astrophysics Data System (ADS)

Carter-Bond, Jade C.; O'Brien, David P.; Raymond, Sean N.

2014-04-01

A diverse range of terrestrial planet compositions is believed to exist within known extrasolar planetary systems, ranging from those that are relatively Earth-like to those that are highly unusual, dominated by species such as refractory elements (Al and Ca) or C (as pure C, TiC and SiC)(Bond et al. 2010b). However, all prior simulations have ignored the impact that giant planet migration during planetary accretion may have on the final terrestrial planetary composition. Here, we combined chemical equilibrium models of the disk around five known planetary host stars (Solar, HD4203, HD19994, HD213240 and Gl777) with dynamical models of terrestrial planet formation incorporating various degrees of giant planet migration. Giant planet migration is found to drastically impact terrestrial planet composition by 1) increasing the amount of Mg-silicate species present in the final body; and 2) dramatically increasing the efficiency and amount of water delivered to the terrestrial bodies during their formation process.

The Atmospheres of the Terrestrial Planets:Clues to the Origins and Early Evolution of Venus, Earth, and Mars

NASA Technical Reports Server (NTRS)

Baines, Kevin H.; Atreya, Sushil K.; Bullock, Mark A.; Grinspoon, David H,; Mahaffy, Paul; Russell, Christopher T.; Schubert, Gerald; Zahnle, Kevin

2015-01-01

We review the current state of knowledge of the origin and early evolution of the three largest terrestrial planets - Venus, Earth, and Mars - setting the stage for the chapters on comparative climatological processes to follow. We summarize current models of planetary formation, as revealed by studies of solid materials from Earth and meteorites from Mars. For Venus, we emphasize the known differences and similarities in planetary bulk properties and composition with Earth and Mars, focusing on key properties indicative of planetary formation and early evolution, particularly of the atmospheres of all three planets. We review the need for future in situ measurements for improving our understanding of the origin and evolution of the atmospheres of our planetary neighbors and Earth, and suggest the accuracies required of such new in situ data. Finally, we discuss the role new measurements of Mars and Venus have in understanding the state and evolution of planets found in the habitable zones of other stars.

From Dust to Planets: Connecting the Dots

NASA Astrophysics Data System (ADS)

Weidenschilling, Stuart

The principal objective is to construct a self-consistent model linking two key early stages of planetary origins: formation of planetesimals by collisional growth of aggregate bodies from grains in the solar nebula, and accretion of those planetesimals into planetary embryos. We will simulate these processes by using a series of numerical codes to model (i) particle settling and coagulation, using the latest and most comprehensive experimental data on collisional outcomes, (ii) detailed vertical structure of a particle layer in the nebular midplane subject to shear-generated turbulence, and possible streaming instability due to transverse particle motions, and (iii) accretion of planetary embryos from planetesimals that have grown large enough to decouple from the gas and experience Keplerian motion dominated by gravitational forces. The proposed work will clarify conditions necessary for planetesimal formation and the effects of turbulence on this process, and will bridge the gap between the dynamical regimes controlled by forces of gas drag and gravity. It will also determine how initial sizes of planetesimals affect the timescales and outcomes of planetary accretion.

Rise of planetary bodies.

NASA Astrophysics Data System (ADS)

Czechowski, Z.; Leliwa-Kopystyński, J.; Teisseyre, R.

Contents: 1. On the probability of the formation of planetary systems. 2. Condensation triggered by supernova explosion and tidal capture theory. 3. Foundations of accretion theory. 4. The structure and evolution of the protoplanetary disk. 5. Coagulation of orbiting bodies. 6. Collision phenomena related to planetology: accretion, fragmentation, cratering. 7. Dynamics of planetesimals: Introduction, Safronov's approach, elements of the kinetic theory of gases, Nakagawa's approach, approaches considering inelastic collisions and gravitational encounters of planetesimals, Hämeen-Anttila approach, planetesimals with different masses. 8. Growth of the planetary embryo: Basic equations, model of growth of planetary embryos. 9. Origin of the Moon and the satellites.

The Germanium Dichotomy in Martian Meteorites

NASA Technical Reports Server (NTRS)

Humayun, M.; Yang, S.; Righter, K.; Zanda, B.; Hewins, R. H.

2016-01-01

Germanium is a moderately volatile and siderophile element that follows silicon in its compatibility during partial melting of planetary mantles. Despite its obvious usefulness in planetary geochemistry germanium is not analyzed routinely, with there being only three prior studies reporting germanium abundances in Martian meteorites. The broad range (1-3 ppm) observed in Martian igneous rocks is in stark contrast to the narrow range of germanium observed in terrestrial basalts (1.5 plus or minus 0.1 ppm). The germanium data from these studies indicates that nakhlites contain 2-3 ppm germanium, while shergottites contain approximately 1 ppm germanium, a dichotomy with important implications for core formation models. There have been no reliable germanium abundances on chassignites. The ancient meteoritic breccia, NWA 7533 (and paired meteorites) contains numerous clasts, some pristine and some impact melt rocks, that are being studied individually. Because germanium is depleted in the Martian crust relative to chondritic impactors, it has proven useful as an indicator of meteoritic contamination of impact melt clasts in NWA 7533. The germanium/silicon ratio can be applied to minerals that might not partition nickel and iridium, like feldspars. We report germanium in minerals from the 3 known chassignites, 2 nakhlites and 5 shergottites by LAICP- MS using a method optimized for precise germanium analysis.

Origins of Inner Solar Systems

NASA Astrophysics Data System (ADS)

Dawson, Rebekah Ilene

2017-06-01

Over the past couple decades, thousands of extra-solar planetshave been discovered orbiting other stars. The exoplanets discovered to date exhibit a wide variety of orbital and compositional properties; most are dramatically different from the planets in our own Solar System. Our classical theories for the origins of planetary systems were crafted to account for the Solar System and fail to account for the diversity of planets now known. We are working to establish a new blueprint for the origin of planetary systems and identify the key parameters of planet formation and evolution that establish the distribution of planetary properties observed today. The new blueprint must account for the properties of planets in inner solar systems, regions of planetary systems closer to their star than Earth’s separation from the Sun and home to most exoplanets detected to data. I present work combining simulations and theory with data analysis and statistics of observed planets to test theories of the origins of inner solars, including hot Jupiters, warm Jupiters, and tightly-packed systems of super-Earths. Ultimately a comprehensive blueprint for planetary systems will allow us to better situate discovered planets in the context of their system’s formation and evolution, important factors in whether the planets may harbor life.

Partitioning of K, U, and TH between sulfide and silicate liquids: Implications for radioactive heating of planetary cores

NASA Astrophysics Data System (ADS)

Murrell, M. T.; Burnett, D. S.

1986-07-01

The possibility of heating of planetary cores by K radioactivity has been extensively discussed, as well as the possibility that K partitioning into the terrestrial core is the reason for the difference between the terrestrial and chondritic K/U. We had previously suggested that U and Th partitioning into FeFeS liquids was more important than K. Laboratory FeFeS liquid, silicate liquid partition coefficient measurements (D) for K, U, and Th were made to test this suggestion. For a basaltic liquid at 1450°C and 1.5 GPa, DU is 0.013 and DK is 0.0026; thus U partitioning into FeFeS liquids is 5 times greater than K partitioning under these conditions. There are problems with 1-atm experiments in that they do not appear to equilibrate or reverse. However, measurable U and Th partitioning into sulfide was nearly always observed, but K partitioning was normally not observed (DK <~ 10-4). A typical value for DU from a granitic silicate liquid at one atmosphere, 1150°C, and low f02 is about 0.02; DTh is similar. At low f02 and higher temperature, experiments with basaltic liquids produce strong Ca and U partitioning into the sulfide liquid with DU > 1. DTh is less strongly affected. Because of the consistently low DK/DU, pressure effects near the core-mantle boundary would need to increase DK by factors of ~103 with much smaller increases in DU in order to have the terrestrial K and U abundances at chondritic levels. In addition, if radioactive heating is important for planetary cores, U and Th will be more important than K unless the lower mantle has K/U greater than 10 times chondritic or large changes in partition coefficients with conditions reverse the relative importance of K versus U and Th from our measurements.

Does asteroid 4 Vesta, with watery 1 Ceres and the Galilean moons, record the Ringwood-mode iron core construction now predicated for Earth and even apply to the other terrestrial planets?

NASA Astrophysics Data System (ADS)

Osmaston, M. F.

2014-04-01

I reason that Vesta, the source of HED but too small for appreciable magmatic resurfacing after accretion had ended, preserves valuable clues as to how the Earth and the other terrestrials were built. Setting the scene. Core formation in the terrestrial planets has long been attributed to the percolation of molten iron accreted from the solar nebula, either inward from the surface or from a magma ocean at depth. But it has been found [1,2] that the 56Fe/54Fe ratio in Earth peridotites still has a chondritic ratio, which rules out that Fe percolation has occurred. So we must revert now to Ringwood's model (1960-1978) e.g.[3] for core formation. This uses the nebula to reduce hot FeO in lavas erupted in volcanoes at the protoplanet's surface. The Fe, which then drains to the bottom of the magma chamber and solidifies, is subsequently 'loadsubducted' rapidly to form the core. For Earth's core alone this would generate ~400 earth-ocean volumes of reaction water, a Solar System benefit already foreseen by Ringwood, water being low in star-forming clouds. The heat for the volcanism is internal (accretion, gravitation, radiogenic) so orbital distance in the presence of nebular opacity is immaterial; and important for making the cores in the Galilean moons, otherwise labelled as being at the 'snowline' in the disc. In order to work, prior iron accretion to form the body must have been in oxide form. Thermodynamically this is correct if the nebula is cool (<600K [4]), and should be achieved naturally if the protoplanetary disc material were acquired while the protoSun traversed a further dust cloud (typical 10K or less) [5,6]. Related 'contamination' of the outer Sun, an unmixed star, would explain why its spectrum nearly matches the planets. Ringwood-mode core formation needs nebular presence for the reaction, so it would cease at nebular departure on exit from that cloud, leaving the body's mantle replete with reaction water. For Earth, we see this in the 4374Ma detrital zircons from water-requiring granitoids [7], and its continuing abundance in water-rich ringwoodite at the bottom of the upper mantle [8]. Vesta as a record of Ringwood-mode (RM) core formation. Based on its 220km diameter core [9] and a 500km mean overall diameter, the water generated by RM core formation would have given it a water-laden atmosphere containing an effective surface water layer over 30km deep. Current flows in this, presumably below a frozen lid, appear to have carved early deep channels in the uncoherent regolith, well seen as a.m.- conserving spiral channels (5.3hr rotationperiod) outboard of the later southern impact. Circum-equatorial similar grooves all seem to predate the impact cratering, made possible by loss of the water/ice. Character of an RM volcano interior. We can construct a vertical section from the meteoritic record, with eucrites at the top, diogenites in-between, pallasites (stonyiron) below and finally irons at the bottom. Eucrites are lavas whose FeO reduction reaction with the nebular H is recorded by clouding in the pyroxenes and plagioclase [10]. Pallasites are typical magma-chamber cumulate high-Mg olivines surrounded by an FeNi matrix which arrived by percolation from above. Lower still, the Fe/Ni 'irons' represent the pool below the lower-density olivines. Thus all these have been accessible to impact without breaking up long-solid iron cores. The >50-fold variety of observed FeNi compositions in 'irons' [11] could thus be natural volcanic variation, even on a single body, without invoking the rupture of so many separate cores. Finally, we suppose that Ceres and the Galileans, being further out, have (bar Io) managed to retain their Ringwood-mode water. For Europa [12,13], in particular, the ratio of core to preserved water seems close to the Ringwood-mode expectation. On the compulsive evidence [1,2] and our evidence [3,4] for Earth, it seems that Ringwood-mode core formation may have applied throughout the Inner Solar System. [1] Craddock PR et al. (2013) Abyssal peridotites reveal the near-chondritic Feisotopic composition of the Earth. EPSL 365, 63-76. [2] Halliday AN (2013) Small differences in sameness. Nature 497, 43-45. [3] Ringwood AE (1979) Origin of the Earth and Moon. Springer-Verlag. [4] Wood JA & Hashimoto A (1993)Mineral equilibrium in fractionated nebular systems. GCA 57, 2377-2388. [5] Osmaston MF (2009) What can we learn about solar planetary construction and early evolution of the inner members of the system from their present dynamics? Importance of a 2-stage scenario. EPSC Abstracts 4, EPSC2009-265, 2009. [6] Osmaston MF (2010) Providing solar system water and high planetary angular momentum, using a return to Ringwood's core formation model, supported by the behavioural evolution of the mantle. Goldschmidt 2010, GCA 74(S1), A 779. [7] Valley JW et al. (2014) Hadean age for a post-magma-ocean zircon confirmed by atom-probe tomography. Nature Geoscience 7, 219-223. [8] Pearson DG et al. (2014) Hydrous mantle transition zone indicated by ringwoodite included within diamond. Nature 507, 221-224. [9] Raymond CA et al. (2013) The Crust and Mantle of Vesta's Southern Hemisphere. EPSC Abstracts - 8, EPSC2013-1002. [10] Hutchison R (2004) Meteorites: a petrologic, chemical and isotopic synthesis. CUP. See p.284. [11] Burbine TH et al. (1996) Mantle material in the main belt: battered to bits? Meteorit. Planet. Sci. 31, 607-620. [12] Greenberg R (2005) Europa - the ocean moon: search for an alien biosphere. Springer/Praxis. [13] Kuskov OL et al. (2011) Internal structure of of icy satellites of Jupiter and Saturn and subsurface oceans. Miner. Mag. Goldschmidt 2011, Prague, Abstr. 1257

The Earth's Thorium and Uranium Abundance and Distribution

NASA Astrophysics Data System (ADS)

McDonough, W. F.; Guo, M.; Wipperfurth, S. A.

2017-12-01

The abundance and distribution of thorium (Th) and uranium (U) and its Th/U value have been assessed for the bulk silicate Earth (BSE), core, modern mantle and continental crust. These heat producing elements power the Earth's engine and are recorders of atmospheric oxidation and biologically mediated processes. More than 50,000 measured Th/U values (Kappa) and a couple of thousand Kappa-Pb values, the time-integrated Pb isotopic values from the decay of Th and U, are evaluated for the BSE, continental crust (CC) and modern mantle (MM), with the latter represented by mid-ocean ridge basalts (MORB) and ocean island basalt (OIB). The Kappa-Pb values for these complementary enriched and depleted domains of the BSE (i.e., CC_Kappa-Pb = 4.1 +/- 0.2 and MM_Kappa-Pb = 3.8 +/- 0.1, respectively) narrowly bracket the solar system initial (SSi_Kappa-Pb = 3.88 +/- 0.02) with an uncertainty of +/-5%) and demonstrate that negligible Th/U fractionation accompanied accretion, core formation, and crust - mantle differentiation. Experimental studies find marked differences in the partitioning of U and Th during core formation and thus, the BSE_Kappa-Pb = of 3.9 +/- 0.2 dictates that Th and U were excluded from the core. The <4% differences between the CC_Kappa-Pb and MM_Kappa-Pb reveals that U6+ recycling back into the mantle has either been a relatively recent process or that its recycling following atmospheric oxygenation at 2.4 Ga was limited and evolved slowly with time. Recent data from geoneutrino flux measurements at KamLAND observes a Th/U of 4.1 (+5.5, -3.3); although these uncertainties are large, future experiments, with annual count rates that are 10 to 40 times greater than that at KamLAND, will provide greater statistics, a critical measure of the planetary Th/U ratio, and an assessment of the assumption of chondritic ratio for the Earth.

Stratospheric Observatory for Infrared Astornomy and Planetary Science

NASA Astrophysics Data System (ADS)

Reach, William T.; SOFIA Sciece Mission Operations

2016-10-01

The Stratospheric Observatory for Infrared Astronomy enables observations at far-infrared wavelengths, including the range 30-300 microns that is nearly completely obscured from the ground. By flying in the stratosphere above 95% of atmospheric water vapor, access is opened to photometric, spectroscopic, and polarimetric observations of Solar System targets spanning small bodies through major planets. Extrasolar planetary systems can be observed through their debris disks or transits, and forming planetary systems through protoplanetary disks, protostellar envelopes, and molecular cloud cores. SOFIA operates out of Southern California most of the year. For the summer of 2016, we deployed to New Zealand with 3 scientific instruments. The HAWC+ far-infrared photopolarimeter was recently flown and is in commissioning, and two projects are in Phase A study to downselect to one new facility instrument. The Cycle 5 observing proposal results are anticipated to be be released by the time of this DPS meeting, and successful planetary proposals will be advertised.

Constraining the Drag Coefficients of Meteors in Dark Flight

NASA Technical Reports Server (NTRS)

Carter, R. T.; Jandir, P. S.; Kress, M. E.

2011-01-01

Based on data in the aeronautics literature, we have derived functions for the drag coefficients of spheres and cubes as a function of Mach number. Experiments have shown that spheres and cubes exhibit an abrupt factor-of-two decrease in the drag coefficient as the object slows through the transonic regime. Irregularly shaped objects such as meteorites likely exhibit a similar trend. These functions are implemented in an otherwise simple projectile motion model, which is applicable to the non-ablative dark flight of meteors (speeds less than .+3 km/s). We demonstrate how these functions may be used as upper and lower limits on the drag coefficient of meteors whose shape is unknown. A Mach-dependent drag coefficient is potentially important in other planetary and astrophysical situations, for instance, in the core accretion scenario for giant planet formation.

Seeing the Missing Half

NASA Technical Reports Server (NTRS)

Neumann, Gregory A.; Mazarico, Erwan

2009-01-01

The Moon is our closest planetary neighbor and the only extraterrestrial body to which humans have traveled, yet many questions about its origin and early history remain unanswered. Four papers published in this issue by scientific teams of the Japanese SELENE (Kaguya) mission offer a new global view of the Moon that helps to elucidate how the Moon evolved to its present state. The Moon is lopsided: Its visible nearside (tidally locked to face the Earth) is covered with smooth, dark volcanic mare, whereas the farside mainly consists of more heavily cratered, bright highland material. The differences in crustal thickness and density, apparent surface age, composition, and volcanic activity between the two sides are variously ascribed to external causes (such as a giant impact) or to internal causes (such as core formation, mantle convection, and crustal differentiation). The key to resolving these questions will be better data.

Water and complex organic molecules in the warm inner regions of solar-type protostars

NASA Astrophysics Data System (ADS)

Coutens, A.; Jørgensen, J. K.; Persson, M. V.; Lykke, J. M.; Taquet, V.; van Dishoeck, E. F.; Vastel, C.; Wampfler, S. F.

2015-12-01

Water and complex organic molecules play an important role in the emergence of Life. They have been detected in different types of astrophysical environments (protostars, prestellar cores, outflows, protoplanetary disks, comets, etc). In particular, they show high abundances towards the warm inner regions of protostars, where the icy grain mantles thermally desorb. Can a part of the molecular content observed in these regions be preserved during the star formation process and incorporated into asteroids and comets, that can deliver it to planetary embryos through impacts? By comparison with cometary studies, interferometric observations of solar-type protostars can help to address this important question. We present recent results obtained with the Plateau de Bure interferometer about water deuteration, glycolaldehyde and ethylene glycol towards the low-mass protostar NGC 1333 IRAS2A.

Space Station Planetology Experiments (SSPEX)

NASA Technical Reports Server (NTRS)

Greeley, R. (Editor); Williams, R. J. (Editor)

1986-01-01

A meeting of 50 planetary scientists considered the uses of the Space Station to support experiments in their various disciplines. Abstracts (28) present concepts for impact and aeolian processes, particle formation and interaction, and other planetary science experiments. Summaries of the rationale, hardware concepts, accomodations, and recommendations are included.

Lunar and Planetary Science XXXIII

NASA Technical Reports Server (NTRS)

2002-01-01

This CD-ROM publication contains the extended abstracts that were accepted for presentation at the 33rd Lunar and Planetary Science Conference held in Houston, TX, March 11-15, 2002. The papers are presented in PDF format and are indexed by author, keyword, meteorite, program and samples for quick reference.

Lunar and Planetary Science XXXII

NASA Technical Reports Server (NTRS)

2001-01-01

This CD-ROM publication contains the extended abstracts that were accepted for presentation at the 32nd Lunar and Planetary Science Conference held at Houston, TX, March 12-16, 2001. The papers are presented in PDF format and are indexed by author, keyword, meteorite, program and samples for quick reference.

Realization of thermal Convection into the initial Earth's Core on the Stage of planetary Accumulation

NASA Astrophysics Data System (ADS)

Professor Khachay, Yurie

2015-04-01

Convection in the Earth's core is not only the main mechanism of heat-mass transfer, but the significant component of the MHD mechanism of geomagnetic field generation. However the research of different convection forms on the Earth's accumulation stage had been so far not produced. Regarding the convection realization into the initial core of the growing proto planet we can distinguish some qualitative different stages. The earliest from them for the area of the planets of the Earth's group had been realized in to the pre planetary bodies, when the energy dissipation by the decay of the short living radioactive, first of all 26Al, provided the melted state of the inner areas of the proto planet. By that the masses and relative velocities of body's impacts during the process of accumulation had been small. That stipulated the low temperature values of the growing proto planetary surface [1] and the background of Raleigh heat convection realization. On the next stage of the planetary accumulation the contribution of short living isotopes to the energetic process during the decay 26Al decreased, but the energy contribution from the body's impact increased. The balance of the energy on the surface of the proto planet leaded to the melted state of the upper envelope and to the inelastic character of the impact. Further during the increase of the proto planetary mass, increase of the pressure and the melting temperature with the depth and decrease of the intensity of the dissipate energy by the body's impact, which became more elastic because of the silicate part, the background of the Raleigh heat convection can be realized [2]. However the falling of accumulated bodies can lead to the random distribution of the heat anomalies, which we could research only in the frame of the 3-D model [3-4]. For researching of the MHD mechanism of geomagnetic field generation developing yet on the stage of Earth's accumulation in that paper are presented the results of numerical modeling of PT- conditions and revealed the conditions, when the random distribution of 3D thermal heterogeneities does not destroy the thermal convection into the forming outer Earth's core. Reference 1Anfilogov V.N.,Khachay Y.V.DAN (2005) ,V 403, N 6, 803-806. 2 Anfilogov V.N.,Khachay Y.V.Litosphere (2012), N6, 3-1 3.Khachay Y.V. Magnetohydrodynamics. ( 2013), 49 N 1-3, 81-86 4.Khachay Y., Antipin A.Ural'skij geofiziceskij vestnik (2014), N1,81-85

Post-main-sequence planetary system evolution

PubMed Central

Veras, Dimitri

2016-01-01

The fates of planetary systems provide unassailable insights into their formation and represent rich cross-disciplinary dynamical laboratories. Mounting observations of post-main-sequence planetary systems necessitate a complementary level of theoretical scrutiny. Here, I review the diverse dynamical processes which affect planets, asteroids, comets and pebbles as their parent stars evolve into giant branch, white dwarf and neutron stars. This reference provides a foundation for the interpretation and modelling of currently known systems and upcoming discoveries. PMID:26998326

The Role of Carbon in Exotic Crust Formation on Mercury

NASA Technical Reports Server (NTRS)

Vander Kaaden, Kathleen E.; McCubbin, Francis M.

2018-01-01

The terrestrial planets that comprise our inner Solar System, including the Moon, are all rocky bodies that have differentiated into a crust, mantle, and core. Furthermore, all of these bodies have undergone various igneous processes since their time of primary crust formation. These processes have resurfaced each of these bodies, at least in part, resulting in the production of a secondary crust, to which Mercury is no exception. From its first flyby encounter with Mercury on January 14, 2008, the MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft collected data on the structure, chemical makeup, and density of the planet among other important characteristics. The X-Ray Spectrometer on board MESSENGER measured elevated abundances of sulfur and low abundances of iron, suggesting the planets oxygen fugacity (fO2) is several log10 units below the Iron-Wustite buffer. Similar to the role of other volatiles (e.g. sulfur) on highly reducing planetary bodies, carbon is expected to behave differently in an oxygen starved environment than it does in an oxygen enriched environment (e.g., Earth).

The Search for Young Planetary Systems And the Evolution of Young Stars

NASA Technical Reports Server (NTRS)

Beichman, Charles A.; Boden, Andrew; Ghez, Andrea; Hartman, Lee W.; Hillenbrand, Lynn; Lunine, Jonathan I.; Simon, Michael J.; Stauffer, John R.; Velusamy, Thangasamy

2004-01-01

The Space Interferometer Mission (SIM) will provide a census of planetary systems by con- ducting a broad survey of 2,000 stars that will be sensitive to the presence of planets with masses as small as approx. 15 Earth masses (1 Uranus mass) and a deep survey of approx. 250 of the nearest, stars with a mass limit of approx.3 Earth masses. The broad survey will include stars spanning a wide range of ages, spectral types, metallicity, and other important parameters. Within this larger context, the Young Stars and Planets Key Project will study approx. 200 stars with ages from 1 Myr to 100 Myr to understand the formation and dynamical evolution of gas giant planets. The SIM Young Stars and Planets Project will investigate both the frequency of giant planet formation and the early dynamical history of planetary systems. We will gain insight into how common the basic architecture of our solar system is compared with recently discovered systems with close-in giant planets by examining 200 of the nearest (less than 150 pc) and youngest (1-100 Myr) solar-type stars for planets. The sensitivity of the survey for stars located 140 pc away is shown in the planet mass-separation plane. We expect to find anywhere from 10 (assuming that only the presently known fraction of stars. 5-7%, has planets) to 200 (all young stars have planets) planetary systems. W-e have set our sensitivity threshold to ensure the detection of Jupiter-mass planets in the critical orbital range of 1 to 5 AU. These observations, when combined with the results of planetary searches of mature stars, will allow us to test theories of planetary formation and early solar system evolution. By searching for planets around pre-main sequence stars carefully selected to span an age range from 1 to 100 Myr, we will learn a t what epoch and with what frequency giant planets are found at the water-ice snowline where they are expected to form. This will provide insight into the physical mechanisms by which planets form and migrate from their place of birth, and about their survival rate. With these data in hand, we will provide data, for the first time, on such important questions as: What processes affect the formation and dynamical evolution of planets? When and where do planets form? What is initial mass distribution of planetary systems around young stars? How might planets be destroyed? What is the origin of the eccentricity of planetary orbits? What is the origin of the apparent dearth of companion objects between planets and brown dwarfs seen in mature stars? The observational strategy is a compromise between the desire to extend the planetary mass function as low as possible and the essential need to build up sufficient statistics on planetary occurrence. About half of the sample will be used to address the "where" and "when" of planet formation. We will study classical T Tauri stars (cTTs) which have massive accretion disks and post- accretion, weak-lined T Tauri stars (wTTs). Preliminary estimates suggest the sample will consist of approx. 30% cTTs and approx. 70% wTTs, driven in part by the difficulty of making accurate astrometric measurements toward objects with strong variability or prominent disks.

Partition Coefficients at High Pressure and Temperature

NASA Astrophysics Data System (ADS)

Righter, K.; Drake, M. J.

2003-12-01

Differentiation of terrestrial planets includes separation of a metallic core and possible later fractionation of mineral phases within either a solid or molten mantle (Figure 1). Lithophile and siderophile elements can be used to understand these two different physical processes, and ascertain whether they operated in the early Earth. The distribution of elements in planets can be understood by measuring the partition coefficient, D (ratio of concentrations of an element in different phases (minerals, metals, or melts)). (14K)Figure 1. Schematic cross-section through the Earth, showing: (a) an early magma ocean stage and (b) a later cool and differentiated stage. The siderophile elements (iron-loving) encompass over 30 elements and are defined as those elements for which D(metal/silicate)>1, and are useful for deciphering the details of core formation. This group of elements is commonly broken up into several subclasses, including the slightly siderophile elements (1104). Because these three groups encompass a wide range of partition coefficient values, they can be very useful in trying to determine the conditions under which metal may have equilibrated with the mantle (or a magma ocean). Because metal and silicate may equilibrate by several different mechanisms, such as at the base of a deep magma ocean, or as metal droplets descend through a molten mantle, partition coefficients can potentially shed light on which mechanism may be most important, thus linking the physics and chemistry of core formation. In this chapter, we summarize metal/silicate partitioning of siderophile elements and show how they may be used to understand planetary core formation.Once a planet is differentiated into core and mantle, a mantle will cool during convection, and can start in either a molten or solid state, depending upon the initial thermal conditions. If hot enough, minerals will crystallize from a molten mantle, and become entrained in the convecting melt, or eventually settle out at the bottom. The entrainment and settling process has been studied in detail (e.g., Tonks and Melosh, 1990), and is a potential mechanism for differentiation between the deep and shallow parts of Earth's mantle. The lithophile elements, those elements that have D(metal/silicate) <1, fall into many different subclasses and all hold information about the deep mineral structure of the mantle. Rare-earth elements (REEs) have proven to be useful: europium anomalies have helped elucidate the role of plagioclase in lunar crust formation (e.g., Schnetzler and Philpotts, 1971; Weill et al., 1974), and LREE/HREE depletion and enrichment are indicators of partial melting in the presence of garnet in the mantle. High-field-strength elements (HFSEs) - niobium, zirconium, tantalum, and hafnium - are all refractory and hence more resilient to fractionation processes such as volatility or condensation. They also have an affinity for ilmenite and rutile, and can explain differences between lunar and martian samples as well as features of Earth's continental crust ( Taylor and McLennan, 1985). Alkaline-earth and alkaline elements include rubidium, strontium, barium, potassium, caesium, and calcium, some of which are involved in radioactive decay couples, e.g., Rb-Sr and K-Ar. The latter is important in understanding the contribution of radioactive decay to planetary heat production, and potential deep sources of radiogenic argon (see Chapter 2.06). Rubidium and potassium are further useful as tracers of hydrous phases such as mica and amphibole. Possible fractionation of any of these elements from chondritic abundances (see Chapter 2.01) can be assessed with the knowledge of partition coefficients. In this chapter we summarize our understanding of mineral/melt fractionation of minor and trace elements at high pressures and temperatures and discuss the implications for mantle differentiation.

Geochemistry of Groundwater

NASA Astrophysics Data System (ADS)

Chapelle, F. H.

