Shock Wave Propagation in Layered Planetary Interiors: Revisited

NASA Astrophysics Data System (ADS)

Arkani-Hamed, J.; Monteux, J.

2017-12-01

The end of the terrestrial planet accretion is characterized by numerous large impacts. About 90% of the mass of a large planet is accreted while the core mantle separation is occurring, because of the accretionary and the short-lived radio-isotope heating. The characteristics of the shockwave propagation, hence the existing scaling laws are poorly known within the layered planets. Here, we use iSALE-2D hydrocode simulations to calculate shock pressure in a differentiated Mars type body for impact velocities of 5-20 km/s, and impactor sizes of 100-400 km. We use two different rheologies for the target interior, an inviscid model ("no-stress model") and a pressure and damage-dependent strength model ("elaborated model"). To better characterize the shock pressure within the whole mantle as a function of distance from the impact site, we propose the following distribution: (1) a near field zone larger than the isobaric core that extends to 7-15 times the projectile radius into the target, where the peak shock pressure decays exponentially with increasing distance, (2) a far field zone where the pressure decays with distance following a power law. The shock pressure decreases more rapidly with distance in the near field for the elaborated model than for the no-stress model because of the influence of acoustic fluidization and damage. However to better illustrate the influence of the rheology on the shock propagation, we use the same expressions to fit the shock pressure with distance for both models. At the core-mantle boundary, CMB, the peak shock pressure jumps as the shock wave enters the core. We derived the boundary condition at CMB for the peak shock pressure. It is less sensitive to the impact velocity or the impactor size, but strongly depends on the rheology of the planet's mantle. Because of the lower shock wave velocity in the core compared to that in the mantle, the refracted shockwave propagates toward the symmetry axis of the planet, and the shock pressure in the core decreases following a second power law. In this study, we express the output obtained from iSALE hydrocodes by scaling laws to illustrate the influence of the ray angle relative to the axis of symmetry, the target rheology, the impactor size and the impact velocity. We use these shock-pressure scaling laws to determine the impact heating of terrestrial planets.

A sub-Mercury-sized exoplanet.

PubMed

Barclay, Thomas; Rowe, Jason F; Lissauer, Jack J; Huber, Daniel; Fressin, François; Howell, Steve B; Bryson, Stephen T; Chaplin, William J; Désert, Jean-Michel; Lopez, Eric D; Marcy, Geoffrey W; Mullally, Fergal; Ragozzine, Darin; Torres, Guillermo; Adams, Elisabeth R; Agol, Eric; Barrado, David; Basu, Sarbani; Bedding, Timothy R; Buchhave, Lars A; Charbonneau, David; Christiansen, Jessie L; Christensen-Dalsgaard, Jørgen; Ciardi, David; Cochran, William D; Dupree, Andrea K; Elsworth, Yvonne; Everett, Mark; Fischer, Debra A; Ford, Eric B; Fortney, Jonathan J; Geary, John C; Haas, Michael R; Handberg, Rasmus; Hekker, Saskia; Henze, Christopher E; Horch, Elliott; Howard, Andrew W; Hunter, Roger C; Isaacson, Howard; Jenkins, Jon M; Karoff, Christoffer; Kawaler, Steven D; Kjeldsen, Hans; Klaus, Todd C; Latham, David W; Li, Jie; Lillo-Box, Jorge; Lund, Mikkel N; Lundkvist, Mia; Metcalfe, Travis S; Miglio, Andrea; Morris, Robert L; Quintana, Elisa V; Stello, Dennis; Smith, Jeffrey C; Still, Martin; Thompson, Susan E

2013-02-28

Since the discovery of the first exoplanets, it has been known that other planetary systems can look quite unlike our own. Until fairly recently, we have been able to probe only the upper range of the planet size distribution, and, since last year, to detect planets that are the size of Earth or somewhat smaller. Hitherto, no planets have been found that are smaller than those we see in the Solar System. Here we report a planet significantly smaller than Mercury. This tiny planet is the innermost of three that orbit the Sun-like host star, which we have designated Kepler-37. Owing to its extremely small size, similar to that of the Moon, and highly irradiated surface, the planet, Kepler-37b, is probably rocky with no atmosphere or water, similar to Mercury.

Kepler Mission: a Discovery-Class Mission Designed to Determine the Frequency of Earth-Size and Larger Planets Around Solar-Like Stars

NASA Technical Reports Server (NTRS)

Borucki, William; Koch, David; Lissauer, Jack; Basri, Gibor; Caldwell, John; Cochran, William; Dunham, Edward W.; Gilliland, Ronald; Caldwell, Douglas; Kondo, Yoji;

Temperate Earth-sized planets transiting a nearby ultracool dwarf star

NASA Astrophysics Data System (ADS)

Gillon, Michaël; Jehin, Emmanuël; Lederer, Susan M.; Delrez, Laetitia; de Wit, Julien; Burdanov, Artem; Van Grootel, Valérie; Burgasser, Adam J.; Triaud, Amaury H. M. J.; Opitom, Cyrielle; Demory, Brice-Olivier; Sahu, Devendra K.; Bardalez Gagliuffi, Daniella; Magain, Pierre; Queloz, Didier

2016-05-01

Star-like objects with effective temperatures of less than 2,700 kelvin are referred to as ‘ultracool dwarfs’. This heterogeneous group includes stars of extremely low mass as well as brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion), and represents about 15 per cent of the population of astronomical objects near the Sun. Core-accretion theory predicts that, given the small masses of these ultracool dwarfs, and the small sizes of their protoplanetary disks, there should be a large but hitherto undetected population of terrestrial planets orbiting them—ranging from metal-rich Mercury-sized planets to more hospitable volatile-rich Earth-sized planets. Here we report observations of three short-period Earth-sized planets transiting an ultracool dwarf star only 12 parsecs away. The inner two planets receive four times and two times the irradiation of Earth, respectively, placing them close to the inner edge of the habitable zone of the star. Our data suggest that 11 orbits remain possible for the third planet, the most likely resulting in irradiation significantly less than that received by Earth. The infrared brightness of the host star, combined with its Jupiter-like size, offers the possibility of thoroughly characterizing the components of this nearby planetary system.

Temperate Earth-sized planets transiting a nearby ultracool dwarf star.

PubMed

Gillon, Michaël; Jehin, Emmanuël; Lederer, Susan M; Delrez, Laetitia; de Wit, Julien; Burdanov, Artem; Van Grootel, Valérie; Burgasser, Adam J; Triaud, Amaury H M J; Opitom, Cyrielle; Demory, Brice-Olivier; Sahu, Devendra K; Bardalez Gagliuffi, Daniella; Magain, Pierre; Queloz, Didier

2016-05-12

Star-like objects with effective temperatures of less than 2,700 kelvin are referred to as 'ultracool dwarfs'. This heterogeneous group includes stars of extremely low mass as well as brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion), and represents about 15 per cent of the population of astronomical objects near the Sun. Core-accretion theory predicts that, given the small masses of these ultracool dwarfs, and the small sizes of their protoplanetary disks, there should be a large but hitherto undetected population of terrestrial planets orbiting them--ranging from metal-rich Mercury-sized planets to more hospitable volatile-rich Earth-sized planets. Here we report observations of three short-period Earth-sized planets transiting an ultracool dwarf star only 12 parsecs away. The inner two planets receive four times and two times the irradiation of Earth, respectively, placing them close to the inner edge of the habitable zone of the star. Our data suggest that 11 orbits remain possible for the third planet, the most likely resulting in irradiation significantly less than that received by Earth. The infrared brightness of the host star, combined with its Jupiter-like size, offers the possibility of thoroughly characterizing the components of this nearby planetary system.

Kepler Confirms First Earth-Sized Planet Outside Our Solar System (Kepler-20) (Reporter Package)

NASA Image and Video Library

2011-12-19

NASA's Kepler mission has confirmed the discovery of the first Earth-size planets outside our solar system orbiting a sun-like star. Located about 1,000 light years from Earth, the Kepler-20 solar system has five planets orbiting a star similar to the Sun. Kepler-20f, the 4th planet in the system, is about 90 percent the size of Earth. Kepler-20f is slightly larger than Earth,with a radius that is 3 percent larger.

The Kepler Mission: A Photometric Search for Earthlike Planets

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; Borucki, William; Koch, David; Young, Richard E. (Technical Monitor)

1998-01-01

If Earth lies in or near the orbital plane of an extrasolar planet, that planet passes in front of the disk of its star once each orbit as viewed from Earth. Precise photometry can reveal such transits, which can be distinguished from rotationally-modulated starspots and intrinsic stellar variability by their periodicity, square-well shapes and relative spectral neutrality. Transit observations would provide the size and orbital period of the detected planet. Although geometrical considerations limit the fraction of planets detectable by this technique, many stars can be surveyed within the field of view of one telescope, so transit photometry is quite efficient. Scintillation in and variability of Earth's atmosphere limit photometric precision to roughly one-thousandth of a magnitude, allowing detection of transits by Jupiter-sized planets but not by Earth-sized planets from the ground. The COROT spacecraft will be able to detect Uranus-sized planets orbiting near stars. The Kepler Mission, which is being proposed to NASA's Discovery Program this year, will have a photometer with a larger aperture (1 meter) than will COROT, so it will be able to detect transits by planets as small as Earth. Moreover, the Kepler mission will examine the same star field for four years, allowing confirmation of planets with orbital periods of a year. If the Sun's planetary system is typical for single stars, Kepler should detect approximately 480 terrestrial planets. Assuming the statistics from radial velocity surveys are typical, Kepler should also detect transits of 150 inner giant planets and reflected light variations of 1400 giant planets with orbital periods of less than one week.

DENSITY AND ECCENTRICITY OF KEPLER PLANETS

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

Wu Yanqin; Lithwick, Yoram

2013-07-20

We analyze the transit timing variations (TTV) obtained by the Kepler mission for 22 sub-Jovian planet pairs (19 published, 3 new) that lie close to mean motion resonances. We find that the TTV phases for most of these pairs lie close to zero, consistent with an eccentricity distribution that has a very low root-mean-squared value of e {approx} 0.01; but about a quarter of the pairs possess much higher eccentricities, up to e {approx} 0.1-0.4. For the low-eccentricity pairs, we are able to statistically remove the effect of eccentricity to obtain planet masses from TTV data. These masses, together withmore » those measured by radial velocity, yield a best-fit mass-radius relation M {approx} 3 M{sub Circled-Plus }(R/R{sub Circled-Plus }). This corresponds to a constant surface escape velocity of {approx}20 km s{sup -1}. We separate the planets into two distinct groups: ''mid-sized'' (those greater than 3 R{sub Circled-Plus }) and 'compact' (those smaller). All mid-sized planets are found to be less dense than water and therefore must contain extensive H/He envelopes that are comparable in mass to that of their cores. We argue that these planets have been significantly sculpted by photoevaporation. Surprisingly, mid-sized planets, a minority among Kepler candidates, are discovered exclusively around stars more massive than 0.8 M{sub Sun }. The compact planets, on the other hand, are often denser than water. Combining our density measurements with those from radial velocity studies, we find that hotter compact planets tend to be denser, with the hottest ones reaching rock density. Moreover, hotter planets tend to be smaller in size. These results can be explained if the compact planets are made of rocky cores overlaid with a small amount of hydrogen, {<=}1% in mass, with water contributing little to their masses or sizes. Photoevaporation has exposed bare rocky cores in cases of the hottest planets. Our conclusion that these planets are likely not water worlds contrasts with some previous studies. While mid-sized planets most likely accreted their hydrogen envelope from the proto-planetary disks, compact planets could have obtained theirs via either accretion or outgassing. The presence of the two distinct classes suggests that 3 R{sub Circled-Plus} could be identified as the dividing line between 'hot Neptunes' and 'super-Earths'.« less

The Prevalence of Earth-size Planets Orbiting Sun-like Stars

NASA Astrophysics Data System (ADS)

Petigura, Erik; Marcy, Geoffrey W.; Howard, Andrew

2015-01-01

In less than two decades since the discovery of the first planet orbiting another Sun-like star, the study of extrasolar planets has matured beyond individual discoveries to detailed characterization of the planet population as a whole. No mission has played more of a role in this paradigm shift than NASA's Kepler mission. Kepler photometry has shown that planets like Earth are common throughout the Milky Way Galaxy. Our group performed an independent search of Kepler photometry using our custom transit-finding pipeline, TERRA, and produced our own catalog of planet candidates. We conducted spectroscopic follow-up of their host stars in order to rule out false positive scenarios and to better constrain host star properties. We measured TERRA's sensitivity to planets of different sizes and orbital periods by injecting synthetic planets into raw Kepler photometry and measuring the recovery rate. Correcting for orbital tilt and survey completeness, we found that ~80% of GK stars harbor one or more planets within 1 AU and that ~22% of Sun-like stars harbor an Earth-size planet that receives similar levels of stellar radiation as Earth. I will present the latest results from our efforts to characterize the demographics of small planets revealed by Kepler.

Astronomy: A small star with an Earth-like planet

NASA Astrophysics Data System (ADS)

Deming, Drake

2015-11-01

A rocky planet close in size to Earth has been discovered in the cosmic vicinity of our Sun. The small size and proximity of the associated star bode well for studies of the planet's atmosphere. See Letter p.204

Detectability of the Reflection Signal from Inner Planets

NASA Technical Reports Server (NTRS)

Borucki, W. J.; Jenkins, J. M.; Scargle, J.; Koch, D.; Doyle, L. R.; Cuzzi, Jeffrey (Technical Monitor)

1996-01-01

Mayor and Queloz (1996) and Marcy and Butler (1996) have found massive planets with orbital periods Tp=approx.4 days around two solar-like stars (51 Pegasi and v Andromeda). These planets are most likely similar in size and composition to the gas giants in our solar system (Burrows et al 1996). Based on this expectation and assuming the same albedo as Jupiter, we examined the feasibility of searching for similar planets with a dedicated space-based 1-m telescope. The Kepler mission will survey approximately 70,000 main-sequence dwarf stars from 9 to 14 mag continuously for four years to detect transiting Earthlike planets. Based on the detection statistics of Marcy and Butler, we expect to detect 1400 inner-orbit giant planets. Such planets in a much wider range of orbital inclinations (i) will produce nearly sinusoidal modulations of the star light flux due to the varying planetary phases. The relative signal amplitudes are of order 2x10(exp -5) and decrease as Tp(exp 4/3) for i >> 0deg. We estimated the expected signal to noise ratio (SNR) using the solar irradiance measurements from the ACRIM 1 experiment along with expected shot and detector noises. The figure shows SNR as a function of Tp for a 12 mag star, and indicates the planet radius required for detection. The survey will be sensitive to planets with periods from 12 hr to approx.8 days at the 6 sigma level.

An Earth-sized planet in the habitable zone of a cool star.

PubMed

Quintana, Elisa V; Barclay, Thomas; Raymond, Sean N; Rowe, Jason F; Bolmont, Emeline; Caldwell, Douglas A; Howell, Steve B; Kane, Stephen R; Huber, Daniel; Crepp, Justin R; Lissauer, Jack J; Ciardi, David R; Coughlin, Jeffrey L; Everett, Mark E; Henze, Christopher E; Horch, Elliott; Isaacson, Howard; Ford, Eric B; Adams, Fred C; Still, Martin; Hunter, Roger C; Quarles, Billy; Selsis, Franck

2014-04-18

The quest for Earth-like planets is a major focus of current exoplanet research. Although planets that are Earth-sized and smaller have been detected, these planets reside in orbits that are too close to their host star to allow liquid water on their surfaces. We present the detection of Kepler-186f, a 1.11 ± 0.14 Earth-radius planet that is the outermost of five planets, all roughly Earth-sized, that transit a 0.47 ± 0.05 solar-radius star. The intensity and spectrum of the star's radiation place Kepler-186f in the stellar habitable zone, implying that if Kepler-186f has an Earth-like atmosphere and water at its surface, then some of this water is likely to be in liquid form.

An Earth-sized planet with an Earth-like density.

PubMed

Pepe, Francesco; Cameron, Andrew Collier; Latham, David W; Molinari, Emilio; Udry, Stéphane; Bonomo, Aldo S; Buchhave, Lars A; Charbonneau, David; Cosentino, Rosario; Dressing, Courtney D; Dumusque, Xavier; Figueira, Pedro; Fiorenzano, Aldo F M; Gettel, Sara; Harutyunyan, Avet; Haywood, Raphaëlle D; Horne, Keith; Lopez-Morales, Mercedes; Lovis, Christophe; Malavolta, Luca; Mayor, Michel; Micela, Giusi; Motalebi, Fatemeh; Nascimbeni, Valerio; Phillips, David; Piotto, Giampaolo; Pollacco, Don; Queloz, Didier; Rice, Ken; Sasselov, Dimitar; Ségransan, Damien; Sozzetti, Alessandro; Szentgyorgyi, Andrew; Watson, Christopher A

2013-11-21

Recent analyses of data from the NASA Kepler spacecraft have established that planets with radii within 25 per cent of the Earth's (R Earth symbol) are commonplace throughout the Galaxy, orbiting at least 16.5 per cent of Sun-like stars. Because these studies were sensitive to the sizes of the planets but not their masses, the question remains whether these Earth-sized planets are indeed similar to the Earth in bulk composition. The smallest planets for which masses have been accurately determined are Kepler-10b (1.42 R Earth symbol) and Kepler-36b (1.49 R Earth symbol), which are both significantly larger than the Earth. Recently, the planet Kepler-78b was discovered and found to have a radius of only 1.16 R Earth symbol. Here we report that the mass of this planet is 1.86 Earth masses. The resulting mean density of the planet is 5.57 g cm(-3), which is similar to that of the Earth and implies a composition of iron and rock.

An abundance of small exoplanets around stars with a wide range of metallicities.

PubMed

Buchhave, Lars A; Latham, David W; Johansen, Anders; Bizzarro, Martin; Torres, Guillermo; Rowe, Jason F; Batalha, Natalie M; Borucki, William J; Brugamyer, Erik; Caldwell, Caroline; Bryson, Stephen T; Ciardi, David R; Cochran, William D; Endl, Michael; Esquerdo, Gilbert A; Ford, Eric B; Geary, John C; Gilliland, Ronald L; Hansen, Terese; Isaacson, Howard; Laird, John B; Lucas, Philip W; Marcy, Geoffrey W; Morse, Jon A; Robertson, Paul; Shporer, Avi; Stefanik, Robert P; Still, Martin; Quinn, Samuel N

2012-06-13

The abundance of heavy elements (metallicity) in the photospheres of stars similar to the Sun provides a 'fossil' record of the chemical composition of the initial protoplanetary disk. Metal-rich stars are much more likely to harbour gas giant planets, supporting the model that planets form by accumulation of dust and ice particles. Recent ground-based surveys suggest that this correlation is weakened for Neptunian-sized planets. However, how the relationship between size and metallicity extends into the regime of terrestrial-sized exoplanets is unknown. Here we report spectroscopic metallicities of the host stars of 226 small exoplanet candidates discovered by NASA's Kepler mission, including objects that are comparable in size to the terrestrial planets in the Solar System. We find that planets with radii less than four Earth radii form around host stars with a wide range of metallicities (but on average a metallicity close to that of the Sun), whereas large planets preferentially form around stars with higher metallicities. This observation suggests that terrestrial planets may be widespread in the disk of the Galaxy, with no special requirement of enhanced metallicity for their formation.

M Stars as Targets for Terrestrial Exoplanet Searches And Biosignature Detection

NASA Astrophysics Data System (ADS)

Scalo, John; Kaltenegger, Lisa; Segura, Ant Gona; Fridlund, Malcolm; Ribas, Ignasi; Kulikov, Yu. N.; Grenfell, John L.; Rauer, Hieke; Odert, Petra; Leitzinger, Martin; Selsis, F.; Khodachenko, Maxim L.; Eiroa, Carlos; Kasting, Jim; Lammer, Helmut

2007-02-01

The changing view of planets orbiting low mass stars, M stars, as potentially hospitable worlds for life and its remote detection was motivated by several factors, including the demonstration of viable atmospheres and oceans on tidally locked planets, normal incidence of dust disks, including debris disks, detection of planets with masses in the 5-20 M⊕ range, and predictions of unusually strong spectral biosignatures. We present a critical discussion of M star properties that are relevant for the long- and short-term thermal, dynamical, geological, and environmental stability of conventional liquid water habitable zone (HZ) M star planets, and the advantages and disadvantages of M stars as targets in searches for terrestrial HZ planets using various detection techniques. Biological viability seems supported by unmatched very long-term stability conferred by tidal locking, small HZ size, an apparent short-fall of gas giant planet perturbers, immunity to large astrosphere compressions, and several other factors, assuming incidence and evolutionary rate of life benefit from lack of variability. Tectonic regulation of climate and dynamo generation of a protective magnetic field, especially for a planet in synchronous rotation, are important unresolved questions that must await improved geodynamic models, though they both probably impose constraints on the planet mass. M star HZ terrestrial planets must survive a number of early trials in order to enjoy their many Gyr of stability. Their formation may be jeopardized by an insufficient initial disk supply of solids, resulting in the formation of objects too small and/or dry for habitability. The small empirical gas giant fraction for M stars reduces the risk of formation suppression or orbit disruption from either migrating or nonmigrating giant planets, but effects of perturbations from lower mass planets in these systems are uncertain. During the first ~1 Gyr, atmospheric retention is at peril because of intense and frequent stellar flares and sporadic energetic particle events, and impact erosion, both enhanced, the former dramatically, for M star HZ semimajor axes. Loss of atmosphere by interactions with energetic particles is likely unless the planetary magnetic moment is sufficiently large. For the smallest stellar masses a period of high planetary surface temperature, while the parent star approaches the main sequence, must be endured. The formation and retention of a thick atmosphere and a strong magnetic field as buffers for a sufficiently massive planet emerge as prerequisites for an M star planet to enter a long period of stability with its habitability intact. However, the star will then be subjected to short-term fluctuations with consequences including frequent unpredictable variation in atmospheric chemistry and surficial radiation field. After a review of evidence concerning disks and planets associated with M stars, we evaluate M stars as targets for future HZ planet search programs. Strong advantages of M stars for most approaches to HZ detection are offset by their faintness, leading to severe constraints due to accessible sample size, stellar crowding (transits), or angular size of the HZ (direct imaging). Gravitational lensing is unlikely to detect HZ M star planets because the HZ size decreases with mass faster than the Einstein ring size to which the method is sensitive. M star Earth-twin planets are predicted to exhibit surprisingly strong bands of nitrous oxide, methyl chloride, and methane, and work on signatures for other climate categories is summarized. The rest of the paper is devoted to an examination of evidence and implications of the unusual radiation and particle environments for atmospheric chemistry and surface radiation doses, and is summarized in the Synopsis. We conclude that attempts at remote sensing of biosignatures and nonbiological markers from M star planets are important, not as tests of any quantitative theories or rational arguments, but instead because they offer an inspection of the residues from a Gyr-long biochemistry experiment in the presence of extreme environmental fluctuations. A detection or repeated nondetections could provide a unique opportunity to partially answer a fundamental and recurrent question about the relation between stability and complexity, one that is not addressed by remote detection from a planet orbiting a solar-like star, and can only be studied on Earth using restricted microbial systems in serial evolution experiments or in artificial life simulations. This proposal requires a planet that has retained its atmosphere and a water supply. The discussion given here suggests that observations of M star exoplanets can decide this latter question with only slight modifications to plans already in place for direct imaging terrestrial exoplanet missions. Key Words: M star planets-Habitable planets - Life and stellar activity - Spectral biosignatures - Terrestrial planet formation - Exoplanet properties. Astrobiology 7(1), 85 - 166.

Temperate Earth-sized planets transiting a nearby ultracool dwarf star

PubMed Central

Gillon, Michaël; Jehin, Emmanuël; Lederer, Susan M.; Delrez, Laetitia; de Wit, Julien; Burdanov, Artem; Van Grootel, Valérie; Burgasser, Adam; Triaud, Amaury H. M. J.; Opitom, Cyrielle; Demory, Brice-Olivier; Sahu, Devendra K.; Bardalez Gagliuffi, Daniella; Magain, Pierre; Queloz, Didier

2017-01-01

Stellar-like objects with effective temperatures of 2700K and below are referred to as “ultracool dwarfs”1. This heterogeneous group includes both extremely low-mass stars and brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion), and represents about 15% of the stellar-like objects in the vicinity of the Sun2. Based on the small masses and sizes of their protoplanetary disks3,4, core-accretion theory for ultracool dwarfs predicts a large, but heretofore undetected population of close-in terrestrial planets5, ranging from metal-rich Mercury-sized planets6 to more hospitable volatile-rich Earth-sized planets7. Here we report the discovery of three short-period Earth-sized planets transiting an ultracool dwarf star 12 parsecs away using data collected by the TRAPPIST8 telescope as part of an ongoing prototype transit survey9. The inner two planets receive four and two times the irradiation of Earth, respectively, placing them close to the inner edge of the habitable zone of the star10. Eleven orbits remain possible for the third planet based on our data, the most likely resulting in an irradiation significantly smaller than Earth's. The infrared brightness of the host star combined with its Jupiter-like size offer the possibility of thoroughly characterizing the components of this nearby planetary system. PMID:27135924

Detection of Extrasolar Planets by Transit Photometry

NASA Technical Reports Server (NTRS)

Borucki, William; Koch, David; Webster, Larry; Dunham, Edward; Witteborn, Fred; Jenkins, Jon; Caldwell, Douglas; Showen, Robert; DeVincenzi, Donald L. (Technical Monitor)

2000-01-01

A knowledge of other planetary systems that includes information on the number, size, mass, and spacing of the planets around a variety of star types is needed to deepen our understanding of planetary system formation and processes that give rise to their final configurations. Recent discoveries show that many planetary systems are quite different from the solar system in that they often possess giant planets in short period orbits. The inferred evolution of these planets and their orbital characteristics imply the absence of Earth-like planets near the habitable zone. Information on the properties of the giant-inner planets is now being obtained by both the Doppler velocity and the transit photometry techniques. The combination of the two techniques provides the mass, size, and density of the planets. For the planet orbiting star HD209458, transit photometry provided the first independent confirmation and measurement of the diameter of an extrasolar planet. The observations indicate a planet 1.27 the diameter of Jupiter with 0.63 of its mass (Charbonneau et al. 1999). The results are in excellent agreement with the theory of planetary atmospheres for a planet of the indicated mass and distance from a solar-like star. The observation of the November 23, 1999 transit of that planet made by the Ames Vulcan photometer at Lick Observatory is presented. In the future, the combination of the two techniques will greatly increase the number of discoveries and the richness of the science yield. Small rocky planets at orbital distances from 0.9 to 1.2 AU are more likely to harbor life than the gas giant planets that are now being discovered. However, new technology is needed to find smaller, Earth-like planets, which are about three hundred times less massive than Jupiter-like planets. The Kepler project is a space craft mission designed to discover hundreds of Earth-size planets in and near the habitable zone around a wide variety of stars. To demonstrate that the technology exists to find such small planets, our group has conducted an end-to-end system test. The results of the laboratory tests are presented and show that we are ready to start the search for Earth-size planets.

