Comet Dust: The Story of Planet Formation as Told by the Tiniest of Particles

NASA Technical Reports Server (NTRS)

Wooden, D. H.

2005-01-01

Our planetary system formed out of a gas-rich disk-shaped nebula with the early Sun at its center. Many small icy bodies were consumed by the formation of the giant planets. However, many km-size icy bodies were tossed out of the giant-planet region to the cold, distant reaches of our solar system. Comets remained in their places of cold storage until perturbed into orbits that carry them into the inner solar system where they pass relatively close to the Sun. Comets are warmed by the Sun and shed material from their outer layers. The ices and gases shed by comets reveal simple and complex organic molecules were present at the time and in the region of the formation of the giant planets. Where the Earth was forming was too hot and had too intense sunlight for many of these ices and molecules to survive. The dust shed by comets tells us that some stardust survived unaltered but much of the dust was heated and crystallized before becoming part of the comet. Therefore, comet dust grains tell of large radial migrations from the cold outer reaches near Neptune into the hot regions near the forming Sun, and then back out to the cold regions where icy comets were accreting and forming. On 2005 July 4, the NASA Deep Impact Mission hit a comet and ejected primitive materials fiom its interior. These materials were not released into the comet s coma during normal activity. Despite the many passages of this comet close to the Sun, these primitive volatile gases and dust grains survived in its interior. Comet dust grains show that cold and hot materials were mixed into the same tiny particle very early in the formation of the solar system, and these aggregate dust grains never saw high temperatures again. The survival of primitive materials in comet nuclei suggests comets could have delivered organic molecules and primitive dust grains to early Earth.

Outer planets and icy satellites

NASA Technical Reports Server (NTRS)

Drobyshevski, E. M.

1991-01-01

The resources offered by the outer bodies in the Solar System, starting with the main belt asteroids and Jovian System, are not only larger and more diverse but may even be easier to reach than, say, those of Mars. The use of their material, including water and organic matter, depends exclusively on the general strategy of exploration of the Solar System. Of major interest in this respect are the large ice satellites - Titan, Ganymede, and Callisto. Motion through the planetary magnetospheres excites in their ice envelopes megampere currents which, in the presence of rocky, etc., inclusions with electronic conduction should lead to the bulk electrolysis of ice and accumulation in it of 2H2 + O2 in the form of a solid solution. With the concentration of 2H2 + O2 reaching about 15 wt. percent, the solution becomes capable of detonation by a strong meteoritic impact. An explosion of Ganymede's ice envelope about 0.5 By ago could account for the formation of the Trojans and irregular satellites, all known differences between Ganymede and Callisto, and many other things. The explosion of a small icy planet with M approx less than 0.5 Moon created the asteroid belt. Two to three explosions occurred on Io, and two on Europa. The specific features of the longperiod comets close to Saturn's orbit permit dating Titan's envelope explosion as 10,000 yr ago, which produced its thick atmosphere, young Saturn's rings, as well as a reservoir of ice fragments saturated by 2H2 + O2, i.e., cometary nuclei between the orbits of Jupiter and Saturn. Thus these nuclei should contain, besides organic matter, also 2H2 + O2, which could be used for their transportation as well as for fuel for spaceships. Ices of such composition can reside deep inside Deimos, the Trojans, C-asteroids, etc. The danger of a future explosion of Callisto's electrolyzed ices, which would result in a catastrophic bombardment of the Earth by comets, may be high enough to warrant a revision of the priorities and

Outer planets and icy satellites

NASA Astrophysics Data System (ADS)

Drobyshevski, E. M.

The resources offered by the outer bodies in the Solar System, starting with the main belt asteroids and Jovian System, are not only larger and more diverse but may even be easier to reach than, say, those of Mars. The use of their material, including water and organic matter, depends exclusively on the general strategy of exploration of the Solar System. Of major interest in this respect are the large ice satellites - Titan, Ganymede, and Callisto. Motion through the planetary magnetospheres excites in their ice envelopes megampere currents which, in the presence of rocky, etc., inclusions with electronic conduction should lead to the bulk electrolysis of ice and accumulation in it of 2H2 + O2 in the form of a solid solution. With the concentration of 2H2 + O2 reaching about 15 wt. percent, the solution becomes capable of detonation by a strong meteoritic impact. An explosion of Ganymede's ice envelope about 0.5 By ago could account for the formation of the Trojans and irregular satellites, all known differences between Ganymede and Callisto, and many other things. The explosion of a small icy planet with M approx less than 0.5 Moon created the asteroid belt. Two to three explosions occurred on Io, and two on Europa. The specific features of the longperiod comets close to Saturn's orbit permit dating Titan's envelope explosion as 10,000 yr ago, which produced its thick atmosphere, young Saturn's rings, as well as a reservoir of ice fragments saturated by 2H2 + O2, i.e., cometary nuclei between the orbits of Jupiter and Saturn. Thus these nuclei should contain, besides organic matter, also 2H2 + O2, which could be used for their transportation as well as for fuel for spaceships. Ices of such composition can reside deep inside Deimos, the Trojans, C-asteroids, etc. The danger of a future explosion of Callisto's electrolyzed ices, which would result in a catastrophic bombardment of the Earth by comets, may be high enough to warrant a revision of the priorities and

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.

Inside-out Planet Formation. IV. Pebble Evolution and Planet Formation Timescales

NASA Astrophysics Data System (ADS)

Hu, Xiao; Tan, Jonathan C.; Zhu, Zhaohuan; Chatterjee, Sourav; Birnstiel, Tilman; Youdin, Andrew N.; Mohanty, Subhanjoy

2018-04-01

Systems with tightly packed inner planets (STIPs) are very common. Chatterjee & Tan proposed Inside-out Planet Formation (IOPF), an in situ formation theory, to explain these planets. IOPF involves sequential planet formation from pebble-rich rings that are fed from the outer disk and trapped at the pressure maximum associated with the dead zone inner boundary (DZIB). Planet masses are set by their ability to open a gap and cause the DZIB to retreat outwards. We present models for the disk density and temperature structures that are relevant to the conditions of IOPF. For a wide range of DZIB conditions, we evaluate the gap-opening masses of planets in these disks that are expected to lead to the truncation of pebble accretion onto the forming planet. We then consider the evolution of dust and pebbles in the disk, estimating that pebbles typically grow to sizes of a few centimeters during their radial drift from several tens of astronomical units to the inner, ≲1 au scale disk. A large fraction of the accretion flux of solids is expected to be in such pebbles. This allows us to estimate the timescales for individual planet formation and the entire planetary system formation in the IOPF scenario. We find that to produce realistic STIPs within reasonable timescales similar to disk lifetimes requires disk accretion rates of ∼10‑9 M ⊙ yr‑1 and relatively low viscosity conditions in the DZIB region, i.e., a Shakura–Sunyaev parameter of α ∼ 10‑4.

Terrestrial planet formation.

PubMed

Righter, K; O'Brien, D P

2011-11-29

Advances in our understanding of terrestrial planet formation have come from a multidisciplinary approach. Studies of the ages and compositions of primitive meteorites with compositions similar to the Sun have helped to constrain the nature of the building blocks of planets. This information helps to guide numerical models for the three stages of planet formation from dust to planetesimals (~10(6) y), followed by planetesimals to embryos (lunar to Mars-sized objects; few 10(6) y), and finally embryos to planets (10(7)-10(8) y). Defining the role of turbulence in the early nebula is a key to understanding the growth of solids larger than meter size. The initiation of runaway growth of embryos from planetesimals ultimately leads to the growth of large terrestrial planets via large impacts. Dynamical models can produce inner Solar System configurations that closely resemble our Solar System, especially when the orbital effects of large planets (Jupiter and Saturn) and damping mechanisms, such as gas drag, are included. Experimental studies of terrestrial planet interiors provide additional constraints on the conditions of differentiation and, therefore, origin. A more complete understanding of terrestrial planet formation might be possible via a combination of chemical and physical modeling, as well as obtaining samples and new geophysical data from other planets (Venus, Mars, or Mercury) and asteroids.

Terrestrial planet formation

PubMed Central

Righter, K.; O’Brien, D. P.

2011-01-01

Advances in our understanding of terrestrial planet formation have come from a multidisciplinary approach. Studies of the ages and compositions of primitive meteorites with compositions similar to the Sun have helped to constrain the nature of the building blocks of planets. This information helps to guide numerical models for the three stages of planet formation from dust to planetesimals (∼106 y), followed by planetesimals to embryos (lunar to Mars-sized objects; few × 106 y), and finally embryos to planets (107–108 y). Defining the role of turbulence in the early nebula is a key to understanding the growth of solids larger than meter size. The initiation of runaway growth of embryos from planetesimals ultimately leads to the growth of large terrestrial planets via large impacts. Dynamical models can produce inner Solar System configurations that closely resemble our Solar System, especially when the orbital effects of large planets (Jupiter and Saturn) and damping mechanisms, such as gas drag, are included. Experimental studies of terrestrial planet interiors provide additional constraints on the conditions of differentiation and, therefore, origin. A more complete understanding of terrestrial planet formation might be possible via a combination of chemical and physical modeling, as well as obtaining samples and new geophysical data from other planets (Venus, Mars, or Mercury) and asteroids. PMID:21709256

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.

Planet Formation and the Characteristics of Extrasolar Planets

NASA Technical Reports Server (NTRS)

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

2000-01-01

An overview of current theories of planetary growth, emphasizing the formation of extrasolar planets, is presented. Models of planet formation are based upon observations of the Solar System, extrasolar planets, and 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 like terrestrial planets, but if they become massive enough before the protoplanetary disk dissipates, then they are able to accumulate substantial amounts of gas. 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.

Laser-driven shock experiments on precompressed water: Implications for "icy" giant planets.

PubMed

Lee, Kanani K M; Benedetti, L Robin; Jeanloz, Raymond; Celliers, Peter M; Eggert, Jon H; Hicks, Damien G; Moon, Stephen J; Mackinnon, Andrew; Da Silva, Luis B; Bradley, David K; Unites, Walter; Collins, Gilbert W; Henry, Emeric; Koenig, Michel; Benuzzi-Mounaix, Alessandra; Pasley, John; Neely, David

2006-07-07

Laser-driven shock compression of samples precompressed to 1 GPa produces high-pressure-temperature conditions inducing two significant changes in the optical properties of water: the onset of opacity followed by enhanced reflectivity in the initially transparent water. The onset of reflectivity at infrared wavelengths can be interpreted as a semiconductor<-->electronic conductor transition in water, and is found at pressures above approximately 130 GPa for single-shocked samples precompressed to 1 GPa. Our results indicate that conductivity in the deep interior of "icy" giant planets is greater than realized previously because of an additional contribution from electrons.

Planet Formation in Binaries

NASA Astrophysics Data System (ADS)

Thebault, P.; Haghighipour, N.

Spurred by the discovery of numerous exoplanets in multiple systems, binaries have become in recent years one of the main topics in planet formation research. Numerous studies have investigated to what extent the presence of a stellar companion can affect the planet formation process. Such studies have implications that can reach beyond the sole context of binaries, as they allow to test certain aspects of the planet formation scenario by submitting them to extreme environments. We review here the current understanding on this complex problem. We show in particular how each of the different stages of the planet-formation process is affected differently by binary perturbations. We focus especially on the intermediate stage of kilometre-sized planetesimal accretion, which has proven to be the most sensitive to binarity and for which the presence of some exoplanets observed in tight binaries is difficult to explain by in-situ formation following the "standard" planet-formation scenario. Some tentative solutions to this apparent paradox are presented. The last part of our review presents a thorough description of the problem of planet habitability, for which the binary environment creates a complex situation because of the presence of two irradation sources of varying distance.

Planet formation

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.

1993-01-01

Models of planetary formation are developed using the present single example of a planetary system, supplemented by limited astrophysical observations of star-forming regions and circumstellar disks. The solar nebula theory and the planetesimal hypothesis are discussed. The latter is found to provide a viable theory of the growth of the terrestrial planets, the cores of the giant planets, and the smaller bodies present in the solar system. The formation of solid bodies of planetary size should be a common event, at least around young stars which do not have binary companions orbiting at planetary distances. Stochastic impacts of large bodies provide sufficient angular momentum to produce the obliquities of the planets. The masses and bulk compositions of the planets can be understood in a gross sense as resulting from planetary growth within a disk whose temperature and surface density decreased with distance from the growing sun.

Icy Profile

NASA Image and Video Library

2008-10-20

The Cassini spacecraft looks toward Rhea cratered, icy landscape with the dark line of Saturn ringplane and the planet murky atmosphere as a background. Rhea is Saturn second-largest moon, at 1,528 kilometers 949 miles across.

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.

Debris disks as signposts of terrestrial planet formation

NASA Astrophysics Data System (ADS)

Raymond, S. N.; Armitage, P. J.; Moro-Martín, A.; Booth, M.; Wyatt, M. C.; Armstrong, J. C.; Mandell, A. M.; Selsis, F.; West, A. A.

2011-06-01

There exists strong circumstantial evidence from their eccentric orbits that most of the known extra-solar planetary systems are the survivors of violent dynamical instabilities. Here we explore the effect of giant planet instabilities on the formation and survival of terrestrial planets. We numerically simulate the evolution of planetary systems around Sun-like stars that include three components: (i) an inner disk of planetesimals and planetary embryos; (ii) three giant planets at Jupiter-Saturn distances; and (iii) an outer disk of planetesimals comparable to estimates of the primitive Kuiper belt. We calculate the dust production and spectral energy distribution of each system by assuming that each planetesimal particle represents an ensemble of smaller bodies in collisional equilibrium. Our main result is a strong correlation between the evolution of the inner and outer parts of planetary systems, i.e. between the presence of terrestrial planets and debris disks. Strong giant planet instabilities - that produce very eccentric surviving planets - destroy all rocky material in the system, including fully-formed terrestrial planets if the instabilities occur late, and also destroy the icy planetesimal population. Stable or weakly unstable systems allow terrestrial planets to accrete in their inner regions and significant dust to be produced in their outer regions, detectable at mid-infrared wavelengths as debris disks. Stars older than ~100 Myr with bright cold dust emission (in particular at λ ~ 70 μm) signpost dynamically calm environments that were conducive to efficient terrestrial accretion. Such emission is present around ~16% of billion-year old Solar-type stars. Our simulations yield numerous secondary results: 1) the typical eccentricities of as-yet undetected terrestrial planets are ~0.1 but there exists a novel class of terrestrial planet system whose single planet undergoes large amplitude oscillations in orbital eccentricity and inclination; 2) by

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.

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.

Post-main-sequence Evolution of Icy Minor Planets. III. Water Retention in Dwarf Planets and Exomoons and Implications for White Dwarf Pollution

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

Malamud, Uri; Perets, Hagai B., E-mail: uri.mal@tx.technion.ac.il, E-mail: hperets@physics.technion.ac.il

Studies suggest that the pollution of white dwarf (WD) atmospheres arises from the accretion of minor planets, but the exact properties of polluting material, and in particular the evidence for water in some cases are not yet understood. Several previous works studied the possibility of water surviving inside minor planets around evolving stars. However, they all focused on small, comet-sized to moonlet-sized minor planets, when the inferred mass inside the convection zones of He-dominated WDs could actually be compatible with much more massive minor planets. Here we explore for the first time, the water retention inside exoplanetary dwarf planets, ormore » moderate-sized moons, with radii of the order of hundreds of kilometers. This paper concludes a series of papers that has now covered nearly the entire potential mass range of minor planets, in addition to the full mass range of their host stars. We find that water retention is (a) affected by the mass of the WD progenitor, and (b) it is on average at least 5%, irrespective of the assumed initial water composition, if it came from a single accretion event of an icy dwarf planet or moon. The latter prediction strengthens the possibility of habitability in WD planetary systems, and it may also be used in order to distinguish between pollution originating from multiple small accretion events and singular large accretion events. To conclude our work, we provide a code that calculates ice and water retention by interpolation and may be freely used as a service to the community.« less

Formation of Outer Planets: Overview

NASA Technical Reports Server (NTRS)

Lissauer, Jack

2003-01-01

An overview of current theories of planetary formation, with emphasis on giant planets is presented. The most detailed models are based upon observation of our own Solar System and of young stars and their environments. Terrestrial planets are believe 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. 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 cores become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk disspates. The primary questions regarding the core instability model is whether planets with small cores can accrete gaseous enveloples within the lifetimes of gaseous protoplanetary disks. The main alternative giant planet formation model is the disk instability model, in which gaseous planets form directly via gravitational instabilities within protoplanetary disks. Formation of giant planets via gas instability has never been demonstrated for realistic disk conditions. Moreover, this model has difficulty explaining the supersolar abundances of heavy elements in Jupiter and Saturn, and it does not explain the orgin of planets like Uranus and Neptune.

Extrasolar binary planets. I. Formation by tidal capture during planet-planet scattering

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

Ochiai, H.; Nagasawa, M.; Ida, S., E-mail: nagasawa.m.ad@m.titech.ac.jp

2014-08-01

We have investigated (1) the formation of gravitationally bounded pairs of gas-giant planets (which we call 'binary planets') from capturing each other through planet-planet dynamical tide during their close encounters and (2) the subsequent long-term orbital evolution due to planet-planet and planet-star quasi-static tides. For the initial evolution in phase 1, we carried out N-body simulations of the systems consisting of three Jupiter-mass planets taking into account the dynamical tide. The formation rate of the binary planets is as much as 10% of the systems that undergo orbital crossing, and this fraction is almost independent of the initial stellarcentric semimajormore » axes of the planets, while ejection and merging rates sensitively depend on the semimajor axes. As a result of circularization by the planet-planet dynamical tide, typical binary separations are a few times the sum of the physical radii of the planets. After the orbital circularization, the evolution of the binary system is governed by long-term quasi-static tide. We analytically calculated the quasi-static tidal evolution in phase 2. The binary planets first enter the spin-orbit synchronous state by the planet-planet tide. The planet-star tide removes angular momentum of the binary motion, eventually resulting in a collision between the planets. However, we found that the binary planets survive the tidal decay for the main-sequence lifetime of solar-type stars (∼10 Gyr), if the binary planets are beyond ∼0.3 AU from the central stars. These results suggest that the binary planets can be detected by transit observations at ≳ 0.3 AU.« less

Planet formation: constraints from transiting extrasolar planets

NASA Astrophysics Data System (ADS)

Guillot, T.; Santos, N.; Pont, F.; Iro, N.; Melo, C.; Ribas, I.

Ten extrasolar planets with masses between 105 and 430M⊕ are known to transit their star. The knowledge of their mass and radius allows an estimate of their composition, but uncertainties on equations of state, opacities and possible missing energy sources imply that only inaccurate constraints can be derived when considering each planet separately. This is illustrated by HD209458b and XO-1b, two planets that appear to be larger than models would predict. Using a relatively simple evolution model, we show that the radius anomaly, i.e. the difference between the measured and theoretically calculated radii, is anticorrelated with the metallicity of the parent star. This implies that the present size, structure and composition of these planets is largely determined by the initial metallicity of the protoplanetary disk, and not, or to a lesser extent, by other processes such as the differences in the planets' orbital evolutions, tides due to finite eccentricities/inclinations and planet evaporation. Using evolution models including the presence of a core and parametrized missing physics, we show that all nine planets belong to a same ensemble characterized by a mass of heavy elements MZ that is a steep function of the stellar metallicity: from ˜ 10 M⊕ around a solar composition star, to ˜ 100 M⊕ for twice the solar metallicity. Together with the observed lack of giant planets in close orbits around metal-poor stars, these results imply that heavy elements play a key role in the formation of close-in giant planets. The large values of MZ and of the planet enrichments for metal-rich stars shows the need for alternative theories of planet formation including migration and subsequent collection of planetesimals.

EVAPORATION OF ICY PLANETESIMALS DUE TO BOW SHOCKS

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

Tanaka, Kyoko K.; Yamamoto, Tetsuo; Tanaka, Hidekazu

2013-02-20

We present the novel concept of evaporation of planetesimals as a result of bow shocks associated with planetesimals orbiting with supersonic velocities relative to the gas in a protoplanetary disk. We evaluate the evaporation rates of the planetesimals based on a simple model describing planetesimal heating and evaporation by the bow shock. We find that icy planetesimals with radius {approx}>100 km evaporate efficiently even outside the snow line in the stage of planetary oligarchic growth, where strong bow shocks are produced by gravitational perturbations from protoplanets. The obtained results suggest that the formation of gas giant planets is suppressed owingmore » to insufficient accretion of icy planetesimals onto the protoplanet within the {approx}<5 AU disk region.« less

Abrupt Climate Transition of Icy Worlds from Snowball to Moist or Runaway Greenhouse

NASA Astrophysics Data System (ADS)

Yang, J.; Ding, F.; Ramirez, R. M.; Peltier, W. R.; Hu, Y.; Liu, Y.

2017-12-01

Ongoing and future space missions aim to identify potentially habitable planets in our Solar System and beyond. Planetary habitability is determined not only by a planet's current stellar insolation and atmospheric properties, but also by the evolutionary history of its climate. It has been suggested that icy planets and moons become habitable after their initial ice shield melts as their host stars brighten. Here we show from global climate model simulations that a habitable state is not achieved in the climatic evolution of those icy planets and moons that possess an inactive carbonate-silicate cycle and low concentrations of greenhouse gases. Examples for such planetary bodies are the icy moons Europa and Enceladus, and certain icy exoplanets orbiting G and F stars. We find that the stellar fluxes that are required to overcome a planet's initial snowball state are so large that they lead to significant water loss and preclude a habitable planet. Specifically, they exceed the moist greenhouse limit, at which water vapour accumulates at high altitudes where it can readily escape, or the runaway greenhouse limit, at which the strength of the greenhouse increases until the oceans boil away. We suggest that some icy planetary bodies may transition directly to a moist or runaway greenhouse without passing through a habitable Earth-like state.

Abrupt climate transition of icy worlds from snowball to moist or runaway greenhouse

NASA Astrophysics Data System (ADS)

Yang, Jun; Ding, Feng; Ramirez, Ramses M.; Peltier, W. R.; Hu, Yongyun; Liu, Yonggang

2017-08-01

Ongoing and future space missions aim to identify potentially habitable planets in our Solar System and beyond. Planetary habitability is determined not only by a planet's current stellar insolation and atmospheric properties, but also by the evolutionary history of its climate. It has been suggested that icy planets and moons become habitable after their initial ice shield melts as their host stars brighten. Here we show from global climate model simulations that a habitable state is not achieved in the climatic evolution of those icy planets and moons that possess an inactive carbonate-silicate cycle and low concentrations of greenhouse gases. Examples for such planetary bodies are the icy moons Europa and Enceladus, and certain icy exoplanets orbiting G and F stars. We find that the stellar fluxes that are required to overcome a planet's initial snowball state are so large that they lead to significant water loss and preclude a habitable planet. Specifically, they exceed the moist greenhouse limit, at which water vapour accumulates at high altitudes where it can readily escape, or the runaway greenhouse limit, at which the strength of the greenhouse increases until the oceans boil away. We suggest that some icy planetary bodies may transition directly to a moist or runaway greenhouse without passing through a habitable Earth-like state.

Formation of terrestrial planets in eccentric and inclined giant planet systems

NASA Astrophysics Data System (ADS)

Sotiriadis, Sotiris; Libert, Anne-Sophie; Raymond, Sean N.

2018-06-01

Aims: Evidence of mutually inclined planetary orbits has been reported for giant planets in recent years. Here we aim to study the impact of eccentric and inclined massive giant planets on the terrestrial planet formation process, and investigate whether it can possibly lead to the formation of inclined terrestrial planets. Methods: We performed 126 simulations of the late-stage planetary accretion in eccentric and inclined giant planet systems. The physical and orbital parameters of the giant planet systems result from n-body simulations of three giant planets in the late stage of the gas disc, under the combined action of Type II migration and planet-planet scattering. Fourteen two- and three-planet configurations were selected, with diversified masses, semi-major axes (resonant configurations or not), eccentricities, and inclinations (including coplanar systems) at the dispersal of the gas disc. We then followed the gravitational interactions of these systems with an inner disc of planetesimals and embryos (nine runs per system), studying in detail the final configurations of the formed terrestrial planets. Results: In addition to the well-known secular and resonant interactions between the giant planets and the outer part of the disc, giant planets on inclined orbits also strongly excite the planetesimals and embryos in the inner part of the disc through the combined action of nodal resonance and the Lidov-Kozai mechanism. This has deep consequences on the formation of terrestrial planets. While coplanar giant systems harbour several terrestrial planets, generally as massive as the Earth and mainly on low-eccentric and low-inclined orbits, terrestrial planets formed in systems with mutually inclined giant planets are usually fewer, less massive (<0.5 M⊕), and with higher eccentricities and inclinations. This work shows that terrestrial planets can form on stable inclined orbits through the classical accretion theory, even in coplanar giant planet systems

Planet Formation in Binary Star Systems

NASA Astrophysics Data System (ADS)

Martin, Rebecca

About half of observed exoplanets are estimated to be in binary systems. Understanding planet formation and evolution in binaries is therefore essential for explaining observed exoplanet properties. Recently, we discovered that a highly misaligned circumstellar disk in a binary system can undergo global Kozai-Lidov (KL) oscillations of the disk inclination and eccentricity. These oscillations likely have a significant impact on the formation and orbital evolution of planets in binary star systems. Planet formation by core accretion cannot operate during KL oscillations of the disk. First, we propose to consider the process of disk mass transfer between the binary members. Secondly, we will investigate the possibility of planet formation by disk fragmentation. Disk self gravity can weaken or suppress the oscillations during the early disk evolution when the disk mass is relatively high for a narrow range of parameters. Thirdly, we will investigate the evolution of a planet whose orbit is initially aligned with respect to the disk, but misaligned with respect to the orbit of the binary. We will study how these processes relate to observations of star-spin and planet orbit misalignment and to observations of planets that appear to be undergoing KL oscillations. Finally, we will analyze the evolution of misaligned multi-planet systems. This theoretical work will involve a combination of analytic and numerical techniques. The aim of this research is to shed some light on the formation of planets in binary star systems and to contribute to NASA's goal of understanding of the origins of exoplanetary systems.

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.

The Chemistry of Planet Formation

NASA Astrophysics Data System (ADS)

Oberg, Karin I.

2017-01-01

Exo-planets are common, and they span a large range of compositions. The origins of the observed diversity of planetary compositions is largely unconstrained, but must be linked to the planet formation physics and chemistry. Among planets that are Earth-like, a second question is how often such planets form hospitable to life. A fraction of exo-planets are observed to be ‘physically habitable’, i.e. of the right temperature and bulk composition to sustain a water-based prebiotic chemistry, but this does not automatically imply that they are rich in the building blocks of life, in organic molecules of different sizes and kinds, i.e. that they are chemically habitable. In this talk I will argue that characterizing the chemistry of protoplanetary disks, the formation sites of planets, is key to address both the origins of planetary bulk compositions and the likelihood of finding organic matter on planets. The most direct path to constrain the chemistry in disks is to directly observe it. In the age of ALMA it is for the first time possible to image the chemistry of planet formation, to determine locations of disk snowlines, and to map the distributions of different organic molecules. Recent ALMA highlights include constraints on CO snowline locations, the discovery of spectacular chemical ring systems, and first detections of more complex organic molecules. Observations can only provide chemical snapshots, however, and even ALMA is blind to the majority of the chemistry that shapes planet formation. To interpret observations and address the full chemical complexity in disks requires models, both toy models and astrochemical simulations. These models in turn must be informed by laboratory experiments, some of which will be shown in this talk. It is thus only when we combine observational, theoretical and experimental constraints that we can hope to characterize the chemistry of disks, and further, the chemical compositions of nascent planets.

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

Sublimation of icy planetesimals and the delivery of water to the habitable zone around solar type stars

NASA Astrophysics Data System (ADS)

Brunini, Adrián; López, María Cristina

2018-06-01

We present a semi analytic model to evaluate the delivery of water to the habitable zone around a solar type star carried by icy planetesimals born beyond the snow line. The model includes sublimation of ice, gas drag and scattering by an outer giant planet located near the snow line. The sublimation model is general and could be applicable to planetary synthesis models or N-Body simulations of the formation of planetary systems. We perform a short series of simulations to asses the potential relevance of sublimation of volatiles in the process of delivery of water to the inner regions of a planetary system during early stages of its formation. We could anticipate that erosion by sublimation would prevent the arrival of much water to the habitable zone of protoplanetary disks in the form of icy planetesimals. Close encounters with a massive planet orbiting near the outer edge of the snow line could make possible for planetesimals to reach the habitable zone somewhat less eroded. However, only large planetesimals could provide appreciable amounts of water. Massive disks and sharp gas surface density profiles favor icy planetesimals to reach inner regions of a protoplanetary disk.

Inside-out Planet Formation. III. Planet-Disk Interaction at the Dead Zone Inner Boundary

NASA Astrophysics Data System (ADS)

Hu, Xiao; Zhu, Zhaohuan; Tan, Jonathan C.; Chatterjee, Sourav

2016-01-01

The Kepler mission has discovered more than 4000 exoplanet candidates. Many of them are in systems with tightly packed inner planets. Inside-out planet formation (IOPF) has been proposed as a scenario to explain these systems. It involves sequential in situ planet formation at the local pressure maximum of a retreating dead zone inner boundary (DZIB). Pebbles accumulate at this pressure trap, which builds up a pebble ring and then a planet. The planet is expected to grow in mass until it opens a gap, which helps to both truncate pebble accretion and also induce DZIB retreat that sets the location of formation of the next planet. This simple scenario may be modified if the planet undergoes significant migration from its formation location. Thus, planet-disk interactions play a crucial role in the IOPF scenario. Here we present numerical simulations that first assess the degree of migration for planets of various masses that are forming at the DZIB of an active accretion disk, where the effective viscosity is undergoing a rapid increase in the radially inward direction. We find that torques exerted on the planet by the disk tend to trap the planet at a location very close to the initial pressure maximum where it formed. We then study gap opening by these planets to assess at what mass a significant gap is created. Finally, we present a simple model for DZIB retreat due to penetration of X-rays from the star to the disk midplane. Overall, these simulations help to quantify both the mass scale of first (“Vulcan”) planet formation and the orbital separation to the location of second planet formation.

ON THE LIKELIHOOD OF PLANET FORMATION IN CLOSE BINARIES

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

Jang-Condell, Hannah, E-mail: hjangcon@uwyo.edu

2015-02-01

To date, several exoplanets have been discovered orbiting stars with close binary companions (a ≲ 30 AU). The fact that planets can form in these dynamically challenging environments implies that planet formation must be a robust process. The initial protoplanetary disks in these systems from which planets must form should be tidally truncated to radii of a few AU, which indicates that the efficiency of planet formation must be high. Here, we examine the truncation of circumstellar protoplanetary disks in close binary systems, studying how the likelihood of planet formation is affected over a range of disk parameters. If themore » semimajor axis of the binary is too small or its eccentricity is too high, the disk will have too little mass for planet formation to occur. However, we find that the stars in the binary systems known to have planets should have once hosted circumstellar disks that were capable of supporting planet formation despite their truncation. We present a way to characterize the feasibility of planet formation based on binary orbital parameters such as stellar mass, companion mass, eccentricity, and semimajor axis. Using this measure, we can quantify the robustness of planet formation in close binaries and better understand the overall efficiency of planet formation in general.« less

Ice-gas interactions during planet formation

NASA Astrophysics Data System (ADS)

Öberg, Karin I.

2016-10-01

Planets form in disks around young stars. In these disks, condensation fronts or snowlines of water, CO2, CO and other abundant molecules regulate the outcome of planet formation. Snowline locations determine how the elemental and molecular compositions of the gaseous and solid building blocks of planets evolve with distance from the central star. Snowlines may also locally increase the planet formation efficiency. Observations of snowlines have only become possible in the past couple of years. This proceeding reviews these observations as well as the theory on the physical and chemical processes in disks that affect snowline locations.

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.

On the history and future of cosmic planet formation

NASA Astrophysics Data System (ADS)

Behroozi, Peter; Peeples, Molly S.

2015-12-01

We combine constraints on galaxy formation histories with planet formation models, yielding the Earth-like and giant planet formation histories of the Milky Way and the Universe as a whole. In the Hubble volume (1013 Mpc3), we expect there to be ˜1020 Earth-like and ˜1020 giant planets; our own galaxy is expected to host ˜109 and ˜1010 Earth-like and giant planets, respectively. Proposed metallicity thresholds for planet formation do not significantly affect these numbers. However, the metallicity dependence for giant planets results in later typical formation times and larger host galaxies than for Earth-like planets. The Solar system formed at the median age for existing giant planets in the Milky Way, and consistent with past estimates, formed after 80 per cent of Earth-like planets. However, if existing gas within virialized dark matter haloes continues to collapse and form stars and planets, the Universe will form over 10 times more planets than currently exist. We show that this would imply at least a 92 per cent chance that we are not the only civilization the Universe will ever have, independent of arguments involving the Drake equation.

On The History and Future of Cosmic Planet Formation

NASA Astrophysics Data System (ADS)

Behroozi, Peter

2016-03-01

We combine constraints on galaxy formation histories with planet formation models, yielding the Earth-like and giant planet formation histories of the Milky Way and the Universe as a whole. In the Hubble Volume (1013 Mpc3), we expect there to be ~1020 Earth-like and ~1020 giant planets; our own galaxy is expected to host ~109 and ~1010 Earth-like and giant planets, respectively. Proposed metallicity thresholds for planet formation do not significantly affect these numbers. However, the metallicity dependence for giant planets results in later typical formation times and larger host galaxies than for Earth-like planets. The Solar System formed at the median age for existing giant planets in the Milky Way, and consistent with past estimates, formed after 80% of Earth-like planets. However, if existing gas within virialised dark matter haloes continues to collapse and form stars and planets, the Universe will form over 10 times more planets than currently exist. We show that this would imply at least a 92% chance that we are not the only civilisation the Universe will ever have, independent of arguments involving the Drake Equation.

Impact of planet-planet scattering on the formation and survival of debris discs

NASA Astrophysics Data System (ADS)

Marzari, F.

2014-10-01

Planet-planet scattering is a major dynamical mechanism able to significantly alter the architecture of a planetary system. In addition to that, it may also affect the formation and retention of a debris disc by the system. A violent chaotic evolution of the planets can easily clear leftover planetesimal belts preventing the ignition of a substantial collisional cascade that can give origin to a debris disc. On the other end, a mild evolution with limited steps in eccentricity and semimajor axis can trigger the formation of a debris disc by stirring an initially quiet planetesimal belt. The variety of possible effects that planet-planet scattering can have on the formation of debris discs is analysed and the statistical probability of the different outcomes is evaluated. This leads to the prediction that systems which underwent an episode of chaotic evolution might have a lower probability of harbouring a debris disc.

Recipes for planet formation

NASA Astrophysics Data System (ADS)

Meyer, Michael R.

2009-11-01

Anyone who has ever used baking soda instead of baking powder when trying to make a cake knows a simple truth: ingredients matter. The same is true for planet formation. Planets are made from the materials that coalesce in a rotating disk around young stars - essentially the "leftovers" from when the stars themselves formed through the gravitational collapse of rotating clouds of gas and dust. The planet-making disk should therefore initially have the same gas-to-dust ratio as the interstellar medium: about 100 to 1, by mass. Similarly, it seems logical that the elemental composition of the disk should match that of the star, reflecting the initial conditions at that particular spot in the galaxy.

Benzene Formation on Interstellar Icy Mantles Containing Propargyl Alcohol

NASA Astrophysics Data System (ADS)

Sivaraman, B.; Mukherjee, R.; Subramanian, K. P.; Banerjee, S. B.

2015-01-01

Propargyl alcohol (CHCCH2OH) is a known stable isomer of the propenal (CH2CHCHO) molecule that was reported to be present in the interstellar medium (ISM). At astrochemical conditions in the laboratory, icy layers of propargyl alcohol grown at 85 K were irradiated by 2 keV electrons and probed by a Fourier Transform InfraRed spectrometer in the mid-infrared (IR) region, 4000-500 cm-1. Propargyl alcohol ice under astrochemical conditions was studied for the first time; therefore, IR spectra of reported amorphous (85 K) and crystalline (180 K) propargyl alcohol ices can be used to detect its presence in the ISM. Moreover, our experiments clearly show benzene (C6H6) formation to be the major product from propargyl alcohol irradiation, confirming the role of propargyl radicals (C3H3) formed from propargyl alcohol dissociation that was long expected based on theoretical modeling to effectively synthesize C6H6 in the interstellar icy mantles.

Planetary system formation: Effects of planet-disk tidal interaction

NASA Astrophysics Data System (ADS)

Bryden, Geoffrey

The standard theory of planet formation begins with the coagulation of solid planetesimals (Safronov 1969, Wetherill & Stewart 1989) followed by the accretion of disk gas once the solid core reaches a critical mass >~10M⊕ (Perri & Cameron 1974, Mizuno 1980, Bodenheimer & Pollack 1986). The classic picture of planet formation, in which each planet's position in the nebula remain fixed, is challenged by the observed distribution of extra-solar planets (e.g. Mayor & Queloz 1995, Butler et al. 1999). The majority of these planets are on short-period orbits ( P<~10 days) very close to their central stars ( ap<~0.1 AU), suggesting that orbital migration plays an important role in the formation of planetary systems. The intent of this thesis is to explore the inclusion of protoplanetary tidal forces into the classical theory of planetary system formation. Protoplanetary interaction with the surrounding gaseous nebulae directly determines giant planets' semi-major axes, masses, gas/solid ratio, and relative spacing. In essence, the process of gap formation determines the primary observational characteristics of both individual planets and their composite systems. Detailed simulations of gap formation produce a range of planetary masses consistent with the observed distribution. Fully self-interacting models of planetary system formation can be used to create a wide variety of planetary systems, ranging from the solar system to Upsilon Andromeda (Butler et al. 1999).

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.

Origins and Destinations: Tracking Planet Composition through Planet Formation Simulations

NASA Astrophysics Data System (ADS)

Chance, Quadry; Ballard, Sarah

2018-01-01

There are now several thousand confirmed exoplanets, a number which far exceeds our resources to study them all in detail. In particular, planets around M dwarfs provide the best opportunity for in-depth study of their atmospheres by telescopes in the near future. The question of which M dwarf planets most merit follow-up resources is a pressing one, given that NASA’s TESS mission will soon find hundreds of such planets orbiting stars bright enough for both ground and spaced-based follow-up.Our work aims to predict the approximate composition of planets around these stars through n-body simulations of the last stage of planet formation. With a variety of initial disk conditions, we investigate how the relative abundances of both refractory and volatile compounds in the primordial planetesimals are mapped to the final planet outcomes. These predictions can serve to provide a basis for making an educated guess about (a) which planets to observe with precious resources like JWST and (b) how to identify them based on dynamical clues.

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

Influence of stellar multiplicity on planet formation. I. Evidence of suppressed planet formation due to stellar companions within 20 au and validation of four planets from the Kepler multiple planet candidates

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

Wang, Ji; Fischer, Debra A.; Xie, Ji-Wei

2014-03-01

The planet occurrence rate for multiple stars is important in two aspects. First, almost half of stellar systems in the solar neighborhood are multiple systems. Second, the comparison of the planet occurrence rate for multiple stars to that for single stars sheds light on the influence of stellar multiplicity on planet formation and evolution. We developed a method of distinguishing planet occurrence rates for single and multiple stars. From a sample of 138 bright (K{sub P} < 13.5) Kepler multi-planet candidate systems, we compared the stellar multiplicity rate of these planet host stars to that of field stars. Using dynamicalmore » stability analyses and archival Doppler measurements, we find that the stellar multiplicity rate of planet host stars is significantly lower than field stars for semimajor axes less than 20 AU, suggesting that planet formation and evolution are suppressed by the presence of a close-in companion star at these separations. The influence of stellar multiplicity at larger separations is uncertain because of search incompleteness due to a limited Doppler observation time baseline and a lack of high-resolution imaging observation. We calculated the planet confidence for the sample of multi-planet candidates and find that the planet confidences for KOI 82.01, KOI 115.01, KOI 282.01, and KOI 1781.02 are higher than 99.7% and thus validate the planetary nature of these four planet candidates. This sample of bright Kepler multi-planet candidates with refined stellar and orbital parameters, planet confidence estimation, and nearby stellar companion identification offers a well-characterized sample for future theoretical and observational study.« less

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.

BENZENE FORMATION ON INTERSTELLAR ICY MANTLES CONTAINING PROPARGYL ALCOHOL

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

Sivaraman, B.; Mukherjee, R.; Subramanian, K. P.

Propargyl alcohol (CHCCH{sub 2}OH) is a known stable isomer of the propenal (CH{sub 2}CHCHO) molecule that was reported to be present in the interstellar medium (ISM). At astrochemical conditions in the laboratory, icy layers of propargyl alcohol grown at 85 K were irradiated by 2 keV electrons and probed by a Fourier Transform InfraRed spectrometer in the mid-infrared (IR) region, 4000-500 cm{sup –1}. Propargyl alcohol ice under astrochemical conditions was studied for the first time; therefore, IR spectra of reported amorphous (85 K) and crystalline (180 K) propargyl alcohol ices can be used to detect its presence in the ISM.more » Moreover, our experiments clearly show benzene (C{sub 6}H{sub 6}) formation to be the major product from propargyl alcohol irradiation, confirming the role of propargyl radicals (C{sub 3}H{sub 3}) formed from propargyl alcohol dissociation that was long expected based on theoretical modeling to effectively synthesize C{sub 6}H{sub 6} in the interstellar icy mantles.« less

Large Impact Features on Icy Galilean Satellites

NASA Technical Reports Server (NTRS)

Moore, J. M.; Schenk, P. M.; Korycansky, D. G.

2017-01-01

Impact crater morphology can be a very useful tool for probing planetary interiors, but nowhere in the solar system is a greater variety of crater morphologies observed (Fig. 1) than on the large icy Galilean satellites Ganymede and Callisto [e.g., 1- 3]. As on the rocky terrestrial planets, impact crater morphology becomes more complex with increasing size on these satellites. With increasing size, however, these same craters become less like their counterparts on the rocky planets. Several impact landforms and structures (multiring furrows, palimpsests, and central domes, for example), have no obvious analogs on any other planets. Further, several studies [e.g., 4-6] have drawn attention to impact landforms on Europa which are unusual, even by Galilean satellite standards. These radical differences in morphology suggest that impact into icy lithospheres that are mechanically distinct from silicate lithospheres may be responsible. As such, large impact structures may be important probes of the interiors of these bodies over time [e.g., 7]. The first goal of this work is to integrate and correlate the detailed morphologic and morphometric measurements and observations of craters on icy Galilean satellites [e.g., 4, 8-12] with new detailed mapping of these structures from Galileo high-resolution images. As a result, we put forward a revised crater taxonomy for Ganymede and Callisto in order to simplify the nonuniform impact crater nomenclature cluttering the literature. We develop and present an integrated model for the development of these unusual crater morphologies and their implications for the thermal evolution of these bodies.

Status of the Planet Formation Imager (PFI) concept

NASA Astrophysics Data System (ADS)

Ireland, Michael J.; Monnier, John D.; Kraus, Stefan; Isella, Andrea; Minardi, Stefano; Petrov, Romain; ten Brummelaar, Theo; Young, John; Vasisht, Gautam; Mozurkewich, David; Rinehart, Stephen; Michael, Ernest A.; van Belle, Gerard; Woillez, Julien

2016-08-01

The Planet Formation Imager (PFI) project aims to image the period of planet assembly directly, resolving structures as small as a giant planet's Hill sphere. These images will be required in order to determine the key mechanisms for planet formation at the time when processes of grain growth, protoplanet assembly, magnetic fields, disk/planet dynamical interactions and complex radiative transfer all interact - making some planetary systems habitable and others inhospitable. We will present the overall vision for the PFI concept, focusing on the key technologies and requirements that are needed to achieve the science goals. Based on these key requirements, we will define a cost envelope range for the design and highlight where the largest uncertainties lie at this conceptual stage.

Formation of the giant planets

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.

2006-01-01

The observed properties of giant planets, models of their evolution and observations of protoplanetary disks provide constraints on the formation of gas giant planets. The four largest planets in our Solar System contain considerable quantities of hydrogen and helium, which could not have condensed into solid planetesimals within the protoplanetary disk. All three (transiting) extrasolar giant planets with well determined masses and radii also must contain substantial amounts of these light gases. Jupiter and Saturn are mostly hydrogen and helium, but have larger abundances of heavier elements than does the Sun. Neptune and Uranus are primarily composed of heavier elements. HD 149026 b, which is slightly more massive than is Saturn, appears to have comparable quantities of light gases and heavy elements. HD 209458 b and TrES-1 are primarily hydrogen and helium, but may contain supersolar abundances of heavy elements. Spacecraft flybys and observations of satellite orbits provide estimates of the gravitational moments of the giant planets in our Solar System, which in turn provide information on the internal distribution of matter within Jupiter, Saturn, Uranus and Neptune. Atmospheric thermal structure and heat flow measurements constrain the interior temperatures of planets. Internal processes may cause giant planets to become more compositionally differentiated or alternatively more homogeneous; high-pressure laboratory .experiments provide data useful for modeling these processes. The preponderance of evidence supports the core nucleated gas accretion model. According to this 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. The primary questions regarding the core nucleated growth model is under what conditions

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?

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.

Terrestrial Planet Formation in Binary Star Systems

NASA Technical Reports Server (NTRS)

Lissauer, J. J.; Quintana, E. V.; Adams, F. C.; Chambers, J. E.

2006-01-01

Most stars reside in binary/multiple star systems; however, previous models of planet formation have studied growth of bodies orbiting an isolated single star. Disk material has been observed around one or both components of various young close binary star systems. If planets form at the right places within such disks, they can remain dynamically stable for very long times. We have simulated the late stages of growth of terrestrial planets in both circumbinary disks around 'close' binary star systems with stellar separations ($a_B$) in the range 0.05 AU $\\le a_B \\le$ 0.4 AU and binary eccentricities in the range $0 \\le e \\le 0.8$ and circumstellar disks around individual stars with binary separations of tens of AU. 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 around individual stars in the Alpha Centauri system (Quintana et al. 2002, A.J., 576, 982); giant planets analogous to Jupiter and Saturn are included if their orbits are stable. The planetary systems formed around close binaries with stellar apastron distances less than or equal to 0.2 AU with small stellar eccentricities are very similar to those formed in the Sun-Jupiter-Saturn, whereas planetary systems formed around binaries with larger maximum separations tend to be sparser, with fewer planets, especially interior to 1 AU. Likewise, when the binary periastron exceeds 10 AU, terrestrial planets can form over essentially the entire range of orbits allowed for single stars with Jupiter-like planets, although fewer terrestrial planets tend to form within high eccentricity binary systems. As the binary periastron decreases, the radial extent of the terrestrial planet systems is reduced accordingly. When the periastron is 5 AU, the formation of Earth-like planets near 1 AU is compromised.

Chemical fingerprints of hot Jupiter planet formation

NASA Astrophysics Data System (ADS)

Maldonado, J.; Villaver, E.; Eiroa, C.

2018-05-01

Context. The current paradigm to explain the presence of Jupiter-like planets with small orbital periods (P < 10 days; hot Jupiters), which involves their formation beyond the snow line following inward migration, has been challenged by recent works that explore the possibility of in situ formation. Aims: We aim to test whether stars harbouring hot Jupiters and stars with more distant gas-giant planets show any chemical peculiarity that could be related to different formation processes. Methods: Our methodology is based on the analysis of high-resolution échelle spectra. Stellar parameters and abundances of C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn for a sample of 88 planet hosts are derived. The sample is divided into stars hosting hot (a < 0.1 au) and cool (a > 0.1 au) Jupiter-like planets. The metallicity and abundance trends of the two sub-samples are compared and set in the context of current models of planet formation and migration. Results: Our results show that stars with hot Jupiters have higher metallicities than stars with cool distant gas-giant planets in the metallicity range +0.00/+0.20 dex. The data also shows a tendency of stars with cool Jupiters to show larger abundances of α elements. No abundance differences between stars with cool and hot Jupiters are found when considering iron peak, volatile elements or the C/O, and Mg/Si ratios. The corresponding p-values from the statistical tests comparing the cumulative distributions of cool and hot planet hosts are 0.20, <0.01, 0.81, and 0.16 for metallicity, α, iron-peak, and volatile elements, respectively. We confirm previous works suggesting that more distant planets show higher planetary masses as well as larger eccentricities. We note differences in age and spectral type between the hot and cool planet host samples that might affect the abundance comparison. Conclusions: The differences in the distribution of planetary mass, period, eccentricity, and stellar host

Formation of ions and radicals from icy grains in comets

NASA Technical Reports Server (NTRS)

Jackson, William M.; Gerth, Christopher; Hendricks, Charles

1991-01-01

Ion and radical formation in comets are thought to occur primarily by photodissociation of gas phase molecules. Experimental evidence and theoretical calculations are presented that show that some of the radical and ions can come directly from ice grains. The experimental evidence suggest that if the frozen molecules on the surface of grains undergo direct dissociation then they may be able to release radicals directly in the gas phase. If the molecules undergo predissociation it is unlikely that they will release radicals in the gas phase since they should be quenched. Calculations of this direct photodissociation mechanism further indicate that even if the parent molecule undergoes direct dissociation, the yield will not be high enough to explain the rays structure in comets unless the radicals are stored in the grains and then released when the grain evaporates. Calculations were also performed to determine the maximum number of ions that can be stored in an icy grain's radius. This number is compared with the ratio of the ion to neutral molecular density. The comparison suggests that some of the ions observed near the nucleus of the comet could have originally been present in the cometary nucleus. It is also pointed out that the presence of these ions in icy grains could lead to radical formation via electron recombination. Finally, an avalanche process was evaluated as another means of producing ions in comets.

Migration of icy planetesimals to forming terrestrial planets

NASA Astrophysics Data System (ADS)

Ipatov, Sergei I.; Marov, Mikhail

2016-07-01

Our studies of migration of planetesimals from the feeding zone of Jupiter and Saturn to forming terrestrial planets were based on computer simulations of the orbital evolution of 10^4 planetesimals under the gravitational influence of planets. In series JN, all planets were considered in present orbits with present masses, and in series JS, Uranus and Neptune were excluded. Initial eccentricities and inclinations of planetesimals were 0.3 and 0.15 rad, respectively. Their initial semi-major axes were between 4.5 and 12 AU. Masses of planets moving in the orbits of the terrestrial planets were equal to present masses of the planets in series JS and JN, and were smaller by a factor of 10 in series JS_{01} and JN_{01}. The obtained results show that the ratio of the fraction of the planetesimals collided with an embryo of the Earth's embryo was about 2\\cdot10^{-6} and 4\\cdot10^{-7} for the mass of the embryo equal to the Earth mass and to 10% of the Earth mass, respectively. We concluded that during the growth of the mass of the Earth's embryo up to a half of the present mass of the Earth, the amount of water delivered to the embryo could be about 30% of all water delivered to the Earth from the feeding zone of Jupiter and Saturn. The total mass of water delivered to the Earth from the feeding zones of the giant planets and beyond these zones could be comparable with the mass of the Earth's oceans. A half of this water could come from the feeding zone of Jupiter and Saturn, and another half from more distant regions. Most of the water that was delivered from the distant regions to the Earth's embryo came when its mass was not small (e.g., was mainly greater than a half of the Earth mass). In series JS, the ratio of the mass of water delivered to a planet to the mass of the planet for the Earth was smaller by a factor of 2, 1.25, and 1.3 than for Mars, Venus and Mercury, respectively. For series JN, the above values of the factor were equal to 3.4, 0.7 i 0.8. For

Formation of S-type planets in close binaries: scattering induced tidal capture of circumbinary planets

NASA Astrophysics Data System (ADS)

Gong, Yan-Xiang; Ji, Jianghui

2018-05-01

Although several S-type and P-type planets in binary systems were discovered in past years, S-type planets have not yet been found in close binaries with an orbital separation not more than 5 au. Recent studies suggest that S-type planets in close binaries may be detected through high-accuracy observations. However, nowadays planet formation theories imply that it is difficult for S-type planets in close binaries systems to form in situ. In this work, we extensively perform numerical simulations to explore scenarios of planet-planet scattering among circumbinary planets and subsequent tidal capture in various binary configurations, to examine whether the mechanism can play a part in producing such kind of planets. Our results show that this mechanism is robust. The maximum capture probability is ˜10%, which can be comparable to the tidal capture probability of hot Jupiters in single star systems. The capture probability is related to binary configurations, where a smaller eccentricity or a low mass ratio of the binary will lead to a larger probability of capture, and vice versa. Furthermore, we find that S-type planets with retrograde orbits can be naturally produced via capture process. These planets on retrograde orbits can help us distinguish in situ formation and post-capture origin for S-type planet in close binaries systems. The forthcoming missions (PLATO) will provide the opportunity and feasibility to detect such planets. Our work provides several suggestions for selecting target binaries in search for S-type planets in the near future.

The onset of planet formation in brown dwarf disks.

PubMed

Apai, Dániel; Pascucci, Ilaria; Bouwman, Jeroen; Natta, Antonella; Henning, Thomas; Dullemond, Cornelis P

2005-11-04

The onset of planet formation in protoplanetary disks is marked by the growth and crystallization of sub-micrometer-sized dust grains accompanied by dust settling toward the disk mid-plane. Here, we present infrared spectra of disks around brown dwarfs and brown dwarf candidates. We show that all three processes occur in such cool disks in a way similar or identical to that in disks around low- and intermediate-mass stars. These results indicate that the onset of planet formation extends to disks around brown dwarfs, suggesting that planet formation is a robust process occurring in most young circumstellar disks.

The Longevity of Water Ice on Ganymedes and Europas around Migrated Giant Planets

NASA Astrophysics Data System (ADS)

Lehmer, Owen R.; Catling, David C.; Zahnle, Kevin J.