2003-12-01

Differentiation of terrestrial planets includes separation of a metallic core and possible later fractionation of mineral phases within either a solid or molten mantle (Figure 1). Lithophile and siderophile elements can be used to understand these two different physical processes, and ascertain whether they operated in the early Earth. The distribution of elements in planets can be understood by measuring the partition coefficient, D (ratio of concentrations of an element in different phases (minerals, metals, or melts)). (14K)Figure 1. Schematic cross-section through the Earth, showing: (a) an early magma ocean stage and (b) a later cool and differentiated stage. The siderophile elements (iron-loving) encompass over 30 elements and are defined as those elements for which D(metal/silicate)>1, and are useful for deciphering the details of core formation. This group of elements is commonly broken up into several subclasses, including the slightly siderophile elements (1104). Because these three groups encompass a wide range of partition coefficient values, they can be very useful in trying to determine the conditions under which metal may have equilibrated with the mantle (or a magma ocean). Because metal and silicate may equilibrate by several different mechanisms, such as at the base of a deep magma ocean, or as metal droplets descend through a molten mantle, partition coefficients can potentially shed light on which mechanism may be most important, thus linking the physics and chemistry of core formation. In this chapter, we summarize metal/silicate partitioning of siderophile elements and show how they may be used to understand planetary core formation.Once a planet is differentiated into core and mantle, a mantle will cool during convection, and can start in either a molten or solid state, depending upon the initial thermal conditions. If hot enough, minerals will crystallize from a molten mantle, and become entrained in the convecting melt, or eventually settle out at the bottom. The entrainment and settling process has been studied in detail (e.g., Tonks and Melosh, 1990), and is a potential mechanism for differentiation between the deep and shallow parts of Earth's mantle. The lithophile elements, those elements that have D(metal/silicate) <1, fall into many different subclasses and all hold information about the deep mineral structure of the mantle. Rare-earth elements (REEs) have proven to be useful: europium anomalies have helped elucidate the role of plagioclase in lunar crust formation (e.g., Schnetzler and Philpotts, 1971; Weill et al., 1974), and LREE/HREE depletion and enrichment are indicators of partial melting in the presence of garnet in the mantle. High-field-strength elements (HFSEs) - niobium, zirconium, tantalum, and hafnium - are all refractory and hence more resilient to fractionation processes such as volatility or condensation. They also have an affinity for ilmenite and rutile, and can explain differences between lunar and martian samples as well as features of Earth's continental crust ( Taylor and McLennan, 1985). Alkaline-earth and alkaline elements include rubidium, strontium, barium, potassium, caesium, and calcium, some of which are involved in radioactive decay couples, e.g., Rb-Sr and K-Ar. The latter is important in understanding the contribution of radioactive decay to planetary heat production, and potential deep sources of radiogenic argon (see Chapter 2.06). Rubidium and potassium are further useful as tracers of hydrous phases such as mica and amphibole. Possible fractionation of any of these elements from chondritic abundances (see Chapter 2.01) can be assessed with the knowledge of partition coefficients. In this chapter we summarize our understanding of mineral/melt fractionation of minor and trace elements at high pressures and temperatures and discuss the implications for mantle differentiation.

Origin and evolution of the atmospheres of early Venus, Earth and Mars

NASA Astrophysics Data System (ADS)

Lammer, Helmut; Zerkle, Aubrey L.; Gebauer, Stefanie; Tosi, Nicola; Noack, Lena; Scherf, Manuel; Pilat-Lohinger, Elke; Güdel, Manuel; Grenfell, John Lee; Godolt, Mareike; Nikolaou, Athanasia

2018-05-01

We review the origin and evolution of the atmospheres of Earth, Venus and Mars from the time when their accreting bodies were released from the protoplanetary disk a few million years after the origin of the Sun. If the accreting planetary cores reached masses ≥ 0.5 M_Earth before the gas in the disk disappeared, primordial atmospheres consisting mainly of H_2 form around the young planetary body, contrary to late-stage planet formation, where terrestrial planets accrete material after the nebula phase of the disk. The differences between these two scenarios are explored by investigating non-radiogenic atmospheric noble gas isotope anomalies observed on the three terrestrial planets. The role of the young Sun's more efficient EUV radiation and of the plasma environment into the escape of early atmospheres is also addressed. We discuss the catastrophic outgassing of volatiles and the formation and cooling of steam atmospheres after the solidification of magma oceans and we describe the geochemical evidence for additional delivery of volatile-rich chondritic materials during the main stages of terrestrial planet formation. The evolution scenario of early Earth is then compared with the atmospheric evolution of planets where no active plate tectonics emerged like on Venus and Mars. We look at the diversity between early Earth, Venus and Mars, which is found to be related to their differing geochemical, geodynamical and geophysical conditions, including plate tectonics, crust and mantle oxidation processes and their involvement in degassing processes of secondary N_2 atmospheres. The buildup of atmospheric N_2, O_2, and the role of greenhouse gases such as CO_2 and CH_4 to counter the Faint Young Sun Paradox (FYSP), when the earliest life forms on Earth originated until the Great Oxidation Event ≈ 2.3 Gyr ago, are addressed. This review concludes with a discussion on the implications of understanding Earth's geophysical and related atmospheric evolution in relation to the discovery of potential habitable terrestrial exoplanets.

Coupling between Mercury and its nightside magnetosphere: Cross-tail current sheet asymmetry and substorm current wedge formation

NASA Astrophysics Data System (ADS)

Poh, Gangkai; Slavin, James A.; Jia, Xianzhe; Raines, Jim M.; Imber, Suzanne M.; Sun, Wei-Jie; Gershman, Daniel J.; DiBraccio, Gina A.; Genestreti, Kevin J.; Smith, Andy W.

2017-08-01

We analyzed MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) magnetic field and plasma measurements taken during 319 crossings of Mercury's cross-tail current sheet. We found that the measured BZ in the current sheet is higher on the dawnside than the duskside by a factor of ≈3 and the asymmetry decreases with downtail distance. This result is consistent with expectations based upon MHD stress balance. The magnetic fields threading the more stretched current sheet in the duskside have a higher plasma beta than those on the dawnside, where they are less stretched. This asymmetric behavior is confirmed by mean current sheet thickness being greatest on the dawnside. We propose that heavy planetary ion (e.g., Na+) enhancements in the duskside current sheet provides the most likely explanation for the dawn-dusk current sheet asymmetries. We also report the direct measurement of Mercury's substorm current wedge (SCW) formation and estimate the total current due to pileup of magnetic flux to be ≈11 kA. The conductance at the foot of the field lines required to close the SCW current is found to be ≈1.2 S, which is similar to earlier results derived from modeling of Mercury's Region 1 field-aligned currents. Hence, Mercury's regolith is sufficiently conductive for the current to flow radially then across the surface of Mercury's highly conductive iron core. Mercury appears to be closely coupled to its nightside magnetosphere by mass loading of upward flowing heavy planetary ions and electrodynamically by field-aligned currents that transfer momentum and energy to the nightside auroral oval crust and interior. Heavy planetary ion enhancements in Mercury's duskside current sheet provide explanation for cross-tail asymmetries found in this study. The total current due to the pileup of magnetic flux and conductance required to close the SCW current is found to be ≈11 kA and 1.2 S. Mercury is coupled to magnetotail by mass loading of heavy ions and field-aligned currents driven by reconnection-related fast plasma flow.

Lunar and Planetary Science XXXVI, Part 13

NASA Technical Reports Server (NTRS)

2005-01-01

Contents include the following: A Fast, Non-Destructive Method for Classifying Ordinary Chondrite Falls Using Density and Magnetic Susceptibility. An Update on Results from the Magnetic Properties Experiments on the Mars Exploration Rovers, Spirit and Opportunity. Measurement Protocols for In Situ Analysis of Organic Compounds at Mars and Comets. Piping Structures on Earth and Possibly Mars: Astrobiological Implications. Uranium and Lead in the Early Planetary Core Formation: New Insights Given by High Pressure and Temperature Experiments. The Mast Cameras and Mars Descent Imager (MARDI) for the 2009 Mars Science Laboratory. MGS MOC: First Views of Mars at Sub-Meter Resolution from Orbit. Analysis of Candor Chasma Interior Layered Deposits from OMEGA/MEX Spectra. Analysis of Valley Networks on Valles Marineris Plateau Using HRSC/MEX Data. Solar Abundance of Elements from Neutron-Capture Cross Sections. Preliminary Evaluation of the Secondary Ion/Accelerator Mass Spectrometer, MegaSIMS. Equilibrium Landforms in the Dry Valleys of Antarctica: Implications for Landscape Evolution and Climate Change on Mars. Continued Study of Ba Isotopic Compositions of Presolar Silicon Carbide Grains from Supernovae. Paleoenviromental Evolution of the Holden-Uzboi Area. Stability of Magnesium Sulfate Minerals in Martian Environments. Tungsten Isotopic Constraints on the Formation and Evolution of Iron Meteorite Parent Bodies. Migration of Dust Particles and Volatiles Delivery to the Inner Planets. On the Sitting of Trapped Noble Gases in Insoluble Organic Matter of Primitive Meteorites. Trapping of Xenon Upon Evaporation-Condensation of Organic Matter Under UV Irradiation: Isotopic Fractionation and Electron Paramagnetic Resonance Analysis. Stability of Water on Mars. A Didactic Activity. Analysis of Coronae in the Parga Chasma Region, Venus. Photometric and Compositional Surface Properties of the Gusev Crater Region, Mars, as Derived from Multi-Angle, Multi-Spectral Investigation of Mars Express HRSC Data. Mapping Compositional Diversity on Mars: Spatial Distribution and Geological Implications. A New Simulation Chamber for Studying Planetary Environments. Folded Structure in Terra Sirenum. Mars. Nitrogen-Noble Gas Static Mass Spectrometry of Genesis Collector Materials. Neon Isotope Heterogeneity in the Terrestrial Mantle: Implication for the Acquisition of Volatile Elements in Terrestrial Planets. The Cosmic Clock, the Cycle of Terrestrial Mass Extinctions.

IODP/ICDP Expedition 364-Drilling the Cretaceous-Paleogene Chicxulub impact crater: Insights into large craters formation and their effect on life.

NASA Astrophysics Data System (ADS)

Gulick, S. P. S.; Morgan, J. V.; Fucugauchi, J. U.; Bralower, T. J.; Chenot, É.; Christeson, G. L.; Claeys, P.; Cockell, C. S.; Collins, G. S.; Coolen, M.; Gebhardt, C.; Goto, K.; Kring, D. A.; Xiao, L.; Lowery, C.; Mellett, C.; Ocampo-Torres, R.; Osinski, G. R.; Perez-Cruz, L. L.; Pickersgill, A.; Poelchau, M.; Rae, A.; Rasmussen, C.; Rebolledo-Vieyra, M.; Riller, U. P.; Sato, H.; Schmitt, D. R.; Smit, J.; Tikoo, S.; Tomioka, N.; Whalen, M. T.; Zylberman, W.; Jones, H.; Gareth, C.; Wittmann, A.; Lofi, J.; Yamaguchi, K. E.; Ferrière, L.

2016-12-01

An international project to drill the Chicxulub impact crater was conducted in April and May, 2016 as Expedition 364 of the International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Project (ICDP). Site M0077 is located offshore Yucatan in the southern Gulf of Mexico. The target was to core the only pristine terrestrial peak ring and to measure physical properties of the entire borehole. Specific questions included: What rocks comprise a topographic peak ring? How are peak rings formed? How are rocks weakened during large impacts to allow them to collapse and form relatively wide, flat craters? What insights arise from biologic recovery in the Paleogene within a potentially "toxic" ocean basin? Are impact craters (including peak rings) habitats for life? Coring occurred from 503 - 1334.7 mbsf with nearly 100% recovery. Wireline logs were collected from ultra slimline tools to total depth including gamma ray, magnetic susceptibility, sonic, borehole fluid temperature and conductivity, resistivity data, borehole images, and a finely spaced vertical seismic profile. Stratigraphy cored included 110 m of Eocene and Paleocene carbonates, 130 m of allochthonous impactites, and 590 m of crustal basement with dikes. All cores were measured using a shipboard core logger (density, gamma ray, magnetic susceptibility and resistivity) and shorebased dual energy, 0.3 mm resolution CT scanner. These data allow us to: 1) refine numerical models of the formation of the Chicxulub impact structure; 2) place constraints on environmental perturbations that led to the K-Pg mass extinction; 3) improve simulations of impact craters on other planetary bodies; 4) examine deformation mechanisms for insights into how rocks weaken during impacts; 5) study impact generated hydrothermal systems and 6) understand the effects of impacts on the deep biosphere including as a habitat for microbial life with implications for evolution on Earth and astrobiology. Key results are that the Chicxulub peak ring is formed from fractured basement rocks that may host a subsurface biosphere. The impactite layer overlying the peak ring in turn provides insight into resurge and tsunami processes, while the Paleogene sediments contain the record of the recovery of life after the mass extinction event.

The Thermal States of Accreting Planets: From Mars-like Embryos to a MAD Earth

NASA Astrophysics Data System (ADS)

Stewart, S. T.; Lock, S. J.

2015-12-01

The thermal states of rocky planets can vary widely during the process of accretion. The thermal structure affects several major processes on the growing planet, including the mechanics of core formation, pressure-temperature conditions for metal-silicate equilibration, mixing, and atmospheric erosion. Because impact energy is distributed heterogeneously, accretional energy is preferentially deposited in the gravitationally re-equilibrated outer layers of the planet for both small and giant impacts. The resulting stably stratified structure inhibits complete mixing within the mantle. Initially, the specific energy of giant impacts between Mars-mass embryos leads to melting of the mantle. However, as planet formation progresses, the specific energies of giant impacts increase and can drive the mantle into a transient supercritical state. In the hottest regions of the planet, metal and silicates are miscible, and metal exsolution occurs as the structure cools. The cooling time of the supercritical structure is typically longer than the timescale for metal segregation to the core. Thus, these high temperature excursions during planet formation are significant for understanding metal-silicate equilibration. Furthermore, when a supercritical planet is also rapidly rotating, the mantle, atmosphere and disk (MAD) form a continuous dynamic and thermodynamic structure. Lunar origin by condensation from a MAD Earth can explain the major characteristics of the Moon (Lock et al., this meeting). One of the greatest uncertainties in understanding the thermal states of planets during accretion is the changing composition and mass of the atmosphere. After the dispersal of the solar nebula, the thermal boundary condition imposed by the atmosphere can vary between silicate vapor and condensed ices. The coupled problem of atmospheric origin and planetary accretion can be used to constrain the many uncertainties in the growth and divergence of the terrestrial planets in our solar system.

Outcomes of planetary close encounters - A systematic comparison of methodologies

NASA Technical Reports Server (NTRS)

Greenberg, Richard; Carusi, Andrea; Valsecchi, G. B.

1988-01-01

Several methods for estimating the outcomes of close planetary encounters are compared on the basis of the numerical integration of a range of encounter types. An attempt is made to lay the foundation for the development of predictive rules concerning the encounter outcomes applicable to the refinement of the statistical mechanics that apply to planet-formation and similar problems concerning planetary swarms. Attention is given to Oepik's (1976) formulation of the two-body approximation, whose predicted motion differs from the correct three-body behavior.

International Planetary Data Alliance (IPDA) Information Model

NASA Technical Reports Server (NTRS)

Hughes, John Steven; Beebe, R.; Guinness, E.; Heather, D.; Huang, M.; Kasaba, Y.; Osuna, P.; Rye, E.; Savorskiy, V.

2007-01-01

This document is the third deliverable of the International Planetary Data Alliance (IPDA) Archive Data Standards Requirements Identification project. The goal of the project is to identify a subset of the standards currently in use by NASAs Planetary Data System (PDS) that are appropriate for internationalization. As shown in the highlighted sections of Figure 1, the focus of this project is the Information Model component of the Data Architecture Standards, namely the object models, a data dictionary, and a set of data formats.

FRESIP: A Discovery Mission Concept To Find Earth-Sized Planets Around Solar Like Stars

NASA Technical Reports Server (NTRS)

Borucki, William; Koch, D.; Dunham, E.; Cullers, D.; Webster, L.; Granados, A.; Ford, C.; Reitsema, H.; Cochran, W.; Bell, J.;

Early formation of planetary building blocks inferred from Pb isotopic ages of chondrules

PubMed Central

Bollard, Jean; Connelly, James N.; Whitehouse, Martin J.; Pringle, Emily A.; Bonal, Lydie; Jørgensen, Jes K.; Nordlund, Åke; Moynier, Frédéric; Bizzarro, Martin

2017-01-01

The most abundant components of primitive meteorites (chondrites) are millimeter-sized glassy spherical chondrules formed by transient melting events in the solar protoplanetary disk. Using Pb-Pb dates of 22 individual chondrules, we show that primary production of chondrules in the early solar system was restricted to the first million years after the formation of the Sun and that these existing chondrules were recycled for the remaining lifetime of the protoplanetary disk. This finding is consistent with a primary chondrule formation episode during the early high-mass accretion phase of the protoplanetary disk that transitions into a longer period of chondrule reworking. An abundance of chondrules at early times provides the precursor material required to drive the efficient and rapid formation of planetary objects via chondrule accretion. PMID:28808680

Precise masses for the transiting planetary system HD 106315 with HARPS

NASA Astrophysics Data System (ADS)

Barros, S. C. C.; Gosselin, H.; Lillo-Box, J.; Bayliss, D.; Delgado Mena, E.; Brugger, B.; Santerne, A.; Armstrong, D. J.; Adibekyan, V.; Armstrong, J. D.; Barrado, D.; Bento, J.; Boisse, I.; Bonomo, A. S.; Bouchy, F.; Brown, D. J. A.; Cochran, W. D.; Collier Cameron, A.; Deleuil, M.; Demangeon, O.; Díaz, R. F.; Doyle, A.; Dumusque, X.; Ehrenreich, D.; Espinoza, N.; Faedi, F.; Faria, J. P.; Figueira, P.; Foxell, E.; Hébrard, G.; Hojjatpanah, S.; Jackman, J.; Lendl, M.; Ligi, R.; Lovis, C.; Melo, C.; Mousis, O.; Neal, J. J.; Osborn, H. P.; Pollacco, D.; Santos, N. C.; Sefako, R.; Shporer, A.; Sousa, S. G.; Triaud, A. H. M. J.; Udry, S.; Vigan, A.; Wyttenbach, A.

2017-12-01

Context. The multi-planetary system HD 106315 was recently found in K2 data. The planets have periods of Pb 9.55 and Pc 21.06 days, and radii of rb = 2.44 ± 0.17 R⊕ and rc = 4.35 ± 0.23 R⊕ . The brightness of the host star (V = 9.0 mag) makes it an excellent target for transmission spectroscopy. However, to interpret transmission spectra it is crucial to measure the planetary masses. Aims: We obtained high precision radial velocities for HD 106315 to determine the mass of the two transiting planets discovered with Kepler K2. Our successful observation strategy was carefully tailored to mitigate the effect of stellar variability. Methods: We modelled the new radial velocity data together with the K2 transit photometry and a new ground-based partial transit of HD 106315c to derive system parameters. Results: We estimate the mass of HD 106315b to be 12.6 ± 3.2 M⊕ and the density to be 4.7 ± 1.7 g cm-3, while for HD 106315c we estimate a mass of 15.2 ± 3.7 M⊕ and a density of 1.01 ± 0.29 g cm-3. Hence, despite planet c having a radius almost twice as large as planet b, their masses are consistent with one another. Conclusions: We conclude that HD 106315c has a thick hydrogen-helium gaseous envelope. A detailed investigation of HD 106315b using a planetary interior model constrains the core mass fraction to be 5-29%, and the water mass fraction to be 10-50%. An alternative, not considered by our model, is that HD 106315b is composed of a large rocky core with a thick H-He envelope. Transmission spectroscopy of these planets will give insight into their atmospheric compositions and also help constrain their core compositions. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 198.C-0168.

Trends in Planetary Data Analysis. Executive summary of the Planetary Data Workshop

NASA Technical Reports Server (NTRS)

Evans, N.

1984-01-01

Planetary data include non-imaging remote sensing data, which includes spectrometric, radiometric, and polarimetric remote sensing observations. Also included are in-situ, radio/radar data, and Earth based observation. Also discussed is development of a planetary data system. A catalog to identify observations will be the initial entry point for all levels of users into the data system. There are seven distinct data support services: encyclopedia, data index, data inventory, browse, search, sample, and acquire. Data systems for planetary science users must provide access to data, process, store, and display data. Two standards will be incorporated into the planetary data system: Standard communications protocol and Standard format data unit. The data system configuration must combine a distributed system with those of a centralized system. Fiscal constraints have made prioritization important. Activities include saving previous mission data, planning/cost analysis, and publishing of proceedings.

Planetary Data Archiving Plan at JAXA

NASA Astrophysics Data System (ADS)

Shinohara, Iku; Kasaba, Yasumasa; Yamamoto, Yukio; Abe, Masanao; Okada, Tatsuaki; Imamura, Takeshi; Sobue, Shinichi; Takashima, Takeshi; Terazono, Jun-Ya

After the successful rendezvous of Hayabusa with the small-body planet Itokawa, and the successful launch of Kaguya to the moon, Japanese planetary community has gotten their own and full-scale data. However, at this moment, these datasets are only available from the data sites managed by each mission team. The databases are individually constructed in the different formats, and the user interface of these data sites is not compatible with foreign databases. To improve the usability of the planetary archives at JAXA and to enable the international data exchange smooth, we are investigating to make a new planetary database. Within a coming decade, Japan will have fruitful datasets in the planetary science field, Venus (Planet-C), Mercury (BepiColombo), and several missions in planning phase (small-bodies). In order to strongly assist the international scientific collaboration using these mission archive data, the planned planetary data archive at JAXA should be managed in an unified manner and the database should be constructed in the international planetary database standard style. In this presentation, we will show the current status and future plans of the planetary data archiving at JAXA.

Scientific rationale for Uranus and Neptune in situ explorations

NASA Astrophysics Data System (ADS)

Mousis, O.; Atkinson, D. H.; Cavalié, T.; Fletcher, L. N.; Amato, M. J.; Aslam, S.; Ferri, F.; Renard, J.-B.; Spilker, T.; Venkatapathy, E.; Wurz, P.; Aplin, K.; Coustenis, A.; Deleuil, M.; Dobrijevic, M.; Fouchet, T.; Guillot, T.; Hartogh, P.; Hewagama, T.; Hofstadter, M. D.; Hue, V.; Hueso, R.; Lebreton, J.-P.; Lellouch, E.; Moses, J.; Orton, G. S.; Pearl, J. C.; Sánchez-Lavega, A.; Simon, A.; Venot, O.; Waite, J. H.; Achterberg, R. K.; Atreya, S.; Billebaud, F.; Blanc, M.; Borget, F.; Brugger, B.; Charnoz, S.; Chiavassa, T.; Cottini, V.; d'Hendecourt, L.; Danger, G.; Encrenaz, T.; Gorius, N. J. P.; Jorda, L.; Marty, B.; Moreno, R.; Morse, A.; Nixon, C.; Reh, K.; Ronnet, T.; Schmider, F.-X.; Sheridan, S.; Sotin, C.; Vernazza, P.; Villanueva, G. L.

2018-06-01

The ice giants Uranus and Neptune are the least understood class of planets in our solar system but the most frequently observed type of exoplanets. Presumed to have a small rocky core, a deep interior comprising ∼70% heavy elements surrounded by a more dilute outer envelope of H2 and He, Uranus and Neptune are fundamentally different from the better-explored gas giants Jupiter and Saturn. Because of the lack of dedicated exploration missions, our knowledge of the composition and atmospheric processes of these distant worlds is primarily derived from remote sensing from Earth-based observatories and space telescopes. As a result, Uranus's and Neptune's physical and atmospheric properties remain poorly constrained and their roles in the evolution of the Solar System not well understood. Exploration of an ice giant system is therefore a high-priority science objective as these systems (including the magnetosphere, satellites, rings, atmosphere, and interior) challenge our understanding of planetary formation and evolution. Here we describe the main scientific goals to be addressed by a future in situ exploration of an ice giant. An atmospheric entry probe targeting the 10-bar level, about 5 scale heights beneath the tropopause, would yield insight into two broad themes: i) the formation history of the ice giants and, in a broader extent, that of the Solar System, and ii) the processes at play in planetary atmospheres. The probe would descend under parachute to measure composition, structure, and dynamics, with data returned to Earth using a Carrier Relay Spacecraft as a relay station. In addition, possible mission concepts and partnerships are presented, and a strawman ice-giant probe payload is described. An ice-giant atmospheric probe could represent a significant ESA contribution to a future NASA ice-giant flagship mission.

C Diffusion in Fe: Isotope Effects and Other Complexities

NASA Astrophysics Data System (ADS)

Watson, E. B.; Muller, T.; Trail, D.; Van Orman, J. A.; Papineau, D.

2011-12-01

Carbon is a minor but significant component of iron meteorites, and probably also of planetary cores, including that of Earth. Given the dynamical nature of core-forming processes, C diffusion in the metal phase may play a role in C equilibration between Fe-Ni metal and silicate, carbide or oxide at some stage. Despite its relevance to steel-making, C diffusion in Fe is not well characterized over the range of conditions of interest in planetary bodies, and the likelihood of an isotope mass effect on C diffusion has not been explored. The prospect of incomplete diffusive equilibration of carbon in Fe-Ni raises the possibility that carbon isotopes might be fractionated by diffusion during core formation and evolution-perhaps to an extent that could affect the C isotope ratio of the bulk silicate Earth. Here we report results of preliminary experiments addressing the isotopic mass effect on C diffusion in Fe. Initial low-pressure experiments were conducted by placing a layer of ^{13}C-enriched graphite ( 20% ^{13}C) at the end of a high-purity, polycrystalline Fe cylinder in a silica glass container. These diffusion couples were run in a piston-cylinder apparatus at 1.5 GPa and 1000-1100^{o}C for several hours, and the resulting C-uptake profiles in the Fe cylinders were measured by EPMA and SIMS. In traverses moving away from the original C-Fe interface, total carbon decreases monotonically and becomes significantly lighter, indicating that ^{12}C diffuses faster than ^{13}C. Preliminary estimates of β in the relative isotope diffusivity relation D_{1}/D_{2} = [M_{2}/M_{1}]^{β} (where D is diffusivity and M is mass of isotopes 1 and 2) suggest values as high as 0.5, corresponding to predictions for gaseous diffusion. Isotope mass effects approaching this magnitude have been observed previously for diffusion in metals, and are expected to be highest for interstitial diffusion. Such a high β value will lead to major C isotope fractionation in some partial equilibration scenarios in planets and meteorite parent bodies. Caution is warranted at this point, however, because D_{carbon} is sensitive to carbon concentration, complicating quantification of the isotope effect.

The physics of the earth's core: An introduction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Melchior, P.

1986-01-01

This book is a reference text providing information on physical topics of recent developments in internal geophysics. The text summarizes papers covering theoretical geophysics. Basic formulae, definitions and theorems are not explained in detail due to the limited space. The contents include applications to geodesy, geophysics, astronomy, astrophysics, geophysics and planetary physics. The formal contents include: The Earth's model; Thermodynamics; Hydrodynamics; Geomagnetism; Geophysical implications in the Earth's core.

Long-Period Planets in Open Clusters and the Evolution of Planetary Systems

NASA Astrophysics Data System (ADS)

Quinn, Samuel N.; White, Russel; Latham, David W.; Stefanik, Robert

2018-01-01

Recent discoveries of giant planets in open clusters confirm that they do form and migrate in relatively dense stellar groups, though overall occurrence rates are not yet well constrained because the small sample of giant planets discovered thus far predominantly have short periods. Moreover, planet formation rates and the architectures of planetary systems in clusters may vary significantly -- e.g., due to intercluster differences in the chemical properties that regulate the growth of planetary embryos or in the stellar space density and binary populations, which can influence the dynamical evolution of planetary systems. Constraints on the population of long-period Jovian planets -- those representing the reservoir from which many hot Jupiters likely form, and which are most vulnerable to intracluster dynamical interactions -- can help quantify how the birth environment affects formation and evolution, particularly through comparison of populations possessing a range of ages and chemical and dynamical properties. From our ongoing RV survey of open clusters, we present the discovery of several long-period planets and candidate substellar companions in the Praesepe, Coma Berenices, and Hyades open clusters. From these discoveries, we improve estimates of giant planet occurrence rates in clusters, and we note that high eccentricities in several of these systems support the prediction that the birth environment helps shape planetary system architectures.

Three regimes of extrasolar planet radius inferred from host star metallicities.

PubMed

Buchhave, Lars A; Bizzarro, Martin; Latham, David W; Sasselov, Dimitar; Cochran, William D; Endl, Michael; Isaacson, Howard; Juncher, Diana; Marcy, Geoffrey W

2014-05-29

Approximately half of the extrasolar planets (exoplanets) with radii less than four Earth radii are in orbits with short periods. Despite their sheer abundance, the compositions of such planets are largely unknown. The available evidence suggests that they range in composition from small, high-density rocky planets to low-density planets consisting of rocky cores surrounded by thick hydrogen and helium gas envelopes. Here we report the metallicities (that is, the abundances of elements heavier than hydrogen and helium) of more than 400 stars hosting 600 exoplanet candidates, and find that the exoplanets can be categorized into three populations defined by statistically distinct (∼4.5σ) metallicity regions. We interpret these regions as reflecting the formation regimes of terrestrial-like planets (radii less than 1.7 Earth radii), gas dwarf planets with rocky cores and hydrogen-helium envelopes (radii between 1.7 and 3.9 Earth radii) and ice or gas giant planets (radii greater than 3.9 Earth radii). These transitions correspond well with those inferred from dynamical mass estimates, implying that host star metallicity, which is a proxy for the initial solids inventory of the protoplanetary disk, is a key ingredient regulating the structure of planetary systems.

Three regimes of extrasolar planet radius inferred from host star metallicities

PubMed Central

Buchhave, Lars A.; Bizzarro, Martin; Latham, David W.; Sasselov, Dimitar; Cochran, William D.; Endl, Michael; Isaacson, Howard; Juncher, Diana; Marcy, Geoffrey W.

2014-01-01

Approximately half of the extrasolar planets (exoplanets) with radii less than four Earth radii are in orbits with short periods1. Despite their sheer abundance, the compositions of such planets are largely unknown. The available evidence suggests that they range in composition from small, high-density rocky planets to low-density planets consisting of rocky cores surrounded by thick hydrogen and helium gas envelopes. Here we report the metallicities (that is, the abundances of elements heavier than hydrogen and helium) of more than 400 stars hosting 600 exoplanet candidates, and find that the exoplanets can be categorized into three populations defined by statistically distinct (~4.5σ) metallicity regions. We interpret these regions as reflecting the formation regimes of terrestrial-like planets (radii less than 1.7 Earth radii), gas dwarf planets with rocky cores and hydrogen-helium envelopes (radii between 1.7 and 3.9 Earth radii) and ice or gas giant planets (radii greater than 3.9 Earth radii). These transitions correspond well with those inferred from dynamical mass estimates2,3, implying that host star metallicity, which is a proxy for the initial solids inventory of the protoplanetary disk, is a key ingredient regulating the structure of planetary systems. PMID:24870544

Geophysical Monitoring Station (GEMS)

NASA Astrophysics Data System (ADS)

Banerdt, B.; Dehant, V. M.; Lognonne, P.; Smrekar, S. E.; Spohn, T.; GEMS Mission Team

2011-12-01

GEMS (GEophysical Monitoring Station) is one of three missions undergoing Phase A development for possible selection by NASA's Discovery Program. If selected, GEMS will perform the first comprehensive surface-based geophysical investigation of Mars, filling a longstanding gap in the scientific exploration of the solar system. It will illuminate the fundamental processes of terrestrial planet formation and evolution, providing unique and critical information about the initial accretion of the planet, the formation and differentiation of the core and crust, and the subsequent evolution of the interior. The scientific goals of GEMS are to understand the formation and evolution of terrestrial planets through investigation of the interior structure and processes of Mars and to determine its present level of tectonic activity and impact flux. A straightforward set of scientific objectives address these goals: 1) Determine the size, composition and physical state of the core; 2) Determine the thickness and structure of the crust; 3) Determine the composition and structure of the mantle; 4) Determine the thermal state of the interior; 5) Measure the rate and distribution of internal seismic activity; and 6) Measure the rate of impacts on the surface. To accomplish these objectives, GEMS carries a tightly-focused payload consisting of 3 investigations: 1) SEIS, a 6-component, very-broad-band seismometer, with careful thermal compensation/control and a sensitivity comparable to the best terrestrial instruments across a frequency range of 1 mHz to 50 Hz; 2) HP3 (Heat Flow and Physical Properties Package), an instrumented self-penetrating mole system that trails a string of temperature sensors to measure the thermal gradient and conductivity of the upper several meters, and thus the planetary heat flux; and 3) RISE (Rotation and Interior Structure Experiment), which would use the spacecraft X-band communication system to provide precision tracking for planetary dynamical studies. The two instruments are moved from the lander deck to the martian surface by an Instrument Deployment Arm, with an appropriate location identified using an Instrument Deployment Camera. In order to ensure low risk within the tight Discovery cost limits, GEMS reuses the successful Lockheed Martin Phoenix spacecraft design, with a cruise and EDL system that has demonstrated capability for safe landing on Mars with well-understood costs. To take full advantage of this approach, all science requirements (such as instrument mass and power, landing site, and downlinked data volume) strictly conform to existing, demonstrated capabilities of the spacecraft and mission system. It is widely believed that multiple landers making simultaneous measurements (a network) are required to address the objectives for understanding terrestrial planet interiors. Nonetheless, comprehensive measurements from a single geophysical station are extremely valuable, because observations constraining the structure and processes of the deep interior of Mars are virtually nonexistent. GEMS would utilize sophisticated analysis techniques specific to single-station measurements to determine crustal thickness, mantle structure, core state and size, and heat flow, providing our first real look deep beneath the surface of Mars.