Size of Kepler Planet Candidates

NASA Image and Video Library

2013-01-07

Kepler data has increased by 20 percent and now totals 2,740 potential planets orbiting 2,036 stars; dramatic increases are seen in the number of Earth-size and super Earth-size candidates discovered.

Kepler-186f, the First Earth-size Planet in the Habitable Zone Artist Concept

NASA Image and Video Library

2014-04-17

This artist concept depicts Kepler-186f, the first validated Earth-size planet to orbit a distant star in the habitable zone, a range of distance from a star where liquid water might pool on the planet surface.

New worlds on the horizon: Earth-sized planets close to other stars.

PubMed

Gaidos, Eric; Haghighipour, Nader; Agol, Eric; Latham, David; Raymond, Sean; Rayner, John

2007-10-12

The search for habitable planets like Earth around other stars fulfills an ancient imperative to understand our origins and place in the cosmos. The past decade has seen the discovery of hundreds of planets, but nearly all are gas giants like Jupiter and Saturn. Recent advances in instrumentation and new missions are extending searches to planets the size of Earth but closer to their host stars. There are several possible ways such planets could form, and future observations will soon test those theories. Many of these planets we discover may be quite unlike Earth in their surface temperature and composition, but their study will nonetheless inform us about the process of planet formation and the frequency of Earth-like planets around other stars.

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

NASA Astrophysics Data System (ADS)

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

2015-12-01

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

NASA's Kepler Mission Discovers First Earth-size Planet in Habitable Zone of Another Star (Reporter Package)

NASA Image and Video Library

2014-04-17

NASA's Kepler mission has discovered the first Earth-size planet orbiting in the habitable zone of a star outside our solar system. The newly discovered planet is called Kepler-186f and is about 10 percent larger than Earth.

Kepler Mission: A Wide-FOV Photometer Designed to Determine the Frequency of Earth-Size and Larger Planets Around Solar-like stars

NASA Technical Reports Server (NTRS)

Borucki, William; Koch, David; Lissauer, Jack; Basri, Gibor; Caldwell, John; Cochran, William; Dunham, Edward W.; Gilliland, Ronald; Jenkins, Jon M.; Caldwell, Douglas;

The Death Spiral of the Hot Jupiter Exoplanet HD 189733b

NASA Astrophysics Data System (ADS)

Dowling Jones, Liam; Marchioni, Lucas; Guinan, Edward; Engle, Scott

2018-01-01

HD 189733 is a quintessential example of hot Jupiter-type exoplanet systems in which a gas giant planet with a mass similar to Jupiter is orbiting extremely close to its host star. HD 189733 is the nearest and brightest hot Jupiter system discovered so far and undergoes transit eclipses. Because of this, HD 189733 is well studied across the electromagnetic spectrum. It consists of a 7.7 mag K1.5 V host star and a Jupiter-size planet orbiting with a period of P =2.22 days, only located only 0.030 AU from its host star.About ten years ago HD 189733 system was discovered to be accompanied by gravitationally-bound red dwarf M4 V star companion (HD 189733 B). It was found previously by Guinan et al. (2017) that the age measurement (~0.7 Gyr) of the K-type star indicated by its 11.95 day rotation period and corresponding moderately high levels of coronal X-ray and chromospheric emissions do not agree with the much older age of ~6 - 9 Gyr indicated from the low X-ray activity of the dM companion star. This age discrepancy is can be resolved by assuming an increase in angular momentum or “spin-up” of the HD 189733A by its hosted planet. It is probable is that this extra angular momentum was acquired from the orbiting exoplanet from the tidal and magnetic interactions of the planet and host star.Photometric observations of the planetary transit eclipses of HD 189733b have been carried out for over 11 years. Using new transit timings that we have obtained with the 1.3-m Robotically Controlled Telescope (RCT) when combined with numerous timings available in the literature, we have discovered a very small decrease in the orbital period of the HD 189733b. The change in period is dP/dt = 0.87 sec/100 yrs. This finding support the transfer of orbital angular momentum of the planet to the host star - thus spinning-up the host star and shrinking the orbit of the planet. At this rate of period decrease, the planet will be tidally disrupted in less than 40 million years. However, this planetary disruption will likely occur much sooner because the decrease in the planet’s orbital period is expected to speed-up as the planet gets closer to the star.

The size distribution of inhabited planets

NASA Astrophysics Data System (ADS)

Simpson, Fergus

2016-02-01

Earth-like planets are expected to provide the greatest opportunity for the detection of life beyond the Solar system. However, our planet cannot be considered a fair sample, especially if intelligent life exists elsewhere. Just as a person's country of origin is a biased sample among countries, so too their planet of origin may be a biased sample among planets. The magnitude of this effect can be substantial: over 98 per cent of the world's population live in a country larger than the median. In the context of a simple model where the mean population density is invariant to planet size, we infer that a given inhabited planet (such as our nearest neighbour) has a radius r < 1.2r⊕ (95 per cent confidence bound). We show that this result is likely to hold not only for planets hosting advanced life, but also for those which harbour primitive life forms. Further, inferences may be drawn for any variable which influences population size. For example, since population density is widely observed to decline with increasing body mass, we conclude that most intelligent species are expected to exceed 300 kg.

TRAPPIST-1 Planet Animations

NASA Image and Video Library

2018-02-05

This still from a video shows illustrations of the seven Earth-size planets of TRAPPIST-1, an exoplanet system about 40 light-years away, based on data current as of February 2018. Each planet is shown in sequence, starting with the innermost TRAPPIST-1b and ending with the outermost TRAPPIST-1h. The video presents the planets' relative sizes as well as the relative scale of the central star as seen from each planet. The art highlights possibilities for how the surfaces of these intriguing worlds might look based on their newly calculated properties. The seven planets of TRAPPIST-1 are all Earth-sized and terrestrial. TRAPPIST-1 is an ultra-cool dwarf star in the constellation Aquarius, and its planets orbit very close to it. In the background, slightly distorted versions our familiar constellations, including Orion and Taurus, are shown as they would appear from the location of TRAPPIST-1 (backdrop image courtesy California Academy of Sciences/Dan Tell). An animation is available at https://photojournal.jpl.nasa.gov/catalog/PIA22098

Kepler planet-detection mission: introduction and first results.

PubMed

Borucki, William J; Koch, David; Basri, Gibor; Batalha, Natalie; Brown, Timothy; Caldwell, Douglas; Caldwell, John; Christensen-Dalsgaard, Jørgen; Cochran, William D; DeVore, Edna; Dunham, Edward W; Dupree, Andrea K; Gautier, Thomas N; Geary, John C; Gilliland, Ronald; Gould, Alan; Howell, Steve B; Jenkins, Jon M; Kondo, Yoji; Latham, David W; Marcy, Geoffrey W; Meibom, Søren; Kjeldsen, Hans; Lissauer, Jack J; Monet, David G; Morrison, David; Sasselov, Dimitar; Tarter, Jill; Boss, Alan; Brownlee, Don; Owen, Toby; Buzasi, Derek; Charbonneau, David; Doyle, Laurance; Fortney, Jonathan; Ford, Eric B; Holman, Matthew J; Seager, Sara; Steffen, Jason H; Welsh, William F; Rowe, Jason; Anderson, Howard; Buchhave, Lars; Ciardi, David; Walkowicz, Lucianne; Sherry, William; Horch, Elliott; Isaacson, Howard; Everett, Mark E; Fischer, Debra; Torres, Guillermo; Johnson, John Asher; Endl, Michael; MacQueen, Phillip; Bryson, Stephen T; Dotson, Jessie; Haas, Michael; Kolodziejczak, Jeffrey; Van Cleve, Jeffrey; Chandrasekaran, Hema; Twicken, Joseph D; Quintana, Elisa V; Clarke, Bruce D; Allen, Christopher; Li, Jie; Wu, Haley; Tenenbaum, Peter; Verner, Ekaterina; Bruhweiler, Frederick; Barnes, Jason; Prsa, Andrej

2010-02-19

The Kepler mission was designed to determine the frequency of Earth-sized planets in and near the habitable zone of Sun-like stars. The habitable zone is the region where planetary temperatures are suitable for water to exist on a planet's surface. During the first 6 weeks of observations, Kepler monitored 156,000 stars, and five new exoplanets with sizes between 0.37 and 1.6 Jupiter radii and orbital periods from 3.2 to 4.9 days were discovered. The density of the Neptune-sized Kepler-4b is similar to that of Neptune and GJ 436b, even though the irradiation level is 800,000 times higher. Kepler-7b is one of the lowest-density planets (approximately 0.17 gram per cubic centimeter) yet detected. Kepler-5b, -6b, and -8b confirm the existence of planets with densities lower than those predicted for gas giant planets.

Detection of Terrestrial Planets Using Transit Photometry

NASA Technical Reports Server (NTRS)

Koch, David; Witteborn, Fred; Jenkins, Jon; Dunham, Edward; Boruci, William; DeVincenzi, Donald (Technical Monitor)

2001-01-01

Transit photometry detection of planets offers many advantages: an ability to detect terrestrial size planets, direct determination of the planet's size, applicability to all main-sequence stars, and a differential brightness change of the periodic signature being independent of stellar distance or planetary orbital semi-major axis. Ground and space based photometry have already been successful in detecting transits of the giant planet HD209458b. However, photometry 100 times better is required to detect terrestrial planets. We present results of laboratory measurements of an end-to-end photometric system incorporating all of the important confounding noise features of both the sky and a space based photometer including spacecraft jitter. In addition to demonstrating an instrumental noise of less than 10 ppm (an Earth transit of a solar-like star is 80 ppm), the brightnesses of individual stars were dimmed to simulate Earth-size transit signals. These 'transits' were reliably detected as part of the tests.

Equilibrium Conditions of Sediment Suspending Flows on Earth, Mars and Titan

NASA Astrophysics Data System (ADS)

Amy, L. A.; Dorrell, R. M.

2016-12-01

Sediment entrainment, erosion and deposition by liquid water on Earth is one of the key processes controlling planetary surface evolution. Similar modification of planetary surfaces by liquids associated with a volatile cycle are also inferred to have occurred on other planets (e.g., water on Mars and methane-ethane on Titan). Here we explore conditions for equilibrium flow - the threshold between net sediment erosion and deposition - on different planets. We use a new theoretical model for particle erosion-suspension-deposition: this model shows a better fit to empirical data than comparative suspension criterions (e.g., Rouse Number) since it takes into account both flow competence and capacity, and particle size distribution effects. Shear stresses required to initially entrain sediment and maintain equilibrium flow vary significantly, being several times lower on Mars and more than ten times lower on Titan resulting principally from lower gravities. On all planets it is harder to maintain equilibrium flow as sediment mixtures become poorer sorted (higher shear stresses are needed as standard deviation increases). In comparison to large differences in critical shear stresses, critical slopes for equilibrium flow are similar for planets. Compared to Earth, equilibrium slopes on Mars should be slightly lower whilst those on Titan will be higher or lower for organic and ice particle systems, respectively. Particle size distribution has a similar, order of magnitude effect, on equilibrium slope on each planet. The results highlight that whilst reduced gravity on Titan and Mars significantly decreases the bed shear stress required for particle transport, it also proportionally effects the bed shear stress of moving fluid, such that similar slope gradients are required for equilibrium flow; minor variations in equilibrium slopes are related to differences in the particle-fluid density contrasts as well as fluid viscosities. These results help explain why planetary surfaces share striking similarities in their present or past landscapes and shows that particle size distribution is critical to sediment transport dynamics. Interestingly, particle distribution may vary between planets depending on the particle compositions and weathering regimes, imposing differences in equilibrium conditions.

M stars as targets for terrestrial exoplanet searches and biosignature detection.

PubMed

Scalo, John; Kaltenegger, Lisa; Segura, Antígona; Segura, Ant Gona; Fridlund, Malcolm; Ribas, Ignasi; Kulikov, Yu N; Grenfell, John L; Rauer, Heike; Odert, Petra; Leitzinger, Martin; Selsis, F; Khodachenko, Maxim L; Eiroa, Carlos; Kasting, Jim; Lammer, Helmut

2007-02-01

The changing view of planets orbiting low mass stars, M stars, as potentially hospitable worlds for life and its remote detection was motivated by several factors, including the demonstration of viable atmospheres and oceans on tidally locked planets, normal incidence of dust disks, including debris disks, detection of planets with masses in the 5-20 M() range, and predictions of unusually strong spectral biosignatures. We present a critical discussion of M star properties that are relevant for the long- and short-term thermal, dynamical, geological, and environmental stability of conventional liquid water habitable zone (HZ) M star planets, and the advantages and disadvantages of M stars as targets in searches for terrestrial HZ planets using various detection techniques. Biological viability seems supported by unmatched very long-term stability conferred by tidal locking, small HZ size, an apparent short-fall of gas giant planet perturbers, immunity to large astrosphere compressions, and several other factors, assuming incidence and evolutionary rate of life benefit from lack of variability. Tectonic regulation of climate and dynamo generation of a protective magnetic field, especially for a planet in synchronous rotation, are important unresolved questions that must await improved geodynamic models, though they both probably impose constraints on the planet mass. M star HZ terrestrial planets must survive a number of early trials in order to enjoy their many Gyr of stability. Their formation may be jeopardized by an insufficient initial disk supply of solids, resulting in the formation of objects too small and/or dry for habitability. The small empirical gas giant fraction for M stars reduces the risk of formation suppression or orbit disruption from either migrating or nonmigrating giant planets, but effects of perturbations from lower mass planets in these systems are uncertain. During the first approximately 1 Gyr, atmospheric retention is at peril because of intense and frequent stellar flares and sporadic energetic particle events, and impact erosion, both enhanced, the former dramatically, for M star HZ semimajor axes. Loss of atmosphere by interactions with energetic particles is likely unless the planetary magnetic moment is sufficiently large. For the smallest stellar masses a period of high planetary surface temperature, while the parent star approaches the main sequence, must be endured. The formation and retention of a thick atmosphere and a strong magnetic field as buffers for a sufficiently massive planet emerge as prerequisites for an M star planet to enter a long period of stability with its habitability intact. However, the star will then be subjected to short-term fluctuations with consequences including frequent unpredictable variation in atmospheric chemistry and surficial radiation field. After a review of evidence concerning disks and planets associated with M stars, we evaluate M stars as targets for future HZ planet search programs. Strong advantages of M stars for most approaches to HZ detection are offset by their faintness, leading to severe constraints due to accessible sample size, stellar crowding (transits), or angular size of the HZ (direct imaging). Gravitational lensing is unlikely to detect HZ M star planets because the HZ size decreases with mass faster than the Einstein ring size to which the method is sensitive. M star Earth-twin planets are predicted to exhibit surprisingly strong bands of nitrous oxide, methyl chloride, and methane, and work on signatures for other climate categories is summarized. The rest of the paper is devoted to an examination of evidence and implications of the unusual radiation and particle environments for atmospheric chemistry and surface radiation doses, and is summarized in the Synopsis. We conclude that attempts at remote sensing of biosignatures and nonbiological markers from M star planets are important, not as tests of any quantitative theories or rational arguments, but instead because they offer an inspection of the residues from a Gyr-long biochemistry experiment in the presence of extreme environmental fluctuations. A detection or repeated nondetections could provide a unique opportunity to partially answer a fundamental and recurrent question about the relation between stability and complexity, one that is not addressed by remote detection from a planet orbiting a solar-like star, and can only be studied on Earth using restricted microbial systems in serial evolution experiments or in artificial life simulations. This proposal requires a planet that has retained its atmosphere and a water supply. The discussion given here suggests that observations of M star exoplanets can decide this latter question with only slight modifications to plans already in place for direct imaging terrestrial exoplanet missions.

KEPLER Mission: development and overview

NASA Astrophysics Data System (ADS)

Borucki, William J.

2016-03-01

The Kepler Mission is a space observatory launched in 2009 by NASA to monitor 170 000 stars over a period of four years to determine the frequency of Earth-size and larger planets in and near the habitable zone of Sun-like stars, the size and orbital distributions of these planets, and the types of stars they orbit. Kepler is the tenth in the series of NASA Discovery Program missions that are competitively-selected, PI-directed, medium-cost missions. The Mission concept and various instrument prototypes were developed at the Ames Research Center over a period of 18 years starting in 1983. The development of techniques to do the 10 ppm photometry required for Mission success took years of experimentation, several workshops, and the exploration of many ‘blind alleys’ before the construction of the flight instrument. Beginning in 1992 at the start of the NASA Discovery Program, the Kepler Mission concept was proposed five times before its acceptance for mission development in 2001. During that period, the concept evolved from a photometer in an L2 orbit that monitored 6000 stars in a 50 sq deg field-of-view (FOV) to one that was in a heliocentric orbit that simultaneously monitored 170 000 stars with a 105 sq deg FOV. Analysis of the data to date has detected over 4600 planetary candidates which include several hundred Earth-size planetary candidates, over a thousand confirmed planets, and Earth-size planets in the habitable zone (HZ). These discoveries provide the information required for estimates of the frequency of planets in our galaxy. The Mission results show that most stars have planets, many of these planets are similar in size to the Earth, and that systems with several planets are common. Although planets in the HZ are common, many are substantially larger than Earth.

KEPLER Mission: development and overview.

PubMed

Borucki, William J

2016-03-01

The Kepler Mission is a space observatory launched in 2009 by NASA to monitor 170,000 stars over a period of four years to determine the frequency of Earth-size and larger planets in and near the habitable zone of Sun-like stars, the size and orbital distributions of these planets, and the types of stars they orbit. Kepler is the tenth in the series of NASA Discovery Program missions that are competitively-selected, PI-directed, medium-cost missions. The Mission concept and various instrument prototypes were developed at the Ames Research Center over a period of 18 years starting in 1983. The development of techniques to do the 10 ppm photometry required for Mission success took years of experimentation, several workshops, and the exploration of many 'blind alleys' before the construction of the flight instrument. Beginning in 1992 at the start of the NASA Discovery Program, the Kepler Mission concept was proposed five times before its acceptance for mission development in 2001. During that period, the concept evolved from a photometer in an L2 orbit that monitored 6000 stars in a 50 sq deg field-of-view (FOV) to one that was in a heliocentric orbit that simultaneously monitored 170,000 stars with a 105 sq deg FOV. Analysis of the data to date has detected over 4600 planetary candidates which include several hundred Earth-size planetary candidates, over a thousand confirmed planets, and Earth-size planets in the habitable zone (HZ). These discoveries provide the information required for estimates of the frequency of planets in our galaxy. The Mission results show that most stars have planets, many of these planets are similar in size to the Earth, and that systems with several planets are common. Although planets in the HZ are common, many are substantially larger than Earth.

Low-speed impact phenomena and orbital resonances in the moon- and planet-building process

NASA Technical Reports Server (NTRS)

Chapman, C. R.

1977-01-01

A simulation of collisional and gravitational interaction in the early solar system generates planets approximately 1000 km in diameter from an initial swarm of kilometer sized planetesimals. The model treats collisions according to experimental and theoretical impact results (such as rebound, cratering, and catastrophic fragmentation) for a variety of materials whose parameters span plausible values for early solid objects. The small planets form in approximately 1000 yr, during which time most of the mass of the system continues to reside in particles near the original size. The simulation is terminated when the largest objects' random motion is of smaller dimension than their collision cross-sections. The few 1000 km planets may act as seeds for the subsequent, gradual, accretional growth into full-sized planets.

KEPLER PLANETS: A TALE OF EVAPORATION

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

Owen, James E.; Wu, Yanqin, E-mail: jowen@cita.utoronto.ca, E-mail: wu@astro.utoronto.ca

2013-10-01

Inspired by the Kepler mission's planet discoveries, we consider the thermal contraction of planets close to their parent star, under the influence of evaporation. The mass-loss rates are based on hydrodynamic models of evaporation that include both X-ray and EUV irradiation. We find that only low mass planets with hydrogen envelopes are significantly affected by evaporation, with evaporation being able to remove massive hydrogen envelopes inward of ∼0.1 AU for Neptune-mass objects, while evaporation is negligible for Jupiter-mass objects. Moreover, most of the evaporation occurs in the first 100 Myr of stars' lives when they are more chromospherically active. Wemore » construct a theoretical population of planets with varying core masses, envelope masses, orbital separations, and stellar spectral types, and compare this population with the sizes and densities measured for low-mass planets, both in the Kepler mission and from radial velocity surveys. This exercise leads us to conclude that evaporation is the driving force of evolution for close-in Kepler planets. In fact, some 50% of the Kepler planet candidates may have been significantly eroded. Evaporation explains two striking correlations observed in these objects: a lack of large radius/low density planets close to the stars and a possible bimodal distribution in planet sizes with a deficit of planets around 2 R{sub ⊕}. Planets that have experienced high X-ray exposures are generally smaller than this size, and those with lower X-ray exposures are typically larger. A bimodal planet size distribution is naturally predicted by the evaporation model, where, depending on their X-ray exposure, close-in planets can either hold on to hydrogen envelopes ∼0.5%-1% in mass or be stripped entirely. To quantitatively reproduce the observed features, we argue that not only do low-mass Kepler planets need to be made of rocky cores surrounded with hydrogen envelopes, but few of them should have initial masses above 20 M{sub ⊕} and the majority of them should have core masses of a few Earth masses.« less

Formation of Jupiter and Saturn

NASA Technical Reports Server (NTRS)

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

1998-01-01

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

Formation of Jupiter and Saturn

NASA Technical Reports Server (NTRS)

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

1998-01-01

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

The Kepler Mission: A Search for Terrestrial Planets - Development Status

NASA Technical Reports Server (NTRS)

Koch, David; Borucki, W.; Mayer, D.; Caldwell, D.; Jenkens, J.; Dunham, E.; Geary, J.; Bachtell, E.; Deininger, W.; Philbrick, R.

2003-01-01

We have embarked on a mission to detect terrestrial planets. The space mission has been optimized to search for earth-size planets (0.5 to 10 earth masses) in the habitable zone (HZ) of solar-like stars. Given this design, the mission will necessarily be capable of not only detecting Earth analogs, but a wide range of planetary types and characteristics ranging from Mercury-size objects with orbital periods of days to gas-giants in decade long orbits that have undeniable signatures even with only one transit detected. The mission is designed to survey the full range of spectral-type dwarf stars. The approach is to detect the periodic signal of transiting planets. Three or more transits of a star exceeding a combined threshold of eight sigma with a statistically consistent period, brightness change and duration provide a rigorous method of detection. From the relative brightness change the planet size can be calculated. From the period the orbital size can be calculated and its location relative to the HZ determined. Presented here are: the mission goals, the top level system design requirements derived from these goals that drive the flight system design, a number of the trades that have lead to the mission concept, expected photometric performance dependence on stellar brightness and spectral type based on the system 'noise tree' analysis. Updated estimates are presented of the numbers of detectable planets versus size, orbit, stellar spectral type and distances based on a planet frequency hypothesis. The current project schedule and organization are given.

Earth-class Planets Line Up

NASA Image and Video Library

2011-12-20

This chart compares the first Earth-size planets found around a sun-like star to planets in our own solar system, Earth and Venus. NASA Kepler mission discovered the newfound planets, called Kepler-20e and Kepler-20f.

Illustration of TRAPPIST-1 Planets as of Feb. 2018

NASA Image and Video Library

2018-02-05

This illustration shows the seven Earth-size planets of TRAPPIST-1, an exoplanet system about 40 light-years away, based on data current as of February 2018. The image shows the planets' relative sizes but does not represent their orbits to scale. The art highlights possibilities for how the surfaces of these intriguing worlds might look based on their newly calculated properties. The seven planets of TRAPPIST-1 are all Earth-sized and terrestrial. TRAPPIST-1 is an ultra-cool dwarf star in the constellation Aquarius, and its planets orbit very close to it. In the background, slightly distorted versions the familiar constellations of Orion and Taurus are shown as they would appear from the location of TRAPPIST-1 (courtesy of California Academy of Sciences/Dan Tell). https://photojournal.jpl.nasa.gov/catalog/PIA22097

Kepler Planets Tend to Have Siblings of the Same Size

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-11-01

After 8.5 years of observations with the Kepler space observatory, weve discovered a large number of close-in, tightly-spaced, multiple-planet systems orbiting distant stars. In the process, weve learned a lot about the properties about these systems and discovered some unexpected behavior. A new study explores one of the properties that has surprised us: planets of the same size tend to live together.Orbital architectures for 25 of the authors multiplanet systems. The dots are sized according to the planets relative radii and colored according to mass. Planets of similar sizes and masses tend to live together in the same system. [Millholland et al. 2017]Ordering of SystemsFrom Keplers observations of extrasolar multiplanet systems, we have seen that the sizes of planets in a given system arent completely random. Systems that contain a large planet, for example, are more likely to contain additional large planets rather than additional planets of random size. So though there is a large spread in the radii weve observed for transiting exoplanets, the spread within any given multiplanet system tends to be much smaller.This odd behavior has led us to ask whether this clustering occurs not just for radius, but also for mass. Since the multiplanet systems discovered by Kepler most often contain super-Earths and mini-Neptunes, which have an extremely large spread in densities, the fact that two such planets have similar radii does not guarantee that they have similar masses.If planets dont cluster in mass within a system, this would raise the question of why planets coordinate only their radii within a given system. If they do cluster in mass, it implies that planets within the same system tend to have similar densities, potentially allowing us to predict the sizes and masses of planets we might find in a given system.Insight into MassesLed by NSF graduate research fellow Sarah Millholland, a team of scientists at Yale University used recently determined masses for planets in 37 Kepler multiplanet systems to explore this question of whether exoplanets in a multiplanet system are more likely to have similar masses rather than random ones.Millholland and collaborators find that the masses do show the same clustering trend as radii in multiplanet systems i.e., sibling planets in the same system tend to have both masses and radii that are more similar than if the system were randomly assembled from the total population of planets weve observed. Furthermore, the masses and radii tend to be ordered within a system when the planets are ranked by their periods.The host stars metallicity is correlated with the median planetary radius for a system. [Adapted from Millholland et al. 2017]The authors note two important implications of these results:The scatter in the relation between mass and radius of observed exoplanets is primarily due to system-to-system variability, rather than the variability within each system.Knowing the properties of a star and its primordial protoplanetary disk might allow us to predict the outcome of the planet formation process for the system.Following up on the second point, the authors test whether certain properties of the host star correlate with properties of the planets. They find that the stellar mass and metallicity have a significant effect on the planet properties and the structure of the system.Continuing to explore multiplanet systems like these appears to be an excellent path forward for understanding the hidden order in the broad variety of exoplanets weve observed.CitationSarah Millholland et al 2017 ApJL 849 L33. doi:10.3847/2041-8213/aa9714

A Binary System in the Hyades Cluster Hosting a Neptune-Sized Planet

NASA Astrophysics Data System (ADS)

Feinstein, Adina; Ciardi, David; Crossfield, Ian; Schlieder, Joshua; Petigura, Erik; David, Trevor J.; Bristow, Makennah; Patel, Rahul; Arnold, Lauren; Benneke, Björn; Christiansen, Jessie; Dressing, Courtney; Fulton, Benjamin; Howard, Andrew; Isaacson, Howard; Sinukoff, Evan; Thackeray, Beverly

2018-01-01

We report the discovery of a Neptune-size planet (Rp = 3.0Rearth) in the Hyades Cluster. The host star is in a binary system, comprising a K5V star and M7/8V star with a projected separation of 40 AU. The planet orbits the primary star with an orbital period of 17.3 days and a transit duration of 3 hours. The host star is bright (V = 11.2, J = 9.1) and so may be a good target for precise radial velocity measurements. The planet is the first Neptune-sized planet to be found orbiting in a binary system within an open cluster. The Hyades is the nearest star cluster to the Sun, has an age of 625-750 Myr, and forms one of the fundamental rungs in the distance ladder; understanding the planet population in such a well-studied cluster can help us understand and set contraints on the formation and evolution of planetary systems.