2017-04-01

The gas giant planets in the Solar System have a retinue of icy moons, and we expect giant exoplanets to have similar satellite systems. If a Jupiter-like planet were to migrate toward its parent star the icy moons orbiting it would evaporate, creating atmospheres and possible habitable surface oceans. Here, we examine how long the surface ice and possible oceans would last before being hydrodynamically lost to space. The hydrodynamic loss rate from the moons is determined, in large part, by the stellar flux available for absorption, which increases as the giant planet and icy moons migrate closer to the star. At some planet-star distance the stellar flux incident on the icy moons becomes so great that they enter a runaway greenhouse state. This runaway greenhouse state rapidly transfers all available surface water to the atmosphere as vapor, where it is easily lost from the small moons. However, for icy moons of Ganymede’s size around a Sun-like star we found that surface water (either ice or liquid) can persist indefinitely outside the runaway greenhouse orbital distance. In contrast, the surface water on smaller moons of Europa’s size will only persist on timescales greater than 1 Gyr at distances ranging 1.49-0.74 au around a Sun-like star for Bond albedos of 0.2 and 0.8, where the lower albedo becomes relevant if ice melts. Consequently, small moons can lose their icy shells, which would create a torus of H atoms around their host planet that might be detectable in future observations.

Scenarios of giant planet formation and evolution and their impact on the formation of habitable terrestrial planets.

PubMed

Morbidelli, Alessandro

2014-04-28

In our Solar System, there is a clear divide between the terrestrial and giant planets. These two categories of planets formed and evolved separately, almost in isolation from each other. This was possible because Jupiter avoided migrating into the inner Solar System, most probably due to the presence of Saturn, and never acquired a large-eccentricity orbit, even during the phase of orbital instability that the giant planets most likely experienced. Thus, the Earth formed on a time scale of several tens of millions of years, by collision of Moon- to Mars-mass planetary embryos, in a gas-free and volatile-depleted environment. We do not expect, however, that this clear cleavage between the giant and terrestrial planets is generic. In many extrasolar planetary systems discovered to date, the giant planets migrated into the vicinity of the parent star and/or acquired eccentric orbits. In this way, the evolution and destiny of the giant and terrestrial planets become intimately linked. This paper discusses several evolutionary patterns for the giant planets, with an emphasis on the consequences for the formation and survival of habitable terrestrial planets. The conclusion is that we should not expect Earth-like planets to be typical in terms of physical and orbital properties and accretion history. Most habitable worlds are probably different, exotic worlds.

The Planet Formation Imager (PFI) Project

NASA Astrophysics Data System (ADS)

Aarnio, Alicia; Monnier, John; Kraus, Stefan; Ireland, Michael

2016-07-01

Among the most fascinating and hotly-debated areas in contemporary astrophysics are the means by which planetary systems are assembled from the large rotating disks of gas and dust which attend a stellar birth. Although important work is being done both in theory and observation, a full understanding of the physics of planet formation can only be achieved by opening observational windows able to directly witness the process in action. The key requirement is then to probe planet-forming systems at the natural spatial scales over which material is being assembled. By definition, this is the so-called Hill Sphere, which delineates the region of influence of a gravitating body within its surrounding environment. The Planet Formation Imager project has crystallized around this challenging goal: to deliver resolved images of Hill-Sphere-sized structures within candidate planet-hosting disks in the nearest star-forming regions. In this contribution I outline the primary science case of PFI and give an overview about the work of the PFI science and technical working group and present radiation-hydrodynamics simulations from which we derive preliminary specifications that guide the design of the facility. Finally, I give an overview about the technologies that we are investigating in order to meet the specifications.

FORMATION OF CIRCUMBINARY PLANETS IN A DEAD ZONE

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

Martin, Rebecca G.; Armitage, Philip J.; Alexander, Richard D.

Circumbinary planets have been observed at orbital radii where binary perturbations may have significant effects on the gas disk structure, on planetesimal velocity dispersion, and on the coupling between turbulence and planetesimals. Here, we note that the impact of all of these effects on planet formation is qualitatively altered if the circumbinary disk structure is layered, with a non-turbulent midplane layer (dead zone) and strongly turbulent surface layers. For close binaries, we find that the dead zone typically extends from a radius close to the inner disk edge up to a radius of around 10-20 AU from the center ofmore » mass of the binary. The peak in the surface density occurs within the dead zone, far from the inner disk edge, close to the snow line, and may act as a trap for aerodynamically coupled solids. We suggest that circumbinary planet formation may be easier near this preferential location than for disks around single stars. However, dead zones around wide binaries are less likely, and hence planet formation may be more difficult there.« less

Formation of Circumbinary Planets in a Dead Zone

NASA Astrophysics Data System (ADS)

Martin, Rebecca G.; Armitage, Philip J.; Alexander, Richard D.

2013-08-01

Circumbinary planets have been observed at orbital radii where binary perturbations may have significant effects on the gas disk structure, on planetesimal velocity dispersion, and on the coupling between turbulence and planetesimals. Here, we note that the impact of all of these effects on planet formation is qualitatively altered if the circumbinary disk structure is layered, with a non-turbulent midplane layer (dead zone) and strongly turbulent surface layers. For close binaries, we find that the dead zone typically extends from a radius close to the inner disk edge up to a radius of around 10-20 AU from the center of mass of the binary. The peak in the surface density occurs within the dead zone, far from the inner disk edge, close to the snow line, and may act as a trap for aerodynamically coupled solids. We suggest that circumbinary planet formation may be easier near this preferential location than for disks around single stars. However, dead zones around wide binaries are less likely, and hence planet formation may be more difficult there.

Imaging Planet Formation Inside the Diffraction Limit

NASA Astrophysics Data System (ADS)

Sallum, Stephanie Elise

For decades, astronomers have used observations of mature planetary systems to constrain planet formation theories, beginning with our own solar system and now the thousands of known exoplanets. Recent advances in instrumentation have given us a direct view of some steps in the planet formation process, such as large-scale protostar and protoplanetary disk features and evolution. However, understanding the details of how planets accrete and interact with their environment requires direct observations of protoplanets themselves. Transition disks, protoplanetary disks with inner clearings that may be caused by forming planets, are the best targets for these studies. Their large distances, compared to the stars normally targeted for direct imaging of exoplanets, make protoplanet detection difficult and necessitate novel imaging techniques. In this dissertation, I describe the results of using non-redundant masking (NRM) to search for forming planets in transition disk clearings. I first present a data reduction pipeline that I wrote to this end, using example datasets and simulations to demonstrate reduction and imaging optimizations. I discuss two transition disk NRM case studies: T Cha and LkCa 15. In the case of T Cha, while we detect significant asymmetries, the data cannot be explained by orbiting companions. The fluxes and orbital motion of the LkCa 15 companion signals, however, can be naturally explained by protoplanets in the disk clearing. I use these datasets and simulated observations to illustrate the effects of scattered light from transition disk material on NRM protoplanet searches. I then demonstrate the utility of the dual-aperture Large Binocular Telescope Interferometer's NRM mode on the bright B[e] star MWC 349A. I discuss the implications of this work for planet formation studies as well as future prospects for NRM and related techniques on next generation instruments.

Accretion of Planetesimals and the Formation of Rocky Planets

NASA Astrophysics Data System (ADS)

Chambers, John E.; O'Brien, David P.; Davis, Andrew M.

2010-02-01

Here we describe the formation of rocky planets and asteroids in the context of the planetesimal hypothesis. Small dust grains in protoplanetary disks readily stick together forming mm-to-cm-sized aggregates, many of which experience brief heating episodes causing melting. Growth to km-sized planetesimals might proceed via continued pairwise sticking, turbulent concentration, or gravitational instability of a thin particle layer. Gravitational interactions between planetesimals lead to rapid runaway and oligarchic growth forming lunar-to-Mars-sized protoplanets in 10^5 to 10^6 years. Giant impacts between protoplanets form Earth-mass planets in 10^7 to 10^8 years, and occasionally lead to the formation of large satellites. Protoplanets may migrate far from their formation locations due to tidal interactions with the surrounding disk. Radioactive decay and impact heating cause melting and differentiation of planetesimals and protoplanets, forming iron-rich cores and silicate mantles, and leading to some loss of volatiles. Dynamical perturbations from giant planets eject most planetesimals and protoplanets from regions near orbital resonances, leading to asteroid-belt formation. Some of this scattered material will collide with growing terrestrial planets, altering their composition as a result. Numerical simulations and radioisotope dating indicate that the terrestrial planets of the Solar System were essentially fully formed in 100-200 million years.

The Terrestrial Planets Formation in the Solar-System Analogs

NASA Astrophysics Data System (ADS)

Ji, Jianghui; Liu, L.; Chambers, J. E.; Butler, R. P.

2006-09-01

In this work, we numerically studied the terrestrial planets formation in the Solar-Systems Analogs using MERCURY (Chambers 1999). The Solar-System Analogs are herein defined as a solar-system like planetary system, where the system consists of two wide-separated Jupiter-like planets (e.g., 47 UMa, Ji et al. 2005) move about the central star on nearly circular orbits with low inclinations, then low-mass terrestrial planets can be formed there, and life would be possibly evolved. We further explored the terrestrial planets formation due to the current uncertainties of the eccentricities for two giant planets. In addition, we place a great many of the planetesimals between two Jupiter-like planets to investigate the potential asteroidal structure in such systems. We showed that the secular resonances and mean motion resonances can play an important role in shaping the asteroidal structure. We acknowledge the financial support by National Natural Science Foundation of China (Grant No.10573040, 10233020, 10203005) and Foundation of Minor Planets of Purple Mountain Observatory.

The search for other planets: clues from the solar system.

PubMed

Owen, T

1994-01-01

Studies of element abundances and values of D/H in the atmospheres of the outer planets and Titan support a two-step model for the formation of these bodies. This model suggests that the dimensions of Uranus provide a good index for the sensitivity required to detect planets around other stars. The high proportion of N2 on the surfaces of Pluto and Triton indicates that this gas was the dominant reservoir of nitrogen in the early solar nebula. It should also be abundant on pristine comets. There is evidence that some of these comets may well have brought a large store of volatiles to the inner planets, while others were falling into the sun. In other systems, icy planetesimals falling into stars should reveal themselves through high values of D/H.

Forced-folding by laccolith and saucer-shaped sill intrusions on the Earth, planets and icy satellites

NASA Astrophysics Data System (ADS)

Michaut, Chloé

2017-04-01

Horizontal intrusions probably initially start as cracks, with negligible surface deformation. Once their horizontal extents become large enough compared to their depths, they make room for themselves by lifting up their overlying roofs, creating characteristic surface deformations that can be observed at the surface of planets. We present a model where magma flows below a thin elastic overlying layer characterized by a flexural wavelength Λ and study the dynamics and morphology of such a magmatic intrusion. Our results show that, depending on its size, the intrusion present different shapes and thickness-to-radius relationships. During a first phase, elastic bending of the overlying layer is the main source of driving pressure in the flow; the pressure decreases as the flow radius increases, the intrusion is bell-shaped and its thickness is close to being proportional to its radius. When the intrusion radius becomes larger than 4 times Λ, the flow enters a gravity current regime and progressively develops a pancake shape with a flat top. We study the effect of topography on flow spreading in particular in the case where the flow is constrained by a lithostatic barrier within a depression, such as an impact crater on planets or a caldera on Earth. We show that the resulting shape for the flow depends on the ratio between the flexural wavelength of the layer overlying the intrusion and the depression radius. The model is tested against terrestrial data and is shown to well explain the size and morphology of laccoliths and saucer-shaped sills on Earth. We use our results to detect and characterize shallow solidified magma reservoirs in the crust of terrestrial planets and potential shallow water reservoirs in the ice shell of icy satellites.

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.

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?

Post-main-sequence Evolution of Icy Minor Planets. II. Water Retention and White Dwarf Pollution around Massive Progenitor Stars

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

Malamud, Uri; Perets, Hagai B., E-mail: uri.mal@tx.technion.ac.il, E-mail: hperets@physics.technion.ac.il

Most studies suggest that the pollution of white dwarf (WD) atmospheres arises from the accretion of minor planets, but the exact properties of polluting material, and in particular the evidence for water in some cases, are not yet understood. Here we study the water retention of small icy bodies in exo-solar planetary systems, as their respective host stars evolve through and off the main sequence and eventually become WDs. We explore, for the first time, a wide range of star masses and metallicities. We find that the mass of the WD progenitor star is of crucial importance for the retentionmore » of water, while its metallicity is relatively unimportant. We predict that minor planets around lower-mass WD progenitors would generally retain more water and would do so at closer distances from the WD than compared with high-mass progenitors. The dependence of water retention on progenitor mass and other parameters has direct implications for the origin of observed WD pollution, and we discuss how our results and predictions might be tested in the future as more observations of WDs with long cooling ages become available.« less

Star and Planet Formation through Cosmic Time

NASA Astrophysics Data System (ADS)

Lee, Aaron Thomas

The computational advances of the past several decades have allowed theoretical astrophysics to proceed at a dramatic pace. Numerical simulations can now simulate the formation of individual molecules all the way up to the evolution of the entire universe. Observational astrophysics is producing data at a prodigious rate, and sophisticated analysis techniques of large data sets continue to be developed. It is now possible for terabytes of data to be effectively turned into stunning astrophysical results. This is especially true for the field of star and planet formation. Theorists are now simulating the formation of individual planets and stars, and observing facilities are finally capturing snapshots of these processes within the Milky Way galaxy and other galaxies. While a coherent theory remains incomplete, great strides have been made toward this goal. This dissertation discusses several projects that develop models of star and planet forma- tion. This work spans large spatial and temporal scales: from the AU-scale of protoplanetary disks all the way up to the parsec-scale of star-forming clouds, and taking place in both contemporary environments like the Milky Way galaxy and primordial environments at redshifts of z 20. Particularly, I show that planet formation need not proceed in incremental stages, where planets grow from millimeter-sized dust grains all the way up to planets, but instead can proceed directly from small dust grains to large kilometer-sized boulders. The requirements for this model to operate effectively are supported by observations. Additionally, I draw suspicion toward one model for how you form high mass stars (stars with masses exceeding 8 Msun), which postulates that high-mass stars are built up from the gradual accretion of mass from the cloud onto low-mass stars. I show that magnetic fields in star forming clouds thwart this transfer of mass, and instead it is likely that high mass stars are created from the gravitational collapse of

Direct imaging search for the "missing link" in giant planet formation

NASA Astrophysics Data System (ADS)

Ngo, Henry; Mawet, Dimitri; Ruane, Garreth; Xuan, Wenhao; Bowler, Brendan; Cook, Therese; Zawol, Zoe

2018-01-01

While transit and radial velocity detection techniques have probed giant planet populations at close separations (within a few au), current direct imaging surveys are finding giant planets at separations of 10s-100s au. Furthermore, these directly imaged planets are very massive, including some with masses above the deuterium burning limit. It is not certain whether these objects represent the high mass end of planet formation scenarios or the low mass end of star formation. We present a direct imaging survey to search for the "missing link" population between the close-in RV and transiting giant planets and the extremely distant directly imaged giant planets (i.e. giant planets between 5-10 au). Finding and characterizing this population allows for comparisons with the formation models of closer-in planets and connects directly imaged planets with closer-in planets in semi-major axis phase space. In addition, microlensing surveys have suggested a large reservoir of giant planets exist in this region. To find these "missing link" giant planets, our survey searches for giant planets around M-stars. The ubiquity of M-stars provide a large number of nearby targets and their L-band contrast with planets allow for sensitivities to smaller planet masses than surveys conducted at shorter wavelengths. Along with careful target selection, we use Keck's L-band vector vortex coronagraph to enable sensitivities of a few Jupiter masses as close as 4 au to their host stars. We present our completed 2-year survey targeting 200 young (10-150 Myr), nearby M-stars and our ongoing work to follow-up over 40 candidate objects.

The formation of giant planets in wide orbits by photoevaporation-synchronized migration

NASA Astrophysics Data System (ADS)

Guilera, O. M.; Miller Bertolami, M. M.; Ronco, M. P.

2017-10-01

The discovery of giant planets in wide orbits represents a major challenge for planet formation theory. In the standard core accretion paradigm, planets are expected to form at radial distances ≲20 au in order to form massive cores (with masses ≳10 M⊕) able to trigger the gaseous runaway growth before the dissipation of the disc. This has encouraged authors to find modifications of the standard scenario as well as alternative theories like the formation of planets by gravitational instabilities in the disc to explain the existence of giant planets in wide orbits. However, there is not yet consensus on how these systems are formed. In this Letter, we present a new natural mechanism for the formation of giant planets in wide orbits within the core accretion paradigm. If photoevaporation is considered, after a few Myr of viscous evolution a gap in the gaseous disc is opened. We found that, under particular circumstances planet migration becomes synchronized with the evolution of the gap, which results in an efficient outward planet migration. This mechanism is found to allow the formation of giant planets with masses Mp ≲ 1MJup in wide stable orbits as large as ∼130 au from the central star.

A Preliminary Analysis of College Students’ Preinstructional Ideas About Planet Formation

NASA Astrophysics Data System (ADS)

Simon, Molly; Impey, Chris David; Buxner, Sanlyn

2017-01-01

From as early as nursery school, children are taught about planet Earth and “our place in space.” Learning about the Solar System transcends K-12 education, and is considered one of the top-ten most frequently discussed topics in undergraduate introductory astronomy courses for non-majors. All too frequently, however, the discussion stops after a brief overview of each planet, and students are left to ponder how the Solar System came to be in the first place. The topic of planet formation has grown in importance in any astronomy class in light of the discovery of nearly 5,000 exoplanet candidates, where the properties of exoplanetary systems have cast light on the general process of planet formation. This highly active research field has been slow to be properly represented in the astronomy classroom for non-majors. For this work, we presented students in six undergraduate 100 and 200-level astronomy courses at the University of Arizona with one of three short answer questions on the topic of planet formation. The questions were administered on the first day of the Fall 2016 semester before any related material was taught. We will present an analysis of these responses, and discuss any common trends, themes, and misconceptions that appear from the dataset. These responses will lend to the development of the Planet Formation Concept Inventory (PFCI) that will be used by ASTR 101 instructors to evaluate students’ understanding of planet formation before and after instruction.

Influence of Stellar Multiplicity On Planet Formation. III. Adaptive Optics Imaging of Kepler Stars With Gas Giant Planets

NASA Astrophysics Data System (ADS)

Wang, Ji; Fischer, Debra A.; Horch, Elliott P.; Xie, Ji-Wei

2015-06-01

As hundreds of gas giant planets have been discovered, we study how these planets form and evolve in different stellar environments, specifically in multiple stellar systems. In such systems, stellar companions may have a profound influence on gas giant planet formation and evolution via several dynamical effects such as truncation and perturbation. We select 84 Kepler Objects of Interest (KOIs) with gas giant planet candidates. We obtain high-angular resolution images using telescopes with adaptive optics (AO) systems. Together with the AO data, we use archival radial velocity data and dynamical analysis to constrain the presence of stellar companions. We detect 59 stellar companions around 40 KOIs for which we develop methods of testing their physical association. These methods are based on color information and galactic stellar population statistics. We find evidence of suppressive planet formation within 20 AU by comparing stellar multiplicity. The stellar multiplicity rate (MR) for planet host stars is {0}-0+5% within 20 AU. In comparison, the stellar MR is 18% ± 2% for the control sample, i.e., field stars in the solar neighborhood. The stellar MR for planet host stars is 34% ± 8% for separations between 20 and 200 AU, which is higher than the control sample at 12% ± 2%. Beyond 200 AU, stellar MRs are comparable between planet host stars and the control sample. We discuss the implications of the results on gas giant planet formation and evolution.

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.

Reduction of post injury neointima formation due to 17β-estradiol and phytoestrogen treatment is not influenced by the pure synthetic estrogen receptor antagonist ICI 182,780 in vitro

PubMed Central

Finking, Gerald; Lenz, Christina; Schochat, Thomas; Hanke, Hartmut

2002-01-01

Background Animal and organ culture experiments have shown beneficial inhibitory estrogen effects on post injury neointima development. The purpose of this study was to investigate whether such estrogen effects are influenced by the estrogen receptor antagonist ICI 182,780. Different concentrations of 17β-estradiol and the phytoestrogens genistein and daidzein were tested. Methods F emale New Zealand White rabbits were benumbed. In situ vascular injury of the thoracic and abdominal aorta was performed by a 3F Fogarty catheter. Segments of 5 mm were randomised and held in culture for 21 days. Three test series were performed: 1) control group – 20 μM ICI – 30 μM ICI – 40 μM ICI. 2) control group – 20 μM ICI – 40 μM 17β-estradiol – 40 μM 17β-estradiol + 20 μM ICI. 3) control group – 20 μM ICI – 40 μM daidzein – 40 μM daidzein + 20 μM ICI – 20 μM genistein – 20 μM genistein + 20 μM ICI. After 21 days the neointima-media-ratio was evaluated. Results 1) Treatment with ICI 182,780 did not reduce neointima formation significantly (p = 0.05). 2) 40 μM 17β-estradiol alone (p < 0.0001) and in combination with 20 μM ICI (p < 0.0001) reduced neointima formation significantly. 3) 20 μM genistein alone (p = 0.0083) and combined with 20 μM ICI (p = 0.0053) reduced neointima formation significantly. 40 μM daidzein did not have a significant (p = 0.0637) effect. Conclusions The estrogen receptor antagonist ICI 182,780 did not modulate the inhibitory estrogen effects on post injury neointima formation. These results do not support the idea that such effects are mediated by vascular estrogen receptors. PMID:12162794

The Maximum Mass Solar Nebula and the early formation of planets

NASA Astrophysics Data System (ADS)

Nixon, C. J.; King, A. R.; Pringle, J. E.

2018-03-01

Current planet formation theories provide successful frameworks with which to interpret the array of new observational data in this field. However, each of the two main theories (core accretion, gravitational instability) is unable to explain some key aspects. In many planet formation calculations, it is usual to treat the initial properties of the planet forming disc (mass, radius, etc.) as free parameters. In this paper, we stress the importance of setting the formation of planet forming discs within the context of the formation of the central stars. By exploring the early stages of disc formation, we introduce the concept of the Maximum Mass Solar Nebula (MMSN), as opposed to the oft-used Minimum Mass Solar Nebula (here mmsn). It is evident that almost all protoplanetary discs start their evolution in a strongly self-gravitating state. In agreement with almost all previous work in this area, we conclude that on the scales relevant to planet formation these discs are not gravitationally unstable to gas fragmentation, but instead form strong, transient spiral arms. These spiral arms can act as efficient dust traps allowing the accumulation and subsequent fragmentation of the dust (but not the gas). This phase is likely to populate the disc with relatively large planetesimals on short timescales while the disc is still veiled by a dusty-gas envelope. Crucially, the early formation of large planetesimals overcomes the main barriers remaining within the core accretion model. A prediction of this picture is that essentially all observable protoplanetary discs are already planet hosting.

The Maximum Mass Solar Nebula and the early formation of planets

NASA Astrophysics Data System (ADS)

Nixon, C. J.; King, A. R.; Pringle, J. E.

2018-07-01

Current planet formation theories provide successful frameworks with which to interpret the array of new observational data in this field. However, each of the two main theories (core accretion, gravitational instability) is unable to explain some key aspects. In many planet formation calculations, it is usual to treat the initial properties of the planet-forming disc (mass, radius, etc.) as free parameters. In this paper, we stress the importance of setting the formation of planet-forming discs within the context of the formation of the central stars. By exploring the early stages of disc formation, we introduce the concept of the Maximum Mass Solar Nebula, as opposed to the oft-used minimum mass solar nebula. It is evident that almost all protoplanetary discs start their evolution in a strongly self-gravitating state. In agreement with almost all previous work in this area, we conclude that on the scales relevant to planet formation these discs are not gravitationally unstable to gas fragmentation, but instead form strong, transient spiral arms. These spiral arms can act as efficient dust traps allowing the accumulation and subsequent fragmentation of the dust (but not the gas). This phase is likely to populate the disc with relatively large planetesimals on short time-scales while the disc is still veiled by a dusty-gas envelope. Crucially, the early formation of large planetesimals overcomes the main barriers remaining within the core accretion model. A prediction of this picture is that essentially all observable protoplanetary discs are already planet hosting.

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.

The Longevity of Water Ice on Ganymedes and Europas around Migrated Giant Planets

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

Lehmer, Owen R.; Catling, David C.; Zahnle, Kevin J., E-mail: olehmer@gmail.com

The gas giant planets in the Solar System have a retinue of icy moons, and we expect giant exoplanets to have similar satellite systems. If a Jupiter-like planet were to migrate toward its parent star the icy moons orbiting it would evaporate, creating atmospheres and possible habitable surface oceans. Here, we examine how long the surface ice and possible oceans would last before being hydrodynamically lost to space. The hydrodynamic loss rate from the moons is determined, in large part, by the stellar flux available for absorption, which increases as the giant planet and icy moons migrate closer to themore » star. At some planet–star distance the stellar flux incident on the icy moons becomes so great that they enter a runaway greenhouse state. This runaway greenhouse state rapidly transfers all available surface water to the atmosphere as vapor, where it is easily lost from the small moons. However, for icy moons of Ganymede’s size around a Sun-like star we found that surface water (either ice or liquid) can persist indefinitely outside the runaway greenhouse orbital distance. In contrast, the surface water on smaller moons of Europa’s size will only persist on timescales greater than 1 Gyr at distances ranging 1.49–0.74 au around a Sun-like star for Bond albedos of 0.2 and 0.8, where the lower albedo becomes relevant if ice melts. Consequently, small moons can lose their icy shells, which would create a torus of H atoms around their host planet that might be detectable in future observations.« less

Birth of an Earth-like Planet (Artist concept)

NASA Technical Reports Server (NTRS)

2007-01-01

This artist's conception shows a binary-star, or two-star, system, called HD 113766, where astronomers suspect a rocky Earth-like planet is forming around one of the stars. At approximately 10 to 16 million years old, astronomers suspect this star is at just the right age for forming rocky planets. The system is located approximately 424 light-years away from Earth.

The two yellow spots in the image represent the system's two stars. The brown ring of material circling closest to the central star depicts a huge belt of dusty material, more than 100 times as much as in our asteroid belt, or enough to build a Mars-size planet or larger. The rocky material in the belt represents the early stages of planet formation, when dust grains clump together to form rocks, and rocks collide to form even more massive rocky bodies called planetesimals. The belt is located in the middle of the system's terrestrial habitable zone, or the region around a star where liquid water could exist on any rocky planets that might form. Earth is located in the middle of our sun's terrestrial habitable zone.

Using NASA's Spitzer Space Telescope, astronomers learned that the belt material in HD 113866 is more processed than the snowball-like stuff that makes up infant solar systems and comets, which contain pristine ingredients from the early solar system. However, it is not as processed as the stuff found in mature planets and asteroids. This means that the dust belt is made out of just the right mix of materials to be forming an Earth-like planet. It is composed mainly of rocky silicates and metal sulfides (like fool's gold), similar to the material found in lava flows.

The white outer ring shows a concentration of icy dust also detected in the system. This material is at the equivalent position of the asteroid belt in our solar system, but only contains about one-sixth as much material as the inner ring. Astronomers say it is not clear from the Spitzer observations if

Sizing up the planets

NASA Technical Reports Server (NTRS)

Meszaros, S. P.

1985-01-01

Visual, scaled comparisons are made among prominent volcanic, tectonic, crater and impact basin features photographed on various planets and moons in the solar system. The volcanic formation Olympus Mons, on Mars, is 27 km tall, while Io volcanic plumes reach 200-300 km altitude. Valles Marineris, a tectonic fault on Mars, is several thousand kilometers long, and the Ithasa Chasma on the Saturnian moon Tethys extends two-thirds the circumference of the moon. Craters on the Saturnian moons Tethys and Mimas are large enough to suggest a collision by objects which almost shattered the planetoids. Large meteorite impacts may leave large impact basins or merely ripples, such as found on Callisto, whose icy surface could not support high mountains formed by giant body impacts.

Planetary Analogs in Antarctica: Icy Satellites

NASA Technical Reports Server (NTRS)

Malin, M. C.

1985-01-01

As part of a study to provide semi-quantitative techniques to date past Antarctic glaciations, sponsored by the Antarctic Research Program, field observations pertinent to other planets were also acquired. The extremely diverse surface conditions, marked by extreme cold and large amounts of ice, provide potential terrain and process analogs to the icy satellites of Jupiter and Saturn. Thin ice tectonic features and explosion craters (on sea ice) and deformation features on thicker ice (glaciers) are specifically addressed.

INSIDE-OUT PLANET FORMATION. III. PLANET–DISK INTERACTION AT THE DEAD ZONE INNER BOUNDARY

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

Hu, Xiao; Tan, Jonathan C.; Chatterjee, Sourav

The Kepler mission has discovered more than 4000 exoplanet candidates. Many of them are in systems with tightly packed inner planets. Inside-out planet formation (IOPF) has been proposed as a scenario to explain these systems. It involves sequential in situ planet formation at the local pressure maximum of a retreating dead zone inner boundary (DZIB). Pebbles accumulate at this pressure trap, which builds up a pebble ring and then a planet. The planet is expected to grow in mass until it opens a gap, which helps to both truncate pebble accretion and also induce DZIB retreat that sets the location ofmore » formation of the next planet. This simple scenario may be modified if the planet undergoes significant migration from its formation location. Thus, planet–disk interactions play a crucial role in the IOPF scenario. Here we present numerical simulations that first assess the degree of migration for planets of various masses that are forming at the DZIB of an active accretion disk, where the effective viscosity is undergoing a rapid increase in the radially inward direction. We find that torques exerted on the planet by the disk tend to trap the planet at a location very close to the initial pressure maximum where it formed. We then study gap opening by these planets to assess at what mass a significant gap is created. Finally, we present a simple model for DZIB retreat due to penetration of X-rays from the star to the disk midplane. Overall, these simulations help to quantify both the mass scale of first (“Vulcan”) planet formation and the orbital separation to the location of second planet formation.« less

Sequential planet formation in transition disks: The case of HD 100546

NASA Astrophysics Data System (ADS)

Pinilla, Paola; Birnsitel, Til; Walsh, Catherine; van Dishoeck, Ewine

2015-08-01

Transition disks are circumstellar disks with dust inner cavities and may reveal an intermediate step of the ongoing disk dispersal process, where planet formation might happen. The recent gas and dust observations of transition disks have given major support to the presence of massive planets in transition disks. The analysis of such observations help to constrain the properties of the potential unseen planets. An excellent candidate to analyse the dust evolution when planets are embedded in disks is the transition disk around the Herbig Ae star HD 100546. Near-infrared observations of HD 100546 suggested the presence on an inner planet at 10 AU distance from the star (e.g. Mulders et al. 2013), while an outer planet has been directly imaged at 70 AU distance, which may be in the act of formation (Quant et al. 2013, 2015; Currie et al. 2014). The two embedded planets can lead to remarkable dust structures due to the particle trapping at the edges of the gaps caved by such planets (e.g. Pinilla et al. 2012, 2015). Recent ALMA Cycle 0 observations of this disk reveal a two-ring like structure consistent with particle trapping induced by the two companions (Walsh et al. 2014). The comparison of these observations with dust evolution models, that include the coagulation and fragmentation of dust grains, suggest that the outer companion must be at least two million of years younger than the inner companion, revealing sequential planet formation in this disk (Pinilla et al. 2015, under revision).

Star & Planet Formation Studies and Opportunities with SOFIA

NASA Technical Reports Server (NTRS)

Smith, Kimberly Ennico

2018-01-01

Star formation, the most fundamental process in the universe, is linked to planet formation and thus to the origin and evolution of life. We have a general outline of how planets and stars form, yet unraveling the details of the physics and chemistry continues to challenge us. The infrared and submillimeter part of the spectrum hold the most promise for studying the beginnings of star formation. The observational landscape recently shaped by Spitzer, Herschel and ALMA, continues to challenge our current theories. SOFIA, the Stratospheric Observatory for Infrared Astronomy, equipped with state-of-the-art infrared instrumentation to a vantage point at 45,000 feet (13.7 kilometers) flight altitude that is above 99.9 percent of the Earth's water vapor, enables observations in the infrared through terahertz frequencies not possible from the ground. SOFIA is a community observatory, about to start its sixth annual observing cycle. My talk will focus on recent results in advancing star and planet formation processes using SOFIA's imaging and polarimetric capabilities, and the upcoming science enabled by the 3rd generation instrument High-Resolution Mid-Infrared Spectrometer (HIRMES) to be commissioned in 2019. I will show how mid-infrared imaging is used to test massive star formation theories, how far-infrared polarimetry on sub-parsec scales is directly testing the role of magnetic fields in molecular clouds, and how velocity-resolved high-resolution spectroscopy will push forward our understanding of proto-planetary disk science. I will also summarize upcoming opportunities with the SOFIA observatory. For the latest news about your flying observatory, see https://sofia.usra.edu/.

A CONTINUUM OF PLANET FORMATION BETWEEN 1 AND 4 EARTH RADII

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

Schlaufman, Kevin C., E-mail: kschlauf@mit.edu

2015-02-01

It has long been known that stars with high metallicity are more likely to host giant planets than stars with low metallicity. Yet the connection between host star metallicity and the properties of small planets is only just beginning to be investigated. It has recently been argued that the metallicity distribution of stars with exoplanet candidates identified by Kepler provides evidence for three distinct clusters of exoplanets, distinguished by planet radius boundaries at 1.7 R{sub ⨁} and 3.9 R{sub ⨁}. This would suggest that there are three distinct planet formation pathways for super-Earths, mini-Neptunes, and giant planets. However, as Imore » show through three independent analyses, there is actually no evidence for the proposed radius boundary at 1.7 R{sub ⨁}. On the other hand, a more rigorous calculation demonstrates that a single, continuous relationship between planet radius and metallicity is a better fit to the data. The planet radius and metallicity data therefore provides no evidence for distinct categories of small planets. This suggests that the planet formation process in a typical protoplanetary disk produces a continuum of planet sizes between 1 R{sub ⨁} and 4 R{sub ⨁}. As a result, the currently available planet radius and metallicity data for solar-metallicity F and G stars give no reason to expect that the amount of solid material in a protoplanetary disk determines whether super-Earths or mini-Neptunes are formed.« less

Developing New Pedagogy to Teach Planet Formation to Undergraduate Non-Science Majors

NASA Astrophysics Data System (ADS)

Simon, Molly; Impey, Chris David; Buxner, Sanlyn

2016-06-01

A first order understanding of planet formation and the scientific concepts therein is critical in order for undergraduate students to understand our place in the Universe. Furthermore, planet formation integrates the topics of gravity, angular momentum, migration, and condensation in a “story-book” fashion where students can apply these concepts to a specific event. We collected syllabi and course topics from over 30 undergraduate general-education astrobiology courses from around the globe in order to determine the extent to which professors address planet formation. Additionally, we were looking to see if faculty had developed specific or original pedagogy to teach this topic. We find on average, instructors spend ½ of a lecture discussing planet formation or they leave it out all together. In the classes where planet formation is taught more extensively, instructors use PowerPoint slides or occasional videos to teach the topic. We aim to develop new pedagogy that will allow us to better determine learning gains and student understanding of this critical topic. If students in an astrobiology class are unable to understand how our own Solar System forms, it is significantly more challenging to make parallels (or find differences) between our home in the Universe and extrasolar planetary systems.

X-MIME: An Imaging X-ray Spectrometer for Detailed Study of Jupiter's Icy Moons and the Planet's X-ray Aurora

NASA Technical Reports Server (NTRS)

Elsner, R. F.; Ramsey, B. D.; Waite, J. H.; Rehak, P.; Johnson, R. E.; Cooper, J. F.; Swartz, D. A.

2004-01-01

Remote observations with the Chandra X-ray Observatory and the XMM-Newton Observatory have shown that the Jovian system is a source of x-rays with a rich and complicated structure. The planet's polar auroral zones and its disk are powerful sources of x-ray emission. Chandra observations revealed x-ray emission from the Io Plasma Torus and from the Galilean moons Io, Europa, and possibly Ganymede. The emission from these moons is certainly due to bombardment of their surfaces of highly energetic protons, oxygen and sulfur ions from the region near the Torus exciting atoms in their surfaces and leading to fluorescent x-ray emission lines. Although the x-ray emission from the Galilean moons is faint when observed from Earth orbit, an imaging x-ray spectrometer in orbit around these moons, operating at 200 eV and above with 150 eV energy resolution, would provide a detailed mapping (down to 40 m spatial resolution) of the elemental composition in their surfaces. Such maps would provide important constraints on formation and evolution scenarios for the surfaces of these moons. Here we describe the characteristics of X-MIME, an imaging x-ray spectrometer under going a feasibility study for the JIMO mission, with the ultimate goal of providing unprecedented x-ray studies of the elemental composition of the surfaces of Jupiter's icy moons and Io, as well as of Jupiter's auroral x-ray emission.

Planet Formation by Coagulation: A Focus on Uranus and Neptune

NASA Astrophysics Data System (ADS)

Goldreich, Peter; Lithwick, Yoram; Sari, Re'em

2004-09-01

Planets form in the circumstellar disks of young stars. We review the basic physical processes by which solid bodies accrete each other and alter each others' random velocities, and we provide order-of-magnitude derivations for the rates of these processes. We discuss and exercise the two-groups approximation, a simple yet powerful technique for solving the evolution equations for protoplanet growth. We describe orderly, runaway, neutral, and oligarchic growth. We also delineate the conditions under which each occurs. We refute a popular misconception by showing that the outer planets formed quickly by accreting small bodies. Then we address the final stages of planet formation. Oligarchy ends when the surface density of the oligarchs becomes comparable to that of the small bodies. Dynamical friction is no longer able to balance viscous stirring and the oligarchs' random velocities increase. In the inner-planet system, oligarchs collide and coalesce. In the outer-planet system, some of the oligarchs are ejected. In both the inner- and outer-planet systems, this stage ends once the number of big bodies has been reduced to the point that their mutual interactions no longer produce large-scale chaos. Subsequently, dynamical friction by the residual small bodies circularizes and flattens their orbits. The final stage of planet formation involves the clean up of the residual small bodies. Clean up has been poorly explored.

New Directions in Giant Planet Formation

NASA Astrophysics Data System (ADS)

Youdin, Andrew

The proposed research will explore the limits of the core accretion mechanism for forming giant planets, both in terms of timescale and orbital distance. This theoretical research will be useful in interpreting the results of ongoing exoplanet searches. The effects of radiogenic heating and aerodynamic accretion of pebbles and boulders will be included in time-dependent models of atmospheric structure and growth. To investigate these issues, we will develop and publicly share a protoplanet atmospheric evolution code as an extension of the MESA stellar evolution code. By focusing on relevant processes in the early stages of giant planet formation, we can refine model predictions for exoplanet searches at a wide range of stellar ages and distances from the host star.

MISCIBILITY CALCULATIONS FOR WATER AND HYDROGEN IN GIANT PLANETS

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

Soubiran, François; Militzer, Burkhard

2015-06-20

We present results from ab initio simulations of liquid water–hydrogen mixtures in the range from 2 to 70 GPa and from 1000 to 6000 K, covering conditions in the interiors of ice giant planets and parts of the outer envelope of gas giant planets. In addition to computing the pressure and the internal energy, we derive the Gibbs free energy by performing a thermodynamic integration. For all conditions under consideration, our simulations predict hydrogen and water to mix in all proportions. The thermodynamic behavior of the mixture can be well described with an ideal mixing approximation. We suggest that amore » substantial fraction of water and hydrogen in giant planets may occur in homogeneously mixed form rather than in separate layers. The extent of mixing depends on the planet’s interior dynamics and its conditions of formation, in particular on how much hydrogen was present when icy planetesimals were delivered. Based on our results, we do not predict water–hydrogen mixtures to phase separate during any stage of the evolution of giant planets. We also show that the hydrogen content of an exoplanet is much higher if the mixed interior is assumed.« less

X-ray insights into star and planet formation

PubMed Central

Feigelson, Eric D.

2010-01-01

Although stars and planets form in cold environments, X-rays are produced in abundance by young stars. This review examines the implications of stellar X-rays for star and planet formation studies, highlighting the contributions of NASA’s (National Aeronautics and Space Administration) Chandra X-ray Observatory. Seven topics are covered: X-rays from protostellar outflow shocks, X-rays from the youngest protostars, the stellar initial mass function, the structure of young stellar clusters, the fate of massive stellar winds, X-ray irradiation of protoplanetary disks, and X-ray flare effects on ancient meteorites. Chandra observations of star-forming regions often show dramatic star clusters, powerful magnetic reconnection flares, and parsec-scale diffuse plasma. X-ray selected samples of premain sequence stars significantly advance studies of star cluster formation, the stellar initial mass function, triggered star-formation processes, and protoplanetary disk evolution. Although X-rays themselves may not play a critical role in the physics of star formation, they likely have important effects on protoplanetary disks by heating and ionizing disk gases. PMID:20404197

X-ray insights into star and planet formation.

PubMed

Feigelson, Eric D

2010-04-20

Although stars and planets form in cold environments, X-rays are produced in abundance by young stars. This review examines the implications of stellar X-rays for star and planet formation studies, highlighting the contributions of NASA's (National Aeronautics and Space Administration) Chandra X-ray Observatory. Seven topics are covered: X-rays from protostellar outflow shocks, X-rays from the youngest protostars, the stellar initial mass function, the structure of young stellar clusters, the fate of massive stellar winds, X-ray irradiation of protoplanetary disks, and X-ray flare effects on ancient meteorites. Chandra observations of star-forming regions often show dramatic star clusters, powerful magnetic reconnection flares, and parsec-scale diffuse plasma. X-ray selected samples of premain sequence stars significantly advance studies of star cluster formation, the stellar initial mass function, triggered star-formation processes, and protoplanetary disk evolution. Although X-rays themselves may not play a critical role in the physics of star formation, they likely have important effects on protoplanetary disks by heating and ionizing disk gases.

Influence of stellar multiplicity on planet formation. II. Planets are less common in multiple-star systems with separations smaller than 1500 AU

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

Wang, Ji; Fischer, Debra A.; Xie, Ji-Wei

2014-08-20

Almost half of the stellar systems in the solar neighborhood are made up of multiple stars. In multiple-star systems, planet formation is under the dynamical influence of stellar companions, and the planet occurrence rate is expected to be different from that of single stars. There have been numerous studies on the planet occurrence rate of single star systems. However, to fully understand planet formation, the planet occurrence rate in multiple-star systems needs to be addressed. In this work, we infer the planet occurrence rate in multiple-star systems by measuring the stellar multiplicity rate for planet host stars. For a subsamplemore » of 56 Kepler planet host stars, we use adaptive optics (AO) imaging and the radial velocity (RV) technique to search for stellar companions. The combination of these two techniques results in high search completeness for stellar companions. We detect 59 visual stellar companions to 25 planet host stars with AO data. Three stellar companions are within 2'' and 27 within 6''. We also detect two possible stellar companions (KOI 5 and KOI 69) showing long-term RV acceleration. After correcting for a bias against planet detection in multiple-star systems due to flux contamination, we find that planet formation is suppressed in multiple-star systems with separations smaller than 1500 AU. Specifically, we find that compared to single star systems, planets in multiple-star systems occur 4.5 ± 3.2, 2.6 ± 1.0, and 1.7 ± 0.5 times less frequently when a stellar companion is present at a distance of 10, 100, and 1000 AU, respectively. This conclusion applies only to circumstellar planets; the planet occurrence rate for circumbinary planets requires further investigation.« less

Tc Trends and Terrestrial Planet Formation: The Case of Zeta Reticuli

NASA Astrophysics Data System (ADS)

Adibekyan, Vardan; Delgado-Mena, Elisa; Figueira, Pedro; Sousa, Sergio; Santos, Nuno; Faria, Joao; González Hernández, Jonay; Israelian, Garik; Harutyunyan, Gohar; Suárez-Andrés, Lucia; Hakobyan, Artur

2016-11-01

During the last decade astronomers have been trying to search for chemical signatures of terrestrial planet formation in the atmospheres of the hosting stars. Several studies suggested that the chemical abundance trend with the condensation temperature, Tc, is a signature of rocky planet formation. In particular, it was suggested that the Sun shows 'peculiar' chemical abundances due to the presence of the terrestrial planets in our solar-system. However, the rocky material accretion or the trap of rocky materials in terrestrial planets is not the only explanation for the chemical 'peculiarity' of the Sun, or other Sun-like stars with planets. In this talk I madea very brief review of this topic, and presented our last results for the particular case of Zeta Reticuli binary system: A very interesting and well-known system (known in science fiction and ufology as the world of Grey Aliens, or Reticulans) where one of the components hosts an exo-Kuiper belt, and the other component is a 'single', 'lonely' star.

Planet-driven Spiral Arms in Protoplanetary Disks. I. Formation Mechanism

NASA Astrophysics Data System (ADS)

Bae, Jaehan; Zhu, Zhaohuan

2018-06-01

Protoplanetary disk simulations show that a single planet can excite more than one spiral arm, possibly explaining the recent observations of multiple spiral arms in some systems. In this paper, we explain the mechanism by which a planet excites multiple spiral arms in a protoplanetary disk. Contrary to previous speculations, the formation of both primary and additional arms can be understood as a linear process when the planet mass is sufficiently small. A planet resonantly interacts with epicyclic oscillations in the disk, launching spiral wave modes around the Lindblad resonances. When a set of wave modes is in phase, they can constructively interfere with each other and create a spiral arm. More than one spiral arm can form because such constructive interference can occur for different sets of wave modes, with the exact number and launching position of the spiral arms being dependent on the planet mass as well as the disk temperature profile. Nonlinear effects become increasingly important as the planet mass increases, resulting in spiral arms with stronger shocks and thus larger pitch angles. This is found to be common for both primary and additional arms. When a planet has a sufficiently large mass (≳3 thermal masses for (h/r) p = 0.1), only two spiral arms form interior to its orbit. The wave modes that would form a tertiary arm for smaller mass planets merge with the primary arm. Improvements in our understanding of the formation of spiral arms can provide crucial insights into the origin of observed spiral arms in protoplanetary disks.

Carbon-rich Giant Planets: Atmospheric Chemistry, Thermal Inversions, Spectra, and Formation Conditions

NASA Astrophysics Data System (ADS)

Madhusudhan, Nikku; Mousis, Olivier; Johnson, Torrence V.; Lunine, Jonathan I.

2011-12-01

The recent inference of a carbon-rich atmosphere, with C/O >= 1, in the hot Jupiter WASP-12b motivates the exotic new class of carbon-rich planets (CRPs). We report a detailed study of the atmospheric chemistry and spectroscopic signatures of carbon-rich giant (CRG) planets, the possibility of thermal inversions in their atmospheres, the compositions of icy planetesimals required for their formation via core accretion, and the apportionment of ices, rock, and volatiles in their envelopes. Our results show that CRG atmospheres probe a unique region in composition space, especially at high temperature (T). For atmospheres with C/O >= 1, and T >~ 1400 K in the observable atmosphere, most of the oxygen is bound up in CO, while H2O is depleted and CH4 is enhanced by up to two or three orders of magnitude each, compared to equilibrium compositions with solar abundances (C/O = 0.54). These differences in the spectroscopically dominant species for the different C/O ratios cause equally distinct observable signatures in the spectra. As such, highly irradiated transiting giant exoplanets form ideal candidates to estimate atmospheric C/O ratios and to search for CRPs. We also find that the C/O ratio strongly affects the abundances of TiO and VO, which have been suggested to cause thermal inversions in highly irradiated hot Jupiter atmospheres. A C/O = 1 yields TiO and VO abundances of ~100 times lower than those obtained with equilibrium chemistry assuming solar abundances, at P ~ 1 bar. Such a depletion is adequate to rule out thermal inversions due to TiO/VO even in the most highly irradiated hot Jupiters, such as WASP-12b. We estimate the compositions of the protoplanetary disk, the planetesimals, and the envelope of WASP-12b, and the mass of ices dissolved in the envelope, based on the observed atmospheric abundances. Adopting stellar abundances (C/O = 0.44) for the primordial disk composition and low-temperature formation conditions (T <~ 30 K) for WASP-12b lead to a C

Water transport to circumprimary habitable zones from icy planetesimal disks in binary star systems

NASA Astrophysics Data System (ADS)

Bancelin, D.; Pilat-Lohinger, E.; Maindl, T. I.; Bazsó, Á.

2017-03-01

So far, more than 130 extrasolar planets have been found in multiple stellar systems. Dynamical simulations show that the outcome of the planetary formation process can lead to different planetary architectures (i.e. location, size, mass, and water content) when the star system is single or double. In the late phase of planetary formation, when embryo-sized objects dominate the inner region of the system, asteroids are also present and can provide additional material for objects inside the habitable zone (HZ). In this study, we make a comparison of several binary star systems and aim to show how efficient they are at moving icy asteroids from beyond the snow line into orbits crossing the HZ. We also analyze the influence of secular and mean motion resonances on the water transport towards the HZ. Our study shows that small bodies also participate in bearing a non-negligible amount of water to the HZ. The proximity of a companion moving on an eccentric orbit increases the flux of asteroids to the HZ, which could result in a more efficient water transport on a short timescale, causing a heavy bombardment. In contrast to asteroids moving under the gravitational perturbations of one G-type star and a gas giant, we show that the presence of a companion star not only favors a faster depletion of our disk of planetesimals, but can also bring 4-5 times more water into the whole HZ. However, due to the secular resonance located either inside the HZ or inside the asteroid belt, impacts between icy planetesimals from the disk and big objects in the HZ can occur at high impact speed. Therefore, real collision modeling using a GPU 3D-SPH code show that in reality, the water content of the projectile is greatly reduced and therefore, also the water transported to planets or embryos initially inside the HZ.

Messages from the Reversing Layer: Clues to Planet Formation in Spectral Abundances

NASA Astrophysics Data System (ADS)

Brewer, John Michael; Fischer, Debra; Basu, Sarbani

2017-01-01

The abundances of elements in the protoplanetary disk evolve over time, but stellar abundances will reflect the initial chemical composition of the disk and this can provide constraints on the range of possible outcomes for planet interiors. Rocky planet habitability depends not just on the availability of liquid water, but also on volcansim and plate tectonics that can stabilize the climate on long timescales. The slow evolution of abundances in stellar photospheres, particularly abundance ratios between elements, makes them ideal laboratories to study primordial disk compositions.In my thesis work, I developed a new spectroscopic analysis procedure that derives gravities consistent with asteroseismology to within 0.05 dex as well as abundances for 15 elements. Using this procedure, we analyzed and published a catalog of accurate stellar parameters and precise abundances for more than 1600 stars and used those to investigate questions of planet formation. The C/O and Mg/Si ratios in the solar neighborhood could affect rocky planet habitability. For lucky cases where planet atmosphereic abundances can be measured, the stellar host C/O and [O/H] ratios carry information about the formation site and migration of hot Jupiters. I will present results on both rocky planet compositions and hot Jupiter migration and discuss how they can help us identify potentially habitable systems and discriminate between different planet formation models.

Emergence of Habitable Environments in Icy World Interiors

NASA Astrophysics Data System (ADS)

Neveu, Marc

2016-07-01

Finding habitable worlds is a key driver of solar system exploration. Many solar system missions seek environments providing liquid water, energy, and nutrients, the three ingredients necessary to sustain life [1]. Such environments include hydrothermal systems, spatially confined systems where hot aqueous fluid circulates through rock by convection. Hydrothermal activity may be widespread in the solar system. Most solar system worlds larger than 200 km in radius are icy moons and dwarf planets, likely composed of an icy, cometary mantle surrounding a rocky, chondritic core [2]. By improving an icy world evolution code [3] to include the effects of core fracturing and hydrothermal circulation, I show that several icy moons and dwarf planets likely have undergone extensive water-rock interaction [4,5]. This supports observations of aqueous products on their surfaces [6,7]. I simulated the alteration of chondritic rock [8] by pure water or fluid of cometary composition [9] to show that aqueous alteration feeds back on geophysical evolution: it modifies the fluid antifreeze content, affecting its persistence over geological timescales; and the distribution of radionuclides, whose decay is a chief heat source on dwarf planets [10]. Hydrothermal circulation also efficiently transports heat from the core into the ocean, thereby increasing ocean persistence [4]. Thus, these coupled geophysical-geochemical models provide a comprehensive picture of icy world evolution and the emergence of liquid environments in chemical disequilibrium with underlying rock in their interiors. Habitable settings also require a suitable supply of bioessential elements; but what constitutes "suitable"? I sought to quantify the bulk elemental composition of hydrothermal microbial communities, collected in hot spring sediments and mats at Yellowstone National Park, USA. To do so, one must minimize the contribution of non-biological material to the samples analyzed. This was achieved using a

The Icy Mountains of Pluto

NASA Image and Video Library

2015-07-15

New close-up images of a region near Pluto's equator reveal a giant surprise: a range of youthful mountains rising as high as 11,000 feet (3,500 meters) above the surface of the icy body. The mountains likely formed no more than 100 million years ago -- mere youngsters relative to the 4.56-billion-year age of the solar system -- and may still be in the process of building. That suggests the close-up region, which covers less than one percent of Pluto's surface, may still be geologically active today. The youthful age estimate is based on the lack of craters in this scene. Like the rest of Pluto, this region would presumably have been pummeled by space debris for billions of years and would have once been heavily cratered -- unless recent activity had given the region a facelift, erasing those pockmarks. Unlike the icy moons of giant planets, Pluto cannot be heated by gravitational interactions with a much larger planetary body. Some other process must be generating the mountainous landscape. The mountains are probably composed of Pluto's water-ice "bedrock." Although methane and nitrogen ice covers much of the surface of Pluto, these materials are not strong enough to build the mountains. Instead, a stiffer material, most likely water-ice, created the peaks. The close-up image was taken about 1.5 hours before New Horizons closest approach to Pluto, when the craft was 47,800 miles (770,000 kilometers) from the surface of the planet. The image easily resolves structures smaller than a mile across. http://photojournal.jpl.nasa.gov/catalog/PIA19710

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.