Zodiacal Exoplanets in Time: Searching for Young Stars in K2

NASA Astrophysics Data System (ADS)

Morris, Nathan Ryan; Mann, Andrew; Rizzuto, Aaron

2018-01-01

Observations of planetary systems around young stars provide insight into the early stages of planetary system formation. Nearby young open clusters such as the Hyades, Pleiades, and Praesepe provide important benchmarks for the properties of stellar systems in general. These clusters are all known to be less than 1 Gyr old, making them ideal targets for a survey of young planetary systems. Few transiting planets have been detected around clusters stars, however, so this alone is too small of a sample. K2, the revived Kepler mission, has provided a vast number of light curves for young stars in clusters and elsewhere in the K2 field. This provides us with the opportunity to extend the sample of young systems to field stars while calibrating with cluster stars. We compute rotational periods from starspot patterns for ~36,000 K2 targets and use gyrochronological relationships derived from cluster stars to determine their ages. From there, we have begun searching for planets around young stars outside the clusters with the ultimate goal of shedding light on how planets and planetary systems evolve in their early, most formative years.

Scaling up Planetary Dynamo Modeling to Massively Parallel Computing Systems: The Rayleigh Code at ALCF

NASA Astrophysics Data System (ADS)

Featherstone, N. A.; Aurnou, J. M.; Yadav, R. K.; Heimpel, M. H.; Soderlund, K. M.; Matsui, H.; Stanley, S.; Brown, B. P.; Glatzmaier, G.; Olson, P.; Buffett, B. A.; Hwang, L.; Kellogg, L. H.

2017-12-01

In the past three years, CIG's Dynamo Working Group has successfully ported the Rayleigh Code to the Argonne Leadership Computer Facility's Mira BG/Q device. In this poster, we present some our first results, showing simulations of 1) convection in the solar convection zone; 2) dynamo action in Earth's core and 3) convection in the jovian deep atmosphere. These simulations have made efficient use of 131 thousand cores, 131 thousand cores and 232 thousand cores, respectively, on Mira. In addition to our novel results, the joys and logistical challenges of carrying out such large runs will also be discussed.

Shock compression of stishovite and melting of silica at planetary interior conditions

NASA Astrophysics Data System (ADS)

Millot, M.; Dubrovinskaia, N.; Černok, A.; Blaha, S.; Dubrovinsky, L.; Braun, D. G.; Celliers, P. M.; Collins, G. W.; Eggert, J. H.; Jeanloz, R.

2015-01-01

Deep inside planets, extreme density, pressure, and temperature strongly modify the properties of the constituent materials. In particular, how much heat solids can sustain before melting under pressure is key to determining a planet’s internal structure and evolution. We report laser-driven shock experiments on fused silica, α-quartz, and stishovite yielding equation-of-state and electronic conductivity data at unprecedented conditions and showing that the melting temperature of SiO2 rises to 8300 K at a pressure of 500 gigapascals, comparable to the core-mantle boundary conditions for a 5-Earth mass super-Earth. We show that mantle silicates and core metal have comparable melting temperatures above 500 to 700 gigapascals, which could favor long-lived magma oceans for large terrestrial planets with implications for planetary magnetic-field generation in silicate magma layers deep inside such planets.

Partitioning of K, U, and Th between sulfide and silicate liquids - Implications for radioactive heating of planetary cores

NASA Technical Reports Server (NTRS)

Murrell, M. T.; Burnett, D. S.

1986-01-01

Experimental partitioning studies are reported of K, U, and Th between silicate and FeFeS liquids designed to test the proposal that actinide partitioning into sulfide liquids is more important then K partitioning in the radioactive heating of planetary cores. For a basaltic liquid at 1450 C and 1.5 GPa, U partitioning into FeFeS liquids is five times greater than K partitioning. A typical value for the liquid partition coefficient for U from a granitic silicate liquid at one atmosphere at 1150 C and low fO2 is about 0.02; the coefficient for Th is similar. At low fO2 and higher temperature, experiments with basaltic liquids produce strong Ca and U partitioning into the sulfide liquid with U coefficient greater than one. The Th coefficient is less strongly affected.

The relationship between crustal tectonics and internal evolution in the moon and Mercury

NASA Technical Reports Server (NTRS)

Solomon, S. C.

1977-01-01

The relationship between crustal tectonics and thermal evolution is discussed in terms of the moon and Mercury. Finite strain theory and depth and temperature-dependent thermal expansion are used to evaluate previous conclusions about early lunar history. Factors bringing about core differentiation in the first 0.6 b.y. of Mercurian evolution are described. The influence of concentrating radioactive heat sources located in Mercury's crust on the predicted contraction is outlined. The predicted planetary volume change is explored with regard to quantitative limits on the extent of Mercurian core solidification. Lunar and Mercurian thermal stresses involved in thermal evolution are reviewed, noting the history of surface volcanism. It is concluded that surface faulting and volcanism are closely associated with the thermal evolution of the whole planetary volume. As the planet cools or is heated, several types of tectonic and volcanic effects may be produced by thermal stress occurring in the lithosphere.

A New well-constrained surface density profile of solids in Sun's protoplanetary disk: Implications for the formation of the inner Solar System

NASA Astrophysics Data System (ADS)

Aggarwal, Y. P.

2016-12-01

We present a highly correlated and significant relationship between a planet's rock mass of solids/heavy elements and its orbital radius found by non-linear regression analysis using existing data for all 8 planets except Mars. On its basis, we define the area A(r) of a planet's accretionary zone (AZ) and the surface density of solids σ(r) in Sun's disk that differs markedly from the commonly used minimum-mass solar nebula (MMSN) profile, and unlike MMSN is well constrained and does not produce contradictory results. A(r) ≈ π (1.59 r2 ̶ 0.16); and σ(r) = (5.95±0.1) (r - 6.4)- α where r is the heliocentric distance in astronomical units (AU), A(r) in AU², σ(r) in gm/cm², and α=0 for r ≤7.4AU, and α=1.39±0.04 for r ˃7.4AU. Using these relationships we determine the isolation masses of planetary embryos, define each planet's AZ, and analyze the size and spatial distribution of protoplanets within the AZ of terrestrial planets assuming typical protoplanet separations of 7-10 mutual Hill radii. The results: 1) show that Mars mass matches (±1%) with the isolation mass of its embryo and that its orbit at 1.52AU lies within its predicted AZ (1.47-1.54AU), establishing that Mars is a planetary embryo that formed in situ; 2) reveal that Mars failed to grow fully because there were not enough solids interior to Mars orbit to fully form all four terrestrial planets and because Jupiter accreted planetary embryos and planetesimals from the Mars-asteroid region, essentially depleting it; 3) imply that asteroids are remnant planetesimals that escaped accretion by Jupiter; 4) indicate that despite its small mass, Mercury is not a planetary embryo and that it probably completed its formation much earlier than Earth; and 5) suggest that Theia, the protoplanet thought to have impacted proto-Earth forming the Moon, originated near 1.45 AU with a mass and possibly composition similar to that of Mars. Notably, the results do not support the Grand Tack model or the Viscously Stirred Pebble-Accretion model for the structure of the Mars-asteroid region; nor do they support the hypothesis that the high iron content of Mercury's core is the result of an impact with a large planetesimal that stripped away much of Mercury's crust and mantle.

Feasibility of Dynamic Stability Measurements of Planetary Entry Capsules Using MSBS

NASA Technical Reports Server (NTRS)

Britcher, Colin; Schoenenberger, Mark

2015-01-01

The feasibility of conducting dynamic stability testing of planetary entry capsules at low supersonic Mach numbers using a Magnetic Suspension and Balance System (MSBS) is reviewed. The proposed approach would employ a spherical magnetic core, exert control in three degrees-of-freedom (i.e. x, y, z translations) and allow the model to freely rotate in pitch, yaw, and roll. A proof-of-concept system using an existing MSBS electromagnet array in a subsonic wind tunnel is described, with future potential for development of a new system for a supersonic wind tunnel.

KSC-2011-6318

NASA Image and Video Library

2011-08-05

CAPE CANAVERAL, Fla. -- Reflected in water surrounding Space Launch Complex 41 on Cape Canaveral Air Force Station in Florida, fire lights up a crystal-clear blue sky as a United Launch Alliance Atlas V rocket lofts NASA's Juno planetary probe into space. Liftoff was at 12:25 p.m. EDT Aug. 5. The solar-powered spacecraft will orbit Jupiter's poles 33 times to find out more about the gas giant's origins, structure, atmosphere and magnetosphere and investigate the existence of a solid planetary core. For more information, visit www.nasa.gov/juno. Photo credit: Courtesy Scott Andrews

KSC-2011-6313

NASA Image and Video Library

2011-08-05

CAPE CANAVERAL, Fla. -- Fire lights up a crystal-clear blue sky on Space Launch Complex 41 on Cape Canaveral Air Force Station in Florida as a United Launch Alliance Atlas V rocket lofts NASA's Juno planetary probe into space. Liftoff was at 12:25 p.m. EDT Aug. 5. The solar-powered spacecraft will orbit Jupiter's poles 33 times to find out more about the gas giant's origins, structure, atmosphere and magnetosphere and investigate the existence of a solid planetary core. For more information, visit www.nasa.gov/juno. Photo credit: NASA/Tony Gray and Don Kight

KSC-2011-6311

NASA Image and Video Library

2011-08-05

CAPE CANAVERAL, Fla. -- Fire lights up a crystal-clear blue sky on Space Launch Complex 41 on Cape Canaveral Air Force Station in Florida as a United Launch Alliance Atlas V rocket lofts NASA's Juno planetary probe into space. Liftoff was at 12:25 p.m. EDT Aug. 5. The solar-powered spacecraft will orbit Jupiter's poles 33 times to find out more about the gas giant's origins, structure, atmosphere and magnetosphere and investigate the existence of a solid planetary core. For more information, visit www.nasa.gov/juno. Photo credit: NASA/Tony Gray and Don Kight

KSC-2011-6317

NASA Image and Video Library

2011-08-05

CAPE CANAVERAL, Fla. -- Fire lights up a crystal-clear blue sky on Space Launch Complex 41 on Cape Canaveral Air Force Station in Florida as a United Launch Alliance Atlas V rocket lofts NASA's Juno planetary probe into space. Liftoff was at 12:25 p.m. EDT Aug. 5. The solar-powered spacecraft will orbit Jupiter's poles 33 times to find out more about the gas giant's origins, structure, atmosphere and magnetosphere and investigate the existence of a solid planetary core. For more information, visit www.nasa.gov/juno. Photo credit: Courtesy Scott Andrews

KSC-2011-6312

NASA Image and Video Library

2011-08-05

CAPE CANAVERAL, Fla. -- Fire lights up a crystal-clear blue sky on Space Launch Complex 41 on Cape Canaveral Air Force Station in Florida as a United Launch Alliance Atlas V rocket lofts NASA's Juno planetary probe into space. Liftoff was at 12:25 p.m. EDT Aug. 5. The solar-powered spacecraft will orbit Jupiter's poles 33 times to find out more about the gas giant's origins, structure, atmosphere and magnetosphere and investigate the existence of a solid planetary core. For more information, visit www.nasa.gov/juno. Photo credit: NASA/Tony Gray and Don Kight

What's new on the moon?

NASA Technical Reports Server (NTRS)

1976-01-01

As a result of the Apollo program and other lunar probes, questions that remained unsolved during centuries of speculation and scientific study can now be answered concerning the composition, core, surface, age, and history of the moon. Data obtained from lunar samples and instruments on the lunar surface are being used to gain insight into the history of the earth and the other planets, planetary evolution, the development of planetary magnetic fields, the nature of the solar wind, and how the Sun operates. Projects suggested for using the moon to increase understanding of geophysics are described.

TRIGGERING COLLAPSE OF THE PRESOLAR DENSE CLOUD CORE AND INJECTING SHORT-LIVED RADIOISOTOPES WITH A SHOCK WAVE. II. VARIED SHOCK WAVE AND CLOUD CORE PARAMETERS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boss, Alan P.; Keiser, Sandra A., E-mail: boss@dtm.ciw.edu, E-mail: keiser@dtm.ciw.edu

2013-06-10

A variety of stellar sources have been proposed for the origin of the short-lived radioisotopes that existed at the time of the formation of the earliest solar system solids, including Type II supernovae (SNe), asymptotic giant branch (AGB) and super-AGB stars, and Wolf-Rayet star winds. Our previous adaptive mesh hydrodynamics models with the FLASH2.5 code have shown which combinations of shock wave parameters are able to simultaneously trigger the gravitational collapse of a target dense cloud core and inject significant amounts of shock wave gas and dust, showing that thin SN shocks may be uniquely suited for the task. However,more » recent meteoritical studies have weakened the case for a direct SN injection to the presolar cloud, motivating us to re-examine a wider range of shock wave and cloud core parameters, including rotation, in order to better estimate the injection efficiencies for a variety of stellar sources. We find that SN shocks remain as the most promising stellar source, though planetary nebulae resulting from AGB star evolution cannot be conclusively ruled out. Wolf-Rayet (WR) star winds, however, are likely to lead to cloud core shredding, rather than to collapse. Injection efficiencies can be increased when the cloud is rotating about an axis aligned with the direction of the shock wave, by as much as a factor of {approx}10. The amount of gas and dust accreted from the post-shock wind can exceed that injected from the shock wave, with implications for the isotopic abundances expected for a SN source.« less

Free and Open Source Software for Geospatial in the field of planetary science

NASA Astrophysics Data System (ADS)

Frigeri, A.

2012-12-01

Information technology applied to geospatial analyses has spread quickly in the last ten years. The availability of OpenData and data from collaborative mapping projects increased the interest on tools, procedures and methods to handle spatially-related information. Free Open Source Software projects devoted to geospatial data handling are gaining a good success as the use of interoperable formats and protocols allow the user to choose what pipeline of tools and libraries is needed to solve a particular task, adapting the software scene to his specific problem. In particular, the Free Open Source model of development mimics the scientific method very well, and researchers should be naturally encouraged to take part to the development process of these software projects, as this represent a very agile way to interact among several institutions. When it comes to planetary sciences, geospatial Free Open Source Software is gaining a key role in projects that commonly involve different subjects in an international scenario. Very popular software suites for processing scientific mission data (for example, ISIS) and for navigation/planning (SPICE) are being distributed along with the source code and the interaction between user and developer is often very strict, creating a continuum between these two figures. A very widely spread library for handling geospatial data (GDAL) has started to support planetary data from the Planetary Data System, and recent contributions enabled the support to other popular data formats used in planetary science, as the Vicar one. The use of Geographic Information System in planetary science is now diffused, and Free Open Source GIS, open GIS formats and network protocols allow to extend existing tools and methods developed to solve Earth based problems, also to the case of the study of solar system bodies. A day in the working life of a researcher using Free Open Source Software for geospatial will be presented, as well as benefits and solutions to possible detriments coming from the effort required by using, supporting and contributing.

The Chicxulub Multiring Impact Crater and the Cretaceous/Paleogene Boundary: Results From Geophysical Surveys and Drilling

NASA Astrophysics Data System (ADS)

Urrutia-Fucugauchi, J.; Perez-Cruz, Ligia

2010-03-01

The Chicxulub crater has attracted considerable attention as one of the three largest terrestrial impact structures and its association with the Cretaceous/Paleogene boundary (K/Pg). Chicxulub is a 200 km-diameter multi-ring structure formed 65.5 Ma ago in the Yucatan carbonate platform in the southern Gulf of Mexico and which has since been buried by Paleogene and Neogene carbonates. Chicxulub is one of few large craters with preserved ejecta deposits, which include the world-wide K/Pg boundary clay layer. The impact has been related to the global major environmental and climatic effects and the organism mass extinction that mark the K/Pg boundary, which affected more than 70 % of organisms, including the dinosaurs, marine and flying reptiles, ammonites and a large part of the marine microorganisms. The impact and crater formation occur instantaneously, with excavation of the crust down to 25 km depths in fractions of second and lower crust uplift and crater formation in a few hundreds of seconds. Energy released by impact and crustal deformation generates seismic waves traveling the whole Earth, and resulting in intense fracturing and deformation at the target site. Understanding of the physics of impacts on planetary surfaces and modeling of processes of crustal deformation, rheological behavior of materials at high temperatures and pressures remain a major challenge in geosciences. Study of the Chicxulub crater and the global effects and mass extinction requires inter- and multidisciplinary approaches, with researchers from many diverse fields beyond the geosciences. With no surface exposures, geophysical surveys and drilling are required to study the crater. Differential compaction between the impact breccias and the surrounding carbonate rocks has produced a ring-fracture structure that at the surface reflects in a small topographic depression and the karstic cenote ring. The crater structure, located half offshore and half on-land, has been imaged by different geophysical aerial, land and marine methods including gravity, magnetics, electromagnetics and seismic refraction and reflection. The impact lithologies and carbonate sequence have been cored as part of several drilling projects. Here we analyze the stratigraphy of Chicxulub from borehole logging data and core analyses, with particular reference to studies on CSDP Yaxcopoil-1 and UNAM Santa Elena boreholes. Analyses of core samples have examined the stratigraphy of the cover carbonate sequence, impact breccia contact and implications for impact age, K/Pg global correlations and paleoenvironmental conditions following impact. The K/Pg age for Chicxulub has been supported from different studies, including Ar/Ar dating, magnetic polarity stratigraphy, geochemistry and biostratigraphy. A Late Maastrichtian age has also been proposed for Chicxulub from studies in Yaxcopoil-1 basal Paleocene carbonates, with impact occurring 300 ka earlier predating the K/Pg boundary. This proposal calls attention to the temporal resolution of stratigraphic and chronological methods, and the need for further detailed analyses of the basal carbonate sections in existing boreholes and new drilling/coring projects. Stratigraphy of impact ejecta and basal sediments in Yaxcopoil-1 and UNAM boreholes indicates a hiatus in the basal sequence. Modeling of post- impact processes suggest erosion effects due to seawater back surge, block slumping and partial rim collapse of post-impact crater modification. Analyses of stable isotopes and magnetostratigraphic data for the Paleocene carbonate sequences in Yaxcopoil-1 and Santa Elena boreholes permit to investigate the post- impact processes, depositional conditions and age of basal sediments. Correlation of stable isotopes with the global pattern for marine carbonate sediments provides a stratigraphic framework for the basal Paleocene carbonates. The analyses confirm a K/Pg boundary age for the Chicxulub impact. References: Collins et al, 2008. Earth Planetary Science Letters 270, 221-230; Gulick et al, 2008. Nature Geoscience 1, 131-135; Hildebrand et al, 1991. Geology 19: 867-871; Hildebrand, A.R. et al, 1998. Geological Society Sp. Publ 140, 153-173; Kring et al., 2004. Meteoritics Planetary Science 39, 879-897; Sharpton et al, 1992. Nature 359: 819-821; Urrutia Fucugauchi et al, 2004. Meteoritics Planetary Science 39: 787-790; Urrutia Fucugauchi et al, 2008. Comptes Rendus Geosciences 341, 801-810; Urrutia Fucugauchi & Perez Cruz, 2009. International Geology Review 51, doi: 10.1080/00206810902867161.

Giant Planets: Good Neighbors for Habitable Worlds?

NASA Astrophysics Data System (ADS)

Georgakarakos, Nikolaos; Eggl, Siegfried; Dobbs-Dixon, Ian

2018-04-01

The presence of giant planets influences potentially habitable worlds in numerous ways. Massive celestial neighbors can facilitate the formation of planetary cores and modify the influx of asteroids and comets toward Earth analogs later on. Furthermore, giant planets can indirectly change the climate of terrestrial worlds by gravitationally altering their orbits. Investigating 147 well-characterized exoplanetary systems known to date that host a main-sequence star and a giant planet, we show that the presence of “giant neighbors” can reduce a terrestrial planet’s chances to remain habitable, even if both planets have stable orbits. In a small fraction of systems, however, giant planets slightly increase the extent of habitable zones provided that the terrestrial world has a high climate inertia. In providing constraints on where giant planets cease to affect the habitable zone size in a detrimental fashion, we identify prime targets in the search for habitable worlds.

Tidal disruption of inviscid protoplanets

NASA Technical Reports Server (NTRS)

Boss, Alan P.; Cameron, A. G. W.; Benz, W.

1991-01-01

Roche showed that equilibrium is impossible for a small fluid body synchronously orbiting a primary within a critical radius now termed the Roche limit. Tidal disruption of orbitally unbound bodies is a potentially important process for planetary formation through collisional accumulation, because the area of the Roche limit is considerably larger then the physical cross section of a protoplanet. Several previous studies were made of dynamical tidal disruption and different models of disruption were proposed. Because of the limitation of these analytical models, we have used a smoothed particle hydrodynamics (SPH) code to model the tidal disruption process. The code is basically the same as the one used to model giant impacts; we simply choose impact parameters large enough to avoid collisions. The primary and secondary both have iron cores and silicate mantles, and are initially isothermal at a molten temperature. The conclusions based on the analytical and numerical models are summarized.

Testing the Planet-Metallicity Correlation in M-dwarfs with Gemini GNIRS Spectra

NASA Astrophysics Data System (ADS)

Hobson, M. J.; Jofré, E.; García, L.; Petrucci, R.; Gómez, M.

2018-04-01

While the planet-metallicity correlation for FGK main-sequence stars hosting giant planets is well established, it is less clear for M-dwarf stars. We determine stellar parameters and metallicities for 16 M-dwarf stars, 11 of which host planets, with near-infrared spectra from the Gemini Near-Infrared Spectrograph (GNIRS). We find that M-dwarfs with planets are preferentially metal-rich compared to those without planets. This result is supported by the analysis of a larger catalogue of 18 M stars with planets and 213 M stars without known planets T15, and demonstrates the utility of GNIRS spectra to obtain reliable stellar parameters of M stars. We also find that M dwarfs with giant planets are preferentially more metallic than those with low-mass planets, in agreement with previous results for solar-type stars. These results favor the core accretion model of planetary formation.

Metal-Silicate Segregation in Asteroidal Meteorites

NASA Technical Reports Server (NTRS)

Herrin, Jason S.; Mittlefehldt, D. W.

2006-01-01

A fundamental process of planetary differentiation is the segregation of metal-sulfide and silicate phases, leading eventually to the formation of a metallic core. Asteroidal meteorites provide a glimpse of this process frozen in time from the early solar system. While chondrites represent starting materials, iron meteorites provide an end product where metal has been completely concentrated in a region of the parent asteroid. A complimentary end product is seen in metal-poor achondrites that have undergone significant igneous processing, such as angrites, HED's and the majority of aubrites. Metal-rich achondrites such as acapulcoite/lodranites, winonaites, ureilites, and metal-rich aubrites may represent intermediate stages in the metal segregation process. Among these, acapulcoite-lodranites and ureilites are examples of primary metal-bearing mantle restites, and therefore provide an opportunity to observe the metal segregation process that was captured in progress. In this study we use bulk trace element compositions of acapulcoites-lodranites and ureilites for this purpose.

SHINE, The SpHere INfrared survey for Exoplanets

NASA Astrophysics Data System (ADS)

Chauvin, G.; Desidera, S.; Lagrange, A.-M.; Vigan, A.; Feldt, M.; Gratton, R.; Langlois, M.; Cheetham, A.; Bonnefoy, M.; Meyer, M.

2017-12-01

The SHINE survey for SPHERE High-contrast ImagiNg survey for Exoplanets, is a large near-infrared survey of 400-600 young, nearby stars and represents a significant component of the SPHERE consortium Guaranteed Time Observations consisting in 200 observing nights. The scientific goals are: i) to characterize known planetary systems (architecture, orbit, stability, luminosity, atmosphere); ii) to search for new planetary systems using SPHERE's unprecedented performance; and finally iii) to determine the occurrence and orbital and mass function properties of the wide-orbit, giant planet population as a function of the stellar host mass and age. Combined, the results will increase our understanding of planetary atmospheric physics and the processes of planetary formation and evolution.

From planets to crops and back: Remote sensing makes sense

NASA Astrophysics Data System (ADS)

Mustard, John F.

2017-04-01

Remotely sensed data and the instruments that acquire them are core parts of Earth and planetary observation systems. They are used to quantify the Earth's interconnected systems, and remote sensing is the only way to get a daily, or more frequent, snapshot of the status of the Earth. It really is the Earth's stethoscope. In a similar manner remote sensing is the rock hammer of the planetary scientist and the only way comprehensive data sets can be acquired. To risk offending many remotely sensed data acquired across the electromagnetic spectrum, it is the tricorder to explore known and unknown planets. Arriving where we are today in the use of remotely sensed data in the solar system has been a continually evolving synergy between Earth observation, planetary exploration, and fundamental laboratory work.

Fluorine-Rich Planetary Environments as Possible Habitats for Life

PubMed Central

Budisa, Nediljko; Kubyshkin, Vladimir; Schulze-Makuch, Dirk

2014-01-01

In polar aprotic organic solvents, fluorine might be an element of choice for life that uses selected fluorinated building blocks as monomers of choice for self-assembling of its catalytic polymers. Organofluorine compounds are extremely rare in the chemistry of life as we know it. Biomolecules, when fluorinated such as peptides or proteins, exhibit a “fluorous effect”, i.e., they are fluorophilic (neither hydrophilic nor lipophilic). Such polymers, capable of creating self-sorting assemblies, resist denaturation by organic solvents by exclusion of fluorocarbon side chains from the organic phase. Fluorous cores consist of a compact interior, which is shielded from the surrounding solvent. Thus, we can anticipate that fluorine-containing “teflon”-like or “non-sticking” building blocks might be monomers of choice for the synthesis of organized polymeric structures in fluorine-rich planetary environments. Although no fluorine-rich planetary environment is known, theoretical considerations might help us to define chemistries that might support life in such environments. For example, one scenario is that all molecular oxygen may be used up by oxidation reactions on a planetary surface and fluorine gas could be released from F-rich magma later in the history of a planetary body to result in a fluorine-rich planetary environment. PMID:25370378

Hot super-Earths and giant planet cores from different migration histories

NASA Astrophysics Data System (ADS)

Cossou, Christophe; Raymond, Sean N.; Hersant, Franck; Pierens, Arnaud

2014-09-01

Planetary embryos embedded in gaseous protoplanetary disks undergo Type I orbital migration. Migration can be inward or outward depending on the local disk properties but, in general, only planets more massive than several M⊕ can migrate outward. Here we propose that an embryo's migration history determines whether it becomes a hot super-Earth or the core of a giant planet. Systems of hot super-Earths (or mini-Neptunes) form when embryos migrate inward and pile up at the inner edge of the disk. Giant planet cores form when inward-migrating embryos become massive enough to switch direction and migrate outward. We present simulations of this process using a modified N-body code, starting from a swarm of planetary embryos. Systems of hot super-Earths form in resonant chains with the innermost planet at or interior to the disk inner edge. Resonant chains are disrupted by late dynamical instabilities triggered by the dispersal of the gaseous disk. Giant planet cores migrate outward toward zero-torque zones, which move inward and eventually disappear as the disk disperses. Giant planet cores migrate inward with these zones and are stranded at ~1-5 AU. Our model reproduces several properties of the observed extra-solar planet populations. The frequency of giant planet cores increases strongly when the mass in solids is increased, consistent with the observed giant exoplanet - stellar metallicity correlation. The frequency of hot super-Earths is not a function of stellar metallicity, also in agreement with observations. Our simulations can reproduce the broad characteristics of the observed super-Earth population.

First Numerical Simulations of Turbulent Dynamos Driven by Libration, Precession and Tides in Triaxial Ellipsoids - An Alternative Route for Planetary Magnetism

NASA Astrophysics Data System (ADS)

Le Bars, M.; Kanuganti, S. R.; Favier, B.

2017-12-01

Most of the time, planetary dynamos are - tacitly or not - associated with thermo-solutal convection. The convective dynamo model has indeed proven successful to explain the current Earth's magnetic field. However, its results are sometimes difficult to reconcile with observational data and its validity can be questioned for several celestial bodies. For instance, the small size of the Moon and Ganymede makes it difficult to maintain a sufficient temperature gradient to sustain convection and to explain their past and present magnetic fields, respectively. The same caveat applies to the growing number of planetesimals shown to have generated magnetic fields in their early history. Finally, the energy budget of the early Earth is difficult to reconcile with a convective dynamo before the onset of inner core growth. Significant effort has thus been put into finding new routes for planetary dynamo. In particular, the rotational dynamics of planets, moons and small bodies, where their average spinning motion is periodically perturbed by the small mechanical forcings of libration, precession and/or tides, is now widely accepted as an efficient source of core turbulence. The underlying mechanism relies on a parametric instability where the inertial waves of the rotating fluid core are resonantly excited by the small forcing, leading to exponential growth and bulk filling intense motions, pumping their energy from the orbital dynamics. Dynamos driven by mechanical forcing have been suggested for the Moon, Mars, Io, the early Earth, etc. However, the real dynamo capacity of the corresponding flows has up-to-now been studied only in very limited cases, with simplified spherical/spheroidal geometries and/or overly viscous fluids. We will present here the first numerical simulations of dynamos driven by libration, precession and tides, in the triaxial ellipsoidal geometry and in the turbulent regime relevant for planetary cores. We will describe the numerical techniques required to tackle this challenge and present the first results describing the associated magnetic field in terms of amplitude, energy budget, and spatiotemporal signature. We hope to motivate others to participate in the exploration of the wide parameter space, a necessary work for addressing the variety of observed past and present magnetic fields.

Application of shock wave data to earth and planetary science

NASA Technical Reports Server (NTRS)

Ahrens, T. J.