Orbital evolution and accretion of protoplanets tidally interacting with a gas disk. II. Solid surface density evolution with type-I migration

NASA Astrophysics Data System (ADS)

Daisaka, Junko K.; Tanaka, Hidekazu; Ida, Shigeru

2006-12-01

This paper investigates the surface density evolution of a planetesimal disk due to the effect of type-I migration by carrying out N-body simulation and through analytical method, focusing on terrestrial planet formation. The coagulation and the growth of the planetesimals take place in the abundant gas disk except for a final stage. A protoplanet excites density waves in the gas disk, which causes the torque on the protoplanet. The torque imbalance makes the protoplanet suffer radial migration, which is known as type-I migration. Type-I migration time scale derived by the linear theory may be too short for the terrestrial planets to survive, which is one of the major problems in the planet formation scenario. Although the linear theory assumes a protoplanet being in a gas disk alone, Kominami et al. [Kominami, J., Tanaka, H., Ida, S., 2005. Icarus 167, 231-243] showed that the effect of the interaction with the planetesimal disk and the neighboring protoplanets on type-I migration is negligible. The migration becomes pronounced before the planet's mass reaches the isolation mass, and decreases the solid component in the disk. Runaway protoplanets form again in the planetesimal disk with decreased surface density. In this paper, we present the analytical formulas that describe the evolution of the solid surface density of the disk as a function of gas-to-dust ratio, gas depletion time scale and semimajor axis, which agree well with our results of N-body simulations. In general, significant depletion of solid material is likely to take place in inner regions of disks. This might be responsible for the fact that there is no planet inside Mercury's orbit in our Solar System. Our most important result is that the final surface density of solid components ( Σ) and mass of surviving planets depend on gas surface density ( Σ) and its depletion time scale ( τ) but not on initial Σ; they decrease with increase in Σ and τ. For a fixed gas-to-dust ratio and τ, larger initial Σ results in smaller final Σ and smaller surviving planets, because of larger Σ. To retain a specific amount of Σ, the efficient disk condition is not an initially large Σ but the initial Σ as small as the specified final one and a smaller gas-to-dust ratio. To retain Σ comparable to that of the minimum mass solar nebula (MMSN), a disk must have the same Σ and a gas-to-dust ratio that is smaller than that of MMSN by a factor of 1.3×(τ/1 Myr) at ˜1 AU. (Equivalently, type-I migration speed is slower than that predicted by the linear theory by the same factor.) The surviving planets are Mars-sized ones in this case; in order to form Earth-sized planets, their eccentricities must be pumped up to start orbit crossing and coagulation among them. At ˜5 AU, Σ of MMSN is retained under the same condition, but to form a core massive enough to start runaway gas accretion, a gas-to-dust ratio must be smaller than that of MMSN by a factor of 3×τ/1 Myr.

The Most Earth Size, Habitable Zone Planets around a Single Star on This Week @NASA – 02/24/2017

NASA Image and Video Library

2017-02-24

NASA held a news conference Feb. 22 at the agency’s headquarters to discuss the finding by the agency’s Spitzer Space Telescope of seven Earth-sized planets around a tiny, relatively nearby, ultra-cool dwarf star. Three of the planets in this system, known as TRAPPIST-1, are in the habitable zone – the region around the star in which liquid water is most likely to thrive on a rocky planet. This is the first time so many planets have been found in a single star's habitable zone outside our solar system, and is the best target yet for studying the atmospheres of potentially habitable, Earth-sized worlds. Also, Kennedy’s Pad 39A, Back in Business, Russian Cargo Ship Arrives at Space Station, RS-25 Engine Tests Resume at Stennis, Structural Testing Begins on SLS Hardware, and 55th Anniversary of Friendship 7 Flight!

AN ANCIENT EXTRASOLAR SYSTEM WITH FIVE SUB-EARTH-SIZE PLANETS

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

Campante, T. L.; Davies, G. R.; Chaplin, W. J.

The chemical composition of stars hosting small exoplanets (with radii less than four Earth radii) appears to be more diverse than that of gas-giant hosts, which tend to be metal-rich. This implies that small, including Earth-size, planets may have readily formed at earlier epochs in the universe's history when metals were more scarce. We report Kepler spacecraft observations of Kepler-444, a metal-poor Sun-like star from the old population of the Galactic thick disk and the host to a compact system of five transiting planets with sizes between those of Mercury and Venus. We validate this system as a true five-planetmore » system orbiting the target star and provide a detailed characterization of its planetary and orbital parameters based on an analysis of the transit photometry. Kepler-444 is the densest star with detected solar-like oscillations. We use asteroseismology to directly measure a precise age of 11.2 ± 1.0 Gyr for the host star, indicating that Kepler-444 formed when the universe was less than 20% of its current age and making it the oldest known system of terrestrial-size planets. We thus show that Earth-size planets have formed throughout most of the universe's 13.8 billion year history, leaving open the possibility for the existence of ancient life in the Galaxy. The age of Kepler-444 not only suggests that thick-disk stars were among the hosts to the first Galactic planets, but may also help to pinpoint the beginning of the era of planet formation.« less

Modeling Kepler Transit Light Curves as False Positives: Rejection of Blend Scenarios for Kepler-9, and Validation of Kepler-9 d, a Super-Earth-Size Planet in a Multiple System

DTIC Science & Technology

2011-01-20

of 2009, was de- signed to address the important question of the frequency of Earth -size planets around Sun -like stars, and to characterize ex...physically associated with the candidate (hierarchical triple systems) and in a long-period orbit around their common center of mass would often be spatially...positive scenar- ios that is complementary to other diagnostics, and should play an important role in the discovery of Earth -size planets around other

Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1

PubMed Central

Gillon, Michaël; Triaud, Amaury H. M. J.; Demory, Brice-Olivier; Jehin, Emmanuël; Agol, Eric; Deck, Katherine M.; Lederer, Susan M.; de Wit, Julien; Burdanov, Artem; Ingalls, James G.; Bolmont, Emeline; Leconte, Jeremy; Raymond, Sean N.; Selsis, Franck; Turbet, Martin; Barkaoui, Khalid; Burgasser, Adam; Burleigh, Matthew R.; Carey, Sean J.; Chaushev, Aleksander; Copperwheat, Chris M.; Delrez, Laetitia; Fernandes, Catarina S.; Holdsworth, Daniel L.; Kotze, Enrico J.; Van Grootel, Valérie; Almleaky, Yaseen; Benkhaldoun, Zouhair; Magain, Pierre; Queloz, Didier

2017-01-01

One focus of modern astronomy is to detect temperate terrestrial exoplanets well-suited for atmospheric characterisation. A milestone was recently achieved with the detection of three Earth-sized planets transiting (i.e. passing in front of) a star just 8% the mass of the Sun 12 parsecs away1. Indeed, the transiting configuration of these planets combined with the Jupiter-like size of their host star - named TRAPPIST-1 - makes possible in-depth studies of their atmospheric properties with current and future astronomical facilities1,2,3. Here we report the results of an intensive photometric monitoring campaign of that star from the ground and with the Spitzer Space Telescope. Our observations reveal that at least seven planets with sizes and masses similar to the Earth revolve around TRAPPIST-1. The six inner planets form a near-resonant chain such that their orbital periods (1.51, 2.42, 4.04, 6.06, 9.21, 12.35 days) are near ratios of small integers. This architecture suggests that the planets formed farther from the star and migrated inward4,5. The seven planets have equilibrium temperatures low enough to make possible liquid water on their surfaces6,7,8. PMID:28230125

Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1.

PubMed

Gillon, Michaël; Triaud, Amaury H M J; Demory, Brice-Olivier; Jehin, Emmanuël; Agol, Eric; Deck, Katherine M; Lederer, Susan M; de Wit, Julien; Burdanov, Artem; Ingalls, James G; Bolmont, Emeline; Leconte, Jeremy; Raymond, Sean N; Selsis, Franck; Turbet, Martin; Barkaoui, Khalid; Burgasser, Adam; Burleigh, Matthew R; Carey, Sean J; Chaushev, Aleksander; Copperwheat, Chris M; Delrez, Laetitia; Fernandes, Catarina S; Holdsworth, Daniel L; Kotze, Enrico J; Van Grootel, Valérie; Almleaky, Yaseen; Benkhaldoun, Zouhair; Magain, Pierre; Queloz, Didier

2017-02-22

One aim of modern astronomy is to detect temperate, Earth-like exoplanets that are well suited for atmospheric characterization. Recently, three Earth-sized planets were detected that transit (that is, pass in front of) a star with a mass just eight per cent that of the Sun, located 12 parsecs away. The transiting configuration of these planets, combined with the Jupiter-like size of their host star-named TRAPPIST-1-makes possible in-depth studies of their atmospheric properties with present-day and future astronomical facilities. Here we report the results of a photometric monitoring campaign of that star from the ground and space. Our observations reveal that at least seven planets with sizes and masses similar to those of Earth revolve around TRAPPIST-1. The six inner planets form a near-resonant chain, such that their orbital periods (1.51, 2.42, 4.04, 6.06, 9.1 and 12.35 days) are near-ratios of small integers. This architecture suggests that the planets formed farther from the star and migrated inwards. Moreover, the seven planets have equilibrium temperatures low enough to make possible the presence of liquid water on their surfaces.

Occurrence and core-envelope structure of 1-4× Earth-size planets around Sun-like stars.

PubMed

Marcy, Geoffrey W; Weiss, Lauren M; Petigura, Erik A; Isaacson, Howard; Howard, Andrew W; Buchhave, Lars A

2014-09-02

Small planets, 1-4× the size of Earth, are extremely common around Sun-like stars, and surprisingly so, as they are missing in our solar system. Recent detections have yielded enough information about this class of exoplanets to begin characterizing their occurrence rates, orbits, masses, densities, and internal structures. The Kepler mission finds the smallest planets to be most common, as 26% of Sun-like stars have small, 1-2 R⊕ planets with orbital periods under 100 d, and 11% have 1-2 R⊕ planets that receive 1-4× the incident stellar flux that warms our Earth. These Earth-size planets are sprinkled uniformly with orbital distance (logarithmically) out to 0.4 the Earth-Sun distance, and probably beyond. Mass measurements for 33 transiting planets of 1-4 R⊕ show that the smallest of them, R < 1.5 R⊕, have the density expected for rocky planets. Their densities increase with increasing radius, likely caused by gravitational compression. Including solar system planets yields a relation: ρ = 2:32 + 3:19 R=R ⊕ [g cm(-3)]. Larger planets, in the radius range 1.5-4.0 R⊕, have densities that decline with increasing radius, revealing increasing amounts of low-density material (H and He or ices) in an envelope surrounding a rocky core, befitting the appellation ''mini-Neptunes.'' The gas giant planets occur preferentially around stars that are rich in heavy elements, while rocky planets occur around stars having a range of heavy element abundances. Defining habitable zones remains difficult, without benefit of either detections of life elsewhere or an understanding of life's biochemical origins.

Occurrence and core-envelope structure of 1–4× Earth-size planets around Sun-like stars

PubMed Central

Marcy, Geoffrey W.; Weiss, Lauren M.; Petigura, Erik A.; Isaacson, Howard; Howard, Andrew W.; Buchhave, Lars A.

2014-01-01

Small planets, 1–4× the size of Earth, are extremely common around Sun-like stars, and surprisingly so, as they are missing in our solar system. Recent detections have yielded enough information about this class of exoplanets to begin characterizing their occurrence rates, orbits, masses, densities, and internal structures. The Kepler mission finds the smallest planets to be most common, as 26% of Sun-like stars have small, 1–2 R⊕ planets with orbital periods under 100 d, and 11% have 1–2 R⊕ planets that receive 1–4× the incident stellar flux that warms our Earth. These Earth-size planets are sprinkled uniformly with orbital distance (logarithmically) out to 0.4 the Earth–Sun distance, and probably beyond. Mass measurements for 33 transiting planets of 1–4 R⊕ show that the smallest of them, R < 1.5 R⊕, have the density expected for rocky planets. Their densities increase with increasing radius, likely caused by gravitational compression. Including solar system planets yields a relation: ρ=2.32+3.19R/R⊕ [g cm−3]. Larger planets, in the radius range 1.5–4.0 R⊕, have densities that decline with increasing radius, revealing increasing amounts of low-density material (H and He or ices) in an envelope surrounding a rocky core, befitting the appellation ‘‘mini-Neptunes.’’ The gas giant planets occur preferentially around stars that are rich in heavy elements, while rocky planets occur around stars having a range of heavy element abundances. Defining habitable zones remains difficult, without benefit of either detections of life elsewhere or an understanding of life’s biochemical origins. PMID:24912169

Kepler-62: a five-planet system with planets of 1.4 and 1.6 Earth radii in the habitable zone.

PubMed

Borucki, William J; Agol, Eric; Fressin, Francois; Kaltenegger, Lisa; Rowe, Jason; Isaacson, Howard; Fischer, Debra; Batalha, Natalie; Lissauer, Jack J; Marcy, Geoffrey W; Fabrycky, Daniel; Désert, Jean-Michel; Bryson, Stephen T; Barclay, Thomas; Bastien, Fabienne; Boss, Alan; Brugamyer, Erik; Buchhave, Lars A; Burke, Chris; Caldwell, Douglas A; Carter, Josh; Charbonneau, David; Crepp, Justin R; Christensen-Dalsgaard, Jørgen; Christiansen, Jessie L; Ciardi, David; Cochran, William D; DeVore, Edna; Doyle, Laurance; Dupree, Andrea K; Endl, Michael; Everett, Mark E; Ford, Eric B; Fortney, Jonathan; Gautier, Thomas N; Geary, John C; Gould, Alan; Haas, Michael; Henze, Christopher; Howard, Andrew W; Howell, Steve B; Huber, Daniel; Jenkins, Jon M; Kjeldsen, Hans; Kolbl, Rea; Kolodziejczak, Jeffery; Latham, David W; Lee, Brian L; Lopez, Eric; Mullally, Fergal; Orosz, Jerome A; Prsa, Andrej; Quintana, Elisa V; Sanchis-Ojeda, Roberto; Sasselov, Dimitar; Seader, Shawn; Shporer, Avi; Steffen, Jason H; Still, Martin; Tenenbaum, Peter; Thompson, Susan E; Torres, Guillermo; Twicken, Joseph D; Welsh, William F; Winn, Joshua N

2013-05-03

We present the detection of five planets--Kepler-62b, c, d, e, and f--of size 1.31, 0.54, 1.95, 1.61 and 1.41 Earth radii (R⊕), orbiting a K2V star at periods of 5.7, 12.4, 18.2, 122.4, and 267.3 days, respectively. The outermost planets, Kepler-62e and -62f, are super-Earth-size (1.25 R⊕ < planet radius ≤ 2.0 R⊕) planets in the habitable zone of their host star, respectively receiving 1.2 ± 0.2 times and 0.41 ± 0.05 times the solar flux at Earth's orbit. Theoretical models of Kepler-62e and -62f for a stellar age of ~7 billion years suggest that both planets could be solid, either with a rocky composition or composed of mostly solid water in their bulk.

Effects of Planetary Gear Ratio on Mean Service Life

NASA Technical Reports Server (NTRS)

Savage, M.; Rubadeux, K. L.; Coe, H. H.

1996-01-01

Planetary gear transmissions are compact, high-power speed reductions which use parallel load paths. The range of possible reduction ratios is bounded from below and above by limits on the relative size of the planet gears. For a single plane transmission, the planet gear has no size at a ratio of two. As the ratio increases, so does the size of the planets relative to the sizes of the sun and ring. Which ratio is best for a planetary reduction can be resolved by studying a series of optimal designs. In this series, each design is obtained by maximizing the service life for a planetary with a fixed size, gear ratio, input speed power and materials. The planetary gear reduction service life is modeled as a function of the two-parameter Weibull distributed service lives of the bearings and gears in the reduction. Planet bearing life strongly influences the optimal reduction lives which point to an optimal planetary reduction ratio in the neighborhood of four to five.

Discovery of Temperate Earth-Sized Planets Transiting a Nearby Ultracool Dwarf Star

NASA Technical Reports Server (NTRS)

Jehin, Emmanuel; Gillon, Michael; Lederer, Susan M.; Delrez, Laetitia; De Wit, Julien; Burdanov, Artem; Van Grootel, Valerie; Burgasser, Adam; Triaud, Amaury; Demory, Brice-Olivier;

Kepler Small Habitable Zone Planets

NASA Image and Video Library

2015-07-23

Of the 1,030 confirmed planets from Kepler, a dozen are less than twice the size of Earth and reside in the habitable zone of their host stars. In this diagram, the sizes of the exoplanets are represented by the size of each sphere. These are arranged by size from left to right, and by the type of star they orbit, from the M stars that are significantly cooler and smaller than the sun, to the K stars that are somewhat cooler and smaller than the sun, to the G stars that include the sun. The sizes of the planets are enlarged by 25 times compared to the stars. The Earth is shown for reference. http://photojournal.jpl.nasa.gov/catalog/PIA19827

Growing the terrestrial planets from the gradual accumulation of submeter-sized objects

PubMed Central

Levison, Harold F.; Kretke, Katherine A.; Walsh, Kevin J.; Bottke, William F.

2015-01-01

Building the terrestrial planets has been a challenge for planet formation models. In particular, classical theories have been unable to reproduce the small mass of Mars and instead predict that a planet near 1.5 astronomical units (AU) should roughly be the same mass as Earth. Recently, a new model called Viscously Stirred Pebble Accretion (VSPA) has been developed that can explain the formation of the gas giants. This model envisions that the cores of the giant planets formed from 100- to 1,000-km bodies that directly accreted a population of pebbles—submeter-sized objects that slowly grew in the protoplanetary disk. Here we apply this model to the terrestrial planet region and find that it can reproduce the basic structure of the inner solar system, including a small Mars and a low-mass asteroid belt. Our models show that for an initial population of planetesimals with sizes similar to those of the main belt asteroids, VSPA becomes inefficient beyond ∼ 1.5 AU. As a result, Mars’s growth is stunted, and nothing large in the asteroid belt can accumulate. PMID:26512109

Growing the terrestrial planets from the gradual accumulation of submeter-sized objects.

PubMed

Levison, Harold F; Kretke, Katherine A; Walsh, Kevin J; Bottke, William F

2015-11-17

Building the terrestrial planets has been a challenge for planet formation models. In particular, classical theories have been unable to reproduce the small mass of Mars and instead predict that a planet near 1.5 astronomical units (AU) should roughly be the same mass as Earth. Recently, a new model called Viscously Stirred Pebble Accretion (VSPA) has been developed that can explain the formation of the gas giants. This model envisions that the cores of the giant planets formed from 100- to 1,000-km bodies that directly accreted a population of pebbles-submeter-sized objects that slowly grew in the protoplanetary disk. Here we apply this model to the terrestrial planet region and find that it can reproduce the basic structure of the inner solar system, including a small Mars and a low-mass asteroid belt. Our models show that for an initial population of planetesimals with sizes similar to those of the main belt asteroids, VSPA becomes inefficient beyond ∼ 1.5 AU. As a result, Mars's growth is stunted, and nothing large in the asteroid belt can accumulate.

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.

The Atmospheric Diversity of Mini-Neptunes in Multi-planet Systems

NASA Astrophysics Data System (ADS)

Crossfield, Ian

2017-08-01

Mini-Neptunes, planets 2-4 times the size of the Earth, are anintriguing population. They are an abundant outcome of planetformation and occur around more than a quarter of all stars -- yetthey are absent in the Solar System. Mini-Neptunes bridge the gapbetween terrestrial planets and gas giants, and atmospherecharacterization of these planets has much to reveal about their currentproperties, origins, and evolutionary histories. However, only a handful of mini-Neptunes have been amenable to atmospheric study so far.We propose a survey of four mini-Neptunes recently discovered by ourteam around bright, nearby stars. These observations will nearlydouble the number of planets in this size range with measuredtransmission spectra. Our observations will yield high-precisionconstraints on the planets' atmospheric metallicities, elementalabundances, C/O ratios, and aerosol content. With a greatly expandedmini-Neptune sample, we will identify trends in planet properties as afunction of equilibrium temperature, UV irradiation, planet mass, andstellar spectral type. These trends will also identify specificpromising targets for further study with JWST, and will help usprioritize follow-up and atmospheric characterization of themany small planets expected from the TESS survey.

The effect of giant impactors on the magnetic field energy of an early Martian dynamo.

NASA Astrophysics Data System (ADS)

Drummond, McGregor; Thieulot, Cedric; Monteux, Julien

2016-04-01

Through the cratering record embedded on its surface, Mars is one of the key planets required for investigating the formation and impact frequency in the early history of our Solar System. This record also holds clues to the events that may have caused the observed hemispheric dichotomy and cessation of the magnetic field that was present within the first 500 Myr of the planets' formation. We investigate the influence of giant impacts on the early Martian dynamo using the numerical dynamo modelling code PARODY-JA [1]. We hypothesize that the input heat from a giant impact will decrease the total heat flux at the CMB through mantle heating which leads to a decrease in the Rayleigh number of the core. As boundary conditions for the heat flux anomaly size, we use numerical results of a 750 km diameter impactor from the Monteux and Arkani-Hamed, 2014 [2] study which investigated impact heating and core merging of giant impacts in early Mars. We also determine the decrease in Rayleigh number from the change in total heat flux at the CMB using these results, where the decrease after impact is due to shock heating at the CMB. We calculate the time-averaged total magnetic field energy for an initial homogeneous heat flux model using a range of Rayleigh numbers (5 x 103 - 1 x 10^5). The Rayleigh number is then decreased for three new models - homogeneous, north pole impact and equatorial impact - and the time-averaged energy again determined. We find that the energy decreases more in our impact models, compared with the homogeneous, along with a variation in energy between the north pole and equatorial impact models. We conclude that giant impacts in Mars' early history would have decreased the total magnetic energy of the field and the decrease in energy is also dependent on the location of the impact. The magnetic field could have been disrupted beyond recovery from a planetesimal-sized collision; such as the suggested Borealis basin forming impact, or through the cumulative effect of multiple large impactors; such as Utopia, Hellas and Isidis basin forming impacts. [1] Aubert, J., Aurnou, J. & Wicht, J., 2008. The magnetic structure of convection-driven numerical dynamos. Geophys. J. Int., 172, 945--956. [2] Monteux, J., Arkani-Hamed, J., 2014. Consequences of giant impacts in early Mars: core merging and Martian dynamo evolution. J. Geophys. Res. (Planets) 119, 480--505.

Early Hydrodynamic Escape Limits Rocky Planets to Less Than or Equal to 1.6 Earth Radii

NASA Technical Reports Server (NTRS)

Lehmer, O. R.; Catling, D. C.

2017-01-01

In the past decade thousands of exoplanet candidates and hundreds of confirmed exoplanets have been found. For sub-Neptune-sized planets, those less than approx. 10 Earth masses, we can separate planets into two broad categories: predominantly rocky planets, and gaseous planets with thick volatile sheaths. Observations and subsequent analysis of these planets show that rocky planets are only found with radii less than approx. 1.6 Earth radii. No rocky planet has yet been found that violates this limit. We propose that hydrodynamic escape of hydrogen rich protoatmospheres, accreted by forming planets, explains the limit in rocky planet size. Following the hydrodynamic escape model employed by Luger et al. (2015), we modelled the XUV driven escape from young planets (less than approx.100 Myr in age) around a Sun-like star. With a simple, first-order model we found that the rocky planet radii limit occurs consistently at approx. 1.6 Earth radii across a wide range of plausible parameter spaces. Our model shows that hydrodynamic escape can explain the observed cutoff between rocky and gaseous planets. Fig. 1 shows the results of our model for rocky planets between 0.5 and 10 Earth masses that accrete 3 wt. % H2/He during formation. The simulation was run for 100 Myr, after that time the XUV flux drops off exponentially and hydrodynamic escape drops with it. A cutoff between rocky planets and gaseous ones is clearly seen at approx. 1.5-1.6 Earth radii. We are only interested in the upper size limit for rocky planets. As such, we assumed pure hydrogen atmospheres and the highest possible isothermal atmospheric temperatures, which will produce an upper limit on the hydrodynamic loss rate. Previous work shows that a reasonable approximation for an upper temperature limit in a hydrogen rich protoatmosphere is 2000-3000 K, consistent with our assumptions. From these results, we propose that the observed dichotomy between mini-Neptunes and rocky worlds is simply explained by an early episode of thermally-driven hydrodynamic escape when host stars have saturated XUV fluxes.