Terrestrial Planet Formation from an Annulus -- Revisited

NASA Astrophysics Data System (ADS)

Deienno, Rogerio; Walsh, Kevin J.; Kretke, Katherine A.; Levison, Harold F.

2018-04-01

Numerous recent theories of terrestrial planet formation suggest that, in order to reproduce the observed large Earth to Mars mass ratio, planets formed from an annulus of material within 1 au. The success of these models typically rely on a Mars sized embryo being scattered outside 1 au (to ~1.5 au) and starving, while those remaining inside 1 au continue growing, forming Earth and Venus. In some models the scattering is instigated by the migration of giant planets, while in others an embryo-instability naturally occurs due to the dissipation of the gaseous solar nebula. While these models can typically succeed in reproducing the overall mass ratio among the planets, the final angular momentum deficit (AMD) of the present terrestrial planets in our Solar System, and their radial mass concentration (RMC), namely the position where Mars end up in the simulations, are not always well reproduced. Assuming that the gas nebula may not be entirely dissipated when such an embryo-instability happens, here, we study the effects that the time of such an instability can have on the final AMD and RMC. In addition, we also included energy dissipation within embryo-embryo collisions by assuming a given coefficient of restitution for collisions. Our results show that: i) dissipation within embryo-embryo collisions do not play any important role in the final terrestrial planetary system; ii) the final AMD decreases only when the number of final planets formed increases; iii) the RMC tends to always be lower than the present value no matter the number of final planets; and iv) depending on the time that the embryo-instability happen, if too early, with too much gas still present, a second instability will generally happen after the dissipation of the gas nebula.

Laboratory Simulations of Ammonia-Rich Oceans in Icy Worlds

NASA Technical Reports Server (NTRS)

Vance, S. D.; Brown, J. M.

2011-01-01

Improved equations of state for ammonia-water solutions are important for properly understanding the interiors of large icy satellites hosting deep interior oceans. Titan is the primary example of such a world, but water-rich dwarf planets Measurements of solution density are now possible at relevant pressures (above approx. 250 megapascals) using the Simulator for Icy World Interiors. Analysis of sound velocity measurements in aqueous magnesium sulfate obtained in our laboratory, shows a correction on the order of 5% to 700 megapascals (7 kilobar) from -20 to 100 C and to 3 m (approx. 30 percentage by weight) concentration. Accurate prediction of density as a function of pressure, temperature, and ammonia concentration are needed for interpretation of remote observations to address questions of interior liquid layer depth, composition, and fluid dynamics.

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.

Constraining the volatile fraction of planets from transit observations

NASA Astrophysics Data System (ADS)

Alibert, Y.

2016-06-01

Context. The determination of the abundance of volatiles in extrasolar planets is very important as it can provide constraints on transport in protoplanetary disks and on the formation location of planets. However, constraining the internal structure of low-mass planets from transit measurements is known to be a degenerate problem. Aims: Using planetary structure and evolution models, we show how observations of transiting planets can be used to constrain their internal composition, in particular the amount of volatiles in the planetary interior, and consequently the amount of gas (defined in this paper to be only H and He) that the planet harbors. We first explore planets that are located close enough to their star to have lost their gas envelope. We then concentrate on planets at larger distances and show that the observation of transiting planets at different evolutionary ages can provide statistical information on their internal composition, in particular on their volatile fraction. Methods: We computed the evolution of low-mass planets (super-Earths to Neptune-like) for different fractions of volatiles and gas. We used a four-layer model (core, silicate mantle, icy mantle, and gas envelope) and computed the internal structure of planets for different luminosities. With this internal structure model, we computed the internal and gravitational energy of planets, which was then used to derive the time evolution of the planet. Since the total energy of a planet depends on its heat capacity and density distribution and therefore on its composition, planets with different ice fractions have different evolution tracks. Results: We show for low-mass gas-poor planets that are located close to their central star that assuming evaporation has efficiently removed the entire gas envelope, it is possible to constrain the volatile fraction of close-in transiting planets. We illustrate this method on the example of 55 Cnc e and show that under the assumption of the absence of

Terrestrial planet formation in a protoplanetary disk with a local mass depletion: A successful scenario for the formation of Mars

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

Izidoro, A.; Winter, O. C.; Haghighipour, N.

Models of terrestrial planet formation for our solar system have been successful in producing planets with masses and orbits similar to those of Venus and Earth. However, these models have generally failed to produce Mars-sized objects around 1.5 AU. The body that is usually formed around Mars' semimajor axis is, in general, much more massive than Mars. Only when Jupiter and Saturn are assumed to have initially very eccentric orbits (e ∼ 0.1), which seems fairly unlikely for the solar system, or alternately, if the protoplanetary disk is truncated at 1.0 AU, simulations have been able to produce Mars-like bodiesmore » in the correct location. In this paper, we examine an alternative scenario for the formation of Mars in which a local depletion in the density of the protosolar nebula results in a non-uniform formation of planetary embryos and ultimately the formation of Mars-sized planets around 1.5 AU. We have carried out extensive numerical simulations of the formation of terrestrial planets in such a disk for different scales of the local density depletion, and for different orbital configurations of the giant planets. Our simulations point to the possibility of the formation of Mars-sized bodies around 1.5 AU, specifically when the scale of the disk local mass-depletion is moderately high (50%-75%) and Jupiter and Saturn are initially in their current orbits. In these systems, Mars-analogs are formed from the protoplanetary materials that originate in the regions of disk interior or exterior to the local mass-depletion. Results also indicate that Earth-sized planets can form around 1 AU with a substantial amount of water accreted via primitive water-rich planetesimals and planetary embryos. We present the results of our study and discuss their implications for the formation of terrestrial planets in our solar system.« less

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.

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.

Icy Dwarf Planets: Colored Popsicles in the Outer Solar System

NASA Astrophysics Data System (ADS)

Pinilla-Alonso, Noemi

2016-10-01

We update the list of candidates to be considered by the IAU as dwarf planets using the criterium suggested by Tancredi & Favre (2008). We add here the information collected in the last 10 years (mostly the sizes and albedos by the herschel hey program TNOs Are Cool). We compare the physical characteristics of these candidates with the physical characteristics of the rest of the TNOs. Our goal is to study if there are common physical properties among the candidates that enable the identification of a dwarf planet.

Circumbinary planet formation in the Kepler-16 system. II. A toy model for in situ planet formation within a debris belt

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

Meschiari, Stefano, E-mail: stefano@astro.as.utexas.edu

2014-07-20

Recent simulations have shown that the formation of planets in circumbinary configurations (such as those recently discovered by Kepler) is dramatically hindered at the planetesimal accretion stage. The combined action of the binary and the protoplanetary disk acts to raise impact velocities between kilometer-sized planetesimals beyond their destruction threshold, halting planet formation within at least 10 AU from the binary. It has been proposed that a primordial population of 'large' planetesimals (100 km or more in size), as produced by turbulent concentration mechanisms, would be able to bypass this bottleneck; however, it is not clear whether these processes are viablemore » in the highly perturbed circumbinary environments. We perform two-dimensional hydrodynamical and N-body simulations to show that kilometer-sized planetesimals and collisional debris can drift and be trapped in a belt close to the central binary. Within this belt, planetesimals could initially grow by accreting debris, ultimately becoming 'indestructible' seeds that can accrete other planetesimals in situ despite the large impact speeds. We find that large, indestructible planetesimals can be formed close to the central binary within 10{sup 5} yr, therefore showing that even a primordial population of 'small' planetesimals can feasibly form a planet.« less

Decision-aided ICI mitigation with time-domain average approximation in CO-OFDM

NASA Astrophysics Data System (ADS)

Ren, Hongliang; Cai, Jiaxing; Ye, Xin; Lu, Jin; Cao, Quanjun; Guo, Shuqin; Xue, Lin-lin; Qin, Yali; Hu, Weisheng

2015-07-01

We introduce and investigate the feasibility of a novel iterative blind phase noise inter-carrier interference (ICI) mitigation scheme for coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. The ICI mitigation scheme is performed through the combination of frequency-domain symbol decision-aided estimation and the ICI phase noise time-average approximation. An additional initial decision process with suitable threshold is introduced in order to suppress the decision error symbols. Our proposed ICI mitigation scheme is proved to be effective in removing the ICI for a simulated CO-OFDM with 16-QAM modulation format. With the slightly high computational complexity, it outperforms the time-domain average blind ICI (Avg-BL-ICI) algorithm at a relatively wide laser line-width and high OSNR.

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.

The Constraint of Coplanarity: Compact multi-planet system outer architectures and formation.-UP

NASA Astrophysics Data System (ADS)

Jontof-Hutter, Daniel

The Kepler mission discovered 92 systems with 4 or more transiting exoplanets. Systems like Kepler-11 with six "mini-Neptunes" on orbital periods well inside that of Venus pose a challenge to planet formation theory which is broadly split into two competing paradigms. One theory invokes the formation of Neptunes beyond the "snow line", followed by inward migration and assembly into compact configurations near the star. The alternative is that low density planets form in situ at all distances in the protoplanetary nebula. The two paradigms disagree on the occurrence of Jovian planets at longer orbital periods than the transiting exoplanets since such massive planets would impede the inward migration of multiple volatile-rich planets to within a fraction of 1 AU. The likelihood of all the known planets at systems like Kepler-11 to be transiting is very sensitive to presence of outer Jovian planets for a wide range in orbital distance and relative inclination of the Jovian planet. This can put upper limits on the occurrence of Jovian planets by the condition that the six known planets have to have low mutual inclinations most of the time in order for their current cotransiting state to be plausible. Most of these systems have little or no RV data. Hence, our upper limits may be the best constraints on the occurrence of Jovian planets in compact co-planar systems for years to come, and may help distinguish the two leading paradigms of planet formation theory. Methodology. We propose to use an established n-body code (MERCURY) to perform long-term simulations of systems like Kepler-11 with the addition of a putative Jovian planet considering a range of orbital distances. These simulations will test for which initial conditions a Jovian planet would prevent the known planets from all transiting at the same time. We will 1) determine at what orbital distances and inclinations an outer Jovian planet would make the observed configuration of Kepler-11 very unlikely. 2) Test

Collisional and dynamical processes in moon and planet formation

NASA Technical Reports Server (NTRS)

1979-01-01

The collisional and dynamical processes in moon and planet formation are discussed. A hydrodynamic code of collision calculations, the orbital element changes due to gravitational scattering, a validation of the mass shifting algorithm, a theory of rotations, and the origin of asteroids are studied. A numerical model of planet growth is discussed and a methodology to evaluate the rate at which megaregolith increases its depth as a function of total accumulate number of impacts on an initially smooth, coherent surface is described.

DYNAMICS AND ECCENTRICITY FORMATION OF PLANETS IN OGLE-06-109L SYSTEM

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

Wang Su; Zhao Gang; Zhou Jilin, E-mail: zhoujl@nju.edu.c

2009-11-20

Recent observation of the microlensing technique reveals two giant planets at 2.3 AU and 4.6 AU around the star OGLE-06-109L. The eccentricity of the outer planet (e{sub c} ) is estimated to be 0.11{sup +0.17}{sub -0.04}, comparable to that of Saturn (0.01-0.09). The similarities between the OGLE-06-109L system and the solar system indicate that they may have passed through similar histories during their formation stage. In this paper, we investigate the dynamics and formation of the orbital architecture in the OGLE-06-109L system. For the present two planets with their nominal locations, the secular motions are stable as long as theirmore » eccentricities (e{sub b} , e{sub c} ) fulfill e {sup 2} {sub b} + e {sup 2} {sub c} <= 0.3{sup 2}. Earth-size bodies might be formed and are stable in the habitable zone (0.25-0.36 AU) of the system. Three possible scenarios may be accounted for the formation of e{sub b} and e{sub c} : (1) convergent migration of two planets and the 3:1 mean motion resonance (MMR) trapping; (2) planetary scattering; and (3) divergent migration and the 3:1 MMR crossing. As we showed that the probability for the two giant planets in 3:1 MMR is low (approx3%), scenario (1) is less likely. According to models (2) and (3), the final eccentricity of inner planet (e{sub b} ) may oscillate between [0-0.06], comparable to that of Jupiter (0.03-0.06). An inspection of e{sub b} , e{sub c} 's secular motion may be helpful to understand which model is really responsible for the eccentricity formation.« less

Planet formation: is it good or bad to have a stellar companion?

NASA Astrophysics Data System (ADS)

Marzari, F.; Thebault, P.; Scholl, H.

2010-04-01

Planet formation in binary star systems is a complex issue due to the gravitational perturbations of the companion star. One of the crucial steps of the core-accretion model is planetesimal accretion into large protoplanets which finally coalesce into planets. In a planetesimal swarm surrounding the primary star, the average mutual impact velocity determines if larger bodies form or if the population is grinded down to dust, halting the planet formation process. This velocity is strongly influenced by the companion gravitational pull and by gas drag. The combined effect of these two forces may act in favour of or against planet formation, setting a lower or equal probability of the existence of extrasolar planets around single or binary stars. Planetesimal accretion in binaries has been studied so far with two different approaches. N-body codes based on the assumption that the disk is axisymmetric are very cost-effective since they allow the study of the mutual relative velocity with limited CPU usage. A large amount of planetesimal trajectories can be computed making it possible to outline the regions around the star where planet formation is possible. The main limitation of the N-body codes is the axisymmetric assumption. The companion perturbations affect not only the planetesimal orbits, but also the gaseous disk, by forcing spiral density waves. In addition, the overall shape of the disk changes from circular to elliptic. Hybrid codes have been recently developed which solve the equations for the disk with a hydrodynamical grid code and use the computed gas density and velocity vector to calculate an accurate value of the gas drag force on the planetesimals. These codes are more complex and may compute the trajectories of only a limited number of planetesimals.

Fluffy dust forms icy planetesimals by static compression

NASA Astrophysics Data System (ADS)

Kataoka, Akimasa; Tanaka, Hidekazu; Okuzumi, Satoshi; Wada, Koji

2013-09-01

Context. Several barriers have been proposed in planetesimal formation theory: bouncing, fragmentation, and radial drift problems. Understanding the structure evolution of dust aggregates is a key in planetesimal formation. Dust grains become fluffy by coagulation in protoplanetary disks. However, once they are fluffy, they are not sufficiently compressed by collisional compression to form compact planetesimals. Aims: We aim to reveal the pathway of dust structure evolution from dust grains to compact planetesimals. Methods: Using the compressive strength formula, we analytically investigate how fluffy dust aggregates are compressed by static compression due to ram pressure of the disk gas and self-gravity of the aggregates in protoplanetary disks. Results: We reveal the pathway of the porosity evolution from dust grains via fluffy aggregates to form planetesimals, circumventing the barriers in planetesimal formation. The aggregates are compressed by the disk gas to a density of 10-3 g/cm3 in coagulation, which is more compact than is the case with collisional compression. Then, they are compressed more by self-gravity to 10-1 g/cm3 when the radius is 10 km. Although the gas compression decelerates the growth, the aggregates grow rapidly enough to avoid the radial drift barrier when the orbital radius is ≲6 AU in a typical disk. Conclusions: We propose a fluffy dust growth scenario from grains to planetesimals. It enables icy planetesimal formation in a wide range beyond the snowline in protoplanetary disks. This result proposes a concrete initial condition of planetesimals for the later stages of the planet formation.

Polygonal Craters on Dwarf-Planet Ceres

NASA Astrophysics Data System (ADS)

Otto, K. A.; Jaumann, R.; Krohn, K.; Buczkowski, D. L.; von der Gathen, I.; Kersten, E.; Mest, S. C.; Preusker, F.; Roatsch, T.; Schenk, P. M.; Schröder, S.; Schulzeck, F.; Scully, J. E. C.; Stepahn, K.; Wagner, R.; Williams, D. A.; Raymond, C. A.; Russell, C. T.

2015-10-01

With approximately 950 km diameter and a mass of #1/3 of the total mass of the asteroid belt, (1) Ceres is the largest and most massive object in the Main Asteroid Belt. As an intact proto-planet, Ceres is key to understanding the origin and evolution of the terrestrialplanets [1]. In particular, the role of water during planet formation is of interest, because the differentiated dwarf-planet is thought to possess a water rich mantle overlying a rocky core [2]. The Dawn space craft arrived at Ceres in March this year after completing its mission at (4) Vesta. At Ceres, the on-board Framing Camera (FC) collected image data which revealed a large variety of impact crater morphologies including polygonal craters (Figure 1). Polygonal craters show straight rim sections aligned to form an angular shape. They are commonly associated with fractures in the target material. Simple polygonal craters develop during the excavation stage when the excavation flow propagates faster along preexisting fractures [3, 5]. Complex polygonal craters adopt their shape during the modification stage when slumping along fractures is favoured [3]. Polygonal craters are known from a variety of planetary bodies including Earth [e.g. 4], the Moon [e.g. 5], Mars [e.g. 6], Mercury [e.g. 7], Venus [e.g. 8] and outer Solar System icy satellites [e.g. 9].

The physical and chemical evolution of disks during planet formation

NASA Astrophysics Data System (ADS)

Gorti, Uma

2018-06-01

Protoplanetary disks evolve and disperse rapidly during the early stages of star and planet formation. While disks initially inherit a full complement of interstellar cloud material that is mainly accreted on to the central star, their gas and dust components appear to evolve along distinct pathways. Dust accumulates to form rocky planets, whereas only a small fraction of the available gas may be incorporated into gas giants in a typical exoplanetary system. However, the radial distribution of gas and its chemistry are expected to impact the architecture and composition of formed planets. Recent ALMA results have underscored the importance of ices and grain surface chemistry in disks, and their significance for planet formation. I will describe disk models that aim to probe the physical and chemical processes in the disk at various stages of evolution, and specifically discuss diagnostics of conditions in the innermost regions of disks which will become accessible for the first time with the launch of JWST. Current theoretical modeling is however hindered by many uncertainties in input parameters and poorly known chemical and physical processes. I will highlight some gaps in our current understanding, and discuss how laboratory astrophysics can help in preparing for the JWST era and aid in the interpretation of future line and continuum emission studies.

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.

Planet Formation in Disks with Inclined Binary Companions: Can Primordial Spin-Orbit Misalignment be Produced?

NASA Astrophysics Data System (ADS)

Zanazzi, J. J.; Lai, Dong

2018-04-01

Many hot Jupiter (HJ) systems have been observed to have their stellar spin axis misaligned with the planet's orbital angular momentum axis. The origin of this spin-orbit misalignment and the formation mechanism of HJs remain poorly understood. A number of recent works have suggested that gravitational interactions between host stars, protoplanetary disks, and inclined binary companions may tilt the stellar spin axis with respect to the disk's angular angular momentum axis, producing planetary systems with misaligned orbits. These previous works considered idealized disk evolution models and neglected the gravitational influence of newly formed planets. In this paper, we explore how disk photoevaporation and planet formation and migration affect the inclination evolution of planet-star-disk-binary systems. We take into account planet-disk interactions and the gravitational spin-orbit coupling between the host star and the planet. We find that the rapid depletion of the inner disk via photoevaporation reduces the excitation of stellar obliquities. Depending on the formation and migration history of HJs, the spin-orbit coupling between the star and the planet may reduces and even completely suppress the excitation of stellar obliquities. Our work constrains the formation/migration history of HJs. On the other hand, planetary systems with "cold" Jupiters or close-in super-earths may experience excitation of stellar obliquities in the presence of distant inclined companions.

Planet formation in discs with inclined binary companions: can primordial spin-orbit misalignment be produced?

NASA Astrophysics Data System (ADS)

Zanazzi, J. J.; Lai, Dong

2018-07-01

Many hot Jupiter (HJ) systems have been observed to have their stellar spin axis misaligned with the planet's orbital angular momentum axis. The origin of this spin-orbit misalignment and the formation mechanism of HJs remain poorly understood. A number of recent works have suggested that gravitational interactions between host stars, protoplanetary discs, and inclined binary companions may tilt the stellar spin axis with respect to the disc's angular angular momentum axis, producing planetary systems with misaligned orbits. These previous works considered idealized disc evolution models and neglected the gravitational influence of newly formed planets. In this paper, we explore how disc photoevaporation and planet formation and migration affect the inclination evolution of planet-star-disc-binary systems. We take into account planet-disc interactions and the gravitational spin-orbit coupling between the host star and the planet. We find that the rapid depletion of the inner disc via photoevaporation reduces the excitation of stellar obliquities. Depending on the formation and migration history of HJs, the spin-orbit coupling between the star and the planet may reduces and even completely suppress the excitation of stellar obliquities. Our work constrains the formation/migration history of HJs. On the other hand, planetary systems with `cold' Jupiters or close-in super-earths may experience excitation of stellar obliquities in the presence of distant inclined companions.

Satellites of giant planets — possible sites for origin and existence of biospheres

NASA Astrophysics Data System (ADS)

Simakov, Michael B.

All giant planets of the Solar system have a big number of satellites (61 of Jupiter, 52 of Saturn, known in 2003). A small part of them consist very large bodies, quite comparable to planets of terrestrial type, but including very significant share of water ice. Some from them have an atmosphere. E.g., the mass of a column of the Titan’s atmosphere exceeds 15 times the mass of the Earth atmosphere column. Formation (or capture) of satellites is a natural phenomenon, and satellite systems definitely should exist at extrasolar planets. As an example, we can see on Titan, the largest satellite of Saturn, which has a dense nitrogen atmosphere and a large quantity of liquid water under ice cover and so has a great exobiological significance. The most recent models of the Titan’s interior lead to the conclusion that a substantial liquid layer exists today under relatively thin ice cover inside Titan. The putative internal water ocean along with complex atmospheric photochemistry provide some exobiological niches on this body: (1) an upper layer of the internal water ocean; (2) pores, veins, channels and pockets filled with brines inside of the lowest part of the icy layer; (3) the places of cryogenic volcanism; (4) set of caves in icy layer connecting with cryovolcanic processes; (5) the brine-filled cracks in icy crust caused by tidal forces; (6) liquid water pools on the surface originated from meteoritic strikes; (7) the sites of hydrothermal activity on the bottom of the ocean. We can see all conditions needed for origin and evolution of biosphere — liquid water, complex organic chemistry and energy sources for support of biological processes — are on the Saturnian moon. Galileo spacecraft has given indications, primarily from magnetometer and gravity data, of the possibility that three of Jupiter’s four large moons, Europa, Ganymede and Callisto have such oceans also. The existing of liquid water ocean within icy world can be consequences of the physical

N-body simulations of terrestrial planet formation under the influence of a hot Jupiter

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

Ogihara, Masahiro; Kobayashi, Hiroshi; Inutsuka, Shu-ichiro, E-mail: omasahiro@oca.eu, E-mail: ogihara@nagoya-u.jp

We investigate the formation of multiple-planet systems in the presence of a hot Jupiter (HJ) using extended N-body simulations that are performed simultaneously with semianalytic calculations. Our primary aims are to describe the planet formation process starting from planetesimals using high-resolution simulations, and to examine the dependences of the architecture of planetary systems on input parameters (e.g., disk mass, disk viscosity). We observe that protoplanets that arise from oligarchic growth and undergo type I migration stop migrating when they join a chain of resonant planets outside the orbit of an HJ. The formation of a resonant chain is almost independentmore » of our model parameters, and is thus a robust process. At the end of our simulations, several terrestrial planets remain at around 0.1 AU. The formed planets are not equal mass; the largest planet constitutes more than 50% of the total mass in the close-in region, which is also less dependent on parameters. In the previous work of this paper, we have found a new physical mechanism of induced migration of the HJ, which is called a crowding-out. If the HJ opens up a wide gap in the disk (e.g., owing to low disk viscosity), crowding-out becomes less efficient and the HJ remains. We also discuss angular momentum transfer between the planets and disk.« less

SOLARIS: Software for planet formation and orbital integrations

NASA Astrophysics Data System (ADS)

Süli software, Á.

2013-11-01

I present SOLARIS a general purpose software package for doing N-body and planet formation simulations. SOLARIS is capable to (i) to follow the orbital evolution of the solar system's major planets and minor bodies, (ii) to study the dynamics of exoplanetary systems, and (iii) to study the early and later phases of planetary formation. The process to bring bodies with different epochs to one common epoch, i.e. synchronization is implemented. Apart from the Newtonian gravitational forces, aerodynamic drag force, and type I and II migration forces are also implemented. The code also includes a nebula model. To speed up the computation, SOLARIS treats particles with different interaction properties. Several two-body events are monitored, such as collision, ejection etc. Arbitrary chemical composition can be assigned to massive bodies and during collisions the new body's composition is based on the mergers. The input is given in XML to define the parameters in a well-structured and flexible way. SOLARIS is designed to be versatile and easy to use, accepting initial conditions in either Cartesian coordinates or Keplerian orbital elements.

The Icy Cold Heart of Pluto

NASA Astrophysics Data System (ADS)

Hamilton, Douglas P.

2015-11-01

The locations of large deposits of frozen volatiles on planetary surfaces are largely coincident with areas receiving the minimum annual influx of solar energy; familiar examples include the polar caps of Earth and Mars. For planets tilted by more than 45 degrees, however, the poles actually receive more energy than some other latitudes. Pluto, with its current obliquity of 119 degrees, has minima in its average annual insolation at +/- 27 degrees latitude, with ~1.5% more energy flux going to the equator and ~15% more to the poles. Remarkably, the fraction of annual solar energy incident on different latitudes depends only on the obliquity of the planet and not on any of its orbital parameters.Over millions of years, Pluto's obliquity varies sinusoidally from 102-126 degrees, significantly affecting the latitudinal profile of solar energy deposition. Roughly 1Myr ago, the poles received 15% more energy that today while the equator received 13% less. The energy flux to latitudes between 25-35 degrees is far more stable, remaining low over the presumably billions of years since Pluto acquired its current spin properties. Like the poles at Earth, these mid latitudes on Pluto should be favored for the long-term deposition of volatile ices. This is, indeed, the location of the bright icy heart of Pluto, Sputnik Planum.Reflected light and emitted thermal radiation from Charon increases annual insolation to one side of Pluto by of order 0.02%. Although small, the bulk of the energy is delivered at night to Pluto's cold equatorial regions. Furthermore, Charon's thermal infrared radiation is easily absorbed by icy deposits on Pluto, slowing deposition and facilitating sublimation of volatiles. We argue that the slight but persistent preference for ices to form and survive in the anti-Charon Pluto's heart.

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

Modeling of light scattering by icy bodies

NASA Astrophysics Data System (ADS)

Kolokolova, L.; Mackowski, D.; Pitman, K.; Verbiscer, A.; Buratti, B.; Momary, T.

2014-07-01

As a result of ground-based, space-based, and in-situ spacecraft mission observations, a great amount of photometric, polarimetric, and spectroscopic data of icy bodies (satellites of giant planets, Kuiper Belt objects, comet nuclei, and icy particles in cometary comae and rings) has been accumulated. These data have revealed fascinating light-scattering phenomena, such as the opposition surge resulting from coherent backscattering and shadow hiding and the negative polarization associated with them. Near-infrared (NIR) spectra of these bodies are especially informative as the depth, width, and shape of the absorption bands of ice are sensitive not only to the ice abundance but also to the size of icy grains. Numerous NIR spectra obtained by Cassini's Visual and Infrared Mapping Spectrometer (VIMS) have been used to map the microcharacteristics of the icy satellites [1] and rings of Saturn [2]. VIMS data have also permitted a study of the opposition surge for icy satellites of Saturn [3], showing that coherent backscattering affects not only brightness and polarization of icy bodies but also their spectra [4]. To study all of the light-scattering phenomena that affect the photopolarimetric and spectroscopic characteristics of icy bodies, including coherent backscattering, requires computer modeling that rigorously considers light scattering by a large number of densely packed small particles that form either layers (in the case of regolith) or big clusters (ring and comet particles) . Such opportunity has appeared recently with a development of a new version MSTM4 of the Multi-Sphere T-Matrix code [5]. Simulations of reflectance and absorbance spectra of a ''target'' (particle layer or cluster) require that the dimensions of the target be significantly larger than the wavelength, sphere radius, and layer thickness. For wavelength-sized spheres and packing fractions typical of regolith, targets can contain dozens of thousands of spheres that, with the original MSTM

Planet formation in transition disks: Modeling, spectroscopy, and theory

NASA Astrophysics Data System (ADS)

Liskowsky, Joseph Paul

An important field of modern astronomy is the study of planets. Literally for millennia, careful observers of the night sky have tracked these 'wanderers', with their peculiar motions initiating avenues of inquiry not able to elucidated by a study of the stars alone: we have discovered that the planets (as well as Earth) orbit the sun and that the stars are so far away, even their relative positions do not seem to shift perceptibly when Earth's position moves hundreds of millions of miles. With the advent of the telescope, and subsequent improvements upon it over the course of centuries, accelerating to the dramatically immense telescopes available today and those on the horizon, we have been able to continuously probe farther and in more detail than the previous generation of scientists and telescopes allowed. Now, we are just entering the time when detection of planets outside of our own solar system has become possible, and we have found that planets are extraordinarily common in the galaxy (and by extrapolation, the universe). At the time of this document's composition, there are several thousand such examples of planets around other stars (being dubbed 'exoplanets'). We have discovered that planets are plentiful, but multiple open questions remain which are relevant to this work: How do planets form and, when a planet does form from its circumstellar envelope, what are the important processes that influence its formation? This work adds to the understanding of circumstellar disks, the intermediate stage between a cold collapsing cloud (of gas and dust) and a mature planetary system. Specifically, we study circumstellar disks in an evolved state termed 'transition disks'. This state corresponds to a time period where the dust in the disk has either undergone grain growth—where the microscopic grains have clumped together to form far fewer dust particles of much higher mass, or the inner portion (or an inner annulus) of the disk has lost a large amount of gas

FORMATION OF CENTAURS’ RINGS THROUGH THEIR PARTIAL TIDAL DISRUPTION DURING PLANETARY ENCOUNTERS

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

Hyodo, Ryuki; Charnoz, Sébastien; Genda, Hidenori

Centaurs are minor planets orbiting between Jupiter and Neptune that have or had crossing orbits with one or more giant planets. Recent observations and reinterpretation of previous observations have revealed the existence of ring systems around 10199 Chariklo and 2060 Chiron. However, the origin of the ring systems around such a minor planet is still an open question. Here, we propose that the tidal disruption of a differentiated object that experiences a close encounter with a giant planet could naturally form diverse ring–satellite systems around the Centaurs. During the close encounter, the icy mantle of the passing object is preferentiallymore » ripped off by the planet's tidal force and the debris is distributed mostly within the Roche limit of the largest remnant body. Assuming the existence of a 20−50 wt% silicate core below the icy mantle, a disk of particles is formed when the objects pass within 0.4–0.8 of the planet's Roche limit with the relative velocity at infinity 3−6 km s{sup −1} and 8 hr initial spin period of the body. The resultant ring mass is 0.1%–10% of the central object's mass. Such particle disks are expected to spread radially, and materials spreading beyond the Roche limit would accrete into satellites. Our numerical results suggest that ring formation would be a natural outcome of such extreme close encounters, and Centaurs can naturally have such ring systems because they cross the orbits of the giant planets.« less

The formation of co-orbital planets and their resulting transit signatures

NASA Astrophysics Data System (ADS)

Granados Contreras, Agueda Paula; Boley, Aaron

2018-04-01

Systems with Tightly-packed Inner Planets (STIPs) are metastable, exhibiting sudden transitions to an unstable state that can potentially lead to planet consolidation. When these systems are embedded in a gaseous disc, planet-disc interactions can significantly reduce the frequency of instabilities, and if they do occur, disc torques alter the dynamical outcomes. We ran a suite of N-body simulations of synthetic 6-planet STIPs using an independent implementation of IAS15 that includes a prescription for gaseous tidal damping. The algorithm is based on the results of disc simulations that self-consistently evolve gas and planets. Even for very compact configurations, the STIPS are resistant to instability when gas is present. However, instability can still occur, and in some cases, the combination of system instability and gaseous damping leads to the formation of co-orbiting planets that are stable even when gas damping is removed. While rare, such systems should be detectable in transit surveys, although the dynamics of the system can make the transit signature difficult to identify.

Lunar and terrestrial planet formation in the Grand Tack scenario

PubMed Central

Jacobson, S. A.; Morbidelli, A.

2014-01-01

We present conclusions from a large number of N-body simulations of the giant impact phase of terrestrial planet formation. We focus on new results obtained from the recently proposed Grand Tack model, which couples the gas-driven migration of giant planets to the accretion of the terrestrial planets. The giant impact phase follows the oligarchic growth phase, which builds a bi-modal mass distribution within the disc of embryos and planetesimals. By varying the ratio of the total mass in the embryo population to the total mass in the planetesimal population and the mass of the individual embryos, we explore how different disc conditions control the final planets. The total mass ratio of embryos to planetesimals controls the timing of the last giant (Moon-forming) impact and its violence. The initial embryo mass sets the size of the lunar impactor and the growth rate of Mars. After comparing our simulated outcomes with the actual orbits of the terrestrial planets (angular momentum deficit, mass concentration) and taking into account independent geochemical constraints on the mass accreted by the Earth after the Moon-forming event and on the time scale for the growth of Mars, we conclude that the protoplanetary disc at the beginning of the giant impact phase must have had most of its mass in Mars-sized embryos and only a small fraction of the total disc mass in the planetesimal population. From this, we infer that the Moon-forming event occurred between approximately 60 and approximately 130 Myr after the formation of the first solids and was caused most likely by an object with a mass similar to that of Mars. PMID:25114304

Seismic Wave Propagation in Icy Ocean Worlds

NASA Astrophysics Data System (ADS)

Stähler, Simon C.; Panning, Mark P.; Vance, Steven D.; Lorenz, Ralph D.; van Driel, Martin; Nissen-Meyer, Tarje; Kedar, Sharon

2018-01-01

Seismology was developed on Earth and shaped our model of the Earth's interior over the twentieth century. With the exception of the Philae lander, all in situ extraterrestrial seismological effort to date was limited to other terrestrial planets. All have in common a rigid crust above a solid mantle. The coming years may see the installation of seismometers on Europa, Titan, and Enceladus, so it is necessary to adapt seismological concepts to the setting of worlds with global oceans covered in ice. Here we use waveform analyses to identify and classify wave types, developing a lexicon for icy ocean world seismology intended to be useful to both seismologists and planetary scientists. We use results from spectral-element simulations of broadband seismic wavefields to adapt seismological concepts to icy ocean worlds. We present a concise naming scheme for seismic waves and an overview of the features of the seismic wavefield on Europa, Titan, Ganymede, and Enceladus. In close connection with geophysical interior models, we analyze simulated seismic measurements of Europa and Titan that might be used to constrain geochemical parameters governing the habitability of a sub-ice ocean.

The Development of the Planet Formation Concept Inventory: A Preliminary Analysis of Version 1

NASA Astrophysics Data System (ADS)

Simon, Molly; Impey, Chris David; Buxner, Sanlyn

2018-01-01

The topic of planet formation is poorly represented in the educational literature, especially at the college level. As recently as 2014, when developing the Test of Astronomy Standards (TOAST), Slater (2014) noted that for two topics (formation of the Solar System and cosmology), “high quality test items that reflect our current understanding of students’ conceptions were not available [in the literature]” (Slater,2014, p. 8). Furthermore, nearly half of ASTR 101 enrollments are at 2 year/community colleges where both instructors and students have little access to current research and models of planet formation. In response, we administered six student replied response (SSR) short answer questions on the topic of planet formation to n = 1,050 students enrolled in introductory astronomy and planetary science courses at The University of Arizona in the Fall 2016 and Spring 2017 semesters. After analyzing and coding the data from the SSR questions, we developed a preliminary version of the Planet Formation Concept Inventory (PFCI). The PFCI is a multiple-choice instrument with 20 planet formation-related questions, and 4 demographic-related questions. We administered version 1 of the PFCI to six introductory astronomy and planetary science courses (n ~ 700 students) during the Fall 2017 semester. We provided students with 7-8 multiple-choice with explanation of reasoning (MCER) questions from the PFCI. Students selected an answer (similar to a traditional multiple-choice test), and then briefly explained why they chose the answer they did. We also conducted interviews with ~15 students to receive feedback on the quality of the questions and clarity of the instrument. We will present an analysis of the MCER responses and student interviews, and discuss any modifications that will be made to the instrument as a result.

Lunar and terrestrial planet formation in the Grand Tack scenario.

PubMed

Jacobson, S A; Morbidelli, A

2014-09-13

We present conclusions from a large number of N-body simulations of the giant impact phase of terrestrial planet formation. We focus on new results obtained from the recently proposed Grand Tack model, which couples the gas-driven migration of giant planets to the accretion of the terrestrial planets. The giant impact phase follows the oligarchic growth phase, which builds a bi-modal mass distribution within the disc of embryos and planetesimals. By varying the ratio of the total mass in the embryo population to the total mass in the planetesimal population and the mass of the individual embryos, we explore how different disc conditions control the final planets. The total mass ratio of embryos to planetesimals controls the timing of the last giant (Moon-forming) impact and its violence. The initial embryo mass sets the size of the lunar impactor and the growth rate of Mars. After comparing our simulated outcomes with the actual orbits of the terrestrial planets (angular momentum deficit, mass concentration) and taking into account independent geochemical constraints on the mass accreted by the Earth after the Moon-forming event and on the time scale for the growth of Mars, we conclude that the protoplanetary disc at the beginning of the giant impact phase must have had most of its mass in Mars-sized embryos and only a small fraction of the total disc mass in the planetesimal population. From this, we infer that the Moon-forming event occurred between approximately 60 and approximately 130 Myr after the formation of the first solids and was caused most likely by an object with a mass similar to that of Mars. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Gap formation by inclined massive planets in locally isothermal three-dimensional discs

NASA Astrophysics Data System (ADS)

Chametla, Raúl O.; Sánchez-Salcedo, F. J.; Masset, F. S.; Hidalgo-Gámez, A. M.

2017-07-01

We study gap formation in gaseous protoplanetary discs by a Jupiter mass planet. The planet's orbit is circular and inclined relative to the mid-plane of the disc. We use the impulse approximation to estimate the gravitational tidal torque between the planet and the disc, and infer the gap profile. For low-mass discs, we provide a criterion for gap opening when the orbital inclination is ≤30°. Using the fargo3d code, we simulate the disc response to an inclined massive planet. The dependence of the depth and width of the gap obtained in the simulations on the inclination of the planet is broadly consistent with the scaling laws derived in the impulse approximation. Although we mainly focus on planets kept on fixed orbits, the formalism permits to infer the temporal evolution of the gap profile in the cases where the inclination of the planet changes with time. This study may be useful to understand the migration of massive planets on inclined orbit, because the strength of the interaction with the disc depends on whether a gap is opened or not.

Constraints on planetary formation from the discovery & study of transiting Extrasolar Planets

NASA Astrophysics Data System (ADS)

Triaud, A. H. M. J.

2011-08-01

After centuries of wondering about the presence of other worlds outside our Solar System, the first extrasolar planets were discovered about fifteen years ago. Since the quest continued. The greatest discovery of our new line of research, exoplanetology, has probably been the large diversity that those new worlds have brought forward; a diversity in mass, in size, in orbital periods, as well as in the architecture of the systems we discover. Planets very different from those composing our system have been detected. As such, we found hot Jupiters, gas giants which orbital period is only of a few days, mini-Neptunes, bodies five to ten time the mass of the Earth but covered by a thick gas layer, super-Earths of similar masses but rocky, lava worlds, and more recently, maybe the first ocean planet. Many more surprises probably await us. This thesis has for subject this very particular planet class: the hot Jupiters. Those astonishing worlds are still badly understood. Yet, thanks to the evolution of observational techniques and of the treatment of their signals, we probably have gathered as much knowledge from these worlds, than what was known of our own gas giants prior to their visit by probes. They are laboratories for a series of intense physical phenomena caused by their proximity to their star. Notably, these planets are found in average much larger than expected. In addition to these curiosities, their presence so close to their star is abnormal, the necessary conditions for the formation of such massive bodies, this close, not being plausible. Thus it is more reasonable to explain their current orbits by a formation far from their star, followed by an orbital migration. It is on this last subject that this thesis is on: the origin of hot Jupiters. The laws of physics are universal. Therefore, using the same physical phenomena, we need to explain the existence of hot Jupiters, while explaining why the Jupiter within our Solar System is found five times the

Compositional Remote Sensing of Icy Planets and Satellites Beyond Jupiter

NASA Technical Reports Server (NTRS)

Roush, T. L.

2002-01-01

The peak of the solar energy distribution occurs at visual wavelengths and falls off rapidly in the infrared. This fact, improvements in infrared detector technology, and the low surface temperatures for most icy objects in the outer solar system have resulted in the bulk of telescopic and spacecraft observations being performed at visual and near-infrared wavelengths. Such observations, begun in the early 1970's and continuing to present, have provided compositional information regarding the surfaces of the satellites of Saturn and Uranus, Neptune's moon Triton, Pluto, Pluto's moon Charon, Centaur objects, and Kuiper belt objects. Because the incident sunlight penetrates the surface and interacts with the materials present there, the measured reflected sunlight contains information regarding the surface materials, and the ratio of the reflected to incident sunlight provides a mechanism of identifying the materials that are present.

Migrating Jupiter up to the habitable zone: Earth-like planet formation and water delivery

NASA Astrophysics Data System (ADS)

Darriba, L. A.; de Elía, G. C.; Guilera, O. M.; Brunini, A.

2017-11-01

Context. Several observational works have shown the existence of Jupiter-mass planets covering a wide range of semi-major axes around Sun-like stars. Aims: We aim to analyse the planetary formation processes around Sun-like stars that host a Jupiter-mass planet at intermediate distances ranging from 1 au to 2 au. Our study focusses on the formation and evolution of terrestrial-like planets and water delivery in the habitable zone (HZ) of the system. Our goal is also to analyse the long-term dynamical stability of the resulting systems. Methods: A semi-analytic model was used to define the properties of a protoplanetary disk that produces a Jupiter-mass planet around the snow line, which is located at 2.7 au for a solar-mass star. Then, it was used to describe the evolution of embryos and planetesimals during the gaseous phase up to the formation of the Jupiter-mass planet, and we used the results as the initial conditions to carry out N-body simulations of planetary accretion. We developed sixty N-body simulations to describe the dynamical processes involved during and after the migration of the gas giant. Results: Our simulations produce three different classes of planets in the HZ: "water worlds", with masses between 2.75 M⊕ and 3.57 M⊕ and water contents of 58% and 75% by mass, terrestrial-like planets, with masses ranging from 0.58 M⊕ to 3.8 M⊕ and water contents less than 1.2% by mass, and "dry worlds", simulations of which show no water. A relevant result suggests the efficient coexistence in the HZ of a Jupiter-mass planet and a terrestrial-like planet with a percentage of water by mass comparable to the Earth. Moreover, our study indicates that these planetary systems are dynamically stable for at least 1 Gyr. Conclusions: Systems with a Jupiter-mass planet located at 1.5-2 au around solar-type stars are of astrobiological interest. These systems are likely to harbour terrestrial-like planets in the HZ with a wide diversity of water contents.

Laboratory studies on low-energy electron penetration depths into amorphous ice - consequence to astrobiology on icy surfaces

NASA Astrophysics Data System (ADS)

Gudipati, M. S.; Li, I.; Lignell, A. A.

2009-12-01

Penetration of electrons through icy surfaces plays an important role in radiation processing of solar system icy bodies. However, to date, there is no quantitative data available on the penetration depths of electrons through cryogenic water-ices. Penetration of high-energy incident electrons also results in the in-situ formation of secondary low-energy electrons, such as on the surface of Europa (Herring-Captain et al., 2005; Johnson et al., 2004). Low-energy electrons can also be produced through photoionization process such as on comet surfaces, or through bombardment by solar wind on icy surfaces (Bodewits et al., 2004). Present models use the laboratory penetration data of high-energy (>10 keV) electrons through silicon as a proxy for the ice (Cooper et al., 2001), normalized by the density of the medium. So far no laboratory studies have been conducted that deal with the penetration of electrons through amorphous or crystalline ices. In order to address this issue, we adopted a new experimental strategy by using aromatic molecules as probes. To begin with, we carried out systematic studies on the penetration depths of low-energy electrons (5 eV - 2 keV) through amorphous ice films of defined thickness at cryogenic temperatures (5 - 30 K). The results of these experiments will be analyzed and their relevance to survival of organic material on solar system icy surfaces will be presented. References: Bodewits, D., et al., 2004. X-ray and Far-Ultraviolet emission from comets: Relevant charge exchange processes. Physica Scripta. 70, C17-C20. Cooper, J. F., et al., 2001. Energetic ion and electron irradiation of the icy Galilean satellites. Icarus. 149, 133-159. Herring-Captain, J., et al., 2005. Low-energy (5-250 eV) electron-stimulated desorption of H+, H2+, and H+(H2O)nfrom low-temperature water ice surfaces. Physical Review B. 72, 035431-10. Johnson, R. E., et al., Radiation Effects on the Surfaces of the Galilean Satellites. In: F. Bagenal, et al., Eds

To melt is not enough: Retention of volatile species through internal processing in icy bodies

NASA Astrophysics Data System (ADS)

Sarid, G.; Stewart-Mukhopadhyay, S.

2014-07-01

The outer Solar System hosts a vast population of small icy bodies, considered to be primitive remnants from the planet-formation epoch. Early thermal and collisional processes affected such planetesimals to varying degrees depending on the time scale and dynamics of early planet growth. Recent observations have revealed that many large (>˜1000 km in diameter) transneptunian objects (TNOs) exhibit features of crystalline water ice in their surface spectra [1], as well as spectral features of more volatile ices, such as methane or hydrated ammonia [2]. These telltale observations should be accounted for when considering the alteration history and bulk processing of dwarf planets and their icy progeny. We will discuss preliminary calculations of early evolution scenarios for small icy-rocky bodies formed beyond the water-ice snow line. Such objects should also contain non-negligible fractions of pre-organic volatile compounds. The volatile composition and interior structure of these objects may change considerably due to internal heating and/or collisional modification prior to settling in their current (relatively quiescent) dynamical niches. Our initial model for the objects in question is that of a porous aggregate of various volatile compounds (as ices or trapped gases) and refractory silicate-metal solid grains, comprising the bulk matrix [3]. Chemical compositions for these objects are taken from existing simulations of chemical and dynamical evolution of disk material [4]. The key volatile species (e.g., H_2O, CO, CO_2, NH_3, CH_4, and CH_3OH) are also the most commonly observed in comets [5], which are remnants of such an early planetesimal population. Thermal and chemical internal evolution is examined self-consistently, as the abundances and locations of all species evolve, and we record mass ratios, temperatures, pressures, and porosity variations. The presence of volatile species in the interior can affect the overall heat balance and accompanied phase

Radiative Hydrodynamics and the Formation of Gas Giant Planets

NASA Astrophysics Data System (ADS)

Durisen, Richard H.

2009-05-01

Gas giant planets undoubtedly form from the orbiting gas and dust disks commonly observed around young stars, and there are two principal mechanisms proposed for how this may occur. The core accretion plus gas capture model argues that a solid core forms first and then accretes gas from the surrounding disk once the core becomes massive enough (about 10 Earth masses). The gas accumulation process is comparatively slow but becomes hydrodynamic at later times. The disk instability model alternatively suggests that gas giant planet formation is initiated by gas-phase gravitational instabilities (GIs) that fragment protoplanetary disks into bound gaseous protoplanets rapidly, on disk orbit period time scales. Solid cores then form more slowly by accretion of solid planetesimals and settling. The overall formation time scales for these two mechanisms can differ by orders of magnitude. Both involve multidimensional hydrodynamic flows at some phase, late in the process for core accretion and early on for disk instability. The ability of cores to accrete gas and the ability of GIs to produce bound clumps depend on how rapidly gas can lose energy by radiation. This regulatory process, while important for controlling the time scale for core accretion plus gas capture, turns out to be absolutely critical for disk instability to work at all. For this reason, I will focus in my talk on the use of radiation hydrodynamics simulations to determine whether and where disk instability can actually form gas giant planets in disks. Results remain controversial, but simulations by several different research groups support analytic arguments that disk instability leading to fragmentation probably cannot occur in disks around Sun-like stars at orbit radii of 10's of Earth-Sun distances or less. On the other hand, very recent simulations suggest that very young, rapidly accreting disks with much larger radii (100's of times the Sun-Earth distance) can indeed readily fragment by disk

The long-period librations of large synchronous icy moons

NASA Astrophysics Data System (ADS)

Yseboodt, Marie; Van Hoolst, Tim

2014-11-01

A moon in synchronous rotation has longitudinal librations because of its non-spherical mass distribution and its elliptical orbit around the planet. We study the long-period librations of the Galilean satellites and Titan and include deformation effects and the existence of a subsurface ocean. We take into account the fact that the orbit is not keplerian and has other periodicities than the main period of orbital motion around Jupiter or Saturn due to perturbations by the Sun, other planets and moons. An orbital theory is used to compute the orbital perturbations due to these other bodies. For Titan we also take into account the large atmospheric torque at the semi-annual period of Saturn around the Sun.We numerically evaluate the amplitude and phase of the long-period librations for many interior structure models of the icy moons constrained by the mass, radius and gravity field.

Numerical modelling of the formation process of planets from protoplanetary cloud

NASA Technical Reports Server (NTRS)

Kozlov, N. N.; Eneyev, T. M.

1979-01-01

Evolution of the plane protoplanetary cloud, consisting of a great number of gravitationally interacting and uniting under collision bodies (protoplanets) moving in the central field of a large mass (the Sun or a planet), is considered. It is shown that in the course of protoplanetary cloud evolution the ring zones of matter expansion and compression occur with the subsequent development leading to formation of planets, rotating about their axes mainly directly. The principal numerical results were obtained through digital simulation of planetary accumulation.

An extrasolar planetary system with three Neptune-mass planets.

PubMed

Lovis, Christophe; Mayor, Michel; Pepe, Francesco; Alibert, Yann; Benz, Willy; Bouchy, François; Correia, Alexandre C M; Laskar, Jacques; Mordasini, Christoph; Queloz, Didier; Santos, Nuno C; Udry, Stéphane; Bertaux, Jean-Loup; Sivan, Jean-Pierre

2006-05-18

Over the past two years, the search for low-mass extrasolar planets has led to the detection of seven so-called 'hot Neptunes' or 'super-Earths' around Sun-like stars. These planets have masses 5-20 times larger than the Earth and are mainly found on close-in orbits with periods of 2-15 days. Here we report a system of three Neptune-mass planets with periods of 8.67, 31.6 and 197 days, orbiting the nearby star HD 69830. This star was already known to show an infrared excess possibly caused by an asteroid belt within 1 au (the Sun-Earth distance). Simulations show that the system is in a dynamically stable configuration. Theoretical calculations favour a mainly rocky composition for both inner planets, while the outer planet probably has a significant gaseous envelope surrounding its rocky/icy core; the outer planet orbits within the habitable zone of this star.

Planet Formation in Small Separation Binaries: Not so Secularly Excited by the Companion

NASA Astrophysics Data System (ADS)

Rafikov, Roman R.

2013-03-01

The existence of planets in binaries with relatively small separations (around 20 AU), such as α Centauri or γ Cephei, poses severe challenges to standard planet formation theories. The problem lies in the vigorous secular excitation of planetesimal eccentricities at separations of several AU, where some of the planets are found, by the massive, eccentric stellar companions. High relative velocities of planetesimals preclude their growth in mutual collisions for a wide range of sizes, from below 1 km up to several hundred km, resulting in a fragmentation barrier to planet formation. Here we show that, for the case of an axisymmetric circumstellar protoplanetary disk, the rapid apsidal precession of planetesimal orbits caused by the disk gravity acts to strongly reduce the direct secular eccentricity excitation by the companion, lowering planetesimal velocities by an order of magnitude or even more at 1 AU. By examining the details of planetesimal dynamics, we demonstrate that this effect eliminates the fragmentation barrier for in situ growth of planetesimals as small as <~ 10 km even at separations as wide as 2.6 AU (the semimajor axis of the giant planet in HD 196885), provided that the circumstellar protoplanetary disk has a small eccentricity and is relatively massive, ~0.1 M ⊙.

The effects of circumstellar gas on terrestrial planet formation: Theory and observation

NASA Astrophysics Data System (ADS)

Mandell, Avram M.

Our understanding of the evolution of circumstellar material from dust and gas to fully-formed planets has taken dramatic steps forward in the last decade, driven by rapid improvements in our ability to study gas- and dust-rich disks around young stars and the discovery of more than 200 extra-solar planetary systems around other stars. In addition, our ability to model the formation of both terrestrial and giant planets has improved significantly due to new computing techniques and the continued exponential increase in computing power. In this dissertation I expand on existing theories of terrestrial planet formation to include systems similar to those currently being detected around nearby stars, and I develop new observational techniques to probe the chemistry of gas-rich circumstellar disks where such planetary systems may be forming. One of the most significant characteristics of observed extrasolar planetary systems is the presence of giant planets located much closer to their parent star than was thought to be possible. The presence of "Hot Jupiters", Jovian-mass planets with very short orbital periods detected around nearby main sequence stars, has been proposed to be primarily due to the inward migration of planets formed in orbits initially much further from the parent star. Close-in giant planets are thought to have formed in the cold outer regions of planetary systems and migrated inward, passing through the orbital parameter space occupied by the terrestrial planets in our own Solar System; the migration of these planets would have profound effects on the evolution of inner terrestrial planets in these systems. I first explore this scenario with numerical simulations showing that a significant fraction of terrestrial planets could survive the migration process; damping forces could then eventually re-circularize the orbits at distances relatively close to their original positions. Calculations suggest that the final orbits of a significant fraction of

Theoretical studies of the radar properties of the icy Galilean moons of Jupiter

NASA Technical Reports Server (NTRS)

Eshleman, Von R.