1985-01-01

It is pointed out that shock wave data for: (1) low temperature condensable gases H2 and He, (2) H2O, CH4, NH3, CO, CO2, and N2 ices, and (3) silicates, metals, oxides and sulfides have many applications in geophysics and planetary science. The present paper is concerned with such applications. The composition of planetary interiors is discussed, taking into account the division of the major constituent of the planets in three groups on the basis of 'cosmic abundance' arguments, the H-He mixtures in the case of Jupiter and Saturn, shock wave data for hydrogen, and constraints on the internal structure of Uranus and Neptune. Attention is also given to the earth's mantle, shock wave data for mantle materials, the earth's core, impacts on planetary surfaces, elastic wave velocities as a function of pressure along the Hugoniot of iron, and reactions which yield the CO2 bearing atmospheres for Venus, earth, and Mars.

Tectonomagmatic evolution of the Earth and Moon

NASA Astrophysics Data System (ADS)

Sharkov, E. V.; Bogatikov, O. A.

2010-03-01

The Earth and Moon evolved following a similar scenario. The formation of their protocrusts started with upward crystallization of global magmatic oceans. As a result of this process, easily fusible components accumulated in the course of fractional crystallization of melt migrating toward the surface. The protocrusts (granitic in the Earth and anorthositic in the Moon) are retained in ancient continents. The tectonomagmatic activity at the early stage of planet evolution was related to the ascent of mantle plume of the first generation composed of mantle material depleted due to the formation of protocrusts. The regions of extension, rise, and denudation were formed in the Earth above the diffluent heads of such superplumes (Archean granite-greenstone domains and Paleoproterozoic cratons), whereas granulite belts as regions of compression, subsidence, and sedimentation arose above descending mantle flows. The situation may be described in terms of plume tectonics. Gentle uplifts and basins ( thalassoids) in lunar continents are probable analogues of these structural elements in the Moon. The period of 2.3-2.0 Ga ago was a turning point in the tectonomagmatic evolution of the Earth, when geochemically enriched Fe-Ti picrites and basalts typical of Phanerozoic within-plate magmatism became widespread. The environmental setting on the Earth’s surface changed at that time, as well. Plate tectonics, currently operating on a global scale, started to develop about ˜2 Ga ago. This turn was related to the origination of thermochemical mantle plumes of the second generation at the interface of the liquid Fe-Ni core and silicate mantle. A similar turning point in the lunar evolution probably occurred 4.2-3.9 Ga ago and completed with the formation of large depressions ( seas) with thinned crust and vigorous basaltic magmatism. Such a sequence of events suggests that qualitatively new material previously retained in the planets’ cores was involved in tectonomagmatic processes at the middle stage of planetary evolution. This implies that the considered bodies initially were heterogeneous and were then heated from above to the bottom by propagation of a thermal wave accompanied by cooling of outer shells. Going through the depleted mantle, this wave generated thermal superplumes of the first generation. Cores close to the Fe + FeS eutectics in composition were affected by this wave in the last turn. The melting of the cores resulted in the appearance of thermochemical superplumes and corresponding irreversible rearrangement of geotectonic processes.

Communicating Scientific Research to Non-Specialists

NASA Astrophysics Data System (ADS)

Holman, Megan

Public outreach to effectively communicate current scientific advances is an essential component of the scientific process. The challenge in making this information accessible is forming a clear, accurate, and concise version of the information from a variety of different sources, so that the information is understandable and compelling to non-specialists in the general public. We are preparing a magazine article about planetary system formation. This article will include background information about star formation and different theories and observations of planet formation to provide context. We will then discuss the latest research and theories describing how planetary systems may be forming in different areas of the universe. We demonstrate here the original professional-level scientific work alongside our public-level explanations and original graphics to demonstrate our editorial process.

Formation of Planetary Systems

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; DeVincenzi, Donald (Technical Monitor)

1999-01-01

An overview of current theories of star and planet formation is presented. These models are based upon observations of the Solar System and of young stars and their environments. They predict that rocky planets should form around most single stars, although it is possible that in some cases such planets are lost to orbital decay within the protoplanetary disk. The frequency of formation of gas giant planets is more difficult to predict theoretically. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth like terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates.

Growth and evolution of satellites in a Jovian massive disc

NASA Astrophysics Data System (ADS)

Moraes, R. A.; Kley, W.; Vieira Neto, E.

2018-03-01

The formation of satellite systems in circum-planetary discs is considered to be similar to the formation of rocky planets in a proto-planetary disc, especially super-Earths. Thus, it is possible to use systems with large satellites to test formation theories that are also applicable to extrasolar planets. Furthermore, a better understanding of the origin of satellites might yield important information about the environment near the growing planet during the last stages of planet formation. In this work, we investigate the formation and migration of the Jovian satellites through N-body simulations. We simulated a massive, static, low-viscosity, circum-planetary disc in agreement with the minimum mass sub-nebula model prescriptions for its total mass. In hydrodynamic simulations, we found no signs of gaps, therefore type II migration is not expected. Hence, we used analytic prescriptions for type I migration, eccentricity and inclination damping, and performed N-body simulations with damping forces added. Detailed parameter studies showed that the number of final satellites is strong influenced by the initial distribution of embryos, the disc temperature, and the initial gas density profile. For steeper initial density profiles, it is possible to form systems with multiple satellites in resonance while a flatter profile favours the formation of satellites close to the region of the Galilean satellites. We show that the formation of massive satellites such as Ganymede and Callisto can be achieved for hotter discs with an aspect ratio of H/r ˜ 0.15 for which the ice line was located around 30RJ.

Testing the chondrule-rich accretion model for planetary embryos using calcium isotopes

NASA Astrophysics Data System (ADS)

Amsellem, Elsa; Moynier, Frédéric; Pringle, Emily A.; Bouvier, Audrey; Chen, Heng; Day, James M. D.

2017-07-01

Understanding the composition of raw materials that formed the Earth is a crucial step towards understanding the formation of terrestrial planets and their bulk composition. Calcium is the fifth most abundant element in terrestrial planets and, therefore, is a key element with which to trace planetary composition. However, in order to use Ca isotopes as a tracer of Earth's accretion history, it is first necessary to understand the isotopic behavior of Ca during the earliest stages of planetary formation. Chondrites are some of the oldest materials of the Solar System, and the study of their isotopic composition enables understanding of how and in what conditions the Solar System formed. Here we present Ca isotope data for a suite of bulk chondrites as well as Allende (CV) chondrules. We show that most groups of carbonaceous chondrites (CV, CI, CR and CM) are significantly enriched in the lighter Ca isotopes (δ 44 / 40 Ca = + 0.1 to + 0.93 ‰) compared with bulk silicate Earth (δ 44 / 40 Ca = + 1.05 ± 0.04 ‰, Huang et al., 2010) or Mars, while enstatite chondrites are indistinguishable from Earth in Ca isotope composition (δ 44 / 40 Ca = + 0.91 to + 1.06 ‰). Chondrules from Allende are enriched in the heavier isotopes of Ca compared to the bulk and the matrix of the meteorite (δ 44 / 40 Ca = + 1.00 to + 1.21 ‰). This implies that Earth and Mars have Ca isotope compositions that are distinct from most carbonaceous chondrites but that may be like chondrules. This Ca isotopic similarity between Earth, Mars, and chondrules is permissive of recent dynamical models of planetary formation that propose a chondrule-rich accretion model for planetary embryos.

The SOAPS project - Spin-orbit alignment of planetary systems. Exoplanets' evolution histories in systems with different architectures

NASA Astrophysics Data System (ADS)

Faedi, F.; Gómez Maqueo Chew, Y.; Fossati, L.; Pollacco, D.; McQuillan, A.; Hebb, L.; Chaplin, W. J.; Aigrain, S.

2013-04-01

The wealth of information rendered by Kepler planets and planet candidates is indispensable for statistically significant studies of distinct planet populations, in both single and multiple systems. Empirical evidences suggest that Kepler's planet population shows different physical properties as compared to the bulk of known exoplanets. The SOAPS project, aims to shed light on Kepler's planets formation, their migration and architecture. By measuring v sini accurately for Kepler hosts with rotation periods measured from their high-precision light curves, we will assess the alignment of the planetary orbit with respect to the stellar spin axis. This degree of alignment traces the formation history and evolution of the planetary systems, and thus, allows to distinguish between different proposed migration theories. SOAPS will increase by a factor of 2 the number of spin-orbit alignment measurements pushing the parameters space down to the SuperEarth domain. Here we present our preliminary results.

Occurrence of Earth-like bodies in planetary systems.

PubMed

Wetherill, G W

1991-08-02

Present theories of terrestrial planet formation predict the rapid ;;runaway formation'' of planetary embryos. The sizes of the embryos increase with heliocentric distance. These embryos then merge to form planets. In earlier Monte Carlo simulations of the merger of these embryos it was assumed that embryos did not form in the asteroid belt, but this assumption may not be valid. Simulations in which runaways were allowed to form in the asteroid belt show that, although the initial distributions of mass, energy, and angular momentum are different from those observed today, during the growth of the planets these distributions spontaneously evolve toward those observed, simply as a result of known solar system processes. Even when a large planet analogous to ;;Jupiter'' does not form, an Earth-sized planet is almost always found near Earth's heliocentric distance. These results suggest that occurrence of Earth-like planets may be a common feature of planetary systems.

Occurrence of earth-like bodies in planetary systems

NASA Technical Reports Server (NTRS)

Wetherill, George W.

1991-01-01

Present theories of terrestrial planet formation predict the rapid 'runaway formation' of planetary embryos. The sizes of the embryos increase with heliocentric distance. These embryos then emerge to form planets. In earlier Monte Carlo simulations of the merger of these embryos it was assumed that embryos did not form in the asteroid belt, but this assumption may not be valid. Simulations in which runaways were allowed to form in the asteroid belt show that, although the initial distributions of mass, energy, and angular momentum are different from those observed today, during the growth of the planets these distributions spontaneously evolve toward those observed, simply as a result of known solar system processes. Even when a large planet analogous to 'Jupiter' does not form, an earth-sized planet is almost always found near earth's heliocentric distance. These results suggest that occurrence of earthlike planets may be a common feature of planetary systems.

The (Un)Lonely Planet Guide: Formation and Evolution of Planetary Systems from a ``Blue Dots'' Perspective

NASA Astrophysics Data System (ADS)

Meyer, M. R.

2010-10-01

In this contribution I summarize some recent successes, and focus on remaining challenges, in understanding the formation and evolution of planetary systems in the context of the Blue Dots initiative. Because our understanding is incomplete, we cannot yet articulate a design reference mission engineering matrix suitable for an exploration mission where success is defined as obtaining a spectrum of a potentially habitable world around a nearby star. However, as progress accelerates, we can identify observational programs that would address fundamental scientific questions through hypothesis testing such that the null result is interesting.

Evidence for dust grain growth in young circumstellar disks.

PubMed

Throop, H B; Bally, J; Esposito, L W; McCaughrean, M J

2001-06-01

Hundreds of circumstellar disks in the Orion nebula are being rapidly destroyed by the intense ultraviolet radiation produced by nearby bright stars. These young, million-year-old disks may not survive long enough to form planetary systems. Nevertheless, the first stage of planet formation-the growth of dust grains into larger particles-may have begun in these systems. Observational evidence for these large particles in Orion's disks is presented. A model of grain evolution in externally irradiated protoplanetary disks is developed and predicts rapid particle size evolution and sharp outer disk boundaries. We discuss implications for the formation rates of planetary systems.

The Role of Cooling in Pahohoe Emplacement on Planetary Surfaces.

NASA Technical Reports Server (NTRS)

Glaze, L. S.; Baloga, S. M.

2015-01-01

Abundant evidence is emerging that many lavas on Mars were emplaced as slow-moving pahoehoe flows. Models for such scenarios contrast sharply with those for steep-sloped applications where gravity is the dominant force. The mode of flow emplacement on low slopes is characterized by toe formation and inflation. In the latter phase of pahoehoe flow emplacement, stagnation, inflation, and toe formation are most closely tied to the final topography, dimensions, and morphologic features. This mode of emplacement is particularly relevant to the low slopes of planetary surfaces such as the plains of Mars, Io and the Moon.

Shock wave propagation in layered planetary embryos

NASA Astrophysics Data System (ADS)

Arkani-Hamed, Jafar; Ivanov, Boris A.

2014-05-01

The propagation of impact-induced shock wave inside a planetary embryo is investigated using the Hugoniot equations and a new scaling law, governing the particle velocity variations along a shock ray inside a spherical body. The scaling law is adopted to determine the impact heating of a growing embryo in its early stage when it is an undifferentiated and uniform body. The new scaling law, similar to other existing scaling laws, is not suitable for a large differentiated embryo consisting of a silicate mantle overlying an iron core. An algorithm is developed in this study on the basis of the ray theory in a spherically symmetric body which relates the shock parameters at the top of the core to those at the base of the mantle, thus enabling the adoption of scaling laws to estimate the impact heating of both the mantle and the core. The algorithm is applied to two embryo models: a simple two-layered model with a uniform mantle overlying a uniform core, and a model where the pre-shock density and acoustic velocity of the embryo are radially dependent. The former illustrates details of the particle velocity, shock pressure, and temperature increase behind the shock front in a 2D axisymmetric geometry. The latter provides a means to compare the results with those obtained by a hydrocode simulation. The agreement between the results of the two techniques in revealing the effects of the core-mantle boundary on the shock wave transmission across the boundary is encouraging.

A working environment for digital planetary data processing and mapping using ISIS and GRASS GIS

USGS Publications Warehouse

Frigeri, A.; Hare, T.; Neteler, M.; Coradini, A.; Federico, C.; Orosei, R.

2011-01-01

Since the beginning of planetary exploration, mapping has been fundamental to summarize observations returned by scientific missions. Sensor-based mapping has been used to highlight specific features from the planetary surfaces by means of processing. Interpretative mapping makes use of instrumental observations to produce thematic maps that summarize observations of actual data into a specific theme. Geologic maps, for example, are thematic interpretative maps that focus on the representation of materials and processes and their relative timing. The advancements in technology of the last 30 years have allowed us to develop specialized systems where the mapping process can be made entirely in the digital domain. The spread of networked computers on a global scale allowed the rapid propagation of software and digital data such that every researcher can now access digital mapping facilities on his desktop. The efforts to maintain planetary missions data accessible to the scientific community have led to the creation of standardized digital archives that facilitate the access to different datasets by software capable of processing these data from the raw level to the map projected one. Geographic Information Systems (GIS) have been developed to optimize the storage, the analysis, and the retrieval of spatially referenced Earth based environmental geodata; since the last decade these computer programs have become popular among the planetary science community, and recent mission data start to be distributed in formats compatible with these systems. Among all the systems developed for the analysis of planetary and spatially referenced data, we have created a working environment combining two software suites that have similar characteristics in their modular design, their development history, their policy of distribution and their support system. The first, the Integrated Software for Imagers and Spectrometers (ISIS) developed by the United States Geological Survey, represents the state of the art for processing planetary remote sensing data, from the raw unprocessed state to the map projected product. The second, the Geographic Resources Analysis Support System (GRASS) is a Geographic Information System developed by an international team of developers, and one of the core projects promoted by the Open Source Geospatial Foundation (OSGeo). We have worked on enabling the combined use of these software systems throughout the set-up of a common user interface, the unification of the cartographic reference system nomenclature and the minimization of data conversion. Both software packages are distributed with free open source licenses, as well as the source code, scripts and configuration files hereafter presented. In this paper we describe our work done to merge these working environments into a common one, where the user benefits from functionalities of both systems without the need to switch or transfer data from one software suite to the other one. Thereafter we provide an example of its usage in the handling of planetary data and the crafting of a digital geologic map. ?? 2010 Elsevier Ltd. All rights reserved.

Effect of rotation on fingering convection in stellar and planetary interiors

NASA Astrophysics Data System (ADS)

Sengupta, Sutirtha; Garaud, Pascale

2018-01-01

We study the effects of global rotation on the growth and saturation of the fingering (double-diffusive) instability at low Prandtl numbers and estimate the compositional transport rates as a function of the relevant non-dimensional parameters - the Taylor number, Ta^* (defined in terms of the rotation rate, Ω, thermal diffusivity κ_T and associated finger length scale d) and density ratio through direct numerical simulations. Within our explored range of parameters, we find rotation to have very little effect on vertical transport apart for an exceptional case where a cyclonic large scale vortex (LSV) is observed at low density ratio and fairly high Taylor number. The LSV leads to significant enhancement in the fingering transport rates by concentrating high composition fluid at its core which moves downward. The formation of such LSVs is of particular interest for solving the missing mixing problem in the astrophysical context of RGB stars though the parameter regime in which we observe the emergence of this LSV seems to be quite far from the stellar scenario. However, understanding the basic mechanism driving such large scale structures as observed frequently in polar regions of planets (e.g. those seen by Juno near the poles of Jupiter) is important in general for studies of rotating turbulence and its applications to stellar and planetary interior studies, and will be investigated in further detail in a forthcoming work.

Does the planetary dynamo go cycling on? Re-examining the evidence for cycles in magnetic reversal rate

NASA Astrophysics Data System (ADS)

Melott, Adrian L.; Pivarunas, Anthony; Meert, Joseph G.; Lieberman, Bruce S.

2018-01-01

The record of reversals of the geomagnetic field has played an integral role in the development of plate tectonic theory. Statistical analyses of the reversal record are aimed at detailing patterns and linking those patterns to core-mantle processes. The geomagnetic polarity timescale is a dynamic record and new paleomagnetic and geochronologic data provide additional detail. In this paper, we examine the periodicity revealed in the reversal record back to 375 million years ago (Ma) using Fourier analysis. Four significant peaks were found in the reversal power spectra within the 16-40-million-year range (Myr). Plotting the function constructed from the sum of the frequencies of the proximal peaks yield a transient 26 Myr periodicity, suggesting chaotic motion with a periodic attractor. The possible 16 Myr periodicity, a previously recognized result, may be correlated with `pulsation' of mantle plumes and perhaps; more tentatively, with core-mantle dynamics originating near the large low shear velocity layers in the Pacific and Africa. Planetary magnetic fields shield against charged particles, which can give rise to radiation at the surface and ionize the atmosphere, which is a loss mechanism particularly relevant to M stars. Understanding the origin and development of planetary magnetic fields can shed light on the habitable zone.

The Devil in the Dark: A Fully Self-Consistent Seismic Model for Venus

NASA Astrophysics Data System (ADS)

Unterborn, C. T.; Schmerr, N. C.; Irving, J. C. E.

2017-12-01

The bulk composition and structure of Venus is unknown despite accounting for 40% of the mass of all the terrestrial planets in our Solar System. As we expand the scope of planetary science to include those planets around other stars, the lack of measurements of basic planetary properties such as moment of inertia, core-size and thermal profile for Venus hinders our ability to compare the potential uniqueness of the Earth and our Solar System to other planetary systems. Here we present fully self-consistent, whole-planet density and seismic velocity profiles calculated using the ExoPlex and BurnMan software packages for various potential Venusian compositions. Using these models, we explore the seismological implications of the different thermal and compositional initial conditions, taking into account phase transitions due to changes in pressure, temperature as well as composition. Using mass-radius constraints, we examine both the centre frequencies of normal mode oscillations and the waveforms and travel times of body waves. Seismic phases which interact with the core, phase transitions in the mantle, and shallower parts of Venus are considered. We also consider the detectability and transmission of these seismic waves from within the dense atmosphere of Venus. Our work provides coupled compositional-seismological reference models for the terrestrial planet in our Solar System of which we know the least. Furthermore, these results point to the potential wealth of fundamental scientific insights into Venus and Earth, as well as exoplanets, which could be gained by including a seismometer on future planetary exploration missions to Venus, the devil in the dark.

Cool DZ white dwarfs II: compositions and evolution of old remnant planetary systems

NASA Astrophysics Data System (ADS)

Hollands, M. A.; Gänsicke, B. T.; Koester, D.

2018-06-01

In a previous study, we analysed the spectra of 230 cool (Teff < 9000 K) white dwarfs exhibiting strong metal contamination, measuring abundances for Ca, Mg, Fe and in some cases Na, Cr, Ti, or Ni. Here, we interpret these abundances in terms of the accretion of debris from extrasolar planetesimals, and infer parent body compositions ranging from crust-like (rich in Ca and Ti) to core-like (rich in Fe and Ni). In particular, two white dwarfs, SDSS J0823+0546 and SDSS J0741+3146, which show log [Fe/Ca] > 1.9 dex, and Fe to Ni ratios similar to the bulk Earth, have accreted by far the most core-like exoplanetesimals discovered to date. With cooling ages in the range 1-8 Gyr, these white dwarfs are among the oldest stellar remnants in the Milky Way, making it possible to probe the long-term evolution of their ancient planetary systems. From the decrease in maximum abundances as a function of cooling age, we find evidence that the arrival rate of material on to the white dwarfs decreases by three orders of magnitude over a ≃ 6.5 Gyr span in white dwarf cooling ages, indicating that the mass-reservoirs of post-main sequence planetary systems are depleted on a ≃ 1 Gyr e-folding time-scale. Finally, we find that two white dwarfs in our sample are members of wide binaries, and both exhibit atypically high abundances, thus providing strong evidence that distant binary companions can dynamically perturb white dwarf planetary systems.

A new model for the (geo)magnetic power spectrum, with application to planetary dynamo radii

NASA Astrophysics Data System (ADS)

Langlais, Benoit; Amit, Hagay; Larnier, Hugo; Thébault, Erwan; Mocquet, Antoine

2014-09-01

We propose two new analytical expressions to fit the Mauersberger-Lowes geomagnetic field spectrum at the core-mantle boundary. These can be used to estimate the radius of the outer liquid core where the geodynamo operates, or more generally the radius of the planetary dynamo regions. We show that two sub-families of the geomagnetic field are independent of spherical harmonics degree n at the core-mantle boundary and exhibit flat spectra. The first is the non-zonal field, i.e., for spherical harmonics order m different from zero. The second is the quadrupole family, i.e., n+m even. The flatness of their spectra is motivated by the nearly axisymmetric time-average paleomagnetic field (for the non-zonal field) and the dominance of rotational effects in core dynamics (for the quadrupole family). We test our two expressions with two approaches using the reference case of the Earth. First we estimate at the seismic core radius the agreement between the actual spectrum and the theoretical one. Second we estimate the magnetic core radius, where the spectrum flattens. We show that both sub-families offer a better agreement with the actual spectrum compared with previously proposed analytical expressions, and predict a magnetic core radius within less than 10 km of the Earth's seismic core radius. These new expressions supersede previous ones to infer the core radius from geomagnetic field information because the low degree terms are not ignored. Our formalism is then applied to infer the radius of the dynamo regions on Jupiter, Saturn, Uranus and Neptune. The axisymmetric nature of the magnetic field of Saturn prevents the use of the non-zonal expression. For the three other planets both expressions converge and offer independent constraints on the internal structure of these planets. These non-zonal and quadrupole family expressions may be implemented to extrapolate the geomagnetic field spectrum beyond observable degrees, or to further regularize magnetic field models constructed from modern or historical observations.

Tidal stress and failure in the moon of binary asteroid systems: Application to asteroid (65803) Didymos

NASA Astrophysics Data System (ADS)

Sophal Pou, Laurent; Garcia, Raphael F.; Mimoun, David; Murdoch, Naomi; Karatekin, Ozgur

2017-04-01

Rocky remnants left over from the early formation of the Solar System, asteroids are a target of choice for planetary science since much about the history of planetary formation and small body evolution processes can be learnt by studying them. Here we consider the case of the binary asteroid (65803) Didymos, the target of several mission proposals e.g., AIM [1] and DART [2]. A mission to Didymos would be a great opportunity for in-situ geophysical investigation, providing information on the surface and interior of asteroids. Such studies would improve our knowledge of binary asteroid formation and subsequent evolution of asteroids, thus of the history of the Solar System. As Didymos is a binary asteroid [3] with the main 800-meter diameter asteroid named Didymain and a 150-meter sized moon named Didymoon, both are subject to tidal stress. Recent investigations suggest that Didymoon is tidally locked and moves in a retrograde motion around Didymain along an elliptic orbit with a 0.03 eccentricity at most. In the case of an eccentric orbit, the tidal stress varies periodically and may be strong enough to cause tidal quakes on Didymoon at some points of the orbit. For this study, we modelled Didymoon as a spherical, layered body with different internal structures: a homogeneous model, and two models with a 1-meter and 10-meter regolith layer on top of a stronger internal core. Simulations show that, for a cohesionless body with an internal friction angle of 30°, tidal stress is strong enough to cause failure at the surface of Didymoon. A maximal stress is reached around the poles and for a mean anomaly of 90°. These results would mean that if tidal quakes occur on Didymoon, then they are likely to happen at these locations. An extension of these results to an ellipsoidal model of Didymoon is also presented for comparison with the spherical case and for application to other bodies. [1]: P. Michel et al., Science case for the asteroid impact mission (aim): A component of the asteroid impact and deflection assessment (aida) mission, Advances in Space Research 57 (12) (2016) 2529 - 2547. doi:http://dx.doi.org/10.1016/j.asr.2016.03.031. [2]: A. F. Cheng et al., Asteroid Impact & Deflection Assessment mission: Kinetic impactor, Planetary and Space Science 121 (2016) 27-35. doi:10.1016/j.pss.2015.12.004. [3]:"AIM-A Team", ASTEROID IMPACT MISSION: DIDYMOS REFERENCE MODEL v10, ESA document reference: AD3-AIMA.

The Extended Region Around the Planetary Nebula NGC 3242

NASA Technical Reports Server (NTRS)

2009-01-01

This ultraviolet image from NASA's Galaxy Evolution Explorer shows NGC 3242, a planetary nebula frequently referred to as 'Jupiter's Ghost.'

The unfortunate name of 'planetary nebula' for this class of celestial object is a historical legacy credited to William Herschel during the 18th century a time when telescopes where small and objects like these, at least the central region, looked very similar to gas-giant planets such as Saturn and Jupiter. In fact, NGC 3242 has no relation to Jupiter or any other planet.

Telescopes and their detectors have dramatically improved over the past few centuries. Our understanding of what planetary nebulae truly are has improved accordingly.

When stars with a mass similar to our sun approach the end of their lives by exhausting supplies of hydrogen and helium fuel in their cores, they swell up into cool red-giant stars. In a last gasp before death, they expel the layers of gas in their outer atmosphere. This exposes the core of the dying star, a dense hot ball of carbon and oxygen called a white dwarf. The white dwarf is so hot that it shines very brightly in the ultraviolet. The ultraviolet light from the white dwarf, in turn, ionizes the gaseous material expelled by the star causing it to glow. A planetary nebula is really the death of a low-mass star.

Although low-mass stars like our sun live for billions of years, planetary nebulae only last for about ten thousand years. As the central white dwarf quickly cools and the ultraviolet light dwindles, the surrounding gas also cools and fades.

In this image of NGC 3242 from the Galaxy Evolution Explorer, the extended region around the planetary nebula is shown in dramatic detail. The small circular white and blue area at the center of the image is the well-known portion of the famous planetary nebula. The precise origin and composition of the extended wispy white features is not known for certain. It is most likely material ejected during the star's red-giant phase before the white dwarf was exposed. However, it may be possible that the extended material is simply interstellar gas that, by coincidence, is located close enough to the white dwarf to be energized by it, and induced to glow with ultraviolet light.

NGC 3242 is located 1,400 to 2,500 light-years away in the constellation Hydra. It was discovered by William Herschel in 1785.

VISTA: A μ-Thermogravimeter for Investigation of Volatile Compounds in Planetary Environments.

PubMed

Palomba, Ernesto; Longobardo, Andrea; Dirri, Fabrizio; Zampetti, Emiliano; Biondi, David; Saggin, Bortolino; Bearzotti, Andrea; Macagnano, Antonella

2016-06-01

This paper presents the VISTA (Volatile In Situ Thermogravimetry Analyser) instrument, conceived to perform planetary in-situ measurements. VISTA can detect and quantify the presence of volatile compounds of astrobiological interest, such as water and organics, in planetary samples. These measurements can be particularly relevant when performed on primitive asteroids or comets, or on targets of potential astrobiological interest such as Mars or Jupiter's satellite Europa. VISTA is based on a micro-thermogravimetry technique, widely used in different environments to study absorption and sublimation processes. The instrument core is a piezoelectric crystal microbalance, whose frequency variations are affected by variations of the mass of the deposited sample, due to chemical processes such as sublimation, condensation or absorption/desorption. The low mass (i.e. 40 g), the low volume (less than 10 cm(3)) and the low power (less than 1 W) required makes this kind of instrument very suitable for space missions. This paper discusses the planetary applications of VISTA, and shows the calibration operations performed on the breadboard, as well as the performance tests which demonstrate the capability of the breadboard to characterize volatile compounds of planetary interests.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heller, René; Zuluaga, Jorge I., E-mail: rheller@physics.mcmaster.ca, E-mail: jzuluaga@fisica.udea.edu.co

With most planets and planetary candidates detected in the stellar habitable zone (HZ) being super-Earths and gas giants rather than Earth-like planets, we naturally wonder if their moons could be habitable. The first detection of such an exomoon has now become feasible, and due to observational biases it will be at least twice as massive as Mars. However, formation models predict that moons can hardly be as massive as Earth. Hence, a giant planet's magnetosphere could be the only possibility for such a moon to be shielded from cosmic and stellar high-energy radiation. Yet, the planetary radiation belt could alsomore » have detrimental effects on exomoon habitability. Here we synthesize models for the evolution of the magnetic environment of giant planets with thresholds from the runaway greenhouse (RG) effect to assess the habitability of exomoons. For modest eccentricities, we find that satellites around Neptune-sized planets in the center of the HZ around K dwarf stars will either be in an RG state and not be habitable, or they will be in wide orbits where they will not be affected by the planetary magnetosphere. Saturn-like planets have stronger fields, and Jupiter-like planets could coat close-in habitable moons soon after formation. Moons at distances between about 5 and 20 planetary radii from a giant planet can be habitable from an illumination and tidal heating point of view, but still the planetary magnetosphere would critically influence their habitability.« less

Constraints on the spin evolution of young planetary-mass companions

NASA Astrophysics Data System (ADS)

Bryan, Marta L.; Benneke, Björn; Knutson, Heather A.; Batygin, Konstantin; Bowler, Brendan P.

2018-02-01

Surveys of young star-forming regions have discovered a growing population of planetary-mass (<13 MJup) companions around young stars1. There is an ongoing debate as to whether these companions formed like planets (that is, from the circumstellar disk)2, or if they represent the low-mass tail of the star-formation process3. In this study, we utilize high-resolution spectroscopy to measure rotation rates of three young (2-300 Myr) planetary-mass companions and combine these measurements with published rotation rates for two additional companions4,5 to provide a picture of the spin distribution of these objects. We compare this distribution to complementary rotation-rate measurements for six brown dwarfs with masses <20 MJup, and show that these distributions are indistinguishable. This suggests that either these two populations formed via the same mechanism, or that processes regulating rotation rates are independent of formation mechanism. We find that rotation rates for both populations are well below their break-up velocities and do not evolve significantly during the first few hundred million years after the end of accretion. This suggests that rotation rates are set during the late stages of accretion, possibly by interactions with a circumplanetary disk. This result has important implications for our understanding of the processes regulating the angular momentum evolution of young planetary-mass objects, and of the physics of gas accretion and disk coupling in the planetary-mass regime.