Modeling Kepler Transit Light Curves as False Positives: Rejection of Blend Scenarios for Kepler-9, and Validation of Kepler-9 d, a Super-Earth-Size Planet in a Multiple System

NASA Technical Reports Server (NTRS)

Torres, Guillermo; Fressin, Francois; Batalha, Natalie M.; Borucki, William J.; Brown, Timothy M.; Bryson, Stephen T.; Buchhave, Lars A.; Charbonneau, David; Ciardi, David R.; Dunham, Edward W.;

Giant Planets around FGK Stars Probably Form through Core Accretion

NASA Astrophysics Data System (ADS)

Wang, Wei; Wang, Liang; Li, Xiang; Chen, Yuqin; Zhao, Gang

2018-06-01

We present a statistical study of the planet–metallicity (P–M) correlation by comparing the 744 stars with candidate planets (SWPs) in the Kepler field that have been observed with LAMOST, and a sample of distance-independent, fake “twin” stars in the Kepler field with no planet reported (CKSNPs) yet. With well-defined and carefully selected large samples, we find for the first time a turnoff P–M correlation of Δ[Fe/H]SWPs–SNPs, which on average increases from ∼0.00 ± 0.03 dex to 0.06 ± 0.03 dex, and to 0.12 ± 0.03 for stars with Earth-, Neptune-, and Jupiter-sized planets successively, and then declines to ∼‑0.01 ± 0.03 dex for more massive planets or brown dwarfs. Moreover, the percentage of those systems with positive Δ[Fe/H] has the same turnoff pattern. We also find that FG-type stars follow this general trend, but K-type stars are different. Moderate metal enhancement (∼0.1–0.2 dex) for K-type stars with planets of radii between 2 and 4 R ⊕, compared to CKSNPs is observed, which indicates much higher metallicities are required for Super-Earths and Neptune-sized planets to form around K-type stars. We point out that the P–M correlation is actually metallicity-dependent, i.e., the correlation is positive at solar and supersolar metallicities, and negative at subsolar metallicities. No steady increase of Δ[Fe/H] against planet sizes is observed for rocky planets, excluding the pollution scenario as a major mechanism for the P–M correlation. All these clues suggest that giant planets probably form differently from rocky planets or more massive planets/brown dwarfs, and the core accretion scenario is highly favored, and high metallicity is a prerequisite for massive planets to form.

Chasing Exoplanets

NASA Technical Reports Server (NTRS)

Jenkins, Jon M.

2017-01-01

NASA's Kepler Mission was launched in March 2009 as NASA's first mission capable of finding Earth-size planets orbiting in the habitable zone of Sun-like stars, that range of distances for which liquid water would pool on the surface of a rocky planet. Kepler has discovered over 1000 planets and over 4600 candidates, many of them as small as the Earth. Today, Kepler's amazing success seems to be a fait accompli to those unfamiliar with her history. But twenty years ago, there were no planets known outside our solar system, and few people believed it was possible to detect tiny Earth-size planets orbiting other stars. Motivating NASA to select Kepler for launch required a confluence of the right detector technology, advances in signal processing and algorithms, and the power of supercomputing.

Spin evolution of Earth-sized exoplanets, including atmospheric tides and core-mantle friction

NASA Astrophysics Data System (ADS)

Cunha, Diana; Correia, Alexandre C. M.; Laskar, Jacques

2015-04-01

Planets with masses between 0.1 and 10 M ⊕ are believed to host dense atmospheres. These atmospheres can play an important role on the planet's spin evolution, since thermal atmospheric tides, driven by the host star, may counterbalance gravitational tides. In this work, we study the long-term spin evolution of Earth-sized exoplanets. We generalize previous works by including the effect of eccentric orbits and obliquity. We show that under the effect of tides and core-mantle friction, the obliquity of the planets evolves either to 0° or 180°. The rotation of these planets is also expected to evolve into a very restricted number of equilibrium configurations. In general, none of these equilibria is synchronous with the orbital mean motion. The role of thermal atmospheric tides becomes more important for Earth-sized planets in the habitable zones of their systems; so they cannot be neglected when we search for their potential habitability.

Soaking up the Rays of a Sun-like Star Artist Concept

NASA Image and Video Library

2015-07-23

This artist's concept depicts one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of star that is similar to our sun. The habitable zone is a region around a star where temperatures are right for water -- an essential ingredient for life as we know it -- to pool on the surface. Scientists do not know if Kepler-452b can support life or not. What is known about the planet is that it is about 60 percent larger than Earth, placing it in a class of planets dubbed "super-Earths." While its mass and composition are not yet determined, previous research suggests that planets the size of Kepler-452b have a better than even chance of being rocky. Kepler-452b orbits its star every 385 days. The planet's star is about 1,400 light-years away in the constellation Cygnus. It is a G2-type star like our sun, with nearly the same temperature and mass. This star is 6 billion years old, 1.5 billion years older than our sun. As stars age, they grow in size and give out more energy, warming up their planets over time. Scientists and artists considered these facts when creating this illustration. If the planet Kepler-452b does in fact have liquid on its surface and has grown warmer due to the older age of its star, it could possibly be experiencing a runaway greenhouse effect, where oceans would begin to evaporate and contribute to increased cloud cover. This, plus other factors such as the planet's large size, was factored into the hypothetical scenario depicted in this illustration. http://photojournal.jpl.nasa.gov/catalog/PIA19824

Hubble Sees a “Behemoth” Bleeding Atmosphere Around a Warm Exoplanet

NASA Image and Video Library

2015-06-24

Astronomers using NASA’s Hubble Space Telescope have discovered an immense cloud of hydrogen dubbed “The Behemoth” bleeding from a planet orbiting a nearby star. The enormous, comet-like feature is about 50 times the size of the parent star. The hydrogen is evaporating from a warm, Neptune-sized planet, due to extreme radiation from the star. This phenomenon has never been seen around an exoplanet so small. It may offer clues to how other planets with hydrogen-enveloped atmospheres could have their outer layers evaporated by their parent star, leaving behind solid, rocky cores. Hot, rocky planets such as these that roughly the size of Earth are known as Hot-Super Earths. “This cloud is very spectacular, though the evaporation rate does not threaten the planet right now,” explains the study’s leader, David Ehrenreich of the Observatory of the University of Geneva in Switzerland. “But we know that in the past, the star, which is a faint red dwarf, was more active. This means that the planet evaporated faster during its first billion years of existence because of the strong radiation from the young star. Overall, we estimate that it may have lost up to 10 percent of its atmosphere over the past several billion years.” Caption: This artist's concept shows "The Behemoth," an enormous comet-like cloud of hydrogen bleeding off of a warm, Neptune-sized planet just 30 light-years from Earth. Also depicted is the parent star, which is a faint red dwarf named GJ 436. The hydrogen is evaporating from the planet due to extreme radiation from the star. A phenomenon this large has never before been seen around any exoplanet. Credits: NASA, ESA, and G. Bacon (STScI)

Model Atmospheres for Massive Gas Giants with Thick Clouds: Application to the HR 8799 Planets and Predictions for Future Detections

NASA Astrophysics Data System (ADS)

Madhusudhan, Nikku; Burrows, Adam; Currie, Thayne

2011-08-01

We have generated an extensive new suite of massive giant planet atmosphere models and used it to obtain fits to photometric data for the planets HR 8799b, c, and d. We consider a wide range of cloudy and cloud-free models. The cloudy models incorporate different geometrical and optical thicknesses, modal particle sizes, and metallicities. For each planet and set of cloud parameters, we explore grids in gravity and effective temperature, with which we determine constraints on the planet's mass and age. Our new models yield statistically significant fits to the data, and conclusively confirm that the HR 8799 planets have much thicker clouds than those required to explain data for typical L and T dwarfs. Both models with (1) physically thick forsterite clouds and a 60 μm modal particle size and (2) clouds made of 1 μm sized pure iron droplets and 1% supersaturation fit the data. Current data are insufficient to accurately constrain the microscopic cloud properties, such as composition and particle size. The range of best-estimated masses for HR 8799b, HR 8799c, and HR 8799d conservatively span 2-12 MJ , 6-13 MJ , and 3-11 MJ , respectively, and imply coeval ages between ~10 and ~150 Myr, consistent with previously reported stellar ages. The best-fit temperatures and gravities are slightly lower than values obtained by Currie et al. using even thicker cloud models. Finally, we use these models to predict the near-to-mid-IR colors of soon-to-be imaged planets. Our models predict that planet-mass objects follow a locus in some near-to-mid-IR color-magnitude diagrams that is clearly separable from the standard L/T dwarf locus for field brown dwarfs.

Zodiacal Exoplanets in Time (ZEIT). VI. A Three-planet System in the Hyades Cluster Including an Earth-sized Planet

NASA Astrophysics Data System (ADS)

Mann, Andrew W.; Vanderburg, Andrew; Rizzuto, Aaron C.; Kraus, Adam L.; Berlind, Perry; Bieryla, Allyson; Calkins, Michael L.; Esquerdo, Gilbert A.; Latham, David W.; Mace, Gregory N.; Morris, Nathan R.; Quinn, Samuel N.; Sokal, Kimberly R.; Stefanik, Robert P.

2018-01-01

Planets in young clusters are powerful probes of the evolution of planetary systems. Here we report the discovery of three planets transiting EPIC 247589423, a late-K dwarf in the Hyades (≃800 Myr) cluster, and robust detection limits for additional planets in the system. The planets were identified from their K2 light curves as part of our survey of young clusters and star-forming regions. The smallest planet has a radius comparable to Earth ({0.99}-0.04+0.06{R}\\oplus ), making it one of the few Earth-sized planets with a known, young age. The two larger planets are likely a mini-Neptune and a super-Earth, with radii of {2.91}-0.10+0.11{R}\\oplus and {1.45}-0.08+0.11{R}\\oplus , respectively. The predicted radial velocity signals from these planets are between 0.4 and 2 m s-1, achievable with modern precision RV spectrographs. Because the target star is bright (V = 11.2) and has relatively low-amplitude stellar variability for a young star (2-6 mmag), EPIC 247589423 hosts the best known planets in a young open cluster for precise radial velocity follow-up, enabling a robust test of earlier claims that young planets are less dense than their older counterparts.

The occurrence of planets and other substellar bodies around white dwarfs using K2

NASA Astrophysics Data System (ADS)

van Sluijs, L.; Van Eylen, V.

2018-03-01

The majority of stars both host planetary systems and evolve into a white dwarf (WD). To understand their post-main-sequence planetary system evolution, we present a search for transiting/eclipsing planets and other substellar bodies (SBs) around WDs using a sample of 1148 WDs observed by K2. Using transit injections, we estimate the completeness of our search. We place constraints on the occurrence of planets and SBs around WDs as a function of planet radius and orbital period. For short-period (P < 40 d) small objects, from asteroid-sized to 1.5 R⊕, these are the strongest constraints known to date. We further constrain the occurrence of hot Jupiters ( < 1.5 per cent), habitable zone Earth-sized planets ( < 28 per cent), and disintegrating short-period planets ( ˜ 12 per cent). We blindly recovered all previously known eclipsing objects, providing confidence in our analysis, and make all light curves publicly available.

Assessing the Effect of Stellar Companions to Kepler Objects of Interest

NASA Astrophysics Data System (ADS)

Hirsch, Lea; Ciardi, David R.; Howard, Andrew

2017-01-01

Unknown stellar companions to Kepler planet host stars dilute the transit signal, causing the planetary radii to be underestimated. We report on the analysis of 165 stellar companions detected with high-resolution imaging to be within 2" of 159 KOI host stars. The majority of the planets and planet candidates in these systems have nominal radii smaller than 6 REarth. Using multi-filter photometry on each companion, we assess the likelihood that the companion is bound and estimate its stellar properties, including stellar radius and flux. We then recalculate the planet radii in these systems, determining how much each planet's size is underestimated if it is assumed to 1) orbit the primary star, 2) orbit the companion star, or 3) be equally likely to orbit either star in the system. We demonstrate the overall effect of unknown stellar companions on our understanding of Kepler planet sizes.

Occurrence of Earth-like bodies in planetary systems.

PubMed

Wetherill, G W

1991-08-02

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

Occurrence of earth-like bodies in planetary systems

NASA Technical Reports Server (NTRS)

Wetherill, George W.

1991-01-01

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

Habitability of the TRAPPIST-1 System

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-04-01

The recent discovery of seven Earth-sized, terrestrial planets around an M dwarf star was met with excitement and optimism. But how habitable are these planets actually likely to be? A recent study of these planets likely climates may provide an answer to this question.An Optimistic OutlookIn February of this year, the TRAPPIST-1 system was announced: seven roughly Earth-sized, transiting, terrestrial planets all orbiting their host ultracool dwarf star within a distance the size of Mercurys orbit. Three of the planets were initially declared to be in the stars habitable zone and scientists speculated that even those outside the habitable zone could potentially still harbor liquid water making the system especially exciting.In Wolfs simulations, the surface temperature (solid lines) of TRAPPIST-1d grows to more than 380K in just 40 years. [Adapted from Wolf 2017]The planets were labeled as temperate because all seven have equilibrium temperatures that are under 400K. Since liquid water requires a surface temperature of 273-373K, this certainly seems promising!Finding Realistic TemperaturesBut theres a catch: equilibrium temperatures are not actual measurements of the planets surface temperature, theyre just very rudimentary estimates based on how much light the planet receives. To get a better estimate of the real temperature of the planet and therefore assess its habitability you need advanced climate modeling of the planet that include factors like the greenhouse effect and planetary albedo.In Wolfs simulations, the surface temperature of TRAPPIST-1f plummets rapidly even when modeled with dense carbon dioxide atmosphere (purple line). The bottom panel shows the corresponding rapid growth of sea-ice on the surface oceans for the different atmospheric models. [Wolf 2017]To that end, scientist Eric Wolf (University of Colorado Boulder) has conducted state-of-the-art 3D climate calculations for the three center-most planets planets d, e, and f in the TRAPPIST-1 system. Wolf assumed traditional terrestrial-planet atmospheres composed of nitrogen, carbon dioxide, and water, and he examined what would happen if these planets had large water supplies in the form of surface oceans.Runaway and Snowball PlanetsWolfs climate model indicates that the closest-in of the three planets, planet d, would undergo thermal runaway even in the best case scenario. In just 40 years of the simulation, the planets surface temperature exceeds 380K, suggesting it couldnt continue to sustain liquid water. Wolf argues that planet d and the two planets interior to it, b and c, all lie inside of the traditional liquid water habitable zone they are hot, dry, and uninhabitable.Next, Wolf models the outermost of the three center planets, planet f. Even when planet f is modeled with a dense carbon dioxide atmosphere, it cant avoid its fate of becoming completely ice-covered within roughly 60 years. Wolf concludes that planets f, g and h all lie outside of the traditional habitable zone defined by the maximum carbon dioxide greenhouse limit.Equilibrium solutions for TRAPPIST-1e with various atmospheric conditions. Top panel: mean surface temperature. Middle panel: sea-ice coverage. Bottom panel: habitable surface area. [Wolf 2017]Goldilocks?Lastly, Wolf turns to planet e, the central planet in the system. This planet, he finds, is the most viable candidate for a robustly habitable world. The simulations show that planet e can maintain habitable surface conditions for a variety of atmospheric compositions.While astrobiologists eyeing TRAPPIST-1 may be disappointed that at second glance the planets are not quite as inhabitable as they first seemed, it is promising to see that the habitability of the central planet holds up reasonably well to some more realistic testing. Either way, future examinations of all seven of these planets should help us learn more about terrestrial, Earth-sized planets.CitationEric T. Wolf 2017 ApJL 839 L1. doi:10.3847/2041-8213/aa693a

The problem of scale in planetary geomorphology

NASA Technical Reports Server (NTRS)

Rossbacher, L. A.

1985-01-01

Recent planetary exploration has shown that specific landforms exhibit a significant range in size between planets. Similar features on Earth and Mars offer some of the best examples of this scale difference. The difference in heights of volcanic features between the two planets has been cited often; the Martian volcano Olympus Mons stands approximately 26 km high, but Mauna Loa rises only 11 km above the Pacific Ocean floor. Polygonally fractured ground in the northern plains of Mars has diameters up to 20 km across; the largest terrestrial polygons are only 500 m in diameter. Mars also has landslides, aeolian features, and apparent rift valleys larger than any known on Earth. No single factor can explain the variations in landform size between planets. Controls on variation on Earth, related to climate, lithology, or elevation, have seldom been considered in detail. The size differences between features on Earth and other planets seem to be caused by a complex group of interacting relationships. The major planetary parameters that may affect landform size are discussed.

A septet of Earth-sized planets

NASA Astrophysics Data System (ADS)

Triaud, Amaury; SPECULOOS Team; TRAPPIST-1 Team

2017-10-01

Understanding the astronomical requirements for life to emerge, and to persist, on a planet is one of the most important and exciting scientific endeavours, yet without empirical answers. To resolve this, multiple planets whose sizes and surface temperatures are similar to the Earth, need to be discovered. Those planets also need to possess properties enabling detailed atmospheric characterisation with forthcoming facilities, from which chemical traces produced by biological activity can in principle be identified.I will describe a dedicated search for such planets called SPECULOOS. Our first detection is the TRAPPIST-1 system. Intensive ground-based and space-based observations have revealed that at least seven planets populate this system. We measured their radii and obtained first estimates of their masses thanks to transit-timing variations. I will describe our on-going observational efforts aiming to reduce our uncertainties on the planet properties. The incident flux on the planets ranges from Mercury to Ceres, comprising the Earth, and permitting climatic comparisons between each of those worlds such as is not possible within our Solar system. All seven planets have the potential to harbour liquid water on at least a fraction of their surfaces, given some atmospheric and geological conditions.

Transit Illustration of TRAPPIST-1

NASA Image and Video Library

2017-02-22

This illustration shows the seven TRAPPIST-1 planets as they might look as viewed from Earth using a fictional, incredibly powerful telescope. The sizes and relative positions are correctly to scale: This is such a tiny planetary system that its sun, TRAPPIST-1, is not much bigger than our planet Jupiter, and all the planets are very close to the size of Earth. Their orbits all fall well within what, in our solar system, would be the orbital distance of our innermost planet, Mercury. With such small orbits, the TRAPPIST-1 planets complete a "year" in a matter of a few Earth days: 1.5 for the innermost planet, TRAPPIST-1b, and 20 for the outermost, TRAPPIST-1h. This particular arrangement of planets with a double-transit reflect an actual configuration of the system during the 21 days of observations made by NASA's Spitzer Space Telescope in late 2016. 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. http://photojournal.jpl.nasa.gov/catalog/PIA21429

A Revised Estimate of the Occurrence Rate of Terrestrial Planets in the Habitable Zones around Kepler M-dwarfs

NASA Astrophysics Data System (ADS)

Kopparapu, Ravi Kumar

2013-04-01

Because of their large numbers, low-mass stars may be the most abundant planet hosts in our Galaxy. Furthermore, terrestrial planets in the habitable zones (HZs) around M-dwarfs can potentially be characterized in the near future and hence may be the first such planets to be studied. Recently, Dressing & Charbonneau used Kepler data and calculated the frequency of terrestrial planets in the HZ of cool stars to be 0.15^{+0.13}_{-0.06} per star for Earth-size planets (0.5-1.4 R ⊕). However, this estimate was derived using the Kasting et al. HZ limits, which were not valid for stars with effective temperatures lower than 3700 K. Here we update their result using new HZ limits from Kopparapu et al. for stars with effective temperatures between 2600 K and 7200 K, which includes the cool M stars in the Kepler target list. The new HZ boundaries increase the number of planet candidates in the HZ. Assuming Earth-size planets as 0.5-1.4 R ⊕, when we reanalyze their results, we obtain a terrestrial planet frequency of 0.48^{+0.12}_{-0.24} and 0.53^{+0.08}_{-0.17} planets per M-dwarf star for conservative and optimistic limits of the HZ boundaries, respectively. Assuming Earth-size planets as 0.5-2 R ⊕, the frequency increases to 0.51^{+0.10}_{-0.20} per star for the conservative estimate and to 0.61^{+0.07}_{-0.15} per star for the optimistic estimate. Within uncertainties, our optimistic estimates are in agreement with a similar optimistic estimate from the radial velocity survey of M-dwarfs (0.41^{+0.54}_{-0.13}). So, the potential for finding Earth-like planets around M stars may be higher than previously reported.

A REVISED ESTIMATE OF THE OCCURRENCE RATE OF TERRESTRIAL PLANETS IN THE HABITABLE ZONES AROUND KEPLER M-DWARFS

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

Kopparapu, Ravi Kumar

Because of their large numbers, low-mass stars may be the most abundant planet hosts in our Galaxy. Furthermore, terrestrial planets in the habitable zones (HZs) around M-dwarfs can potentially be characterized in the near future and hence may be the first such planets to be studied. Recently, Dressing and Charbonneau used Kepler data and calculated the frequency of terrestrial planets in the HZ of cool stars to be 0.15{sup +0.13}{sub -0.06} per star for Earth-size planets (0.5-1.4 R{sub Circled-Plus }). However, this estimate was derived using the Kasting et al. HZ limits, which were not valid for stars with effectivemore » temperatures lower than 3700 K. Here we update their result using new HZ limits from Kopparapu et al. for stars with effective temperatures between 2600 K and 7200 K, which includes the cool M stars in the Kepler target list. The new HZ boundaries increase the number of planet candidates in the HZ. Assuming Earth-size planets as 0.5-1.4 R{sub Circled-Plus }, when we reanalyze their results, we obtain a terrestrial planet frequency of 0.48{sup +0.12}{sub -0.24} and 0.53{sup +0.08}{sub -0.17} planets per M-dwarf star for conservative and optimistic limits of the HZ boundaries, respectively. Assuming Earth-size planets as 0.5-2 R{sub Circled-Plus }, the frequency increases to 0.51{sup +0.10}{sub -0.20} per star for the conservative estimate and to 0.61{sup +0.07}{sub -0.15} per star for the optimistic estimate. Within uncertainties, our optimistic estimates are in agreement with a similar optimistic estimate from the radial velocity survey of M-dwarfs (0.41{sup +0.54}{sub -0.13}). So, the potential for finding Earth-like planets around M stars may be higher than previously reported.« less

Kepler Mission: A Mission to Find Earth-size Planets in the Habitable Zone

NASA Technical Reports Server (NTRS)

Borucki, W. J.

2003-01-01

The Kepler Mission is a Discovery-class mission designed to continuously monitor the brightness of 100,000 solar-like stars to detect the transits of Earth-size and larger planets. It is a wide field of view photometer Schmidt-type telescope with an array of 42 CCDs. It has a 0.95 m aperture and 1.4 m primary and is designed to attain a photometric precision of 2 parts in 10(exp 5) for 12th magnitude solar-like stars for a 6 hr transit duration. It will continuously observe 100,000 main-sequence stars from 9th to 14th magnitude in the Cygnus constellation for a period of four years with a cadence of 4/hour. An additional 250 stars can be monitored at a cadence of l/minute to do astro-seismology of stars brighter than 11.5 mv. The photometer is scheduled to be launched into heliocentric orbit in 2007. When combined with ground-based spectrometric observations of these stars, the positions of the planets relative to the habitable zone can be found. The spectra of the stars are also used to determine the relationships between the characteristics of terrestrial planets and the characteristics of the stars they orbit. In particular, the association of planet size and occurrence frequency with stellar mass and metallicity will be investigated. Based on the results of the current Doppler-velocity discoveries, over a thousand giant planets will also be found. Information on the albedos and densities of those giants showing transits will be obtained. At the end of the four year mission, hundreds of Earth-size planets should be discovered in and near the HZ of their stars if such planets are common. A null result would imply that terrestrial planets in the HZ are very rare and that life might also be quite rare.

A Population of planetary systems characterized by short-period, Earth-sized planets.

PubMed

Steffen, Jason H; Coughlin, Jeffrey L

2016-10-25

We analyze data from the Quarter 1-17 Data Release 24 (Q1-Q17 DR24) planet candidate catalog from NASA's Kepler mission, specifically comparing systems with single transiting planets to systems with multiple transiting planets, and identify a population of exoplanets with a necessarily distinct system architecture. Such an architecture likely indicates a different branch in their evolutionary past relative to the typical Kepler system. The key feature of these planetary systems is an isolated, Earth-sized planet with a roughly 1-d orbital period. We estimate that at least 24 of the 144 systems we examined ([Formula: see text]17%) are members of this population. Accounting for detection efficiency, such planetary systems occur with a frequency similar to the hot Jupiters.

A Population of planetary systems characterized by short-period, Earth-sized planets

PubMed Central

Steffen, Jason H.; Coughlin, Jeffrey L.

2016-01-01

We analyze data from the Quarter 1–17 Data Release 24 (Q1–Q17 DR24) planet candidate catalog from NASA’s Kepler mission, specifically comparing systems with single transiting planets to systems with multiple transiting planets, and identify a population of exoplanets with a necessarily distinct system architecture. Such an architecture likely indicates a different branch in their evolutionary past relative to the typical Kepler system. The key feature of these planetary systems is an isolated, Earth-sized planet with a roughly 1-d orbital period. We estimate that at least 24 of the 144 systems we examined (≳17%) are members of this population. Accounting for detection efficiency, such planetary systems occur with a frequency similar to the hot Jupiters. PMID:27790984

Eccentricity evolution during planet-disc interaction

NASA Astrophysics Data System (ADS)

Ragusa, Enrico; Rosotti, Giovanni; Teyssandier, Jean; Booth, Richard; Clarke, Cathie J.; Lodato, Giuseppe

2018-03-01

During the process of planet formation, the planet-disc interactions might excite (or damp) the orbital eccentricity of the planet. In this paper, we present two long (t ˜ 3 × 105 orbits) numerical simulations: (a) one (with a relatively light disc, Md/Mp = 0.2), where the eccentricity initially stalls before growing at later times and (b) one (with a more massive disc, Md/Mp = 0.65) with fast growth and a late decrease of the eccentricity. We recover the well-known result that a more massive disc promotes a faster initial growth of the planet eccentricity. However, at late times the planet eccentricity decreases in the massive disc case, but increases in the light disc case. Both simulations show periodic eccentricity oscillations superimposed on a growing/decreasing trend and a rapid transition between fast and slow pericentre precession. The peculiar and contrasting evolution of the eccentricity of both planet and disc in the two simulations can be understood by invoking a simple toy model where the disc is treated as a second point-like gravitating body, subject to secular planet-planet interaction and eccentricity pumping/damping provided by the disc. We show how the counterintuitive result that the more massive simulation produces a lower planet eccentricity at late times can be understood in terms of the different ratios of the disc-to-planet angular momentum in the two simulations. In our interpretation, at late times the planet eccentricity can increase more in low-mass discs rather than in high-mass discs, contrary to previous claims in the literature.