1993-01-01

The icy Galilean satellites of Jupiter - Europa, Ganymede, and Callisto - have unusual radar scattering properties compared with those of the terrestrial planets or Earth's Moon. There are three main features of the data that distinguish these targets: (1) the radar cross-section normalized by the geometrical cross-section is an order of magnitude larger than that of any terrestrial planet; (2) the reflected power is almost evenly distributed between two orthogonal polarizations with more power being returned in the same circular polarization as was transmitted whereas virtually all of the power returned from the terrestrial planets is contained in the opposite circular polarization to the one that was transmitted; and (3) the echo power spectra have a broad shape indicating a nearly uniformly radar-bright surface in contrast to the spectra from the terrestrial planets that contain a strong quasi-specular component from the vicinity of the sub-radar point and very little reflected power from the rest of the surface. The normalized radar cross-sections decrease as the areal water ice coverage decreases from Europa to Ganymede to Callisto. Recently, radar echoes from the polar caps of Mars and Mercury, and from Saturn's satellite Titan imply similarly strong cross-sections and have classically unexpected polarization properties and it is also thought that this is due to the presence of ice on the surface. A model called the radar glory model is analyzed and it is shown that the main features of the radar echoes calculated from this model agree well with the observations from all three icy Galilean satellites. This model involves long radar paths in the ice below the surface and special structures in which the refractive index decreases abruptly at a hemispherical boundary. It is not known whether such structures exist or how they could be created, but possible scenarios can be imagined such as the formation of an impact crater followed by deposition of a frost layer

The Formation of Terrestrial Planets from the Direct Accretion of Pebbles

NASA Astrophysics Data System (ADS)

Levison, Harold F.; Kretke, Katherine; Walsh, Kevin

2014-11-01

A radical new scenario has recently been suggested for the formation of giant planet cores that reports to solve this long-standing problem. This scenario, known as pebble accretion, envisions: 1) Planetesimals form directly from millimeter- to meter-sized objects (the pebbles) that are concentrated by turbulent eddies and then gravitationally collapse to form 100 — 1000 km objects (Cuzzi+ 2008, AJ 687, 1432; Johansen+ 2007, Nature 448, 1022). 2) These planetesimals quickly sweep up the remaining pebbles because their capture cross sections are significantly enhanced by aerodynamic drag (Lambrechts & Johansen 2012, A&A 544, A32; Ormel & Klahr (2010) A&A Volume 520, id.A43). Calculations show that a single 1000 km object embedded in a swarm of pebbles can grow to ~10 Earth-masses in less than 10,000 years. These short timescales present a problem in the terrestrial planet region because it took many tens of millions of years for the Earth to form (Touboul+ 2007, Nature 450, 1206). However, recent full-scale simulations of core formation have shown that the only way to grow a small number of giant planets in the Solar System is for the pebbles to form over a long period of time (Kretke & Levison 2014, AJ, submitted; Levison & Kretke in prep.) in a process we call 'Slow Pebble Accretion'. Thus, here we will present preliminary results of a study of slow pebble accretion in the terrestrial planet zone.

Convection and plate tectonics on extrasolar planets

NASA Astrophysics Data System (ADS)

Sotin, C.; Grasset, O.; Schubert, G.

2012-04-01

The number of potential Earth-like exoplanets is still very limited compared to the overall number of detected exoplanets. But the different methods keep improving, giving hope for this number to increase significantly in the coming years. Based on the relationship between mass and radius, two of the easiest parameters that can be known for exoplanets, four categories of planets have been identified: (i) the gas giants including hot Jupiters, (ii) the icy giants that can be like their solar system cousins Uranus and Neptune or that can have lost their H2-He atmosphere and have become the so-called ocean planets, (iii) the Earth-like planets with a fraction of silicates and iron similar to that of the Earth, and (iv) the Mercury like planet that have a much larger fraction of iron. The hunt for exoplanets is very much focused on Earth-like planets because of the desire to find alien forms of life and the science goal to understand how life started and developed on Earth. One science question is whether heat transfer by subsolidus convection can lead to plate tectonics, a process that allows material to be recycled in the interior on timescales of hundreds of millions of years. Earth-like exoplanets may have conditions quite different from Earth. For example, COROT-7b is so close to its star that it is likely locked in synchronous orbit with one very hot hemisphere and one very cold hemisphere. It is also worth noting that among the three Earth-like planets of the solar system (Earth, Venus and Mars), only Earth is subject to plate tectonics at present time. Venus may have experienced plate tectonics before the resurfacing event that erased any clue that such a process existed. This study investigates some of the parameters that can influence the transition from stagnant-lid convection to mobile-lid convection. Numerical simulations of convective heat transfer have been performed in 3D spherical geometry in order to determine the stress field generated by convection

PENTACLE: Parallelized particle-particle particle-tree code for planet formation

NASA Astrophysics Data System (ADS)

Iwasawa, Masaki; Oshino, Shoichi; Fujii, Michiko S.; Hori, Yasunori

2017-10-01

We have newly developed a parallelized particle-particle particle-tree code for planet formation, PENTACLE, which is a parallelized hybrid N-body integrator executed on a CPU-based (super)computer. PENTACLE uses a fourth-order Hermite algorithm to calculate gravitational interactions between particles within a cut-off radius and a Barnes-Hut tree method for gravity from particles beyond. It also implements an open-source library designed for full automatic parallelization of particle simulations, FDPS (Framework for Developing Particle Simulator), to parallelize a Barnes-Hut tree algorithm for a memory-distributed supercomputer. These allow us to handle 1-10 million particles in a high-resolution N-body simulation on CPU clusters for collisional dynamics, including physical collisions in a planetesimal disc. In this paper, we show the performance and the accuracy of PENTACLE in terms of \\tilde{R}_cut and a time-step Δt. It turns out that the accuracy of a hybrid N-body simulation is controlled through Δ t / \\tilde{R}_cut and Δ t / \\tilde{R}_cut ˜ 0.1 is necessary to simulate accurately the accretion process of a planet for ≥106 yr. For all those interested in large-scale particle simulations, PENTACLE, customized for planet formation, will be freely available from https://github.com/PENTACLE-Team/PENTACLE under the MIT licence.

New steps in testing the Tidal Downsizing hypothesis for planet formation

NASA Astrophysics Data System (ADS)

Nayakshin, S.

2013-09-01

Broadly speaking, there are two opposite views on how planet formation proceeds. The first of these is the Core Accretion (CA), a well established theory in which assembly of all planets occurs in the bottom-up direction. The second one is a modified gravitational disc in- stability model, which originally was thought to form only giant gaseous planets at large distances from the tar (e.g., Rafikov 2005). Now it emerges that migrating gaseous clumps may form not only giant planets but also terrestrial-like planets if dust sediments into the cores and the clumps' gas is removed by tidal disruption (Boley et al 2010, Nayakshin 2010; also reviewed in the upcoming PPVI by Helled et al 2013). This top-down scenario is referred to as "Tidal Downsizing" (TD) hypothesis. While TD hypothesis may potentially explain all of planet populations at any separation from the parent star (as planets migrate from 100 AU all the way to their disruption at ˜0.1 AU; Nayakshin and Lodato 2012), this scenario is currently in the embryonic state and needs further detailed calculations. Here we present several new calculations aimed at testing the theory with observations of exoplanets and young accreting stars possibly in the process of planet formation. (1) Nayakshin (2011) proposed that young massive "hot jupiters" may actually be tidally disrupted by the gravity of their parent stars if they migrate inward too quickly. If a significant fraction of dust grains managed to sediment into the centres of these gas clumps before they are disrupted, the solid cores are left behind as hot super-Earths and "hot neptunes". The discplanet interaction before and during planet disruption was modelled in detail by Nayakshin and Lodato (2012), who showed that the process of tidal disruption produces FU-Ori like accretion events onto the parent star. This model thus may account for both the hot planets observed and episodic accretion of young stars (Dunham and Vorobyov 2012). Another crucial prediction

Heating of Porous Icy Dust Aggregates

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

Sirono, Sin-iti

At the beginning of planetary formation, highly porous dust aggregates are formed through coagulation of dust grains. Outside the snowline, the main component of an aggregate is H{sub 2}O ice. Because H{sub 2}O ice is formed in amorphous form, its thermal conductivity is extremely small. Therefore, the thermal conductivity of an icy dust aggregate is low. There is a possibility of heating inside an aggregate owing to the decay of radionuclides. It is shown that the temperature increases substantially inside an aggregate, leading to crystallization of amorphous ice. During the crystallization, the temperature further increases sufficiently to continue sintering. Themore » mechanical properties of icy dust aggregates change, and the collisional evolution of dust aggregates is affected by the sintering.« less

Steamworlds: Atmospheric Structure and Critical Mass of Planets Accreting Icy Pebbles

NASA Astrophysics Data System (ADS)

Chambers, John

2017-11-01

In the core accretion model, gas-giant planets first form a solid core, which then accretes gas from a protoplanetary disk when the core exceeds a critical mass. Here, we model the atmosphere of a core that grows by accreting ice-rich pebbles. The ice fraction of pebbles evaporates in warm regions of the atmosphere, saturating it with water vapor. Excess water precipitates to lower altitudes. Beneath an outer radiative region, the atmosphere is convective, following a moist adiabat in saturated regions due to water condensation and precipitation. Atmospheric mass, density, and temperature increase with core mass. For nominal model parameters, planets with core masses (ice + rock) between 0.08 and 0.16 Earth masses have surface temperatures between 273 and 647 K and form an ocean. In more massive planets, water exists as a supercritical convecting fluid mixed with gas from the disk. Typically, the core mass reaches a maximum (the critical mass) as a function of the total mass when the core is 2-5 Earth masses. The critical mass depends in a complicated way on pebble size, mass flux, and dust opacity due to the occasional appearance of multiple core-mass maxima. The core mass for an atmosphere of 50% hydrogen and helium may be a more robust indicator of the onset of gas accretion. This mass is typically 1-3 Earth masses for pebbles that are 50% ice by mass, increasing with opacity and pebble flux and decreasing with pebble ice/rock ratio.

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.

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.

Accurate Treatment of Collisions and Water-Delivery in Models of Terrestrial Planet Formation

NASA Astrophysics Data System (ADS)

Haghighipour, Nader; Maindl, Thomas; Schaefer, Christoph

2017-10-01

It is widely accepted that collisions among solid bodies, ignited by their interactions with planetary embryos is the key process in the formation of terrestrial planets and transport of volatiles and chemical compounds to their accretion zones. Unfortunately, due to computational complexities, these collisions are often treated in a rudimentary way. Impacts are considered to be perfectly inelastic and volatiles are considered to be fully transferred from one object to the other. This perfect-merging assumption has profound effects on the mass and composition of final planetary bodies as it grossly overestimates the masses of these objects and the amounts of volatiles and chemical elements transferred to them. It also entirely neglects collisional-loss of volatiles (e.g., water) and draws an unrealistic connection between these properties and the chemical structure of the protoplanetary disk (i.e., the location of their original carriers). We have developed a new and comprehensive methodology to simulate growth of embryos to planetary bodies where we use a combination of SPH and N-body codes to accurately model collisions as well as the transport/transfer of chemical compounds. Our methodology accounts for the loss of volatiles (e.g., ice sublimation) during the orbital evolution of their careers and accurately tracks their transfer from one body to another. Results of our simulations show that traditional N-body modeling of terrestrial planet formation overestimates the amount of the mass and water contents of the final planets by over 60% implying that not only the amount of water they suggest is far from being realistic, small planets such as Mars can also form in these simulations when collisions are treated properly. We will present details of our methodology and discuss its implications for terrestrial planet formation and water delivery to Earth.

Debris disks as signposts of terrestrial planet formation. II. Dependence of exoplanet architectures on giant planet and disk properties

NASA Astrophysics Data System (ADS)

Raymond, S. N.; Armitage, P. J.; Moro-Martín, A.; Booth, M.; Wyatt, M. C.; Armstrong, J. C.; Mandell, A. M.; Selsis, F.; West, A. A.

2012-05-01

We present models for the formation of terrestrial planets, and the collisional evolution of debris disks, in planetary systems that contain multiple marginally unstable gas giants. We previously showed that in such systems, the dynamics of the giant planets introduces a correlation between the presence of terrestrial planets and cold dust, i.e., debris disks, which is particularly pronounced at λ ~ 70 μm. Here we present new simulations that show that this connection is qualitatively robust to a range of parameters: the mass distribution of the giant planets, the width and mass distribution of the outer planetesimal disk, and the presence of gas in the disk when the giant planets become unstable. We discuss how variations in these parameters affect the evolution. We find that systems with equal-mass giant planets undergo the most violent instabilities, and that these destroy both terrestrial planets and the outer planetesimal disks that produce debris disks. In contrast, systems with low-mass giant planets efficiently produce both terrestrial planets and debris disks. A large fraction of systems with low-mass (M ≲ 30 M⊕) outermost giant planets have final planetary separations that, scaled to the planets' masses, are as large or larger than the Saturn-Uranus and Uranus-Neptune separations in the solar system. We find that the gaps between these planets are not only dynamically stable to test particles, but are frequently populated by planetesimals. The possibility of planetesimal belts between outer giant planets should be taken into account when interpreting debris disk SEDs. In addition, the presence of ~ Earth-mass "seeds" in outer planetesimal disks causes the disks to radially spread to colder temperatures, and leads to a slow depletion of the outer planetesimal disk from the inside out. We argue that this may explain the very low frequency of >1 Gyr-old solar-type stars with observed 24 μm excesses. Our simulations do not sample the full range of

Thermodynamics of giant planet formation: shocking hot surfaces on circumplanetary discs

NASA Astrophysics Data System (ADS)

Szulágyi, J.; Mordasini, C.

2017-02-01

The luminosity of young giant planets can inform about their formation and accretion history. The directly imaged planets detected so far are consistent with the `hot-start' scenario of high entropy and luminosity. If nebular gas passes through a shock front before being accreted into a protoplanet, the entropy can be substantially altered. To investigate this, we present high-resolution, three-dimensional radiative hydrodynamic simulations of accreting giant planets. The accreted gas is found to fall with supersonic speed in the gap from the circumstellar disc's upper layers on to the surface of the circumplanetary disc and polar region of the protoplanet. There it shocks, creating an extended hot supercritical shock surface. This shock front is optically thick; therefore, it can conceal the planet's intrinsic luminosity beneath. The gas in the vertical influx has high entropy which when passing through the shock front decreases significantly while the gas becomes part of the disc and protoplanet. This shows that circumplanetary discs play a key role in regulating a planet's thermodynamic state. Our simulations furthermore indicate that around the shock surface extended regions of atomic - sometimes ionized - hydrogen develop. Therefore, circumplanetary disc shock surfaces could influence significantly the observational appearance of forming gas giants.

Possible formation pathways for the low-density Neptune-mass planet HAT-P-26b

NASA Astrophysics Data System (ADS)

Ali-Dib, Mohamad; Lakhlani, Gunjan

2018-01-01

We investigate possible pathways for the formation of the low-density Neptune-mass planet HAT-P-26b. We use two different formation models based on pebble and planetesimal accretion, and includes gas accretion, disc migration and simple photoevaporation. The models track the atmospheric oxygen abundance, in addition to the orbital period, and mass of the forming planets, which we compare to HAT-P-26b. We find that pebble accretion can explain this planet more naturally than planetesimal accretion that fails completely unless we artificially enhance the disc metallicity significantly. Pebble accretion models can reproduce HAT-P-26b with either a high initial core mass and low amount of envelope enrichment through core erosion or pebbles dissolution, or the opposite, with both scenarios being possible. Assuming a low envelope enrichment factor as expected from convection theory and comparable to the values we can infer from the D/H measurements in Uranus and Neptune, our most probable formation pathway for HAT-P-26b is through pebble accretion starting around 10 au early in the disc's lifetime.

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.

Glaciers and Ice Sheets As Analog Environments of Potentially Habitable Icy Worlds

PubMed Central

Garcia-Lopez, Eva; Cid, Cristina

2017-01-01

Icy worlds in the solar system and beyond have attracted a remarkable attention as possible habitats for life. The current consideration about whether life exists beyond Earth is based on our knowledge of life in terrestrial cold environments. On Earth, glaciers and ice sheets have been considered uninhabited for a long time as they seemed too hostile to harbor life. However, these environments are unique biomes dominated by microbial communities which maintain active biochemical routes. Thanks to techniques such as microscopy and more recently DNA sequencing methods, a great biodiversity of prokaryote and eukaryote microorganisms have been discovered. These microorganisms are adapted to a harsh environment, in which the most extreme features are the lack of liquid water, extremely cold temperatures, high solar radiation and nutrient shortage. Here we compare the environmental characteristics of icy worlds, and the environmental characteristics of terrestrial glaciers and ice sheets in order to address some interesting questions: (i) which are the characteristics of habitability known for the frozen worlds, and which could be compatible with life, (ii) what are the environmental characteristics of terrestrial glaciers and ice sheets that can be life-limiting, (iii) What are the microbial communities of prokaryotic and eukaryotic microorganisms that can live in them, and (iv) taking into account these observations, could any of these planets or satellites meet the conditions of habitability? In this review, the icy worlds are considered from the point of view of astrobiological exploration. With the aim of determining whether icy worlds could be potentially habitable, they have been compared with the environmental features of glaciers and ice sheets on Earth. We also reviewed some field and laboratory investigations about microorganisms that live in analog environments of icy worlds, where they are not only viable but also metabolically active. PMID:28804477

Glaciers and Ice Sheets As Analog Environments of Potentially Habitable Icy Worlds.

PubMed

Garcia-Lopez, Eva; Cid, Cristina

2017-01-01

Icy worlds in the solar system and beyond have attracted a remarkable attention as possible habitats for life. The current consideration about whether life exists beyond Earth is based on our knowledge of life in terrestrial cold environments. On Earth, glaciers and ice sheets have been considered uninhabited for a long time as they seemed too hostile to harbor life. However, these environments are unique biomes dominated by microbial communities which maintain active biochemical routes. Thanks to techniques such as microscopy and more recently DNA sequencing methods, a great biodiversity of prokaryote and eukaryote microorganisms have been discovered. These microorganisms are adapted to a harsh environment, in which the most extreme features are the lack of liquid water, extremely cold temperatures, high solar radiation and nutrient shortage. Here we compare the environmental characteristics of icy worlds, and the environmental characteristics of terrestrial glaciers and ice sheets in order to address some interesting questions: (i) which are the characteristics of habitability known for the frozen worlds, and which could be compatible with life, (ii) what are the environmental characteristics of terrestrial glaciers and ice sheets that can be life-limiting, (iii) What are the microbial communities of prokaryotic and eukaryotic microorganisms that can live in them, and (iv) taking into account these observations, could any of these planets or satellites meet the conditions of habitability? In this review, the icy worlds are considered from the point of view of astrobiological exploration. With the aim of determining whether icy worlds could be potentially habitable, they have been compared with the environmental features of glaciers and ice sheets on Earth. We also reviewed some field and laboratory investigations about microorganisms that live in analog environments of icy worlds, where they are not only viable but also metabolically active.

Anelastic tidal dissipation in multi-layer planets

NASA Astrophysics Data System (ADS)

Remus, F.; Mathis, S.; Zahn, J.-P.; Lainey, V.

2012-09-01

Earth-like planets have anelastic mantles, whereas giant planets may have anelastic cores. As for the fluid parts of a body, the tidal dissipation of such solid regions, gravitationally perturbed by a companion body, highly depends on its internal friction, and thus on its internal structure. Therefore, modelling this kind of interaction presents a high interest to provide constraints on planets interiors, whose properties are still quite uncertain. Here, we examine the equilibrium tide in the solid part of a planet, taking into account the presence of a fluid envelope. We derive the different Love numbers that describe its deformation and discuss the dependence of the quality factor Q on the chosen anelastic model and the size of the core. Taking plausible values for the anelastic parameters, and discussing the frequency-dependence of the solid dissipation, we show how this mechanism may compete with the dissipation in fluid layers, when applied to Jupiter- and Saturn-like planets. We also discuss the case of the icy giants Uranus and Neptune. Finally, we present the way to implement the results in the equations that describe the dynamical evolution of planetary systems.

Formation Of the Giant Planets By Concurrent Accretion Of Solids And Gas

NASA Technical Reports Server (NTRS)

Pollack, James B.; Hubickyj, Olenka; Bodenheimer, Peter; Lissauer, Jack J.; Podolak, Morris; Greenzweig, Yuval; Cuzzi, Jeffery N. (Technical Monitor)

1995-01-01

New numerical simulations of the formation of the giant planets are presented, in which for the first time both the gas and planetesimal accretion rates are calculated in a self-consistent, interactive fashion. The simulations combine three elements: 1) three-body accretion cross-sections of solids onto an isolated planetary embryo, 2) a stellar evolution code for the planet's gaseous envelope, and 3) a planetesimal dissolution code within the envelope, used to evaluate the planet's effective capture radius and the energy deposition profile of accreted material. Major assumptions include: The planet is embedded in a disk of gas and small planetesimals with locally uniform initial surface mass density, and planetesimals are not allowed to migrate into or out of the planet's feeding zone. All simulations are characterized by three major phases. During the first phase, the planet's mass consists primarily of solid material. The planetesimal accretion rate, which dominates that of gas, rapidly increases owing to runaway accretion, then decreases as the planet's feeding zone is depleted. During the second phase, both solid and gas accretion rates are small and nearly independent of time. The third phase, marked by runaway gas accretion, starts when the solid and gas masses are about equal. It is engendered by a strong positive feedback on the gas accretion rates, driven by the rapid contraction of the gaseous envelope and the rapid expansion of the outer boundary, which depends on the planet's total mass. The overall evolutionary time scale is generally determined by the length of the second phase. The actual rates at which the giant planets accreted small planetesimals is probably intermediate between the constant rates assumed in most previous studies and the highly variable rates that we have used. Within the context, of the adopted model of planetesimal accretion, the joint constraints of the time scale for dissipation of the solar nebula and the current high

Unraveling the Reaction Chemistry of Icy Ocean World Surfaces

NASA Astrophysics Data System (ADS)

Hudson, R.; Loeffler, M. J.; Gerakines, P.

2017-12-01

The diverse endogenic chemistry of ocean worlds can be divided among interior, surface, and above-surface process, with contributions from exogenic agents such as solar, cosmic, and magnetospheric radiation. Bombardment from micrometeorites to comets also can influence chemistry by both delivering new materials and altering pre-existing ones, and providing energy to drive reactions. Geological processes further complicate the chemistry by transporting materials from one environment to another. In this presentation the focus will be on some of the thermally driven and radiation-induced changes expected from icy materials, primarily covalent and ionic compounds. Low-temperature conversions of a few relatively simple molecules into ions possessing distinct infrared (IR) features will be covered, with an emphasis on such features as might be identified through either orbiting spacecraft or landers. The low-temperature degradation of a few bioorganic molecules, such as DNA nucleobases and some common amino acids, will be used as examples of the more complex, and potentially misleading, chemistry expected for icy moons of the outer solar system. This work was supported by NASA's Emerging Worlds and Outer Planets Research programs, as well as the NASA Astrobiology Institute's Goddard Center for Astrobiology.

New Insights on Planet Formation in WASP-47 from a Simultaneous Analysis of Radial Velocities and Transit Timing Variations

NASA Astrophysics Data System (ADS)

Weiss, Lauren M.; Deck, Katherine M.; Sinukoff, Evan; Petigura, Erik A.; Agol, Eric; Lee, Eve J.; Becker, Juliette C.; Howard, Andrew W.; Isaacson, Howard; Crossfield, Ian J. M.; Fulton, Benjamin J.; Hirsch, Lea; Benneke, Björn

2017-06-01

Measuring precise planet masses, densities, and orbital dynamics in individual planetary systems is an important pathway toward understanding planet formation. The WASP-47 system has an unusual architecture that motivates a complex formation theory. The system includes a hot Jupiter (“b”) neighbored by interior (“e”) and exterior (“d”) sub-Neptunes, and a long-period eccentric giant planet (“c”). We simultaneously modeled transit times from the Kepler K2 mission and 118 radial velocities to determine the precise masses, densities, and Keplerian orbital elements of the WASP-47 planets. Combining RVs and TTVs provides a better estimate of the mass of planet d (13.6+/- 2.0 {M}\\oplus ) than that obtained with only RVs (12.75+/- 2.70 {M}\\oplus ) or TTVs (16.1+/- 3.8 {M}\\oplus ). Planets e and d have high densities for their size, consistent with a history of photoevaporation and/or formation in a volatile-poor environment. Through our RV and TTV analysis, we find that the planetary orbits have eccentricities similar to the solar system planets. The WASP-47 system has three similarities to our own solar system: (1) the planetary orbits are nearly circular and coplanar, (2) the planets are not trapped in mean motion resonances, and (3) the planets have diverse compositions. None of the current single-process exoplanet formation theories adequately reproduce these three characteristics of the WASP-47 system (or our solar system). We propose that WASP-47, like the solar system, formed in two stages: first, the giant planets formed in a gas-rich disk and migrated to their present locations, and second, the high-density sub-Neptunes formed in situ in a gas-poor environment.

Searching for signatures of planet formation in stars with circumstellar debris discs

NASA Astrophysics Data System (ADS)

Maldonado, J.; Eiroa, C.; Villaver, E.; Montesinos, B.; Mora, A.

2015-07-01

Context. Tentative correlations between the presence of dusty circumstellar debris discs and low-mass planets have recently been presented. In parallel, detailed chemical abundance studies have reported different trends between samples of planet and non-planet hosts. Whether these chemical differences are indeed related to the presence of planets is still strongly debated. Aims: We aim to test whether solar-type stars with debris discs show any chemical peculiarity that could be related to the planet formation process. Methods: We determine in a homogeneous way the metallicity, [Fe/H], and abundances of individual elements of a sample of 251 stars including stars with known debris discs, stars harbouring simultaneously debris discs and planets, stars hosting exclusively planets, and a comparison sample of stars without known discs or planets. High-resolution échelle spectra (R ~ 57 000) from 2-3 m class telescopes are used. Our methodology includes the calculation of the fundamental stellar parameters (Teff, log g, microturbulent velocity, and metallicity) by applying the iron ionisation and equilibrium conditions to several isolated Fe i and Fe ii lines, as well as individual abundances of C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn. Results: No significant differences have been found in metallicity, individual abundances or abundance-condensation temperature trends between stars with debris discs and stars with neither debris nor planets. Stars with debris discs and planets have the same metallicity behaviour as stars hosting planets, and they also show a similar ⟨[ X/Fe ] ⟩ - TC trend. Different behaviour in the ⟨[ X/Fe ] ⟩ - TC trends is found between the samples of stars without planets and the samples of planet hosts. In particular, when considering only refractory elements, negative slopes are shown in cool giant planet hosts, whilst positive ones are shown in stars hosting low-mass planets. The statistical significance of the

TRAPPIST-1 Planets - Flyaround Animation

NASA Image and Video Library

2017-02-22

This frame from a video depicts artist concepts of each of the seven planets orbiting TRAPPIST-1, an ultra-cool dwarf stars. Over 21 days, NASA's Spitzer Space Telescope measured the drop in light as each planet passed in front of the star. Spitzer was able to identify a total of seven rocky worlds, including three in the habitable zone where life is possible. The study established the planets' size, distance from their sun and, for some of them, their approximate mass and density. It also established that some, if not all, these planets are tidally locked, meaning one face of the planet permanently faces their sun. The planets appear in the order of innermost to outermost planets. These artist's concepts were designed as follows: TRAPPIST-1b, closest to the star, was modeled on Jupiter's moon Io, which has volcanic features due to strong gravitational tugs. TRAPPIST-1c is shown as a rocky, warm world with a small ice cap on the side that never faces the star. TRAPPSIT-1d is rocky and has water only in a thin band along the terminator, dividing the day side and night side. TRAPPIST-1e and TRAPPIST-1f are both shown covered in water, but with progressively larger ice caps on the night side. TRAPPIST-1g is portrayed with an atmosphere like Neptune's, although it is still a rocky world. The farthest planet, TRAPPIST-1h, is shown as covered in ice, similar to Jupiter's icy moon Europa. The background stars are what you would see if you were in the TRAPPIST-1 system. Orion passes behind the planets, recognizable but distorted from what we're familiar with, in addition to Taurus and Pleiades. A video is available at http://photojournal.jpl.nasa.gov/catalog/PIA21468

Polymerization of Building Blocks of Life on Europa and Other Icy Moons.

PubMed

Kimura, Jun; Kitadai, Norio

2015-06-01

The outer Solar System may provide a potential habitat for extraterrestrial life. Remote sensing data from the Galileo spacecraft suggest that the jovian icy moons--Europa, Ganymede, and possibly Callisto--may harbor liquid water oceans underneath their icy crusts. Although compositional information required for the discussion of habitability is limited because of significantly restricted observation data, organic molecules are ubiquitous in the Universe. Recently, in situ spacecraft measurements and experiments suggest that amino acids can be formed abiotically on interstellar ices and comets. These amino acids could be continuously delivered by meteorite or comet impacts to icy moons. Here, we show that polymerization of organic monomers, in particular amino acids and nucleotides, could proceed spontaneously in the cold environment of icy moons, in particular the jovian icy moon Europa as a typical example, based on thermodynamic calculations, though kinetics of formation are not addressed. Observed surface temperature on Europa is 120 and 80 K in the equatorial region and polar region, respectively. At such low temperatures, Gibbs energies of polymerization become negative, and the estimated thermal structure of the icy crust should contain a shallow region (i.e., at a depth of only a few kilometers) favorable for polymerization. Investigation of the possibility of organic monomer polymerization on icy moons could provide good constraints on the origin and early evolution of extraterrestrial life.

Gas in Debris Disks and the Volatiles of Terrestrial Planet Formation

NASA Technical Reports Server (NTRS)

Kuchner, Marc

2010-01-01

Debris disks are a kind of protoplanetary disk that likely corresponds to the epoch of terrestrial planet and outer planet formation. Previously pictured to be gas-free, some debris disks are now revealing gas components, sometimes with strikingly non-solar abundance patterns. Understanding the nature and distribution of this gas may eventually help us understand the origin of volatiles on the Earth, the carbon depletion of the asteroids, and even the origin of life. I'll describe what we know about these systems observationally, some of the leading hypotheses about the sources and sinks of the gas, and how these new astronomical discoveries may bear on solar-system science.

Protoplanetary Disks and Planet Formation a Computational Perspective

NASA Astrophysics Data System (ADS)

Backus, Isaac

In this thesis I present my research on the early stages of planet formation. Using advanced computational modeling techniques, I study global gas and gravitational dynamics in proto- planetary disks (PPDs) on length scales from the radius of Jupiter to the size of the solar system. In that environment, I investigate the formation of gas giants and the migration, enhancement, and distribution of small solids--the precursors to planetesimals and gas giant cores. I examine numerical techniques used in planet formation and PPD modeling, especially methods for generating initial conditions (ICs) in these unstable, chaotic systems. Disk simulation outcomes may depend strongly on ICs, which may explain results in the literature. I present the largest suite of high resolution PPD simulations to-date and argue that direct fragmentations of PPDs around M-Dwarfs is a plausible path to rapidly forming gas giants. I implement dust physics to track the migration of centimeter and smaller dust grains in very high resolution PPD simulations. While current dust methods are slow, with strict resolution and/or time-stepping requirements, and have some serious numerical issues, we can still demonstrate that dust does not concentrate at the pressure maxima of spiral arms, an indication that spiral features observed in the dust component are at least as well resolved in the gas. Additionally, coherent spiral arms do not limit dust settling. We suggest a novel mechanism for disk fragmentation at large radii driven by dust accretion from the surrounding nebula. We also investigate self induced dust traps, a mechanism which may help explain the growth of solids beyond meter sizes. We argue that current apparent demonstrations of this mechanism may be due to numerical artifacts and require further investigation.

Alpha Elements' Effects on Planet Formation and the Hunt for Extragalactic Planets

NASA Astrophysics Data System (ADS)

Penny, Matthew; Rodriguez, Joseph E.; Beatty, Thomas; Zhou, George

2018-01-01

A star's likelihood of hosting a giant planet is well known to be strongly dependent on metallicity. However, little is known about what elements cause this correlation (e.g. bulk metals, iron, or alpha elements such as silicon and oxygen). This is likely because most planet searches target stars in the Galactic disk, and due to Galactic chemical evolution, alpha element abundances are themselves correlated with metallicity within a population. We investigate the feasibility of simultaneous transiting planet search towards the alpha-poor Sagittarius dwarf galaxy and alpha-rich Galactic bulge in a single field of view of DECam, that would enable a comparative study of planet frequency over an [alpha/Fe] baseline of ~0.4 dex. We show that a modestly sized survey could detect planet candidates in both populations, but that false positive rejection in Sgr Dwarf may be prohibitively expensive. Conversely, two-filter survey observations alone would be sufficient to rule out a large fraction of bulge false positives, enabling statistical validation of candidates with a modest follow-up investment. Although over a shorter [alpha/Fe] baseline, this survey would provide a test of whether it is alpha or iron that causes the planet metallicity correlation.

Carbon-rich Planets: Atmospheric Spectra, Thermal Inversions, And Formation Conditions

NASA Astrophysics Data System (ADS)

Madhusudhan, Nikku; Mousis, O.; Lunine, J.; Johnson, T.

2011-05-01

Carbon-rich planets (CRPs) are the exotic new members in the repertoire of extrasolar planets. The first CRP atmosphere was discovered recently, for the extremely irradiated hot Jupiter WASP-12b. In this work, we report several candidate carbon-rich planets amongst the known sample of transiting exoplanets, along with follow-up theoretical and observational efforts that aim at confirming these candidates. We also discuss the atmospheric chemistry and temperature structure of carbon-rich giant planets, their formation via core accretion, and the chemistry and apportionment of ices, rock, and volatiles in their envelopes. Our results show that CRP atmospheres probe a unique region in composition space, especially at high T. For C/O ≥ 1, most of the oxygen is occupied by CO for T > 1400 K and P < 1bar, causing a substantial depletion in water vapor, and an overabundance of methane compared to equilibrium chemistry with solar abundances. Adopting gas phase elemental abundances in the disk similar to those estimated in the star gives a C/O ratio in planetesimals and then in the envelope of WASP-12b similar to or below the solar C/O. Under these conditions, a C/O ratio of 1 in WASP-12b would require that the oxygen abundance in the disk is depleted by a factor of 0.41.

TRAPPIST-1 Planet Lineup

NASA Image and Video Library

2017-02-22

This artist's concept shows what the TRAPPIST-1 planetary system may look like, based on available data about the planets' diameters, masses and distances from the host star. The system has been revealed through observations from NASA's Spitzer Space Telescope and the ground-based TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) telescope, as well as other ground-based observatories. The system was named for the TRAPPIST telescope. The seven planets of TRAPPIST-1 are all Earth-sized and terrestrial, according to research published in 2017 in the journal Nature. TRAPPIST-1 is an ultra-cool dwarf star in the constellation Aquarius, and its planets orbit very close to it. They are likely all tidally locked, meaning the same face of the planet is always pointed at the star, as the same side of our moon is always pointed at Earth. This creates a perpetual night side and perpetual day side on each planet. TRAPPIST-1b and c receive the most light from the star and would be the warmest. TRAPPIST-1e, f and g all orbit in the habitable zone, the area where liquid water is most likely to be detected. But any of the planets could potentially harbor liquid water, depending on their compositions. In the imagined planets shown here, TRAPPIST-1b is shown as a larger analogue to Jupiter's moon Io. TRAPPIST-1d is depicted with a narrow band of water near the terminator, the divide between a hot, dry day and an ice-covered night side. TRAPPIST-1e and TRAPPIST-1f are both shown covered in water, but with progressively larger ice caps on the night side. TRAPPIST-1g is portrayed with an atmosphere like Neptune's, although it is still a rocky world. TRAPPIST-1h, the farthest from the star, would be the coldest. It is portrayed here as an icy world, similar to Jupiter's moon Europa, but the least is known about it. http://photojournal.jpl.nasa.gov/catalog/PIA21422

An Overview of the Formation and Attitude Control System for the Terrestrial Planet Finder Formation Flying Interferometer

NASA Technical Reports Server (NTRS)

Scharf, Daniel P.; Hadaegh, Fred Y.; Rahman, Zahidul H.; Shields, Joel F.; Singh, Gurkipal; Wette, Matthew R.

2004-01-01

The Terrestrial Planet Finder formation flying Interferometer (TPF-I) will be a five-spacecraft, precision formation operating near the second Sun-Earth Lagrange point. As part of technology development for TPF-I, a formation and attitude control system (FACS) is being developed that achieves the precision and functionality needed for the TPF-I formation and that will be demonstrated in a distributed, real-time simulation environment. In this paper we present an overview of FACS and discuss in detail its formation estimation, guidance and control architectures and algorithms. Since FACS is currently being integrated into a high-fidelity simulation environment, component simulations demonstrating algorithm performance are presented.

An Overview of the Formation and Attitude Control System for the Terrestrial Planet Finder Formation Flying Interferometer

NASA Technical Reports Server (NTRS)

Scharf, Daniel P.; Hadaegh, Fred Y.; Rahman, Zahidul H.; Shields, Joel F.; Singh, Gurkipal

2004-01-01

The Terrestrial Planet Finder formation flying Interferometer (TPF-I) will be a five-spacecraft, precision formation operating near a Sun-Earth Lagrange point. As part of technology development for TPF-I, a formation and attitude control system (FACS) is being developed that achieves the precision and functionality associated with the TPF-I formation. This FACS will be demonstrated in a distributed, real-time simulation environment. In this paper we present an overview of the FACS and discuss in detail its constituent formation estimation, guidance and control architectures and algorithms. Since the FACS is currently being integrated into a high-fidelity simulation environment, component simulations demonstrating algorithm performance are presented.

Extrasolar Planets

NASA Astrophysics Data System (ADS)

Deeg, Hans; Belmonte, Juan Antonio; Aparicio, Antonio

2012-03-01

Participants; Preface; Acknowledgements; 1. Extrasolar planet detection methods Laurance R. Doyle; 2. Statistical properties of exoplanets Stéphane Udry; 3. Characterizing extrasolar planets Timothy M. Brown; 4. From clouds to planet systems: formation and evolution of stars and planets Günther Wuchterl; 5. Abundances in stars with extrasolar planetary systems Garik Israelian; 6. Brown dwarfs: the bridge between stars and planets Rafael Rebolo; 7. The perspective: a panorama of the Solar System Agustín Sánchez-Lavega; 8. Habitable planets around the Sun and other stars James F. Kasting; 9. Biomarkers of extrasolar planets and their observability Franck Selsis, Jimmy Paillet and France Allard; Index.

Analyzing surface features on icy satellites using a new two-layer analogue model

NASA Astrophysics Data System (ADS)

Morales, K. M.; Leonard, E. J.; Pappalardo, R. T.; Yin, A.

2017-12-01

The appearance of similar surface morphologies across many icy satellites suggests potentially unified formation mechanisms. Constraining the processes that shape the surfaces of these icy worlds is fundamental to understanding their rheology and thermal evolution—factors that have implications for potential habitability. Analogue models have proven useful for investigating and quantifying surface structure formation on Earth, but have only been sparsely applied to icy bodies. In this study, we employ an innovative two-layer analogue model that simulates a warm, ductile ice layer overlain by brittle surface ice on satellites such as Europa and Enceladus. The top, brittle layer is composed of fine-grained sand while the ductile, lower viscosity layer is made of putty. These materials were chosen because they scale up reasonably to the conditions on Europa and Enceladus. Using this analogue model, we investigate the role of the ductile layer in forming contractional structures (e.g. folds) that would compensate for the over-abundance of extensional features observed on icy satellites. We do this by simulating different compressional scenarios in the analogue model and analyzing whether the resulting features resemble those on icy bodies. If the resulting structures are similar, then the model can be used to quantify the deformation by calculating strain. These values can then be scaled up to Europa or Enceladus and used to quantity the observed surface morphologies and the amount of extensional strain accommodated by certain features. This presentation will focus on the resulting surface morphologies and the calculated strain values from several analogue experiments. The methods and findings from this work can then be expanded and used to study other icy bodies, such as Triton, Miranda, Ariel, and Pluto.

JUpiter ICy moons Explorer (JUICE): An ESA mission to orbit Ganymede and to characterise the Jupiter system

NASA Astrophysics Data System (ADS)

Grasset, O.; Dougherty, M. K.; Coustenis, A.; Bunce, E. J.; Erd, C.; Titov, D.; Blanc, M.; Coates, A.; Drossart, P.; Fletcher, L. N.; Hussmann, H.; Jaumann, R.; Krupp, N.; Lebreton, J.-P.; Prieto-Ballesteros, O.; Tortora, P.; Tosi, F.; Van Hoolst, T.

2013-04-01

Past exploration of Jupiter's diverse satellite system has forever changed our understanding of the unique environments to be found around gas giants, both in our solar system and beyond. The detailed investigation of three of Jupiter's Galilean satellites (Ganymede, Europa, and Callisto), which are believed to harbour subsurface water oceans, is central to elucidating the conditions for habitability of icy worlds in planetary systems in general. The study of the Jupiter system and the possible existence of habitable environments offer the best opportunity for understanding the origins and formation of the gas giants and their satellite systems. The JUpiter ICy moons Explorer (JUICE) mission, selected by ESA in May 2012 to be the first large mission within the Cosmic Vision Program 2015-2025, will perform detailed investigations of Jupiter and its system in all their inter-relations and complexity with particular emphasis on Ganymede as a planetary body and potential habitat. The investigations of the neighbouring moons, Europa and Callisto, will complete a comparative picture of the Galilean moons and their potential habitability. Here we describe the scientific motivation for this exciting new European-led exploration of the Jupiter system in the context of our current knowledge and future aspirations for exploration, and the paradigm it will bring in the study of giant (exo) planets in general.

Two-phase convection in the high-pressure ice layer of the large icy moons: geodynamical implications

NASA Astrophysics Data System (ADS)

Kalousova, K.; Sotin, C.; Tobie, G.; Choblet, G.; Grasset, O.

2015-12-01

The H2O layers of large icy satellites such as Ganymede, Callisto, or Titan probably include a liquid water ocean sandwiched between the deep high-pressure ice layer and the outer ice I shell [1]. It has been recently suggested that the high-pressure ice layer could be decoupled from the silicate core by a salty liquid water layer [2]. However, it is not clear whether accumulation of liquids at the bottom of the high-pressure layer is possible due to positive buoyancy of water with respect to high-pressure ice. Numerical simulation of this two-phase (i.e. ice and water) problem is challenging, which explains why very few studies have self-consistently handled the presence and transport of liquids within the solid ice [e.g. 3]. While using a simplified description of water production and transport, it was recently showed in [4] that (i) a significant fraction of the high-pressure layer reaches the melting point and (ii) the melt generation and its extraction to the overlying ocean significantly influence the global thermal evolution and interior structure of the large icy moons.Here, we treat the high-pressure ice layer as a compressible mixture of solid ice and liquid water [5]. Several aspects are investigated: (i) the effect of the water formation on the vigor of solid-state convection and its influence on the amount of heat that is transferred from the silicate mantle to the ocean; (ii) the fate of liquids within the upper thermal boundary layer - whether they freeze or reach the ocean; and (iii) the effect of salts and volatile compounds (potentially released from the rocky core) on the melting/freezing processes. Investigation of these aspects will allow us to address the thermo-chemical evolution of the internal ocean which is crucial to evaluate the astrobiological potential of large icy moons. This work has been performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. [1] Hussmann et al. (2007), Treatise of

Gas-phase spectra of MgO molecules: a possible connection from gas-phase molecules to planet formation

NASA Astrophysics Data System (ADS)

Kloska, Katherine A.; Fortenberry, Ryan C.

2018-02-01

A more fine-tuned method for probing planet-forming regions, such as protoplanetary discs, could be rovibrational molecular spectroscopy observation of particular premineral molecules instead of more common but ultimately less related volatile organic compounds. Planets are created when grains aggregate, but how molecules form grains is an ongoing topic of discussion in astrophysics and planetary science. Using the spectroscopic data of molecules specifically involved in mineral formation could help to map regions where planet formation is believed to be occurring in order to examine the interplay between gas and dust. Four atoms are frequently associated with planetary formation: Fe, Si, Mg and O. Magnesium, in particular, has been shown to be in higher relative abundance in planet-hosting stars. Magnesium oxide crystals comprise the mineral periclase making it the chemically simplest magnesium-bearing mineral and a natural choice for analysis. The monomer, dimer and trimer forms of (MgO)n with n = 1-3 are analysed in this work using high-level quantum chemical computations known to produce accurate results. Strong vibrational transitions at 12.5, 15.0 and 16.5 μm are indicative of magnesium oxide monomer, dimer and trimer making these wavelengths of particular interest for the observation of protoplanetary discs and even potentially planet-forming regions around stars. If such transitions are observed in emission from the accretion discs or absorptions from stellar spectra, the beginning stages of mineral and, subsequently, rocky body formation could be indicated.

The Delivery of Water During Terrestrial Planet Formation

NASA Astrophysics Data System (ADS)

O'Brien, David P.; Izidoro, Andre; Jacobson, Seth A.; Raymond, Sean N.; Rubie, David C.

2018-02-01

The planetary building blocks that formed in the terrestrial planet region were likely very dry, yet water is comparatively abundant on Earth. Here we review the various mechanisms proposed for the origin of water on the terrestrial planets. Various in-situ mechanisms have been suggested, which allow for the incorporation of water into the local planetesimals in the terrestrial planet region or into the planets themselves from local sources, although all of those mechanisms have difficulties. Comets have also been proposed as a source, although there may be problems fitting isotopic constraints, and the delivery efficiency is very low, such that it may be difficult to deliver even a single Earth ocean of water this way. The most promising route for water delivery is the accretion of material from beyond the snow line, similar to carbonaceous chondrites, that is scattered into the terrestrial planet region as the planets are growing. Two main scenarios are discussed in detail. First is the classical scenario in which the giant planets begin roughly in their final locations and the disk of planetesimals and embryos in the terrestrial planet region extends all the way into the outer asteroid belt region. Second is the Grand Tack scenario, where early inward and outward migration of the giant planets implants material from beyond the snow line into the asteroid belt and terrestrial planet region, where it can be accreted by the growing planets. Sufficient water is delivered to the terrestrial planets in both scenarios. While the Grand Tack scenario provides a better fit to most constraints, namely the small mass of Mars, planets may form too fast in the nominal case discussed here. This discrepancy may be reduced as a wider range of initial conditions is explored. Finally, we discuss several more recent models that may have important implications for water delivery to the terrestrial planets.

ICI Showcase House Prototype

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

None

2009-02-16

Building Science Corporation collaborated with ICI Homes in Daytona Beach, FL on a 2008 prototype Showcase House that demonstrates the energy efficiency and durability upgrades that ICI currently promotes through its in-house efficiency program called EFactor.

Development and Testing of a Laser-Powered Cryobot for Outer Planet Icy Moon Exploration

NASA Astrophysics Data System (ADS)

Siegel, V.; Stone, W.; Hogan, B.; Lelievre, S.; Flesher, C.

2013-12-01

Project VALKYRIE (Very-deep Autonomous Laser-powered Kilowatt-class Yo-yoing Robotic Ice Explorer) is a NASA-funded effort to develop the first laser powered cryobot - a self-contained intelligent ice penetrator capable of delivering science payloads through ice caps of the outer planet icy moons. The long range objective is to enable a full-scale Europa lander mission in which an autonomous life-searching underwater vehicle is transported by the cryobot and launched into the sub-surface Europan ocean. Mission readiness testing will involve an Antarctic sub-glacial lake cryobot sample return through kilometers of ice cap thickness. A key element of VALKYRIE's design is the use of a high energy laser as the primary power source. 1070 nm laser light is transmitted at a power level of 5 kW from a surface-based laser and injected into a custom-designed optical waveguide that is spooled out from the descending cryobot. Light exits the downstream end of the fiber, travels through diverging optics, and strikes a beam dump, which channels thermal power to hot water jets that melt the descent hole. Some beam energy is converted, via photovoltaic cells, to electricity for running onboard electronics and jet pumps. Since the vehicle can be sterilized prior to deployment and the melt path freezes behind it, preventing forward contamination, expansions on VALKYRIE concepts may enable cleaner and faster access to sub-glacial Antarctic lakes. Testing at Stone Aerospace between 2010 and 2013 has already demonstrated high power optical energy transfer over relevant (kilometer scale) distances as well as the feasibility of a vehicle-deployed optical waveguide (through which the power is transferred). The test vehicle is equipped with a forward-looking synthetic aperture radar (SAR) that can detect obstacles out to 1 kilometer from the vehicle. The initial ASTEP test vehicle will carry a science payload consisting of a DUV flow cytometer and a water sampling sub-system that will be

Polymerization of Building Blocks of Life on Europa and Other Icy Moons

PubMed Central

Kitadai, Norio

2015-01-01

Abstract The outer Solar System may provide a potential habitat for extraterrestrial life. Remote sensing data from the Galileo spacecraft suggest that the jovian icy moons—Europa, Ganymede, and possibly Callisto—may harbor liquid water oceans underneath their icy crusts. Although compositional information required for the discussion of habitability is limited because of significantly restricted observation data, organic molecules are ubiquitous in the Universe. Recently, in situ spacecraft measurements and experiments suggest that amino acids can be formed abiotically on interstellar ices and comets. These amino acids could be continuously delivered by meteorite or comet impacts to icy moons. Here, we show that polymerization of organic monomers, in particular amino acids and nucleotides, could proceed spontaneously in the cold environment of icy moons, in particular the jovian icy moon Europa as a typical example, based on thermodynamic calculations, though kinetics of formation are not addressed. Observed surface temperature on Europa is 120 and 80 K in the equatorial region and polar region, respectively. At such low temperatures, Gibbs energies of polymerization become negative, and the estimated thermal structure of the icy crust should contain a shallow region (i.e., at a depth of only a few kilometers) favorable for polymerization. Investigation of the possibility of organic monomer polymerization on icy moons could provide good constraints on the origin and early evolution of extraterrestrial life. Key Words: Planetary science—Europa—Planetary habitability and biosignatures—Extraterrestrial life—Extraterrestrial organic compounds. Astrobiology 15, 430–441. PMID:26060981

Formation of the Giant Planets by Concurrent Accretion of Solids and Gas

NASA Technical Reports Server (NTRS)

Hubickyj, Olenka

1997-01-01

Models were developed to simulate planet formation. Three major phases are characterized in the simulations: (1) planetesimal accretion rate, which dominates that of gas, rapidly increases owing to runaway accretion, then decreases as the planet's feeding zone is depleted; (2) occurs when both solid and gas accretion rates are small and nearly independent of time; and (3) starts when the solid and gas masses are about equal and is marked by runaway gas accretion. The models applicability to planets in our Solar System are judged using two basic "yardsticks". The results suggest that the solar nebula dissipated while Uranus and Neptune were in the second phase, during which, for a relatively long time, the masses of their gaseous envelopes were small but not negligible compared to the total masses. Background information, results and a published article are included in the report.

Planetesimal formation starts at the snow line

NASA Astrophysics Data System (ADS)

Drążkowska, J.; Alibert, Y.