Using Laboratory Methods to Better Understand Refractory Cloud Formation in Exoplanet Atmospheres

NASA Astrophysics Data System (ADS)

Kohler, E.; Ferguson, F.

2017-12-01

The high number of extrasolar planets found in recent years has brought a new importance to planetary atmospheres. These recently discovered planets show a large diversity in their masses, temperatures, orbital periods, and other properties. With such a diverse mix of planetary parameters, it is safe to assume that the atmospheric properties are just as varied. Recent literature suggests silicates and metals as possible condensates in extrasolar planetary atmospheres as well as the atmospheres of brown dwarfs. While theoretical studies have laid the foundation of cloud formation analysis, their findings still need to be validated via experiments. A verification of the condensation and vaporization predictions of refractory materials needs to be found in order to assist global circulation models in being as accurate as possible. The stability of minerals identified in the literature as potential candidates, will be tested in a thermogravimetric balance. The minerals will be pumped under vacuum for twenty-four hours under room temperature and then heated to a predetermined high temperature, dependent on the expected vaporization temperature of that sample. If there is apparent mass loss, then the temperature will be lowered at preset durations and mass measurements will be taken in similar measured increments. The data will be processed by a computer program in order to calculate the mass loss as a function of temperature. The current cloud formation and global circulation models are very important to the field of planetary science but their accuracy is hindered by the lack of experimental data. The aim of this work is to investigate the mineral stability of potential condensates in an effort to explain the formation of refractory clouds in the atmospheres of extrasolar planets and brown dwarfs.

Dynamics of the Final Stages of Terrestrial Planet Growth and the Formation of the Earth-Moon System

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; Rivera, Eugenio J.; DeVincenzi, Donald (Technical Monitor)

2000-01-01

An overview of current theories of star and planet formation, with emphasis on terrestrial planet accretion and the formation of the Earth-Moon system is presented. These models predict that rocky planets should form around most single stars, although it is possible that in some cases such planets are lost to orbital decay within the protoplanetary disk. The frequency of formation of gas giant planets is more difficult to predict theoretically. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant impacts during the final stages of growth can produce large planetary satellites, such as Earth's Moon. Giant planets begin their growth like terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates.

In situ measurements of the photochemical formation rates and optical properties of organic aerosols in CH4/CO2 mixtures.

NASA Astrophysics Data System (ADS)

Adamkovics, M.; Boering, K. A.

2003-12-01

The presence of photochemically-generated hazes has a significant impact on radiative transfer in planetary atmospheres. While the rates of particle formation have been inferred from photochemical or microphysical models constrained to match observations, these rates have not been determined experimentally. Thus, the fundamental kinetics of particle formation are not known and remain highly parameterized in planetary atmospheric models. We have developed instrumentation for measuring the formation rates and optical properties of organic aerosols produced by irradiating mixtures of precursor gases via in situ optical (633nm) scattering and online quadrupole mass spectrometry (1-200 amu). Results for the generation of particulate hydrocarbons from the irradiation of pure, gas-phase CH4 as well as CH4/CO2 mixtures with vacuum ultraviolet (120-160nm) light, along with simultaneous measurements of the evolution of higher gas-phase hydrocarbons will be presented.

Theories of Giant Planet Formation

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; Young, Richard E. (Technical Monitor)

1998-01-01

An overview of current theories of planetary formation, with emphasis on giant planets, is presented. The most detailed models are based upon observations of our own Solar System and of young stars and their environments. While these models predict that rocky planets should form around most single stars, the frequency of formation of gas giant planets is more difficult to predict theoretically. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth as do terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. Most models for extrasolar giant planets suggest that they formed as did Jupiter and Saturn (in nearly circular orbits, far enough from the star that ice could), and subsequently migrated to their current positions, although some models suggest in situ formation.

Linear and nonlinear dynamics of liquid planetary cores

NASA Astrophysics Data System (ADS)

Lathrop, D. P.

2013-12-01

This is the 50th anniversary of Ed Lorenz brilliant paper "Deterministic Nonperiodic Flow.'' Lorenz's work, along with many other founders' efforts, gave rise to the study of nonlinear dynamics. That field has allowed us to move beyond simple linear characterizations of nature, and to open up a deeper understanding of the Earth, other planets, and stars. Of the many things that make the Earth a habitable home, one is the existence of a planetary magnetic field generated in our liquid iron outer core. The generation process is known to be strongly nonlinear, and thereby almost certainly turbulent. Yet it is not a simple homogeneous isotropic turbulent flow, but is instead heavily modified by rotation and magnetic forces. We attempt to better understand the Earth's core using a three-meter liquid sodium laboratory model of the core. Our work in sodium in this system has just begun. The system exhibits a variety of behaviors with at least twelve different states, drawing different amounts of power, and causing varying levels of magnetic field amplification. In some states, rotation and magnetic fields cause the dynamics to simplify relative to more general turbulent flows in comparable conditions. Acknowledgements: I gratefully acknowledge my collaborators Daniel Zimmerman, Santiago Triana, Donald Martin, Nolan Balew, Henri-Claude Nataf, and Barbara Brawn-Cinani, and funding from the National Science Foundation Earth Sciences Instrumentation and Geophysics programs.

Origin of igneous meteorites and differentiated asteroids

NASA Astrophysics Data System (ADS)

Scott, E.; Goldstein, J.; Asphaug, E.; Bottke, W.; Moskovitz, N.; Keil, K.

2014-07-01

Introduction: Igneously formed meteorites and asteroids provide major challenges to our understanding of the formation and evolution of the asteroid belt. The numbers and types of differentiated meteorites and non-chondritic asteroids appear to be incompatible with an origin by fragmentation of numerous Vesta-like bodies by hypervelocity impacts in the asteroid belt over 4 Gyr. We lack asteroids and achondrites from the olivine-rich mantles of the parent bodies of the 12 groups of iron meteorites and the ˜70 ungrouped irons, the 2 groups of pallasites and the 4--6 ungrouped pallasites. We lack mantle and core samples from the parent asteroids of the basaltic achondrites that do not come from Vesta, viz., angrites and the ungrouped eucrites like NWA 011 and Ibitira. How could core samples have been extracted from numerous differentiated bodies when Vesta's basaltic crust was preserved? Where is the missing Psyche family of differentiated asteroids including the complementary mantle and crustal asteroids [1]? Why are meteorites derived from far more differentiated parent bodies than chondritic parent bodies even though C and S class chondritic asteroids dominate the asteroid belt? New paradigm. Our studies of meteorites, impact modeling, and dynamical studies suggest a new paradigm in which differentiated asteroids accreted at 1--2 au less than 2 Myr after CAI formation [2]. They were rapidly melted by 26Al and disrupted by hit-and-run impacts [3] while still molten or semi-molten when planetary embryos were accreting. Metallic Fe-Ni bodies derived from core material cooled rapidly with little or no silicate insulation less than 4 Myr after CAI formation [4]. Fragments of differentiated planetesimals were subsequently tossed into the asteroid belt. Meteorite evidence for early disruption of differentiated asteroids. If iron meteorites were samples of Fe-Ni cores of bodies that cooled slowly inside silicate mantles over ˜50--100 Myr, irons from each core would have almost indistinguishable cooling rates as thermal gradients across cores would have been minimal. Irons in groups IIIAB, IVA, and IVB have chemical crystallization trends showing that they cooled in three separate bodies. However, each shows a wide range of cooling rates [4]. Group IVA irons cooled through 500°C at 6600--100 °C/Myr in a metallic body of radius 150 ± 50 km with scarcely any silicate insulation [5]. The Pb-Pb age of 4565.3 ± 0.1 Myr for a IVA iron [6] confirms that these irons cooled to ˜300°C only 2--3 Myr after CAI formation. Multiple hit-and-run impacts may have separated core and mantle material during accretion [7] as hypervelocity impacts do not efficiently separate cores from mantles. Thermal histories and magnetic properties of main group pallasites also require early catastrophic disruption of their primary parent body [8,9]. Conclusions. The anomalous properties of differentiated asteroids and meteorites cannot be explained by concealing differentiated planetesimals under chondritic crusts [10] as meteorite breccias and the apparent compositional homogeneity of asteroid families are inconsistent with this model. Like Burbine et al. [11], we attribute the lack of olivine mantle meteorites and asteroids to collisional grinding of weaker silicate and the preferential survival of stronger metallic Fe,Ni fragments. But we infer that asteroid break up occurred very early inside 2 au, not in the asteroid belt over 4 Gyr. Vesta may have preserved its crust due to early ejection into the asteroid belt. It is the smallest terrestrial planet --- not an archetypal differentiated asteroid.

Geostrophic balance with a full Coriolis Force: implications for low latitutde studies

NASA Technical Reports Server (NTRS)

Juarez, M. de la Torre

2002-01-01

In its standard form, geostrophic balance uses a partial representation of the Coriolis force. The resulting formation has a singularity at the equator, and violates mass and momentum conservation. When the horizontal projection of the planetary rotation vector is considered, the singularity at the equator disappears, continuity can be preserved, and quasigeostrophy can be formulated at planetary scale.

Planetary geodesy. [review of research 1975-1979

NASA Technical Reports Server (NTRS)

Ferrari, A. J.; Bills, B. G.

1979-01-01

An attempt is made to review progress in planetary geodesy during the past four years. The discussion is limited to the traditional subjects of geometrical and physical geodesy, with emphasis on gravity, topography, rotation, and their physical significance. The format is kept flexible to accommodate the varied amount of information available for Mercury, Venus, the Moon, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.

Instrumentation development for In Situ 40Ar/39Ar planetary geochronology

USGS Publications Warehouse

Morgan, Leah; Munk, Madicken; Davidheiser-Kroll, Brett; Warner, Nicholas H.; Gupta, Sanjeev; Slaybaugh, Rachel; Harkness, Patrick; Mark, Darren

2017-01-01

The chronology of the Solar System, particularly the timing of formation of extra-terrestrial bodies and their features, is an outstanding problem in planetary science. Although various chronological methods for in situ geochronology have been proposed (e.g., Rb-Sr, K-Ar), and even applied (K-Ar), the reliability, accuracy, and applicability of the 40Ar/39Ar method makes it by far the most desirable chronometer for dating extra-terrestrial bodies. The method however relies on the neutron irradiation of samples, and thus a neutron source. Herein, we discuss the challenges and feasibility of deploying a passive neutron source to planetary surfaces for the in situ application of the 40Ar/39Ar chronometer. Requirements in generating and shielding neutrons, as well as analysing samples are described, along with an exploration of limitations such as mass, power and cost. Two potential solutions for the in situ extra-terrestrial deployment of the 40Ar/39Ar method are presented. Although this represents a challenging task, developing the technology to apply the 40Ar/39Ar method on planetary surfaces would represent a major advance towards constraining the timescale of solar system formation and evolution.

Core formation and core composition from coupled geochemical and geophysical constraints

DOE PAGES

Badro, James; Brodholt, John P.; Piet, Helene; ...

2015-09-21

The formation of Earth’s core left behind geophysical and geochemical signatures in both the core and mantle that remain to this day. Seismology requires that the core be lighter than pure iron and therefore must contain light elements, and the geochemistry of mantle-derived rocks reveals extensive siderophile element depletion and fractionation. Both features are inherited from metal–silicate differentiation in primitive Earth and depend upon the nature of physiochemical conditions that prevailed during core formation. To date, core formation models have only attempted to address the evolution of core and mantle compositional signatures separately, rather than seeking a joint solution. Heremore » we combine experimental petrology, geochemistry, mineral physics and seismology to constrain a range of core formation conditions that satisfy both constraints. We find that core formation occurred in a hot (liquidus) yet moderately deep magma ocean not exceeding 1,800 km depth, under redox conditions more oxidized than present-day Earth. This new scenario, at odds with the current belief that core formation occurred under reducing conditions, proposes that Earth’s magma ocean started oxidized and has become reduced through time, by oxygen incorporation into the core. As a result, this core formation model produces a core that contains 2.7–5% oxygen along with 2–3.6% silicon, with densities and velocities in accord with radial seismic models, and leaves behind a silicate mantle that matches the observed mantle abundances of nickel, cobalt, chromium, and vanadium.« less

Core formation and core composition from coupled geochemical and geophysical constraints

DOE Office of Scientific and Technical Information (OSTI.GOV)

Badro, James; Brodholt, John P.; Piet, Helene

The formation of Earth’s core left behind geophysical and geochemical signatures in both the core and mantle that remain to this day. Seismology requires that the core be lighter than pure iron and therefore must contain light elements, and the geochemistry of mantle-derived rocks reveals extensive siderophile element depletion and fractionation. Both features are inherited from metal–silicate differentiation in primitive Earth and depend upon the nature of physiochemical conditions that prevailed during core formation. To date, core formation models have only attempted to address the evolution of core and mantle compositional signatures separately, rather than seeking a joint solution. Heremore » we combine experimental petrology, geochemistry, mineral physics and seismology to constrain a range of core formation conditions that satisfy both constraints. We find that core formation occurred in a hot (liquidus) yet moderately deep magma ocean not exceeding 1,800 km depth, under redox conditions more oxidized than present-day Earth. This new scenario, at odds with the current belief that core formation occurred under reducing conditions, proposes that Earth’s magma ocean started oxidized and has become reduced through time, by oxygen incorporation into the core. As a result, this core formation model produces a core that contains 2.7–5% oxygen along with 2–3.6% silicon, with densities and velocities in accord with radial seismic models, and leaves behind a silicate mantle that matches the observed mantle abundances of nickel, cobalt, chromium, and vanadium.« less

Workshop on Oxygen in the Terrestrial Planets

NASA Technical Reports Server (NTRS)

2004-01-01

This volume contains abstracts that have been accepted for presentation at the Workshop on Oxygen in the Terrestrial Planets, July 20-23,2004, Santa Fe, New Mexico. The contents include: 1) Experimental Constraints on Oxygen and Other Light Element Partitioning During Planetary Core Formation; 2) In Situ Determination of Fe(3+)/SigmaFe of Spinels by Electron Microprobe: An Evaluation of the Flank Method; 3) The Effect of Oxygen Fugacity on Large-Strain Deformation and Recrystallization of Olivine; 4) Plagioclase-Liquid Trace Element Oxygen Barometry and Oxygen Behaviour in Closed and Open System Magmatic Processes; 5) Core Formation in the Earth: Constraints from Ni and Co; 6) Oxygen Isotopic Compositions of the Terrestrial Planets; 7) The Effect of Oxygen Fugacity on Electrical Conduction of Olivine and Implications for Earth s Mantle; 8) Redox Chemical Diffusion in Silicate Melts: The Impact of the Semiconductor Condition; 9) Ultra-High Temperature Effects in Earth s Magma Ocean: Pt and W Partitioning; 10) Terrestrial Oxygen and Hydrogen Isotope Variations: Primordial Values, Systematics, Subsolidus Effects, Planetary Comparisons, and the Role of Water; 11) Redox State of the Moon s Interior; 12) How did the Terrestrial Planets Acquire Their Water?; 13) Molecular Oxygen Mixing Ratio and Its Seasonal Variability in the Martian Atmosphere; 14) Exchange Between the Atmosphere and the Regolith of Mars: Discussion of Oxygen and Sulfur Isotope Evidence; 15) Oxygen and Hydrogen Isotope Systematics of Atmospheric Water Vapor and Meteoric Waters: Evidence from North Texas; 16) Implications of Isotopic and Redox Heterogeneities in Silicate Reservoirs on Mars; 17) Oxygen Isotopic Variation of the Terrestrial Planets; 18) Redox Exchanges in Hydrous Magma; 19) Hydrothermal Systems on Terrestrial Planets: Lessons from Earth; 20) Oxygen in Martian Meteorites: A Review of Results from Mineral Equilibria Oxybarometers; 21) Non-Linear Fractionation of Oxygen Isotopes Implanted in Lunar Metal Grains: Solar, Lunar or Terrestrial Origin? 22) Isotopic Zoning in the Inner Solar System; 23) Redox Conditions on Small Bodies; 24) Determining the Oxygen Fugacity of Lunar Pyroclastic Glasses Using Vanadium Valence - An Update; 25) Mantle Redox Evolution and the Rise of Atmospheric O2; 26) Variation of Kd for Fe-Mg Exchange Between Olivine and Melt for Compositions Ranging from Alkaline Basalt to Rhyolite; 27) Determining the Partial Pressure of Oxygen (PO,) in Solutions on Mars; 28) The Influence of Oxygen Environment on Kinetic Properties of Silicate Rocks and Minerals; 29) Redox Evolution of Magmatic Systems; 30) The Constancy of Upper Mantlefo, Through Time Inferred from V/Sc Ratios in Basalts: Implications for the Rise in Atmospheric 0 2; 31) Nitrogen Solubility in Basaltic Melt. Effects of Oxygen Fugacity, Melt Composition and Gas Speciation; 32) Oxygen Isotope Anomalies in the Atmospheres of Earth and Mars; 33) The Effect of Oxygen Fugacity on Interdiffusion of Iron and Magnesium in Magnesiowiistite 34) The Calibration of the Pyroxene Eu-Oxybarometer for the Martian Meteorites; 35) The Europium Oxybarometer: Power and Pitfalls; 36) Oxygen Fugacity of the Martian Mantle from PigeoniteMelt Partitioning of Samarium, Europium and Gadolinium; 37) Oxidation-Reduction Processes on the Moon: Experimental Verification of Graphite Oxidation in the Apollo 17 Orange Glasses; 38) Oxygen and Core Formation in the Earth; 39) Geologic Record of the Atmospheric Sulfur Chemistry Before the Oxygenation of the Early Earth s Atmosphere; 40) Comparative Planetary Mineralogy: V/(CrCAl) Systematics in Chromite as an Indicator of Relative Oxygen Fugacity; 41) How Well do Sulfur Isotopes Constrain Oxygen Abundance in the Ancient Atmospheres? 42) Experimental Constraints on the Oxygen Isotope (O-18/ O-16) Fractionation in the Ice vapor and Adsorbant vapor Systems of CO2 at Conditions Relevant to the Surface of Mars; 43) Micro-XANES Measurements on Experimental Spinels andhe Oxidation State of Vanadium in Spinel-Melt Pairs; 44) Testing the Magma Ocean Hypothesis Using Metal-Silicate Partitioning of Te, Se and S; 45) Solubility of Oxygen in Liquid Iron at High Pressure and Consequences for the Early Differentiation of Earth and Mars Metallic Liquid Segregation in Planetesimals; 46) Oxygen Fugacity of Lunar Basalts and the Lunar Mantle. Range of fo2 and the Effectiveness of Oxybarometers; 47) Thermodynamic Study of Dissociation Processes of Molecular Oxygen in Vapor over Oxide Compounds; 48) Oxygen Profile of a Thermo-Haliophilic Community in the Badwater Salt Flat; 49) Oxygen Barometry Using Synchrotron MicroXANES of Vanadium; 50) Mass-Independent Isotopic Fractionation of Sulfur from Sulfides in the Huronian Supergroup, Canada; 51) Mass Independent Isotopes and Applications to Planetary Atmospheres; 52) Electrical Conductivity, Oxygen Fugacity, and Mantle Materials; 53) Crustal Evolution and Maturation on Earth: Oxygen Isotope Evidence; 54) The Oxygen Isotope Composition of the Moon: Implications for Planet Formation; 55) Oxygen Isotope Composition of Eucrites and Implications for the Formation of Crust on the HED Parent Body; and 56) The Role of Water in Determining the Oxygen Isotopic Composition of Planets.

Sustainability. Planetary boundaries: guiding human development on a changing planet.

PubMed

Steffen, Will; Richardson, Katherine; Rockström, Johan; Cornell, Sarah E; Fetzer, Ingo; Bennett, Elena M; Biggs, Reinette; Carpenter, Stephen R; de Vries, Wim; de Wit, Cynthia A; Folke, Carl; Gerten, Dieter; Heinke, Jens; Mace, Georgina M; Persson, Linn M; Ramanathan, Veerabhadran; Reyers, Belinda; Sörlin, Sverker

2015-02-13

The planetary boundaries framework defines a safe operating space for humanity based on the intrinsic biophysical processes that regulate the stability of the Earth system. Here, we revise and update the planetary boundary framework, with a focus on the underpinning biophysical science, based on targeted input from expert research communities and on more general scientific advances over the past 5 years. Several of the boundaries now have a two-tier approach, reflecting the importance of cross-scale interactions and the regional-level heterogeneity of the processes that underpin the boundaries. Two core boundaries—climate change and biosphere integrity—have been identified, each of which has the potential on its own to drive the Earth system into a new state should they be substantially and persistently transgressed. Copyright © 2015, American Association for the Advancement of Science.

The contribution of the ARIEL space mission to the study of planetary formation

NASA Astrophysics Data System (ADS)

Turrini, D.; Miguel, Y.; Zingales, T.; Piccialli, A.; Helled, R.; Vazan, A.; Oliva, F.; Sindoni, G.; Panić, O.; Leconte, J.; Min, M.; Pirani, S.; Selsis, F.; Coudé du Foresto, V.; Mura, A.; Wolkenberg, P.

2018-01-01

The study of extrasolar planets and of the Solar System provides complementary pieces of the mosaic represented by the process of planetary formation. Exoplanets are essential to fully grasp the huge diversity of outcomes that planetary formation and the subsequent evolution of the planetary systems can produce. The orbital and basic physical data we currently possess for the bulk of the exoplanetary population, however, do not provide enough information to break the intrinsic degeneracy of their histories, as different evolutionary tracks can result in the same final configurations. The lessons learned from the Solar System indicate us that the solution to this problem lies in the information contained in the composition of planets. The goal of the Atmospheric Remote-Sensing Infrared Exoplanet Large-survey (ARIEL), one of the three candidates as ESA M4 space mission, is to observe a large and diversified population of transiting planets around a range of host star types to collect information on their atmospheric composition. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres, which should show minimal condensation and sequestration of high-Z materials and thus reveal their bulk composition across all main cosmochemical elements. In this work we will review the most outstanding open questions concerning the way planets form and the mechanisms that contribute to create habitable environments that the compositional information gathered by ARIEL will allow to tackle.

Origin and Diversity of Planetary Systems

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; Young, Richard E. (Technical Monitor)

1997-01-01

Modern theories of star and planet formation, which are based upon observations of the Solar System and of young stars and their environments, predict that rocky planets should form around most single stars, although it is possible that most such planets are lost to orbital decay within the protoplanetary disk. The frequency of formation of gas giant planets is more difficult to predict theoretically. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth like terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. Models for the formation of the giant planets found in recent radial velocity searches are discussed.

M31 Globular Clusters and Galaxy Formation

NASA Astrophysics Data System (ADS)

Gregg, M. D.; Karick, A. M.

2005-12-01

The brightest globular cluster in the halo of M31, cluster G1, has properties which suggest that it is not an ordinary globular but an ultra-compact dwarf galaxy: its velocity dispersion, M/L, and ellipticity are all atypically large, and its color-magnitude diagram suggests an abundance spread. Using the Keck Laser Guide Star Adaptive Optics system with NIRC2, we have begun an imaging campaign of globular clusters in M31 to measure their core sizes. Combining these data with high dispersion spectroscopy will produce masses and M/L ratios to determine if there are additional UCDs masquerading as M31 globulars. UCDs are thought to be the remnant nuclei from tidally stripped dwarf ellipticals or small spirals; finding additional examples in the cluster system of M31 has implications for galaxy formation processes. The K-band image quality during our first LGS run was very stable over many hours, with Strehl ratios of 0.35 or better, producing point sources with FWHM of 0\\farcs05. The core sizes of the clusters, which range from 0\\farcs2 to 0\\farcs8 can be easily measured from these data. The observing conditions were nearly as good in the J-band, and we obtained both colors for a number of clusters. We discuss our efforts to produce photometrically-calibrated color-magnitude diagrams of the clusters. This work is supported by National Science Foundation Grant No. 0407445 and was done at the Institute of Geophysics and Planetary Physics, under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.

THE INFLUENCE OF PRESSURE-DEPENDENT VISCOSITY ON THE THERMAL EVOLUTION OF SUPER-EARTHS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stamenkovic, Vlada; Noack, Lena; Spohn, Tilman

2012-03-20

We study the thermal evolution of super-Earths with a one-dimensional (1D) parameterized convection model that has been adopted to account for a strong pressure dependence of the viscosity. A comparison with a 2D spherical convection model shows that the derived parameterization satisfactorily represents the main characteristics of the thermal evolution of massive rocky planets. We find that the pressure dependence of the viscosity strongly influences the thermal evolution of super-Earths-resulting in a highly sluggish convection regime in the lower mantles of those planets. Depending on the effective activation volume and for cooler initial conditions, we observe with growing planetary massmore » even the formation of a conductive lid above the core-mantle boundary (CMB), a so-called CMB-lid. For initially molten planets our results suggest no CMB-lids but instead a hot lower mantle and core as well as sluggish lower mantle convection. This implies that the initial interior temperatures, especially in the lower mantle, become crucial for the thermal evolution-the thermostat effect suggested to regulate the interior temperatures in terrestrial planets does not work for massive planets if the viscosity is strongly pressure dependent. The sluggish convection and the potential formation of the CMB-lid reduce the convective vigor throughout the mantle, thereby affecting convective stresses, lithospheric thicknesses, and heat fluxes. The pressure dependence of the viscosity may therefore also strongly affect the propensity of plate tectonics, volcanic activity, and the generation of a magnetic field of super-Earths.« less

Clouds in Super-Earth Atmospheres: Chemical Equilibrium Calculations

NASA Astrophysics Data System (ADS)

Mbarek, Rostom; Kempton, Eliza M.-R.

2016-08-01

Recent studies have unequivocally proven the existence of clouds in super-Earth atmospheres. Here we provide a theoretical context for the formation of super-Earth clouds by determining which condensates are likely to form under the assumption of chemical equilibrium. We study super-Earth atmospheres of diverse bulk composition, which are assumed to form by outgassing from a solid core of chondritic material, following Schaefer & Fegley. The super-Earth atmospheres that we study arise from planetary cores made up of individual types of chondritic meteorites. They range from highly reducing to oxidizing and have carbon to oxygen (C:O) ratios that are both sub-solar and super-solar, thereby spanning a range of atmospheric composition that is appropriate for low-mass exoplanets. Given the atomic makeup of these atmospheres, we minimize the global Gibbs free energy of formation for over 550 gases and condensates to obtain the molecular composition of the atmospheres over a temperature range of 350-3000 K. Clouds should form along the temperature-pressure boundaries where the condensed species appear in our calculation. We find that the composition of condensate clouds depends strongly on both the H:O and C:O ratios. For the super-Earth archetype GJ 1214b, KCl and ZnS are the primary cloud-forming condensates at solar composition, in agreement with previous work. However, for oxidizing atmospheres, K2SO4 and ZnO condensates are favored instead, and for carbon-rich atmospheres with super-solar C:O ratios, graphite clouds appear. For even hotter planets, clouds form from a wide variety of rock-forming and metallic species.

A Microbial Oasis in the Hypersaline Atacama Subsurface Discovered by a Life Detector Chip: Implications for the Search for Life on Mars

PubMed Central

de Diego-Castilla, Graciela; Moreno-Paz, Mercedes; Blanco, Yolanda; Cruz-Gil, Patricia; Rodríguez-Manfredi, José A.; Fernández-Remolar, David; Gómez, Felipe; Gómez, Manuel J.; Rivas, Luis A.; Demergasso, Cecilia; Echeverría, Alex; Urtuvia, Viviana N.; Ruiz-Bermejo, Marta; García-Villadangos, Miriam; Postigo, Marina; Sánchez-Román, Mónica; Chong-Díaz, Guillermo; Gómez-Elvira, Javier

2011-01-01

Abstract The Atacama Desert has long been considered a good Mars analogue for testing instrumentation for planetary exploration, but very few data (if any) have been reported about the geomicrobiology of its salt-rich subsurface. We performed a Mars analogue drilling campaign next to the Salar Grande (Atacama, Chile) in July 2009, and several cores and powder samples from up to 5 m deep were analyzed in situ with LDChip300 (a Life Detector Chip containing 300 antibodies). Here, we show the discovery of a hypersaline subsurface microbial habitat associated with halite-, nitrate-, and perchlorate-containing salts at 2 m deep. LDChip300 detected bacteria, archaea, and other biological material (DNA, exopolysaccharides, some peptides) from the analysis of less than 0.5 g of ground core sample. The results were supported by oligonucleotide microarray hybridization in the field and finally confirmed by molecular phylogenetic analysis and direct visualization of microbial cells bound to halite crystals in the laboratory. Geochemical analyses revealed a habitat with abundant hygroscopic salts like halite (up to 260 g kg−1) and perchlorate (41.13 μg g−1 maximum), which allow deliquescence events at low relative humidity. Thin liquid water films would permit microbes to proliferate by using detected organic acids like acetate (19.14 μg g−1) or formate (76.06 μg g−1) as electron donors, and sulfate (15875 μg g−1), nitrate (13490 μg g−1), or perchlorate as acceptors. Our results correlate with the discovery of similar hygroscopic salts and possible deliquescence processes on Mars, and open new search strategies for subsurface martian biota. The performance demonstrated by our LDChip300 validates this technology for planetary exploration, particularly for the search for life on Mars. Key Words: Atacama Desert—Life detection—Biosensor—Biopolymers—In situ measurement. Astrobiology 11, 969–996. PMID:22149750

A microbial oasis in the hypersaline Atacama subsurface discovered by a life detector chip: implications for the search for life on Mars.

PubMed

Parro, Victor; de Diego-Castilla, Graciela; Moreno-Paz, Mercedes; Blanco, Yolanda; Cruz-Gil, Patricia; Rodríguez-Manfredi, José A; Fernández-Remolar, David; Gómez, Felipe; Gómez, Manuel J; Rivas, Luis A; Demergasso, Cecilia; Echeverría, Alex; Urtuvia, Viviana N; Ruiz-Bermejo, Marta; García-Villadangos, Miriam; Postigo, Marina; Sánchez-Román, Mónica; Chong-Díaz, Guillermo; Gómez-Elvira, Javier

2011-12-01

The Atacama Desert has long been considered a good Mars analogue for testing instrumentation for planetary exploration, but very few data (if any) have been reported about the geomicrobiology of its salt-rich subsurface. We performed a Mars analogue drilling campaign next to the Salar Grande (Atacama, Chile) in July 2009, and several cores and powder samples from up to 5 m deep were analyzed in situ with LDChip300 (a Life Detector Chip containing 300 antibodies). Here, we show the discovery of a hypersaline subsurface microbial habitat associated with halite-, nitrate-, and perchlorate-containing salts at 2 m deep. LDChip300 detected bacteria, archaea, and other biological material (DNA, exopolysaccharides, some peptides) from the analysis of less than 0.5 g of ground core sample. The results were supported by oligonucleotide microarray hybridization in the field and finally confirmed by molecular phylogenetic analysis and direct visualization of microbial cells bound to halite crystals in the laboratory. Geochemical analyses revealed a habitat with abundant hygroscopic salts like halite (up to 260 g kg(-1)) and perchlorate (41.13 μg g(-1) maximum), which allow deliquescence events at low relative humidity. Thin liquid water films would permit microbes to proliferate by using detected organic acids like acetate (19.14 μg g(-1)) or formate (76.06 μg g(-1)) as electron donors, and sulfate (15875 μg g(-1)), nitrate (13490 μg g(-1)), or perchlorate as acceptors. Our results correlate with the discovery of similar hygroscopic salts and possible deliquescence processes on Mars, and open new search strategies for subsurface martian biota. The performance demonstrated by our LDChip300 validates this technology for planetary exploration, particularly for the search for life on Mars.