Seeing Starlight Through a Planet Rim Artist Concept

NASA Image and Video Library

2014-09-24

A Neptune-size planet with a clear atmosphere is shown crossing in front of its star in this artist depiction. Such crossings, or transits, are observed by telescopes like NASA Hubble and Spitzer to glean information about planets atmospheres.

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

A matched filter method for ground-based sub-noise detection of terrestrial extrasolar planets in eclipsing binaries: application to CM Draconis.

PubMed

Jenkins, J M; Doyle, L R; Cullers, D K

1996-02-01

The photometric detection of extrasolar planets by transits in eclipsing binary systems can be significantly improved by cross-correlating the observational light curves with synthetic models of possible planetary transit features, essentially a matched filter approach. We demonstrate the utility and application of this transit detection algorithm for ground-based detections of terrestrial-sized (Earth-to-Neptune radii) extrasolar planets in the dwarf M-star eclipsing binary system CM Draconis. Preliminary photometric observational data of this system demonstrate that the observational noise is well characterized as white and Gaussian at the observational time steps required for precision photometric measurements. Depending on planet formation scenarios, terrestrial-sized planets may form quite close to this low-luminosity system. We demonstrate, for example, that planets as small as 1.4 Earth radii with periods on the order of a few months in the CM Draconis system could be detected at the 99.9% confidence level in less than a year using 1-m class telescopes from the ground. This result contradicts commonly held assumptions limiting present ground-based efforts to, at best, detections of gas giant planets after several years of observation. This method can be readily extended to a number of other larger star systems with the utilization of larger telescopes and longer observing times. Its extension to spacecraft observations should also allow the determination of the presence of terrestrial-sized planets in nearly 100 other known eclipsing binary systems.

A matched filter method for ground-based sub-noise detection of terrestrial extrasolar planets in eclipsing binaries: application to CM Draconis

NASA Technical Reports Server (NTRS)

Jenkins, J. M.; Doyle, L. R.; Cullers, D. K.

1996-01-01

The photometric detection of extrasolar planets by transits in eclipsing binary systems can be significantly improved by cross-correlating the observational light curves with synthetic models of possible planetary transit features, essentially a matched filter approach. We demonstrate the utility and application of this transit detection algorithm for ground-based detections of terrestrial-sized (Earth-to-Neptune radii) extrasolar planets in the dwarf M-star eclipsing binary system CM Draconis. Preliminary photometric observational data of this system demonstrate that the observational noise is well characterized as white and Gaussian at the observational time steps required for precision photometric measurements. Depending on planet formation scenarios, terrestrial-sized planets may form quite close to this low-luminosity system. We demonstrate, for example, that planets as small as 1.4 Earth radii with periods on the order of a few months in the CM Draconis system could be detected at the 99.9% confidence level in less than a year using 1-m class telescopes from the ground. This result contradicts commonly held assumptions limiting present ground-based efforts to, at best, detections of gas giant planets after several years of observation. This method can be readily extended to a number of other larger star systems with the utilization of larger telescopes and longer observing times. Its extension to spacecraft observations should also allow the determination of the presence of terrestrial-sized planets in nearly 100 other known eclipsing binary systems.

Hot, Rocky World Artist Concept

NASA Image and Video Library

2015-07-30

This artist's rendition shows one possible appearance for the planet HD 219134b, the nearest confirmed rocky exoplanet found to date outside our solar system. The planet is 1.6 times the size of Earth, and whips around its star in just three days. Scientists predict that the scorching-hot planet -- known to be rocky through measurements of its mass and size -- would have a rocky, partially molten surface with geological activity, including possibly volcanoes. http://photojournal.jpl.nasa.gov/catalog/PIA19833

Protoplanetary Disks in Multiple Star Systems

NASA Astrophysics Data System (ADS)

Harris, Robert J.

Most stars are born in multiple systems, so the presence of a stellar companion may commonly influence planet formation. Theory indicates that companions may inhibit planet formation in two ways. First, dynamical interactions can tidally truncate circumstellar disks. Truncation reduces disk lifetimes and masses, leaving less time and material for planet formation. Second, these interactions might reduce grain-coagulation efficiency, slowing planet formation in its earliest stages. I present three observational studies investigating these issues. First is a spatially resolved Submillimeter Array (SMA) census of disks in young multiple systems in the Taurus-Auriga star-forming region to study their bulk properties. With this survey, I confirmed that disk lifetimes are preferentially decreased in multiples: single stars have detectable millimeter-wave continuum emission twice as often as components of multiples. I also verified that millimeter luminosity (proportional to disk mass) declines with decreasing stellar separation. Furthermore, by measuring resolved-disk radii, I quantitatively tested tidal-truncation theories: results were mixed, with a few disks much larger than expected. I then switch focus to the grain-growth properties of disks in multiple star systems. By combining SMA, Combined Array for Research in Millimeter Astronomy (CARMA), and Jansky Very Large Array (VLA) observations of the circumbinary disk in the UZ Tau quadruple system, I detected radial variations in the grain-size distribution: large particles preferentially inhabit the inner disk. Detections of these theoretically predicted variations have been rare. I related this to models of grain coagulation in gas disks and find that our results are consistent with growth limited by radial drift. I then present a study of grain growth in the disks of the AS 205 and UX Tau multiple systems. By combining SMA, Atacama Large Millimeter/submillimeter Array (ALMA), and VLA observations, I detected radial variations of the grain-size distribution in the AS 205 A disk, but not in the UX Tau A disk. I find that some combination of radial drift and fragmentation limits growth in the AS 205 A disk. In the final chapter, I summarize my findings that, while multiplicity clearly influences bulk disk properties, it does not obviously inhibit grain growth. Other investigations are suggested.

Development of the Terrestrial Planet Finder Coronagraph membrane V-grooves

NASA Technical Reports Server (NTRS)

Fang, Houfei; Ho, Timothy; Chen, Gun-Shing; Quijano, Ubaldo

2004-01-01

The Terrestrial Planet Finder mission will study all aaspecs of planets outside our solar system: from their formation and development in disks of dust and gas around newly forming stars to the presence of those planets orbiting the nearest stars; from the numbers at various sizes and places to their suitability as an abode for life.

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

A STATISTICAL RECONSTRUCTION OF THE PLANET POPULATION AROUND KEPLER SOLAR-TYPE STARS

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

Silburt, Ari; Wu, Yanqin; Gaidos, Eric

2015-02-01

Using the cumulative catalog of planets detected by the NASA Kepler mission, we reconstruct the intrinsic occurrence of Earth- to Neptune-size (1-4 R {sub ⊕}) planets and their distributions with radius and orbital period. We analyze 76,711 solar-type (0.8 < R {sub *}/R {sub ☉} < 1.2) stars with 430 planets on 20-200 day orbits, excluding close-in planets that may have been affected by the proximity to the host star. Our analysis considers errors in planet radii and includes an ''iterative simulation'' technique that does not bin the data. We find a radius distribution that peaks at 2-2.8 Earth radii, with lowermore » numbers of smaller and larger planets. These planets are uniformly distributed with logarithmic period, and the mean number of such planets per star is 0.46 ± 0.03. The occurrence is ∼0.66 if planets interior to 20 days are included. We estimate the occurrence of Earth-size planets in the ''habitable zone'' (defined as 1-2 R {sub ⊕}, 0.99-1.7 AU for solar-twin stars) as 6.4{sub −1.1}{sup +3.4}%. Our results largely agree with those of Petigura et al., although we find a higher occurrence of 2.8-4 Earth-radii planets. The reasons for this excess are the inclusion of errors in planet radius, updated Huber et al. stellar parameters, and also the exclusion of planets that may have been affected by proximity to the host star.« less

Atmospheric expansion in runaway greenhouse atmospheres: the inner edge of the habitable zone depends on planet mass

NASA Astrophysics Data System (ADS)

Goldblatt, C.; Zahnle, K. J.

2014-12-01

As a wet planet becomes hot, evaporation of the ocean provides a thick steam atmosphere. As the atmosphere thickens, the level at which optical depth is unity (whence radiative emission and absorption dominantly occur) rises into the atmosphere, first for thermal wavelengths and later for solar wavelengths. Consequently, two radiation limits emerge. First, an asymptotic limit on the thermal radiation, as the level at which thermal emission occurs tends towards a fixed temperature, decoupled from surface temperature. Next, a limit the albedo of the planet, as all incoming sunlight is either reflected or absorbed in the atmosphere and almost none reaches the surface. A runaway greenhouse occurs when the product of co-albedo and area-averaged incoming sunlight exceeds the thermal radiation limit. Earth today is perilously close to this [1].Returning to the first sentence, we generate a thick atmosphere: the height of optical depth of unity becomes a non-trivial fraction of the planetary radius. Hence the area of the absorbing and emitting surfaces increase. Thermal emission wins slightly, as this occurs higher, increasing thermal emission in all cases. The underlying tendency is for a larger thermal limit for heavier planets due to pressure effects, making these appear more resistant to a runaway. However, atmospheric expansion affects light planets more, making these seem much more resilient. The least resilient planet would be between Mars-size and Venus-size (Figure 1). It would be foolish to regard small planets as habitable. As the atmospheres become large, so does the problem of atmospheric escape. Theoretical considerations show hydrodynamic escape to happen disastrously for a Europa-size planet. The observation is that Mars is too feeble to hold on to any hefty atmosphere, even far from the Sun as it is, is probably relevant too. The take home points for habitable zone nerds are: (1) planet size matters (2) for small planets, atmospheric escape from a "moist greenhouse" state, with habitable surface temperatures, is the mortal wound. [1] Goldblatt, C., Robinson, T.D., Zahnle, K.J. & Crisp, D., Low simulated radiation limit for runaway greenhouse climates, Nat. Geosci, 6, 661-667, doi:10.1038/NGEO1892

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.

The Kepler Mission: Search for Habitable Planets

NASA Technical Reports Server (NTRS)

Borucki, William; Likins, B.; DeVincenzi, Donald L. (Technical Monitor)

1998-01-01

Detecting extrasolar terrestrial planets orbiting main-sequence stars is of great interest and importance. Current ground-based methods are only capable of detecting objects about the size or mass of Jupiter or larger. The difficulties encountered with direct imaging of Earth-size planets from space are expected to be resolved in the next twenty years. Spacebased photometry of planetary transits is currently the only viable method for detection of terrestrial planets (30-600 times less massive than Jupiter). This method searches the extended solar neighborhood, providing a statistically large sample and the detailed characteristics of each individual case. A robust concept has been developed and proposed as a Discovery-class mission. Its capabilities and strengths are presented.

A rocky planet transiting a nearby low-mass star.

PubMed

Berta-Thompson, Zachory K; Irwin, Jonathan; Charbonneau, David; Newton, Elisabeth R; Dittmann, Jason A; Astudillo-Defru, Nicola; Bonfils, Xavier; Gillon, Michaël; Jehin, Emmanuël; Stark, Antony A; Stalder, Brian; Bouchy, Francois; Delfosse, Xavier; Forveille, Thierry; Lovis, Christophe; Mayor, Michel; Neves, Vasco; Pepe, Francesco; Santos, Nuno C; Udry, Stéphane; Wünsche, Anaël

2015-11-12

M-dwarf stars--hydrogen-burning stars that are smaller than 60 per cent of the size of the Sun--are the most common class of star in our Galaxy and outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M dwarfs host Earth-sized planets in great numbers: the average number of M-dwarf planets that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per star. The nearest such planets known to transit their star are 39 parsecs away, too distant for detailed follow-up observations to measure the planetary masses or to study their atmospheres. Here we report observations of GJ 1132b, a planet with a size of 1.2 Earth radii that is transiting a small star 12 parsecs away. Our Doppler mass measurement of GJ 1132b yields a density consistent with an Earth-like bulk composition, similar to the compositions of the six known exoplanets with masses less than six times that of the Earth and precisely measured densities. Receiving 19 times more stellar radiation than the Earth, the planet is too hot to be habitable but is cool enough to support a substantial atmosphere, one that has probably been considerably depleted of hydrogen. Because the host star is nearby and only 21 per cent the radius of the Sun, existing and upcoming telescopes will be able to observe the composition and dynamics of the planetary atmosphere.

Characterizing the Variable Dust Permeability of Planet-induced Gaps

NASA Astrophysics Data System (ADS)

Weber, Philipp; Benítez-Llambay, Pablo; Gressel, Oliver; Krapp, Leonardo; Pessah, Martin E.

2018-02-01

Aerodynamic theory predicts that dust grains in protoplanetary disks will drift radially inward on comparatively short timescales. In this context, it has long been known that the presence of a gap opened by a planet can significantly alter the dust dynamics. In this paper, we carry out a systematic study employing long-term numerical simulations aimed at characterizing the critical particle size for retention outside a gap as a function of particle size, as well as various key parameters defining the protoplanetary disk model. To this end, we perform multifluid hydrodynamical simulations in two dimensions, including different dust species, which we treat as pressureless fluids. We initialize the dust outside of the planet’s orbit and study under which conditions dust grains are able to cross the gap carved by the planet. In agreement with previous work, we find that the permeability of the gap depends both on dust dynamical properties and the gas disk structure: while small dust follows the viscously accreting gas through the gap, dust grains approaching a critical size are progressively filtered out. Moreover, we introduce and compute a depletion factor that enables us to quantify the way in which higher viscosity, smaller planet mass, or a more massive disk can shift this critical size to larger values. Our results indicate that gap-opening planets may act to deplete the inner reaches of protoplanetary disks of large dust grains—potentially limiting the accretion of solids onto forming terrestrial planets.

Kepler False Positive Rate & Occurrence of Earth-size and Larger Planets

NASA Astrophysics Data System (ADS)

Fressin, Francois; Torres, G.; Charbonneau, D.; Kepler Team

2013-01-01

We model the Kepler exoplanet survey targets and their background stars to estimate the occurrence of astrophysical configurations which could mimic an exoplanetary transit. Using real noise level estimates, we compute the number and the characteristics of detectable eclipsing pairs involving stars or planets. We select the fraction of those that would pass the Kepler candidate vetting procedure, including the modeling of the centroid shift of their position on the Kepler camera. By comparing their distribution with that of the Kepler Object Interests from the first 6 quarters of Kepler data, we quantify the false positive rate of Kepler, as a function of candidate planet size and period. Most importantly, this approach allows quantifying and characterizing the distribution of planets, with no assumption of any prior, as the remaining population of the Kepler candidate list minus the simulated population of alternate astrophysical causes. We study the actual detection recovery rate for Kepler that allows reproducing both the KOI size and period distribution as well as their SNR distribution. We estimate the occurrence of planets down to Earth-size, and study if their frequency is correlated with their host star spectral type. This work is supported by the Spitzer General Observer Proposal #80117 - Validating the First Habitable-Zone Planet Candidates Identified by the NASA Kepler Mission, and by the Kepler Participating Scientist Contract led by David Charbonneau, to confirm the planetary nature of candidates identified by the Kepler mission

Supercomputing in the Age of Discovering Superearths, Earths and Exoplanet Systems

NASA Technical Reports Server (NTRS)

Jenkins, Jon M.

2015-01-01

NASA's Kepler Mission was launched in March 2009 as NASA's first mission capable of finding Earth-size planets orbiting in the habitable zone of Sun-like stars, that range of distances for which liquid water would pool on the surface of a rocky planet. Kepler has discovered over 1000 planets and over 4600 candidates, many of them as small as the Earth. Today, Kepler's amazing success seems to be a fait accompli to those unfamiliar with her history. But twenty years ago, there were no planets known outside our solar system, and few people believed it was possible to detect tiny Earth-size planets orbiting other stars. Motivating NASA to select Kepler for launch required a confluence of the right detector technology, advances in signal processing and algorithms, and the power of supercomputing.

Light-curve analysis of KOI 2700b: the second extrasolar planet with a comet-like tail

NASA Astrophysics Data System (ADS)

Garai, Z.

2018-03-01

Context. The Kepler object KOI 2700b (KIC 8639908b) was discovered recently as the second exoplanet with a comet-like tail. It exhibits a distinctly asymmetric transit profile, likely indicative of the emission of dusty effluents and reminiscent of KIC 12557548b, the first exoplanet with a comet-like tail. Aim. The scientific goal of this work is to verify the disintegrating-planet scenario of KOI 2700b by modeling its light curve and to put constraints on various tail and planet properties, as was done in the case of KIC 12557548b. Methods: We obtained the phase-folded and binned transit light curve of KOI 2700b, which we subsequently iteratively modeled using the radiative-transfer code SHELLSPEC. We modeled the comet-like tail as part of a ring around the parent star and we also included the solid body of the planet in the model. During the modeling we applied selected species and dust particle sizes. Results: We confirmed the disintegrating-planet scenario of KOI 2700b. Furthermore, via modeling, we derived some interesting features of KOI 2700b and its comet-like tail. It turns out that the orbital plane of the planet and its tail are not edge-on, but the orbital inclination angle is from the interval [85.1, 88.6] deg. In comparison with KIC 12557548b, KOI 2700b exhibits a relatively low dust density decreasing in its tail. We also derived the dust density at the beginning of the ring and the highest optical depth through the tail in front of the star, based on a tail-model with a cross-section of 0.05 × 0.05 R⊙ at the beginning and 0.09 × 0.09 R⊙ at its end. Our results show that the dimension of the planet is Rp/Rs ≤ 0.014 (Rp ≤ 0.871 R⊕, or ≤5551 km). We also estimated the mass-loss rate from KOI 2700b, and we obtained Ṁ values from the interval [5.05 × 107, 4.41 × 1015] g s-1. On the other hand, we could not draw any satisfactory conclusions about the typical grain size in the dust tail.

Stellar variability and its implications for photometric planet detection with Kepler

NASA Astrophysics Data System (ADS)

Batalha, N. M.; Jenkins, J.; Basri, G. S.; Borucki, W. J.; Koch, D. G.

2002-01-01

Kepler is one of three candidates for the next NASA Discovery Mission and will survey the extended solar neighborhood to detect and characterize hundreds of terrestrial (and larger) planets in or near the habitable zone. Its strength lies in its ability to detect large numbers of Earth-sized planets - planets which produced a 10-4 change in relative stellar brightness during a transit across the disk of a sun-like parent star. Such a detection requires high instrumental relative precision and is facilitated by observing stars which are photometrically quiet on hourly timescales. Probing stellar variability across the HR diagram, one finds that many of the photometrically quietest stars are the F and G dwarfs. The Hipparcos photometric database shows the lowest photometric variances among stars of this spectral class. Our own Sun is a prime example with RMS variations over a few rotational cycles of typically (3 - 4)×10-4 (computed from VIRGO/DIARAD data taken Jan-Mar 2001). And variability on the hourly time scales crucial for planet detection is significantly smaller: just (2 - 5)×10-5. This bodes well for planet detection programs such as Kepler and Eddington. With significant numbers of photometrically quiet solar-type stars, Earth-sized planets should be readily identified provided they are abundant in the solar neighborhood. In support of the Kepler science objectives, we have initiated a study of stellar variability and its implications for planet detection. Herein, we summarize existing observational and theoretrical work with the objective of determining the percentage of stars in the Kepler field of view expected to be photometrically stable at a level which allows for Earth-sized planet detection.

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

Third Workshop on Photometry

NASA Technical Reports Server (NTRS)

Borucki, William J. (Editor); Lasher, Lawrence E. (Editor)

2001-01-01

The discoveries of extrasolar planets by Wolszczan, Mayor and Queloz, Butler et al., and others have stimulated a widespread effort to obtain a body of data sufficient to understand their occurrence and characteristics. Doppler velocity techniques have found dozens of extrasolar planets with masses similar to that of Jupiter. Approximately ten percent of the stars that show planets with orbital periods of a few days to a week are expected to show transits. With the mass obtained from Doppler velocity measurements and the size from transit photometry, the densities of the planets can be determined. Theoretical models of the structure of "hot Jupiters" (i.e., those planets within a tenth of an astronomical unit (AU) of the parent star) indicate that these planets should be substantially larger in size and lower in density than Jupiter. Thus the combination of transit and Doppler velocity measurements provide a critical test of the theories of planetary structure. Furthermore, because photometry can be done with small-aperture telescopes rather than requiring the use of much larger telescopes, transit photometry should also reduce the cost of discovering extrasolar planets.

Habitability of waterworlds: runaway greenhouses, atmospheric expansion, and multiple climate states of pure water atmospheres.

PubMed

Goldblatt, Colin

2015-05-01

There are four different stable climate states for pure water atmospheres, as might exist on so-called "waterworlds." I map these as a function of solar constant for planets ranging in size from Mars-sized to 10 Earth-mass. The states are as follows: globally ice covered (Ts ⪅ 245 K), cold and damp (270 ⪅ Ts ⪅ 290 K), hot and moist (350 ⪅ Ts ⪅ 550 K), and very hot and dry (Tsx2A86;900 K). No stable climate exists for 290 ⪅ T s ⪅ 350 K or 550 ⪅ Ts ⪅ 900 K. The union of hot moist and cold damp climates describes the liquid water habitable zone, the width and location of which depends on planet mass. At each solar constant, two or three different climate states are stable. This is a consequence of strong nonlinearities in both thermal emission and the net absorption of sunlight. Across the range of planet sizes, I account for the atmospheres expanding to high altitudes as they warm. The emitting and absorbing surfaces (optical depth of unity) move to high altitude, making their area larger than the planet surface, so more thermal radiation is emitted and more sunlight absorbed (the former dominates). The atmospheres of small planets expand more due to weaker gravity; the effective runaway greenhouse threshold is about 35 W m(-2) higher for Mars, 10 W m(-2) higher for Earth or Venus, but only a few W m(-2) higher for a 10 Earth-mass planet. There is an underlying (expansion-neglected) trend of increasing runaway greenhouse threshold with planetary size (40 W m(-2) higher for a 10 Earth-mass planet than for Mars). Summing these opposing trends means that Venus-sized (or slightly smaller) planets are most susceptible to a runaway greenhouse. The habitable zone for pure water atmospheres is very narrow, with an insolation range of 0.07 times the solar constant. A wider habitable zone requires background gas and greenhouse gas: N2 and CO2 on Earth, which are biologically controlled. Thus, habitability depends on inhabitance.

Planetary size comparisons: A photographic study

NASA Technical Reports Server (NTRS)

Meszaros, S. P.

1983-01-01

Over the past two decades NASA spacecraft missions obtained photographs permitting accurate size measurements of the planets and moons, and their surface features. Planetary global views are displayed at the same scale, in each picture to allow visual size comparisons. Additionally, special geographical features on some of the planets are compared with selected Earth areas, again at the same scale. Artist renderings and estimated sizes are used for worlds not yet reached by spacecraft. Included with each picture is number designation for use in ordering copies of the photos.

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

Bear, Ealeal; Soker, Noam, E-mail: ealeal@physics.technion.ac.il, E-mail: soker@physics.technion.ac.il

We propose that the two newly detected Earth-size planets around the hot B subdwarf star KIC 05807616 are remnant of the tidally destructed metallic core of a massive planet. A single massive gas-giant planet was spiralling-in inside the envelope of the red giant branch star progenitor of the extreme horizontal branch (EHB) star KIC 05807616. The released gravitational energy unbound most of the stellar envelope, turning it into an EHB star. The massive planet reached the tidal-destruction radius of {approx}1 R{sub Sun} from the core, where the planet's gaseous envelope was tidally removed. In our scenario, the metallic core ofmore » the massive planet was tidally destructed into several Earth-like bodies immediately after the gaseous envelope of the planet was removed. Two, and possibly more, Earth-size fragments survived at orbital separations of {approx}> 1 R{sub Sun} within the gaseous disk. The bodies interact with the disk and among themselves, and migrated to reach orbits close to a 3:2 resonance. These observed planets can have a planetary magnetic field about 10 times as strong as that of Earth. This strong magnetic field can substantially reduce the evaporation rate from the planets and explain their survivability against the strong UV radiation of the EHB star.« less

Educational And Public Outreach Software On Planet Detection For The Macintosh (TM)

NASA Technical Reports Server (NTRS)

Koch, David; Brady, Victoria; Cannara, Rachel; Witteborn, Fred C. (Technical Monitor)

1996-01-01

The possibility of extra-solar planets has been a very popular topic with the general public for years. Considerable media coverage of recent detections has only heightened the interest in the topic. School children are particularly interested in learning about space. Astronomers have the knowledge and responsibility to present this information in both an understandable and interesting format. Since most classrooms and homes are now equipped with computers this media can be utilized to provide more than a traditional "flat" presentation. An interactive "stack" has been developed using Hyperstudio (TM). 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 Earth-Sized Planets"; and "A Mission Simulator". Using the simulator, the student records simulated observations and then analyzes and interprets the data within the program stacks to determine the orbit and planet size, the planet's temperature and surface gravity, and finally determines if the planet is habitable. Additional related sections are also included. Many of the figures are animated to assist in comprehension of the material. A set of a dozen lesson plans for the middle school has also been drafted.

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.

Detection of Terrestrial Planets Using Transit Photometry

NASA Astrophysics Data System (ADS)

Koch, D.; Witteborn, F.; Jenkins, J.; Dunham, E.; Borucki, W.

2000-12-01

Transit photometry detection of planets offers many advantages: an ability to detect terrestrial-size planets, direct determination of the planet's size, applicability to all main-sequence stars, and a periodic signature (differential brightness change) being independent of stellar distance or planetary orbital semi-major axis. Ground and space based photometry have already been successful in detecting transits of the giant planet HD209458b (Charbonneau, et al. 2000, Castellano et al. 2000 and references therein). However, photometry 100 times better is required to detect terrestrial planets. We present results of measurements of an end-to-end photometric system incorporating all of the important confounding noise features of both the sky and a spacebased photometer including spacecraft jitter. In addition to demonstrating an instrumental noise of less than 10 ppm per transit (an Earth transit of a solar-like star is 80 ppm), the brightnesses of individual stars were dimmed to simulate Earth-size transit signals. These "transits" were reliably detected as part of the tests. Funding for this work was provided by NASA's Discovery and Origins programs and by NASA Ames. Charbonneau, D.; Brown, T.M.; Latham, D.W.; Mayor, M., ApJ, 529, L45, 2000. Castellano, T., Jenkins, J., Trilling, D. E., Doyle, L., and Koch, D., ApJ Let. 532, L51-L53 (2000)

Time for Gas Planets to Grow

NASA Technical Reports Server (NTRS)

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

2001-01-01

Giant planets like Jupiter need a large reservoir of gas to grow to full size. New observations indicate that such planetary nurseries last twice as long as previously thought. These observations, and their implications for the abundance of Jupiter-like planets within our galaxy, are discussed herein.