2017-12-01

Context. The formation stage of planetesimals represents a major gap in our understanding of the planet formation process. Late-stage planet accretion models typically make arbitrary assumptions about planetesimal and pebble distribution, while dust evolution models predict that planetesimal formation is only possible at some orbital distances. Aims: We wish to test the importance of the water snow line in triggering the formation of the first planetesimals during the gas-rich phase of a protoplanetary disk, when cores of giant planets have to form. Methods: We connected prescriptions for gas disk evolution, dust growth and fragmentation, water ice evaporation and recondensation, the transport of both solids and water vapor, and planetesimal formation via streaming instability into a single one-dimensional model for protoplanetary disk evolution. Results: We find that processes taking place around the snow line facilitate planetesimal formation in two ways. First, because the sticking properties between wet and dry aggregates change, a "traffic jam" inside of the snow line slows the fall of solids onto the star. Second, ice evaporation and outward diffusion of water followed by its recondensation increases the abundance of icy pebbles that trigger planetesimal formation via streaming instability just outside of the snow line. Conclusions: Planetesimal formation is hindered by growth barriers and radial drift and thus requires particular conditions to take place. The snow line is a favorable location where planetesimal formation is possible for a wide range of conditions, but not in every protoplanetary disk model, however. This process is particularly promoted in large cool disks with low intrinsic turbulence and an increased initial dust-to-gas ratio. The movie attached to Fig. 3 is only available at http://www.aanda.org

Using the Bombardment History of the Moon to Understand Planet Formation

NASA Astrophysics Data System (ADS)

Bottke, W. F.; NASA/NLSI CenterLunar Origin; Evolution (CLOE)

2011-12-01

The Moon is unique. It is the only object that is both relatively accessible and still bears scars from practically every epoch of solar system formation. This is both a challenge and a blessing. It is a challenge because to understand the Moon's complex bombardment history, we need to understand the formation and evolution of the solar system as a whole. It is a blessing because the Moon is an irreplaceable resource for the study of events that have shaped the Earth and other planets. For example, we can now show the Moon's bombardment history can be broken into several episodes defined by planet formation processes. The earliest phase lasts for several hundreds of My after the first solids form. Here many planets grow via a new process called "planetesimal-driven migration", with embryos moving outward in the disk by gravitationally-scattering planetesimals. This mobility assists accretion and may explain the interesting properties of certain worlds (e.g., Mars). In the outer solar system, the giant planets form on different orbits than their observed ones via a variety of processes that we are still struggling to understand. The evidence they had a different configuration, however, can be found in (i) the orbital distribution of the asteroid belt, with particular unusual asteroids residing where Jupiter used to have its mean motion resonances, and (ii) in the lunar crater record, with the oldest craters formed at half the impact velocity than more recent ones. The lunar impact flux over this interval constrains how these worlds evolved. The second episode occurred near 4.1 Ga and is often called the "Nice model". It was triggered by a dynamical instability taking place among the giant planets, who quickly moved to their current orbits via interactions with both themselves and comet-like planetesimals scattered out of a disk residing beyond 12 AU. A by-product of this planetary reconfiguration was the ejection of comets and asteroids from stable reservoirs across

Architecture design study and technology road map for the Planet Formation Imager (PFI)

NASA Astrophysics Data System (ADS)

Monnier, John D.; Ireland, Michael J.; Kraus, Stefan; Baron, Fabien; Creech-Eakman, Michelle; Dong, Ruobing; Isella, Andrea; Merand, Antoine; Michael, Ernest; Minardi, Stefano; Mozurkewich, David; Petrov, Romain; Rinehart, Stephen; ten Brummelaar, Theo; Vasisht, Gautam; Wishnow, Ed; Young, John; Zhu, Zhaohuan

2016-08-01

The Planet Formation Imager (PFI) Project has formed a Technical Working Group (TWG) to explore possible facility architectures to meet the primary PFI science goal of imaging planet formation in situ in nearby starforming regions. The goals of being sensitive to dust emission on solar system scales and resolving the Hill-sphere around forming giant planets can best be accomplished through sub-milliarcsecond imaging in the thermal infrared. Exploiting the 8-13 micron atmospheric window, a ground-based long-baseline interferometer with approximately 20 apertures including 10km baselines will have the necessary resolution to image structure down 0.1 milliarcseconds (0.014 AU) for T Tauri disks in Taurus. Even with large telescopes, this array will not have the sensitivity to directly track fringes in the mid-infrared for our prime targets and a fringe tracking system will be necessary in the near-infrared. While a heterodyne architecture using modern mid-IR laser comb technology remains a competitive option (especially for the intriguing 24 and 40μm atmospheric windows), the prioritization of 3-5μm observations of CO/H2O vibrotational levels by the PFI-Science Working Group (SWG) pushes the TWG to require vacuum pipe beam transport with potentially cooled optics. We present here a preliminary study of simulated L- and N-band PFI observations of a realistic 4-planet disk simulation, finding 21x2.5m PFI can easily detect the accreting protoplanets in both L and N-band but can see non-accreting planets only in L band. We also find that even an ambitious PFI will lack sufficient surface brightness sensitivity to image details of the fainter emission from dust structures beyond 5 AU, unless directly illuminated or heated by local energy sources. That said, the utility of PFI at N-band is highly dependent on the stage of planet formation in the disk and we require additional systematic studies in conjunction with the PFI-SWG to better understand the science capabilities

Brine Pockets in the Icy Shell on Europa: Distribution, Chemistry, and Habitability

NASA Technical Reports Server (NTRS)

Zolotov, M. Yu; Shock, E. L.; Barr, A. C.; Pappalardo, R. T.

2004-01-01

On Earth, sea ice is rich in brine, salt, and gas inclusions that form through capturing of seawater during ice formation. Cooling of the ice over time leads to sequential freezing of captured sea-water, precipitation of salts, exsolution of gases, and formation of brine channels and pockets. Distribution and composition of brines in sea ice depend on the rate of ice formation, vertical temperature gradient, and the age of the ice. With aging, the abundance of brine pockets decreases through downward migration. De- spite low temperatures and elevated salinities, brines in sea ice provide a habitat for photosynthetic and chemosynthetic organisms. On Europa, brine pockets and channels could exist in the icy shell that may be from a few km to a few tens of km thick and is probably underlain by a water ocean. If the icy shell is relatively thick, convection could develop, affecting the temperature pattern in the ice. To predict the distribution and chemistry of brine pockets in the icy shell we have combined numerical models of the temperature distribution within a convecting shell, a model for oceanic chemistry, and a model for freezing of Europan oceanic water. Possible effects of brine and gas inclusions on ice rheology and tectonics are discussed.

Ocean-bearing planets near the ice line: How far does the water's edge go?

NASA Astrophysics Data System (ADS)

Gaidos, E.; Seager, S.; Gaudi, S.

2008-12-01

A leading theory for giant planet formation involves the accretion of a solid core, probably ice-rich, that in turn accretes a massive mantle of hydrogen-helium gas from a primordial disk. The relative timing of core formation and disappearance of nebular gas in a few millions of years is critical; the correlation between heavy element abundance in stellar photospheres and their propensity to host giant planets is cited as support for the theory. Conversely, systems that are relatively heavy element-poor or lose their gas earlier should contain either "failed" cores or a set of icy planetary embryos that did not accrete. Indeed, Uranus and Neptune may represent similar embryos that were scattered by Jupiter into the outer disk where they efficiently accreted planetesimals rich in volatiles with low condensation temperatures. We propose that a region straddling the "snowline" (3-5~AU for solar-mass stars) could frequently be inhabited by one or more water ice-rich, super-Earth-mass objects that accreted only a modest amount of nebular gas. We predict that metal-poor bulge and halo stars are more likely to host such objects. Current and future microlensing surveys will be able to determine the population of Earth-mass planets in this range of semimajor axes and test this hypothesis. If they are sufficiently frequent, the nearest examples will be detectable by the Space Interferometer Mission and perhaps a visible-light Terrestrial Planet Finder mission. We show that retention of a ~1~bar hydrogen-helium atmosphere is sufficient to maintain a surface water ocean, depending on semimajor axis and thermal history, and that sufficiently massive, "naked" ice planets can have interior oceans a la Europa. Planets with more substantial (>200~bar) atmospheres will be devoid of a liquid water phase at the surface. The existence of a surface water ocean could be inferred by the absence of highly soluble molecules such as NH3 or SO2 in the atmosphere. Objects with such oceans

TOWARD A DETERMINISTIC MODEL OF PLANETARY FORMATION. VII. ECCENTRICITY DISTRIBUTION OF GAS GIANTS

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

Ida, S.; Lin, D. N. C.; Nagasawa, M., E-mail: ida@geo.titech.ac.jp, E-mail: lin@ucolick.org, E-mail: nagasawa.m.ad@m.titech.ac.jp

2013-09-20

The ubiquity of planets and diversity of planetary systems reveal that planet formation encompasses many complex and competing processes. In this series of papers, we develop and upgrade a population synthesis model as a tool to identify the dominant physical effects and to calibrate the range of physical conditions. Recent planet searches have led to the discovery of many multiple-planet systems. Any theoretical models of their origins must take into account dynamical interactions between emerging protoplanets. Here, we introduce a prescription to approximate the close encounters between multiple planets. We apply this method to simulate the growth, migration, and dynamicalmore » interaction of planetary systems. Our models show that in relatively massive disks, several gas giants and rocky/icy planets emerge, migrate, and undergo dynamical instability. Secular perturbation between planets leads to orbital crossings, eccentricity excitation, and planetary ejection. In disks with modest masses, two or less gas giants form with multiple super-Earths. Orbital stability in these systems is generally maintained and they retain the kinematic structure after gas in their natal disks is depleted. These results reproduce the observed planetary mass-eccentricity and semimajor axis-eccentricity correlations. They also suggest that emerging gas giants can scatter residual cores to the outer disk regions. Subsequent in situ gas accretion onto these cores can lead to the formation of distant (∼> 30 AU) gas giants with nearly circular orbits.« less

Exobiology of icy satellites

NASA Astrophysics Data System (ADS)

Simakov, M. B.

At the beginning of 2004 the total number of discovered planets near other stars was 119 All of them are massive giants and met practically in all orbits In a habitable zone from 0 8 up to 1 1 AU at less 11 planets has been found starting with HD 134987 and up to HD 4203 It would be naive to suppose existence of life in unique known to us amino-nucleic acid form on the gas-liquid giant planets Nevertheless conditions for onset and evolutions of life can be realized on hypothetical satellites extrasolar planets All giant planets of the Solar system have a big number of satellites 61 of Jupiter 52 of Saturn known in 2003 A small part of them consist very large bodies quite comparable to planets of terrestrial type but including very significant share of water ice Some from them have an atmosphere E g the mass of a column of the Titan s atmosphere exceeds 15 times the mass of the Earth atmosphere column Formation or capture of satellites is a natural phenomenon and satellite systems definitely should exist at extrasolar planets A hypothetical satellite of the planet HD 28185 with a dense enough atmosphere and hydrosphere could have biosphere of terrestrial type within the limits of our notion about an origin of terrestrial biosphere As an example we can see on Titan the largest satellite of Saturn which has a dense nitrogen atmosphere and a large quantity of liquid water under ice cover and so has a great exobiological significance The most recent models of the Titan s interior lead to the conclusion that a substantial liquid layer

Planetary Protection for future missions to Europa and other icy moons: the more things change...

NASA Astrophysics Data System (ADS)

Conley, C. A.; Race, M.

2007-12-01

NASA maintains a planetary protection policy regarding contamination of extraterrestrial bodies by terrestrial microorganisms and organic compounds, and sets limits intended to minimize or prevent contamination resulting from spaceflight missions. Europa continues to be a high priority target for astrobiological investigations, and other icy moons of the outer planets are becoming increasingly interesting as data are returned from current missions. In 2000, a study was released by the NRC that provided recommendations on preventing the forward contamination of Europa. This study addressed a number of issues, including cleaning and sterilization requirements, the applicability of protocols derived from Viking and other missions to Mars, and the need to supplement spore based culture methods in assessing spacecraft bioload. The committee also identified a number of future studies that would improve knowledge of Europa and better define issues related to forward contamination of that body. The standard recommended by the 2000 study and adopted by NASA uses a probabilistic approach, such that spacecraft sent to Europa must demonstrate a probability less than 10-4 per mission of contaminating an europan ocean with one viable terrestrial organism. A number of factors enter into the equation for calculating this probability, including at least bioload at launch, probability of survival during flight, probability of reaching the surface of Europa, and probability of reaching an europan ocean. Recently, the NASA Planetary Protection Subcommittee of the NASA Advisory Council has recommended that the probabilistic approach recommended for Europa be applied to all outer planet icy moons, until another NRC study can be convened to reevaluate the issues in light of recent data. This presentation will discuss the status of current and anticipated planetary protection considerations for missions to Europa and other icy moons.

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.

Planet Formation in Stellar Binaries: How Disk Gravity Can Lower theFragmentation Barrier

NASA Astrophysics Data System (ADS)

Silsbee, Kedron; Rafikov, Roman R.

2014-11-01

Binary star systems present a challenge to current theories of planet formation. Perturbations from the companion star dynamically excite the protoplanetary disk, which can lead to destructive collisions between planetesimals, and prevent growth from 1 km to 100 km sized planetesimals. Despite this apparent barrier to coagulation, planets have been discovered within several small-separation (<20 AU), eccentric (eb 0.4) binaries, such as alpha Cen and gamma Cep. We address this problem by analytically exploring planetesimal dynamics under the simultaneous action of (1) binary perturbation, (2) gas drag (which tends to align planetesimal orbits), and (3), the gravity of an eccentric protoplanetary disk. We then use our dynamical solutions to assess the outcomes of planetesimal collisions (growth, destruction, erosion) for a variety of disk models. We find that planets in small-separation binaries can form at their present locations if the primordial protoplanetary disks were massive (>0.01M⊙) and not very eccentric (eccentricity of order several per cent at the location of planet). This constraint on the disk mass is compatible with the high masses of the giant planets in known gamma Cep-like binaries, which require a large mass reservoir for their formation. We show that for these massive disks, disk gravity is dominant over the gravity of the binary companion at the location of the observed planets. Therefore, planetesimal growth is highly sensitive to disk properties. The requirement of low disk eccentricity is in line with the recent hydrodynamic simulations that tend to show gaseous disks in eccentric binaries developing very low eccentricity, at the level of a few percent. A massive purely axisymmetric disk makes for a friendlier environment for planetesimal growth by driving rapid apsidal precession of planetesimals, and averaging out the eccentricity excitation from the binary companion. When the protoplanetary disk is eccentric we find that the most

Planet Imager Discovers Young Kuiper Belt

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-07-01

A debris disk just discovered around a nearby star is the closest thing yet seen to a young version of the Kuiper belt. This disk could be a key to better understanding the interactions between debris disks and planets, as well as how our solar system evolved early on in its lifetime. Hunting for an analog The best way to understand how the Kuiper belt — home to Pluto and thousands of other remnants of early icy planet formation in our solar system — developed would be to witness a similar debris disk in an earlier stage of its life. But before now, none of the disks we've discovered have been similar to our own: the rings are typically too large, the central star too massive, or the stars exist in regions very unlike what we think our Sun's birthplace was like. A collaboration led by Thayne Currie (National Astronomical Observatory of Japan) has changed this using the Gemini Planet Imager (GPI), part of a new generation of extreme adaptive-optics systems. The team discovered a debris disk of roughly the same size as the Kuiper belt orbiting the star HD 115600, located in the nearest OB association. The star is only slightly more massive than our Sun, and it lives in a star-forming region similar to the early Sun's environment. HD 115600 is different in one key way, however: it is only 15 million years old. This means that observing it gives us the perfect opportunity to observe how our solar system might have behaved when it was much younger. A promising future GPI's spatially-resolved spectroscopy, combined with measurements of the reflectivity of the disk, have led the team to suspect that the disk might be composed partly of water ice, just as the Kuiper belt is. The disk also shows evidence of having been sculpted by the motions of giant planets orbiting the central star, in much the same way as the outer planets of our solar system may have shaped the Kuiper belt. The observations of HD 115600 are some of the very first to emerge from GPI and the new

ICI/BASF PP for acrylics swap

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

Alperowicz, N.

ICI (London) and BASF (Ludwigshafen) have announced their long-awaited polypropylene (PP) for acrylics swap deal. ICI is buying BASF's European acrylic resin business, and the German firm will acquire ICI's European PP operations. The deal is due for completion by mid-1993, subject to regulatory approvals. BASF, hitherto a small-scale PP producer, doubles capacity to 600,000 m.t./year and moves up the European PP league to number three, behind Himont and Shell. BASF, whose process is used in the plants, secures a foothold in the UK PP market, where Shell - planning a merger with Himont - is the only other producer,more » with 170,000 m.t./year. ICI's purchase involves BASF's Resart GmbH and Critesa SA subsidiaries, located at Mainz, Germany and near Barcelona, Spain, respectively. The business - which will add about [Brit pounds]60 million ($93 million) to ICI Acrylics [Brit pounds]300-million revenues - employs 400 people, who will transfer to ICI.« less

A DEFINITION FOR GIANT PLANETS BASED ON THE MASS–DENSITY RELATIONSHIP

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

Hatzes, Artie P.; Rauer, Heike, E-mail: artie@tls-tautenburg.de, E-mail: Heike.Rauer@dlr.de

We present the mass–density relationship (log M − log ρ) for objects with masses ranging from planets (M ≈ 0.01 M{sub Jup}) to stars (M > 0.08 M{sub ⊙}). This relationship shows three distinct regions separated by a change in slope in the log M − log ρ plane. In particular, objects with masses in the range 0.3 M{sub Jup}–60 M{sub Jup} follow a tight linear relationship with no distinguishing feature to separate the low-mass end (giant planets) from the high-mass end (brown dwarfs). We propose a new definition of giant planets simply based on changes in the slope ofmore » the log M versus log ρ relationship. By this criterion, objects with masses less than ≈0.3 M{sub Jup} are low-mass planets, either icy or rocky. Giant planets cover the mass range 0.3 M{sub Jup}–60 M{sub Jup}. Analogous to the stellar main sequence, objects on the upper end of the giant planet sequence (brown dwarfs) can simply be referred to as “high-mass giant planets,” while planets with masses near that of Jupiter can be called “low-mass giant planets.”.« less

External supply of oxygen to the atmospheres of the giant planets.

PubMed

Feuchtgruber, H; Lellouch, E; de Graauw, T; Bézard, B; Encrenaz, T; Griffin, M

1997-09-11

The atmospheres of the giant planets are reducing, being mainly composed of hydrogen, helium and methane. But the rings and icy satellites that surround these planets, together with the flux of interplanetary dust, could act as important sources of oxygen, which would be delivered to the atmospheres mainly in the form of water ice or silicate dust. Here we report the detection, by infrared spectroscopy, of gaseous H2O in the upper atmospheres of Saturn, Uranus and Neptune. The implied H2O column densities are 1.5 x 10(15), 9 x 10(13) and 3 x 10(14) molecules cm(-2) respectively. CO2 in comparable amounts was also detected in the atmospheres of Saturn and Neptune. These observations can be accounted for by external fluxes of 10(5)-10(7) H2O molecules cm(-2) s(-1) and subsequent chemical processing in the atmospheres. The presence of gaseous water and infalling dust will affect the photochemistry, energy budget and ionospheric properties of these atmospheres. Moreover, our findings may help to constrain the injection rate and possible activity of distant icy objects in the Solar System.

The SEEDs of Planet Formation: Indirect Signatures of Giant Planets in Transitional Disks

NASA Technical Reports Server (NTRS)

Grady, Carol; Currie, T.

2012-01-01

We live in a planetary system with 2 gas giant planets, and as a resu lt of RV, transit, microlensing, and transit timing studies have ide ntified hundreds of giant planet candidates in the past 15 years. Su ch studies have preferentially concentrated on older, low activity So lar analogs, and thus tell us little about .when, where, and how gian t planets form in their disks, or how frequently they form in disks associated with intermediate-mass stars.

Exploring Disks Around Planets

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-07-01

Giant planets are thought to form in circumstellar disks surrounding young stars, but material may also accrete into a smaller disk around the planet. Weve never detected one of these circumplanetary disks before but thanks to new simulations, we now have a better idea of what to look for.Image from previous work simulating a Jupiter-mass planet forming inside a circumstellar disk. The planet has its own circumplanetary disk of accreted material. [Frdric Masset]Elusive DisksIn the formation of giant planets, we think the final phase consists of accretion onto the planet from a disk that surrounds it. This circumplanetary disk is important to understand, since it both regulates the late gas accretion and forms the birthplace of future satellites of the planet.Weve yet to detect a circumplanetary disk thus far, because the resolution needed to spot one has been out of reach. Now, however, were entering an era where the disk and its kinematics may be observable with high-powered telescopes (like the Atacama Large Millimeter Array).To prepare for such observations, we need models that predict the basic characteristics of these disks like the mass, temperature, and kinematic properties. Now a researcher at the ETH Zrich Institute for Astronomy in Switzerland, Judit Szulgyi, has worked toward this goal.Simulating CoolingSzulgyi performs a series of 3D global radiative hydrodynamic simulations of 1, 3, 5, and 10 Jupiter-mass (MJ) giant planets and their surrounding circumplanetary disks, embedded within the larger circumstellar disk around the central star.Density (left column), temperature (center), and normalized angular momentum (right) for a 1 MJ planet over temperatures cooling from 10,000 K (top) to 1,000 K (bottom). At high temperatures, a spherical circumplanetary envelope surrounds the planet, but as the planet cools, the envelope transitions around 64,000 K to a flattened disk. [Szulgyi 2017]This work explores the effects of different planet temperatures and

Large Impact Features on Saturn's Middle-sized Icy Satellites: Global Image Mosaics and Topography

NASA Technical Reports Server (NTRS)

Schenk, P. M.; Moore, J. M.; McKinnon, W. B.

2003-01-01

With the approach of Cassini to the Saturn system, attention naturally focuses on the planet, its rings and Titan, but the Saturn system is also populated by a number of smaller satellites. The seven middle-sized icy satellites, along with those of Uranus, (between 400 and 1500 km wide) are distinctly different geophysically and geologically from their much larger Galilean-class brethren [e.g., 1]. Topographic mapping of these bodies is a critical part of understanding their geologic evolution. Here we describe our recent efforts to map the topography of these satellites using Voyager data.

TERRESTRIAL PLANET FORMATION FROM AN ANNULUS

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

Walsh, Kevin J.; Levison, Harold F., E-mail: kwalsh@boulder.swri.edu

It has been shown that some aspects of the terrestrial planets can be explained, particularly the Earth/Mars mass ratio, when they form from a truncated disk with an outer edge near 1.0 au. This has been previously modeled starting from an intermediate stage of growth utilizing pre-formed planetary embryos. We present simulations that were designed to test this idea by following the growth process from km-sized objects located between 0.7 and 1.0 au up to terrestrial planets. The simulations explore initial conditions where the solids in the disk are planetesimals with radii initially between 3 and 300 km, alternately includingmore » effects from a dissipating gaseous solar nebula and collisional fragmentation. We use a new Lagrangian code known as LIPAD, which is a particle-based code that models the fragmentation, accretion, and dynamical evolution of a large number of planetesimals, and can model the entire growth process from km-sizes up to planets. A suite of large (∼ Mars mass) planetary embryos is complete in only ∼1 Myr, containing most of the system mass. A quiescent period then persists for 10–20 Myr characterized by slow diffusion of the orbits and continued accretion of the remaining planetesimals. This is interrupted by an instability that leads to embryos crossing orbits and embryo–embryo impacts that eventually produce the final set of planets. While this evolution is different than that found in other works exploring an annulus, the final planetary systems are similar, with roughly the correct number of planets and good Mars-analogs.« less

Aqua-planet simulations of the formation of the South Atlantic convergence zone

NASA Technical Reports Server (NTRS)

Nieto Ferreira, Rosana; Chao, Winston C.

2013-01-01

The impact of Amazon Basin convection and cold fronts on the formation and maintenance of the South Atlantic convergence zone (SACZ) is studied using aqua-planet simulations with a general circulation model. In the model, a circular patch of warm sea-surface temperature (SST) is used to mimic the effect of the Amazon Basin on South American monsoon convection. The aqua-planet simulations were designed to study the effect of the strength and latitude of Amazon Basin convection on the formation of the SACZ. The simulations indicate that the strength of the SACZ increases as the Amazon convection intensifies and is moved away from the equator. Of the two controls studied here, the latitude of the Amazon convection exerts the strongest effect on the strength of the SACZ. An analysis of the synoptic-scale variability in the simulations shows the importance of frontal systems in the formation of the aqua-planet SACZ. Composite time series of frontal systems that occurred in the simulations show that a robust SACZ occurs when fronts penetrate into the subtropics and become stationary there as they cross eastward of the longitude of the Amazon Basin. Moisture convergence associated with these frontal systems produces rainfall not along the model SACZ region and along a large portion of the northern model Amazon Basin. Simulations in which the warm SST patch was too weak or too close to the equator did not produce frontal systems that extended into the tropics and became stationary, and did not form a SACZ. In the model, the SACZ forms as Amazon Basin convection strengthens and migrates far enough southward to allow frontal systems to penetrate into the tropics and stall over South America. This result is in agreement with observations that the SACZ tends to form after the onset of the monsoon season in the Amazon Basin.

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

Physics and Chemistry of Star and Planet Formation in the Alma ERA

NASA Astrophysics Data System (ADS)

Bergin, Edwin

2014-06-01

ALMA will open up new avenues of exploration encompassing the wide range of star formation in our galaxy and peering into the central heart of planet-forming circumstellar disks. As we seek to explore the origins of stars and planets molecular emission will be at the front and center of many studies probing gas physics and chemistry. In this talk I will discus some of the areas where we can expect significant advances due to the increased sensitivity and superb spatial resolution of ALMA. In star-forming cores, a rich chemistry is revealed that may be the simpler molecular precursors to more complex organics, such as amino acids, seen within primitive rocks in our own solar system. ALMA will provide new information regarding the relative spatial distribution within a given source for a host of organics, sampling tens to hundreds of transitions of a variety of molecules, including presumably new ones. In this area there is a rich synergy with existing ground and space-based data, including Herschel/Spitzer. Here the increased sampling of sources to be enabled by ALMA should bring greater clarity toward the key products of interstellar chemistry and further constrain processes. On smaller Solar System scales, for over a decade most observations of planet-forming disks focused on the dust thermal continuum emission as a probe of the gas content and structure. ALMA will enable reliable and direct studies of gas to explore the evolving physics of planet-formation, the gas dissipation timescales (i.e. the upper limit to the timescale for giant planet birth), and also the chemistry. It is this chemistry that sets the composition of gas giants and also influences the ultimate composition of water and organic materials that are delivered to terrestrial worlds. Here I will show how we can use molecular emission to determine the gas thermal structure of a disk system and the total gas content - key astrophysical quantities. This will also enable more constrained chemical

Ejection of rocky and icy material from binary star systems: implications for the origin and composition of 1I/`Oumuamua

NASA Astrophysics Data System (ADS)

Jackson, Alan P.; Tamayo, Daniel; Hammond, Noah; Ali-Dib, Mohamad; Rein, Hanno

2018-06-01

In single-star systems like our own Solar system, comets dominate the mass budget of bodies ejected into interstellar space, since they form further away and are less tightly bound. However, 1I/`Oumuamua, the first interstellar object detected, appears asteroidal in its spectra and lack of detectable activity. We argue that the galactic budget of interstellar objects like 1I/`Oumuamua should be dominated by planetesimal material ejected during planet formation in circumbinary systems, rather than in single-star systems or widely separated binaries. We further show that in circumbinary systems, rocky bodies should be ejected in comparable numbers to icy ones. This suggests that a substantial fraction of interstellar objects discovered in future should display an active coma. We find that the rocky population, of which 1I/`Oumuamua seems to be a member, should be predominantly sourced from A-type and late B-star binaries.

ICIS Model

EPA Pesticide Factsheets

The Integrated Compliance Information System (ICIS) is a web-based system that provides information for the federal enforcement and compliance (FE&C) and the National Pollutant Discharge Elimination System (NPDES) programs.

Chondrule-forming Shock Fronts in the Solar Nebula: A Possible Unified Scenario for Planet and Chondrite Formation

NASA Astrophysics Data System (ADS)

Boss, A. P.; Durisen, R. H.

2005-03-01

Chondrules are millimeter-sized spherules found throughout primitive chondritic meteorites. Flash heating by a shock front is the leading explanation of their formation. However, identifying a mechanism for creating shock fronts inside the solar nebula has been difficult. In a gaseous disk capable of forming Jupiter, the disk must have been marginally gravitationally unstable at and beyond Jupiter's orbit. We show that this instability can drive inward spiral shock fronts with shock speeds of up to ~10 km s-1 at asteroidal orbits, sufficient to account for chondrule formation. The mixing and transport of solids in such a disk, combined with the planet-forming tendencies of gravitational instabilities, results in a unified scenario linking chondrite production with gas giant planet formation.

Stochasticity and predictability in terrestrial planet formation

NASA Astrophysics Data System (ADS)

Hoffmann, Volker; Grimm, Simon L.; Moore, Ben; Stadel, Joachim

2017-02-01

Terrestrial planets are thought to be the result of a vast number of gravitational interactions and collisions between smaller bodies. We use numerical simulations to show that practically identical initial conditions result in a wide array of final planetary configurations. This is a result of the chaotic evolution of trajectories which are highly sensitive to minuscule displacements. We determine that differences between systems evolved from virtually identical initial conditions can be larger than the differences between systems evolved from very different initial conditions. This implies that individual simulations lack predictive power. For example, there is not a reproducible mapping between the initial and final surface density profiles. However, some key global properties can still be extracted if the statistical spread across many simulations is considered. Based on these spreads, we explore the collisional growth and orbital properties of terrestrial planets, which assemble from different initial conditions (we vary the initial planetesimal distribution, planetesimal masses, and giant planet orbits.). Confirming past work, we find that the resulting planetary systems are sculpted by sweeping secular resonances. Configurations with giant planets on eccentric orbits produce fewer and more massive terrestrial planets on tighter orbits than those with giants on circular orbits. This is further enhanced if the initial mass distribution is biased to the inner regions. In all cases, the outer edge of the system is set by the final location of the ν6 resonance and we find that the mass distribution peaks at the ν5 resonance. Using existing observations, we find that extrasolar systems follow similar trends. Although differences between our numerical modelling and exoplanetary systems remain, we suggest that CoRoT-7, HD 20003 and HD 20781 may host undetected giant planets.

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

Steamworlds: Atmospheric Structure and Critical Mass of Planets Accreting Icy Pebbles

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

Chambers, John, E-mail: jchambers@carnegiescience.edu

In the core accretion model, gas-giant planets first form a solid core, which then accretes gas from a protoplanetary disk when the core exceeds a critical mass. Here, we model the atmosphere of a core that grows by accreting ice-rich pebbles. The ice fraction of pebbles evaporates in warm regions of the atmosphere, saturating it with water vapor. Excess water precipitates to lower altitudes. Beneath an outer radiative region, the atmosphere is convective, following a moist adiabat in saturated regions due to water condensation and precipitation. Atmospheric mass, density, and temperature increase with core mass. For nominal model parameters, planetsmore » with core masses (ice + rock) between 0.08 and 0.16 Earth masses have surface temperatures between 273 and 647 K and form an ocean. In more massive planets, water exists as a supercritical convecting fluid mixed with gas from the disk. Typically, the core mass reaches a maximum (the critical mass) as a function of the total mass when the core is 2–5 Earth masses. The critical mass depends in a complicated way on pebble size, mass flux, and dust opacity due to the occasional appearance of multiple core-mass maxima. The core mass for an atmosphere of 50% hydrogen and helium may be a more robust indicator of the onset of gas accretion. This mass is typically 1–3 Earth masses for pebbles that are 50% ice by mass, increasing with opacity and pebble flux and decreasing with pebble ice/rock ratio.« less

It's Far, It's Small, It's Cool: It's an Icy Exoplanet!

NASA Astrophysics Data System (ADS)

2006-01-01

Using a network of telescopes scattered across the globe, including the Danish 1.54m telescope at ESO La Silla (Chile), astronomers [1] discovered a new extrasolar planet significantly more Earth-like than any other planet found so far. The planet, which is only about 5 times as massive as the Earth, circles its parent star in about 10 years. It is the least massive exoplanet around an ordinary star detected so far and also the coolest [2]. The planet most certainly has a rocky/icy surface. Its discovery marks a groundbreaking result in the search for planets that support life. ESO PR Photo 03a/06 ESO PR Photo 03a/06 Artist's Impression of the Newly Found Exoplanet The new planet, designated by the unglamorous identifier of OGLE-2005-BLG-390Lb, orbits a red star five times less massive than the Sun and located at a distance of about 20,000 light years, not far from the centre of our Milky Way galaxy. Its relatively cool parent star and large orbit implies that the likely surface temperature of the planet is 220 degrees Centigrade below zero, too cold for liquid water. It is likely to have a thin atmosphere, like the Earth, but its rocky surface is probably deeply buried beneath frozen oceans. It may therefore more closely resemble a more massive version of Pluto, rather than the rocky inner planets like Earth and Venus. "This planet is actually the first and only planet that has been discovered so far that is in agreement with the theories for how our Solar System formed ", said Uffe Gråe Jørgensen (Niels Bohr Institute, Copenhagen, Denmark), member of the team. The favoured theoretical explanation for the formation of planetary systems proposes that solid 'planetesimals' accumulate to build up planetary cores, which then accrete nebular gas - to form giant planets - if they are sufficiently massive. Around red dwarfs, the most common stars of our Galaxy, this model favours the formation of Earth- to Neptune-mass planets being between 1 and 10 times the Earth

Alternative control techniques document: NOx emissions from industrial/commercial/institutional (ICI) boilers

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

Not Available

1994-03-01

Industrial, commercial, and institutional (ICI) boilers have been identified as a category that emits more than 25 tons of oxides of nitrogen (NOx) per year. This alternative control techniques (ACT) document provides technical information for use by State and local agencies to develop and implement regulatory programs to control NOx emissions from ICI boilers. Additional ACT documents are being developed for other stationary source categories. Chapter 2 summarizes the findings of this study. Chapter 3 presents information on the ICI boiler types, fuels, operation, and industry applications. Chapter 4 discusses NOx formation and uncontrolled NOx emission factors. Chapter 5 coversmore » alternative control techniques and achievable controlled emission levels. Chapter 6 presents the cost and cost effectiveness of each control technique. Chapter 7 describes environmental and energy impacts associated with implementing the NOx control techniques. Finally, Appendices A through G provide the detailed data used in this study to evaluate uncontrolled and controlled emissions and the costs of controls for several retrofit scenarios.« less

Analytical Solutions for Radiative Transfer: Implications for Giant Planet Formation by Disk Instability

NASA Astrophysics Data System (ADS)

Boss, Alan P.

2009-03-01

The disk instability mechanism for giant planet formation is based on the formation of clumps in a marginally gravitationally unstable protoplanetary disk, which must lose thermal energy through a combination of convection and radiative cooling if they are to survive and contract to become giant protoplanets. While there is good observational support for forming at least some giant planets by disk instability, the mechanism has become theoretically contentious, with different three-dimensional radiative hydrodynamics codes often yielding different results. Rigorous code testing is required to make further progress. Here we present two new analytical solutions for radiative transfer in spherical coordinates, suitable for testing the code employed in all of the Boss disk instability calculations. The testing shows that the Boss code radiative transfer routines do an excellent job of relaxing to and maintaining the analytical results for the radial temperature and radiative flux profiles for a spherical cloud with high or moderate optical depths, including the transition from optically thick to optically thin regions. These radial test results are independent of whether the Eddington approximation, diffusion approximation, or flux-limited diffusion approximation routines are employed. The Boss code does an equally excellent job of relaxing to and maintaining the analytical results for the vertical (θ) temperature and radiative flux profiles for a disk with a height proportional to the radial distance. These tests strongly support the disk instability mechanism for forming giant planets.

Titan's Impact Cratering Record: Erosion of Ganymedean (and other) Craters on a Wet Icy Landscape

NASA Astrophysics Data System (ADS)

Schenk, P.; Moore, J.; Howard, A.

2012-04-01

We examine the cratering record of Titan from the perspective of icy satellites undergoing persistent landscape erosion. First we evaluate whether Ganymede (and Callisto) or the smaller low-gravity neighboring icy satellites of Saturn are the proper reference standard for evaluating Titan’s impact crater morphologies, using topographic and morphometric measurements (Schenk, 2002; Schenk et al. (2004) and unpublished data). The special case of Titan’s largest crater, Minrva, is addressed through analysis of large impact basins such as Gilgamesh, Lofn, Odysseus and Turgis. Second, we employ a sophisticated landscape evolution and modification model developed for study of martian and other planetary landforms (e.g., Howard, 2007). This technique applies mass redistribution principles due to erosion by impact, fluvial and hydrological processes to a planetary landscape. The primary advantage of our technique is the possession of a limited but crucial body of areal digital elevation models (DEMs) of Ganymede (and Callisto) impact craters as well as global DEM mapping of Saturn’s midsize icy satellites, in combination with the ability to simulate rainfall and redeposition of granular material to determine whether Ganymede craters can be eroded to resemble Titan craters and the degree of erosion required. References: Howard, A. D., “Simulating the development of martian highland landscapes through the interaction of impact cratering, fluvial erosion, and variable hydrologic forcing”, Geomorphology, 91, 332-363, 2007. Schenk, P. "Thickness constraints on the icy shells of the galilean satellites from impact crater shapes". Nature, 417, 419-421, 2002. Schenk, P.M., et al. "Ages and interiors: the cratering record of the Galilean satellites". In: Jupiter: The Planet, Satellites, and Magnetosphere, Cambridge University Press, Cambridge, UK, pp. 427-456, 2004.

Extrasolar planets.

PubMed

Lissauer, J J; Marcy, G W; Ida, S

2000-11-07

The first known extrasolar planet in orbit around a Sun-like star was discovered in 1995. This object, as well as over two dozen subsequently detected extrasolar planets, were all identified by observing periodic variations of the Doppler shift of light emitted by the stars to which they are bound. All of these extrasolar planets are more massive than Saturn is, and most are more massive than Jupiter. All orbit closer to their stars than do the giant planets in our Solar System, and most of those that do not orbit closer to their star than Mercury is to the Sun travel on highly elliptical paths. Prevailing theories of star and planet formation, which are based on observations of the Solar System and of young stars and their environments, predict that planets should form in orbit about most single stars. However, these models require some modifications to explain the properties of the observed extrasolar planetary systems.

Extrasolar planets

PubMed Central

Lissauer, Jack J.; Marcy, Geoffrey W.; Ida, Shigeru

2000-01-01

The first known extrasolar planet in orbit around a Sun-like star was discovered in 1995. This object, as well as over two dozen subsequently detected extrasolar planets, were all identified by observing periodic variations of the Doppler shift of light emitted by the stars to which they are bound. All of these extrasolar planets are more massive than Saturn is, and most are more massive than Jupiter. All orbit closer to their stars than do the giant planets in our Solar System, and most of those that do not orbit closer to their star than Mercury is to the Sun travel on highly elliptical paths. Prevailing theories of star and planet formation, which are based on observations of the Solar System and of young stars and their environments, predict that planets should form in orbit about most single stars. However, these models require some modifications to explain the properties of the observed extrasolar planetary systems. PMID:11035782

THE LAST STAGES OF TERRESTRIAL PLANET FORMATION: DYNAMICAL FRICTION AND THE LATE VENEER

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

Schlichting, Hilke E.; Warren, Paul H.; Yin Qingzhu, E-mail: hilke@ucla.edu

2012-06-10

The final stage of terrestrial planet formation consists of the clean-up of residual planetesimals after the giant impact phase. Dynamically, a residual planetesimal population is needed to damp the high eccentricities and inclinations of the terrestrial planets to circular and coplanar orbits after the giant impact stage. Geochemically, highly siderophile element (HSE) abundance patterns inferred for the terrestrial planets and the Moon suggest that a total of about 0.01 M{sub Circled-Plus} of chondritic material was delivered as 'late veneer' by planetesimals to the terrestrial planets after the end of giant impacts. Here, we combine these two independent lines of evidencemore » for a leftover population of planetesimals and show that: (1) a residual population of small planetesimals containing 0.01 M{sub Circled-Plus} is able to damp the high eccentricities and inclinations of the terrestrial planets after giant impacts to their observed values. (2) At the same time, this planetesimal population can account for the observed relative amounts of late veneer added to the Earth, Moon, and Mars provided that the majority of the accreted late veneer was delivered by small planetesimals with radii {approx}< 10 m. These small planetesimal sizes are required to ensure efficient damping of the planetesimal's velocity dispersion by mutual collisions, which in turn ensures sufficiently low relative velocities between the terrestrial planets and the planetesimals such that the planets' accretion cross sections are significantly enhanced by gravitational focusing above their geometric values. Specifically, we find that, in the limit that the relative velocity between the terrestrial planets and the planetesimals is significantly less than the terrestrial planets' escape velocities, gravitational focusing yields a mass accretion ratio of Earth/Mars {approx}({rho}{sub Circled-Plus }/{rho}{sub mars})(R{sub Circled-Plus }/R{sub mars}){sup 4} {approx} 17, which agrees well with

High energy electron sintering of icy regoliths: Formation of the PacMan thermal anomalies on the icy Saturnian moons

NASA Astrophysics Data System (ADS)

Schaible, M. J.; Johnson, R. E.; Zhigilei, L. V.; Piqueux, S.

2017-03-01

The so-called 'PacMan' features on the leading hemispheres of the icy Saturnian moons of Mimas, Tethys and Dione were initially identified as anomalous optical discolorations and subsequently shown to have greater thermal inertia than the surrounding regions. The shape of these regions matches calculated deposition contours of high energy plasma electrons moving opposite to the moon's orbital direction, thus suggesting that electron interactions with the grains produce the observed anomalies. Here, descriptions of radiation-induced diffusion processes are given, and various sintering models are considered to calculate the rate of increase in the contact volume between grains in an icy regolith. Estimates of the characteristic sintering timescale, i.e. the time necessary for the thermal inertia to increase from that measured outside the anomalous regions to that within, are given for each of the moons. Since interplanetary dust particle (IDP) impact gardening and E-ring grain infall would be expected to mix the regolith and obscure the effects of high energy electrons, sintering rates are compared to rough estimates of the impact-induced resurfacing rates. Estimates of the sintering timescale determined by extrapolating laboratory measurements are below ∼0.03 Myr, while the regolith renewal timescales are larger than ∼0.1 Myr, thus indicating that irradiation by the high energy electrons should be sufficient to form stable thermal anomalies. More detailed models developed for sintering of spherical grains are able to account for the radiation-induced anomalies on Mimas and Tethys only if the regoliths on those bodies are relatively compact and composed of small (≲ 5 μm) grains or grain aggregates, and/or the grains are highly non-spherical with surface defect densities in the inter-grain contact regions that are much higher than expected for crystalline water ice grains at thermal equilibrium. These results are consistent with regolith thermal conductivity

Large impacts around a solar-analog star in the era of terrestrial planet formation.

PubMed

Meng, Huan Y A; Su, Kate Y L; Rieke, George H; Stevenson, David J; Plavchan, Peter; Rujopakarn, Wiphu; Lisse, Carey M; Poshyachinda, Saran; Reichart, Daniel E

2014-08-29

The final assembly of terrestrial planets occurs via massive collisions, which can launch copious clouds of dust that are warmed by the star and glow in the infrared. We report the real-time detection of a debris-producing impact in the terrestrial planet zone around a 35-million-year-old solar-analog star. We observed a substantial brightening of the debris disk at a wavelength of 3 to 5 micrometers, followed by a decay over a year, with quasi-periodic modulations of the disk flux. The behavior is consistent with the occurrence of a violent impact that produced vapor out of which a thick cloud of silicate spherules condensed that were then ground into dust by collisions. These results demonstrate how the time domain can become a new dimension for the study of terrestrial planet formation. Copyright © 2014, American Association for the Advancement of Science.

Revealing a universal planet-metallicity correlation for planets of different solar-type stars

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

Wang, Ji; Fischer, Debra A., E-mail: ji.wang@yale.edu

2015-01-01

The metallicity of exoplanet systems serves as a critical diagnostic of planet formation mechanisms. Previous studies have demonstrated the planet–metallicity correlation for large planets (R{sub P} ⩾ 4 R{sub E}); however, a correlation has not been found for smaller planets. With a sample of 406 Kepler objects of interest whose stellar properties are determined spectroscopically, we reveal a universal planet–metallicity correlation: not only gas-giant planets (3.9 R{sub E}

ORBITAL DISTRIBUTIONS OF CLOSE-IN PLANETS AND DISTANT PLANETS FORMED BY SCATTERING AND DYNAMICAL TIDES

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

Nagasawa, M.; Ida, S., E-mail: nagasawa.m.ad@m.titech.ac.jp

2011-12-01

We investigated the formation of close-in planets (hot Jupiters) by a combination of mutual scattering, Kozai effect, and tidal circularization, through N-body simulations of three gas giant planets, and compared the results with discovered close-in planets. We found that in about 350 cases out of 1200 runs ({approx}30%), the eccentricity of one of the planets is excited highly enough for tidal circularization by mutual close scatterings followed by secular effects due to outer planets, such as the Kozai mechanism, and the planet becomes a close-in planet through the damping of eccentricity and semimajor axis. The formation probability of close-in planetsmore » by such scattering is not affected significantly by the effect of the general relativity and inclusion of inertial modes in addition to fundamental modes in the tides. Detailed orbital distributions of the formed close-in planets and their counterpart distant planets in our simulations were compared with observational data. We focused on the possibility for close-in planets to retain non-negligible eccentricities ({approx}> 0.1) on timescales of {approx}10{sup 9} yr and have high inclinations, because close-in planets in eccentric or highly inclined orbits have recently been discovered. In our simulations we found that as many as 29% of the close-in planets have retrograde orbits, and the retrograde planets tend to have small eccentricities. On the other hand, eccentric close-in planets tend to have orbits of small inclinations.« less

The SEEDS of Planet Formation: Observations of Transitional Disks

NASA Technical Reports Server (NTRS)

Grady, Carol A.

2011-01-01

As part of its 5-year study, the Strategic Exploration of Exoplanets and Disk Systems (SEEDS) has already observed a number of YSOs with circumstellar disks, including 13 0.5-8 Myr old A-M stars with indications that they host wide gaps or central cavities in their circumstellar disks in millimeter or far-IR observations, or from deficits in warm dust thermal emission. For 8 of the disks, the 0.15" inner working angle of HiCIAO+A0188 samples material in the millimeter or mid-IR identified cavity. In one case we report detection of a previously unrecognized wide gap. For the remaining 4 stars, the SEEDS data sample the outer disk: in 3 cases, we present the first NIR imagery of the disks. The data for the youngest sample members 1-2 Myr) closely resemble coeval primordial disks. After approximately 3 Myr, the transitional disks show a wealth of structure including spiral features, rings, divots, and in some cases, largely cleared gaps in the disks which are not seen in coeval primordial disks. Some of these structural features are predicted consequences of Jovian-mass planets having formed in the disk, while others are novel features. We discuss the implications for massive planet formation timescales and mechanisms.

The SEEDS of Planet Formation: Observations of Transitional Disks

NASA Technical Reports Server (NTRS)

Grady, Carol

2011-01-01

As part of its 5-year study, the Strategic Exploration of Exoplanets and Disk Systems (SEEDS) has already observed a number of YSOs with circumstellar disks, including 13 0.5- 8 Myr old A-M stars with indications that they host wide gaps or central cavities in their circumstellar disks in millimeter or far-IR observations, or from deficits in warm dust thermal emission. For 8 of the disks, the 0.15" inner working angle of HiCIAO+A0188 samples material in the millimeter or mid-IR identified cavity. In one case we reprt detection of a previously unrecognized wide gap. For the remaining 4 stars, the SEEDS data sample the outer disk: in 3 cases, we present the first NIR imagery of the disks. The data for the youngest sample members (less than 1-2 Myr) closely resemble coeval primordial disks. After approximately 3 Myr, the transitional disks show a wealth of structure including spiral features, rings, divots, and in some cases, largely cleared gaps in the disks which are not seen in coeval primordial disks. Some of these structural features are predicted consequences of lovianmass planets having formed in the disk, while others are novel features. We discuss the implications for massive planet formation timescales and mechanisms.

Hemispheric and Topographic Asymmetry of Magnetospheric Particle Irradiation for Icy Moon Surfaces

NASA Technical Reports Server (NTRS)

Cooper, John F.; Sturner, S. J.

2007-01-01

All surfaces of icy moons without significant atmospheres, i.e. all except Titan in the giant planet systems, are irradiated by hot plasma and more energetic charged particles from the local magnetospheric environments. This irradiation can significantly impact the chemical composition, albedo, and detectable presence of signs of life on the sensible surfaces, while also limiting lifetimes and science operations of orbital spacecraft for extreme radiation environments as at Europa. Planning of surface remote sensing and lander operations, and interpretation of remote sensing and in-situ measurements, should include consideration of natural shielding afforded by the body of the moon, by any intrinsic or induced magnetic fields as at Ganyrnede, and by topographic structures.

Infrared Extinction and the Initial Conditions For Star and Planet Formation

NASA Technical Reports Server (NTRS)

Lada, Charles J.

2003-01-01

This grant funds a research program to use infrared extinction measurements to probe the detailed structure of dark molecular clouds and investigate the physical conditions which give rise to star and planet formation. The goals of the this program are to: 1) acquire deep infrared and molecular-line observations of a carefully selected sample of nearby dark clouds, 2) reduce and analyze the data obtained in order to produce detailed extinction maps of the clouds, 3) prepare results, where appropriate, for publication.

Infrared Extinction and the Initial Conditions for Star and Planet Formation

NASA Technical Reports Server (NTRS)

Lada, Charles J.

2002-01-01

This grant funds a research program to use infrared extinction measurements to probe the detailed structure of dark molecular clouds and investigate the physical conditions which give rise to star and planet formation. The goals of the this program are to: (1) acquire deep infrared and molecular-line observations of a carefully selected sample of nearby dark clouds; (2) reduce and analyze the data obtained in order to produce detailed extinction maps of the clouds; and (3) prepare results, where appropriate, for publication.

Hydrothermal systems in small ocean planets.

PubMed

Vance, Steve; Harnmeijer, Jelte; Kimura, Jun; Hussmann, Hauke; Demartin, Brian; Brown, J Michael

2007-12-01

We examine means for driving hydrothermal activity in extraterrestrial oceans on planets and satellites of less than one Earth mass, with implications for sustaining a low level of biological activity over geological timescales. Assuming ocean planets have olivine-dominated lithospheres, a model for cooling-induced thermal cracking shows how variation in planet size and internal thermal energy may drive variation in the dominant type of hydrothermal system-for example, high or low temperature system or chemically driven system. As radiogenic heating diminishes over time, progressive exposure of new rock continues to the current epoch. Where fluid-rock interactions propagate slowly into a deep brittle layer, thermal energy from serpentinization may be the primary cause of hydrothermal activity in small ocean planets. We show that the time-varying hydrostatic head of a tidally forced ice shell may drive hydrothermal fluid flow through the seafloor, which can generate moderate but potentially important heat through viscous interaction with the matrix of porous seafloor rock. Considering all presently known potential ocean planets-Mars, a number of icy satellites, Pluto, and other trans-neptunian objects-and applying Earth-like material properties and cooling rates, we find depths of circulation are more than an order of magnitude greater than in Earth. In Europa and Enceladus, tidal flexing may drive hydrothermal circulation and, in Europa, may generate heat on the same order as present-day radiogenic heat flux at Earth's surface. In all objects, progressive serpentinization generates heat on a globally averaged basis at a fraction of a percent of present-day radiogenic heating and hydrogen is produced at rates between 10(9) and 10(10) molecules cm(2) s(1).

Sublimation of Ices Containing Organics and/or Minerals and Implications for Icy Bodies Surface Structure and Spectral Properties

NASA Astrophysics Data System (ADS)

Poch, O.; Pommerol, A.; Jost, B.; Yoldi, Z.; Carrasco, N.; Szopa, C.; Thomas, N.

2015-12-01

The surfaces of many objects in the Solar System comprise substantial quantities of water ice either in pure form or mixed with minerals and/or organic molecules. Sublimation is a process responsible for shaping and changing the reflectance properties of these objects. We present laboratory data on the evolution of the structure and the visible and near-infrared spectral reflectance of icy surfaces made of mixtures of water ice and non-volatile components (complex organic matter and silicates), as they undergo sublimation of the water ice under low temperature and pressure conditions (Poch et al., under review). We prepared icy surfaces which are potential analogues of ices found on comets, icy satellites or trans-neptunian objects (TNOs). The experiments were carried out in the SCITEAS simulation setup recently built as part of the Laboratory for Outflow Studies of Sublimating Materials (LOSSy) at the University of Bern (Pommerol et al., 2015a). As the water ice sublimated, we observed in situ the formation of a sublimation lag deposit, or sublimation mantle, made of the non-volatiles at the top of the samples. The texture (porosity, internal cohesiveness etc.), the activity (outbursts and ejection of mantle fragments) and the spectro-photometric properties of this mantle are found to differ strongly depending on the chemical nature of the non-volatiles, the size of their particles, the way they are mixed with the volatile component and the dust/ice mass ratio. The results also indicate how the band depths of the sub-surface water ice evolve during the build-up of the sublimation mantle. These data provide useful references for interpreting remote-sensing observations of Rosetta (see Pommerol et al., 2015b), and also New Horizons. Poch, O., et al., under review in IcarusPommerol, A., et al., 2015a, Planet. Space Sci. 109-110, 106-122. http://dx.doi.org/10.1016/j.pss.2015.02.004Pommerol, A., et al., 2015b, Astronomy and Astrophysics, in press. http://dx.doi.org/10.1051/0004-6361/201525977

Astrobiology of Jupiter's icy moons

NASA Astrophysics Data System (ADS)

Lipps, Jere H.; Delory, Gregory; Pitman, Joseph T.; Rieboldt, Sarah

2004-11-01

Jupiter's Icy Moons, Europa, Ganymede and Callisto, may possess energy sources, biogenic molecules, and oceans below their icy crusts, thus indicating a strong possibility that they were abodes for present or past life. Life in Earth's icy areas lives in a wide variety of habitats associated with the ice, in the water column below the ice, and on the floor of the ocean below the ice. Similar habitats may exist on JIM, have been transported to the icy crust, and be exposed in tectonic or impact features. Europa has a young, dynamic surface with many outcrops exposing older ice, fresh ice, possible materials from the subsurface ocean, and a few impact craters. Ganymede has older, darker, tectonized terrains surrounded by light ice. Callisto has a much older, heavily impacted surface devoid of significant tectonic structures. Past and present life habitats may be exposed in these features, making Europa the most favorable target while Ganymede is of interest, and Callisto seems more unlikely to have detectable life. A proper search strategy requires detailed orbital imaging and spectrometry of the likely places, and surface data collection with microscopic, spectrometric, and biochemical instruments.