Resonance Trapping due to Nebula Disk Torques

NASA Astrophysics Data System (ADS)

Hahn, J. M.; Ward, W. R.

1996-03-01

A protoplanet embedded in the solar nebula launches spiral density waves from its Lindblad resonances in the gas disk, and its gravitational attraction for these disturbances results in a mutual torque exerted between the protoplanet and the disk. Consequently the orbit of a sufficiently massive protoplanet may decay on a timescale shorter than the nebula lifetime, and this mechanism is most significant during the formation of the cores of the giant planets. Due to their increased mobility, migrating protoplanets may have been able to accrete large swaths of the disk and/or encounter other protoplanets. Thus disk torques may have played an important role in determining the formation history and orbit spacings of the giant planets. An interesting phenomenon also associated with orbit decay is resonance trapping, whereby a large body is able to halt further orbit decay of smaller bodies at commensurability resonances. Examples of this effect include the trapping of planetesimals experiencing aerodynamic gas drag and dust suffering Poynting-Robertson drag. Below we address the cosmogonic implications of resonance trapping of planetary embryos experiencing orbit decay due to nebula disk torques. The following employs an approach similar to Malhotra's (1993) discussion of the gas drag trapping problem.

Hot subdwarfs in (eclipsing) binaries with brown dwarf or low-mass main-sequence companions

NASA Astrophysics Data System (ADS)

Schaffenroth, Veronika; Geier, Stephan; Heber, Uli

2014-09-01

The formation of hot subdwarf stars (sdBs), which are core helium-burning stars located on the extended horizontal branch, is not yet understood. Many of the known hot subdwarf stars reside in close binary systems with short orbital periods of between a few hours and a few days, with either M-star or white-dwarf companions. Common-envelope ejection is the most probable formation channel. Among these, eclipsing systems are of special importance because it is possible to constrain the parameters of both components tightly by combining spectroscopic and light-curve analyses. They are called HW Virginis systems. Soker (1998) proposed that planetary or brown-dwarf companions could cause the mass loss necessary to form an sdB. Substellar objects with masses greater than >10 M_J were predicted to survive the common-envelope phase and end up in a close orbit around the stellar remnant, while planets with lower masses would entirely evaporate. This raises the question if planets can affect stellar evolution. Here we report on newly discovered eclipsing or not eclipsing hot subdwarf binaries with brown-dwarf or low-mass main-sequence companions and their spectral and photometric analysis to determine the fundamental parameters of both components.

Consequences of eccentricity and inclination damping for the in-situ formation of STIPs

NASA Astrophysics Data System (ADS)

Granados Contreras, Agueda Paula

2018-01-01

In Boley, Granados, and Gladman (2016), we proposed that hot and warm Jupiters could form in-situ from the consolidation of planets in meta-stable, high-multiplicity System with Tightly-packed Inner Planets (STIPs) in the presence of gas. Under this hypothesis, the timing of instability within the STIP relative to the gas depletion timescale can lead to a wide range of planetary diversity, from short-orbital period gas giants to high-density, massive planets. The simulations used Kepler-11 as a base and assumed that a gas giant could form if instability in the gaseous disc led to the consolidation of a 10 Mearth core. The results showed that such consolidation could work, in principle. However, in the simulations we excluded the effects of eccentricity and inclination damping. We present new simulations that explore this effect on the consolidation paradigm. For the parameters so far explored, gas damping significantly increases the stability of the system, although consolidation does occur in some cases. We further find that the eccentricity damping can lead to the formation of stable co-orbiting planets, although this is a rare outcome. Briefly, we explore the implications of the detection of transiting co-orbital planets.

Chondrules: The canonical and noncanonical views

NASA Astrophysics Data System (ADS)

Connolly, Harold C.; Jones, Rhian H.

2016-10-01

Millimeter-scale rock particles called chondrules are the principal components of the most common meteorites, chondrites. Hence, chondrules were arguably the most abundant components of the early solar system at the time of planetesimal accretion. Despite their fundamental importance, the existence of chondrules would not be predicted from current observations and models of young planetary systems. There are many different models for chondrule formation, but no single model satisfies the many constraints determined from their mineralogical and chemical properties and from chondrule analog experiments. Significant recent progress has shown that several models can satisfy first-order constraints and successfully reproduce chondrule thermal histories. However, second- and third-order constraints such as chondrule size ranges, open system behavior, oxidation states, reheating, and chemical diversity have not generally been addressed. Chondrule formation models include those based on processes that are known to occur in protoplanetary disk environments, including interactions with the early active Sun, impacts and collisions between planetary bodies, and radiative heating. Other models for chondrule heating mechanisms are based on hypothetical processes that are possible but have not been observed, like shock waves, planetesimal bow shocks, and lightning. We examine the evidence for the canonical view of chondrule formation, in which chondrules were free-floating particles in the protoplanetary disk, and the noncanonical view, in which chondrules were the by-products of planetesimal formation. The fundamental difference between these approaches has a bearing on the importance of chondrules during planet formation and the relevance of chondrules to interpreting the evolution of protoplanetary disks and planetary systems.

Long-lived planetary vortices and their evolution: Conservative intermediate geostrophic model.

PubMed

Sutyrin, Georgi G.

1994-06-01

Large, long-lived vortices, surviving during many turnaround times and far longer than the dispersive linear Rossby wave packets, are abundant in planetary atmospheres and oceans. Nonlinear effects which prevent dispersive decay of intense cyclones and anticyclones and provide their self-propelling propagation are revised here using shallow water equations and their balanced approximations. The main physical mechanism allowing vortical structures to be long-lived in planetary fluid is the quick fluid rotation inside their cores which prevents growth in the amplitude of asymmetric circulation arising due to the beta-effect. Intense vortices of both signs survive essentially longer than the linear Rossby wave packet if their azimuthal velocity is much larger than the Rossby wave speed. However, in the long-time evolution, cyclonic and anticyclonic vortices behave essentially differently that is illustrated by the conservative intermediate geostrophic model. Asymmetric circulation governing vortex propagation is described by the azimuthal mode m=1 for the initial value problem as well as for steadily propagating solutions. Cyclonic vortices move west-poleward decaying gradually due to Rossby wave radiation while anticyclonic ones adjust to non-radiating solitary vortices. Slow weakening of an intense cyclone with decreasing of its size and shrinking of the core is described assuming zero azimuthal velocity outside the core while drifting poleward. The poleward tendency of the cyclone motion relative to the stirring flow corresponds to characteristic trajectories of tropical cyclones in the Earth's atmosphere. The asymmetry in dispersion-nonlinear properties of cyclones and anticyclones is thought to be one of the essential reasons for the observed predominance of anticyclones among long-lived vortices in the atmospheres of the giant planets and also among intrathermoclinic eddies in the ocean.

Planet Traps and Planetary Cores: Origins of the Planet-Metallicity Correlation

NASA Astrophysics Data System (ADS)

Hasegawa, Yasuhiro; Pudritz, Ralph E.

2014-10-01

Massive exoplanets are observed preferentially around high metallicity ([Fe/H]) stars while low-mass exoplanets do not show such an effect. This so-called planet-metallicity correlation generally favors the idea that most observed gas giants at r < 10 AU are formed via a core accretion process. We investigate the origin of this phenomenon using a semi-analytical model, wherein the standard core accretion takes place at planet traps in protostellar disks where rapid type I migrators are halted. We focus on the three major exoplanetary populations—hot Jupiters, exo-Jupiters located at r ~= 1 AU, and the low-mass planets. We show using a statistical approach that the planet-metallicity correlations are well reproduced in these models. We find that there are specific transition metallicities with values [Fe/H] = -0.2 to -0.4, below which the low-mass population dominates, and above which the Jovian populations take over. The exo-Jupiters significantly exceed the hot Jupiter population at all observed metallicities. The low-mass planets formed via the core accretion are insensitive to metallicity, which may account for a large fraction of the observed super-Earths and hot-Neptunes. Finally, a controlling factor in building massive planets is the critical mass of planetary cores (M c, crit) that regulates the onset of rapid gas accretion. Assuming the current data is roughly complete at [Fe/H] > -0.6, our models predict that the most likely value of the "mean" critical core mass of Jovian planets is langM c, critrang ~= 5 M ⊕ rather than 10 M ⊕. This implies that grain opacities in accreting envelopes should be reduced in order to lower M c, crit.

Planet traps and planetary cores: origins of the planet-metallicity correlation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hasegawa, Yasuhiro; Pudritz, Ralph E., E-mail: yasu@asiaa.sinica.edu.tw, E-mail: pudritz@physics.mcmaster.ca

2014-10-10

Massive exoplanets are observed preferentially around high metallicity ([Fe/H]) stars while low-mass exoplanets do not show such an effect. This so-called planet-metallicity correlation generally favors the idea that most observed gas giants at r < 10 AU are formed via a core accretion process. We investigate the origin of this phenomenon using a semi-analytical model, wherein the standard core accretion takes place at planet traps in protostellar disks where rapid type I migrators are halted. We focus on the three major exoplanetary populations—hot Jupiters, exo-Jupiters located at r ≅ 1 AU, and the low-mass planets. We show using a statisticalmore » approach that the planet-metallicity correlations are well reproduced in these models. We find that there are specific transition metallicities with values [Fe/H] = –0.2 to –0.4, below which the low-mass population dominates, and above which the Jovian populations take over. The exo-Jupiters significantly exceed the hot Jupiter population at all observed metallicities. The low-mass planets formed via the core accretion are insensitive to metallicity, which may account for a large fraction of the observed super-Earths and hot-Neptunes. Finally, a controlling factor in building massive planets is the critical mass of planetary cores (M {sub c,} {sub crit}) that regulates the onset of rapid gas accretion. Assuming the current data is roughly complete at [Fe/H] > –0.6, our models predict that the most likely value of the 'mean' critical core mass of Jovian planets is (M {sub c,} {sub crit}) ≅ 5 M {sub ⊕} rather than 10 M {sub ⊕}. This implies that grain opacities in accreting envelopes should be reduced in order to lower M {sub c,} {sub crit}.« less

Implications for Planetary System Formation from Interstellar Object 1I/2017 U1 (‘Oumuamua)

NASA Astrophysics Data System (ADS)

Trilling, David E.; Robinson, Tyler; Roegge, Alissa; Chandler, Colin Orion; Smith, Nathan; Loeffler, Mark; Trujillo, Chad; Navarro-Meza, Samuel; Glaspie, Lori M.

2017-12-01

The recently discovered minor body 1I/2017 U1 (‘Oumuamua) is the first known object in our solar system that is not bound by the Sun’s gravity. Its hyperbolic orbit (eccentricity greater than unity) strongly suggests that it originated outside our solar system; its red color is consistent with substantial space weathering experienced over a long interstellar journey. We carry out a simple calculation of the probability of detecting such an object. We find that the observed detection rate of 1I-like objects can be satisfied if the average mass of ejected material from nearby stars during the process of planetary formation is ˜20 Earth masses, similar to the expected value for our solar system. The current detection rate of such interstellar interlopers is estimated to be 0.2 yr-1, and the expected number of detections over the past few years is almost exactly one. When the Large Synoptic Survey Telescope begins its wide, fast, deep all-sky survey, the detection rate will increase to 1 yr-1. Those expected detections will provide further constraints on nearby planetary system formation through a better estimate of the number and properties of interstellar objects.

A Novel Theory For The Origin And Evolution Of Stars And Planets, Including Earth, Which Asks, 'Was The Earth Once A Small Bright Star?'

NASA Astrophysics Data System (ADS)

Cimorelli, S. A.; Samuels, C.

2001-12-01

Improved prediction methods for earthquakes and volcanic activity will naturally follow from our theory, based on new concepts of the earth's interior composition, state and activity. In this paper we present a novel hypothesis for the formation and evolution of galaxies, stars (including black holes (BHs), neutron stars, giant, mid-size, dwarf, dying and dead stars), planets (including earth), and moons. Present day phenomenon will be used to substantiate the validity of this hypothesis. Every `body' is a multiple type of star, generated from modified pieces called particle proliferators, of a dislodged/expanded BH (of category 2 (c-2)) which explodes due to a collision with another expanded BH (or explodes on its own). This includes the sun, and the planet earth, which is a type of dead star. Such that, if we remove layers of the earth, starting with the crust, we will find evidence of each preceding star formation, from brown to blue, and the remains of the particle proliferator as the innermost core is reached. We show that the hypothesis is consistent with both the available astronomical data regarding stellar evolution and planetary formation; as well as the evolution of the earth itself, by considerations of the available geophysical data. Where data is not available, reasonably simple experiments are suggested to demonstrate further the consistency and viability of the hypothesis. Theories are presented to help define and explain phenomenon such as how two (or more) c-2 BHs expand and collide to form a small `big bang' (It is postulated that there was a small big bang to form each galaxy, similar to the big bang from a category 1 BH(s) that may have formed our universe. The Great Attractors would be massive c-2 BHs and act on galaxy clusters similar to the massive c-3 BHs at the center of Galaxies acting on stars.). This in turn afforded the material/matter to form all the galactic bodies, including the dark matter inside the galaxies that we catalogue as category-3 BH(s). We conceive that c-3 BHs form gas and dust clouds, inside galaxies, that are the incubators for new stars and planets. The start and development of the planet earth, initially as an emergent piece from the colliding c-2 BHs, is given special attention to explain the continuing expansion/growth that takes place in all stars and planets. We present a new cross section of the earth (as a dead star). Although the dimensions of the inner core, outer core, and the mantle (inner and outer) are about the same as presently known, new insight is given to their formation, evolution and composition. We explain the formation of the land, the growing/expanding earth (proportional to the ocean bed growth), the division of the continents, and the formation of the ocean beds (possibly long before the oceans existed). Attempts will be made to explain the source of the supply of water on earth. We explain various planetary phenomenon including: how/why the earth is growing/expanding (not based on current plate tectonic theory) causing it to retard its rotation; why the oceans are different sizes (the Pacific is about twice the Atlantic); why the masses at the poles are shifting into the Atlantic Ocean (may provide an alternative explanation for the ice ages); why various types of earthquakes occur (a new source is presented), why volcanoes occur (two types are discussed); and improved prediction methods for earthquakes and volcanic eruptions; the making/forming of the mountains from bending and compression buckling, and shear failures of the outer surfaces of the earth's brittle outer skin of the 1st crust (and also from eruptions) due to reduction in curvature of the crust.

10Be Content in Suevite Breccia from the Bosumtwi Impact Crater

NASA Astrophysics Data System (ADS)

Losiak, Anna; Wild, Eva Maria; Michlmayr, Leonard; Koeberl, Christian

2013-04-01

Introduction: According to the current understanding of meteorite impact processes, surface target material is transported from a crater in the form of ejecta or is vaporized/melted (e.g., [1]). The formation model of tektites from the surface of the target rocks has been established using the 10Be content of tektites (e.g., [2]), and chemical comparison with the possible target surface material (e.g., [3]); it was also reproduced by computer modeling (e.g., [4]). On the other hand, some observations ([5, 6]) suggest that part of the surface material may be incorporated into the crater-fill. The aim of this study is to check if surface-derived material is present in suevitic breccias to better understand formation mechanisms of fallback breccias. Also, 10Be can be used to trace contamination of rocks in the top layer of the suevitic layer by meteoric (lake) water. This abstract is an update (based on more data now available) of the previous report presented during the Metsoc75 conference. Samples: The Bosumtwi crater was chosen as study site because of its relatively large size (10.5 km in diameter), young age of 1.07 Ma [7], good state of preservation, and availability of core samples. Clasts from suevitic breccia selected for this study come from the LB-07A and LB-08A cores that are located within the crater and represent fallback breccia (e.g., [7]). Of 41 analyzed samples (22 single clasts and 21 matrix samples - 11 of those being monomictic breccia), 36 came from core LB-07A (in the zone outside the central uplift) and represent depths of 333.7 - 407.9 m and 5 are from core LB-08A (on the flank of the central uplift) from depths 239.5 - 264.9 m. Methods: For each sample, 0.8 g of finely grounded material from clasts containing in situ produced and meteoric 10Be was dissolved in a mixture of HF and HNO3 by microwave digestion. A 9Be carrier (1 mg or 0.6 mg, 10Be/9Be ratio: 2.82±0.31*10-15 [2? uncertainty]) was added to the sample, and then Be was chemically separated from the sample solution. 10Be/9Be ratios were measured at the Vienna Environmental Research Accelerator Facility (VERA) at the University of Vienna. Results: Most samples have 10Be/9Be ratios indistinguishable from the blank value within 2? uncertainty. Samples located just below the boundary between impactites and lake deposits have slightly elevated (1 ? significant) 10Be/9Be ratios. Discussion: The data suggest that none of the analyzed samples present in the suevitic breccia of the Bosumtwi crater come from the surficial layer (0-20 m) of the target. A very small amount of the 10Be present in the layer directly underneath the lake sediments suggests that those two deposits were very efficiently separated from each other. Possibly, this separation was caused by the uppermost impact fallback layer described by Koeberl et al. (2007). Acknowledgment: Supported by University of Vienna doctoral school IK-1045 (Planetology). References: [1] Melosh H.J. 1988. Impact Cratering, Oxford University Press, 256 pp.. [2] Serefiddin F. et al. 2007. Geochimica et Cosmochimica Acta 71: 1574-1582. [3] Son T.H. and Koeberl C. 2007. GFF 29: 161-176. [4] Artemieva N.A. 2000. In: Impacts in Precambrian Shields, Springer, pp. 257-276. [5] Puura V. et al. 2004. Meteoritics & Planetary Science 39: 425-451. [6] Reimold W.U., et al. 1992. Geology 20:1079-1082. [7] Koeberl C. et al. 2007. Meteoritics & Planetary Science 42: 483-511. [8] Koeberl C. et al. 2007. Meteoritics & Planetary Science 42: 709-729.

Collisional and dynamical processes in moon and planet formation

NASA Technical Reports Server (NTRS)

Chapman, C. R.; Davis, D. R.; Weidenschilling, S. J.; Hartmann, W. K.; Spaute, D.

1987-01-01

Research on a variety of dynamical processes relevant to the formation of planets, satellites and ring systems is discussed. The main focus is on studies of accretionary formation of early protoplanets using a numerical model, structures and evolution of ring systems and individual bodies within planetary rings, and theories of lunar origin.

Diffusive Transport and Structural Properties of Liquid Iron Alloys at High Pressure

NASA Astrophysics Data System (ADS)

Posner, E.; Rubie, D. C.; Steinle-Neumann, G.; Frost, D. J.

2017-12-01

Diffusive transport properties of liquid iron alloys at high pressures (P) and temperatures (T) place important kinetic constraints on processes related to the origin and evolution of planetary cores. Earth's core composition is largely controlled by the extent of chemical equilibration achieved between liquid metal bodies and a silicate magma ocean during core formation, which can be estimated using chemical diffusion data. In order to estimate the time and length scales of metal-silicate chemical equilibration, we have measured chemical diffusion rates of Si, O and Cr in liquid iron over the P-T range of 1-18 GPa and 1873-2643 K using a multi-anvil apparatus. We have also performed first-principles molecular dynamic simulations of comparable binary liquid compositions, in addition to pure liquid Fe, over a much wider P-T range (1 bar-330 GPa, 2200-5500 K) in order to both validate the simulation results with experimental data at conditions accessible in the laboratory and to extend our dataset to conditions of the Earth's core. Over the entire P-T range studied using both methods, diffusion coefficients are described consistently and well using an exponential function of the homologous temperature relation. Si, Cr and Fe diffusivities of approximately 5 × 10-9 m2 s-1 are constant along the melting curve from ambient to core pressures, while oxygen diffusion is 2-3 times faster. Our results indicate that in order for the composition of the Earth's core to represent chemical equilibrium, impactor cores must have broken up into liquid droplet sizes no larger than a few tens of cm. Structural properties, analyzed using partial radial distribution functions from the molecular dynamics simulations, reveal a pressure-induced structural change in liquid Fe0.96O0.04 at densities of 8 g cm-3, in agreement with previous experimental studies. For densities above 8 g cm-3, the liquid is essentially close packed with a local CsCl-like (B2) packing of Fe around O under conditions of the Earth's core.

Geochemical Evidence for a Terrestrial Magma Ocean

NASA Technical Reports Server (NTRS)

Agee, Carl B.

1999-01-01

The aftermath of phase separation and crystal-liquid fractionation in a magma ocean should leave a planet geochemically differentiated. Subsequent convective and other mixing processes may operate over time to obscure geochemical evidence of magma ocean differentiation. On the other hand, core formation is probably the most permanent, irreversible part of planetary differentiation. Hence the geochemical traces of core separation should be the most distinct remnants left behind in the mantle and crust, In the case of the Earth, core formation apparently coincided with a magma ocean that extended to a depth of approximately 1000 km. Evidence for this is found in high pressure element partitioning behavior of Ni and Co between liquid silicate and liquid iron alloy, and with the Ni-Co ratio and the abundance of Ni and Co in the Earth's upper mantle. A terrestrial magma ocean with a depth of 1000 km will solidify from the bottom up and first crystallize in the perovskite stability field. The largest effect of perovskite fractionation on major element distribution is to decrease the Si-Mg ratio in the silicate liquid and increase the Si-Mg ratio in the crystalline cumulate. Therefore, if a magma ocean with perovskite fractionation existed, then one could expect to observe an upper mantle with a lower than chondritic Si-Mg ratio. This is indeed observed in modern upper mantle peridotites. Although more experimental work is needed to fully understand the high-pressure behavior of trace element partitioning, it is likely that Hf is more compatible than Lu in perovskite-silicate liquid pairs. Thus, perovskite fractionation produces a molten mantle with a higher than chondritic Lu-Hf ratio. Arndt and Blichert-Toft measured Hf isotope compositions of Barberton komatiites that seem to require a source region with a long-lived, high Lu-Hf ratio. It is plausible that that these Barberton komatiites were generated within the majorite stability field by remelting a perovskite-depleted part of the upper mantle transition zone.

Planetary exploration through year 2000: An augmented program. Part two of a report by the Solar System Exploration Committee of the NASA Advisory Council

NASA Technical Reports Server (NTRS)

1986-01-01

In 1982, the NASA Solar System Exploration Committee (SSEC) published a report on a Core Program of planetary missions, representing the minimum-level program that could be carried out in a cost effective manner, and would yield a continuing return of basic scientific results. This is the second part of the SSEC report, describing missions of the highest scientific merit that lie outside the scope of the previously recommended Core Program because of their cost and technical challenge. These missions include the autonomous operation of a mobile scientific rover on the surface of Mars, the automated collection and return of samples from that planet, the return to Earth of samples from asteroids and comets, projects needed to lay the groundwork for the eventual utilization of near-Earth resources, outer planet missions, observation programs for extra-solar planets, and technological developments essential to make these missions possible.

The importance of dunes on a variety of planetary surfaces

USGS Publications Warehouse

Titus, Timothy N.; Zimbelman, James R.; Radebaugh, Jani

2015-01-01

Scientists observe aeolian bed forms, or dune-like structures, throughout the solar system in a range of locations, from bodies with only transient atmospheres, such as comets, to places with thick atmospheres, such as Venus and the Earth’s ocean floor. Determining the source of sand and the different dune formations that result are thus important to understanding solar system and planetary evolution.

Electronic and magnetic structures of the postperovskite-type Fe2O3 and implications for planetary magnetic records and deep interiors

PubMed Central

Shim, Sang-Heon; Bengtson, Amelia; Morgan, Dane; Sturhahn, Wolfgang; Catalli, Krystle; Zhao, Jiyong; Lerche, Michael; Prakapenka, Vitali

2009-01-01

Recent studies have shown that high pressure (P) induces the metallization of the Fe2+–O bonding, the destruction of magnetic ordering in Fe, and the high-spin (HS) to low-spin (LS) transition of Fe in silicate and oxide phases at the deep planetary interiors. Hematite (Fe2O3) is an important magnetic carrier mineral for deciphering planetary magnetism and a proxy for Fe in the planetary interiors. Here, we present synchrotron Mössbauer spectroscopy and X-ray diffraction combined with ab initio calculations for Fe2O3 revealing the destruction of magnetic ordering at the hematite → Rh2O3-II type (RhII) transition at 70 GPa and 300 K, and then the revival of magnetic ordering at the RhII → postperovskite (PPv) transition after laser heating at 73 GPa. At the latter transition, at least half of Fe3+ ions transform from LS to HS and Fe2O3 changes from a semiconductor to a metal. This result demonstrates that some magnetic carrier minerals may experience a complex sequence of magnetic ordering changes during impact rather than a monotonic demagnetization. Also local Fe enrichment at Earth's core-mantle boundary will lead to changes in the electronic structure and spin state of Fe in silicate PPv. If the ultra-low-velocity zones are composed of Fe-enriched silicate PPv and/or the basaltic materials are accumulated at the lowermost mantle, high electrical conductivity of these regions will play an important role for the electromagnetic coupling between the mantle and the core. PMID:19279204

The role of exogenic factors in the formation of the lunar surface

NASA Technical Reports Server (NTRS)

Florenskiy, K. P.; Bazilevskiy, A. T.; Ivanov, A. V.

1977-01-01

The formation of the surface of planetary bodies is determined by the interaction of endogenic and exogenic forces. Clarification of the mutual role of these forces is one of the most important trends in the geological sciences.

PLANETARY EMBRYO BOW SHOCKS AS A MECHANISM FOR CHONDRULE FORMATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mann, Christopher R.; Boley, Aaron C.; Morris, Melissa A.

2016-02-20

We use radiation hydrodynamics with direct particle integration to explore the feasibility of chondrule formation in planetary embryo bow shocks. The calculations presented here are used to explore the consequences of a Mars-size planetary embryo traveling on a moderately excited orbit through the dusty, early environment of the solar system. The embryo’s eccentric orbit produces a range of supersonic relative velocities between the embryo and the circularly orbiting gas and dust, prompting the formation of bow shocks. Temporary atmospheres around these embryos, which can be created via volatile outgassing and gas capture from the surrounding nebula, can non-trivially affect thermalmore » profiles of solids entering the shock. We explore the thermal environment of solids that traverse the bow shock at different impact radii, the effects that planetoid atmospheres have on shock morphologies, and the stripping efficiency of planetoidal atmospheres in the presence of high relative winds. Simulations are run using adiabatic and radiative conditions, with multiple treatments for the local opacities. Shock speeds of 5, 6, and 7 km s{sup −1} are explored. We find that a high-mass atmosphere and inefficient radiative conditions can produce peak temperatures and cooling rates that are consistent with the constraints set by chondrule furnace studies. For most conditions, the derived cooling rates are potentially too high to be consistent with chondrule formation.« less

Extrasolar planetary systems.

NASA Technical Reports Server (NTRS)

Huang, S.-S.

1973-01-01

The terms 'planet' and 'planet-like objects' are defined. The observational search for extrasolar planetary systems is described, as performable by earthbound optical telescopes, by space probes, by long baseline radio interferometry, and finally by inference from the reception of signals sent by intelligent beings in other worlds. It is shown that any planetary system must be preceded by a rotating disk of gas and dust around a central mass. A brief review of the theories of the formation of the solar system is given, along with a proposed scheme for classification of these theories. The evidence for magnetic activity in the early stages of stellar evolution is presented. The magnetic braking theories of solar and stellar rotation are discussed, and an estimate is made for the frequency of occurrence of planetary systems in the universe.

Planetary System Physics

NASA Technical Reports Server (NTRS)

Peale, S. J.

2002-01-01

Contents include a summary of publications followed by their abstracts titeled: 1. On microlensing rates and optical depth toward the Galactic center. 2. Newly discovered brown dwarfs not seen in microlensing timescale frequency distribution? 3. Origin and evolution of the natural satellites. 4. Probing the structure of the galaxy with microlensing. 5. Tides, Encyclopedia of Astronomy and Astrophysics. 6. The Puzzle of the Titan-Hyperion 4:3 Orbital Resonance. 7. On the Validity of the Coagulation Equation and the Nature of Runaway Growth. 8. Making Hyperion. 9. The MESSENGER mission to Mercury: Scientific objectives and implementation. 10. A Survey of Numerical Solutions to the Coagulation. 11. Probability of detecting a planetary companion during a microlensing event. 12. Dynamics and origin of the 2:l orbital resonances of the GJ876 planets. 13. Planetary Interior Structure Revealed by Spin Dynamics. 14. A primordial origin of the Laplace relation among the Galilean Satellites. 15. A procedure for determining the nature of Mercury's core. 16. Secular evolution of hierarchical planetary systems. 17. Tidally induced volcanism. 18. Extrasolar planets and mean motion resonances. 19. Comparison of a ground-based microlensing search for planets with a search from space.

Multiple zonal jets and convective heat transport barriers in a quasi-geostrophic model of planetary cores

NASA Astrophysics Data System (ADS)

Guervilly, C.; Cardin, P.

2017-10-01

We study rapidly rotating Boussinesq convection driven by internal heating in a full sphere. We use a numerical model based on the quasi-geostrophic approximation for the velocity field, whereas the temperature field is 3-D. This approximation allows us to perform simulations for Ekman numbers down to 10-8, Prandtl numbers relevant for liquid metals (˜10-1) and Reynolds numbers up to 3 × 104. Persistent zonal flows composed of multiple jets form as a result of the mixing of potential vorticity. For the largest Rayleigh numbers computed, the zonal velocity is larger than the convective velocity despite the presence of boundary friction. The convective structures and the zonal jets widen when the thermal forcing increases. Prograde and retrograde zonal jets are dynamically different: in the prograde jets (which correspond to weak potential vorticity gradients) the convection transports heat efficiently and the mean temperature tends to be homogenized; by contrast, in the cores of the retrograde jets (which correspond to steep gradients of potential vorticity) the dynamics is dominated by the propagation of Rossby waves, resulting in the formation of steep mean temperature gradients and the dominance of conduction in the heat transfer process. Consequently, in quasi-geostrophic systems, the width of the retrograde zonal jets controls the efficiency of the heat transfer.

Mass-loss evolution of close-in exoplanets: Evaporation of hot Jupiters and the effect on population

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kurokawa, H.; Nakamoto, T., E-mail: kurokawa@nagoya-u.jp

2014-03-01

During their evolution, short-period exoplanets may lose envelope mass through atmospheric escape owing to intense X-ray and extreme ultraviolet (XUV) radiation from their host stars. Roche-lobe overflow induced by orbital evolution or intense atmospheric escape can also contribute to mass loss. To study the effects of mass loss on inner planet populations, we calculate the evolution of hot Jupiters considering mass loss of their envelopes and thermal contraction. Mass loss is assumed to occur through XUV-driven atmospheric escape and the following Roche-lobe overflow. The runaway effect of mass loss results in a dichotomy of populations: hot Jupiters that retain theirmore » envelopes and super Earths whose envelopes are completely lost. Evolution primarily depends on the core masses of planets and only slightly on migration history. In hot Jupiters with small cores (≅ 10 Earth masses), runaway atmospheric escape followed by Roche-lobe overflow may create sub-Jupiter deserts, as observed in both mass and radius distributions of planetary populations. Comparing our results with formation scenarios and observed exoplanets populations, we propose that populations of closely orbiting exoplanets are formed by capturing planets at/inside the inner edges of protoplanetary disks and subsequent evaporation of sub-Jupiters.« less

Interoperability In The New Planetary Science Archive (PSA)

NASA Astrophysics Data System (ADS)

Rios, C.; Barbarisi, I.; Docasal, R.; Macfarlane, A. J.; Gonzalez, J.; Arviset, C.; Grotheer, E.; Besse, S.; Martinez, S.; Heather, D.; De Marchi, G.; Lim, T.; Fraga, D.; Barthelemy, M.