TRAPPIST-1 Comparison to Solar System and Jovian Moons

NASA Image and Video Library

2017-02-22

All seven planets discovered in orbit around the red dwarf star TRAPPIST-1 could easily fit inside the orbit of Mercury, the innermost planet of our solar system. In fact, they would have room to spare. TRAPPIST-1 also is only a fraction of the size of our sun; it isn't much larger than Jupiter. So the TRAPPIST-1 system's proportions look more like Jupiter and its moons than those of our solar system. 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. 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. http://photojournal.jpl.nasa.gov/catalog/PIA21428

Planet signatures and Size Segregation in Debris Discs

NASA Astrophysics Data System (ADS)

Thébault, Philippe

2014-01-01

The response of a debris disc to a planetary perturber is the result of the complex interplay between gravitational effects, grain collisions and stellar radiation pressure (Stark & Kuchner (2009). We investigate to what extent this response can depart from the pure gravitational case when including grain collisional production and radiation pressure. We use the DyCoSS code (Thébault (2012), designed to study the coupled effect of collisions and dynamics for systems at steady state with one perturbing body. We focus on two outcomes: the 2D surface density profile of the disc+planet system, and the way the Particle Size Distribution (PSD) is spatially segregated within the disc. We consider two set-ups: 1) a narrow ring with an exterior ``shepherding'' planet, and 2) an extended disc in which a planet is embedded. For each case, the planet mass and orbit are explored as free parameters, and an unperturbed ``no-planet'' case is also considered. Another parameter is the disc's collisional activity, as parameterized by its optical depth τ.

Very high-density planets: a possible remnant of gas giants.

PubMed

Mocquet, A; Grasset, O; Sotin, C

2014-04-28

Data extracted from the Extrasolar Planets Encyclopaedia (see http://exoplanet.eu) show the existence of planets that are more massive than iron cores that would have the same size. After meticulous verification of the data, we conclude that the mass of the smallest of these planets is actually not known. However, the three largest planets, Kepler-52b, Kepler-52c and Kepler-57b, which are between 30 and 100 times the mass of the Earth, have indeed density larger than an iron planet of the same size. This observation triggers this study that investigates under which conditions these planets could represent the naked cores of gas giants that would have lost their atmospheres during their migration towards the star. This study shows that for moderate viscosity values (10(25) Pa s or lower), large values of escape rate and associated unloading stress rate during the atmospheric loss process lead to the explosion of extremely massive planets. However, for moderate escape rate, the bulk viscosity and finite-strain incompressibility of the cores of giant planets can be large enough to retain a very high density during geological time scales. This would make those a new kind of planet, which would help in understanding the interior structure of the gas giants. However, this new family of exoplanets adds some degeneracy for characterizing terrestrial exoplanets.

More Planets in the Hyades Cluster

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-12-01

A few weeks ago, Astrobites reported on a Neptune-sized planet discovered orbiting a star in the Hyades cluster. A separate study submitted at the same time, however, reveals that there may be even more planets lurking in this system.Thanks, KeplerArtists impression of the Kepler spacecraft and the mapping of the fields of the current K2 mission. [NASA]As we learn about the formation and evolution of planets outside of our own solar system, its important that we search for planets throughout different types of star clusters; observing both old and young clusters, for instance, can tell us about planets in different stages of their evolutionary histories. Luckily for us, we have a tool that has been doing exactly this: the Kepler mission.In true holiday spirit, Kepler is the gift that just keeps on giving. Though two of its reaction wheels have failed, Kepler now as its reincarnation, K2 just keeps detecting more planet transits. Whats more, detailed analysis of past Kepler/K2 data with ever more powerful techniques as well as the addition of high-precision parallaxes for stars from Gaia in the near future ensures that the Kepler data set will continue to reveal new exoplanet transits for many years to come.Image of the Hyades cluster, a star cluster that is only 800 million years old. [NASA/ESA/STScI]Hunting in the Young HyadesTwo studies using K2 data were recently submitted on exoplanet discoveries around EPIC 247589423 in the Hyades cluster, a nearby star cluster that is only 800 million years old. Astrobites reported on the first study in October and discussed details about the newly discovered mini-Neptune presented in that study.The second study, led by Andrew Mann (University of Texas at Austin and NASA Hubble Fellow at Columbia University), was published this week. This study presented a slightly different outcome: the authors detect the presence of not just the one, but three exoplanets orbiting EPIC 247589423.New DiscoveriesMann and collaborators searched through the K2 light curves of young stars as part of the ZEIT (Zodiacal Exoplanets in Time) Survey. Using these data, they identified the presence of three planets in the EPIC 247589423 system:a roughly Earth-sized planet ( 1.0 Earth radii) with a period of 8.0 days,the mini-Neptune identified in the other study, with a size of 2.9 Earth radii and period of 17 days, anda super-Earth, with a size of 1.5 Earth radii and period of 26 days.Light curve of EPIC 247589423 from K2, with the lower panels showing the transits of the three discovered planets. [Mann et al. 2018]The smallest planet is among the youngest Earth-sized planets ever discovered, allowing us a rare glimpse into the history and evolution of planets similar to our own.But these planetary discoveries are additionally exciting because theyre orbiting a bright star thats relatively quiet for its age making the system an excellent target for dedicated radial-velocity observations to determine the planet masses.Since most young star clusters are much further away, they lie out of range of radial-velocity follow-up, rendering EPIC 247589423 a unique opportunity to explore the properties of young planets in detail. With more discoveries like these from Keplers data, we can hope to soon learn more about planets in all their stages of evolution.CitationAndrew W. Mann et al 2018 AJ 155 4. doi:10.3847/1538-3881/aa9791

K2's First Five-Planet System

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-08-01

Whats the latest from the Kepler K2 mission? K2 has found its first planetary system containing more than three planets an exciting five-planet system located ~380 light-years from Earth!Opportunities From K2Raw K2 light curve (blue, top) and systematic corrected light curve (orange, bottom) for HIP 41378. The three deepest transits are single transits from the three outermost planet candidates. [Vanderburg et al. 2016]The original Kepler mission was enormously successful, discovering thousands of planet candidates. But one side effect of Keplers original observing technique, in which it studied the same field for four years, is that it was very good at detecting extremely faint systems systems that were often too faint to be followed up with other techniques.After Keplers mechanical failure in 2013, the K2 mission was launched, in which the spacecraft uses solar pressure to stabilize it long enough to perform an 80-day searches of each region it examines. Over the course of the K2 mission, Kepler could potentially survey up to 20 times the sky area of the original mission, providing ample opportunity to find planetary systems around bright stars. These stars may be bright enough to be followed up with other techniques.Multi-Planet SystemsTheres a catch to the 80-day observing program: the K2 mission is less likely to detect multiple planets orbiting the same star, due to the short time spent observing the system. While the original Kepler mission detected systems with up to seven planets, K2 had yet to detect systems with more than three candidates until now.Led by Andrew Vanderburg (NSF Graduate Research Fellow at the Harvard-Smithsonian Center for Astrophysics), a team of scientists recentlyanalyzed K2 observations ofthe bright star HIP 41378. Theteamfound that this F-type star hosts five potential planetary candidates!Phase-folded light curve for each of the five transiting planets in the HIP 41378 system. The outermost planet (bottom panel) may provide an excellent target for transmission spectroscopy, to examine its atmosphere. [Vanderburg et al. 2016]Newly Discovered CandidatesThe systems candidates include two sub-Neptune-sized planets, which were both observed over multiple transits. They orbit in what is nearly a 2:1 resonance, with periods of 31.7 and 15.6 days. Based on modeling of their transits, Vanderburg and collaborators estimate that they have radii of 2.6 and 2.9 Earth radii.The system also contains three larger outer-planet candidates: one Neptune-sized (~4 Earth radii), one sub-Saturn-sized (~5 Earth radii), and one Jupiter-sized (~10 Earth radii). These planets were detected with only a single transit each, so their properties are harder to determine with certainty. The authors models, however, suggest that their periods are ~160 days, ~130 days, and ~1 year.This systems brightness, the accessible size of its planets, and its rich architecture make it an excellent target for follow-up observations. In particular, the brightness of the host star and the transit depth of the outermost planet, HIP 41378 f, make this candidate an ideal target for future transit transmission spectroscopy measurements.Since past observations of exoplanet atmospheres have been primarily of short-period, highly irradiated planets, being able to examine the atmosphere of such a long-period gas giant could open up a new regime of exoplanet atmospheric studies.CitationAndrew Vanderburg et al 2016 ApJ 827 L10. doi:10.3847/2041-8205/827/1/L10

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

The Limiting Sizes of the Habitable Planets

NASA Technical Reports Server (NTRS)

Huang, Su-Shu

1960-01-01

The astrobiological problem of the occurrence of life in the universe is discussed from the standpoint of the size and nature of planets upon which living organisms might arise. The conclusion is tentatively drawn that the most likely radius of a habitable planet lies between 10(exp 8) cm and 2 x 10(exp 9) cm. Conditions of temperature and density also bear upon the occurrence of life; thus the moon and Mercury, although both fall within the range of favorable radii, are nevertheless believed uninhabited by indigeneous life.

Kepler: NASA's First Mission Capable of Finding Earth-Size Planets

NASA Technical Reports Server (NTRS)

Borucki, William J.

2009-01-01

Kepler, a NASA Discovery mission, is a spaceborne telescope designed to search a nearby region of our galaxy for Earth-size planets orbiting in the habitable zone of stars like our sun. The habitable zone is that region around a start where the temperature permits water to be liquid on the surface of a planet. Liquid water is considered essential forth existence of life. Mission Phases: Six mission phases have been defined to describe the different periods of activity during Kepler's mission. These are: launch; commissioning; early science operations, science operations: and decommissioning

Architectures of planetary systems and implications for their formation.

PubMed

Ford, Eric B

2014-09-02

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

Architectures of planetary systems and implications for their formation

PubMed Central

Ford, Eric B.

2014-01-01

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

Shifting of the resonance location for planets embedded in circumstellar disks

NASA Astrophysics Data System (ADS)

Marzari, F.

2018-03-01

Context. In the early evolution of a planetary system, a pair of planets may be captured in a mean motion resonance while still embedded in their nesting circumstellar disk. Aims: The goal is to estimate the direction and amount of shift in the semimajor axis of the resonance location due to the disk gravity as a function of the gas density and mass of the planets. The stability of the resonance lock when the disk dissipates is also tested. Methods: The orbital evolution of a large number of systems is numerically integrated within a three-body problem in which the disk potential is computed as a series of expansion. This is a good approximation, at least over a limited amount of time. Results: Two different resonances are studied: the 2:1 and the 3:2. In both cases the shift is inwards, even if by a different amount, when the planets are massive and carve a gap in the disk. For super-Earths, the shift is instead outwards. Different disk densities, Σ, are considered and the resonance shift depends almost linearly on Σ. The gas dissipation leads to destabilization of a significant number of resonant systems, in particular if it is fast. Conclusions: The presence of a massive circumstellar disk may significantly affect the resonant behavior of a pair of planets by shifting the resonant location and by decreasing the size of the stability region. The disk dissipation may explain some systems found close to a resonance but not locked in it.

Adaptive Nulling for Interferometric Detection of Planets

NASA Technical Reports Server (NTRS)

Lay, Oliver P.; Peters, Robert D.

2010-01-01

An adaptive-nulling method has been proposed to augment the nulling-optical- interferometry method of detection of Earth-like planets around distant stars. The method is intended to reduce the cost of building and aligning the highly precise optical components and assemblies needed for nulling. Typically, at the mid-infrared wavelengths used for detecting planets orbiting distant stars, a star is millions of times brighter than an Earth-sized planet. In order to directly detect the light from the planet, it is necessary to remove most of the light coming from the star. Nulling interferometry is one way to suppress the light from the star without appreciably suppressing the light from the planet. In nulling interferometry in its simplest form, one uses two nominally identical telescopes aimed in the same direction and separated laterally by a suitable distance. The light collected by the two telescopes is processed through optical trains and combined on a detector. The optical trains are designed such that the electric fields produced by an on-axis source (the star) are in anti-phase at the detector while the electric fields from the planet, which is slightly off-axis, combine in phase, so that the contrast ratio between the star and the planet is greatly decreased. If the electric fields from the star are exactly equal in amplitude and opposite in phase, then the star is effectively nulled out. Nulling is effective only if it is complete in the sense that it occurs simultaneously in both polarization states and at all wavelengths of interest. The need to ensure complete nulling translates to extremely tight demands upon the design and fabrication of the complex optical trains: The two telescopes must be highly symmetric, the reflectivities of the many mirrors in the telescopes and other optics must be carefully tailored, the optical coatings must be extremely uniform, sources of contamination must be minimized, optical surfaces must be nearly ideal, and alignments must be extremely precise. Satisfaction of all of these requirements entails substantial cost.

Prospecting for Habitable Worlds

NASA Technical Reports Server (NTRS)

Jenkins, Jon M.

2017-01-01

NASAs Kepler Mission was launched in March 2009 as NASAs first mission capable of finding Earth-size planets orbiting in the habitable zone of Sun-like stars, that range of distances for which liquid water would pool on the surface of a rocky planet. Kepler has discovered over 2200 planets and over 2200 candidate planets, many of them as small as the Earth. Forty nine of these are less than twice the size of Earth and orbit in the habitable zone of their stars, all of which are cooler and significantly smaller than the Sun.Today, Keplers amazing success seems to be a fait accompli to those unfamiliar with her history. But twenty years ago, there were no planets known outside our solar system, and few people believed it was possible to detect tiny Earth-size planets orbiting other stars. Indeed, demonstrating that the science was feasible took four proposals to NASAs Discovery Program and extensive research and laboratory demonstrations. Motivating NASA to select Kepler for launch required a confluence of the right detector technology, advances in signal processing and algorithms, and the power of supercomputing. On August 23 2015 we reported the discovery of Kepler-452b, the first small, possibly rocky planet in the habitable zone of a G2 star very similar to our own. Kepler-452b orbits its star once every 385 days in an orbit just 5 larger than that of Earth. This discovery represents an important step towards finding and characterizing small habitable worlds orbiting Sun-like stars.

Stable regions around Exoplanets: the search for Exomoons

NASA Astrophysics Data System (ADS)

Fernandes Guimaraes, Ana Helena; Moretto Tusnski, Luis Ricardo; Vieira-Neto, Ernesto; Silva Valio, Adriana

2015-08-01

There are hundreds of exoplanets which the data are available to a dynamical investigation. We extracted from the data base (exoplanets.org) all planets and candidates which have the necessary data available for the numerical investigation of the orbital stability of a body around a exoplanet in a total of 2749 of those.There is a wealth diversity of exoplanets types and the expectation in find our Earth-living conditions in another planet motivates the search for extra-solar planets, and a satellite around a planet would, in addiction, help to keep a favorable climate.Using the planets class according to PHL@Arecibo, those planets were sorted out in groups. Analyses of density, distance from the primary body, and mass ratios were done beside the suggested classification to fit some no-classified planets into one of the groups.The aim of this work is to derive the upper stability limit (or upper critical orbit) of fictitious direct satellites around exoplanets of any density, or size, orbiting single stars. Our search is for stable regions around the planet, the called S-type orbits. This orbit type determines if there is any chance to exist (or not) bodies around the planets. The investigation is limited to single stars, excluding binaries.We derived such limit purely through numerical simulations. Our proposal involved long-term integration of the circular restricted three bodies problem . Basically, the cut off of the stability zone determined in the previous work by Domingos et al. (2006) were confirmed for any planet type. However, the limitation due the Roche limit of the own satellite showed to be lower. We used this to determined possible size and to adjust orbital range were a third body could orbit the exoplanet.Independently of densities, distance, and sizes of the objects involved, the idea was to delimit where to find celestial bodies in any given system around single stars. Furthermore, we aim to provide tracks to the search for exomoons using planetary transits.

Status of the Terrestrial Planet Finder Interferometer (TPF-I)

NASA Technical Reports Server (NTRS)

Beichman, Charles; Lawson, Peter; Lay, Oliver; Ahmed, Asif; Unwin, Steve; Johnston, K.

2006-01-01

The interferometric version of the Terrestrial Planet Finder (TPF-I) has the potential to find and characterize earth-sized planets in the habitable zones of over 250 nearby stars and to search for life using biomarkers in the atmospheres of any planets found. The scientific case for such a mission continues to be strengthened by on-going progress in the detection of planets via indirect means. This paper summarizes the status of TPF-I, illustrative scientific requirements for the mission, and its enabling technologies.

The Dependence of Tropical Cyclone Count and Size on Rotation Rate

NASA Astrophysics Data System (ADS)

Chavas, D. R.; Reed, K. A.

2017-12-01

Both theory and idealized equilibrium modeling studies indicate that tropical cyclone size decreases with background rotation rate. In contrast, in real-world observations size tends to increase with latitude. Here we seek to resolve this apparent contradiction via a set of reduced-complexity global aquaplanet simulations with varying planetary rotation rates using the NCAR Community Atmosphere Model 5. The latitudinal distribution of both storm count and size are found to vary markedly with rotation rate, yielding insight into the dynamical constraints on tropical cyclone activity on a rotating planet. Moreover, storm size is found to vary non-monotonically with latitude, indicating that non-equilibrium effects are crucial to the life-cycle evolution of size in nature. Results are then compared to experiments in idealized, time-dependent limited-area modeling simulations using CM1 in axisymmetric and three-dimensional geometry. Taken together, this hierarchy of models is used to quantify the role of equilibrium versus transient controls on storm size and the relevance of each to real storms in nature.

TRAPPIST-1 Compared to Jovian Moons and Inner Solar System - Updated Feb. 2018

NASA Image and Video Library

2018-02-05

All seven planets discovered in orbit around the red dwarf star TRAPPIST-1 could easily fit inside the orbit of Mercury, the innermost planet of our solar system. In fact, they would have room to spare. TRAPPIST-1 also is only a fraction of the size of our Sun; it isn't much larger than Jupiter. So, the TRAPPIST-1 system's proportions look more like Jupiter and its moons than those of our solar system. The seven planets of TRAPPIST-1 are all Earth-sized and terrestrial. TRAPPIST-1 is an ultra-cool dwarf star in the constellation Aquarius, and its planets orbit very close to it. https://photojournal.jpl.nasa.gov/catalog/PIA22096

A Kepler Mission, A Search for Habitable Planets: Concept, Capabilities and Strengths

NASA Technical Reports Server (NTRS)

Koch, David; Borucki, William; Lissauer, Jack; Dunham, Edward; Jenkins, Jon; DeVincenzi, D. (Technical Monitor)

1998-01-01

The detection of extrasolar terrestrial planets orbiting main-sequence stars is of great interest and importance. Current ground-based methods are only capable of detecting objects about the size or mass of Jupiter or larger. The technological challenges of direct imaging of Earth-size planets from space are expected to be resolved over the next twenty years. Spacebased photometry of planetary transits is currently the only viable method for detection of terrestrial planets (30-600 times less massive than Jupiter). The method searches the extended solar neighborhood, providing a statistically large sample and the detailed characteristics of each individual case. A robust concept has been developed and proposed as a Discovery-class mission. The concept, its capabilities and strengths are presented.

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

NASA Technical Reports Server (NTRS)

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

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

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

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

DETAILED ABUNDANCES OF STARS WITH SMALL PLANETS DISCOVERED BY KEPLER. I. THE FIRST SAMPLE

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

Schuler, Simon C.; Vaz, Zachary A.; Santrich, Orlando J. Katime

2015-12-10

We present newly derived stellar parameters and the detailed abundances of 19 elements of seven stars with small planets discovered by NASA's Kepler Mission. Each star, save one, has at least one planet with a radius ≤1.6 R{sub ⊕}, suggesting a primarily rocky composition. The stellar parameters and abundances are derived from high signal-to-noise ratio, high-resolution echelle spectroscopy obtained with the 10 m Keck I telescope and High Resolution Echelle Spectrometer using standard spectroscopic techniques. The metallicities of the seven stars range from −0.32 to +0.13 dex, with an average metallicity that is subsolar, supporting previous suggestions that, unlike Jupiter-typemore » giant planets, small planets do not form preferentially around metal-rich stars. The abundances of elements other than iron are in line with a population of Galactic disk stars, and despite our modest sample size, we find hints that the compositions of stars with small planets are similar to stars without known planets and with Neptune-size planets, but not to those of stars with giant planets. This suggests that the formation of small planets does not require exceptional host-star compositions and that small planets may be ubiquitous in the Galaxy. We compare our derived abundances (which have typical uncertainties of ≲0.04 dex) to the condensation temperature of the elements; a correlation between the two has been suggested as a possible signature of rocky planet formation. None of the stars demonstrate the putative rocky planet signature, despite at least three of the stars having rocky planets estimated to contain enough refractory material to produce the signature, if real. More detailed abundance analyses of stars known to host small planets are needed to verify our results and place ever more stringent constraints on planet formation models.« less

SOLAR SYSTEM MOONS AS ANALOGS FOR COMPACT EXOPLANETARY SYSTEMS

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

Kane, Stephen R.; Hinkel, Natalie R.; Raymond, Sean N., E-mail: skane@ipac.caltech.edu

2013-11-01

The field of exoplanetary science has experienced a recent surge of new systems that is largely due to the precision photometry provided by the Kepler mission. The latest discoveries have included compact planetary systems in which the orbits of the planets all lie relatively close to the host star, which presents interesting challenges in terms of formation and dynamical evolution. The compact exoplanetary systems are analogous to the moons orbiting the giant planets in our solar system, in terms of their relative sizes and semimajor axes. We present a study that quantifies the scaled sizes and separations of the solarmore » system moons with respect to their hosts. We perform a similar study for a large sample of confirmed Kepler planets in multi-planet systems. We show that a comparison between the two samples leads to a similar correlation between their scaled sizes and separation distributions. The different gradients of the correlations may be indicative of differences in the formation and/or long-term dynamics of moon and planetary systems.« less

A temperate rocky super-Earth transiting a nearby cool star

NASA Astrophysics Data System (ADS)

Dittmann, Jason A.; Irwin, Jonathan M.; Charbonneau, David; Bonfils, Xavier; Astudillo-Defru, Nicola; Haywood, Raphaëlle D.; Berta-Thompson, Zachory K.; Newton, Elisabeth R.; Rodriguez, Joseph E.; Winters, Jennifer G.; Tan, Thiam-Guan; Almenara, Jose-Manuel; Bouchy, François; Delfosse, Xavier; Forveille, Thierry; Lovis, Christophe; Murgas, Felipe; Pepe, Francesco; Santos, Nuno C.; Udry, Stephane; Wünsche, Anaël; Esquerdo, Gilbert A.; Latham, David W.; Dressing, Courtney D.

2017-04-01

M dwarf stars, which have masses less than 60 per cent that of the Sun, make up 75 per cent of the population of the stars in the Galaxy. The atmospheres of orbiting Earth-sized planets are observationally accessible via transmission spectroscopy when the planets pass in front of these stars. Statistical results suggest that the nearest transiting Earth-sized planet in the liquid-water, habitable zone of an M dwarf star is probably around 10.5 parsecs away. A temperate planet has been discovered orbiting Proxima Centauri, the closest M dwarf, but it probably does not transit and its true mass is unknown. Seven Earth-sized planets transit the very low-mass star TRAPPIST-1, which is 12 parsecs away, but their masses and, particularly, their densities are poorly constrained. Here we report observations of LHS 1140b, a planet with a radius of 1.4 Earth radii transiting a small, cool star (LHS 1140) 12 parsecs away. We measure the mass of the planet to be 6.6 times that of Earth, consistent with a rocky bulk composition. LHS 1140b receives an insolation of 0.46 times that of Earth, placing it within the liquid-water, habitable zone. With 90 per cent confidence, we place an upper limit on the orbital eccentricity of 0.29. The circular orbit is unlikely to be the result of tides and therefore was probably present at formation. Given its large surface gravity and cool insolation, the planet may have retained its atmosphere despite the greater luminosity (compared to the present-day) of its host star in its youth. Because LHS 1140 is nearby, telescopes currently under construction might be able to search for specific atmospheric gases in the future.

Kepler Mission: A Search for Terrestrial Planets

NASA Technical Reports Server (NTRS)

Koch, D.; Borucki, W.; Jenkens, J.; Dunham, E.; DeVincenzi, Donald (Technical Monitor)

2001-01-01

The Kepler Mission is a search for terrestrial planets by monitoring a large ensemble of stars for the periodic transits of planets. The mission consists of a 95-cm aperture photometer with 105 square deg field of view that monitors 100,000 dwarf stars for four years. The mission is unique in its ability to detect Earth-size planets in the habitable zone of other stars in the extended solar neighborhood. An Earth-size transit of a solar-like star causes a change in brightness of about 100 ppm. Laboratory testing has demonstrated that a total system noise level of 20 ppm is readily achievable on the timescale of transits. Earth-like transits have been created and reliably measured in an end-to-end system test that has all known sources of noise including, spacecraft jitter. To detect Earth-size planets, the photometer must be spaceborne; this also eliminates the day-night and seasonal cycle interruptions of ground-based observing. The photometer will stare at a single field of stars for four years, with an option to continue for two more years. This allows for detection of four transits of planets in Mars-like orbits and detection of planets even smaller than Earth especially for short period orbits, since the signal to noise improves as the square root of the number of transits observed. In addition to detection of planets, Kepler data are also useful for understanding the activity cycles and rotation rates of the stars observed. For the 3,000 stars brighter than mv= 11.4 p-mode oscillations are measured. The mission has been selected as one of three candidates for NASA's next Discovery mission.

A temperate rocky super-Earth transiting a nearby cool star.