Habitability potential of icy moons: a comparative study

NASA Astrophysics Data System (ADS)

Solomonidou, Anezina; Coustenis, Athena; Encrenaz, Thérèse; Sohl, Frank; Hussmann, Hauke; Bampasidis, Georgios; Wagner, Frank; Raulin, François; Schulze-Makuch, Dirk; Lopes, Rosaly

2014-05-01

Looking for habitable conditions in the outer solar system our research focuses on the natural satellites rather than the planets themselves. Indeed, the habitable zone as traditionally defined may be larger than originally con-ceived. The strong gravitational pull caused by the giant planets may produce enough energy to sufficiently heat the interiors of orbiting icy moons. The outer solar system satellites then provide a conceptual basis within which new theories for understanding habitability can be constructed. Measurements from the ground but also by the Voyager, Galileo and the Cassini spacecrafts revealed the potential of these satellites in this context, and our understanding of habitability in the solar system and beyond can be greatly enhanced by investigating several of these bodies together [1]. Their environments seem to satisfy many of the "classical" criteria for habitability (liquid water, energy sources to sustain metabolism and chemical compounds that can be used as nutrients over a period of time long enough to allow the development of life). Indeed, several of the moons show promising conditions for habitability and the de-velopment and/or maintenance of life. Europa, Callisto and Ganymede may be hiding, under their icy crust, putative undersurface liquid water oceans [3] which, in the case of Europa [2], may be in direct contact with a silicate mantle floor and kept warm by tidally generated heat [4]. Titan and Enceladus, Saturn's satellites, were found by the Cassini-Huygens mission to possess active organic chemistries with seasonal variations, unique geological features and possibly internal liquid water oceans. Titan's rigid crust and the probable existence of a subsurface ocean create an analogy with terrestrial-type plate tectonics, at least surficial [5], while Enceladus' plumes find an analogue in gey-sers. As revealed by Cassini the liquid hydrocarbon lakes [6] distributed mainly at polar latitudes on Titan are ideal isolated

EPA Facility Registry Service (FRS): ICIS

EPA Pesticide Factsheets

This web feature service contains location and facility identification information from EPA's Facility Registry Service (FRS) for the subset of facilities that link to the Integrated Compliance Information System (ICIS). When complete, ICIS will provide a database that will contain integrated enforcement and compliance information across most of EPA's programs. The vision for ICIS is to replace EPA's independent databases that contain enforcement data with a single repository for that information. Currently, ICIS contains all Federal Administrative and Judicial enforcement actions and a subset of the Permit Compliance System (PCS), which supports the National Pollutant Discharge Elimination System (NPDES). ICIS exchanges non-sensitive enforcement/compliance activities, non-sensitive formal enforcement actions and NPDES information with FRS. This web feature service contains the enforcement/compliance activities and formal enforcement action related facilities; the NPDES facilities are contained in the PCS_NPDES web feature service. FRS identifies and geospatially locates facilities, sites or places subject to environmental regulations or of environmental interest. Using vigorous verification and data management procedures, FRS integrates facility data from EPA's national program systems, other federal agencies, and State and tribal master facility records and provides EPA with a centrally managed, single source of comprehensive and authoritative information on f

ANALYSIS OF TERRESTRIAL PLANET FORMATION BY THE GRAND TACK MODEL: SYSTEM ARCHITECTURE AND TACK LOCATION

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

Brasser, R.; Ida, S.; Matsumura, S.

2016-04-20

The Grand Tack model of terrestrial planet formation has emerged in recent years as the premier scenario used to account for several observed features of the inner solar system. It relies on the early migration of the giant planets to gravitationally sculpt and mix the planetesimal disk down to ∼1 au, after which the terrestrial planets accrete from material remaining in a narrow circumsolar annulus. Here, we investigate how the model fares under a range of initial conditions and migration course-change (“tack”) locations. We run a large number of N-body simulations with tack locations of 1.5 and 2 au andmore » test initial conditions using equal-mass planetary embryos and a semi-analytical approach to oligarchic growth. We make use of a recent model of the protosolar disk that takes into account viscous heating, includes the full effect of type 1 migration, and employs a realistic mass–radius relation for the growing terrestrial planets. Our results show that the canonical tack location of Jupiter at 1.5 au is inconsistent with the most massive planet residing at 1 au at greater than 95% confidence. This favors a tack farther out at 2 au for the disk model and parameters employed. Of the different initial conditions, we find that the oligarchic case is capable of statistically reproducing the orbital architecture and mass distribution of the terrestrial planets, while the equal-mass embryo case is not.« less

Comparison Simulations of Gas Giant Planet Formation via Disk Instability

NASA Astrophysics Data System (ADS)

Pickett, Megan K.; Cai, K.; Durisen, R.; Milne, M.

2011-01-01

There has been disagreement about whether cooling in protoplanetary disks can be sufficiently fast to induce the formation of gas giant protoplanets via gravitational instabilities. Simulations by our own group and others indicate that this method of planet formation does not work for disks around young, low-mass stars inside several tens of AU, while simulations by other groups show fragmentation into protoplanetary clumps in this region. To allow direct comparison in hopes of isolating the cause of the differences, we here present a comparison high-resolution three-dimensional hydrodynamics simulation of a protoplanetary disk,using an improved version of one of our own radiative schemes. We find that the disk does not fragment in our code but instead quickly settles into a state with only low amplitude nonaxisymmetric structure, which persists for at least several outer disk rotations. Further, we see no rapid radiative or convective cooling.

Localized sources of water vapour on the dwarf planet (1) Ceres.

PubMed

Küppers, Michael; O'Rourke, Laurence; Bockelée-Morvan, Dominique; Zakharov, Vladimir; Lee, Seungwon; von Allmen, Paul; Carry, Benoît; Teyssier, David; Marston, Anthony; Müller, Thomas; Crovisier, Jacques; Barucci, M Antonietta; Moreno, Raphael

2014-01-23

The 'snowline' conventionally divides Solar System objects into dry bodies, ranging out to the main asteroid belt, and icy bodies beyond the belt. Models suggest that some of the icy bodies may have migrated into the asteroid belt. Recent observations indicate the presence of water ice on the surface of some asteroids, with sublimation a potential reason for the dust activity observed on others. Hydrated minerals have been found on the surface of the largest object in the asteroid belt, the dwarf planet (1) Ceres, which is thought to be differentiated into a silicate core with an icy mantle. The presence of water vapour around Ceres was suggested by a marginal detection of the photodissociation product of water, hydroxyl (ref. 12), but could not be confirmed by later, more sensitive observations. Here we report the detection of water vapour around Ceres, with at least 10(26) molecules being produced per second, originating from localized sources that seem to be linked to mid-latitude regions on the surface. The water evaporation could be due to comet-like sublimation or to cryo-volcanism, in which volcanoes erupt volatiles such as water instead of molten rocks.

WHY ARE PULSAR PLANETS RARE?

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

Martin, Rebecca G.; Livio, Mario; Palaniswamy, Divya

Pulsar timing observations have revealed planets around only a few pulsars. We suggest that the rarity of these planets is due mainly to two effects. First, we show that the most likely formation mechanism requires the destruction of a companion star. Only pulsars with a suitable companion (with an extreme mass ratio) are able to form planets. Second, while a dead zone (a region of low turbulence) in the disk is generally thought to be essential for planet formation, it is most probably rare in disks around pulsars, because of the irradiation from the pulsar. The irradiation strongly heats themore » inner parts of the disk, thus pushing the inner boundary of the dead zone out. We suggest that the rarity of pulsar planets can be explained by the low probability for these two requirements to be satisfied: a very low-mass companion and a dead zone.« less

Raman Life Detection Instrument Development for Icy Worlds

NASA Technical Reports Server (NTRS)

Thomson, Seamus; Allen, A'Lester; Gutierrez, Daniel; Quinn, Richard C.; Chen, Bin; Koehne, Jessica E.

2017-01-01

The objective of this project is to develop a compact, high sensitivity Raman sensor for detection of life signatures in a flow cell configuration to enable bio-exploration and life detection during future mission to our Solar Systems Icy Worlds. The specific project objectives are the following: 1) Develop a Raman spectroscopy liquid analysis sensor for biosignatures; 2) Demonstrate applicability towards a future Enceladus or other Icy Worlds missions; 3) Establish key parameters for integration with the ARC Sample Processor for Life on Icy Worlds (SPLIce); 4) Position ARC for a successful response to upcoming Enceladus or other Icy World mission instrument opportunities.

Infrared Extinction and the Initial Conditions for Star and Planet Formation

NASA Technical Reports Server (NTRS)

Lada, Charles J.

2004-01-01

This grant funds a research program to use infrared extinction measurements to probe the detailed structure of dark molecular clouds and investigate the physical conditions which give rise to star and planet formation. The goals of the this program are to: 1) acquire deep infrared and molecular-line observations of a carefully selected sample of nearby dark clouds, 2) reduce and analyze the data obtained in order to produce detailed extinction maps of the clouds, 3) prepare results, where appropriate, for publication. A description of how these goals were met are included.

PCS-ICIS Model

EPA Pesticide Factsheets

The Integrated Compliance Information System (ICIS) is a web-based system that provides information for the federal enforcement and compliance (FE&C) and the National Pollutant Discharge Elimination System (NPDES) programs.

Astronomical studies of the major planets, natural satellites and asteroids using the 2.24 m telescope

NASA Technical Reports Server (NTRS)

Jefferies, J. T.

1982-01-01

Directional features in the Jovian sodium torus, high quality CCD images of the major planets, methane bands in the spectrum of Triton, the central wavelength of the SO2 absorption band on Io, a component on the icy surfaces of the satellites of Uranus, fluctuation of Io's volcanic radiation, standard stars, and thermal radiation from the four brightest satellites of Uranus are discussed.

Satellitesimal Formation via Collisional Dust Growth in Steady Circumplanetary Disks

NASA Astrophysics Data System (ADS)

Shibaike, Yuhito; Okuzumi, Satoshi; Sasaki, Takanori; Ida, Shigeru

2017-09-01

The icy satellites around Jupiter are considered to have formed in a circumplanetary disk. While previous models have focused on the formation of the satellites starting from satellitesimals, the question of how satellitesimals themselves form from smaller dust particles has not yet been addressed. In this work, we study the possibility that satellitesimals form in situ in a circumplanetary disk. We calculate the radial distribution of the surface density and representative size of icy dust particles that grow by colliding with each other and drift toward the central planet in a steady circumplanetary disk with a continuous supply of gas and dust from the parent protoplanetary disk. The radial drift barrier is overcome if the ratio of the dust-to-gas accretion rates onto the circumplanetary disk, {\\dot{M}}{{d}}/{\\dot{M}}{{g}}, is high and the strength of turbulence, α, is not too low. The collision velocity is lower than the critical velocity of fragmentation when α is low. Taken together, we find that the conditions for satellitesimal formation via dust coagulation are given by {\\dot{M}}{{d}}/{\\dot{M}}{{g}}≥slant 1 and {10}-4≤slant α < {10}-2. The former condition is generally difficult to achieve, suggesting that the in situ satellitesimal formation via particle sticking is viable only under extreme conditions. We also show that neither satellitesimal formation via the collisional growth of porous aggregates nor via streaming instability is viable as long as {\\dot{M}}{{d}}/{\\dot{M}}{{g}} is low.

DIRECT IMAGING OF THE WATER SNOW LINE AT THE TIME OF PLANET FORMATION USING TWO ALMA CONTINUUM BANDS

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

Banzatti, A.; Pontoppidan, K. M.; Pinilla, P.

2015-12-10

Molecular snow lines in protoplanetary disks have been studied theoretically for decades because of their importance in shaping planetary architectures and compositions. The water snow line lies in the planet formation region at ≲10 AU, and so far its location has been estimated only indirectly from spatially unresolved spectroscopy. This work presents a proof-of-concept method to directly image the water snow line in protoplanetary disks through its physical and chemical imprint on the local dust properties. We adopt a physical disk model that includes dust coagulation, fragmentation, drift, and a change in fragmentation velocities of a factor of 10 betweenmore » dry silicates and icy grains as found by laboratory work. We find that the presence of a water snow line leads to a sharp discontinuity in the radial profile of the dust emission spectral index α{sub mm} due to replenishment of small grains through fragmentation. We use the ALMA simulator to demonstrate that this effect can be observed in protoplanetary disks using spatially resolved ALMA images in two continuum bands. We explore the model dependence on the disk viscosity and find that the spectral index reveals the water snow line for a wide range of conditions, with opposite trends when the emission is optically thin rather than thick. If the disk viscosity is low (α{sub visc} < 10{sup −3}), the snow line produces a ringlike structure with a minimum at α{sub mm} ∼ 2 in the optically thick regime, possibly similar to what has been measured with ALMA in the innermost region of the HL Tau disk.« less

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.

Time-Dependent Simulations of the Formation and Evolution of Disk-Accreted Atmospheres Around Terrestrial Planets

NASA Astrophysics Data System (ADS)

Stoekl, Alexander; Dorfi, Ernst

2014-05-01

formation of a gas planet.

Formation of Valley Networks in a Cold and Icy Early Mars Climate: Predictions for Erosion Rates and Channel Morphology

NASA Astrophysics Data System (ADS)

Cassanelli, J.

2017-12-01

Mars is host to a diverse array of valley networks, systems of linear-to-sinuous depressions which are widely distributed across the surface and which exhibit branching patterns similar to the dendritic drainage patterns of terrestrial fluvial systems. Characteristics of the valley networks are indicative of an origin by fluvial activity, providing among the most compelling evidence for the past presence of flowing liquid water on the surface of Mars. Stratigraphic and crater age dating techniques suggest that the formation of the valley networks occurred predominantly during the early geologic history of Mars ( 3.7 Ga). However, whether the valley networks formed predominantly by rainfall in a relatively warm and wet early Mars climate, or by snowmelt and episodic rainfall in an ambient cold and icy climate, remains disputed. Understanding the formative environment of the valley networks will help distinguish between these warm and cold end-member early Mars climate models. Here we test a conceptual model for channel incision and evolution under cold and icy conditions with a substrate characterized by the presence of an ice-free dry active layer and subjacent ice-cemented regolith, similar to that found in the Antarctic McMurdo Dry Valleys. We implement numerical thermal models, quantitative erosion and transport estimates, and morphometric analyses in order to outline predictions for (1) the precise nature and structure of the substrate, (2) fluvial erosion/incision rates, and (3) channel morphology. Model predictions are compared against morphologic and morphometric observational data to evaluate consistency with the assumed cold climate scenario. In the cold climate scenario, the substrate is predicted to be characterized by a kilometers-thick globally-continuous cryosphere below a 50-100 meter thick desiccated ice-free zone. Initial results suggest that, with the predicted substrate structure, fluvial channel erosion and morphology in a cold early Mars

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.

Observing outer planet satellites (except Titan) with JWST: Science justification and observational requirements

USGS Publications Warehouse

Kestay, Laszlo P.; Grundy, Will; Stansberry, John; Sivaramakrishnan, Anand; Thatte, Deepashri; Gudipati, Murthy; Tsang, Constantine; Greenbaum, Alexandra; McGruder, Chima

2016-01-01

The James Webb Space Telescope (JWST) will allow observations with a unique combination of spectral, spatial, and temporal resolution for the study of outer planet satellites within our Solar System. We highlight the infrared spectroscopy of icy moons and temporal changes on geologically active satellites as two particularly valuable avenues of scientific inquiry. While some care must be taken to avoid saturation issues, JWST has observation modes that should provide excellent infrared data for such studies.

Seeding life on the moons of the outer planets via lithopanspermia.

PubMed

Worth, R J; Sigurdsson, Steinn; House, Christopher H

2013-12-01

Material from the surface of a planet can be ejected into space by a large impact and could carry primitive life-forms with it. We performed n-body simulations of such ejecta to determine where in the Solar System rock from Earth and Mars may end up. We found that, in addition to frequent transfer of material among the terrestrial planets, transfer of material from Earth and Mars to the moons of Jupiter and Saturn is also possible, but rare. We expect that such transfers were most likely to occur during the Late Heavy Bombardment or during the ensuing 1-2 billion years. At this time, the icy moons were warmer and likely had little or no ice shell to prevent meteorites from reaching their liquid interiors. We also note significant rates of re-impact in the first million years after ejection. This could re-seed life on a planet after partial or complete sterilization by a large impact, which would aid the survival of early life during the Late Heavy Bombardment.

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

Using NIRISS to study the formation and evolution of stars, disks, and planets

NASA Astrophysics Data System (ADS)

Johnstone, Doug I.; JWST NIRISS GTO Team

2017-06-01

NIRISS on JWST is a powerful instrument for the study of star, disk, and planet formation and evolution. In this talk I will highlight the Wide Field Slitless Spectroscopy (WFSS) and Aperture Masking Interferometry (AMI) modes of NIRISS, along with lessons learned determining optimal observing strategies and project implementation in APT. The NIRISS WFSS mode uses a grism to provide modest resolution (R ~ 150) spectra of all sources within the observed field of view. Cold low-mass objects are distinct at NIRISS wavelengths (1.5 and 2.0 microns, in this case), and can be characterized through their speactra by their temperature and surface gravity sensitive molecular absorption features. Thus, WFSS observations will be an efficient way to locate and enumerate the young brown dwarfs and rogue planets in nearby star-forming regions. Alternatively, the NIRISS AMI mode offers the highest spatial resolution available on JWST at wavelengths greater than 2.5 micron, 70 - 400 mas, and modest inner working angle contrast, dm ~ 10, for individual bright sources. A significant advantage of observing from space is that, along with the phase closure, the interferometric phase amplitudes can also be recovered allowing some reconstruction of extended emission. Observations with AMI will be made of candidate and postulated planets forming within transition disks around young stars and for somewhat older planets in known extra-solar planetary systems. The AMI mode will also be used to study the zodiacal light in a bright debris disk system and to search for binary companions of Y dwarfs.

The SEEDS of Planet Formation: Indirect Signatures of Giant Planets in Transitional Disks

NASA Technical Reports Server (NTRS)

Grady, Carol

2012-01-01

Circumstellar disks associated with PMS stars are the site where planetesimals form and grow, and ultimately where planets are produced. A key phase in the evolution of such disks is the phase where clearing of the disk has begun, potentially enabling direct detection of giant planets, but the disk retains sufficient material that indirect signatures that these are young planetary systems are also present. After reviewing what has been learned from studies of the IR spectral energy distribution and (sub )mm-interferometry, I will discuss recent results obtained as part of the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS).

Status of the Scorpion Planet Survey: Establishing the Frequency of HR8799b-Like Planets

NASA Astrophysics Data System (ADS)

Wagner, K. R.; Daniel, A.; Kasper, M.

2017-11-01

Wide-orbit giant planets will likely affect plant formation and habitability of inner planets. In this presentation we will review the existing evidence on the occurrence rates of super-Jupiters and present the status of our VLT/SPHERE survey.

Protostars and Planets VI

NASA Astrophysics Data System (ADS)

Beuther, Henrik; Klessen, Ralf S.; Dullemond, Cornelis P.; Henning, Thomas

The Protostars and Planets book and conference series has been a long-standing tradition that commenced with the first meeting led by Tom Gehrels and held in Tucson, Arizona, in 1978. The goal then, as it still is today, was to bridge the gap between the fields of star and planet formation as well as the investigation of planetary systems and planets. As Tom Gehrels stated in the preface to the first Protostars and Planets book, "Cross-fertilization of information and understanding is bound to occur when investigators who are familiar with the stellar and interstellar phases meet with those who study the early phases of solar system formation." The central goal remained the same for the subsequent editions of the books and conferences Protostars and Planets II in 1984, Protostars and Planets III in 1990, Protostars and Planets IV in 1998, and Protostars and Planets V in 2005, but has now been greatly expanded by the flood of new discoveries in the field of exoplanet science. The original concept of the Protostars and Planets series also formed the basis for the sixth conference in the series, which took place on July 15-20, 2013. It was held for the first time outside of the United States in the bustling university town of Heidelberg, Germany. The meeting attracted 852 participants from 32 countries, and was centered around 38 review talks and more than 600 posters. The review talks were expanded to form the 38 chapters of this book, written by a total of 250 contributing authors. This Protostars and Planets volume reflects the current state-of-the-art in star and planet formation, and tightly connects the fields with each other. It is structured into four sections covering key aspects of molecular cloud and star formation, disk formation and evolution, planetary systems, and astrophysical conditions for life. All poster presentations from the conference can be found at www.ppvi.org. In the eight years that have passed since the fifth conference and book in the

The ODINUS Mission Concept: a Mission to the Ice Giant Planets

NASA Astrophysics Data System (ADS)

Turrini, Diego; Politi, Romolo; Peron, Roberto; Grassi, Davide; Plainaki, Christina; Barbieri, Mauro; Massimo Lucchesi, David; Magni, Gianfranco; Altieri, Francesca; Cottini, Valeria; Gorius, Nicolas; Gaulme, Patrick; Schmider, François-Xavier; Adriani, Alberto; Piccioni, Giuseppe

2014-05-01

We present the scientific case and the mission concept for the comparative exploration of the ice giant planets Uranus and Neptune and their satellites with a pair of twin spacecraft: ODINUS (Origins, Dynamics and Interiors of Neptunian and Uranian Systems). The ODINUS proposal was submitted in response to the call for white papers for the definition of the themes of the L2 and L3 mission in the framework of the ESA Cosmic Vision 2015-2025 program. The goal of ODINUS is the advancement of our understanding of the ancient past of the Solar System and, more generally, of how planetary systems form and evolve. The mission concept is focused on providing elements to answer to the scientific themes of the Cosmic Vision 2015-2025 program: What are the conditions for planetary formation and the emergency of life? How does the Solar System work? What are the fundamental physical laws of the Universe? In order to achieve its goals, the ODINUS mission concept proposed the use of two twin spacecraft to be put in orbit around Uranus and Neptune respectively, with selected flybys of their satellites. The proposed measurements aim to study the atmospheres and magnetospheres of the planets, the surfaces of the satellites, and the interior structure and composition of both satellites and planets. An important possibility for performing fundamental physics studies (among them tests of general relativity theory) is offered by the cruise phase. After the extremely positive evaluation of ESA Senior Survey Committee, who stated that 'the exploration of the icy giants appears to be a timely milestone, fully appropriate for an L class mission', we discuss strategies to comparatively study Uranus and Neptune with future international missions.

JUICE: a European mission to Jupiter and its icy moons

NASA Astrophysics Data System (ADS)

Titov, D.; Erd, C.; Duvet, L.; Wielders, A.; Torralba-Elipe, I.; Altobelli, N.

2013-09-01

JUICE (JUpiter ICy moons Explorer) is the first L-class mission selected for the ESA's Cosmic Vision programme 2015-2025 which has just entered the definition phase. JUICE will perform detailed investigations of Jupiter and its system in all their inter-relations and complexity with particular emphasis on Ganymede as a planetary body and potential habitat. Investigations of Europa and Callisto will complete a comparative picture of the Galilean moons. By performing detailed investigations of Jupiter's system, JUICE will address in depth two key questions of the ESA's Cosmic Vision programme: (1) What are the conditions for planet formation and the emergence of life? and (2) How does the Solar System work? The overarching theme for JUICE has been formulated as: The emergence of habitable worlds around gas giants. At Ganymede the mission will characterize in detail the ocean layers; provide topographical, geological and compositional mapping of the surface; study the physical properties of the icy crusts; characterize the internal mass distribution, investigate the exosphere; study Ganymede's intrinsic magnetic field and its interactions with the Jovian magnetosphere. For Europa, the focus will be on the non-ice chemistry, understanding the formation of surface features and subsurface sounding of the icy crust over recently active regions. Callisto will be explored as a witness of the early solar system. JUICE will perform a comprehensive multidisciplinary investigation of the Jupiter system as an archetype for gas giants including exoplanets. The circulation, meteorology, chemistry and structure of the Jovian atmosphere will be studied from the cloud tops to the thermosphere. The focus in Jupiter's magnetosphere will include an investigation of the three dimensional properties of the magnetodisc and in-depth study of the coupling processes within the magnetosphere, ionosphere and thermosphere. Aurora and radio emissions and their response to the solar wind will be

Icy Particle Spray

NASA Image and Video Library

2010-11-18

Images obtained by NASA EPOXI mission spacecraft show an active end of the nucleus of comet Hartley 2. Icy particles spew from the surface. Most of these particles are traveling with the nucleus; fluffy nowballs about 3 centimeters to 30 centimeters.

The Scattering Outcomes of Kepler Circumbinary Planets: Planet Mass Ratio

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

Gong, Yan-Xiang; Ji, Jianghui, E-mail: yxgong@pmo.ac.cn, E-mail: jijh@pmo.ac.cn

Recent studies reveal that the free eccentricities of Kepler-34b and Kepler-413b are much larger than their forced eccentricities, implying that scattering events may take place in their formation. The observed orbital configuration of Kepler-34b cannot be well reproduced in disk-driven migration models, whereas a two-planet scattering scenario can play a significant role of shaping the planetary configuration. These studies indicate that circumbinary planets discovered by Kepler may have experienced scattering process. In this work, we extensively investigate the scattering outcomes of circumbinary planets focusing on the effects of planet mass ratio . We find that the planetary mass ratio andmore » the the initial relative locations of planets act as two important parameters that affect the eccentricity distribution of the surviving planets. As an application of our model, we discuss the observed orbital configurations of Kepler-34b and Kepler-413b. We first adopt the results from the disk-driven models as the initial conditions, then simulate the scattering process that occurs in the late evolution stage of circumbinary planets. We show that the present orbital configurations of Kepler-34b and Kepler-413b can be well reproduced when considering a two unequal-mass planet ejection model. Our work further suggests that some of the currently discovered circumbinary single-planet systems may be survivors of original multiple-planet systems. The disk-driven migration and scattering events occurring in the late stage both play an irreplaceable role in sculpting the final systems.« less

Scattering of Planetesimals by a Planet

NASA Astrophysics Data System (ADS)

Higuchi, A.; Kokubo, E.; Mukai, T.

2004-05-01

We investigate the scattering process of planetesimals by a planet by numerical orbital integration, aiming at construction of theory for the comet (Oort) cloud formation. The standard scenario of the formation of the Oort cloud can be divided into three dynamical stages:(1)The eccentricity and the aphelion distance of planetesimals are increased by planetary perturbation. (2)The eccentricity is reduced and the perihelion distance is increased by the external forces such as the galactic tide. (3)The inclination is randomized also by the external forces. We model the first stage of this scenario as the restricted three-body problem and calculate the orbital evolution of planetesimals scattered by a planet. There are 4 kinds of outcomes for scattering of planetesimals by a planet: to collide with the planet, to fall onto the central star, to escape from the planetary system, and to remain in bound orbits. Here we consider the escape efficiency as the efficiency of formation of highly eccentric planetesimals, which are candidates for the members of the comet cloud. We obtain the dependence of the escape/collision probability on orbital parameters of the planetesimals and the planet. Using these results, we calculate the efficiencies of escaping from the planetary system and collision with the planet. For example, for the minimum-mass disk model, the inner and massive planet is more efficient to eject planetesimals and increase their eccentricities. Planetesimals with high eccentricities and low inclinations are easier to be ejected from the planetary system. We preset the empirical fitting formulae of these efficiencies as a function of the orbital parameters of the planetesimals and the planets. We apply the results to the solar system and discuss the efficiency of the outer giant planets.

Porosity and the ecology of icy satellites

NASA Technical Reports Server (NTRS)

Croft, Steven K.

1993-01-01

The case for a significant role for porosity in the structure and evolution of icy bodies in the Solar System has been difficult to establish. We present a relevant new data set and a series of structure models including a mechanical compression, not thermal creep, model for porosity that accounts satisfactorily for observed densities, moments of inertia, geologic activity, and sizes of tectonic features on icy satellites. Several types of observational data sets have been used to infer significant porosity, but until recently, alternative explanations have been preferred. Our first area of concern is the occurrence of cryovolcanism as a function of satellite radius; simple radiogenic heating models of icy satellites suggest minimum radii for melting and surface cryovolcanism to be 400 to 500 km, yet inferred melt deposits are seen on satellites half that size. One possible explanation is a deep, low conductivity regolith which lowers conductivity and raises internal temperatures, but other possibilities include tidal heating or crustal compositions of low conductivity. Our second area of concern is the occurrence and magnitude of tectonic strain; tectonic structures have been seen on icy satellites as small as Mimas and Proteus. The structures are almost exclusively extensional, with only a few possible compression Al features, and inferred global strains are on the order of 1 percent expansion. Expansions of this order in small bodies like Mimas and prevention of late compressional tectonics due to formation of ice mantles in larger bodies like Rhea are attained only in structure models including low-conductivity, and thus possibly high porosity, crusts. Thirdly, inferred moments of inertia less than 0.4 in Mimas and Tethys can be explained by high-porosity crusts, but also by differentiation of a high density core. Finally, the relatively low densities of smaller satellites like Mimas and Miranda relative to larger neighbors can be explained by deep porosity

The display of sexual behaviors by female rats administered ICI 182,780.

PubMed

Clark, Ann S; Guarraci, Fay A; Megroz, Alison B; Porter, Donna M; Henderson, Leslie P

2003-04-01

ICI 182,780 (ICI) is a pure antiestrogen that when administered systemically does not cross the blood-brain barrier, thus its actions are limited to the periphery. Four experiments were conducted to test the effects of ICI on the display of sexual behaviors in ovariectomized rats. Experiment 1 examined the effects of three doses of ICI (250, 500, and 750 micro g/rat) on sexual receptivity and paced mating behavior in rats primed with estradiol benzoate (EB) in combination with progesterone (P). Experiments 2 and 3 compared the display of sexual behaviors in rats primed with EB+P or EB alone and administered either 250 micro g ICI (Experiment 2) or 500 micro g ICI (Experiment 3). Experiment 4 tested the effects of ICI (250 and 500 micro g) on the expression of estrogen-induced progestin receptors in the uterus. ICI did not affect the display of sexual receptivity in any experiment. In rats primed with EB+P, paced mating behavior was altered by the 500 and 750 micro g, but not the 250 micro g, doses of ICI. The lowest (250 micro g) dose of ICI did alter paced mating behavior in rats primed with EB alone. The effects of ICI on paced mating behavior were manifested by a substantial lengthening of contact-return latencies following intromissions and ejaculations. The percentage of exits were not affected by ICI. Estrogen stimulation of uterine weight and induction of uterine progestin receptors was suppressed by ICI (250 and 500 micro g). ICI effects on paced mating behavior in hormone-primed female rats are likely to reflect antiestrogenic actions in the periphery, including interference with the estrogen induction of progestin receptors.

Radioactive elements on Mercury's surface from MESSENGER: implications for the planet's formation and evolution.

PubMed

Peplowski, Patrick N; Evans, Larry G; Hauck, Steven A; McCoy, Timothy J; Boynton, William V; Gillis-Davis, Jeffery J; Ebel, Denton S; Goldsten, John O; Hamara, David K; Lawrence, David J; McNutt, Ralph L; Nittler, Larry R; Solomon, Sean C; Rhodes, Edgar A; Sprague, Ann L; Starr, Richard D; Stockstill-Cahill, Karen R

2011-09-30

The MESSENGER Gamma-Ray Spectrometer measured the average surface abundances of the radioactive elements potassium (K, 1150 ± 220 parts per million), thorium (Th, 220 ± 60 parts per billion), and uranium (U, 90 ± 20 parts per billion) in Mercury's northern hemisphere. The abundance of the moderately volatile element K, relative to Th and U, is inconsistent with physical models for the formation of Mercury requiring extreme heating of the planet or its precursor materials, and supports formation from volatile-containing material comparable to chondritic meteorites. Abundances of K, Th, and U indicate that internal heat production has declined substantially since Mercury's formation, consistent with widespread volcanism shortly after the end of late heavy bombardment 3.8 billion years ago and limited, isolated volcanic activity since.

PLANETESIMAL FORMATION IN MAGNETOROTATIONALLY DEAD ZONES: CRITICAL DEPENDENCE ON THE NET VERTICAL MAGNETIC FLUX

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

Okuzumi, Satoshi; Hirose, Shigenobu, E-mail: okuzumi@nagoya-u.jp

Turbulence driven by magnetorotational instability (MRI) affects planetesimal formation by inducing diffusion and collisional fragmentation of dust particles. We examine conditions preferred for planetesimal formation in MRI-inactive 'dead zones' using an analytic dead-zone model based on our recent resistive MHD simulations. We argue that successful planetesimal formation requires not only a sufficiently large dead zone (which can be produced by tiny dust grains) but also a sufficiently small net vertical magnetic flux (NVF). Although often ignored, the latter condition is indeed important since the NVF strength determines the saturation level of turbulence in MRI-active layers. We show that direct collisionalmore » formation of icy planetesimal across the fragmentation barrier is possible when the NVF strength is lower than 10 mG (for the minimum-mass solar nebula model). Formation of rocky planetesimals via the secular gravitational instability is also possible within a similar range of the NVF strength. Our results indicate that the fate of planet formation largely depends on how the NVF is radially transported in the initial disk formation and subsequent disk accretion processes.« less

Direct Imaging of Warm Extrasolar Planets

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

Macintosh, B

2005-04-11

One of the most exciting scientific discoveries in the last decade of the twentieth century was the first detection of planets orbiting a star other than our own. By now more than 130 extrasolar planets have been discovered indirectly, by observing the gravitational effects of the planet on the radial velocity of its parent star. This technique has fundamental limitations: it is most sensitive to planets close to their star, and it determines only a planet's orbital period and a lower limit on the planet's mass. As a result, all the planetary systems found so far are very different frommore » our own--they have giant Jupiter-sized planets orbiting close to their star, where the terrestrial planets are found in our solar system. Such systems have overturned the conventional paradigm of planet formation, but have no room in them for habitable Earth-like planets. A powerful complement to radial velocity detections of extrasolar planets will be direct imaging--seeing photons from the planet itself. Such a detection would allow photometric measurements to determine the temperature and radius of a planet. Also, direct detection is most sensitive to planets in wide orbits, and hence more capable of seeing solar systems resembling our own, since a giant planet in a wide orbit does not preclude the presence of an Earth-like planet closer to the star. Direct detection, however, is extremely challenging. Jupiter is roughly a billion times fainter than our sun. Two techniques allowed us to overcome this formidable contrast and attempt to see giant planets directly. The first is adaptive optics (AO) which allows giant earth-based telescopes, such as the 10 meter W.M. Keck telescope, to partially overcome the blurring effects of atmospheric turbulence. The second is looking for young planets: by searching in the infrared for companions to young stars, we can see thermal emission from planets that are still warm with the heat of their formation. Together with a UCLA team that

Atmospheres of the Giant Planets

NASA Technical Reports Server (NTRS)

Ingersoll, Andrew P.

2002-01-01

The giant planets, Jupiter, Saturn, Uranus, and Neptune, are fluid objects. They have no solid surfaces because the light elements constituting them do not condense at solar-system temperatures. Instead, their deep atmospheres grade downward until the distinction between gas and liquid becomes meaningless. The preceding chapter delved into the hot, dark interiors of the Jovian planets. This one focuses on their atmospheres, especially the observable layers from the base of the clouds to the edge of space. These veneers arc only a few hundred kilometers thick, less than one percent of each planet's radius, but they exhibit an incredible variety of dynamic phenomena. The mixtures of elements in these outer layers resemble a cooled-down piece of the Sun. Clouds precipitate out of this gaseous soup in a variety of colors. The cloud patterns are organized by winds, which are powered by heat derived from sunlight (as on Earth) and by internal heat left over from planetary formation. Thus the atmospheres of the Jovian planets are distinctly different both compositionally and dynamically from those of the terrestrial planets. Such differences make them fascinating objects for study, providing clues about the origin and evolution of the planets and the formation of the solar system.

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.

Discovery and spectroscopy of the young jovian planet 51 Eri b with the Gemini Planet Imager

NASA Astrophysics Data System (ADS)

Macintosh, B.; Graham, J. R.; Barman, T.; De Rosa, R. J.; Konopacky, Q.; Marley, M. S.; Marois, C.; Nielsen, E. L.; Pueyo, L.; Rajan, A.; Rameau, J.; Saumon, D.; Wang, J. J.; Patience, J.; Ammons, M.; Arriaga, P.; Artigau, E.; Beckwith, S.; Brewster, J.; Bruzzone, S.; Bulger, J.; Burningham, B.; Burrows, A. S.; Chen, C.; Chiang, E.; Chilcote, J. K.; Dawson, R. I.; Dong, R.; Doyon, R.; Draper, Z. H.; Duchêne, G.; Esposito, T. M.; Fabrycky, D.; Fitzgerald, M. P.; Follette, K. B.; Fortney, J. J.; Gerard, B.; Goodsell, S.; Greenbaum, A. Z.; Hibon, P.; Hinkley, S.; Cotten, T. H.; Hung, L.-W.; Ingraham, P.; Johnson-Groh, M.; Kalas, P.; Lafreniere, D.; Larkin, J. E.; Lee, J.; Line, M.; Long, D.; Maire, J.; Marchis, F.; Matthews, B. C.; Max, C. E.; Metchev, S.; Millar-Blanchaer, M. A.; Mittal, T.; Morley, C. V.; Morzinski, K. M.; Murray-Clay, R.; Oppenheimer, R.; Palmer, D. W.; Patel, R.; Perrin, M. D.; Poyneer, L. A.; Rafikov, R. R.; Rantakyrö, F. T.; Rice, E. L.; Rojo, P.; Rudy, A. R.; Ruffio, J.-B.; Ruiz, M. T.; Sadakuni, N.; Saddlemyer, L.; Salama, M.; Savransky, D.; Schneider, A. C.; Sivaramakrishnan, A.; Song, I.; Soummer, R.; Thomas, S.; Vasisht, G.; Wallace, J. K.; Ward-Duong, K.; Wiktorowicz, S. J.; Wolff, S. G.; Zuckerman, B.

2015-10-01

Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric compositions and luminosities, which are influenced by their formation mechanisms. Using the Gemini Planet Imager, we discovered a planet orbiting the ~20-million-year-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water-vapor absorption. Modeling of the spectra and photometry yields a luminosity (normalized by the luminosity of the Sun) of 1.6 to 4.0 × 10-6 and an effective temperature of 600 to 750 kelvin. For this age and luminosity, “hot-start” formation models indicate a mass twice that of Jupiter. This planet also has a sufficiently low luminosity to be consistent with the “cold-start” core-accretion process that may have formed Jupiter.

DETAILED ABUNDANCES OF THE SOLAR TWINS 16 CYGNI A AND B: CONSTRAINING PLANET FORMATION MODELS

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

Schuler, Simon C.; Cunha, Katia; Smith, Verne V.

2011-08-20

Results of a detailed abundance analysis of the solar twins 16 Cyg A and 16 Cyg B based on high-resolution, high signal-to-noise ratio echelle spectroscopy are presented. 16 Cyg B is known to host a giant planet while no planets have yet been detected around 16 Cyg A. Stellar parameters are derived directly from our high-quality spectra, and the stars are found to be physically similar, with {Delta}T{sub eff} = +43 K, {Delta}log g = -0.02 dex, and {Delta}{xi} = +0.10 km s{sup -1} (in the sense of A - B), consistent with previous findings. Abundances of 15 elements aremore » derived and are found to be indistinguishable between the two stars. The abundances of each element differ by {<=}0.026 dex, and the mean difference is +0.003 {+-} 0.015 ({sigma}) dex. Aside from Li, which has been previously shown to be depleted by a factor of at least 4.5 in 16 Cyg B relative to 16 Cyg A, the two stars appear to be chemically identical. The abundances of each star demonstrate a positive correlation with the condensation temperature of the elements (T{sub c}); the slopes of the trends are also indistinguishable. In accordance with recent suggestions, the positive slopes of the [m/H]-T{sub c} relations may imply that terrestrial planets have not formed around either 16 Cyg A or 16 Cyg B. The physical characteristics of the 16 Cyg system are discussed in terms of planet formation models, and plausible mechanisms that can account for the lack of detected planets around 16 Cyg A, the disparate Li abundances of 16 Cyg A and B, and the eccentricity of the planet 16 Cyg B b are suggested.« less

A hybrid scenario for gas giant planet formation in rings

NASA Astrophysics Data System (ADS)

Durisen, Richard H.; Cai, Kai; Mejía, Annie C.; Pickett, Megan K.

2005-02-01

The core-accretion mechanism for gas giant formation may be too slow to create all observed gas giant planets during reasonable gas disk lifetimes, but it has yet to be firmly established that the disk instability model can produce permanent bound gaseous protoplanets under realistic conditions. Based on our recent simulations of gravitational instabilities in disks around young stars, we suggest that, even if instabilities due to disk self-gravity do not produce gaseous protoplanets directly, they may create persistent dense rings that are conducive to accelerated growth of gas giants through core accretion. The rings occur at and near the boundary between stable and unstable regions of the disk and appear to be produced by resonances with discrete spiral modes on the unstable side.

Modeling Spectra of Icy Satellites and Cometary Icy Particles Using Multi-Sphere T-Matrix Code

NASA Astrophysics Data System (ADS)

Kolokolova, Ludmilla; Mackowski, Daniel; Pitman, Karly M.; Joseph, Emily C. S.; Buratti, Bonnie J.; Protopapa, Silvia; Kelley, Michael S.

2016-10-01

The Multi-Sphere T-matrix code (MSTM) allows rigorous computations of characteristics of the light scattered by a cluster of spherical particles. It was introduced to the scientific community in 1996 (Mackowski & Mishchenko, 1996, JOSA A, 13, 2266). Later it was put online and became one of the most popular codes to study photopolarimetric properties of aggregated particles. Later versions of this code, especially its parallelized version MSTM3 (Mackowski & Mishchenko, 2011, JQSRT, 112, 2182), were used to compute angular and wavelength dependence of the intensity and polarization of light scattered by aggregates of up to 4000 constituent particles (Kolokolova & Mackowski, 2012, JQSRT, 113, 2567). The version MSTM4 considers large thick slabs of spheres (Mackowski, 2014, Proc. of the Workshop ``Scattering by aggregates``, Bremen, Germany, March 2014, Th. Wriedt & Yu. Eremin, Eds., 6) and is significantly different from the earlier versions. It adopts a Discrete Fourier Convolution, implemented using a Fast Fourier Transform, for evaluation of the exciting field. MSTM4 is able to treat dozens of thousands of spheres and is about 100 times faster than the MSTM3 code. This allows us not only to compute the light scattering properties of a large number of electromagnetically interacting constituent particles, but also to perform multi-wavelength and multi-angular computations using computer resources with rather reasonable CPU and computer memory. We used MSTM4 to model near-infrared spectra of icy satellites of Saturn (Rhea, Dione, and Tethys data from Cassini VIMS), and of icy particles observed in the coma of comet 103P/Hartley 2 (data from EPOXI/DI HRII). Results of our modeling show that in the case of icy satellites the best fit to the observed spectra is provided by regolith made of spheres of radius ~1 micron with a porosity in the range 85% - 95%, which slightly varies for the different satellites. Fitting the spectra of the cometary icy particles requires icy

A Venus-mass Planet Orbiting a Brown Dwarf: A Missing Link between Planets and Moons

NASA Astrophysics Data System (ADS)

Udalski, A.; Jung, Y. K.; Han, C.; Gould, A.; Kozłowski, S.; Skowron, J.; Poleski, R.; Soszyński, I.; Pietrukowicz, P.; Mróz, P.; Szymański, M. K.; Wyrzykowski, Ł.; Ulaczyk, K.; Pietrzyński, G.; Shvartzvald, Y.; Maoz, D.; Kaspi, S.; Gaudi, B. S.; Hwang, K.-H.; Choi, J.-Y.; Shin, I.-G.; Park, H.; Bozza, V.

2015-10-01

The co-planarity of solar system planets led Kant to suggest that they formed from an accretion disk, and the discovery of hundreds of such disks around young stars as well as hundreds of co-planar planetary systems by the Kepler satellite demonstrate that this formation mechanism is extremely widespread. Many moons in the solar system, such as the Galilean moons of Jupiter, also formed out of the accretion disks that coalesced into the giant planets. Here we report the discovery of an intermediate system, OGLE-2013-BLG-0723LB/Bb, composed of a Venus-mass planet orbiting a brown dwarf, which may be viewed either as a scaled-down version of a planet plus a star or as a scaled-up version of a moon plus a planet orbiting a star. The latter analogy can be further extended since they orbit in the potential of a larger, stellar body. For ice-rock companions formed in the outer parts of accretion disks, like Uranus and Callisto, the scaled masses and separations of the three types of systems are similar, leading us to suggest that the formation processes of companions within accretion disks around stars, brown dwarfs, and planets are similar.

Thermally-Induced Chemistry and the Jovian Icy Satellites: A Laboratory Study of the Formation of Sulfur Oxyanions

NASA Technical Reports Server (NTRS)

Loeffler, Mark J.; Hudson, Reggie L.

2011-01-01

Laboratory experiments have demonstrated that magnetospheric radiation in the Jovian system drives reaction chemistry in ices at temperatures relevant to Europa and other icy satellites. Here we present new results on thermally-induced reactions at 50-100 K in solid H2O-SO2 mixtures, reactions that take place without the need for a high-radiation environment. We find that H2O and SO2 react to produce sulfur Oxyanions, such as bisulfite, that as much as 30% of the SO2 can be consumed through this reaction, and that the products remain in the ice when the temperature is lowered, indicating that these reactions are irreversible. Our results suggest that thermally-induced reactions can alter the chemistry at temperatures relevant to the icy satellites in the Jovian system.

Searching for Planets Around other Stars

NASA Technical Reports Server (NTRS)

1998-01-01

In this colloquim presentation, Professor of Astronomy, Geoffrey Marcy discusses the discovery of planets orbiting other stars. Using the Doppler shift caused by stellar wobble that is caused by nearby planetary mass, astronomers have been able to infer the existence of Jupiter-sized planets around other stars. Using a special spectrometer at Lick Observatory, the wobble of several stars have been traced over the years required to generate an accurate pattern required to infer the stellar wobble. Professor Marcy, discusses the findings of planets around 47 Ursae Majoris, 16 Cygni B, 51 Pegasus, and 56 Rho 1 Cne. In the case of 56 Rho 1 Cne the planet appears to be close to the star, within 1.5 astronomical units. The observations from the smaller Lick Observatory will be augmented by new observations from the larger telescope at the Kek observatory. This move will allow observations of smaller planets, as opposed to the massive planets thus far discovered. The astronomers also hope to observe smaller stars with the Kek data. Future spaceborne observations will allow the discovery of even smaller planets. A spaceborne interferometer is in the planning stages, and an even larger observatory, called the Terrestrial Planet Finder, is hoped for. Professor Marcy shows artists' renderings of two of the planets thus far discovered. He also briefly discusses planetary formation and shows slides of both observations from the Orion Nebula and models of stellar system formation.

Global hydromagnetic simulations of a planet embedded in a dead zone: Gap opening, gas accretion, and formation of a protoplanetary jet

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

Gressel, O.; Nelson, R. P.; Turner, N. J.

We present global hydrodynamic (HD) and magnetohydrodynamic (MHD) simulations with mesh refinement of accreting planets embedded in protoplanetary disks (PPDs). The magnetized disk includes Ohmic resistivity that depends on the overlying mass column, leading to turbulent surface layers and a dead zone near the midplane. The main results are: (1) the accretion flow in the Hill sphere is intrinsically three-dimensional for HD and MHD models. Net inflow toward the planet is dominated by high-latitude flows. A circumplanetary disk (CPD) forms. Its midplane flows outward in a pattern whose details differ between models. (2) The opening of a gap magnetically couplesmore » and ignites the dead zone near the planet, leading to stochastic accretion, a quasi-turbulent flow in the Hill sphere, and a CPD whose structure displays high levels of variability. (3) Advection of magnetized gas onto the rotating CPD generates helical fields that launch magnetocentrifugally driven outflows. During one specific epoch, a highly collimated, one-sided jet is observed. (4) The CPD's surface density is ∼30 g cm{sup −2}, small enough for significant ionization and turbulence to develop. (5) The accretion rate onto the planet in the MHD simulation reaches a steady value 8 × 10{sup –3} M {sub ⊕} yr{sup –1} and is similar in the viscous HD runs. Our results suggest that gas accretion onto a forming giant planet within a magnetized PPD with a dead zone allows rapid growth from Saturnian to Jovian masses. As well as being relevant for giant planet formation, these results have important implications for the formation of regular satellites around gas giant planets.« less

The Cold and Icy Heart of Pluto

NASA Astrophysics Data System (ADS)

Hamilton, D. P.

2015-12-01

The locations of large deposits of frozen volatiles on planetary surfaces are largely coincident with areas receiving the minimum annual influx of solar energy. Thus we have the familiar polar caps of Earth and Mars, but cold equatorial regions for planets with obliquities between 54 and 126 degrees. Furthermore, for tilts between 45-66 degrees and 114-135 degrees the minimum incident energy occurs neither at the pole nor the equator. We find that the annual average insolation is always symmetric about Pluto's equator and is fully independent of the relative locations of the planet's pericenter and equinoxes. Remarkably, this symmetry holds for arbitrary orbital eccentricities and obliquities, and so we provide a short proof in the margin of this abstract. The current obliquity of Pluto is 119 degrees, giving it minima in average annual insolation at +/- 27 degrees latitude, with ~1.5% more flux to the equator and ~15% more to the poles. But the obliquity of Pluto also varies sinusoidally from 102-126 degrees and so, over the past million years, Pluto's annual equatorial and polar fluxes have changed by +15% and -13%, respectively. Interestingly, the energy flux received by latitudes between 25-35 degrees remains nearly constant over the presumably billions of years since Pluto acquired its current orbit and spin properties. Thus these latitudes are continuously cold and should be favored for the long-term deposition of volatile ices; the bright heart of Pluto, Sputnik Planum, extends not coincidentally across these latitudes. Reflected light and emitted thermal radiation from Charon increases annual insolation to one side of Pluto by of order 0.02%. Although small, the bulk of the energy is delivered at night to Pluto's cold equatorial regions. Furthermore, Charon's thermal IR is delivered very efficiently to icy deposits. Over billions of years, ices have preferentially formed and survived in the anti-Charon hemisphere.

The WFCAM Transit Survey: a search for rocky planets around cool stars

NASA Astrophysics Data System (ADS)

Birkby, Jayne

2010-09-01

The theory of core accretion makes two intriguing, observable predictions: i) that the formation of rocky/icy planets is common around M-dwarfs, and ii) that hot-Jupiters are extremely difficult to produce around low-mass stars. Furthermore, due to their small physical size and lower bolometric luminosity, M-dwarfs are up to 300? more sensitive to planetary transits in their habitable zones than solar-type stars. We present here the WFCAM Transit Survey (WTS); an ambitious, near- infrared photometric monitoring campaign of ˜6000 M-dwarfs across four 1.5 sq deg fields situated >5 degrees above and below the galactic plane. We utilise a unique opportunity provided by the highly efficient queue-scheduled operational mode of the UKIRT to observe our fields, with at least one visible at any time, when atmospheric conditions and RA coverage are unsuitable for other ongoing UKIRT programs. By probing the peak of the M-dwarf spectral energy distribution (13<17), we obtain a statistically significant sample of low-mass stars, which allows us to place meaningful constraints on the occurrence and formation of planets around M-dwarfs. The WTS has achieved one thousand epochs after 2 years in one of our target fields and will continue until April 2012. Our light curves have a per datapoint photometric precision of ˜3-4 mmag for the brightest objects, with RMS scatter < 1% for J<16, sufficient to detect Earth-like transits around M-dwarfs. I report here on the goals of our survey, our most recent results and the properties of our M-dwarf target sample. I also discuss our processing methods and how we combat the challenges encountered when observing occultations of faint red stars and the spectroscopic follow-up required to confirm them. (http://www.ast.cam.ac.uk/˜sth/wts/index.html)

JUICE: A European Mission to Jupiter and its Icy Moons

NASA Astrophysics Data System (ADS)

Grasset, Olivier; Witasse, Olivier; Barabash, Stas; Brandt, Pontus; Bruzzone, Lorenzo; Bunce, Emma; Cecconi, Baptiste; Cavalié, Thibault; Cimo, Giuseppe; Coustenis, Athena; Cremonese, Gabriele; Dougherty, Michele; Fletcher, Leigh N.; Gladstone, Randy; Gurvits, Leonid; Hartogh, Paul; Hoffmann, Holger; Hussmann, Hauke; Iess, Luciano; Jaumann, Ralf; Kasaba, Yasumasa; Kaspi, Yohai; Krupp, Norbert; Langevin, Yves; Mueller-Wodarg, Ingo; Palumbo, Pasquale; Piccioni, Giuseppe; Plaut, Jeffrey; Poulet, Francois; Roatsch, Thomas; Retherford, Kurt D.; Rothkaehl, Hanna; Stevenson, David J.; Tosi, Federico; Van Hoolst, Tim; Wahlund, Jan-Erik; Wurz, Peter; Altobelli, Nicolas; Accomazzo, A.; Boutonnet, Arnaud; Erd, Christian; Vallat, Claire

2016-10-01

JUICE - JUpiter ICy moons Explorer - is the first large mission in the ESA Cosmic Vision programme [1]. The implementation phase started in July 2015. JUICE will arrive at Jupiter in October 2029, and will spend 3 years characterizing the Jovian system, the planet itself, its giant magnetosphere, and the giant icy moons: Ganymede, Callisto and Europa. JUICE will then orbit Ganymede.The first goal of JUICE is to explore the habitable zone around Jupiter [2]. Ganymede is a high-priority target because it provides a unique laboratory for analyzing the nature, evolution and habitability of icy worlds, including the characteristics of subsurface oceans, and because it possesses unique magnetic fields and plasma interactions with the environment. On Europa, the focus will be on recently active zones, where the composition, surface and subsurface features (including putative water reservoirs) will be characterized. Callisto will be explored as a witness of the early Solar System.JUICE will also explore the Jupiter system as an archetype of gas giants. The circulation, meteorology, chemistry and structure of the Jovian atmosphere will be studied from the cloud tops to the thermosphere and ionosphere. JUICE will investigate the 3D properties of the magnetodisc, and study the coupling processes within the magnetosphere, ionosphere and thermosphere. The mission also focuses on characterizing the processes that influence surface and space environments of the moons.The payload consists of 10 instruments plus a ground-based experiment (PRIDE) to better constrain the S/C position. A remote sensing package includes imaging (JANUS) and spectral-imaging capabilities from UV to sub-mm wavelengths (UVS, MAJIS, SWI). A geophysical package consists of a laser altimeter (GALA) and a radar sounder (RIME) for exploring the moons, and a radio science experiment (3GM) to probe the atmospheres and to determine the gravity fields. The in situ package comprises a suite to study plasma and

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

Discovery and spectroscopy of the young jovian planet 51 Eri b with the Gemini Planet Imager.