2015-12-01

As the world becomes increasingly interconnected, there is a greater need to provide interoperability with software and applications that are commonly being used globally. For this purpose, the development of the new Planetary Science Archive (PSA), by the European Space Astronomy Centre (ESAC) Science Data Centre (ESDC), is focused on building a modern science archive that takes into account internationally recognised standards in order to provide access to the archive through tools from third parties, for example by the NASA Planetary Data System (PDS), the VESPA project from the Virtual Observatory of Paris as well as other international institutions. The protocols and standards currently being supported by the new Planetary Science Archive at this time are the Planetary Data Access Protocol (PDAP), the EuroPlanet-Table Access Protocol (EPN-TAP) and Open Geospatial Consortium (OGC) standards. The architecture of the PSA consists of a Geoserver (an open-source map server), the goal of which is to support use cases such as the distribution of search results, sharing and processing data through a OGC Web Feature Service (WFS) and a Web Map Service (WMS). This server also allows the retrieval of requested information in several standard output formats like Keyhole Markup Language (KML), Geography Markup Language (GML), shapefile, JavaScript Object Notation (JSON) and Comma Separated Values (CSV), among others. The provision of these various output formats enables end-users to be able to transfer retrieved data into popular applications such as Google Mars and NASA World Wind.

HUBBLE FINDS AN HOURGLASS NEBULA AROUND A DYING STAR

NASA Technical Reports Server (NTRS)

2002-01-01

This is an image of MyCn18, a young planetary nebula located about 8,000 light-years away, taken with the Wide Field and Planetary Camera 2 (WFPC2) aboard NASA's Hubble Space Telescope (HST). This Hubble image reveals the true shape of MyCn18 to be an hourglass with an intricate pattern of 'etchings' in its walls. This picture has been composed from three separate images taken in the light of ionized nitrogen (represented by red), hydrogen (green), and doubly-ionized oxygen (blue). The results are of great interest because they shed new light on the poorly understood ejection of stellar matter which accompanies the slow death of Sun-like stars. In previous ground-based images, MyCn18 appears to be a pair of large outer rings with a smaller central one, but the fine details cannot be seen. According to one theory for the formation of planetary nebulae, the hourglass shape is produced by the expansion of a fast stellar wind within a slowly expanding cloud which is more dense near its equator than near its poles. What appears as a bright elliptical ring in the center, and at first sight might be mistaken for an equatorially dense region, is seen on closer inspection to be a potato shaped structure with a symmetry axis dramatically different from that of the larger hourglass. The hot star which has been thought to eject and illuminate the nebula, and therefore expected to lie at its center of symmetry, is clearly off center. Hence MyCn18, as revealed by Hubble, does not fulfill some crucial theoretical expectations. Hubble has also revealed other features in MyCn18 which are completely new and unexpected. For example, there is a pair of intersecting elliptical rings in the central region which appear to be the rims of a smaller hourglass. There are the intricate patterns of the etchings on the hourglass walls. The arc-like etchings could be the remnants of discrete shells ejected from the star when it was younger (e.g. as seen in the Egg Nebula), flow instabilities, or could result from the action of a narrow beam of matter impinging on the hourglass walls. An unseen companion star and accompanying gravitational effects may well be necessary in order to explain the structure of MyCn18. BACKGROUND: PLANETARY NEBULAE When Sun-like stars get old, they become cooler and redder, increasing their sizes and energy output tremendously: they are called red giants. Most of the carbon (the basis of life) and particulate matter (crucial building blocks of solar systems like ours) in the universe is manufactured and dispersed by red giant stars. When the red giant star has ejected all of its outer layers, the ultraviolet radiation from the exposed hot stellar core makes the surrounding cloud of matter created during the red giant phase glow: the object becomes a planetary nebula. A long-standing puzzle is how planetary nebulae acquire their complex shapes and symmetries, since red giants and the gas/dust clouds surrounding them are mostly round. Hubble's ability to see very fine structural details (usually blurred beyond recognition in ground-based images) enables us to look for clues to this puzzle. CREDITS: Raghvendra Sahai and John Trauger (JPL), the WFPC2 science team, and NASA Image files in GIF and JPEG format and captions may be accessed on Internet via anonymous ftp from oposite.stsci.edu in /pubinfo.

The chlorine abundance of Earth: Implications for a habitable planet

NASA Astrophysics Data System (ADS)

Sharp, Z. D.; Draper, D. S.

2013-05-01

The Cl, Br and I contents of Earth are depleted by a factor of 10 relative to predicted values from chondritic and solar abundances. Possible explanations for the apparent discrepancy include (1) unrecognized sequestration of Cl in the core, (2) a much higher nebular volatility than normally presumed or (3) a preferential loss of the heavy halogens during planetary accretion. We tested the first assumption by conducting high pressure-temperature equilibration experiments between silicate and metal. At 15 GPa and 1900 °C, the DCl(metal-silicate) value for Cl is less than 0.007, indicating that the core is not a significant reservoir for Cl. The concentration of Cl in all chondritic classes follows a depletion trend very similar to that of Na and Mn, arguing against a low condensation temperature for Cl. Instead, we propose that the depletion of the heavy halogens is due to their unique hydrophilic behavior. Almost half of Earth's Cl and Br inventory resides in the ocean and evaporites, demonstrating the unique affinity for aqueous solutions for these elements. During planetary accretion, there would have been a strong sequestration of halogens into the crustal reservoir. 'Collisional erosion' during planetary accretion provides a mechanism that would uniquely strip the heavy halogens out of an accreting Earth. Had such loss not occurred, the salinity of the oceans would be 10× the present value, and complex life would probably never have evolved.

Strategy of Planetary Data Archives in Japanese Missions for Planetary Data System

NASA Astrophysics Data System (ADS)

Yamamoto, Y.; Ishihara, Y.; Murakami, S. Y.

2017-12-01

To preserve data acquired by Japanese planetary explorations for a long time, we need a data archiving strategy in a form suitable for resources. Planetary Data System(PDS) developed by NASA is an excellent system for saving data over a long period. Especially for the current version 4 (PDS4), it is possible to create a data archive with high completeness using information technology. Historically, the Japanese planetary missions have archived data by scientists in their ways, but in the past decade, JAXA has been aiming to conform data to PDS considering long term preservation. Hayabusa, Akatsuki are archived in PDS3. Kaguya(SELENE) data have been newly converted from the original format to PDS3. Hayabusa2 and BepiColombo, and future planetary explorations will release data in PDS4. The cooperation of engineers who are familiar with information technology is indispensable to create data archives for scientists. In addition, it is essential to have experience, information sharing, and a system to support it. There is a challenge in Japan about the system.

Planetary Rings

NASA Astrophysics Data System (ADS)

Tiscareno, Matthew S.

Planetary rings are the only nearby astrophysical disks and the only disks that have been investigated by spacecraft (especially the Cassini spacecraft orbiting Saturn). Although there are significant differences between rings and other disks, chiefly the large planet/ring mass ratio that greatly enhances the flatness of rings (aspect ratios as small as 10- 7), understanding of disks in general can be enhanced by understanding the dynamical processes observed at close range and in real time in planetary rings.We review the known ring systems of the four giant planets, as well as the prospects for ring systems yet to be discovered. We then review planetary rings by type. The A, B, and C rings of Saturn, plus the Cassini Division, comprise our solar system's only dense broad disk and host many phenomena of general application to disks including spiral waves, gap formation, self-gravity wakes, viscous overstability and normal modes, impact clouds, and orbital evolution of embedded moons. Dense narrow rings are found both at Uranus (where they comprise the main rings entirely) and at Saturn (where they are embedded in the broad disk) and are the primary natural laboratory for understanding shepherding and self-stability. Narrow dusty rings, likely generated by embedded source bodies, are surprisingly found to sport azimuthally confined arcs at Neptune, Saturn, and Jupiter. Finally, every known ring system includes a substantial component of diffuse dusty rings.Planetary rings have shown themselves to be useful as detectors of planetary processes around them, including the planetary magnetic field and interplanetary impactors as well as the gravity of nearby perturbing moons. Experimental rings science has made great progress in recent decades, especially numerical simulations of self-gravity wakes and other processes but also laboratory investigations of coefficient of restitution and spectroscopic ground truth. The age of self-sustained ring systems is a matter of debate; formation scenarios are most plausible in the context of the early solar system, while signs of youthfulness indicate at least that rings have never been static phenomena.

Progress of Interoperability in Planetary Research for Geospatial Data Analysis

NASA Astrophysics Data System (ADS)

Hare, T. M.; Gaddis, L. R.

2015-12-01

For nearly a decade there has been a push in the planetary science community to support interoperable methods of accessing and working with geospatial data. Common geospatial data products for planetary research include image mosaics, digital elevation or terrain models, geologic maps, geographic location databases (i.e., craters, volcanoes) or any data that can be tied to the surface of a planetary body (including moons, comets or asteroids). Several U.S. and international cartographic research institutions have converged on mapping standards that embrace standardized image formats that retain geographic information (e.g., GeoTiff, GeoJpeg2000), digital geologic mapping conventions, planetary extensions for symbols that comply with U.S. Federal Geographic Data Committee cartographic and geospatial metadata standards, and notably on-line mapping services as defined by the Open Geospatial Consortium (OGC). The latter includes defined standards such as the OGC Web Mapping Services (simple image maps), Web Feature Services (feature streaming), Web Coverage Services (rich scientific data streaming), and Catalog Services for the Web (data searching and discoverability). While these standards were developed for application to Earth-based data, they have been modified to support the planetary domain. The motivation to support common, interoperable data format and delivery standards is not only to improve access for higher-level products but also to address the increasingly distributed nature of the rapidly growing volumes of data. The strength of using an OGC approach is that it provides consistent access to data that are distributed across many facilities. While data-steaming standards are well-supported by both the more sophisticated tools used in Geographic Information System (GIS) and remote sensing industries, they are also supported by many light-weight browsers which facilitates large and small focused science applications and public use. Here we provide an overview of the interoperability initiatives that are currently ongoing in the planetary research community, examples of their successful application, and challenges that remain.

Teaching, Learning, and Planetary Exploration

NASA Technical Reports Server (NTRS)

Brown, Robert A.

2002-01-01

This is the final report of a program that examined the fundamentals of education associated with space activities, promoted educational policy development in appropriate forums, and developed pathfinder products and services to demonstrate the utility of advanced communication technologies for space-based education. Our focus was on space astrophysics and planetary exploration, with a special emphasis on the themes of the Origins Program, with which the Principal Investigator (PI) had been involved from the outset. Teaching, Learning, and Planetary Exploration was also the core funding of the Space Telescope Science Institute's (ST ScI) Special Studies Office (SSO), and as such had provided basic support for such important NASA studies as the fix for Hubble Space Telescope (HST) spherical aberration, scientific conception of the HST Advanced Camera, specification of the Next-Generation Space Telescope (NGST), and the strategic plan for the second decade of the HST science program.

Plate tectonics and planetary habitability: current status and future challenges.

PubMed

Korenaga, Jun

2012-07-01

Plate tectonics is one of the major factors affecting the potential habitability of a terrestrial planet. The physics of plate tectonics is, however, still far from being complete, leading to considerable uncertainty when discussing planetary habitability. Here, I summarize recent developments on the evolution of plate tectonics on Earth, which suggest a radically new view on Earth dynamics: convection in the mantle has been speeding up despite its secular cooling, and the operation of plate tectonics has been facilitated throughout Earth's history by the gradual subduction of water into an initially dry mantle. The role of plate tectonics in planetary habitability through its influence on atmospheric evolution is still difficult to quantify, and, to this end, it will be vital to better understand a coupled core-mantle-atmosphere system in the context of solar system evolution. © 2012 New York Academy of Sciences.

Summary and abstracts of the Planetary Data Workshop, June 2012

USGS Publications Warehouse

Gaddis, Lisa R.; Hare, Trent; Beyer, Ross

2014-01-01

The recent boom in the volume of digital data returned by international planetary science missions continues to both delight and confound users of those data. In just the past decade, the Planetary Data System (PDS), NASA’s official archive of scientific results from U.S. planetary missions, has seen a nearly 50-fold increase in the amount of data and now serves nearly half a petabyte. In only a handful of years, this volume is expected to approach 1 petabyte (1,000 terabytes or 1 quadrillion bytes). Although data providers, archivists, users, and developers have done a creditable job of providing search functions, download capabilities, and analysis and visualization tools, the new wealth of data necessitates more frequent and extensive discussion among users and developers about their current capabilities and their needs for improved and new tools. A workshop to address these and other topics, “Planetary Data: A Workshop for Users and Planetary Software Developers,” was held June 25–29, 2012, at Northern Arizona University (NAU) in Flagstaff, Arizona. A goal of the workshop was to present a summary of currently available tools, along with hands-on training and how-to guides, for acquiring, processing and working with a variety of digital planetary data. The meeting emphasized presentations by data users and mission providers during days 1 and 2, and developers had the floor on days 4 and 5 using an “unconference” format for day 5. Day 3 featured keynote talks by Laurence Soderblom (U.S. Geological Survey, USGS) and Dan Crichton (Jet Propulsion Laboratory, JPL) followed by a panel discussion, and then research and technical discussions about tools and capabilities under recent or current development. Software and tool demonstrations were held in break-out sessions in parallel with the oral session. Nearly 150 data users and developers from across the globe attended, and 22 National Aeronautics and space Administration (NASA) and non-NASA data providers and missions were represented. Presentations (some in video format) and tutorials are posted on the meeting site (http://astrogeology.usgs.gov/groups/Planetary-Data-Workshop).

Formation of Planetary Populations I: Metallicity & Envelope Opacity Effects

NASA Astrophysics Data System (ADS)

Alessi, Matthew; Pudritz, Ralph E.

2018-05-01

We present a comprehensive body of simulations of the formation of exoplanetary populations that incorporate the role of planet traps in slowing planetary migration. The traps we include in our model are the water ice line, the disk heat transition, and the dead zone outer edge. We reduce our model parameter set to two physical parameters: the opacity of the accreting planetary atmospheres (κenv) and a measure of the efficiency of planetary accretion after gap opening (fmax). We perform planet population synthesis calculations based on the initial observed distributions of host star and disk properties - their disk masses, lifetimes, and stellar metallicities. We find the frequency of giant planet formation scales with disk metallicity, in agreement with the observed Jovian planet frequency-metallicity relation. We consider both X-ray and cosmic ray disk ionization models, whose differing ionization rates lead to different dead zone trap locations. In both cases, Jovian planets form in our model out to 2-3 AU, with a distribution at smaller radii dependent on the disk ionization source and the setting of envelope opacity. We find that low values of κenv (0.001-0.002 cm2 g-1) and X-ray disk ionization are necessary to obtain a separation between hot Jupiters near 0.1 AU, and warm Jupiters outside 0.6 AU, a feature present in the data. Our model also produces a large number of super Earths, but the majority are outside of 2 AU. As our model assumes a constant dust to gas ratio, we suggest that radial dust evolution must be taken into account to reproduce the observed super Earth population.

ROLE OF NITROGEN OXIDES IN NONURBAN OZONE FORMATION IN THE PLANETARY BOUNDARY LAYER OVER N (NORTH) AMERICA, W (WESTERN) EUROPE AND ADJACENT AREAS OF OCEAN

EPA Science Inventory

The status of knowledge on photochemical ozone formation and the effects of nitrogen oxides and peroxyacyl nitrates on such formation has been evaluated. The literature is reviewed on nonurban ozone and nitrogen oxide concentration distributions, ozone lifetimes, nitrogen oxide l...

Planetary Sciences: American and Soviet Research

NASA Technical Reports Server (NTRS)

Donahue, Thomas M. (Editor); Trivers, Kathleen Kearney (Editor); Abramson, David M. (Editor)

1991-01-01

Papers presented at the US-USSR Workshop on Planetary Sciences are compiled. The purpose of the workshop was to examine the current state of theoretical understanding of how the planets were formed and how they evolved to their present state. The workshop assessed the types of observations and experiments that are needed to advance understanding of the formation and evolution of the solar system based on the current theoretical framework.

NASA thesaurus: Astronomy vocabulary

NASA Technical Reports Server (NTRS)

1988-01-01

A terminology of descriptors used by the NASA Scientific and Technical information effort to index documents in the area of astronomy is presented. The terms are listed in hierarchical format derived from the 1988 edition of the NASA Thesaurus Volume 1 -- Hierarchical Listing. Over 1600 terms are included. In addition to astronomy, space sciences covered include astrophysics, cosmology, lunar flight and exploration, meteors and meteorites, celestial mechanics, planetary flight and exploration, and planetary science.

REVIEWS OF TOPICAL PROBLEMS: Generation of large-scale eddies and zonal winds in planetary atmospheres

NASA Astrophysics Data System (ADS)

Onishchenko, O. G.; Pokhotelov, O. A.; Astafieva, N. M.

2008-06-01

The review deals with a theoretical description of the generation of zonal winds and vortices in a turbulent barotropic atmosphere. These large-scale structures largely determine the dynamics and transport processes in planetary atmospheres. The role of nonlinear effects on the formation of mesoscale vortical structures (cyclones and anticyclones) is examined. A new mechanism for zonal wind generation in planetary atmospheres is discussed. It is based on the parametric generation of convective cells by finite-amplitude Rossby waves. Weakly turbulent spectra of Rossby waves are considered. The theoretical results are compared to the results of satellite microwave monitoring of the Earth's atmosphere.

The Blue Dot Workshop: Spectroscopic Search for Life on Extrasolar Planets

NASA Technical Reports Server (NTRS)

Des Marais, David J. (Editor)

1997-01-01

This workshop explored the key questions and challenges associated with detecting life on an extrasolar planet. The final product will be a NASA Conference Publication which includes the abstracts from 21 talks, summaries of key findings, and recommendations for future research. The workshop included sessions on three related topics: the biogeochemistry of biogenic gases in the atmosphere, the chemistry and spectroscopy of planetary atmospheres, and the remote sensing of planetary atmospheres and surfaces. With the observation that planetary formation is probably a common phenomenon, together with the advent of the technical capability to locate and describe extrasolar planets, this research area indeed has an exciting future.

Dynamical role of Ekman pumping in rapidly rotating convection

NASA Astrophysics Data System (ADS)

Stellmach, Stephan; Julien, Keith; Cheng, Jonathan; Aurnou, Jonathan

2015-04-01

The exact nature of the mechanical boundary conditions (i.e. no-slip versus stress-free) is usually considered to be of secondary importance in the rapidly rotating parameter regime characterizing planetary cores. While they have considerable influence for the Ekman numbers achievable in today's global simulations, for planetary values both the viscous Ekman layers and the associated secondary flows are generally expected to become negligibly small. In fact, usually the main purpose of using stress-free boundary conditions in numerical dynamo simulations is to suppress unrealistically large friction and pumping effects. In this study, we investigate the influence of the mechanical boundary conditions on core convection systematically. By restricting ourselves to the idealized case of rapidly rotating Rayleigh-Bénard convection, we are able to combine results from direct numerical simulations (DNS), laboratory experiments and asymptotic theory into a coherent picture. Contrary to the general expectation, we show that the dynamical effects of Ekman pumping increase with decreasing Ekman number over the investigated parameter range. While stress-free DNS results converge to the asymptotic predictions, both no-slip simulations and laboratory experiments consistently reveal increasingly large deviations from the existing asymptotic theory based on dynamically passive Ekman layers. The implications of these results for core dynamics are discussed briefly.

Globe Browsing: Contextualized Spatio-Temporal Planetary Surface Visualization.

PubMed

Bladin, Karl; Axelsson, Emil; Broberg, Erik; Emmart, Carter; Ljung, Patric; Bock, Alexander; Ynnerman, Anders

2017-08-29

Results of planetary mapping are often shared openly for use in scientific research and mission planning. In its raw format, however, the data is not accessible to non-experts due to the difficulty in grasping the context and the intricate acquisition process. We present work on tailoring and integration of multiple data processing and visualization methods to interactively contextualize geospatial surface data of celestial bodies for use in science communication. As our approach handles dynamic data sources, streamed from online repositories, we are significantly shortening the time between discovery and dissemination of data and results. We describe the image acquisition pipeline, the pre-processing steps to derive a 2.5D terrain, and a chunked level-of-detail, out-of-core rendering approach to enable interactive exploration of global maps and high-resolution digital terrain models. The results are demonstrated for three different celestial bodies. The first case addresses high-resolution map data on the surface of Mars. A second case is showing dynamic processes, such as concurrent weather conditions on Earth that require temporal datasets. As a final example we use data from the New Horizons spacecraft which acquired images during a single flyby of Pluto. We visualize the acquisition process as well as the resulting surface data. Our work has been implemented in the OpenSpace software [8], which enables interactive presentations in a range of environments such as immersive dome theaters, interactive touch tables, and virtual reality headsets.

Osmium Isotope and Highly Siderophile Element Compositions of Lunar Orange and Green Glasses

NASA Technical Reports Server (NTRS)

Walker, R. J.; Horan, M. F.; Shearer, C. K.; Papike, J. J.

2003-01-01

The absolute and relative abundances of the highly siderophile elements (HSE) present in planetary mantles are primarily controlled by: 1) silicate-metal partitioning during core-mantle differentiation, 2) the subsequent addition of HSE to mantles via continued planetary accretion. Consequently, constraints on the absolute and relative abundances of the HSE in the lunar mantle will provide unique insights to the formation and late accretionary history of not only the Moon, but also Earth. Determining the HSE content of the lunar mantle, however, has proven difficult, because no bona fide mantle rocks have been collected from the moon. The only materials presently available for constraining mantle abundances are lunar volcanic rocks. Lunar basalts typically have very low concentrations of HSE and highly fractionated HSE patterns. Because of our extremely limited understanding of mantle melt partitioning of the HSE, even for terrestrial systems, extrapolations to mantle compositions from basaltic compositions are difficult, except possibly for the less compatible HSE Pt and Pd. Primitive, presumably less fractionated materials, such as picritic glasses are potentially more diagnostic of the lunar interior. Here we report Os isotopic composition data and Re, Os, Ir, Ru, Pt and Pd concentration data for green glass (15426,164) and orange glass (74001,1217). As with previous studies utilizing neutron activation analysis, we are examining different size fractions of the spherules to assess the role of surface condensation in the generation of the HSE abundances.

Noble gas Records of Early Evolution of the Earth

NASA Astrophysics Data System (ADS)

Ozima, M.; Podoesk, F. A.

2001-12-01

Comparison between atmospheric noble gases (except for He) and solar (or meteoritic) noble gases clearly suggests that the Earth should have much more Xe than is present in air, and thus that up to about 90 percent of terrestrial Xe is missing from the Earth (1). In this report, we discuss implications of these observations on I-Pu chronology of the Earth and on the origin of terrestrial He3. Whetherill (2) first noted that an estimated I129/I127 ratio (3x10-6) in the proto-Earth was about two orders of magnitude smaller than values commonly observed in meteorites (10-4), and pointed out the possibility that Earth formation postdated meteorites by about 100Ma. Ozima and Podosek (1999) came to a similar conclusion on the basis of I129/I127-Pu244/U238 systematics (1). In this report, we reexamine I-Pu systematics with new data for crustal I content (295 ppb for a bulk crust, (3)). With imposition of an estimated value of 86 percent missing Xe as a constraint on terrestrial Xe inventory, we conclude that the best estimate for a formation age of the Earth is about 28Ma after the initial condensation of the solar nebula (at 4.57Ga). The formation age thus estimated is significantly later than the generally assumed age of meteorites. We also argue from the I-Pu systematics that the missing Xe became missing place about 120Ma after Earth formation. Assuming that the Earth is mostly degassed, the I-Pu formation age of the Earth can be reasonably assumed to represent a whole Earth event. Therefore, we interpret that the I-Pu age of the Earth represents the time when the Earth started to retain noble gases. More specifically, this may correspond to the time when the proto-Earth attained a sufficient size to exert the necessary gravitational force. A giant impact could be another possibility, but it remains to be seen whether or not a giant impact could quantitatively remove heavier noble gases from the Earth. It is interesting to speculate that missing Xe was sequestered in the core during core formation. Core formation time would then be related to the time of the missing Xe event. The above estimated missing Xe age is close to the core formation age suggested from Nb-Zr systematics (4) and from U-Pb systematics (5), but considerably later than that suggested from Hf-W systematics (6). From a comparison of relative elemental abundance of noble gases between the Earth and the solar composition, we show that terrestrial He3 may be totally unrelated to heavier noble gases. This requires independent origin of terrestrial He3 from heavy noble gases. 1.Ozima M. and Podosek F.A. (1999) JGR, 104(BII), 25493. 2.Whetherill G.W. (1975) Ann. Rev. Nuclear Science, 25, 283. 3.Muramatsu Y. and Wedepohl K.H. (1998) Chemical Geology, 147, 201. 4. Jacobsen S.B. and Yin Q.Z. (2001) Lunar Planetary Science, XXXII, 1961.pdf (abstract). 5.Galer S.J.G. and Goldstein S.L. (1995) in Geophysical Monograph 95, 75-98, AGU. 6.Halliday A.N., Lee D.-C. and Jacobsen S.B. (2000) in Origin of the Earth and Moon, 45-62, Univ. Arizona Press.

The Formation of the Earth-Moon System and the Planets

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; Young, Richard E. (Technical Monitor)

1998-01-01

An overview of current theories of star and planet formation, with emphasis on terrestrial planet accretion and the formation of the Earth-Moon system is presented. These models are based upon observations of the Solar System and of young stars and their environments. They predict that rocky planets should form around most single stars, although it is possible that in some cases such planets are lost to orbital decay within the protoplanetary disk. The frequency of formation of gas giant planets is more difficult to predict theoretically. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant impacts during the final stages of growth can produce large planetary satellites, such as Earth's Moon. Giant planets begin their growth like terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates.

Performance Assessment of New Land-Surface and Planetary Boundary Layer Physics in the WRF-ARW

EPA Science Inventory

The Pleim-Xiu land surface model, Pleim surface layer scheme, and Asymmetric Convective Model (version 2) are now options in version 3.0 of the Weather Research and Forecasting model (WRF) Advanced Research WRF (ARW) core. These physics parameterizations were developed for the f...

About the Influence of the initial Atmosphere on the Earth's Temperature Distribution during it's Accumulation

NASA Astrophysics Data System (ADS)

Khachay, Y.; Anfilogov, V.; Antipin, A.

2012-04-01

We suggested a new model for accumulation of planets of the Earth's group [1], which is based on the contemporary results of geochemical analyses, which allow to obtain the concentrations of short living radioactive isotopes of 26Al in the matter of the pre planet cloud [2]. With use of that data new estimations of temperature distribution into the growing planetary pre planetary bodies into the Earth's nebular zone had been obtained. For the further Earth's temperature evolution, as it had been showed by the results of numerical modeling, the main role belongs to the temperature distribution in the forming Earth's core and the existence of a dense and transparent atmosphere. The shadow influence of the initial atmosphere had been researched in the paper [3]. We shall give the main consideration to these problems in that paper. It had been shown in [1], that on the earliest accumulation stage the heat release by the decay of 26Al it is sufficient for forming a central melted area and solid relatively thin mainly silicate upper envelope in the pre planetary body, with dimensions, larger than (50-100) km. The impact velocities on that stage are yet not large, therefore by the bodies impact with these or near dimensions liquid and mainly iron their parts merge, but the masses of the pre planetary bodies are not sufficient to gravitational keeping of silicate parts of the cold solid envelope. On that stage they remain into the nebular zone of the proto planet and the mechanism of matter differentiation for the future core and mantle reservoirs realizes. The process takes place yet in small bodies and is in time to finish during less than 10 million years. The next forming of the core and mantle structure continues according to all known estimations about 100 million years. Because of the merging of inner liquid parts of impacting bodies occur due to inelastic impact, the main part of potential energy transforms into heat. That continues up to that time when the iron core mass increases to the main part of the contemporary mass. The silicate particles of different dimensions remain in the proto planet cloud and in the initial atmosphere, reducing it's transparency and release of the heat radiation. On the finishing stage of the core growing the mass of the pre planetary body is sufficient for keeping of the rising part of the silicate envelope of falling bodies. The matter of the growing planet enriches more and more with a touch of silicates. The impact process of accumulated bodies gradually converts to the mechanism of elastic impact, by which only a small part of kinetic energy transforms into the merging by the pre planet body heat. The atmosphere losses the silicate particles and it's transparency exceeds. It is forming either a non melted mantle, or a mantle with a rising melted layer. That results show that the existence of a dense, nontransparent atmosphere leads to temperature growing in the inner areas of the planet during it's accumulation process. 1.Anfilogov V.N., Khachay Yu.V. A possible variant of matter differentiation on the initial stage of Earth's forming. // DAN. 2005, V. 403, N. 6, 803-806. 2.Merk R.,Breuer D., Spohn T., 2002. Numerical modeling of 26Al - Induced radioactive melting of asteroids concerning accretion, Icarus, 159, 183-191. 3.Hayashi C., Nakazawa K., Mizuno H. Earth's melting due to the blanketing effect of primordial dense atmosphere. // Earth and Plenetary Science Letters. (1979). v. 43, 22-28

TOPS: Toward Other Planetary Systems. A report by the solar system exploration division

NASA Technical Reports Server (NTRS)

1995-01-01

This report describes a general plan and the pertinent technological requirements for TOPS (Toward Other Planetary Systems), a staged program to ascertain the prevalence and character of other planetary systems and to construct a definitive picture of the formation of stars and their planets. The first stages focus on discovering and studying a significant number of fully formed planetary systems, as well as expanding current studies of protoplanetary systems. As the TOPS Program evolves, emphasis will shift toward intensive study of the discovered systems and of individual planets. Early stages of the TOPS Program can be undertaken with ground-based observations and space missions comparable in scale to those now being performed. In the long term, however, TOPS will become an ambitious program that challenges our capabilities and provides impetus for major space initiatives and new technologies.

Near-infrared Spectroscopy of 2M0441+2301 AabBab: A Quadruple System Spanning the Stellar to Planetary Mass Regimes

NASA Astrophysics Data System (ADS)

Bowler, Brendan P.; Hillenbrand, Lynne A.