PubMed

Dittmann, Jason A; Irwin, Jonathan M; Charbonneau, David; Bonfils, Xavier; Astudillo-Defru, Nicola; Haywood, Raphaëlle D; Berta-Thompson, Zachory K; Newton, Elisabeth R; Rodriguez, Joseph E; Winters, Jennifer G; Tan, Thiam-Guan; Almenara, Jose-Manuel; Bouchy, François; Delfosse, Xavier; Forveille, Thierry; Lovis, Christophe; Murgas, Felipe; Pepe, Francesco; Santos, Nuno C; Udry, Stephane; Wünsche, Anaël; Esquerdo, Gilbert A; Latham, David W; Dressing, Courtney D

2017-04-19

M dwarf stars, which have masses less than 60 per cent that of the Sun, make up 75 per cent of the population of the stars in the Galaxy. The atmospheres of orbiting Earth-sized planets are observationally accessible via transmission spectroscopy when the planets pass in front of these stars. Statistical results suggest that the nearest transiting Earth-sized planet in the liquid-water, habitable zone of an M dwarf star is probably around 10.5 parsecs away. A temperate planet has been discovered orbiting Proxima Centauri, the closest M dwarf, but it probably does not transit and its true mass is unknown. Seven Earth-sized planets transit the very low-mass star TRAPPIST-1, which is 12 parsecs away, but their masses and, particularly, their densities are poorly constrained. Here we report observations of LHS 1140b, a planet with a radius of 1.4 Earth radii transiting a small, cool star (LHS 1140) 12 parsecs away. We measure the mass of the planet to be 6.6 times that of Earth, consistent with a rocky bulk composition. LHS 1140b receives an insolation of 0.46 times that of Earth, placing it within the liquid-water, habitable zone. With 90 per cent confidence, we place an upper limit on the orbital eccentricity of 0.29. The circular orbit is unlikely to be the result of tides and therefore was probably present at formation. Given its large surface gravity and cool insolation, the planet may have retained its atmosphere despite the greater luminosity (compared to the present-day) of its host star in its youth. Because LHS 1140 is nearby, telescopes currently under construction might be able to search for specific atmospheric gases in the future.

K2 Finds Earth-Sized Planets Artist Concept

NASA Image and Video Library

2016-07-18

This artist's concept shows NASA's Kepler Space Telescope on its K2 mission. In July 2016, an international team of astronomers announced they had discovered more than 100 new planets using this telescope. The batch includes four planets in the size range of Earth that are orbiting a single dwarf star, depicted in this illustration. Two of these planets are too hot to support life as we know it, but two are in the star's "habitable" zone, where liquid water could exist on the surface. These small, rocky worlds are far closer to their star than Mercury is to our sun. But because the star is smaller and cooler than ours, its habitable zone is much closer. One of the two planets in the habitable zone, K2-72c, has a "year" about 15 Earth-days long -- the time it takes to complete one orbit. This closer planet is likely about 10 percent warmer than Earth. The slightly more distant planet in the habitable zone, K2-72e, has a year lasting 24 Earth days, and would be about 6 percent colder than Earth. http://photojournal.jpl.nasa.gov/catalog/PIA20698

Exploring the Effects of Stellar Multiplicity on Exoplanet Occurrence Rates

NASA Astrophysics Data System (ADS)

Barclay, Thomas; Shabram, Megan

2017-06-01

Determining the frequency of habitable worlds is a key goal of the Kepler mission. During Kepler's four year investigation it detected thousands of transiting exoplanets with sizes varying from smaller than Mercury to larger than Jupiter. Finding planets was just the first step to determining frequency, and for the past few years the mission team has been modeling the reliability and completeness of the Kepler planet sample. One effect that has not typically been built into occurrence rate statistics is that of stellar multiplicity. If a planet orbits the primary star in a binary or triple star system then the transit depth will be somewhat diluted resulting in a modest underestimation in the planet size. However, if a detected planet orbits a fainter star then the error in measured planet radius can be very significant. We have taken a hypothetical star and planet population and passed that through a Kepler detection model. From this we have derived completeness corrections for a realistic case of a Universe with binary stars and compared that with a model Universe where all stars are single. We report on the impact that binaries have on exoplanet population statistics.

A SUPER-EARTH-SIZED PLANET ORBITING IN OR NEAR THE HABITABLE ZONE AROUND A SUN-LIKE STAR

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

Barclay, Thomas; Burke, Christopher J.; Howell, Steve B.

We present the discovery of a super-Earth-sized planet in or near the habitable zone of a Sun-like star. The host is Kepler-69, a 13.7 mag G4V-type star. We detect two periodic sets of transit signals in the 3-year flux time series of Kepler-69, obtained with the Kepler spacecraft. Using the very high precision Kepler photometry, and follow-up observations, our confidence that these signals represent planetary transits is >99.3%. The inner planet, Kepler-69b, has a radius of 2.24{sup +0.44}{sub -0.29} R{sub Circled-Plus} and orbits the host star every 13.7 days. The outer planet, Kepler-69c, is a super-Earth-sized object with a radiusmore » of 1.7{sup +0.34}{sub -0.23} R{sub Circled-Plus} and an orbital period of 242.5 days. Assuming an Earth-like Bond albedo, Kepler-69c has an equilibrium temperature of 299 {+-} 19 K, which places the planet close to the habitable zone around the host star. This is the smallest planet found by Kepler to be orbiting in or near the habitable zone of a Sun-like star and represents an important step on the path to finding the first true Earth analog.« less

Stars and Planets: A New Set of Middle School Activities

NASA Technical Reports Server (NTRS)

Urquhart, M. L.

2002-01-01

A set of lesson plans for grades 6-8 which deal with the sizes and distances of stars and planets using a scale factor of 1 to 10 billion, the life cycle of stars, and the search for planets beyond the solar system. Additional information is contained in the original extended abstract.

Exploring exoplanet populations with NASA's Kepler Mission

NASA Astrophysics Data System (ADS)

Batalha, Natalie M.

2014-09-01

The Kepler Mission is exploring the diversity of planets and planetary systems. Its legacy will be a catalog of discoveries sufficient for computing planet occurrence rates as a function of size, orbital period, star type, and insolation flux. The mission has made significant progress toward achieving that goal. Over 3,500 transiting exoplanets have been identified from the analysis of the first 3 y of data, 100 planets of which are in the habitable zone. The catalog has a high reliability rate (85-90% averaged over the period/radius plane), which is improving as follow-up observations continue. Dynamical (e.g., velocimetry and transit timing) and statistical methods have confirmed and characterized hundreds of planets over a large range of sizes and compositions for both single- and multiple-star systems. Population studies suggest that planets abound in our galaxy and that small planets are particularly frequent. Here, I report on the progress Kepler has made measuring the prevalence of exoplanets orbiting within one astronomical unit of their host stars in support of the National Aeronautics and Space Administration's long-term goal of finding habitable environments beyond the solar system.

Exploring exoplanet populations with NASA's Kepler Mission.

PubMed

Batalha, Natalie M

2014-09-02

The Kepler Mission is exploring the diversity of planets and planetary systems. Its legacy will be a catalog of discoveries sufficient for computing planet occurrence rates as a function of size, orbital period, star type, and insolation flux. The mission has made significant progress toward achieving that goal. Over 3,500 transiting exoplanets have been identified from the analysis of the first 3 y of data, 100 planets of which are in the habitable zone. The catalog has a high reliability rate (85-90% averaged over the period/radius plane), which is improving as follow-up observations continue. Dynamical (e.g., velocimetry and transit timing) and statistical methods have confirmed and characterized hundreds of planets over a large range of sizes and compositions for both single- and multiple-star systems. Population studies suggest that planets abound in our galaxy and that small planets are particularly frequent. Here, I report on the progress Kepler has made measuring the prevalence of exoplanets orbiting within one astronomical unit of their host stars in support of the National Aeronautics and Space Administration's long-term goal of finding habitable environments beyond the solar system.

Report of the IAU/IAG Working Group on cartographic coordinates and rotational elements: 2006

USGS Publications Warehouse

Seidelmann, P.K.; Archinal, B.A.; A'Hearn, M.F.; Conrad, A.; Consolmagno, G.J.; Hestroffer, D.; Hilton, J.L.; Krasinsky, G.A.; Neumann, G.; Oberst, J.; Stooke, P.; Tedesco, E.F.; Tholen, D.J.; Thomas, P.C.; Williams, I.P.

2007-01-01

Every three years the IAU/IAG Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the directions of the poles of rotation and the prime meridians of the planets, satellites, minor planets, and comets. This report introduces improved values for the pole and rotation rate of Pluto, Charon, and Phoebe, the pole of Jupiter, the sizes and shapes of Saturn satellites and Charon, and the poles, rotation rates, and sizes of some minor planets and comets. A high precision realization for the pole and rotation rate of the Moon is provided. The expression for the Sun's rotation has been changed to be consistent with the planets and to account for light travel time ?? 2007 Springer Science+Business Media B.V.

Birth of an Unusual Planetary System

NASA Technical Reports Server (NTRS)

2005-01-01

This artist's animation shows a brown dwarf surrounded by a swirling disc of planet-building dust. NASA's Spitzer Space Telescope spotted such a disc around a surprisingly low-mass brown dwarf, or 'failed star.' The brown dwarf, called OTS 44, is only 15 times the size of Jupiter, making it the smallest brown dwarf known to host a planet-forming, or protoplanetary disc.

Astronomers believe that this unusual system will eventually spawn planets. If so, they speculate that OTS 44's disc has enough mass to make one small gas giant and a few Earth-sized rocky planets.

OTS 44 is about 2 million years old. At this relatively young age, brown dwarfs are warm and appear reddish in color. With age, they grow cooler and darker.

Habitability of Waterworlds: Runaway Greenhouses, Atmospheric Expansion, and Multiple Climate States of Pure Water Atmospheres

PubMed Central

2015-01-01

Abstract There are four different stable climate states for pure water atmospheres, as might exist on so-called “waterworlds.” I map these as a function of solar constant for planets ranging in size from Mars-sized to 10 Earth-mass. The states are as follows: globally ice covered (Ts⪅245 K), cold and damp (270⪅Ts⪅290 K), hot and moist (350⪅Ts⪅550 K), and very hot and dry (Tsx2A86;900 K). No stable climate exists for 290⪅Ts ⪅350 K or 550⪅Ts⪅900 K. The union of hot moist and cold damp climates describes the liquid water habitable zone, the width and location of which depends on planet mass. At each solar constant, two or three different climate states are stable. This is a consequence of strong nonlinearities in both thermal emission and the net absorption of sunlight. Across the range of planet sizes, I account for the atmospheres expanding to high altitudes as they warm. The emitting and absorbing surfaces (optical depth of unity) move to high altitude, making their area larger than the planet surface, so more thermal radiation is emitted and more sunlight absorbed (the former dominates). The atmospheres of small planets expand more due to weaker gravity; the effective runaway greenhouse threshold is about 35 W m−2 higher for Mars, 10 W m−2 higher for Earth or Venus, but only a few W m−2 higher for a 10 Earth-mass planet. There is an underlying (expansion-neglected) trend of increasing runaway greenhouse threshold with planetary size (40 W m−2 higher for a 10 Earth-mass planet than for Mars). Summing these opposing trends means that Venus-sized (or slightly smaller) planets are most susceptible to a runaway greenhouse. The habitable zone for pure water atmospheres is very narrow, with an insolation range of 0.07 times the solar constant. A wider habitable zone requires background gas and greenhouse gas: N2 and CO2 on Earth, which are biologically controlled. Thus, habitability depends on inhabitance. Key Words: Habitable zone—Runaway greenhouse—Waterworld—Climate. Astrobiology 15, 362–370. PMID:25984919

Captain Cook, the Terrestrial Planet Finder and the search for extraterrestrial intelligence

NASA Technical Reports Server (NTRS)

Beichman, C.

2002-01-01

A recently completed NASA study has concluded that a Terrestrial Planet Finder could be launched within a decade to detect terrestrial planets around nearby stars. Such a mission, complemented by projects (Kepler and Eddington) that will provide statistical information on the frequency of Earth-sized planets in the habitable zone, will determine key terms in the Drake equation that describes the number of intelligent civilizations in the Universe.

Analysis of a planetary-rotation system for evaporated optical coatings.

PubMed

Oliver, J B

2016-10-20

The impact of planetary design considerations for optical coating deposition is analyzed, including the ideal number of planets, variations in system performance, and the deviation of planet motion from the ideal. System capacity is maximized for four planets, although substrate size can significantly influence this result. Guidance is provided in the design of high-performance deposition systems based on the relative impact of different error modes. Errors in planet mounting such that the planet surface is not perpendicular to the axis of rotation are particularly problematic, suggesting planetary design modifications would be appropriate.

Band of Rubble

NASA Technical Reports Server (NTRS)

2005-01-01

This artist's animation illustrates a massive asteroid belt in orbit around a star the same age and size as our Sun. Evidence for this possible belt was discovered by NASA's Spitzer Space Telescope when it spotted warm dust around the star, presumably from asteroids smashing together.

The view starts from outside the belt, where planets like the one shown here might possibly reside, then moves into to the dusty belt itself. A collision between two asteroids is depicted near the end of the movie. Collisions like this replenish the dust in the asteroid belt, making it detectable to Spitzer.

The alien belt circles a faint, nearby star called HD 69830 located 41 light-years away in the constellation Puppis. Compared to our own solar system's asteroid belt, this one is larger and closer to its star - it is 25 times as massive, and lies just inside an orbit equivalent to that of Venus. Our asteroid belt circles between the orbits of Mars and Jupiter.

Because Jupiter acts as an outer wall to our asteroid belt, shepherding its debris into a series of bands, it is possible that an unseen planet is likewise marshalling this belt's rubble. Previous observations using the radial velocity technique did not locate any large gas giant planets, indicating that any planets present in this system would have to be the size of Saturn or smaller.

Asteroids are chunks of rock from 'failed' planets, which never managed to coalesce into full-sized planets. Asteroid belts can be thought of as construction sites that accompany the building of rocky planets.

A proposal for climate stability on H2-greenhouse planets

NASA Astrophysics Data System (ADS)

Abbot, D. S.

2015-12-01

A terrestrial planet in an orbit far outside of the standard habitable zone could maintain surface liquid water as a result of H2-H2 collision-induced absorption by a thick H2 atmosphere. Without a stabilizing climate feedback, however, habitability would be accidental and likely brief. We propose a stabilizing climate feedback for such a planet that requires only biological production of H2 to balance net loss to space that has some optimal temperature, and operates less efficiently at higher temperatures. A stable feedback is possible on such a planet through which a perturbation increasing temperature decreases H2 production, which decreases H2 greenhouse warming and therefore temperature. The potential of such a feedback makes H2-warmed planets more attractive astrobiological targets.

Runaway Growth During Planet Formation: Explaining the Size Distribution of Large Kuiper Belt Objects

NASA Astrophysics Data System (ADS)

Schlichting, Hilke E.; Sari, Re'em

2011-02-01

Runaway growth is an important stage in planet formation during which large protoplanets form, while most of the initial mass remains in small planetesimals. The amount of mass converted into large protoplanets and their resulting size distribution are not well understood. Here, we use analytic work, that we confirm by coagulation simulations, to describe runaway growth and the corresponding evolution of the velocity dispersion. We find that runaway growth proceeds as follows. Initially, all the mass resides in small planetesimals, with mass surface density σ, and large protoplanets start to form by accreting small planetesimals. This growth continues until growth by merging large protoplanets becomes comparable to growth by planetesimal accretion. This condition sets in when Σ/σ ~ α3/4 ~ 10-3, where Σ is the mass surface density in protoplanets in a given logarithmic mass interval and α is the ratio of the size of a body to its Hill radius. From then on, protoplanetary growth and the evolution of the velocity dispersion become self-similar and Σ remains roughly constant, since an increase in Σ by accretion of small planetesimals is balanced by a decrease due to merging with large protoplanets. We show that this growth leads to a protoplanet size distribution given by N(>R) vprop R -3, where N(>R) is the number of objects with radii greater than R (i.e., a differential power-law index of 4). Since only the largest bodies grow significantly during runaway growth, Σ and thereby the size distribution are preserved. We apply our results to the Kuiper Belt, which is a relic of runaway growth where planet formation never proceeded to completion. Our results successfully match the observed Kuiper Belt size distribution, they illuminate the physical processes that shaped it and explain the total mass that is present in large Kuiper Belt objects (KBOs) today. This work suggests that the current mass in large KBOs is primordial and that it has not been significantly depleted. We also predict a maximum mass ratio for Kuiper Belt binaries that formed by dynamical processes of α-1/4 ~ 10, which explains the observed clustering in binary companion sizes that is seen in the cold classical belt. Finally, our results also apply to growth in debris disks, as long as frequent planetesimal-planetesimal collisions are not important during the growth.

Collecting the Puzzle Pieces: Completing HST's UV+NIR Survey of the TRAPPIST-1 System ahead of JWST

NASA Astrophysics Data System (ADS)

de Wit, Julien

2017-08-01

Using the Spitzer Space Telescope, our team has discovered 7 Earth-sized planets around the nearby Ultra-cool dwarf star TRAPPIST-1. These planets are the first to be simultaneously Earth-sized, temperate, and amenable for in-depth atmospheric studies with space-based observatories (notably, JWST). TRAPPIST-1's system thus provides us with the first opportunity to probe the atmospheres of Earth-sized exoplanets and search for signs of habitability beyond our solar system, which will require spectral information from the UV to the IR to complete their atmospheric puzzles.We request 114 HST orbits to complete the UV+NIR survey of the 7 planets in preparation for their in-depth followup with JWST. The suggested low-density of the planets combined with their complex orbital resonance chain indicate that they migrated inward to their current positions and may harbor large water rich reservoir or leftover primordial H2 atmospheres. We have already ruled out the presence of clear H2 atmospheres for the 5 innermost planets using WFC3 and are requesting 16 WFC3 orbits to complete the TRAPPIST-1 NIR reconnaissance survey. Our primary request consists in 98 STIS orbits to complete the survey for extended H-exospheres around each of the planets. H-exospheres are the most accessible observables for volatile reservoirs, which have not been ruled out by our WFC3 observations. Exosphere detection is only amenable using HST unique capabilities in the UV and are pivotal to guide JWST's in-depth followup. The combined information from HST's UV and NIR observations will allow us put the first critical pieces of the atmospheric puzzle in place for these temperate earth-sized worlds.

Characterization of the planetary system Kepler-101 with HARPS-N. A hot super-Neptune with an Earth-sized low-mass companion

NASA Astrophysics Data System (ADS)

Bonomo, A. S.; Sozzetti, A.; Lovis, C.; Malavolta, L.; Rice, K.; Buchhave, L. A.; Sasselov, D.; Cameron, A. C.; Latham, D. W.; Molinari, E.; Pepe, F.; Udry, S.; Affer, L.; Charbonneau, D.; Cosentino, R.; Dressing, C. D.; Dumusque, X.; Figueira, P.; Fiorenzano, A. F. M.; Gettel, S.; Harutyunyan, A.; Haywood, R. D.; Horne, K.; Lopez-Morales, M.; Mayor, M.; Micela, G.; Motalebi, F.; Nascimbeni, V.; Phillips, D. F.; Piotto, G.; Pollacco, D.; Queloz, D.; Ségransan, D.; Szentgyorgyi, A.; Watson, C.

2014-12-01

We characterize the planetary system Kepler-101 by performing a combined differential evolution Markov chain Monte Carlo analysis of Kepler data and forty radial velocities obtained with the HARPS-N spectrograph. This system was previously validated and is composed of a hot super-Neptune, Kepler-101b, and an Earth-sized planet, Kepler-101c. These two planets orbit the slightly evolved and metal-rich G-type star in 3.49 and 6.03 days, respectively. With mass Mp = 51.1-4.7+ 5.1 M⊕, radius Rp = 5.77-0.79+ 0.85 R⊕, and density ρp = 1.45-0.48+ 0.83 g cm-3, Kepler-101b is the first fully characterized super-Neptune, and its density suggests that heavy elements make up a significant fraction of its interior; more than 60% of its total mass. Kepler-101c has a radius of 1.25-0.17+ 0.19 R⊕, which implies the absence of any H/He envelope, but its mass could not be determined because of the relative faintness of the parent star for highly precise radial-velocity measurements (Kp = 13.8) and the limited number of radial velocities. The 1σ upper limit, Mp< 3.8 M⊕, excludes a pure iron composition with a probability of 68.3%. The architecture of the planetary system Kepler-101 - containing a close-in giant planet and an outer Earth-sized planet with a period ratio slightly larger than the 3:2 resonance - is certainly of interest for scenarios of planet formation and evolution. This system does not follow thepreviously reported trend that the larger planet has the longer period in the majority of Kepler systems of planet pairs with at least one Neptune-sized or larger planet. Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.Table 2 is available in electronic form at http://www.aanda.org

Hubble Sees a “Behemoth” Bleeding Atmosphere Around a Warm Exoplanet

NASA Image and Video Library

2015-06-24

Astronomers using NASA’s Hubble Space Telescope have discovered an immense cloud of hydrogen dubbed “The Behemoth” bleeding from a planet orbiting a nearby star. The enormous, comet-like feature is about 50 times the size of the parent star. The hydrogen is evaporating from a warm, Neptune-sized planet, due to extreme radiation from the star. This phenomenon has never been seen around an exoplanet so small. It may offer clues to how other planets with hydrogen-enveloped atmospheres could have their outer layers evaporated by their parent star, leaving behind solid, rocky cores. Hot, rocky planets such as these that roughly the size of Earth are known as Hot-Super Earths. “This cloud is very spectacular, though the evaporation rate does not threaten the planet right now,” explains the study’s leader, David Ehrenreich of the Observatory of the University of Geneva in Switzerland. “But we know that in the past, the star, which is a faint red dwarf, was more active. This means that the planet evaporated faster during its first billion years of existence because of the strong radiation from the young star. Overall, we estimate that it may have lost up to 10 percent of its atmosphere over the past several billion years.” Read more: www.nasa.gov/feature/goddard/hubble-sees-a-behemoth-bleed... Caption: This artist's concept shows "The Behemoth," an enormous comet-like cloud of hydrogen bleeding off of a warm, Neptune-sized planet just 30 light-years from Earth. Also depicted is the parent star, which is a faint red dwarf named GJ 436. The hydrogen is evaporating from the planet due to extreme radiation from the star. A phenomenon this large has never before been seen around any exoplanet. Credits: NASA, ESA, and G. Bacon (STScI) NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

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

Gaidos, Eric, E-mail: gaidos@hawaii.edu

A key goal of the Kepler mission is the discovery of Earth-size transiting planets in ''habitable zones'' where stellar irradiance maintains a temperate climate on an Earth-like planet. Robust estimates of planet radius and irradiance require accurate stellar parameters, but most Kepler systems are faint, making spectroscopy difficult and prioritization of targets desirable. The parameters of 2035 host stars were estimated by Bayesian analysis and the probabilities p{sub HZ} that 2738 candidate or confirmed planets orbit in the habitable zone were calculated. Dartmouth Stellar Evolution Program models were compared to photometry from the Kepler Input Catalog, priors for stellar mass,more » age, metallicity and distance, and planet transit duration. The analysis yielded probability density functions for calculating confidence intervals of planet radius and stellar irradiance, as well as p{sub HZ}. Sixty-two planets have p{sub HZ} > 0.5 and a most probable stellar irradiance within habitable zone limits. Fourteen of these have radii less than twice the Earth; the objects most resembling Earth in terms of radius and irradiance are KOIs 2626.01 and 3010.01, which orbit late K/M-type dwarf stars. The fraction of Kepler dwarf stars with Earth-size planets in the habitable zone ({eta}{sub Circled-Plus }) is 0.46, with a 95% confidence interval of 0.31-0.64. Parallaxes from the Gaia mission will reduce uncertainties by more than a factor of five and permit definitive assignments of transiting planets to the habitable zones of Kepler stars.« less

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 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.

A Gap with a Deficit of Large Grains in the Protoplanetary Disk around TW Hya

NASA Astrophysics Data System (ADS)

Tsukagoshi, Takashi; Nomura, Hideko; Muto, Takayuki; Kawabe, Ryohei; Ishimoto, Daiki; Kanagawa, Kazuhiro D.; Okuzumi, Satoshi; Ida, Shigeru; Walsh, Catherine; Millar, T. J.

2016-10-01

We report ˜3 au resolution imaging observations of the protoplanetary disk around TW Hya at 145 and 233 GHz with the Atacama Large Millimeter/submillimeter Array. Our observations revealed two deep gaps (˜25%-50%) at 22 and 37 au and shallower gaps (a few percent) at 6, 28, and 44 au, as recently reported by Andrews et al. The central hole with a radius of ˜3 au was also marginally resolved. The most remarkable finding is that the spectral index α (R) between bands 4 and 6 peaks at the 22 au gap. The derived power-law index of the dust opacity β (R) is ˜1.7 at the 22 au gap and decreases toward the disk center to ˜0. The most prominent gap at 22 au could be caused by the gravitational interaction between the disk and an unseen planet with a mass of ≲1.5 M Neptune, although other origins may be possible. The planet-induced gap is supported by the fact that β (R) is enhanced at the 22 au gap, indicating a deficit of ˜millimeter-sized grains within the gap due to dust filtration by a planet.

NASA KEPLER OPENS THE STUDY OF THE GALAXY’S PLANET POPULATION

NASA Image and Video Library

2017-06-20

NASA's Kepler mission released its eighth Kepler Candidate Catalog, which contains the best measured and most reliable planet candidates from the space telescope's final survey of the Cygnus Field. In the data are 219 new planet candidates, of which 10 are less than twice the size of the Earth and orbit in the habitable zone.

Atmospheric reconnaissance of the habitable-zone Earth-sized planets orbiting TRAPPIST-1

NASA Astrophysics Data System (ADS)

de Wit, Julien; Wakeford, Hannah R.; Lewis, Nikole K.; Delrez, Laetitia; Gillon, Michaël; Selsis, Frank; Leconte, Jérémy; Demory, Brice-Olivier; Bolmont, Emeline; Bourrier, Vincent; Burgasser, Adam J.; Grimm, Simon; Jehin, Emmanuël; Lederer, Susan M.; Owen, James E.; Stamenković, Vlada; Triaud, Amaury H. M. J.

2018-03-01

Seven temperate Earth-sized exoplanets readily amenable for atmospheric studies transit the nearby ultracool dwarf star TRAPPIST-1 (refs 1,2). Their atmospheric regime is unknown and could range from extended primordial hydrogen-dominated to depleted atmospheres3-6. Hydrogen in particular is a powerful greenhouse gas that may prevent the habitability of inner planets while enabling the habitability of outer ones6-8. An atmosphere largely dominated by hydrogen, if cloud-free, should yield prominent spectroscopic signatures in the near-infrared detectable during transits. Observations of the innermost planets have ruled out such signatures9. However, the outermost planets are more likely to have sustained such a Neptune-like atmosphere10, 11. Here, we report observations for the four planets within or near the system's habitable zone, the circumstellar region where liquid water could exist on a planetary surface12-14. These planets do not exhibit prominent spectroscopic signatures at near-infrared wavelengths either, which rules out cloud-free hydrogen-dominated atmospheres for TRAPPIST-1 d, e and f, with significance of 8σ, 6σ and 4σ, respectively. Such an atmosphere is instead not excluded for planet g. As high-altitude clouds and hazes are not expected in hydrogen-dominated atmospheres around planets with such insolation15, 16, these observations further support their terrestrial and potentially habitable nature.