PubMed

Macintosh, B; Graham, J R; Barman, T; De Rosa, R J; Konopacky, Q; Marley, M S; Marois, C; Nielsen, E L; Pueyo, L; Rajan, A; Rameau, J; Saumon, D; Wang, J J; Patience, J; Ammons, M; Arriaga, P; Artigau, E; Beckwith, S; Brewster, J; Bruzzone, S; Bulger, J; Burningham, B; Burrows, A S; Chen, C; Chiang, E; Chilcote, J K; Dawson, R I; Dong, R; Doyon, R; Draper, Z H; Duchêne, G; Esposito, T M; Fabrycky, D; Fitzgerald, M P; Follette, K B; Fortney, J J; Gerard, B; Goodsell, S; Greenbaum, A Z; Hibon, P; Hinkley, S; Cotten, T H; Hung, L-W; Ingraham, P; Johnson-Groh, M; Kalas, P; Lafreniere, D; Larkin, J E; Lee, J; Line, M; Long, D; Maire, J; Marchis, F; Matthews, B C; Max, C E; Metchev, S; Millar-Blanchaer, M A; Mittal, T; Morley, C V; Morzinski, K M; Murray-Clay, R; Oppenheimer, R; Palmer, D W; Patel, R; Perrin, M D; Poyneer, L A; Rafikov, R R; Rantakyrö, F T; Rice, E L; Rojo, P; Rudy, A R; Ruffio, J-B; Ruiz, M T; Sadakuni, N; Saddlemyer, L; Salama, M; Savransky, D; Schneider, A C; Sivaramakrishnan, A; Song, I; Soummer, R; Thomas, S; Vasisht, G; Wallace, J K; Ward-Duong, K; Wiktorowicz, S J; Wolff, S G; Zuckerman, B

2015-10-02

Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric compositions and luminosities, which are influenced by their formation mechanisms. Using the Gemini Planet Imager, we discovered a planet orbiting the ~20-million-year-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water-vapor absorption. Modeling of the spectra and photometry yields a luminosity (normalized by the luminosity of the Sun) of 1.6 to 4.0 × 10(-6) and an effective temperature of 600 to 750 kelvin. For this age and luminosity, "hot-start" formation models indicate a mass twice that of Jupiter. This planet also has a sufficiently low luminosity to be consistent with the "cold-start" core-accretion process that may have formed Jupiter. Copyright © 2015, American Association for the Advancement of Science.

Discovery and spectroscopy of the young Jovian planet 51 Eri b with the Gemini Planet Imager

DOE PAGES

Macintosh, B.; Graham, J. R.; Barman, T.; ...

2015-10-02

Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric compositions and luminosities, which are influenced by their formation mechanisms. Using the Gemini Planet Imager, we discovered a planet orbiting the ~20-million-year-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water-vapor absorption. Modeling of the spectra and photometry yields a luminosity (normalized by the luminosity of the Sun) of 1.6 to 4.0 × 10 –6 and an effective temperature of 600 to 750 kelvin. For this age and luminosity, “hot-start” formation models indicate a massmore » twice that of Jupiter. As a result, this planet also has a sufficiently low luminosity to be consistent with the “cold-start” core-accretion process that may have formed Jupiter.« less

Discovery and spectroscopy of the young Jovian planet 51 Eri b with the Gemini Planet Imager

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

Macintosh, B.; Graham, J. R.; Barman, T.

Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric compositions and luminosities, which are influenced by their formation mechanisms. Using the Gemini Planet Imager, we discovered a planet orbiting the ~20-million-year-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water-vapor absorption. Modeling of the spectra and photometry yields a luminosity (normalized by the luminosity of the Sun) of 1.6 to 4.0 × 10 –6 and an effective temperature of 600 to 750 kelvin. For this age and luminosity, “hot-start” formation models indicate a massmore » twice that of Jupiter. As a result, this planet also has a sufficiently low luminosity to be consistent with the “cold-start” core-accretion process that may have formed Jupiter.« less

Terrestrial planet formation in the presence of migrating super-Earths

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

Izidoro, André; Morbidelli, Alessandro; Raymond, Sean N., E-mail: izidoro.costa@gmail.com, E-mail: morbidelli@oca.eu, E-mail: rayray.sean@gmail.com

Super-Earths with orbital periods less than 100 days are extremely abundant around Sun-like stars. It is unlikely that these planets formed at their current locations. Rather, they likely formed at large distances from the star and subsequently migrated inward. Here we use N-body simulations to study the effect of super-Earths on the accretion of rocky planets. In our simulations, one or more super-Earths migrate inward through a disk of planetary embryos and planetesimals embedded in a gaseous disk. We tested a wide range of migration speeds and configurations. Fast-migrating super-Earths (τ{sub mig} ∼ 0.01-0.1 Myr) only have a modest effectmore » on the protoplanetary embryos and planetesimals. Sufficient material survives to form rocky, Earth-like planets on orbits exterior to the super-Earths'. In contrast, slowly migrating super-Earths shepherd rocky material interior to their orbits and strongly deplete the terrestrial planet-forming zone. In this situation any Earth-sized planets in the habitable zone are extremely volatile-rich and are therefore probably not Earth-like.« 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.

Radiation Induced Chemistry of Icy Surfaces: Laboratory Simulations

NASA Technical Reports Server (NTRS)

Gudipati, Murthy S.; Lignell, Antti; Li, Irene; Yang, Rui; Jacovi, Ronen

2011-01-01

We will discuss laboratory experiments designed to enhance our understanding the chemical processes on icy solar system bodies, enable interpretation of in-situ and remote-sensing data, and help future missions to icy solar system bodies, such as comets, Europa, Ganymede, Enceladus etc.

Outer planets satellites

NASA Technical Reports Server (NTRS)

Morrison, D.

1983-01-01

The present investigation takes into account the published literature on outer planet satellites for 1979-1982. It is pointed out that all but three (the moon and the two Martian satellites) of the known planetary satellites are found in the outer solar system. Most of these are associated with the three regular satellite systems of Jupiter, Saturn, and Uranus. The largest satellites are Titan in the Saturn system and Ganymede and Callisto in the Jupiter system. Intermediate in size between Mercury and Mars, each has a diameter of about 5000 km. Presumably each has an internal composition about 60 percent rock and 40 ice, and each is differentiated with a dense core extending out about 75 percent of the distance to the surface, with a mantle of high-pressure ice and a crust of ordinary ice perhaps 100 km thick. Attention is also given to Io, Europa, the icy satellites of Saturn, the satellites of Uranus, the small satellites of Jupiter and Saturn, Triton and the Pluto system, and plans for future studies.

CORRELATIONS BETWEEN COMPOSITIONS AND ORBITS ESTABLISHED BY THE GIANT IMPACT ERA OF PLANET FORMATION

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

Dawson, Rebekah I.; Lee, Eve J.; Chiang, Eugene, E-mail: rdawson@psu.edu

The giant impact phase of terrestrial planet formation establishes connections between super-Earths’ orbital properties (semimajor axis spacings, eccentricities, mutual inclinations) and interior compositions (the presence or absence of gaseous envelopes). Using N -body simulations and analytic arguments, we show that spacings derive not only from eccentricities, but also from inclinations. Flatter systems attain tighter spacings, a consequence of an eccentricity equilibrium between gravitational scatterings, which increase eccentricities, and mergers, which damp them. Dynamical friction by residual disk gas plays a critical role in regulating mergers and in damping inclinations and eccentricities. Systems with moderate gas damping and high solid surfacemore » density spawn gas-enveloped super-Earths with tight spacings, small eccentricities, and small inclinations. Systems in which super-Earths coagulate without as much ambient gas, in disks with low solid surface density, produce rocky planets with wider spacings, larger eccentricities, and larger mutual inclinations. A combination of both populations can reproduce the observed distributions of spacings, period ratios, transiting planet multiplicities, and transit duration ratios exhibited by Kepler super-Earths. The two populations, both formed in situ, also help to explain observed trends of eccentricity versus planet size, and bulk density versus method of mass measurement (radial velocities versus transit timing variations). Simplifications made in this study—including the limited time span of the simulations, and the approximate treatments of gas dynamical friction and gas depletion history—should be improved on in future work to enable a detailed quantitative comparison to the observations.« less

Probing Initial Conditions and Outcomes: Star and Planet Formation Programs within the NIRCam GTO Program

NASA Astrophysics Data System (ADS)

Meyer, Michael; NIRCam Star and Planet Formation Theme Team

2017-06-01

With its extraordinary sensitivity, wavelength coverage from < 1 to 5 microns, 2.2x4.4 arc minute field of view, and diversity of observing modes, NIRCam on JWST offers very powerful capabilities to explore the origins of stars and planets. Here we describe programs planned within the NIRCam GTO Program including: i) extinction mapping of pre-stellar cores; ii) massive star formation; iii) embedded clusters and the end of the IMF; iv) imaging and spectroscopy of young stellar objects; and v) excitation of PAH features. We will describe the scope of each program, selection of observing modes and rationale, as well as provide some explicit examples of program design. We will also review the expected outcomes, illustrating the power of NIRCam to answer questions fundamental to understanding the origins of stars and planets.

Possible Rapid Gas Giant Planet Formation in the Solar Nebula and Other Protoplanetary Disks.

PubMed

Boss

2000-06-20

Gas giant planets have been detected in orbit around an increasing number of nearby stars. Two theories have been advanced for the formation of such planets: core accretion and disk instability. Core accretion, the generally accepted mechanism, requires several million years or more to form a gas giant planet in a protoplanetary disk like the solar nebula. Disk instability, on the other hand, can form a gas giant protoplanet in a few hundred years. However, disk instability has previously been thought to be important only in relatively massive disks. New three-dimensional, "locally isothermal," hydrodynamical models without velocity damping show that a disk instability can form Jupiter-mass clumps, even in a disk with a mass (0.091 M middle dot in circle within 20 AU) low enough to be in the range inferred for the solar nebula. The clumps form with initially eccentric orbits, and their survival will depend on their ability to contract to higher densities before they can be tidally disrupted at successive periastrons. Because the disk mass in these models is comparable to that apparently required for the core accretion mechanism to operate, the models imply that disk instability could obviate the core accretion mechanism in the solar nebula and elsewhere.

Modeling planetary seismic data for icy worlds and terrestrial planets with AxiSEM/Instaseis: Example data and a model for the Europa noise environment

NASA Astrophysics Data System (ADS)

Panning, Mark Paul; Stähler, Simon; Kedar, Sharon; van Driel, Martin; Nissen-Meyer, Tarje; Vance, Steve

2016-10-01

Seismology is one of our best tools for detailing interior structure of planetary bodies, and seismometers are likely to be considered for future lander missions to other planetary bodies after the planned landing of InSight on Mars in 2018. In order to guide instrument design and mission requirements, however, it is essential to model likely seismic signals in advance to determine the most promising data needed to meet science goals. Seismic data for multiple planetary bodies can now be simulated rapidly for arbitrary source-receiver configurations to frequencies of 1 Hz and above using the numerical wave propagation codes AxiSEM and Instaseis (van Driel et al., 2015) using 1D models derived from thermodynamic constraints (e.g. Cammarano et al., 2006). We present simulations for terrestrial planets and icy worlds to demonstrate the types of seismic signals we may expect to retrieve. We also show an application that takes advantage of the computational strengths of this method to construct a model of the thermal cracking noise environment for Europa under a range of assumptions of activity levels and elastic and anelastic structure.M. van Driel, L. Krischer, S.C. Stähler, K. Hosseini, and T. Nissen-Meyer (2015), "Instaseis: instant global seismograms based on a broadband waveform database," Solid Earth, 6, 701-717, doi: 10.5194/se-6-701-2015.F. Cammarano, V. Lekic, M. Manga, M.P. Panning, and B.A. Romanowicz (2006), "Long-period seismology on Europa: 1. Physically consistent interior models," J. Geophys. Res., 111, E12009, doi: 10.1029/2006JE002710.

Reorientation Histories of the Terrestrial Planets

NASA Astrophysics Data System (ADS)

Keane, J. T.; Matsuyama, I.

2016-12-01

The nature of how a planet spins is controlled by the planet's inertia tensor. In a minimum energy rotation state, planets spin about the maximum principal axis of inertia. Yet, the orientation of this axis is not often constant with time. The redistribution of mass within a planet due to both interior processes (e.g. convection, intrusive volcanism) and surface processes (e.g. extrusive volcanism, impacts) can significantly alter the planet's inertia tensor, resulting in the reorientation of the planet. This form of reorientation is also known as true polar wander. Reorientation can directly alter the topography and gravity field of a planet, generate tectonic stresses, change the insolation geometry (affecting climate and volatile stability), and modify the orientation of the planet's magnetic field. Yet, despite its significance, the reorientation histories of many planets is not well constrained. In this work, we present a new technique for using spacecraft-derived, orbital gravity measurements to directly quantify how individual large geologic features reoriented Mercury, Venus, the Moon, and Mars. When coupled with the geologic record for these respective planets, this enables us to determine the reorientation history for each planet. These mark the first comprehensive, multi-episode reorientation chronologies for these planets. The reorientation histories for the Moon and Mercury are similar; the orientation of both planets is strongly controlled by the presence of large remnant bulges (tidal/rotational for the Moon, and likely thermal for Mercury), but significantly modulated by subsequent, large impacts and volcanic events—resulting in 15° of total reorientation after their formation. Mars experienced larger reorientation due to the formation of the Tharsis rise, punctuated by smaller reorientation events from large impacts. Lastly, Venus's diminutive remnant figure and large volcanic edifices result in the largest possible reorientation events, but the

Seeding Life on the Moons of the Outer Planets via Lithopanspermia

PubMed Central

Sigurdsson, Steinn; House, Christopher H.

2013-01-01

Abstract Material from the surface of a planet can be ejected into space by a large impact and could carry primitive life-forms with it. We performed n-body simulations of such ejecta to determine where in the Solar System rock from Earth and Mars may end up. We found that, in addition to frequent transfer of material among the terrestrial planets, transfer of material from Earth and Mars to the moons of Jupiter and Saturn is also possible, but rare. We expect that such transfers were most likely to occur during the Late Heavy Bombardment or during the ensuing 1–2 billion years. At this time, the icy moons were warmer and likely had little or no ice shell to prevent meteorites from reaching their liquid interiors. We also note significant rates of re-impact in the first million years after ejection. This could re-seed life on a planet after partial or complete sterilization by a large impact, which would aid the survival of early life during the Late Heavy Bombardment. Key Words: Panspermia—Impact—Meteorites—Titan—Europa. Astrobiology 13, 1155–1165. PMID:24341459

The Maximum Mass of a Planet

NASA Astrophysics Data System (ADS)

Schlaufman, Kevin C.

2018-06-01

Giant planet occurrence is a steeply increasing function of FGK dwarf host star metallicity, and this is interpreted as support for the core-accretion model of giant planet formation. On the other hand, the occurrence of low-mass stellar companions to FGK dwarf stars does not appear to depend on stellar metallicity. The mass at which objects no longer prefer metal-rich FGK dwarf host stars can therefore be used to infer the maximum mass of objects that form like planets through core accretion. I'll show that objects more massive than about 10 M_Jup do not orbit metal-rich host stars and that this transition is coincident with a minimum in the occurrence rate of such objects. These facts suggest that the maximum mass of a celestial body formed through core accretion like a planet is less than 10 M_Jup. This observation can be used to infer the properties of protoplanetary disks and reveals that the Type I and Type II disk migration problems---two major issues for the modern model of planet formation---are not problems at all.

The Last Gasp of Gas Giant Planet Formation: A Spitzer Study of the 5 Myr Old Cluster NGC 2362

NASA Astrophysics Data System (ADS)

Currie, Thayne; Lada, Charles J.; Plavchan, Peter; Robitaille, Thomas P.; Irwin, Jonathan; Kenyon, Scott J.

2009-06-01

Expanding upon the Infrared Array Camera (IRAC) survey from Dahm & Hillenbrand, we describe Spitzer IRAC and Multiband Imaging Photometer for Spitzer observations of the populous, 5 Myr old open cluster NGC 2362. We analyze the mid-IR colors of cluster members and compared their spectral energy distributions (SEDs) to star+circumstellar disk models to constrain the disk morphologies and evolutionary states. Early/intermediate-type confirmed/candidate cluster members either have photospheric mid-IR emission or weak, optically thin IR excess emission at λ >= 24 μm consistent with debris disks. Few late-type, solar/subsolar-mass stars have primordial disks. The disk population around late-type stars is dominated by disks with inner holes (canonical "transition disks") and "homologously depleted" disks. Both types of disks represent an intermediate stage between primordial disks and debris disks. Thus, in agreement with previous results, we find that multiple paths for the primordial-to-debris disk transition exist. Because these "evolved primordial disks" greatly outnumber primordial disks, our results undermine standard arguments in favor of a lsim105 yr timescale for the transition based on data from Taurus-Auriga. Because the typical transition timescale is far longer than 105 yr, these data also appear to rule out standard ultraviolet photoevaporation scenarios as the primary mechanism to explain the transition. Combining our data with other Spitzer surveys, we investigate the evolution of debris disks around high/intermediate-mass stars and investigate timescales for giant planet formation. Consistent with Currie et al., the luminosity of 24 μm emission in debris disks due to planet formation peaks at ≈10-20 Myr. If the gas and dust in disks evolve on similar timescales, the formation timescale for gas giant planets surrounding early-type, high/intermediate-mass (gsim1.4 M sun) stars is likely 1-5 Myr. Most solar/subsolar-mass stars detected by Spitzer have

IPPF Co-operative Information Service (ICIS). August 1977.

ERIC Educational Resources Information Center

International Planned Parenthood Federation, London (England).

The pooling of documentation service resources has resulted in the creation of an International Planned Parenthood Federation (IPPF) integrated bibliographic information system. The former Library Bulletin has become IPPF Cooperative Information Service (ICIS). Entries in ICIS are classified according to the following nine categories: (0) General…

IPPF Co-operative Information Service (ICIS). May 1977.

ERIC Educational Resources Information Center

International Planned Parenthood Federation, London (England).

The pooling of documentation service resources has resulted in the creation of an International Planned Parenthood Federation (IPPF) integrated bibliographic information system. Thus, the former Library Bulletin has become IPPF Cooperative Information Service (ICIS). This is the first such publication. Entries in ICIS are classified according to…

Volatile inventory and early evolution of the planetary atmospheres

NASA Astrophysics Data System (ADS)

Marov, Mikhail Ya.; Ipatov, Sergei I.

Formation of atmospheres of the inner planets involved the concurrent processes of mantle degassing and collisions that culminated during the heavy bombardment. Volatile-rich icy planetesimals impacting on the planets as a late veneer strongly contributed to the volatile inventory. Icy remnants of the outer planet accretion significantly complemented the accumulation of the lithophile and atmophile elements forced out onto the surface of the inner planets from silicate basaltic magma enriched in volatiles. Orbital dynamics of small bodies, including near-Earth asteroids, comets, and bodies from the Edgeworth-Kuiper belt evolving to become inner planet crossers, is addressed to examine different plausible amounts of volatile accretion. The relative importance of comets and chondrites in the delivery of volatiles is constrained by the observed fractionation pattern of noble gas abundances in the atmospheres of inner planets. The following development of the early atmospheres depended on the amount of volatiles expelled from the interiors and deposited by impactors, while the position of the planet relative to the Sun and its mass affected its climatic evolution.

Cost-Effective Icy Bodies Exploration using Small Satellite Missions

NASA Technical Reports Server (NTRS)

Jonsson, Jonas; Mauro, David; Stupl, Jan; Nayak, Michael; Aziz, Jonathan; Cohen, Aaron; Colaprete, Anthony; Dono-Perez, Andres; Frost, Chad; Klamm, Benjamin;

IPPF Co-operative Information Service (ICIS). November 1977.

ERIC Educational Resources Information Center

International Planned Parenthood Federation, London (England).

This ICIS bulletin replaces the formal Library Bulletin of the International Planned Parenthood Federation (IPPF). It represents the integration of a bibliographic information network. Entries in ICIS are classified according to the following nine categories: (0) General Reference; (1) IPPF; (2) Family Planning and Health Care; (3) Biomedical…

Identifying new surface constituents of icy moons using mid-infrared spectroscopy

NASA Astrophysics Data System (ADS)

Young, Cindy L.; Wray, James J.; Hand, Kevin P.; Poston, Michael J.; Carlson, Robert W.; Clark, Roger N.; Spencer, John R.; Jennings, Donald E.

2015-11-01

Spectroscopic compositional studies of the icy satellites can help us to better understand the formation and evolution of material in the outer solar system. The spectral complexity of the Saturnian satellite system as seen in reflected visible light suggests additional complexity may be present at mid-infrared wavelengths from which unique compositional information can be gleaned [1]. In addition, the mid-infrared is the region of the stronger fundamental diagnostic vibrational modes of many compounds. However, Cassini Composite Infrared Spectrometer (CIRS) surface compositional studies have received little attention to date.We are exploring the suitability of mid-infrared spectroscopy for discovering non-H2O compounds on icy moon surfaces. On the dark terrain of Iapetus, we find an emissivity feature at ~855 cm-1 and a potential doublet at 660 and 690 cm-1 that do not correspond to any known instrument artifacts [2]. We attribute the 855 cm-1 feature to fine-grained silicates, similar to those found in dust on Mars and in meteorites, which are nearly featureless at shorter wavelengths [3]. Although silicates on the dark terrains of Saturn’s icy moons have been suspected for decades, there have been no definitive prior detections. Serpentines measured at ambient conditions have features near 855 cm-1 and 660 cm-1 [4]. However, peaks can shift depending on temperature, pressure, and grain size, so measurements at Iapetus-like conditions are necessary for more positive identifications [e.g., 5].We measured the vacuum, low temperature (125 K) spectra of various fine-grained powdered silicates. We find that some of these materials do have emissivity features near 855 cm-1 and match the doublet. Identifying a specific silicate would provide clues into the sources and sinks of the dark material in the Saturnian system. We report on our ongoing exploration of the CIRS icy moon dataset and plans for future measurements in JPL’s Icy Worlds Simulation Lab.[1] Flasar, F

OASIS: Organics Analyzer for Sampling Icy Surfaces

NASA Technical Reports Server (NTRS)

Getty, S. A.; Dworkin, J. P.; Glavin, D. P.; Martin, M.; Zheng, Y.; Balvin, M.; Southard, A. E.; Ferrance, J.; Malespin, C.

2012-01-01

Liquid chromatography mass spectrometry (LC-MS) is a well established laboratory technique for detecting and analyzing organic molecules. This approach has been especially fruitful in the analysis of nucleobases, amino acids, and establishing chirol ratios [1 -3]. We are developing OASIS, Organics Analyzer for Sampling Icy Surfaces, for future in situ landed missions to astrochemically important icy bodies, such as asteroids, comets, and icy moons. The OASIS design employs a microfabricated, on-chip analytical column to chromatographically separate liquid ana1ytes using known LC stationary phase chemistries. The elution products are then interfaced through electrospray ionization (ESI) and analyzed by a time-of-flight mass spectrometer (TOF-MS). A particular advantage of this design is its suitability for microgravity environments, such as for a primitive small body.

The ODINUS Mission Concept: a Mission for the exploration the Ice Giant Planets

NASA Astrophysics Data System (ADS)

Peron, Roberto

We present the scientific case and the mission concept of a proposal for the the comparative exploration of the ice giant planets Uranus and Neptune and their satellites with a pair of twin spacecraft: ODINUS (Origins, Dynamics and Interiors of Neptunian and Uranian Systems). The ODINUS proposal was submitted in response to the call for white papers for the definition of the themes of the L2 and L3 mission in the framework of ESA Cosmic Vision 2015-2025 program. The goal of ODINUS is the advancement of our understanding of the ancient past of the Solar System and, more generally, of how planetary systems form and evolve. The mission concept is focused on providing elements to answer to the scientific themes of the Cosmic Vision 2015-2025 program: What are the conditions for planetary formation and the emergency of life? How does the Solar System work? What are the fundamental physical laws of the Universe? In order to achieve its goals, ODINUS foresees the use of two twin spacecraft to be placed in orbit around Uranus and Neptune respectively, with selected flybys of their satellites. The proposed measurements aim to study the atmospheres and magnetospheres of the planets, the surfaces of the satellites, and the interior structure and composition of both satellites and planets. An important possibility for performing fundamental physics studies (among them tests of general relativity theory) is offered by the cruise phase. After the extremely positive evaluation of ESA Senior Survey Committee, who stated that ``the exploration of the icy giants appears to be a timely milestone, fully appropriate for an L class mission'', we discuss strategies to comparatively study Uranus and Neptune with future international missions.

Entry Probe Missions to the Giant Planets

NASA Astrophysics Data System (ADS)

Spilker, T. R.; Atkinson, D. H.; Atreya, S. K.; Colaprete, A.; Cuzzi, J. N.; Spilker, L. J.; Coustenis, A.; Venkatapathy, E.; Reh, K.; Frampton, R.

2009-12-01

The primary motivation for in situ probe missions to the outer planets derives from the need to constrain models of solar system formation and the origin and evolution of atmospheres, to provide a basis for comparative studies of the gas and ice giants, and to provide a valuable link to extrasolar planetary systems. As time capsules of the solar system, the gas and ice giants offer a laboratory to better understand the atmospheric chemistries, dynamics, and interiors of all the planets, including Earth; and it is within the atmospheres and interiors of the giant planets that material diagnostic of the epoch of formation can be found, providing clues to the local chemical and physical conditions existing at the time and location at which each planet formed. Measurements of current conditions and processes in those atmospheres inform us about their evolution since formation and into the future, providing information about our solar system’s evolution, and potentially establishing a framework for recognizing extrasolar giant planets in different stages of their evolution. Detailed explorations and comparative studies of the gas and ice giant planets will provide a foundation for understanding the integrated dynamic, physical, and chemical origins, formation, and evolution of the solar system. To allow reliable conclusions from comparative studies of gas giants Jupiter and Saturn, an entry probe mission to Saturn is needed to complement the Galileo Probe measurements at Jupiter. These measurements provide the basis for a significantly better understanding of gas giant formation in the context of solar system formation. A probe mission to either Uranus or Neptune will be needed for comparative studies of the gas giants and the ice giants, adding knowledge of ice giant origins and thus making further inroads in our understanding of solar system formation. Recognizing Jupiter’s spatial variability and the need to understand its implications for global composition

Methods of Estimating Initial Crater Depths on Icy Satellites using Stereo Topography

NASA Astrophysics Data System (ADS)

Persaud, D. M.; Phillips, C. B.

2014-12-01

Stereo topography, combined with models of viscous relaxation of impact craters, allows for the study of the rheology and thermal history of icy satellites. An important step in calculating relaxation of craters is determining the initial depths of craters before viscous relaxation. Two methods for estimating initial crater depths on the icy satellites of Saturn have been previously discussed. White and Schenk (2013) present the craters of Iapetus as relatively unrelaxed in modeling the relaxation of craters of Rhea. Phillips et al. (2013) assume that Herschel crater on Saturn's satellite Mimas is unrelaxed in relaxation calculations and models of Rhea and Dione. In the second method, the depth of Herschel crater is scaled based on the different crater diameters and the difference in surface gravity on the large moons to predict the initial crater depths for Rhea and Dione. In the first method, since Iapetus is of similar size to Dione and Rhea, no gravity scaling is necessary; craters of similar size on Iapetus were chosen and their depths measured to determine the appropriate initial crater depths for Rhea. We test these methods by first extracting topographic profiles of impact craters on Iapetus from digital elevation models (DEMs) constructed from stereo images from the Cassini ISS instrument. We determined depths from these profiles and used them to calculate initial crater depths and relaxation percentages for Rhea and Dione craters using the methods described above. We first assumed that craters on Iapetus were relaxed, and compared the results to previously calculated relaxation percentages for Rhea and Dione relative to Herschel crater (with appropriate scaling for gravity and crater diameter). We then tested the assumption that craters on Iapetus were unrelaxed and used our new measurements of crater depth to determine relaxation percentages for Dione and Rhea. We will present results and conclusions from both methods and discuss their efficacy for

Deep ice and salty oceans of icy worlds, how high pressures influence their thermodynamics and provide constrains on extraterrestrial habitability

NASA Astrophysics Data System (ADS)

Journaux, B.; Brown, J. M.; Bollengier, O.; Abramson, E.

2017-12-01

As in Earth arctic and Antarctic regions, suspected extraterrestrial deep oceans in icy worlds (i.e. icy moons and water-rich exoplanets) chemistry and thermodynamic state will strongly depend on their equilibrium with H2O ice and present solutes. Na-Mg-Cl-SO4 salt species are currently the main suspected ionic solutes to be present in deep oceans based on remote sensing, magnetic field measurements, cryovolcanism ice grains chemical analysis and chondritic material aqueous alteration chemical models. Unlike on our planet, deep extraterrestrial ocean might also be interacting at depth with high pressure ices (e.g. III, V, VI, VI, X) which have different behavior compared to ice Ih. Unfortunately, the pressures and temperatures inside these hydrospheres differ significantly from the one found in Earth aqueous environments, so most of our current thermodynamic databases do not cover the range of conditions relevant for modeling realistically large icy worlds interiors. Recent experimental results have shown that the presence of solutes, and more particularly salts, in equilibrium with high pressure ices have large effects on the stability, buoyancy and chemistry of all the phases present at these extreme conditions. High pressure in-situ measurements using diamond anvil cell apparatus were operated both at the University of washington and at the European Synchrotron Radiation Facility on aqueous systems phase diagrams with Na-Mg-Cl-SO4 species, salt incorporation in high pressure ices and density inversions between the solid and the fluids. These results suggest a more complex picture of the interior structure, dynamic and chemical evolution of large icy worlds hydrospheres when solutes are taken into account, compared to current models mainly using pure water. Based on our in-situ experimental measurements, we propose the existence of new liquid environments at greater depths and the possibility of solid state transport of solute through the high pressure ices

Laboratory Reference Spectroscopy of Icy Satellite Candidate Surface Materials (Invited)

NASA Astrophysics Data System (ADS)

Dalton, J. B.; Jamieson, C. S.; Shirley, J. H.; Pitman, K. M.; Kariya, M.; Crandall, P.

2013-12-01

Pitman, 2012). We will report on recent results, including spectra of sulfate hydrates, simple organic molecules, and volatile ices measured at PICL in support of past, present and planned missions. We gratefully acknowledge the support of JPL's Research and Technology Development and Strategic Hire Programs, and of the NASA Outer Planets Research and Planetary Geology and Geophysics programs. Dalton, III, J.B., Spectroscopy of icy moon surface materials, Space Sci. Rev. 153:219-247, 2010. Dalton, III, J.B., and Pitman, K.M., Low temperature optical constants of some hydrated sulfates relevant to planetary surfaces, J. Geophys. Res. 117:E09001, doi:10.1029/2011JE004036, 2012. Hapke, B.W., Bidirectional reflectance spectroscopy I. Theory, J. Geophys. Res. 86, 3039-3054, 1981. Shkuratov, Y., L. Starukhina, H. Hoffmann, and G. Arnold, A model of spectral albedo of particulate surfaces: Implications for optical properties of the Moon, Icarus 137, 235-246, 1999.

Investigation of Charon's Craters With Abrupt Terminus Ejecta, Comparisons With Other Icy Bodies, and Formation Implications

NASA Astrophysics Data System (ADS)

Robbins, Stuart J.; Runyon, Kirby; Singer, Kelsi N.; Bray, Veronica J.; Beyer, Ross A.; Schenk, Paul; McKinnon, William B.; Grundy, William M.; Nimmo, Francis; Moore, Jeffrey M.; Spencer, John R.; White, Oliver L.; Binzel, Richard P.; Buie, Marc W.; Buratti, Bonnie J.; Cheng, Andrew F.; Linscott, Ivan R.; Reitsema, Harold J.; Reuter, Dennis C.; Showalter, Mark R.; Tyler, G. Len; Young, Leslie A.; Olkin, Catherine B.; Ennico, Kimberly S.; Weaver, Harold A.; Stern, S. Alan

2018-01-01

On the moon and other airless bodies, ballistically emplaced ejecta transitions from a thinning, continuous inner deposit to become discontinuous beyond approximately one crater radius from the crater rim and can further break into discrete rays and secondary craters. In contrast, on Mars, ejecta often form continuous, distinct, and sometimes thick deposits that transition to a low ridge or escarpment that may be circular or lobate. The Martian ejecta type has been variously termed pancake, rampart, lobate, or layered, and in this work we refer to it as "abrupt termini" ejecta (ATE). Two main formation mechanisms have been proposed, one requiring interaction of the ejecta with the atmosphere and the other mobilization of near-surface volatiles. ATE morphologies are also unambiguously seen on Ganymede, Europa, Dione, and Tethys, but they are not as common as on Mars. We have identified up to 38 craters on Charon that show signs of ATE, including possible distal ramparts and lobate margins. These ejecta show morphologic and morphometric similarities with other moons in the solar system, which are a subset of the properties observed on Mars. From comparison of these ejecta on Charon and other solar system bodies, we find the strongest support for subsurface volatile mobilization and ejecta fluidization as the main formation mechanism for the ATE, at least on airless, icy worlds. This conclusion comes from the bodies on which they are found, an apparent preference for certain terrains, and the observation that craters with ATE can be near to similarly sized craters that only have gradational ejecta.

Discovery of two planets around a millisecond pulsar

NASA Technical Reports Server (NTRS)

Wolszczan, A.

1992-01-01

By timing the arrival of radio signals from a rapidly spinning pulsar at the Arecibo Observatory's radio/radar telescope, the most convincing evidence so far for a planetary system outside our own has been found: two or possibly three planets that orbit the neutron star called PSR1257+12. This finding indicates that planet formation may be a more common process than previously anticipated and that the formation of disks of gas and dust that are sufficiently massive to condense into Earth-sized planets orbiting their central bodies can take place under surprisingly diverse conditions.

Volcanoes and atmospheres; catastrophic influences on the planets

USGS Publications Warehouse

Kieffer, S.W.

1986-01-01

For a rare and brief instant in geologic time, we can imagine that the sulfurous, chromatic surface of Io (one of the satellites of Jupiter) lies quiet. Perhaps stars glisten brilliantly through the tenuous nigh sky. Here and there, thick icy fogs enshroud fumaroles where sulfur dioxide leaks from the underworld. Suddenly, a fissure splits the surface and billowing clouds of sulfurous gases and ice hurl orange and black ash into the atmosphere. Minute by minute, the intensity of the eruption builds; stars begin disappearing from the night sky. The rising plume inhales the nearby atmosphere, mixing it with the exhalations from the volcano. Particles of sulfur, sulfur dioxide snow and ash rise to 300 kilometers, later raining down across the planet a thousand kilometers away. 

The Potential for Volcanism and Tectonics on Extrasolar Terrestrial Planets

NASA Astrophysics Data System (ADS)

Quick, Lynnae C.; Roberge, Aki

2018-01-01

JWST and other next-generation space telescopes (e.g., LUVOIR, HabEx, & OST) will usher in a new era of exoplanet characterization that may lead to the identification of habitable, Earth-like worlds. Like the planets and moons in our solar system, the surfaces and interiors of terrestrial exoplanets may be shaped by volcanism and tectonics (Fu et al., 2010; van Summeren et al., 2011; Henning and Hurford, 2014). The magnitude and rate of occurrence of these dynamic processes can either facilitate or preclude the existence of habitable environments. Likewise, it has been suggested that detections of cryovolcanism on icy exoplanets, in the form of geyser-like plumes, could indicate the presence of subsurface oceans (Quick et al., 2017).The presence of volcanic and tectonic activity on solid exoplanets will be intimately linked to planet size and heat output in the form of radiogenic and/or tidal heating. In order to place bounds on the potential for such activity, we estimated the heat output of a variety of exoplanets observed by Kepler. We considered planets whose masses and radii range from 0.067 ME (super-Ganymede) to 8 ME (super-Earth), and 0.5 to 1.8 RE, respectively. These heat output estimates were then compared to those of planets, moons, and dwarf planets in our solar system for which we have direct evidence for the presence/absence of volcanic and tectonic activity. After exoplanet heating rates were estimated, depths to putative molten layers in their interiors were also calculated. For planets such as TRAPPIST-1h, whose densities, orbital parameters, and effective temperatures are consistent with the presence of significant amounts of H2O (Luger et al., 2017), these calculations reveal the depths to internal oceans which may serve as habitable niches beneath surface ice layers.

Formation of Ocean Sedimentary Rocks as Active Planets and Life-Like Systems

NASA Astrophysics Data System (ADS)

Miura, Y.

2017-10-01

Wet shocked rocks are discarded globally and enriched elements in ocean-sedimentary rocks, which is strong indicator of ocean water of other planets. Ocean-sedimentary rocks are strong indicator of water planets and possible exo-life on planet Mars.

The Formation of Giant Planets and the Collisional Evolution of Planetesimals: Lessons Learned from the Solar System

NASA Astrophysics Data System (ADS)

Turrini, Diego

2013-07-01

The formation of giant planets is one of the milestones in the history of planetary systems, as they shape the evolution of the protoplanetary disks they are embedded in. While observational facilities approach the sensitivity necessary to probe these primordial phases in disks around other stars (e.g. Quanz et al. 2013), there are still lessons we can draw from our own Solar System. Safronov (1969) was the first to recognize that the formation of Jupiter would trigger the first bombardment in the history of the Solar System by scattering of planetesimals residing near its formation region. This scenario was further explored by Weidenschilling (1975) and Weidenschilling et al. (2001), who observed that part of these planetesimals ejected from the outer Solar System would cross the asteroid belt and contribute to the catastrophic destruction of primordial asteroids. Later, Turrini et al. (2011) showed that the appearance of the orbital resonances with Jupiter in the asteroid belt would create a second but dominant population of impactors. The combination of these two populations of impactors represents the Jovian Early Bombardment (Turrini et al. 2011). The formation of Jupiter is the sole necessary condition to trigger the Jovian Early Bombardment, yet migration can play an important role in enhancing its effects due to the sweeping of the resonances through the asteroid belt (Turrini et al. 2011). Across the Jovian Early Bombardment, collisional erosion played a more important role than catastrophic impacts and could bring to the destruction of planetesimals of 200 km in diameter or even larger (Turrini et al. 2012). As pointed out by Turrini et al. (2012), the processes causing the Jovian Early Bombardment are not exclusive to the Solar Nebula: they are general to all circumstellar disks that host forming giant planets. As a consequence, all these results describe an evolutionary path that is common to planetary systems where giant planets are forming and

Formation of a 'planet' by rapid evaporation of a pulsar's companion

NASA Technical Reports Server (NTRS)

Rasio, F. A.; Shapiro, S. L.; Teukolsky, S. A.

1992-01-01

A model based on the binary configuration of the PSR1829-10 pulsar (Bailes et al., 1991) is used to show that the formation of a binary pulsar with a planet-size companion, large original separation, and small eccentricity could result from the rapid evaporation of a much more massive binary companion by the pulsar's radiation. Such an evaporation process is known to be taking place in at least two other binary pulsars: PSR1957 + 20 (Fruchter et al., 1990; Ryba and Taylor, 1991) and PSR1744 - 24A (Lyne et al., 1990). It is shown here that, about one million years ago, the companion mass and binary separation could have been comparable to those currently observed in the eclipsing binary pulsar PSR1957 + 20.

An ALMA Survey of Planet Forming Disks in Rho Ophiuchus

NASA Astrophysics Data System (ADS)

Cox, Erin Guilfoil; Looney, Leslie; Harris, Robert J.; Dong, Jiayin; Segura-Cox, Dominique; Tobin, John J.; Sadavoy, Sarah; Li, Zhi-Yun; Dunham, Michael; Perez, Laura M.; Chandler, Claire J.; Kratter, Kaitlin M.; Melis, Carl; Chiang, Hsin-Fang

2017-01-01

Relatively evolved (~ 1 Myr old) protostars with little residual natal envelope, but massive disks, are commonly assumed to be the sites of ongoing planet formation. Critical to our study of these objects is information about the available mass reservior and dust structure, as they directly tie in to how much mass is available for planets as well as the modes of planet formation that occur (i.e., core-accretion vs. gravitational instability). Millimeter-wave observations provide this critical information as continuum emission is relatively optically thin, allowing for mass estimates, and the availability of high-resolution interferometry, allowing structure constraints. We present high-resolution observations of the population of Class II protostars in the Rho-Ophiuchus cloud (d ~ 130 pc). Our survey observed ~50 of these older protostars at 870µm, using the Atacama Large Millimeter/submillimeter Array (ALMA). Out of these sources, there are ~10 transition disks, where we see a ring of dust emission surrounding the central protostar -- indicative of ongoing planet formation -- as well as many binary systems. Both of these stages have implications for star and planet formation. We present results from both 1-D and 2-D disk modeling, where we try to understand disk substructure that might indicate on-going planet formation, in particular, transition disk cavities, disk gaps, and asymmetries in the dust emission.

A multi-wavelength database of water vapor in planet-forming regions

NASA Astrophysics Data System (ADS)

Pontoppidan, Klaus

The inner few astronomical units of gas-rich protoplanetary disk are environments characterized by a rich and active gaseous chemistry. Primitive material left over from the formation of our own Solar System has for a long time yielded tantalizing clues to a heterogenous nebula with intricate dynamical, thermal and chemical structure that ultimately led to a great diversity in the planets and planetesimals of the Solar System. The discovery of a rich chemistry in protoplanetary disks via a forest of strong 3-40 micron molecular emission lines (H2O, OH, CO2, HCN, C2H2,...) allows us for the first time to investigate chemical diversity in other planet-forming environmments (Salyk et al. 2008; Carr & Najita 2008). Further efforts, supported by the Origins program, has established that this molecular forest is seen in the disks surrounding most young solar- type stars (Pontoppidan et al. 2010). We propose a 3-year program to analyze our growing multi-wavelength database of observations of water, OH and organic molecules in the surfaces of protoplanetary disks. The database includes high (R~25,000-100,000) and medium resolution (R~600-3000) 3- 200 micron spectra from a wide range of facilities (Keck-NIRSPEC, VLT-CRIRES, Spitzer-IRS, VLT-VISIR, Gemini-Michelle and Herschel-PACS). Our previous efforts have focused on demonstrating feasibility for observing water and other molecules in planet-forming regions, building statistics to show that the molecular forest is ubiquitous in disks around low-mass and solar-type stars and taking the first steps in understanding the implied chemical abundances. Now, as the next logical step, we will combine multi- wavelength data from our unique multi-wavelength database to map the radial distribution of, in particular, water and its derivatives. 1) We will use both line profile information from the high-resolution spectra, as well as line strengths, from a combination of high and low temperature lines to constrain the radial abundance

A multi-wavelength database of water vapor in planet-forming regions

NASA Astrophysics Data System (ADS)

Pontoppidan, Klaus

The inner few astronomical units of gas-rich protoplanetary disk are environments characterized by a rich and active gaseous chemistry. Primitive material left over from the formation of our own Solar System has for a long time yielded tantalizing clues to a heterogenous nebula with intricate dynamical, thermal and chemical structure that ultimately led to a great diversity in the planets and planetesimals of the Solar System. The discovery of a rich chemistry in protoplanetary disks via a forest of strong 3-40 micron molecular emission lines (H2O, OH, CO2, HCN, C2H2,...) allows us for the first time to investigate chemical diversity in other planet-forming environmments (Salyk et al. 2008; Carr & Najita 2008). Further efforts, supported by the Origins program, has established that this molecular forest is seen in the disks surrounding most young solar- type stars (Pontoppidan et al. 2010). We propose a 3-year program to analyze our growing multi-wavelength database of observations of water, OH and organic molecules in the surfaces of protoplanetary disks. The database includes high (R~25,000-100,000) and medium resolution (R~600-3000) 3- 200 micron spectra from a wide range of facilities (Keck-NIRSPEC, VLT-CRIRES, Spitzer-IRS, VLT-VISIR, Gemini-Michelle and Herschel-PACS). Our previous efforts have focused on demonstrating feasibility for observing water and other molecules in planet-forming regions, building statistics to show that the molecular forest is ubiquitous in disks around low-mass and solar-type stars and taking the first steps in understanding the implied chemical abundances. Now, as the next logical step, we will combine multi- wavelength data from our unique multi-wavelength database to map the radial distribution of, in particular, water and its derivatives. 1) Â We will use both line profile information from the high-resolution spectra, as well as line strengths, from a combination of high and low temperature lines to constrain the radial

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

Ion implantation in ices and its relevance to the icy moons of the external planets

NASA Astrophysics Data System (ADS)

Strazzulla, G.; Baratta, G. A.; Fulvio, D.; Garozzo, M.; Leto, G.; Palumbo, M. E.; Spinella, F.

2007-08-01

Solid, atmosphere-less objects in the Solar System are continuously irradiated by energetic ions mostly in the keV-MeV energy range. Being the penetration depth of the incoming ions usually much lower than the thickness of the target, they are stopped into the ice. They deposit energy in the target induce the breaking of molecular bonds. The recombination of fragments produce different molecules. Reactive ions (e.g., H, C, N, O, S) induce all of the effects of any other ion, but in addition have a chance, by implantation in the target, to form new species containing the projectile. An ongoing research program performed at our laboratory has the aim to investigate ion implantation of reactive ions in many relevant ice mixtures. The results obtained so far indicate that some molecular species observed on icy planetary surfaces could not be native of that object but formed by implantation of reactive ions. In particular we present data obtained after: • C, N and S implantation in water ice • H implantation in carbon and sulfur dioxide

Peripheral kappa-opioid agonist, ICI 204448, evokes hypothermia in cold-exposed rats.

PubMed

Rawls, Scott M; Ding, Zhe; Gray, Alex M; Cowan, Alan

2005-05-01

ICI 204448, a selective kappa-opioid agonist with limited CNS access, can be used to discriminate central and peripheral opioid actions on physiological systems such as pain and thermoregulation. Therefore, we investigated the effect of ICI 204448 (2.5, 5, and 10 mg/kg, s.c.) on male Sprague-Dawley rats exposed to ambient temperatures of 5, 20, or 32 degrees C. ICI 204448 did not alter the body temperature of rats maintained at 20 or 32 degrees C. However, 5 and 10 mg/kg of ICI 204448 evoked significant hypothermia in rats exposed to 5 degrees C. The i.c.v. administration of nor-BNI, a kappa-opioid antagonist, did not affect the hypothermia produced by the systemic injection of ICI 204448. Thus, an involvement of brain kappa-opioid receptors in ICI 204448-evoked hypothermia is unlikely. The present data demonstrate for the first time that ICI 204448 produces hypothermia in cold-exposed rats and suggest that the role of peripheral kappa-opioid receptors in thermoregulation becomes more significant at cold ambient temperatures. Copyright (c) 2005 S. Karger AG, Basel.

IcyTree: rapid browser-based visualization for phylogenetic trees and networks

PubMed Central

2017-01-01

Abstract Summary: IcyTree is an easy-to-use application which can be used to visualize a wide variety of phylogenetic trees and networks. While numerous phylogenetic tree viewers exist already, IcyTree distinguishes itself by being a purely online tool, having a responsive user interface, supporting phylogenetic networks (ancestral recombination graphs in particular), and efficiently drawing trees that include information such as ancestral locations or trait values. IcyTree also provides intuitive panning and zooming utilities that make exploring large phylogenetic trees of many thousands of taxa feasible. Availability and Implementation: IcyTree is a web application and can be accessed directly at http://tgvaughan.github.com/icytree. Currently supported web browsers include Mozilla Firefox and Google Chrome. IcyTree is written entirely in client-side JavaScript (no plugin required) and, once loaded, does not require network access to run. IcyTree is free software, and the source code is made available at http://github.com/tgvaughan/icytree under version 3 of the GNU General Public License. Contact: tgvaughan@gmail.com PMID:28407035

IcyTree: rapid browser-based visualization for phylogenetic trees and networks.

PubMed

Vaughan, Timothy G

2017-08-01

IcyTree is an easy-to-use application which can be used to visualize a wide variety of phylogenetic trees and networks. While numerous phylogenetic tree viewers exist already, IcyTree distinguishes itself by being a purely online tool, having a responsive user interface, supporting phylogenetic networks (ancestral recombination graphs in particular), and efficiently drawing trees that include information such as ancestral locations or trait values. IcyTree also provides intuitive panning and zooming utilities that make exploring large phylogenetic trees of many thousands of taxa feasible. IcyTree is a web application and can be accessed directly at http://tgvaughan.github.com/icytree . Currently supported web browsers include Mozilla Firefox and Google Chrome. IcyTree is written entirely in client-side JavaScript (no plugin required) and, once loaded, does not require network access to run. IcyTree is free software, and the source code is made available at http://github.com/tgvaughan/icytree under version 3 of the GNU General Public License. tgvaughan@gmail.com. © The Author(s) 2017. Published by Oxford University Press.

Searching for Planets Around Pulsars

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-09-01

Did you know that the very first exoplanets ever confirmed were found around a pulsar? The precise timing measurements of pulsar PSR 1257+12 were what made the discovery of its planetary companions possible. Yet surprisingly, though weve discovered thousands of exoplanets since then, only one other planet has ever been confirmed around a pulsar. Now, a team of CSIRO Astronomy and Space Science researchers are trying to figure out why.Formation ChallengesThe lack of detected pulsar planets may simply reflect the fact that getting a pulsar-planet system is challenging! There are three main pathways:The planet formed before the host star became a pulsar which means it somehow survived its star going supernova (yikes!).The planet formed elsewhere and was captured by the pulsar.The planet formed out of the debris of the supernova explosion.The first two options, if even possible, are likely to be rare occurrences but the third option shows some promise. In this scenario, after the supernova explosion, a small fraction of the material falls back toward the stellar remnant and is recaptured, forming what is known as a supernova fallback disk. According to this model, planets could potentially form out of this disk.Disk ImplicationsLed by Matthew Kerr, the CSIRO astronomers set out to systematically look for these potential planets that might have formed in situ around pulsars. They searched a sample of 151 young, energetic pulsars, scouring seven years of pulse time-of-arrival data for periodic variation that could signal the presence of planetary companions. Their methods to mitigate pulsar timing noise and model realistic orbits allowed them to have good sensitivity to low-mass planets.The results? They found no conclusive evidence that any of these pulsars have planets.This outcome carries with it some significant implications. The pulsar sample spans 2 Myr in age, in which planets should have had enough time to form in debris disks. The fact that none were detected

Phase behavior and thermodynamic modeling of ices - implications for the geophysics of icy satellites. (Invited)

NASA Astrophysics Data System (ADS)

Choukroun, M.

2010-12-01

Ground-based observations and space missions to the outer Solar System (Voyager, Galileo, Cassini-Huygens) have evidenced recent geologic activity on many satellites of the giant planets. The diversity in surface expression of these icy moons’ activity is striking: from a scarred and young surface on Europa,1 with hydrated salts that may originate from a liquid layer buried at depth,2 to the South Polar plumes of Enceladus,3 where water ice particles are expelled along with a myriad of more complex molecules,4 to Titan, largest satellite of Saturn, with a dense atmosphere and a hydrocarbon cycle similar to the hydrological cycle on Earth.5 Large icy moons, i.e. with a radius greater than 500 km, share two particularities: a high content in water (on the order of a 30-70% bulk composition), and an interior segregated between a water-dominated mantle and a silicate-dominated core. The many forms water may have beneath the surface (ice polymorphs, liquid, hydrated compounds) bear a crucial role in the detected or alleged activity, and in the potential for astrobiological relevance. Indeed, any endogenic activity can only be approached through geophysical modelling of the internal structure and the thermal evolution. Current internal structure models for the icy moonse.g.,6 rely mainly on the contribution of each internal layer to the moment of inertia, generating non-unique solutions due to the large variability in density of H2O-bearing phases. Thermal evolution models,e.g.,7 can help constrain further the internal structure and geophysical activity, by starting with a given initial composition and state and investigating the thickening of icy layers through time. However, such models require both observational datasets and a precise description, as a function of pressure, temperature, and composition, of the thermophysical properties of the individual layers. Over the past century, experimental studies have provided a comprehensive view of the phase diagram of

A Planet Detection Tutorial and Simulator

NASA Technical Reports Server (NTRS)

Knoch, David; DeVincenzi, Donald (Technical Monitor)

2001-01-01

Detection of extra-solar planets has been a very popular topic with the general public for years. Considerable media coverage of recent detections (currently at about 50) has only heightened the interest in the topic. School children are particularly interested in learning about recent astronomical discoveries. Scientists have the knowledge and responsibility to present this information in both an understandable and interesting format. Most classrooms and homes are now connected to the internet, which can be utilized to provide more than a traditional 'flat' presentation. An interactive software package on planet detection has been developed. The major topics include: "1996 - The Break Through Year In Planet Detection"; "What Determines If A Planet Is Habitable?"; "How Can We Find Other Planets (Search Methods)"; "All About the Kepler Mission: How To Find Terrestrial Planets"; and "A Planet Detection Simulator". Using the simulator, the student records simulated observations and then analyzes and interprets the data within the program. One can determine the orbit and planet size, the planet's temperature and surface gravity, and finally determine if the planet is habitable. Originally developed for the Macintosh, a web based browser version is being developed.

The Role of Comets as Possible Contributors of Water and Prebiotic Organics to Terrestrial Planets

NASA Technical Reports Server (NTRS)

Mumma, Michael J.; Charnley, S. B.