2015-10-01

We present Keck/NIRC2 and OSIRIS near-infrared imaging and spectroscopy of 2M0441+2301 AabBab, a young (1-3 Myr) hierarchical quadruple system comprising a low-mass star, two brown dwarfs, and a planetary-mass companion in Taurus. All four components show spectroscopic signs of low surface gravity, and both 2M0441+2301 Aa and Ab possess Paβ emission indicating they each harbor accretion subdisks. Astrometry spanning 2008-2014 reveals orbital motion in both the Aab (0.″23 separation) and Bab (0.″095 separation) pairs, although the implied orbital periods of >300 years mean dynamical masses will not be possible in the near future. The faintest component (2M0441+2301 Bb) has an angular H-band shape, strong molecular absorption (VO, CO, H2O, and FeH), and shallow alkali lines, confirming its young age, late spectral type (L1 ± 1), and low temperature (≈1800 K). With individual masses of {200}-50+100 MJup, 35 ± 5 MJup, 19 ± 3 MJup, and 9.8 ± 1.8 MJup, 2M0441+2301 AabBab is the lowest-mass quadruple system known. Its hierarchical orbital architecture and mass ratios imply that it formed from the collapse and fragmentation of a molecular cloud core, demonstrating that planetary-mass companions can originate from a stellar-like pathway analogous to higher-mass quadruple star systems as first speculated by Todorov et al. More generally, cloud fragmentation may be an important formation pathway for the massive exoplanets that are now regularly being imaged on wide orbits. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Large ejecta fragments from asteroids. [Abstract only

NASA Technical Reports Server (NTRS)

Asphaug, E.

1994-01-01

The asteroid 4 Vesta, with its unique basaltic crust, remains a key mystery of planetary evolution. A localized olivine feature suggests excavation of subcrustal material in a crater or impact basin comparable in size to the planetary radius (R(sub vesta) is approximately = 280 km). Furthermore, a 'clan' of small asteroids associated with Vesta (by spectral and orbital similarities) may be ejecta from this impact 151 and direct parents of the basaltic achondrites. To escape, these smaller (about 4-7 km) asteroids had to be ejected at speeds greater than the escape velocity, v(sub esc) is approximately = 350 m/s. This evidence that large fragments were ejected at high speed from Vesta has not been reconciled with the present understanding of impact physics. Analytical spallation models predict that an impactor capable of ejecting these 'chips off Vesta' would be almost the size of Vesta! Such an impact would lead to the catastrophic disruption of both bodies. A simpler analysis is outlined, based on comparison with cratering on Mars, and it is shown that Vesta could survive an impact capable of ejecting kilometer-scale fragments at sufficient speed. To what extent does Vesta survive the formation of such a large crater? This is best addressed using a hydrocode such as SALE 2D with centroidal gravity to predict velocities subsequent to impact. The fragmentation outcome and velocity subsequent to the impact described to demonstrate that Vesta survives without large-scale disassembly or overturning of the crust. Vesta and its clan represent a valuable dataset for testing fragmentation hydrocodes such as SALE 2D and SPH 3D at planetary scales. Resolution required to directly model spallation 'chips' on a body 100 times as large is now marginally possible on modern workstations. These boundaries are important in near-surface ejection processes and in large-scale disruption leading to asteroid families and stripped cores.

Dynamics of core accretion

DOE PAGES

Nelson, Andrew F.; Ruffert, Maximilian

2012-12-21

In this paper, we perform three-dimensional hydrodynamic simulations of gas flowing around a planetary core of mass M pl = 10M ⊕ embedded in a near Keplerian background flow, using a modified shearing box approximation. We assume an ideal gas behaviour following an equation of state with a fixed ratio of the specific heats, γ = 1.42, consistent with the conditions of a moderate-temperature background disc with solar composition. No radiative heating or cooling is included in the models. We employ a nested grid hydrodynamic code implementing the ‘Piecewise Parabolic Method’ with as many as six fixed nested grids, providingmore » spatial resolution on the finest grid comparable to the present-day diameters of Neptune and Uranus. We find that a strongly dynamically active flow develops such that no static envelope can form. The activity is not sensitive to plausible variations in the rotation curve of the underlying disc. It is sensitive to the thermodynamic treatment of the gas, as modelled by prescribed equations of state (either ‘locally isothermal’ or ‘locally isentropic’) and the temperature of the background disc material. The activity is also sensitive to the shape and depth of the core's gravitational potential, through its mass and gravitational softening coefficient. Each of these factors influences the magnitude and character of hydrodynamic feedback of the small-scale flow on the background, and we conclude that accurate modelling of such feedback is critical to a complete understanding of the core accretion process. The varying flow pattern gives rise to large, irregular eruptions of matter from the region around the core which return matter to the background flow: mass in the envelope at one time may not be found in the envelope at any later time. No net mass accretion into the envelope is observed over the course of the simulation and none is expected, due to our neglect of cooling. Except in cases of very rapid cooling however, as defined by locally isothermal or isentropic treatments, any cooling that does affect the envelope material will have limited consequences for the dynamics, since the flow quickly carries cooled material out of the core's environment entirely. The angular momentum of material in the envelope, relative to the core, varies both in magnitude and in sign on time-scales of days to months near the core and on time-scales a few years at distances comparable to the Hill radius. The dynamical activity contrasts with the largely static behaviour typically assumed within the framework of the core accretion model for Jovian planet formation. We show that material entering the dynamically active environment may suffer intense heating and cooling events the durations of which are as short as a few hours to a few days. Shorter durations are not observable in our work due to the limits of our resolution. Peak temperatures in these events range from T ~ 1000 K to as high as T ~ 3–4000 K, with densities ρ ~ 10 -9 to 10 -8 gcm -3. These time-scales, densities and temperatures span a range consistent with those required for chondrule formation in the nebular shock model. Finally, we therefore propose that dynamical activity in the Jovian planet formation environment could be responsible for the production of chondrules and other annealed silicates in the solar nebula.« less

Dynamics of core accretion

NASA Astrophysics Data System (ADS)

Nelson, Andrew F.; Ruffert, Maximilian

2013-02-01

We perform three-dimensional hydrodynamic simulations of gas flowing around a planetary core of mass Mpl = 10M⊕ embedded in a near Keplerian background flow, using a modified shearing box approximation. We assume an ideal gas behaviour following an equation of state with a fixed ratio of the specific heats, γ = 1.42, consistent with the conditions of a moderate-temperature background disc with solar composition. No radiative heating or cooling is included in the models. We employ a nested grid hydrodynamic code implementing the `Piecewise Parabolic Method' with as many as six fixed nested grids, providing spatial resolution on the finest grid comparable to the present-day diameters of Neptune and Uranus. We find that a strongly dynamically active flow develops such that no static envelope can form. The activity is not sensitive to plausible variations in the rotation curve of the underlying disc. It is sensitive to the thermodynamic treatment of the gas, as modelled by prescribed equations of state (either `locally isothermal' or `locally isentropic') and the temperature of the background disc material. The activity is also sensitive to the shape and depth of the core's gravitational potential, through its mass and gravitational softening coefficient. Each of these factors influences the magnitude and character of hydrodynamic feedback of the small-scale flow on the background, and we conclude that accurate modelling of such feedback is critical to a complete understanding of the core accretion process. The varying flow pattern gives rise to large, irregular eruptions of matter from the region around the core which return matter to the background flow: mass in the envelope at one time may not be found in the envelope at any later time. No net mass accretion into the envelope is observed over the course of the simulation and none is expected, due to our neglect of cooling. Except in cases of very rapid cooling however, as defined by locally isothermal or isentropic treatments, any cooling that does affect the envelope material will have limited consequences for the dynamics, since the flow quickly carries cooled material out of the core's environment entirely. The angular momentum of material in the envelope, relative to the core, varies both in magnitude and in sign on time-scales of days to months near the core and on time-scales a few years at distances comparable to the Hill radius. The dynamical activity contrasts with the largely static behaviour typically assumed within the framework of the core accretion model for Jovian planet formation. We show that material entering the dynamically active environment may suffer intense heating and cooling events the durations of which are as short as a few hours to a few days. Shorter durations are not observable in our work due to the limits of our resolution. Peak temperatures in these events range from T ˜ 1000 K to as high as T ˜ 3-4000 K, with densities ρ ˜ 10-9 to 10-8 g cm-3. These time-scales, densities and temperatures span a range consistent with those required for chondrule formation in the nebular shock model. We therefore propose that dynamical activity in the Jovian planet formation environment could be responsible for the production of chondrules and other annealed silicates in the solar nebula.

The Phospholipid:Diacylglycerol Acyltransferase Lro1 Is Responsible for Hepatitis C Virus Core-Induced Lipid Droplet Formation in a Yeast Model System

PubMed Central

Wang, Chao-Wen; Cheng, Yun-Hsin; Irokawa, Hayato; Hwang, Gi-Wook; Naganuma, Akira; Kuge, Shusuke

2016-01-01

Chronic infection with the hepatitis C virus frequently induces steatosis, which is a significant risk factor for liver pathogenesis. Steatosis is characterized by the accumulation of lipid droplets in hepatocytes. The structural protein core of the virus induces lipid droplet formation and localizes on the surface of the lipid droplets. However, the precise molecular mechanisms for the core-induced formation of lipid droplets remain elusive. Recently, we showed that the expression of the core protein in yeast as a model system could induce lipid droplet formation. In this study, we probed the cellular factors responsible for the formation of core-induced lipid-droplets in yeast cells. We demonstrated that one of the enzymes responsible for triglyceride synthesis, a phospholipid:diacylglycerol acyltransferase (Lro1), is required for the core-induced lipid droplet formation. While core proteins inhibit Lro1 degradation and alter Lro1 localization, the characteristic localization of Lro1 adjacent to the lipid droplets appeared to be responsible for the core-induced lipid droplet formation. RNA virus genomes have evolved using high mutation rates to maintain their ability to replicate. Our observations suggest a functional relationship between the core protein with hepatocytes and yeast cells. The possible interactions between core proteins and the endoplasmic reticulum membrane affect the mobilization of specific proteins. PMID:27459103

A Comparison of Three Holistic Approaches to Health: One Health, EcoHealth, and Planetary Health.

PubMed

Lerner, Henrik; Berg, Charlotte

2017-01-01

Several holistic and interdisciplinary approaches exist to safeguard health. Three of the most influential concepts at the moment, One Health, EcoHealth, and Planetary Health, are analyzed in this paper, revealing similarities and differences at the theoretical conceptual level. These approaches may appear synonymous, as they all promote the underlying assumption of humans and other animals sharing the same planet and the same environmental challenges, infections and infectious agents as well as other aspects of physical-and possibly mental-health. However, we would like to illuminate the differences between these three concepts or approaches, and how the choice of terms may, deliberately or involuntary, signal the focus, and underlying values of the approaches. In this paper, we have chosen some proposed and well-known suggestions of definitions. In our theoretical analysis, we will focus on at least two areas. These are (1) the value of the potential scientific areas which could be included and (2) core values present within the approach. In the first area, our main concern is whether the approaches are interdisciplinary and whether the core scientific areas are assigned equal importance. For the second area, which is rather wide, we analyze core values such as biodiversity, health, and how one values humans, animals, and ecosystems. One Health has been described as either a narrow approach combining public health and veterinary medicine or as a wide approach as in the wide-spread "umbrella" depiction including both scientific fields, core concepts, and interdisciplinary research areas. In both cases, however, safeguarding the health of vertebrates is usually in focus although ecosystems are also included in the model. The EcoHealth approach seems to have more of a biodiversity focus, with an emphasis on all living creatures, implying that parasites, unicellular organisms, and possibly also viruses have a value and should be protected. Planetary Health, on the other hand, has been put forward as a fruitful approach to deal with growing threats in the health area, not least globally. We conclude that there are actually important differences between these three approaches, which should be kept in mind when using any of these terms.

The dynamical core of the Aeolus 1.0 statistical-dynamical atmosphere model: validation and parameter optimization

NASA Astrophysics Data System (ADS)

Totz, Sonja; Eliseev, Alexey V.; Petri, Stefan; Flechsig, Michael; Caesar, Levke; Petoukhov, Vladimir; Coumou, Dim

2018-02-01

We present and validate a set of equations for representing the atmosphere's large-scale general circulation in an Earth system model of intermediate complexity (EMIC). These dynamical equations have been implemented in Aeolus 1.0, which is a statistical-dynamical atmosphere model (SDAM) and includes radiative transfer and cloud modules (Coumou et al., 2011; Eliseev et al., 2013). The statistical dynamical approach is computationally efficient and thus enables us to perform climate simulations at multimillennia timescales, which is a prime aim of our model development. Further, this computational efficiency enables us to scan large and high-dimensional parameter space to tune the model parameters, e.g., for sensitivity studies.Here, we present novel equations for the large-scale zonal-mean wind as well as those for planetary waves. Together with synoptic parameterization (as presented by Coumou et al., 2011), these form the mathematical description of the dynamical core of Aeolus 1.0.We optimize the dynamical core parameter values by tuning all relevant dynamical fields to ERA-Interim reanalysis data (1983-2009) forcing the dynamical core with prescribed surface temperature, surface humidity and cumulus cloud fraction. We test the model's performance in reproducing the seasonal cycle and the influence of the El Niño-Southern Oscillation (ENSO). We use a simulated annealing optimization algorithm, which approximates the global minimum of a high-dimensional function.With non-tuned parameter values, the model performs reasonably in terms of its representation of zonal-mean circulation, planetary waves and storm tracks. The simulated annealing optimization improves in particular the model's representation of the Northern Hemisphere jet stream and storm tracks as well as the Hadley circulation.The regions of high azonal wind velocities (planetary waves) are accurately captured for all validation experiments. The zonal-mean zonal wind and the integrated lower troposphere mass flux show good results in particular in the Northern Hemisphere. In the Southern Hemisphere, the model tends to produce too-weak zonal-mean zonal winds and a too-narrow Hadley circulation. We discuss possible reasons for these model biases as well as planned future model improvements and applications.

Experimentally determined sulfur isotope fractionation between metal and silicate and implications for planetary differentiation

NASA Astrophysics Data System (ADS)

Labidi, J.; Shahar, A.; Le Losq, C.; Hillgren, V. J.; Mysen, B. O.; Farquhar, J.

2016-02-01

The Earth's mantle displays a subchondritic 34S/32S ratio. Sulfur is a moderately siderophile element (i.e. iron-loving), and its partitioning into the Earth's core may have left such a distinctive isotope composition on the terrestrial mantle. In order to constrain the sulfur isotope fractionation occurring during core-mantle differentiation, high-pressure and temperature experiments were conducted with synthetic mixtures of metal and silicate melts. With the purpose to identify the mechanism(s) responsible for the S isotope fractionations, we performed our experiments in different capsules - namely, graphite and boron nitride capsules - and thus at different fO2, with varying major element chemistry of the silicate and metal fractions. The S isotope fractionations Δ34Smetal-silicate of equilibrated metal alloys versus silicate melts is +0.2 ± 0.1‰ in a boron-free and aluminum-poor system quenched at 1-1.5 GPa and 1650 °C. The isotope fractionation increases linearly with increasing boron and aluminum content, up to +1.4 ± 0.2‰, and is observed to be independent of the silicon abundance as well as of the fO2 over ∼3.5 log units of variations explored here. The isotope fractionations are also independent of the graphite or nitride saturation of the metal. Only the melt structural changes associated with aluminum and boron concentration in silicate melts have been observed to affect the strength of sulfur bonding. These results establish that the structure of silicate melts has a direct influence on the S2- average bonding strengths. These results can be interpreted in the context of planetary differentiation. Indeed, the structural environments of silicate evolve strongly with pressure. For example, the aluminum, iron or silicon coordination numbers increase under the effect of pressure. Consequently, based on our observations, the sulfur-bonding environment is likely to be affected. In this scheme, we tentatively hypothesize that S isotope fractionations between the silicate mantle and metallic core of terrestrial planetary bodies would depend on the average pressure at which their core-mantle differentiation occurred.

Melting relations in the Fe-S-Si system at high pressure and temperature: implications for the planetary core

NASA Astrophysics Data System (ADS)

Sakairi, Takanori; Ohtani, Eiji; Kamada, Seiji; Sakai, Takeshi; Sakamaki, Tatsuya; Hirao, Naohisa

2017-12-01

The phase and melting relations in the Fe-S-Si system were determined up to 60 GPa by using a double-sided laser-heated diamond anvil cell combined with X-ray diffraction. On the basis of the X-ray diffraction patterns, we confirmed that hcp/fcc Fe-Si alloys and Fe3S are stable phases under subsolidus conditions in the Fe-S-Si system. Both solidus and liquidus temperatures are significantly lower than the melting temperature of pure Fe and both increase with pressure. The slopes of the Fe-S-Si liquidus and solidus curves determined here are smaller than the adiabatic temperature gradients of the liquid cores of Mercury and Mars. Thus, crystallization of their cores started at the core-mantle boundary region.

The origin of comets - Implications for planetary formation

NASA Technical Reports Server (NTRS)

Weissman, P. R.

1985-01-01

Primordial and episodic theories for the origin of comets are discussed. The implications of the former type for the origin of the solar system are considered. Candidate sites for the formation of comets are compared. The possible existence of a massive inner Oort cloud is discussed.

The Emerging Paradigm of Pebble Accretion

NASA Astrophysics Data System (ADS)

Ormel, Chris W.

Pebble accretion is the mechanism in which small particles ("pebbles") accrete onto big bodies big (planetesimals or planetary embryos) in gas-rich environments. In pebble accretion accretion , accretion occurs by settling and depends only on the mass of the gravitating body gravitating , not its radius. I give the conditions under which pebble accretion operates and show that the collisional cross section can become much larger than in the gas-free, ballistic, limit. In particular, pebble accretion requires the pre-existence of a massive planetesimal seed. When pebbles experience strong orbital decay by drift motions or are stirred by turbulence, the accretion efficiency is low and a great number of pebbles are needed to form Earth-mass cores. Pebble accretion is in many ways a more natural and versatile process than the classical, planetesimal-driven paradigm, opening up avenues to understand planet formation in solar and exoplanetary systems.

Restoration and PDS Archive of Apollo Lunar Rock Sample Data

NASA Technical Reports Server (NTRS)

Garcia, P. A.; Todd, N. S.; Lofgren, G. E.; Stefanov, W. L.; Runco, S. K.; LaBasse, D.; Gaddis, L. R.

2011-01-01

In 2008, scientists at the Johnson Space Center (JSC) Lunar Sample Laboratory and Image Science & Analysis Laboratory (under the auspices of the Astromaterials Research and Exploration Science Directorate or ARES) began work on a 4-year project to digitize the original film negatives of Apollo Lunar Rock Sample photographs. These rock samples together with lunar regolith and core samples were collected as part of the lander missions for Apollos 11, 12, 14, 15, 16 and 17. The original film negatives are stored at JSC under cryogenic conditions. This effort is data restoration in the truest sense. The images represent the only record available to scientists which allows them to view the rock samples when making a sample request. As the negatives are being scanned, they are also being formatted and documented for permanent archive in the NASA Planetary Data System (PDS) archive. The ARES group is working collaboratively with the Imaging Node of the PDS on the archiving.

Rotational and Infrared Spectroscopy of Ethanimine: A Route toward Its Astrophysical and Planetary Detection

NASA Astrophysics Data System (ADS)

Melli, Alessio; Melosso, Mattia; Tasinato, Nicola; Bosi, Giulio; Spada, Lorenzo; Bloino, Julien; Mendolicchio, Marco; Dore, Luca; Barone, Vincenzo; Puzzarini, Cristina

2018-03-01

Ethanimine, a possible precursor of amino acids, is considered an important prebiotic molecule and thus may play important roles in the formation of biological building blocks in the interstellar medium. In addition, its identification in Titan’s atmosphere would be important for understanding the abiotic synthesis of organic species. An accurate computational characterization of the molecular structure, energetics, and spectroscopic properties of the E and Z isomers of ethanimine, CH3CHNH, has been carried out by means of a composite scheme based on coupled-cluster techniques, which also account for extrapolation to the complete basis-set limit and core-valence correlation correction, combined with density functional theory for the treatment of vibrational anharmonic effects. By combining the computational results with new millimeter-wave measurements up to 300 GHz, the rotational spectrum of both isomers can be accurately predicted up to 500 GHz. Furthermore, our computations allowed us to revise the infrared spectrum of both E- and Z-CH3CHNH, thus predicting all fundamental bands with high accuracy.

Mercury. [Mariner 10 observations and planetary properties

NASA Technical Reports Server (NTRS)

Gault, D. E.; Cassen, P.; Burns, J. A.; Strom, R. G.

1977-01-01

Information about Mercury obtained with the Mariner 10 spacecraft is summarized together with results of theoretical studies and ground-based observations. It is shown that Mercury is very likely a differentiated body, probably contains a large earthlike iron-rich core, and displays a surface similar to the moon's, which suggests a similar evolutionary history. The size and mass of Mercury are discussed along with its orbit, rotation, atmosphere, magnetic field, and magnetosphere. Surface features of Mercury are described on the basis of Mariner 10 pictures, with detailed attention given to the major physiographic provinces, the structure of the Caloris basin, the tectonic framework of the planet, crater morphology, the planet's optical and thermal properties, and cartography. The composition and structure of the interior are examined, and the thermal history of Mercury is considered. The planet's geologic history is divided into five stages or epochs: (1) accretion and differentiation, (2) terminal heavy bombardment, (3) Caloris basin formation, (4) basin flooding, and (5) postfilling lighter bombardment.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Shang-Fei; Lin, Douglas N. C.; Guillochon, James

A large population of planetary candidates in short-period orbits have been found recently through transit searches, mostly with the Kepler mission. Radial velocity surveys have also revealed several Jupiter-mass planets with highly eccentric orbits. Measurements of the Rossiter-McLaughlin effect indicate that the orbital angular momentum vector of some planets is inclined relative to the spin axis of their host stars. This diversity could be induced by post-formation dynamical processes such as planet-planet scattering, the Kozai effect, or secular chaos which brings planets to the vicinity of their host stars. In this work, we propose a novel mechanism to form close-inmore » super-Earths and Neptune-like planets through the tidal disruption of gas giant planets as a consequence of these dynamical processes. We model the core-envelope structure of gas giant planets with composite polytropes which characterize the distinct chemical composition of the core and envelope. Using three-dimensional hydrodynamical simulations of close encounters between Jupiter-like planets and their host stars, we find that the presence of a core with a mass more than 10 times that of the Earth can significantly increase the fraction of envelope which remains bound to it. After the encounter, planets with cores are more likely to be retained by their host stars in contrast with previous studies which suggested that coreless planets are often ejected. As a substantial fraction of their gaseous envelopes is preferentially lost while the dense incompressible cores retain most of their original mass, the resulting metallicity of the surviving planets is increased. Our results suggest that some gas giant planets can be effectively transformed into either super-Earths or Neptune-like planets after multiple close stellar passages. Finally, we analyze the orbits and structure of known planets and Kepler candidates and find that our model is capable of producing some of the shortest-period objects.« less

Dual Si and O Isotope Measurement of Lunar Samples Using IRMS

NASA Astrophysics Data System (ADS)

Banerjee, N.; Hill, P. J. A.; Osinski, G. R.

2016-12-01

The use of isotopic systems and their associated theoretical models have become an increasingly sophisticated tool for investigating the origin of planetary bodies in the solar system. It was originally hypothesized that evidence for the impact origin of Moon would manifest itself as an isotopic heterogeneity between lunar and terrestrial samples; however, most isotope systems show no difference between the bulk Earth and Moon. The stable isotopes of both silicon (Si) and oxygen (O) have been essential in further understanding planetary processes including core formation. Historically the analysis of the Si and O isotope ratios in terrestrial and extraterrestrial material has primarily been measured independent of each other through three main techniques: isotope ratio mass spectrometry (IRMS), secondary ion mass spectrometry (SIMS), and multi-collector inductively coupled plasma mass-spectrometry (MC-ICPMS). Each technique has its own strength and weakness in regards to resolution and precision; however, one of the main limiting factors in all three of these techniques rests on the requirement of multiple aliquots. As most literature focuses on the measurement of oxygen or silicon isotopes, this unique line allows for the precise analysis of Si and O isotopes from the same aliquot of bulk sample, which cannot be done with SIMS or ICP-MS analysis. To deal with this problem a unique laser line system has been developed in the Laboratory for Stable Isotope Science at Western University, Canada, that simultaneously extracts SiF4 and O2 from the same 1-2 mg aliquot. We present the application of analyzing both isotopic systems from the sample aliquot to Apollo, meteoritic, and terrestrial samples and its implication for the formation of the Moon. Preliminary results from this line suggest that although the O isotopes ratios are consistent with a homogenous Moon-Earth system, a difference is observed in Si isotopes between Apollo and terrestrial samples compared to previous studies.

Ion Chemistry in Atmospheric and Astrophysical Plasmas

NASA Technical Reports Server (NTRS)

Dalgarno, A.; Fox, J. L.

1994-01-01

There are many differences and also remarkable similarities between the ion chemistry and physics of planetary ionospheres and the ion chemistry and physics of astronomical environments beyond the solar system. In the early Universe, an expanded cooling gas of hydrogen and helium was embedded in the cosmic background radiation field and ionized by it. As the Universe cooled by adiabatic expansion, recombination occurred and molecular formation was driven by catalytic reactions involving the relict electrons and protons. Similar chemical processes are effective in the ionized zones of gaseous and planetary nebulae and in stellar winds where the ionization is due to radiation from the central stars, in the envelopes of supernovae where the ionization is initiated by the deposition of gamma-rays, in dissociative shocks where the ionization arises from electron impacts in a hot gas and in quasar broad-line region clouds where the quasar is responsible for the ionization. At high altitudes in the atmospheres of the Jovian planets, the main constituents are hydrogen and helium and the ion chemistry and physics is determined by the same processes, the source of the ionization being solar ultraviolet radiation and cosmic rays. After the collapse of the first distinct astronomical entities to emerge from the uniform flow, heavy elements were created by nuclear burning in the cores of the collapsed objects and distributed throughout the Universe by winds and explosions. The chemistry and physics became more complicated. Over 90 distinct molecular species have been identified in interstellar clouds where they are ionized globally by cosmic ray impacts and locally by radiation and shocks associated with star formation and evolution. Complex molecules have also been found in circumstellar shells of evolved stars. At intermediate and low altitudes in the Jovian atmospheres, the ion chemistry is complicated by the increasing abundance of heavy elements such as carbon, and an extensive array of complex molecules has been predicted. Reactions involving heavy elements dominate the structure of the ionspheres of the terrestrial planets and the satellites Titan and Triton.

The phase diagram and transport properties of MgO from theory and experiment

NASA Astrophysics Data System (ADS)

Shulenburger, Luke

2013-06-01

Planetary structure and the formation of terrestrial planets have received tremendous interest due to the discovery of so called super-earth exoplanets. MgO is a major constituent of Earth's mantle, the rocky cores of gas giants and is a likely component of the interiors of many of these exoplanets. The high pressure - high temperature behavior of MgO directly affects equation of state models for planetary structure and formation. In this work, we examine MgO under extreme conditions using experimental and theoretical methods to determine its phase diagram and transport properties. Using plate impact experiments on Sandia's Z facility the solid-solid phase transition from B1 to B2 is clearly determined. The melting transition, on the other hand, is subtle, involving little to no signal in us-up space. Theoretical work utilizing density functional theory (DFT) provides a complementary picture of the phase diagram. The solid-solid phase transition is identified through a series of quasi-harmonic phonon calculations and thermodynamic integration, while the melt boundary is found using phase coexistence calculations. One issue of particular import is the calculation of reflectivity along the Hugoniot and the influence of the ionic structure on the transport properties. Particular care is necessary because of the underestimation of the band gap and attendant overestimation of transport properties due to the use of semi-local density functional theory. We will explore the impact of this theoretical challenge and its potential solutions in this talk. The integrated use of DFT simulations and high-accuracy shock experiments together provide a comprehensive understanding of MgO under extreme conditions. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Forsterite Shock Temperatures and Entropy: New Scaling Laws for Impact Melting and Vaporization

NASA Astrophysics Data System (ADS)

Davies, E.; Root, S.; Kraus, R. G.; Townsend, J. P.; Spaulding, D.; Stewart, S. T.; Jacobsen, S. B.; Fratanduono, D.; Millot, M. A.; Mattsson, T. R.; Hanshaw, H. L.

2017-12-01

The observed masses, radii and temperatures of thousands of extra-solar planets have challenged our theoretical understanding of planet formation and planetary structures. Planetary materials are subject to extreme pressures and temperatures during formation and within the present-day interiors of large bodies. Here, we focus on improving understanding of the physical properties of rocky planets for calculations of internal structure and the outcomes of giant impacts. We performed flyer plate impact experiments on forsterite [Mg2SiO4] on the Z-Machine at Sandia National Laboratory and decaying shock temperature measurements at the Omega EP laser at U. Rochester. At Z, planar, supported shock waves are generated in single crystal samples, permitting observation of both compressed and released states. Using available static and dynamic thermodynamic data, we calculate absolute entropy and heat capacity along the forsterite shock Hugoniot. Entropy and heat capacity on the Hugoniot are larger than previous estimates. Our data constrain the thermodynamic properties of forsterite liquid at high pressures and temperatures and the amount of melt and vapor produced during impact events. For an ambient pressure of 1 bar, shock-vaporization begins upon reaching the liquid region on the forsterite Hugoniot (about 200 GPa). Using hydrocode simulations of giant impacts between rocky planets with forsterite mantles and iron cores and the new experimentally-constrained forsterite shock entropy, we present a new scaling law for the fraction of mantle that is melted or vaporized by the initial shock wave. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. Prepared by LLNL under Contract DE-AC52-07NA27344. Prepared by the Center for Frontiers in High Energy Density Science

GIANT IMPACT: AN EFFICIENT MECHANISM FOR THE DEVOLATILIZATION OF SUPER-EARTHS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Shang-Fei; Hori, Yasunori; Lin, D. N. C.

Mini-Neptunes and volatile-poor super-Earths coexist on adjacent orbits in proximity to host stars such as Kepler-36 and Kepler-11. Several post-formation processes have been proposed for explaining the origin of the compositional diversity between neighboring planets: mass loss via stellar XUV irradiation, degassing of accreted material, and in situ accumulation of the disk gas. Close-in planets are also likely to experience giant impacts during the advanced stage of planet formation. This study examines the possibility of transforming volatile-rich super-Earths/mini-Neptunes into volatile-depleted super-Earths through giant impacts. We present the results of three-dimensional hydrodynamic simulations of giant impacts in the accretionary and disruptivemore » regimes. Target planets are modeled with a three-layered structure composed of an iron core, silicate mantle, and hydrogen/helium envelope. In the disruptive case, the giant impact can remove most of the H/He atmosphere immediately and homogenize the refractory material in the planetary interior. In the accretionary case, the planet is able to retain more than half of the original gaseous envelope, while a compositional gradient suppresses efficient heat transfer as the planetary interior undergoes double-diffusive convection. After the giant impact, a hot and inflated planet cools and contracts slowly. The extended atmosphere enhances the mass loss via both a Parker wind induced by thermal pressure and hydrodynamic escape driven by the stellar XUV irradiation. As a result, the entire gaseous envelope is expected to be lost due to the combination of those processes in both cases. Based on our results, we propose that Kepler-36b may have been significantly devolatilized by giant impacts, while a substantial fraction of Kepler-36c’s atmosphere may remain intact. Furthermore, the stochastic nature of giant impacts may account for the observed large dispersion in the mass–radius relationship of close-in super-Earths and mini-Neptunes (at least to some extent)« less