2011-01-01

The question of exogenous delivery of organics and water to Earth and other young planets is of critical importance for understanding the origin of Earth's water, and for assessing the prospects for existence of Earth-like exo-planets. Viewed from a cosmic perspective, Earth is a dry planet yet its oceans are enriched in deuterium by a large factor relative to nebular hydrogen. Can comets have delivered Earth's water? The deuterium content of comets is key to ,assessing their role as contributors of water to Earth. Icy bodies today reside in two distinct reservoirs, the Oort Cloud and the Kuiper Disk (divided into the classical disk, the scattered disk, and the detached or extended disk populations). Orbital parameters can indicate the cosmic storage reservoir for a given comet. Knowledge of the diversity of comets within a reservoir assists in assessing their possible contribution to early Earth, but requires quantitative knowledge of their components - dust and ice. Strong gradients in temperature and chemistry in the proto-planetary disk, coupled with dynamical dispersion of an outer disk of icy planetesimals, imply that comets from KD and OC reservoirs should have diverse composition. The primary volatiles (native to the nucleus) provide the preferred metric for building a taxonomy for comets, and the number of comets so quantified is growing rapidly. Taxonomies based on native species (primary volatiles) are now beginning to emerge [1, 2, 3]. The measurement of cosmic parameters such as the nuclear spin temperatures for H2O, NH3 and CH4, and of enrichment factors for isotopologues (D/H in water and hydrogen cyanide, N-14/N-15 in CN and hydrogen cyanide) provide additional tests of the origin of cometary material. I will provide an overview of these aspects, and implications for the origin of Earth's water and prebiotic organics.

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.

Uncovering the Chemistry of Earth-like Planets

NASA Astrophysics Data System (ADS)

Zeng, L.; Jacobsen, S. B.; Sasselov, D. D.

2015-12-01

We propose to use the evidence from our solar system to understand exoplanets, and in particular, to predict their surface chemistry and thereby the possibility of life. An Earth-like planet, born from the same nebula as its host star, is composed primarily of silicate rocks and an iron-nickel metal core, and depleted in volatile content in a systematic manner. The more volatile (easier to vaporize or dissociate into gas form) an element is in an Earth-like planet, the more depleted the element is compared to its host star. After depletion, an Earth-like planet would go through the process of core formation due to heat from radioactive decay and collisions. Core formation depletes a planet's rocky mantle of siderophile (iron-loving) elements, in addition to the volatile depletion. After that, Earth-like planets likely accrete some volatile-rich materials, called "late veneer". The late veneer could be essential to the origins of life on Earth and Earth-like planets, as it also delivers the volatiles such as nitrogen, sulfur, carbon and water to the planet's surface, which are crucial for life to occur. Here we build an integrative model of Earth-like planets from the bottom up. Thus the chemical compositions of Earth-like planets could be inferred from their mass-radius relations and their host stars' elemental abundances, and the origins of volatile contents (especially water) on their surfaces could be understood, and thereby shed light on the origins of life on them. This elemental abundance model could be applied to other rocky exoplanets in exoplanet systems.

ICIS Activity Subject Area Model

EPA Pesticide Factsheets

The Integrated Compliance Information System (ICIS) is a web-based system that provides information for the federal enforcement and compliance (FE&C) and the National Pollutant Discharge Elimination System (NPDES) programs.

ICIS Contacts Subject Area Model

EPA Pesticide Factsheets

The Integrated Compliance Information System (ICIS) is a web-based system that provides information for the federal enforcement and compliance (FE&C) and the National Pollutant Discharge Elimination System (NPDES) programs.

Uncovering the Chemistry of Earth-like Planets

NASA Astrophysics Data System (ADS)

Zeng, Li; Jacobsen, Stein; Sasselov, Dimitar D.

2015-01-01

We propose to use evidence from our solar system to understand exoplanets, and in particular, to predict their surface chemistry and thereby the possibility of life. An Earth-like planet, born from the same nebula as its host star, is composed primarily of silicate rocks and an iron-nickel metal core, and depleted in volatile content in a systematic manner. The more volatile (easier to vaporize or dissociate into gas form) an element is in an Earth-like planet, the more depleted the element is compared to its host star. After depletion, an Earth-like planet would go through the process of core formation due to heat from radioactive decay and collisions. Core formation depletes a planet's rocky mantle of siderophile (iron-loving) elements, in addition to the volatile depletion. After that, Earth-like planets likely accrete some volatile-rich materials, called 'late veneer'. The late veneer could be essential to the origins of life on Earth and Earth-like planets, as it also delivers the volatiles such as nitrogen, sulfur, carbon and water to the planet's surface, which are crucial for life to occur. We plan to build an integrative model of Earth-like planets from the bottom up. We would like to infer their chemical compositions from their mass-radius relations and their host stars' elemental abundances, and understand the origins of volatile contents (especially water) on their surfaces, and thereby shed light on the origins of life on them.

Formation of the terrestrial planets in the solar system around 1 au via radial concentration of planetesimals

NASA Astrophysics Data System (ADS)

Ogihara, Masahiro; Kokubo, Eiichiro; Suzuki, Takeru K.; Morbidelli, Alessandro

2018-05-01

Context. No planets exist inside the orbit of Mercury and the terrestrial planets of the solar system exhibit a localized configuration. According to thermal structure calculation of protoplanetary disks, a silicate condensation line ( 1300 K) is located around 0.1 au from the Sun except for the early phase of disk evolution, and planetesimals could have formed inside the orbit of Mercury. A recent study of disk evolution that includes magnetically driven disk winds showed that the gas disk obtains a positive surface density slope inside 1 au from the central star. In a region with positive midplane pressure gradient, planetesimals undergo outward radial drift. Aims: We investigate the radial drift of planetesimals and type I migration of planetary embryos in a disk that viscously evolves with magnetically driven disk winds. We show a case in which no planets remain in the close-in region. Methods: Radial drifts of planetesimals are simulated using a recent disk evolution model that includes effects of disk winds. The late stage of planet formation is also examined by performing N-body simulations of planetary embryos. Results: We demonstrate that in the middle stage of disk evolution, planetesimals can undergo convergent radial drift in a magnetorotational instability (MRI)-inactive disk, in which the pressure maximum is created, and accumulate in a narrow ring-like region with an inner edge at 0.7 au from the Sun. We also show that planetary embryos that may grow from the narrow planetesimal ring do not exhibit significant type I migration in the late stage of disk evolution. Conclusions: The origin of the localized configuration of the terrestrial planets of the solar system, in particular the deficit of close-in planets, can be explained by the convergent radial drift of planetesimals in disks with a positive pressure gradient in the close-in region.

The rate of planet formation and the solar system's small bodies

NASA Technical Reports Server (NTRS)

Safronov, Viktor S.

1991-01-01

The evolution of random velocities and the mass distribution of preplanetary body at the early stage of accumulation are currently under review. Arguments were presented for and against the view of an extremely rapid, runaway growth of the largest bodies at this stage with parameter values of Theta approximately greater than 10(exp 3). Difficulties are encountered assuming such a large Theta: (1) bodies of the Jovian zone penetrate the asteroid zone too late and do not have time to hinder the formation of a normal-sized planet in the asteroidal zone and thereby remove a significant portion of the mass of solid matter and (2) Uranus and Neptune cannot eject bodies from the solar system into the cometary cloud. Therefore, the values Theta less than 10(exp 2) appear to be preferable.

Volatile components and continental material of planets

NASA Technical Reports Server (NTRS)

Florenskiy, K. P.; Nikolayeva, O. V.

1986-01-01

It is shown that the continental material of the terrestrial planets varies in composition from planet to planet according to the abundances and composition of true volatiles (H20, CO2, etc.) in the outer shells of the planets. The formation of these shells occurs very early in a planet's evolution when the role of endogenous processes is indistinct and continental materials are subject to melting and vaporizing in the absence of an atmosphere. As a result, the chemical properties of continental materials are related not only to fractionation processes but also to meltability and volatility. For planets retaining a certain quantity of true volatile components, the chemical transformation of continental material is characterized by a close interaction between impact melting vaporization and endogeneous geological processes.

The Obliquities of the Giant Planets

NASA Astrophysics Data System (ADS)

Hamilton, D. P.; Ward, Wm. R.

2002-09-01

Jupiter has by far the smallest obliquity ( ~ 3o) of the planets (not counting tidally de-spun Mercury and Venus) which may be reflective of its formation by hydrodynamic gas flow rather than stochastic impacts. Saturn's obliquity ( ~ 26o), however, seems to belie this simple formation picture. But since the spin angular momentum of any planet is much smaller than its orbital angular momentum, post-formation obliquity can be strongly modified by passing through secular spin-orbit resonances, i.e., when the spin axis precession rate of the planet matches one of the frequencies describing the precession of the orbit plane. Spin axis precession is due to the solar torque on both the oblate figure of the planet and any orbiting satellites. In the case of Jupiter, the torque on the Galilean satellites is the principal cause of its 4.5*105 year precession; Saturn's precession of 1.8*106 years is dominated by Titan. In the past, the planetary spin axis precession rates should have been much faster due to the massive circumplanetary disks from which the current satellites condensed. The regression of the orbital node of a planet is due to the gravitational perturbations of the other planets. Nodal regression is not uniform, but is instead a composite of the planetary system's normal modes. For Jupiter and Saturn, the principal frequency is the nu16, with a period of ~ 49,000 years; the amplitude of this term is I ~ 0o.36 for Jupiter and I ~ 0o.90 for Saturn. In spite of the small amplitudes, slow adiabatic passages through this resonance (due to circumplanetary disk dispersal) could increase planetary obliquities from near zero to ~ [tan1/3 I] ~ 10o. We will discuss scenarios in which giant planet obliquities are affected by this and other resonances, and will use Jupiter's low obliquity to constrain the mass and duration of a satellite precursor disk. DPH acknowledges support from NSF Career Grant AST 9733789 and WRW is grateful to the NASA OSS and PGG programs.

The Fate of Unstable Circumbinary Planets

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-03-01

What happens to Tattooine-like planets that are instead in unstable orbits around their binary star system? A new study examines whether such planets will crash into a host star, get ejected from the system, or become captured into orbit around one of their hosts.Orbit Around a DuoAt this point we have unambiguously detected multiple circumbinary planets, raising questions about these planets formation and evolution. Current models suggest that it is unlikely that circumbinary planets would be able to form in the perturbed environment close their host stars. Instead, its thought that the planets formed at a distance and then migrated inwards.One danger such planets face when migrating is encountering ranges of radii where their orbits become unstable. Two scientists at the University of Chicago, Adam Sutherland and Daniel Fabrycky, have studied what happens when circumbinary planets migrate into such a region and develop unstable orbits.Producing Rogue PlanetsTime for planets to either be ejected or collide with one of the two stars, as a function of the planets starting distance (in AU) from the binary barycenter. Colors represent different planetary eccentricities. [Sutherland Fabrycky 2016]Sutherland and Fabrycky used N-body simulations to determine the fates of planets orbiting around a star system consisting of two stars a primary like our Sun and a secondary roughly a tenth of its size that are separated by 1 AU.The authors find that the most common fate for a circumbinary planet with an unstable orbit is ejection from the system; over 80% of unstable planets were ejected. This has interesting implications: if the formation of circumbinary planets is common, this mechanism could be filling the Milky Way with a population of free-floating, rogue planets that no longer are associated with their host star.The next most common outcome for unstable planets is collision with one of their host stars (most often the secondary), resulting inaccretion of the planet

Spectroscopic Characterization of a Newborn Neptune-Sized Planet

NASA Astrophysics Data System (ADS)

Benneke, Bjoern

2016-10-01

The study of planet formation as it occurs has remained an elusive frontier, until now. Our team recently identified a newly-born planet orbiting a young, 5-10 Myr old, pre-main-sequence M star in the Upper Scorpius star-forming region. In its early stage, the close-in planet is about 50% larger than Neptune. Models predict that it will contract over the coming 100-1000 Myr to become a member of the intriguingly abundant class of close-in sub-Neptunes. Spectroscopic observations of this newborn planet will give us the unprecedented opportunity to probe the formation and evolution of low-mass, close-in planets at this early stage. Here, we propose to a reconnaissance study to probe the adolescent state of the gravitationally-bound atmosphere using near-infrared transit spectroscopy and the planet's hydrogen loss rate using far-UV transit spectroscopy. Together, our observations will give us unparalleled insights into the initial state of a young close-in planet as well as into the competing timescales of Kelvin-Helmholtz contraction and envelope mass-loss involved in the early evolution of close-in sub-Neptunes and Neptunes. If the proposed reconnaissance observations detect that molecular absorption in the atmosphere of USco 1610-1919b, then USco 1610-1919b will be one of the prime targets for the 200-hour JWST/NIRISS GTO program to probe the formation and evolution of exoplanets. Mid-cycle observations are required because the final target list for JWST/GTO programs must be locked in by June 2017 before the beginning of HST Cycle 25.

The Global Contribution of Secondary Craters on the Icy Satellites

NASA Astrophysics Data System (ADS)

Hoogenboom, T.; Johnson, K. E.; Schenk, P.

2014-12-01

At present, surface ages of bodies in the Outer Solar System are determined only from crater size-frequency distributions (a method dependent on an understanding of the projectile populations responsible for impact craters in these planetary systems). To derive accurate ages using impact craters, the impactor population must be understood. Impact craters in the Outer Solar System can be primary, secondary or sesquinary. The contribution of secondary craters to the overall population has recently become a "topic of interest." Our objective is to better understand the contribution of dispersed secondary craters to the small crater populations, and ultimately that of small comets to the projectile flux on icy satellites in general. We measure the diameters of obvious secondary craters (determined by e.g. irregular crater shape, small size, clustering) formed by all primary craters on Ganymede for which we have sufficiently high resolution data to map secondary craters. Primary craters mapped range from approximately 40 km to 210 km. Image resolution ranges from 45 to 440 m/pixel. Bright terrain on Ganymede is our primary focus. These resurfaced terrains have relatively low crater densities and serve as a basis for characterizing secondary populations as a function of primary size on an icy body for the first time. Although focusing on Ganymede, we also investigate secondary crater size, frequency, distribution, and formation, as well as secondary crater chain formation on icy satellites throughout the Saturnian and Jovian systems principally Rhea. We compare our results to similar studies of secondary cratering on the Moon and Mercury. Using Galileo and Voyager data, we have identified approximately 3,400 secondary craters on Ganymede. In some cases, we measured crater density as a function of distance from a primary crater. Because of the limitations of the Galileo data, it is necessary to extrapolate from small data sets to the global population of secondary craters

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

Plume Collection Strategies for Icy World Sample Return

NASA Technical Reports Server (NTRS)

Neveu, M.; Glavin, D. P.; Tsou, P.; Anbar, A. D.; Williams, P.

2015-01-01

Three icy worlds in the solar system display evidence of pluming activity. Water vapor and ice particles emanate from cracks near the south pole of Saturn's moon Enceladus. The plume gas contains simple hydrocarbons that could be fragments of larger, more complex organics. More recently, observations using the Hubble and Herschel space telescopes have hinted at transient water vapor plumes at Jupiter's moon Europa and the dwarf planet Ceres. Plume materials may be ejected directly from possible sub-surface oceans, at least on Enceladus. In such oceans, liquid water, organics, and energy may co-exist, making these environments habitable. The venting of habitable ocean material into space provides a unique opportunity to capture this material during a relatively simple flyby mission and return it to Earth. Plume collection strategies should enable investigations of evidence for life in the returned samples via laboratory analyses of the structure, distribution, isotopic composition, and chirality of the chemical components (including biomolecules) of plume materials. Here, we discuss approaches for the collection of dust and volatiles during flybys through Enceladus' plume, based on Cassini results and lessons learned from the Stardust comet sample return mission. We also highlight areas where sample collector and containment technology development and testing may be needed for future plume sample return missions.

Hypothetical Rejuvenated Planets Artist Concept

NASA Image and Video Library

2015-06-25

This artist's concept shows a hypothetical "rejuvenated" planet -- a gas giant that has reclaimed its youthful infrared glow. NASA's Spitzer Space Telescope found tentative evidence for one such planet around a dead star, or white dwarf, called PG 0010+280 (depicted as white dot in illustration). When planets are young, they are warm and toasty due to internal heat left over from their formation. Planets cool over time -- until they are possibly rejuvenated. The theory goes that this Jupiter-like planet, which orbits far from its star, would accumulate some of the material sloughed off by its star as the star was dying. The material would cause the planet to swell in mass. As the material fell onto the planet, it would heat up due to friction and glow with infrared light. The final result would be an old planet, billions of years in age, radiating infrared light as it did in its youth. Spitzer detected an excess infrared light around the white dwarf PG 0010+280. Astronomers aren't sure where the light is coming from, but one possibility is a rejuvenated planet. Future observations may help solve the mystery. A Jupiter-like planet is about ten times the size of a white dwarf. White dwarfs are about the size of Earth, so one white dwarf would easily fit into the Great Red Spot on Jupiter! http://photojournal.jpl.nasa.gov/catalog/PIA19346

The Late-Time Formation and Dynamical Signatures of Small Planets

NASA Astrophysics Data System (ADS)

Lee, Eve Jihyun

The riddle posed by super-Earths is that they are not Jupiters: their core masses are large enough to trigger runaway gas accretion, yet somehow super-Earths accreted atmospheres that weigh only a few percent of their total mass. In this thesis, I demonstrate that this puzzle is solved if super-Earths formed late, in the inner cavities of transitional disks. Super-puffs present the inverse problem of being too voluminous for their small masses. I show that super-puffs most easily acquire their thick atmospheres as dust-free, rapidly cooling worlds outside 1 AU, and then migrate in just after super-Earths appear. Super-Earths and Earth-sized planets around FGKM dwarfs are evenly distributed in log orbital period down to 10 days, but dwindle in number at shorter periods. I demonstrate that both the break at 10 days and the slope of the occurrence rate down to 1 day can be reproduced if planets form in disks that are truncated by their host star magnetospheres at co-rotation. Planets can be brought from disk edges to ultra-short (<1 day) periods by asynchronous equilibrium tides raised on their stars. Small planets may remain ubiquitous out to large orbital distances. I demonstrate that the variety of debris disk morphologies revealed by scattered light images can be explained by viewing an eccentric disk, secularly forced by a planet of just a few Earth masses, from different observing angles. The farthest reaches of planetary systems may be perturbed by eccentric super-Earths.

Polygenic formation model of the planet's bituminous belts

NASA Astrophysics Data System (ADS)

Dmitrievsky, A. N.; Balanyuk, I. E.

2011-05-01

In recent years, much attention has been paid to nontraditional hydrocarbon sources. Today the portion of nontraditional gas in the world extraction is 15% or 450 billion cubic meters, which hat makes up the volume of total gas exports from Russia. As is known, the easy-prospecting oil has been already found. The innovative technologies in geophysics, drilling, and excavation and the increased extraction coefficient expect further development and industrial compliance with these requirements. Based on calculations, the world oil reserves are now one trillion of stock tank barrels and one trillion barrels have been already extracted. The evergrowing demand for energy gives rise to the necessity of searching for and extracting more oil resources, and both these aspects are unique problems. The search for profitable petroleum deposits has become more and more difficult even in the leading companies. The increment of the world resources is a key vital question; therefore, the elaboration of criteria for the discovery of nontraditional deposits take on special significance in the economic respect. The authors are working out a conception that will be a guideline for future finding of the richest oil deposits in active geodynamic zones. For the first time, we suggest the polygenic formation model of the planet's bituminous belts.

Topics in Extrasolar Planet Characterization

NASA Astrophysics Data System (ADS)

Howe, Alex Ryan

I present four papers exploring different topics in the area of characterizing the atmospheric and bulk properties of extrasolar planets. In these papers, I present two new codes, in various forms, for modeling these objects. A code to generate theoretical models of transit spectra of exoplanets is featured in the first paper and is refined and expanded into the APOLLO code for spectral modeling and parameter retrieval in the fourth paper. Another code to model the internal structure and evolution of planets is featured in the second and third papers. The first paper presents transit spectra models of GJ 1214b and other super-Earth and mini-Neptune type planets--planets with a "solid", terrestrial composition and relatively small planets with a thick hydrogen-helium atmosphere, respectively--and fit them to observational data to estimate the atmospheric compositions and cloud properties of these planets. The second paper presents structural models of super-Earth and mini-Neptune type planets and estimates their bulk compositions from mass and radius estimates. The third paper refines these models with evolutionary calculations of thermal contraction and ultraviolet-driven mass loss. Here, we estimate the boundaries of the parameter space in which planets lose their initial hydrogen-helium atmospheres completely, and we also present formation and evolution scenarios for the planets in the Kepler-11 system. The fourth paper uses more refined transit spectra models, this time for hot jupiter type planets, to explore the methods to design optimal observing programs for the James Webb Space Telescope to quantitatively measure the atmospheric compositions and other properties of these planets.

Un-Earth-like interiors of the Earth-like planets

NASA Astrophysics Data System (ADS)

Shim, S. H. D.; Nisr, C.; Pagano, M.; Chen, H.; Ko, B.; Noble, S.; Leinenweber, K. D.; Young, P.; Desch, S. J.

2015-12-01

A number of exoplanets have been described as "Earth-like" planets (or even exo-earths) based on the mass-radius relations. Yet, significant variations have been documented in elemental abundances of planet-hosting stars, which will result in very different structures and processes in the interiors of rocky exoplanets. Recent data suggest that the Mg/Si ratio can be as small as less than 1 and as large as more than 2, opening the possibilities for the upper mantles to be dominated by pyroxene and olivine, respectively, and the lower mantles to be dominated by bridgmanite and ferropericlase, respectively. The changes in mineralogy will alter key properties, such as discontinuity structures (and therefore scale of mantle mixing), viscosity, and volatiles storage, of the mantle. Partial melting of such mantles would result in different compositions of the crusts, affecting the tectonics. However, the prediction should be made carefully because oxygen fugacity and contents of volatiles can change the mineralogy even for the same bulk composition. In extremely reducing proto-planetary disks, carbides will form instead of oxides and silicates, and become main constituents of planets in the system. Because carbides have high thermal conductivity and low thermal expansivity, internal heat transport of such planets may be dominated by conduction and mantle mixing would be much more limited than that of the Earth. However, the behaviors and properties of carbides need to be understood better at high pressure and high temperature. Some rocky exoplanets may have very thick layers of water and other icy materials. Interactions between ice (or fluid) and rock at extreme conditions would be the key to understand dynamics and habitability of such exoplanets.

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.

Planets Around Neutron Stars

NASA Technical Reports Server (NTRS)

Wolszczan, Alexander; Kulkarni, Shrinivas R; Anderson, Stuart B.

2003-01-01

The objective of this proposal was to continue investigations of neutron star planetary systems in an effort to describe and understand their origin, orbital dynamics, basic physical properties and their relationship to planets around normal stars. This research represents an important element of the process of constraining the physics of planet formation around various types of stars. The research goals of this project included long-term timing measurements of the planets pulsar, PSR B1257+12, to search for more planets around it and to study the dynamics of the whole system, and sensitive searches for millisecond pulsars to detect further examples of old, rapidly spinning neutron stars with planetary systems. The instrumentation used in our project included the 305-m Arecibo antenna with the Penn State Pulsar Machine (PSPM), the 100-m Green Bank Telescope with the Berkeley- Caltech Pulsar Machine (BCPM), and the 100-m Effelsberg and 64-m Parkes telescopes equipped with the observatory supplied backend hardware.

Slowly-growing gap-opening planets trigger weaker vortices

NASA Astrophysics Data System (ADS)

Hammer, Michael; Kratter, Kaitlin M.; Lin, Min-Kai

2017-04-01

The presence of a giant planet in a low-viscosity disc can create a gap edge in the disc's radial density profile sharp enough to excite the Rossby wave instability. This instability may evolve into dust-trapping vortices that might explain the 'banana-shaped' features in recently observed asymmetric transition discs with inner cavities. Previous hydrodynamical simulations of planet-induced vortices have neglected the time-scale of hundreds to thousands of orbits to grow a massive planet to Jupiter size. In this work, we study the effect of a giant planet's runaway growth time-scale on the lifetime and characteristics of the resulting vortex. For two different planet masses (1 and 5 Jupiter masses) and two different disc viscosities (α = 3 × 10-4 and 3 × 10-5), we compare the vortices induced by planets with several different growth time-scales between 10 and 4000 planet orbits. In general, we find that slowly-growing planets create significantly weaker vortices with lifetimes and surface densities reduced by more than 50 per cent. For the higher disc viscosity, the longest growth time-scales in our study inhibit vortex formation altogether. Additionally, slowly-growing planets produce vortices that are up to twice as elongated, with azimuthal extents well above 180° in some cases. These unique, elongated vortices likely create a distinct signature in the dust observations that differentiates them from the more concentrated vortices that correspond to planets with faster growth time-scales. Lastly, we find that the low viscosities necessary for vortex formation likely prevent planets from growing quickly enough to trigger the instability in self-consistent models.

Hot-start Giant Planets Form with Radiative Interiors

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

Berardo, David; Cumming, Andrew, E-mail: david.berardo@mcgill.ca, E-mail: andrew.cumming@mcgill.ca

In the hot-start core accretion formation model for gas giants, the interior of a planet is usually assumed to be fully convective. By calculating the detailed internal evolution of a planet assuming hot-start outer boundary conditions, we show that such a planet will in fact form with a radially increasing internal entropy profile, so that its interior will be radiative instead of convective. For a hot outer boundary, there is a minimum value for the entropy of the internal adiabat S {sub min} below which the accreting envelope does not match smoothly onto the interior, but instead deposits high entropymore » material onto the growing interior. One implication of this would be to at least temporarily halt the mixing of heavy elements within the planet, which are deposited by planetesimals accreted during formation. The compositional gradient this would impose could subsequently disrupt convection during post-accretion cooling, which would alter the observed cooling curve of the planet. However, even with a homogeneous composition, for which convection develops as the planet cools, the difference in cooling timescale will change the inferred mass of directly imaged gas giants.« less

Simulations of Tidally Driven Formation of Binary Planet Systems

NASA Astrophysics Data System (ADS)

Murray, R. Zachary P.; Guillochon, James

2018-01-01

In the last decade there have been hundreds of exoplanets discovered by the Kepler, CoRoT and many other initiatives. This wealth of data suggests the possibility of detecting exoplanets with large satellites. This project seeks to model the interactions between orbiting planets using the FLASH hydrodynamics code developed by The Flash Center for Computational Science at University of Chicago. We model the encounters in a wide variety of encounter scenarios and initial conditions including variations in encounter depth, mass ratio, and encounter velocity and attempt to constrain what sorts of binary planet configurations are possible and stable.

Transit of Extrasolar Planets

NASA Technical Reports Server (NTRS)

Doyle, Laurance R.

1998-01-01

During the past five years we have pursued the detection of extrasolar planets by the photometric transit method, i.e. the detection of a planet by watching for a drop in the brightness of the light as it crosses in front of a star. The planetary orbit must cross the line-of-sight and so most systems will not be lined up for such a transit to ever occur. However, we have looked at eclipsing binary systems which are already edge-on. Such systems must be very small in size as this makes the differential light change due to a transit much greater for a given planet size (the brightness difference will be proportional to the area of the transiting planet to the disc area of the star). Also, the planet forming region should be closer to the star as small stars are generally less luminous (that is, if the same thermal regime for planet formation applies as in the solar system). This led to studies of the habitable zone around other stars, as well. Finally, we discovered that our data could be used to detect giant planets without transits as we had been carefully timing the eclipses of the stars (using a GPS antenna for time) and this will drift by being offset by any giant planets orbiting around the system, as well. The best summary of our work may be to just summarize the 21 refereed papers produced during the time of this grant. This will be done is chronological order and in each section separately.

The formation of giant planets and its effects on protoplanetary disks: the case of Jupiter and the Jovian Early Bombardment

NASA Astrophysics Data System (ADS)

Turrini, D.; ISSI Team "Vesta, the key to the origins of the Solar System"; EChO "Planetary Formation" Working Group

The formation of giant planets is accompanied by a short but intense primordial bombardment \\citep{safronov69,weidenschilling75,weidenschilling01,turrini11}: the prototype for this class of events is the Jovian Early Bombardment (JEB) caused by the formation of Jupiter in the Solar System \\citep{turrini11,turrini12}. The JEB affected the collisional evolution of the minor bodies in the inner Solar System by inflicting mass loss to planetesimals \\citep{turrini12,turrini14a,turrini14b} due to cratering erosion and, at the same time, delivering water and volatile materials to the asteroid belt \\citep{turrini14b}. The JEB also resulted in a significant number of collisions between Jupiter and planetesimals formed over a wide orbital range, delivering volatile and refractory materials to the giant planet and its circumplanetary disk \\citep{turrini14c}. In this talk I'll discuss how the study of the effects of the JEB on Vesta can be used to constrain the early evolution of the Solar System \\citep{turrini14a,turrini14b} and how these constraints can, in turn, provide insight on the composition of Jupiter and of its satellites. Finally, I'll discuss the implications of the JEB model for extrasolar planets \\citep{turrini14c}.

Progress in four-beam nulling: results from the Terrestrial Planet Finder planet detection testbed

NASA Technical Reports Server (NTRS)

Martin, Stefan

2006-01-01

The Terrestrial Planet Finder Interferometer (TPF-I) is a large space telescope consisting of four 4 meter diameter telescopes flying in formation in space together with a fifth beam combiner spacecraft.

Progress in four-beam nulling: results from the Terrestrial Planet Finder Planet Detection Testbed

NASA Technical Reports Server (NTRS)

Martin, Stefan

2006-01-01

The Terrestrial Planet Finder Interferometer (TPF-I) is a large space telescope consisting of four 4 meter diameter telescopes flying in formation in space together with a fifth beam combiner spacecraft.

Systemic ICI 182,780 alters the display of sexual behaviors in the female rat.

PubMed

Gardener, H E; Clark, A S

2001-03-01

The present study investigates the effects of the antiestrogen ICI 182,780 (ICI) on the display of sexual behaviors in female rats. ICI 182,780 is a pure anti-estrogen and when given systemically, ICI is thought to act only in the periphery, and is not believed to cross the blood brain barrier. The present study examines the effects of ICI on sexual receptivity and on paced mating behavior following treatment with estradiol benzoate (EB) and progesterone (P) (Experiment 1) or with EB alone (Experiment 2). In Experiment 1, ICI (250.0 microg) did not affect the display of receptivity or paced mating behavior induced by EB and P. In contrast, in Experiment 2 female rats receiving EB alone displayed a decrease in the level of sexual receptivity following treatment with 500.0 and 750.0 microg ICI (but not 250.0 microg ICI). In addition, in Experiment 2 EB-treated female rats receiving 250.0 microg ICI spent more time away from the male rat following an intromission and were more likely to exit from the male compartment following a mount. Last, ICI had potent antiestrogenic effects on vaginal cytology (Experiment 2) and on the uterus (Experiments 1 and 2). The present study supports a role for peripheral estrogen receptors in sexual receptivity and paced mating behavior and suggests that estrogen receptor activation may decrease the aversive sensation associated with sexual stimulation. Copyright 2001 Academic Press.

ICI optical data storage tape: An archival mass storage media

NASA Technical Reports Server (NTRS)

Ruddick, Andrew J.

1993-01-01

At the 1991 Conference on Mass Storage Systems and Technologies, ICI Imagedata presented a paper which introduced ICI Optical Data Storage Tape. This paper placed specific emphasis on the media characteristics and initial data was presented which illustrated the archival stability of the media. More exhaustive analysis that was carried out on the chemical stability of the media is covered. Equally important, it also addresses archive management issues associated with, for example, the benefits of reduced rewind requirements to accommodate tape relaxation effects that result from careful tribology control in ICI Optical Tape media. ICI Optical Tape media was designed to meet the most demanding requirements of archival mass storage. It is envisaged that the volumetric data capacity, long term stability and low maintenance characteristics demonstrated will have major benefits in increasing reliability and reducing the costs associated with archival storage of large data volumes.

Laboratory permittivity measurements of icy planetary analogs in the millimeter and submillimeter domains, in relation with JUICE mission.

NASA Astrophysics Data System (ADS)

Brouet, Y.; Jacob, K.; Murk, A.; Poch, O.; Pommerol, A.; Thomas, N.; Levasseur-Regourd, A. C.

2015-12-01

The European Space Agency's JUpiter ICy moons Explorer (JUICE) spacecraft is planned for launch in 2022 and arrival at Jupiter in 2030. It will observe the planet Jupiter and three of its largest moons, Ganymede, Callisto and Europa. One instrument on the JUICE spacecraft is the Sub-millimeter Wave Instrument (SWI), which will measure brightness temperatures from Jupiter's stratosphere and troposphere, and from subsurfaces of Jupiter's icy moons. In the baseline configuration SWI consists of two tunable sub-millimeter wave receivers operating from 530 to 625 GHz. As an alternative one of the receivers could cover the range of 1080 and 1275 GHz. Inversion models are strongly dependent on the knowledge of the complex relative permittivity (hereafter permittivity) of the target material to retrieve the physical properties of the subsurface (e.g. [1][2]). We set up a laboratory experiment allowing us to perform reproducible measurements of the complex scattering parameters S11 and S21 in the ranges of 70 to 110 GHz, of 100 to 160 GHz, of 140 to 220 GHz, of 140 to 220 GHz and of 510 to 715 GHz. These scattering parameters can be used to retrieve the permittivity of icy analogs of the surfaces and subsurfaces of Jupiter's icy moons in order to prepare the data interpretation of SWI [3]. The measurements are performed under laboratory conditions with a quasi-optical bench (Institute of Applied Physics, University of Bern). The icy analogs that we prepare in the Laboratory for Outflow Studies of Sublimating Materials (LOSSy, Physics Institute, University of Bern), include two different porous water ice samples composed of fine-grained ice particles with a size range of 4 to 6 microns and ice particles with a size range of 50 to 100 microns [4][5]; and possibly CO2 ice. We will present the general experimental set-up and the first results in the context to prepare the data interpretation of SWI. [1] Ulaby, F. T., Long, D. G., 2014. Microwave radar and radiometric remote

Redirection of arachidonic acid metabolism by ICI D1542: effects on thrombus formation in the coronary artery of the anaesthetized dog.

PubMed Central

McAuliffe, S. J.; Moors, J. A.; Snow, H. M.; Wayne, M.; Jessup, R.

1993-01-01

1. The effects of simultaneous redirection of arachidonic acid metabolism, by inhibition of thromboxane A2 (TXA2) synthase and blockade of the platelet thromboxane A2 receptor (TP-receptor), was examined on the rate of thrombus formation in a stenosed coronary artery with damaged endothelium in an anaesthetized dog. 2. Redirection of arachidonic acid metabolism was achieved by intravenous doses of ICI D1542, a selective and potent inhibitor of TXA2 synthase and the TP-receptor. 3. Redirection of arachidonic acid metabolism was demonstrated in whole blood, stimulated ex vivo by collagen. The ED50 for inhibition of TXB2 production was 7.1 micrograms kg-1, i.v.; there were corresponding increases in the production of the eicosanoids prostaglandin D2 (PGD2), PGE2 and PGF2 alpha. 4. Thrombus formation was inhibited by D1542 (ED50 0.55 micrograms kg-1, i.v.), but could be restarted by an intravenous infusion of adrenaline (0.2-38 micrograms kg-1 min-1, i.v.). In the presence of the maximum effective dose of D1542 (1 mg kg-1, i.v.) a 190 fold increase in the infusion rate of adrenaline was required to restore thrombus formation. 5. In the presence of D1542, removal of endoperoxide metabolites by inhibition of cyclo-oxygenase with aspirin (5 mg kg-1, i.v.) caused thrombus formation to restart, indicating the ability of the endoperoxide metabolites to inhibit thrombus formation in vivo. 6. These results indicate that, in the stenosed and damaged coronary artery of the dog, redirection of arachidonic acid metabolism by D1542 is more effective at preventing thrombus formation than inhibition of cyclo-oxygenase by aspirin. PMID:8485629

The comparative effects of ICI 118551 and propranolol on essential tremor.

PubMed Central

Jefferson, D; Wharrad, H J; Birmingham, A T; Patrick, J M

1987-01-01

1. The effects of the selective beta 2-adrenoceptor antagonist ICI 118551 on essential tremor, heart rate and blood pressure were compared with those of propranolol. 2. ICI 118551 (150 mg daily for 7 days) and propranolol (120 mg daily for 7 days) were about equally effective in reducing essential tremor (by about 40%) and were more effective than placebo. 3. When compared with the effect of placebo, propranolol reduced blood pressure and exercise heart rate whereas ICI 118551 had no significant effect on blood pressure and produced a small but significant reduction in exercise-induced tachycardia. 4. ICI 118551 may be useful in the management of essential tremor while having fewer cardiovascular side-effects than non-selective beta-adrenoceptor antagonists. PMID:2894217

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.

The Evaporation Valley in the Kepler Planets

NASA Astrophysics Data System (ADS)

Owen, James E.; Wu, Yanqin

2017-09-01

A new piece of evidence supporting the photoevaporation-driven evolution model for low-mass, close-in exoplanets was recently presented by the California-Kepler Survey. The radius distribution of the Kepler planets is shown to be bimodal, with a “valley” separating two peaks at 1.3 and 2.6 R ⊕. Such an “evaporation valley” had been predicted by numerical models previously. Here, we develop a minimal model to demonstrate that this valley results from the following fact: the timescale for envelope erosion is the longest for those planets with hydrogen/helium-rich envelopes that, while only a few percent in weight, double its radius. The timescale falls for envelopes lighter than this because the planet’s radius remains largely constant for tenuous envelopes. The timescale also drops for heavier envelopes because the planet swells up faster than the addition of envelope mass. Photoevaporation therefore herds planets into either bare cores (˜1.3 R ⊕), or those with double the core’s radius (˜2.6 R ⊕). This process mostly occurs during the first 100 Myr when the stars’ high-energy fluxes are high and nearly constant. The observed radius distribution further requires the Kepler planets to be clustered around 3 M ⊕ in mass, born with H/He envelopes more than a few percent in mass, and that their cores are similar to the Earth in composition. Such envelopes must have been accreted before the dispersal of the gas disks, while the core composition indicates formation inside the ice line. Lastly, the photoevaporation model fails to account for bare planets beyond ˜30-60 days; if these planets are abundant, they may point to a significant second channel for planet formation, resembling the solar system terrestrial planets.

Exploring the Relationship Between Planet Mass and Atmospheric Metallicity for Cool Giant Planets

NASA Astrophysics Data System (ADS)

Thomas, Nancy H.; Wong, Ian; Knutson, Heather; Deming, Drake; Desert, Jean-Michel; Fortney, Jonathan J.; Morley, Caroline; Kammer, Joshua A.; Line, Michael R.

2016-10-01

Measurements of the average densities of exoplanets have begun to help constrain their bulk compositions and to provide insight into their formation locations and accretionary histories. Current mass and radius measurements suggest an inverse relationship between a planet's bulk metallicity and its mass, a relationship also seen in the gas and ice giant planets of our own solar system. We expect atmospheric metallicity to similarly increase with decreasing planet mass, but there are currently few constraints on the atmospheric metallicities of extrasolar giant planets. For hydrogen-dominated atmospheres, equilibrium chemistry models predict a transition from CO to CH4 below ~1200 K. However, with increased atmospheric metallicity the relative abundance of CH4 is depleted and CO is enhanced. In this study we present new secondary eclipse observations of a set of cool (<1200 K) giant exoplanets at 3.6 and 4.5 microns using the Spitzer Space Telescope, which allow us to constrain their relative abundances of CH4 and CO and corresponding atmospheric metallicities. We discuss the implications of our results for the proposed correlation between planet mass and atmospheric metallicity as predicted by the core accretion models and observed in our solar system.

Some laboratory investigations on Bayer 73 and ICI 24223 as molluscicides*

PubMed Central

Meyling, A. H.; Schutte, C. H. J.; Pitchford, R. J.

1962-01-01

The authors report on laboratory tests of the chemical properties and molluscicidal activity of the compounds Bayer 73 (70% wettable powder) and ICI 24223 (acid salt and emulsion), and describe the method used for the determination of ICI 24223. It is suggested that field applications of the ICI 24223 acid salt and of Bayer 73 should produce similar results in running and stagnant soft water. Bayer 73 showed a diminution of molluscicidal activity in hard water. PMID:14473215

Integrated Compliance Information System (ICIS)

EPA Pesticide Factsheets

The purpose of ICIS is to meet evolving Enforcement and Compliance business needs for EPA and State users by integrating information into a single integrated data system that supports both management and programmatic requirements of the Enforcement and Compliance programs.

Exchange processes from the deep interior to the surface of icy moons

NASA Astrophysics Data System (ADS)

Grasset, O.

Space exploration provides outstanding images of planetary surfaces. Galileo space- craft around Jupiter, and now Cassini in the saturnian system have revealed to us the variety of icy surfaces in the solar system. While Europa, Enceladus, and maybe Titan present past or even active tectonic and volcanic activities, many other moons have been dead worlds for more than 3 billions years. Composition of ices is also complex and it is now commonly admitted that icy surfaces are never composed of pure ices. Water ice can be mixed with salts (Europa?), with hydrocarbons (Titan?) or with silicates (Callisto). The present surfaces of icy moons are the results of both internal (tectonic; volcanism; mantle composition; magnetic field; . . . ) and external processes (radiations, atmospheres, impacts, . . . ). Internal activity (past or present) is almost unknown. While the surfaces indicate clearly that an important activity existed (Ganymede, Europa, Titan, . . . ) or still exists (Enceladus, Titan?, . . . ), volcanic and tectonic processes within icy mantles are still very poorly understood. This project proposes some key studies for improving our knowledge of exchange processes within icy moons, which are: 1) Surface compositions: Interpretation of mapping spectrometer data. It addresses the interpretation of remote sensing data. These data are difficult to understand and a debate between people involved in Galileo and those who are now trying to interpret Cassini data might be fruitful. As an example, interpretation of Galileo data on Europa are still controversial. It is impossible to affirm that the "non-icy" material which does not present the classic infrared signature of pure ice is due to the presence of magnesium hydrates, sodium hydrates, magnesium sulfurs, "clays", or even altered water ice. Discussion on the subject are still needed. On Titan, the presence of the atmosphere impedes to link IR data from Cassini to the composition of the surface. 2) Past and

Provenance of the terrestrial planets.

PubMed

Wetherill, G W

1994-01-01

Earlier work on the simultaneous accumulation of the asteroid belt and the terrestrial planets is extended to investigate the relative contribution to the final planets made by material from different heliocentric distances. As before, stochastic variations intrinsic to the accumulation processes lead to a variety of final planetary configurations, but include systems having a number of features similar to our solar system. Fifty-nine new simulations are presented, from which thirteen are selected as more similar to our solar system than the others. It is found that the concept of "local feeding zones" for each final terrestrial planet has no validity for this model. Instead, the final terrestrial planets receive major contributions from bodies ranging from 0.5 to at least 2.5 AU, and often to greater distances. Nevertheless, there is a correlation between the final heliocentric distance of a planet and its average provenance. Together with the effect of stochastic fluctuations, this permits variation in the composition of the terrestrial planets, such as the difference in the decompressed density of Earth and Mars. Biologically important light elements, derived from the asteroidal region, are likely to have been significant constituents of the Earth during its formation.

Isotopic ratios D/H and 15N/14N in giant planets

NASA Astrophysics Data System (ADS)

Marboeuf, Ulysse; Thiabaud, Amaury; Alibert, Yann; Benz, Willy

2018-04-01

The determination of isotopic ratios in planets is important since it allows us to investigate the origins and initial composition of materials. The present work aims to determine the possible range of values for isotopic ratios D/H and 15N/14N in giant planets. The main objective is to provide valuable theoretical assumptions on the isotopic composition of giant planets, their internal structure, and the main reservoirs of species. We use models of ice formation and planet formation that compute the composition of ices and gas accreted in the core and the envelope of planets. Assuming a single initial value for isotopic ratios in volatile species, and disruption of planetesimals in the envelope of gaseous planets, we obtain a wide variety of D/H and 15N/14N ratios in low-mass planets (≤100 Mearth) due to the migration pathway of planets, the accretion time of gas species whose relative abundance evolves with time, and isotope exchanges among species. If giant planets with mass greater than 100 Mearth have solar isotopic ratios such as Jupiter and Saturn due to their higher envelope mass, Neptune-type planets present values ranging between one and three times the solar value. It seems therefore difficult to use isotopic ratios in the envelope of these planets to get information about their formation in the disc. For giant planets, the ratios allow us to constrain the mass fraction of volatile species in the envelope needed to reproduce the observational data by assuming initial values for isotopic ratios in volatile species.

Far Ultraviolet Spectroscopy of Saturn's Icy Moon Rhea

NASA Astrophysics Data System (ADS)

Elowitz, Mark; Hendrix, Amanda; Mason, Nigel J.; Sivaraman, Bhalamurugan

2018-01-01

We present an analysis of spatially resolved, far-UV reflectance spectra of Saturn’s icy satellite Rhea, collected by the Cassini Ultraviolet Imaging Spectrograph (UVIS). In recent years ultraviolet spectroscopy has become an important tool for analysing the icy satellites of the outer solar system (1Hendrix & Hansen, 2008). Far-UV spectroscopy provides unique information about the molecular structure and electronic transitions of chemical species. Many molecules that are suspected to be present in the icy surfaces of moons in the outer solar system have broad absorption features due to electronic transitions that occur in the far-UV portion of the spectrum. The studies show that Rhea, like the other icy satellites of the Saturnian system are dominated by water-ice as evident by the 165-nm absorption edge, with minor UV absorbing contaminants. Far-UV spectra of several Saturnian icy satellites, including Rhea and Dione, show an unexplained weak absorption feature centered near 184 nm. To carry out the geochemical survey of Rhea’s surface, the UVIS observations are compared with vacuum-UV spectra of thin-ice samples measured in laboratory experiments. Thin film laboratory spectra of water-ice and other molecular compounds in the solid phase were collected at near-vacuum conditions and temperatures identical to those at the surface of Rhea. Comparison between the observed far-UV spectra of Rhea’s surface ice and modelled spectra based on laboratory absorption measurements of different non-water-ice compounds show that two possible chemical compounds could explain the 184-nm absorption feature. The two molecular compounds include simple chlorine molecules and hydrazine monohydrate. Attempts to explain the source(s) of these compounds on Rhea and the scientific implications of their possible discovery will be summarized.[1] Hendrix, A. R. & Hansen, C. J. (2008). Icarus, 193, pp. 323-333.

76 FR 28950 - Lynn Canal/Icy Straits Resource Advisory Committee

Federal Register 2010, 2011, 2012, 2013, 2014

2011-05-19

... DEPARTMENT OF AGRICULTURE Forest Service Lynn Canal/Icy Straits Resource Advisory Committee AGENCY: Forest Service, USDA. ACTION: Notice of meeting. SUMMARY: The Lynn Canal/Icy Straits Resource Advisory Committee will hold a teleconference, June 9, 2011. The purpose of this meeting is to discuss metrics and...

Tilted geostrophic convection in icy world oceans caused by the horizontal component of the planetary rotation vector

NASA Astrophysics Data System (ADS)

Goodman, J. C.

2012-12-01

The Coriolis force provides dominant control over the motion of atmospheres and oceans, both on Earth and on many other worlds. At any point on a planet's surface, the planetary rotation vector has both a vertical component and a horizontal (north-south) component. We typically ignore the horizontal component, which is justified if vertical motions are hydrostatic and the fluid is relatively shallow. Neither of these conditions is true for hydrothermal convection within the thick ocean layers of Europa and other icy worlds. Using the MITGCM ocean model, we explore the behavior of buoyant hydrothermal plumes in a deep unstratified ocean, including both components of the planetary rotation vector. We find that warm water does not rise vertically: instead, it spirals along the axis of planetary rotation. Eddies form which are tilted with respect to the local vertical, but parallel to the rotation axis: turbulent exchange of heat between these canted eddies carries the warm water toward the surface. This is not an entirely new idea: however, the implications for icy worlds have not been previously discussed. We observe that when these tilted plumes heat the ice layer above the ocean, the heating "footprint" of these tilted plumes will be more circular near the pole, more ellipsoidal in the tropics. If surface features of the ice crust were created by plume heating, their shapes ought to show consistent latitude trends. Also, we observe that if warm fluid were totally constrained to move along the planetary rotation axis, geothermal heat generated in the icy world's interior could never reach the ice crust near the equator. (For Europa, the "forbidden zone" could extend as far as +/- 20-25° latitude.) In practice, we find that turbulent eddies do allow heat to move perpendicular to the rotation vector, so the "forbidden zone" is not a tight constraint; still, it may affect the overall heating pattern of icy world crusts. Snapshot of ascent of buoyant hydrothermal plume

A Gas-poor Planetesimal Feeding Model for the Formation of Giant Planet Satellite Systems: Disk Size and Formation Timescale

NASA Astrophysics Data System (ADS)

Estrada, P. R.; Mosqueira, I.

2003-05-01

Mosqueira and Estrada (2003a) argue that following giant planet accretion a largely quiescent circumplanetary disk may form with most of the mass inside a radius located outside, but perhaps close to, the centrifugal radius rc = RH/48, where the specific angular momentum of the collapsing giant planet gaseous envelope achieves centrifugal balance, and extending as far as the irregular satellites at RH/5 due to the high specific angular momentum of parcels of gas accreted from distances several times RH during the final stages of planetary growth (Lubow et al. 1999). Provided that allowances are made for the capture of Triton from heliocentric orbit, this picture fits well with the primordial satellite systems of all four giant planets. Because strong gas turbulence would smooth out the gas surface density of the disk, this description can only apply if the turbulence subsides as planetary accretion ceases. Although the viability of a hydrodynamic shear instability in Keplerian disks that can sustain significant post-accretion turbulence and drive evolution of the gas disk is in serious doubt (see Mosqueira et al. this conference), the possibility has not yet been totally ruled out. This leads us to consider gas-poor scenarios that might produce a close-in regular satellite system. To this end, we re-examine the ideas of Safronov et al. (1986) to see whether a gas-free (or nearly gas-free) model can be made consistent with the extent of the regular satellites of the giant planets. In this model, planetesimals containing most of the mass of solids (Mizuno et al. 1978; Weidenschilling 1997) that are de-coupled from the gas and whose dynamics must be followed independently are collisionally captured and form a swarm of circumplanetary objects lasting for perhaps ˜ 106 years. While such a swarm might occupy a significant fraction of the Hill radius of the planet, the small net angular momentum of the swarm might lead to the formation of close-in prograde satellites as

Proposal of ICI cancellation using opposite weightings on symmetric subcarrier pairs in CO-OFDM systems

NASA Astrophysics Data System (ADS)

Zhang, Jing; Chen, Xuemei; Deng, Mingliang; Zeng, Dengke; Yang, Heming; Qiu, Kun

2015-08-01

We propose a novel ICI cancellation using opposite weighting on symmetric subcarrier pairs to combat the linear phase noise of laser source and the nonlinear phase noise resulted from the fiber nonlinearity. We compare the proposed ICI cancellation scheme with conventional OFDM and the ICI self-cancellation at the same raw bit rate of 35.6 Gb/s. In simulations, the proposed ICI cancellation scheme shows better phase noise tolerance compared with conventional OFDM and has similar phase noise tolerance with the ICI self-cancellation. The laser linewidth is about 13 MHz at BER of 2 × 10-3 with ICI cancellation scheme while it is 5 MHz in conventional OFDM. We also study the nonlinearity tolerance and find that the proposed ICI cancellation scheme is better compared with the other two schemes which due to the first order nonlinearity mitigation. The launch power is 7 dBm for the proposed ICI cancellation scheme and its SNR improves by 4 dB or 3 dB compared with the ICI self-cancellation or conventional OFDM at BER of 1.1 × 10-3, respectively.

The evolution of the moon and the terrestrial planets

NASA Technical Reports Server (NTRS)

Toksoez, M. N.; Johnston, D. H.

1974-01-01

The thermal evolutions of the Moon, Mars, Venus and Mercury are calculated theoretically starting from cosmochemical condensation models. An assortment of geological, geochemical and geophysical data are used to constrain both the present day temperatures and the thermal histories of the planets' interiors. Such data imply that the planets were heated during or shortly after formation and that all the terrestrial planets started their differentiations early in their history. The moon, smallest in size, is characterized as a differentiated body with a crust, a thick solid mantle and an interior region which may be partially molten. Mars, intermediate in size, is assumed to have differentiated an Fe-FeS core. Venus is characterized as a planet not unlike the earth in many respects. Core formation has occurred probably during the first billion years after the formation. Mercury, which probably has a large core, may have a 500 km thick solid lithosphere and a partially molten core if it is assumed that some heat sources exist in the core.

The Gemini Planet Imager Exoplanet Survey

NASA Astrophysics Data System (ADS)

Macintosh, Bruce

The Gemini Planet Imager (GPI) is a next-generation coronagraph constructed for the Gemini Observatory. GPI will see first light this fall. It will be the most advanced planet-imaging system in operation - an order of magnitude more sensitive than any current instrument, capable of detecting and spectroscopically characterizing young Jovian planets 107 times fainter than their parent star at separations of 0.2 arcseconds. GPI was built from the beginning as a facility-class survey instrument, and the observatory will employ it that way. Our team has been selected by Gemini Observatory to carry out an 890-hour program - the GPI Exoplanet Survey (GPIES) campaign from 2014-2017. We will observe 600 stars spanning spectral types A-M. We will use published young association catalogs and a proprietary list in preparation that adds several hundred new young (<100 Myr, <75 pc) and adolescent (<300 Myr, <35 pc) stars. The range of separations studied by GPI is completely inaccessible to Doppler and transit techniques (even with Kepler or TESS)— GPI offers a new window into planet formation. We will use GPI to produce the first-ever robust census of giant planet populations in the 5-50 AU range, allowing us to: 1) illuminate the formation pathways of Jovian planets; 2) reconstruct the early dynamical evolution of systems, including migration mechanisms and the interaction with disks and belts of debris; and 3) bridge the gap between Jupiter and the brown dwarfs with the first examples of cool low- gravity planetary atmospheres. Simulations predict this survey will discover approximately 50 exoplanets, increasing the number of exoplanet images by an order of magnitude, enough for statistical investigation. This Origins of Solar Systems proposal will support the execution of the GPI Exoplanet Survey campaign. We will develop tools needed to execute the survey efficiently. We will refine the existing GPI data pipeline to a final version that robustly removes residual speckle