On the Nature of Small Planets around the Coolest Kepler Stars

NASA Astrophysics Data System (ADS)

Gaidos, Eric; Fischer, Debra A.; Mann, Andrew W.; Lépine, Sébastien

2012-02-01

We constrain the densities of Earth- to Neptune-size planets around very cool (Te = 3660-4660 K) Kepler stars by comparing 1202 Keck/HIRES radial velocity measurements of 150 nearby stars to a model based on Kepler candidate planet radii and a power-law mass-radius relation. Our analysis is based on the presumption that the planet populations around the two sets of stars are the same. The model can reproduce the observed distribution of radial velocity variation over a range of parameter values, but, for the expected level of Doppler systematic error, the highest Kolmogorov-Smirnov probabilities occur for a power-law index α ≈ 4, indicating that rocky-metal planets dominate the planet population in this size range. A single population of gas-rich, low-density planets with α = 2 is ruled out unless our Doppler errors are >=5 m s-1, i.e., much larger than expected based on observations and stellar chromospheric emission. If small planets are a mix of γ rocky planets (α = 3.85) and 1 - γ gas-rich planets (α = 2), then γ > 0.5 unless Doppler errors are >=4 m s-1. Our comparison also suggests that Kepler's detection efficiency relative to ideal calculations is less than unity. One possible source of incompleteness is target stars that are misclassified subgiants or giants, for which the transits of small planets would be impossible to detect. Our results are robust to systematic effects, and plausible errors in the estimated radii of Kepler stars have only moderate impact. Some data were obtained at the W. M. Keck Observatory, which is operated by the California Institute of Technology, the University of California, and NASA, and made possible by the financial support of the W. M. Keck Foundation.

Our Solar System Features Eight Planets

NASA Technical Reports Server (NTRS)

2009-01-01

Our solar system features eight planets, seen in this artist's diagram. Although there is some debate within the science community as to whether Pluto should be classified as a Planet or a dwarf planet, the International Astronomical Union has decided on the term plutoid as a name for dwarf planets like Pluto.

This representation is intentionally fanciful, as the planets are depicted far closer together than they really are. Similarly, the bodies' relative sizes are inaccurate. This is done for the purpose of being able to depict the solar system and still represent the bodies with some detail. (Otherwise the Sun would be a mere speck, and the planets even the majestic Jupiter would be far too small to be seen.)

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

Editorial: Special issue “Planetary evolution and life”

NASA Astrophysics Data System (ADS)

Spohn, Tilman

2014-08-01

Given the enormous number of stars in the universe and the number of confirmed and postulated planets in our galaxy, it is generally agreed that our home planet Earth is not likely to be unique (e.g., Sagan, 1980; Bignami et al., 2005; Hawking and Mlodinow, 2010). But is it? Although the number of known extrasolar planets grows almost by the day, observational bias caused by the technological challenges of finding Earth-size, rocky extrasolar planets and determining their masses and sizes have thus far prohibited the detection of a second Earth. But even if a second Earth were to be found-located in what is termed the habitable zone (e.g., Kasting et al., 1993)-can we expect that life would have originated there and have evolved beyond the most primitive forms? Is the universe "bio-friendly" as Paul Davies said (cited after Sullivan and Baross, 2007) using the Anthropic Principle (Barrow and Tipler, 1986) or is the origin of life so complex and our home planet so peculiar (Ward and Brownlee, 2000) that we are the unlikely product of a chain of unlikely events (Gould, 1989)? And if life existed on a second Earth or on many other planets, would we be able to detect it? Would life have shaped these planets such as life has shaped the Earth?

A metallicity recipe for rocky planets

NASA Astrophysics Data System (ADS)

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

2015-10-01

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

Scenarios for the Evolution of Asteroid Belts

NASA Image and Video Library

2012-11-01

This illustration shows three possible scenarios for the evolution of asteroid belts. At the top, a Jupiter-size planet migrates through the asteroid belt, scattering material and inhibiting the formation of life on planets.

Detailed Abundances of Stars with Small Planets Discovered by Kepler. I. The First Sample

NASA Astrophysics Data System (ADS)

Schuler, Simon C.; Vaz, Zachary A.; Katime Santrich, Orlando J.; Cunha, Katia; Smith, Verne V.; King, Jeremy R.; Teske, Johanna K.; Ghezzi, Luan; Howell, Steve B.; Isaacson, Howard

2015-12-01

We present newly derived stellar parameters and the detailed abundances of 19 elements of seven stars with small planets discovered by NASA's Kepler Mission. Each star, save one, has at least one planet with a radius ≤1.6 R⊕, suggesting a primarily rocky composition. The stellar parameters and abundances are derived from high signal-to-noise ratio, high-resolution echelle spectroscopy obtained with the 10 m Keck I telescope and High Resolution Echelle Spectrometer using standard spectroscopic techniques. The metallicities of the seven stars range from -0.32 to +0.13 dex, with an average metallicity that is subsolar, supporting previous suggestions that, unlike Jupiter-type giant planets, small planets do not form preferentially around metal-rich stars. The abundances of elements other than iron are in line with a population of Galactic disk stars, and despite our modest sample size, we find hints that the compositions of stars with small planets are similar to stars without known planets and with Neptune-size planets, but not to those of stars with giant planets. This suggests that the formation of small planets does not require exceptional host-star compositions and that small planets may be ubiquitous in the Galaxy. We compare our derived abundances (which have typical uncertainties of ≲0.04 dex) to the condensation temperature of the elements; a correlation between the two has been suggested as a possible signature of rocky planet formation. None of the stars demonstrate the putative rocky planet signature, despite at least three of the stars having rocky planets estimated to contain enough refractory material to produce the signature, if real. More detailed abundance analyses of stars known to host small planets are needed to verify our results and place ever more stringent constraints on planet formation models. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.

Changes in the metallicity of gas giant planets due to pebble accretion

NASA Astrophysics Data System (ADS)

Humphries, R. J.; Nayakshin, S.

2018-06-01

We run numerical simulations to study the accretion of gas and dust grains on to gas giant planets embedded into massive protoplanetary discs. The outcome is found to depend on the disc cooling rate, planet mass, grain size, and irradiative feedback from the planet. If radiative cooling is efficient, planets accrete both gas and pebbles rapidly, open a gap, and usually become massive brown dwarfs. In the inefficient cooling case, gas is too hot to accrete on to the planet but pebble accretion continues and the planets migrate inward rapidly. Radiative feedback from the planet tends to suppress gas accretion. Our simulations predict that metal enrichment of planets by dust grain accretion inversely correlates with the final planet mass, in accordance with the observed trend in the inferred bulk composition of Solar system and exosolar giant planets. To account for observations, however, as many as ˜30-50 per cent of the dust mass should be in the form of large grains.

Dynamics of exoplanetary systems, links to their habitability

NASA Astrophysics Data System (ADS)

Bolmont, E.; Raymond, S. N.; Selsis, F.

2014-12-01

Our knowledge of planets' orbital dynamics, which was based on Solar System studies, has been challenged by the diversity of exoplanetary systems. Around cool and ultra cool dwarfs, the influence of tides on the orbital and spin evolution of planets can strongly affect their climate and their capacity to host surface liquid water. We illustrate the role of tides and dynamics with the extreme case of planets orbiting around brown dwarfs. In multiple planet systems, the eccentricity is excited by planet-planet interactions. Planets are therefore heated up from the inside by the tidally-induced friction. This process can heat a habitable zone planet to such a level that surface liquid water cannot exist. We also talk about the newly discovered potentially habitable Earth-sized planet Kepler-186f. Given the poorly estimated age of the system, the planet could still be evolving towards synchronization and have a high obliquity or be pseudo-synchronized with a zero obliquity. These two configurations would have a different effect on the climate of this planet.

Precisely measuring the density of small transiting exoplanets with particular emphasis on longer period planet using the HARPS-N spectrograph

NASA Astrophysics Data System (ADS)

Buchhave, Lars A.

2015-08-01

The majority of exoplanets discovered by the Kepler Mission have sizes that range between 1-4 Earth radii, populating a regime of planets with no Solar System analogues. This regime is critical for understanding the frequency of potentially habitable worlds and to help inform planet formation theories, because it contains the transition from lower-density planets with extended H/He envelopes to higher-density rocky planets with compact atmospheres. HARPS-N is an ultra-stable high-resolution spectrograph optimized for the measurement of precise radial velocities, yielding precise planetary masses and thus densities of small transiting exoplanets. In this talk, I will review the progress to populate the mass-radius parameter space with precisely measured densities of small planets. I will in particular focus on the latest HARPS-N results and their implication for our understanding of these super-Earth and small Neptune type planets.Additionally, I will discuss our progress to measure the masses of longer period sub-Neptune sized planets. In Buchhave el al. 2014, we found suggestive observational evidence that the transition from rocky to gaseous planets might depend on the orbital period, such that larger planets further away from their host star could be massive planets without a large gaseous envelope. To test this hypothesis, we have used HARPS-N to observe longer period planet candidates to determine whether they are in fact massive rocky planets or if they have extended H/He envelopes and thus lower bulk densities.HARPS-N at the Telescopio Nazionale Galileo, La Palma is an international collaboration and was funded by the Swiss Space Office, the Harvard Origin of Life Initiative, the Scottish Universities Physics Alliance, the University of Geneva, the Smithsonian Astrophysical Observatory, and the Italian National Astrophysical Institute, University of St. Andrews, Queens University Belfast, and University of Edinburgh.

Analysis of a planetary-rotation system for evaporated optical coatings

DOE PAGES

Oliver, J. B.

2016-01-01

The impact of planetary-design considerations for optical coating deposition is analyzed, including the ideal number of planets, variations in system performance, and the deviation of planet motion from the ideal. System capacity is maximized for four planets, although substrate size can significantly influence this result. Guidance is provided in the design of high-performance deposition systems based on the relative impact of different error modes. As a result, errors in planet mounting such that the planet surface is not perpendicular to its axis of rotation are particularly problematic, suggesting planetary design modifications would be appropriate.

Young Star and Its Infant Planet (Artist animation)

NASA Image and Video Library

2016-06-20

When a planet such as K2-33b passes in front of its host star, it blocks some of the star's light. Observing this periodic dimming, called a transit, from continual monitoring of a star's brightness, allows astronomers to detect planets outside our solar system with a high degree of certainty. This Neptune-sized planet orbits a star that is between 5 and 10 million years old. In addition to the planet, the star hosts a disk of planetary debris, seen as a bright ring encircling the star. An animation is available at: http://photojournal.jpl.nasa.gov/catalog/PIA20692

The Case of the Tail Wagging the Dog: HD 189733 - Evidence of Hot Jupiter Exoplanets Spinning-up Their Host Stars

NASA Astrophysics Data System (ADS)

Guinan, E. F.

2013-06-01

(Abstract only) HD 189733A is an eighth mag K1.5V star that has attracted much attention because it hosts a short period, transiting, hot-Jupiter planet. This planet, HD 189733b, has one of the shortest known orbital periods (P = 2.22 days) and is only 0.031 AU from its host star. Because the system undergoes eclipses and is bright, HD 189733 has been extensively studied. The planet's atmosphere has been found to contain water vapor, methane, CO2, and sodium and possible haze. Spitzer IR observations indicate planet temperature, varying ~970 K to ~1,200 K over its surface (Tinetti (2007). Based on measurements of the K-star's P(rot) from starspot modulations of ~11.95 d, strong coronal X-ray emission and chromospheric Ca II-HK emission indicate a young age of ~0.7 Gyr. But this apparent young age is discrepant with a much older age (> 4 Gyr) inferred from the star's very low Lithium abundance. However, the age of the HD 189733 system can be independently determined by the presence of a faint dM4 companion (HD 189733B) some 12" away. Our Age-Activity relations for this star (no detectable coronal X-ray emission and no H-alpha emission) indicate an age > 4 Gyr (and < 8 Gyr from kinematics and metallicity). This age should apply to its K star companion and its planet. The fast rotation and resultant high activity levels of the K star can best be explained from the increase in its (rotation) angular momentum (AM) from the orbital AM of the planet. This AM transfer occurs from tidal and magnetic interactions of the K star with its planet. Determining the possible decrease in the planet's orbital period is possible from studying the planet eclipse times (which can be done by AAVSO members with CCD photometry). We also discuss the properties of other related short-period exoplanet systems found by the Kepler Mission that show similar behavior - in that close-in hot Jupiter size planets appear to be physically interacting with their host stars. This work is supported by NSF/RUI grant AST-1009903.

How Do Earth-Sized, Short-Period Planets Form?

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-08-01

Matching theory to observation often requires creative detective work. In a new study, scientists have used a clever test to reveal clues about the birth of speedy, Earth-sized planets.Former Hot Jupiters?Artists impression of a hot Jupiter with an evaporating atmosphere. [NASA/Ames/JPL-Caltech]Among the many different types of exoplanets weve observed, one unusual category is that of ultra-short-period planets. These roughly Earth-sized planets speed around their host stars at incredible rates, with periods of less than a day.How do planets in this odd category form? One popular theory is that they were previously hot Jupiters, especially massive gas giants orbiting very close to their host stars. The close orbit caused the planets atmospheres to be stripped away, leaving behind only their dense cores.In a new study, a team of astronomers led by Joshua Winn (Princeton University) has found a clever way to test this theory.Planetary radius vs. orbital period for the authors three statistical samples (colored markers) and the broader sample of stars in the California Kepler Survey. [Winn et al. 2017]Testing MetallicitiesStars hosting hot Jupiters have an interesting quirk: they typically have metallicities that are significantly higher than an average planet-hosting star. It is speculated that this is because planets are born from the same materials as their host stars, and hot Jupiters require the presence of more metals to be able to form.Regardless of the cause of this trend, if ultra-short-period planets are in fact the solid cores of former hot Jupiters, then the two categories of planets should have hosts with the same metallicity distributions. The ultra-short-period-planet hosts should therefore also be weighted to higher metallicities than average planet-hosting stars.To test this, the authors make spectroscopic measurements and gather data for a sample of stellar hosts split into three categories:64 ultra-short-period planets (orbital period shorter than a day)23 hot Jupiters (larger than 4 times Earths radius and orbital period shorter than 10 days)243 small hot planets (smaller than 4 times Earths radius and orbital period between 1 and 10 days)They then compare the metallicity distributions of these three groups.Back to the Drawing BoardMetallicity distributions of the three statistical samples. The hot-Jupiter hosts (orange) have different distribution than the others; it is weighted more toward higher metallicities. [Winn et al. 2017]Winn and collaborators find that hosts of ultra-short-period planets do not have the same metallicity distribution as hot-Jupiter hosts; the metallicities of hot-Jupiter hosts are significantly higher. The metallicity distributions for hosts of ultra-short-period planets and hosts of small hot planets were statistically indistinguishable, however.These results strongly suggest that the majority of ultra-short-period planets are not the cores of former hot Jupiters. Alternative options include the possibility that they are the cores of smaller planets, such as sub-Neptunes, or that they are the short-period extension of the distribution of close-in, small rocky planets that formed by core accretion.This narrowing of the options for the formation of ultra-short-period planets is certainly intriguing. We can hope to further explore possibilities in the future after the Transiting Exoplanet Survey Satellites (TESS) comes online next year; TESS is expected to discover many more ultra-short-period planets that are too faint for Kepler to detect.CitationJoshua N. Winn et al 2017 AJ 154 60. doi:10.3847/1538-3881/aa7b7c

About the Linguistic Impossibility of Claiming that Small Planets are not Planets

NASA Astrophysics Data System (ADS)

Nedeljkovic, A. B.

2012-12-01

Philology, which is, the science of language and literature, must now offer assistance to the science of astronomy, about one question of terminology and logic. Namely, if something belongs to one category, then it is, regardless of its size (large, or medium, or small) a member of that category. Therefore, it was linguistically wrong to claim that Pluto is one of the dwarf planets and therefore not a planet. This mistake, much noticed by the world's public opinion, ought to be corrected immediately.

NASA's Kepler Mission Discovers Its Smallest Habitable Zone Planets (Reporter Pkg)

NASA Image and Video Library

2013-04-18

NASA's Kepler mission has discovered two new planetary systems that include three super-Earth-size planets in the 'habitable zone,' the range of distance from a star where the surface temperature of an orbiting planet might be suitable for liquid water. Scientists do not know whether life could exist on the newfound planets, but their discovery signals we are another step closer to finding a world similar to Earth around a star like our sun. Kepler-62 and -69 systems

The symbiosis of photometry and radial-velocity measurements

NASA Technical Reports Server (NTRS)

Cochran, William D.

1994-01-01

The FRESIP mission is optimized to detect the inner planets of a planetary system. According to the current paradigm of planet formation, these planets will probably be small Earth-sized objects. Ground-based radial-velocity programs now have the sensitivity to detect Jovian-mass planets in orbit around bright solar-type stars. We expect the more massive planets to form in the outer regions of a proto-stellar nebula. These two types of measurements will very nicely complement each other, as they have highest detection probability for very different types of planets. The combination of FRESIP photometry and ground-based spectra will provide independent confirmation of the existence of planetary systems in orbit around other stars. Such detection of both terrestrial and Jovian planets in orbit around the same star is essential to test our understanding of planet formation.

Habitability of planets around red dwarf stars.

PubMed

Heath, M J; Doyle, L R; Joshi, M M; Haberle, R M

1999-08-01

Recent models indicate that relatively moderate climates could exist on Earth-sized planets in synchronous rotation around red dwarf stars. Investigation of the global water cycle, availability of photosynthetically active radiation in red dwarf sunlight, and the biological implications of stellar flares, which can be frequent for red dwarfs, suggests that higher plant habitability of red dwarf planets may be possible.

When Push Comes to Shove: Gap-opening, Disk Clearing and the In Situ Formation of Giant Planets

NASA Technical Reports Server (NTRS)

Mosqueira, I.; Estrada, P. R.

2004-01-01

Here we investigate a scenario in which cores as small as a few Earth masses stall in the terrestrial planet region, but continue to grow as a result of the Type I migration of other Earth sized objects, taking place in a timescale approx. 10(exp 6) years similar to the disk clearing timescale (such migration may thus significantly reduce the accretion efficiency, particularly in the terrestrial planet region). Since the core may intercept such inwardly migrating objects (possibly by altering the surface density to the point that the object stalls within the core's feeding zone) or coalesce with neighboring cores, its growth may continue until it reaches a CCM. The question then arises whether such a core can accrete enough gas to become a Jovian-sized giant planet. In the limit of low opacity (such that the protoplanet s tidal torque fails to clear gas from its feeding zone in time to prevent its accretion), the final mass of the planet is given by the gaseous isolation mass (provided alpha is < or approx. = 10(exp -4) and that the gas component dominates the planet's mass).

Exploring exoplanet populations with NASA’s Kepler Mission

PubMed Central

Batalha, Natalie M.

2014-01-01

The Kepler Mission is exploring the diversity of planets and planetary systems. Its legacy will be a catalog of discoveries sufficient for computing planet occurrence rates as a function of size, orbital period, star type, and insolation flux. The mission has made significant progress toward achieving that goal. Over 3,500 transiting exoplanets have been identified from the analysis of the first 3 y of data, 100 planets of which are in the habitable zone. The catalog has a high reliability rate (85–90% averaged over the period/radius plane), which is improving as follow-up observations continue. Dynamical (e.g., velocimetry and transit timing) and statistical methods have confirmed and characterized hundreds of planets over a large range of sizes and compositions for both single- and multiple-star systems. Population studies suggest that planets abound in our galaxy and that small planets are particularly frequent. Here, I report on the progress Kepler has made measuring the prevalence of exoplanets orbiting within one astronomical unit of their host stars in support of the National Aeronautics and Space Administration’s long-term goal of finding habitable environments beyond the solar system. PMID:25049406

Mars’ Growth Stunted by an Early Giant Planet Instability

NASA Astrophysics Data System (ADS)

Clement, Matthew; Kaib, Nathan A.; Raymond, Sean N.; Walsh, Kevin J.

2017-10-01

Many dynamical aspects of the solar system can be explained by the outer planets experiencing a period of orbital instability. Though often correlated with a perceived delayed spike in the lunar cratering record known as the Late Heavy Bombardment (LHB), recent work suggests that this event may have occurred during the epoch of terrestrial planet formation. Though current simulations of terrestrial accretion can reproduce many observed qualities of the solar system, replicating the small mass of Mars requires modification to standard planet formation models. Here we use direct numerical simulations to show that an early instability in the outer solar system regularly yields properly sized Mars analogues. In 80% of simulations, we produce a Mars of the appropriate mass. Our most successful outcomes occur when the terrestrial planets evolve 10 million years (Myr), and accrete several Mars sized embryos in the Mars forming region before the instability takes place. Mars is left behind as a stranded embryo, while the remainder of these bodies are either ejected from the system or scattered towards the inner solar system where they deliver water to Earth. An early giant planet instability can thus replicate both the inner and outer solar system in a single model.

Transit detection of a `starshade' at the inner lagrange point of an exoplanet

NASA Astrophysics Data System (ADS)

Gaidos, E.

2017-08-01

All water-covered rocky planets in the inner habitable zones of solar-type stars will inevitably experience a catastrophic runaway climate due to increasing stellar luminosity and limits to outgoing infrared radiation from wet greenhouse atmospheres. Reflectors or scatterers placed near Earth's inner Lagrange point (L_1) have been proposed as a "geoengineering' solution to anthropogenic climate change and an advanced version of this could modulate incident irradiation over many Gyr or `rescue' a planet from the interior of the habitable zone. The distance of the starshade from the planet that minimizes its mass is 1.6 times the Earth-L_1 distance. Such a starshade would have to be similar in size to the planet and the mutual occultations during planetary transits could produce a characteristic maximum at mid-transit in the light curve. Because of a fortuitous ratio of densities, Earth-size planets around G dwarf stars present the best opportunity to detect such an artefact. The signal would be persistent and is potentially detectable by a future space photometry mission to characterize transiting planets. The signal could be distinguished from natural phenomenon, I.e. starspots or cometary dust clouds, by its shape, persistence and transmission spectrum.

Possible Disintegrating Planet Artist Concept

NASA Image and Video Library

2012-05-21

This artist concept depicts a comet-like tail of a possible disintegrating super Mercury-size planet candidate as it transits, or crosses, its parent star, named KIC 12557548. The results are based on data from NASA Kepler mission.

An Unusual Planetary System Artist Concept

NASA Image and Video Library

2011-12-20

This still from an artist animation flies through the Kepler-20 star system, where NASA Kepler mission discovered the first Earth-size planets around a star beyond our own. The system is jam-packed with five planets.

Lower Limits on Aperture Size for an ExoEarth Detecting Coronagraphic Mission

NASA Technical Reports Server (NTRS)

Stark, Christopher C.; Roberge, Aki; Mandell, Avi; Clampin, Mark; Domagal-Goldman, Shawn D.; McElwain, Michael W.; Stapelfeldt, Karl R.

2015-01-01

The yield of Earth-like planets will likely be a primary science metric for future space-based missions that will drive telescope aperture size. Maximizing the exoEarth candidate yield is therefore critical to minimizing the required aperture. Here we describe a method for exoEarth candidate yield maximization that simultaneously optimizes, for the first time, the targets chosen for observation, the number of visits to each target, the delay time between visits, and the exposure time of every observation. This code calculates both the detection time and multiwavelength spectral characterization time required for planets. We also refine the astrophysical assumptions used as inputs to these calculations, relying on published estimates of planetary occurrence rates as well as theoretical and observational constraints on terrestrial planet sizes and classical habitable zones. Given these astrophysical assumptions, optimistic telescope and instrument assumptions, and our new completeness code that produces the highest yields to date, we suggest lower limits on the aperture size required to detect and characterize a statistically motivated sample of exoEarths.

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

NASA Technical Reports Server (NTRS)

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

1994-01-01

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

Ground-based detectability of terrestrial and Jovian extrasolar planets: observations of CM Draconis at Lick Observatory.

PubMed

Doyle, L R; Dunham, E T; Deeg, H J; Blue, J E; Jenkins, J M

1996-06-25

The detection of terrestrial-sized extrasolar planets from the ground has been thought to be virtually impossible due to atmospheric scintillation limits. However, we show that this is not the case especially selected (but nevertheless main sequence) stars, namely small eclipsing binaries. For the smallest of these systems, CM Draconis, several months to a few years of photometric observations with 1-m-class telescopes will be sufficient to detect the transits of any short-period planets of sizes > or = 1.5 Earth radii (RE), using cross-correlation analysis with moderately good photometry. Somewhat larger telescopes will be needed to extend this detectability to terrestrial planets in larger eclipsing binary systems. (We arbitrarily define "terrestrial planets" herein as those whose disc areas are closer to that of Earth's than Neptune's i.e., less than about 2.78 RE.) As a "spin-off" of such observations, we will also be able to detect the presence of Jovian-mass planets without transits using the timing of the eclipse minima. Eclipse minima will drift in time as the binary system is offset by a sufficiently massive planet (i.e., one Jupiter mass) about the binary/giant-planet barycenter, causing a periodic variation in the light travel time to the observer. We present here an outline of present observations taking place at the University of California Lick Observatory using the Crossley 0.9-m telescope in collaboration with other observatories (in South Korea, Crete, France, Canary Islands, and New York) to detect or constrain the existence of terrestrial planets around main sequence eclipsing binary star systems, starting with CM Draconis. We demonstrate the applicability of photometric data to the general detection of gas giant planets via eclipse minima timings in many other small-mass eclipsing binary systems as well.

Ground-based detectability of terrestrial and Jovian extrasolar planets: observations of CM Draconis at Lick Observatory

NASA Technical Reports Server (NTRS)

Doyle, L. R.; Dunham, E. T.; Deeg, H. J.; Blue, J. E.; Jenkins, J. M.

1996-01-01

The detection of terrestrial-sized extrasolar planets from the ground has been thought to be virtually impossible due to atmospheric scintillation limits. However, we show that this is not the case especially selected (but nevertheless main sequence) stars, namely small eclipsing binaries. For the smallest of these systems, CM Draconis, several months to a few years of photometric observations with 1-m-class telescopes will be sufficient to detect the transits of any short-period planets of sizes > or = 1.5 Earth radii (RE), using cross-correlation analysis with moderately good photometry. Somewhat larger telescopes will be needed to extend this detectability to terrestrial planets in larger eclipsing binary systems. (We arbitrarily define "terrestrial planets" herein as those whose disc areas are closer to that of Earth's than Neptune's i.e., less than about 2.78 RE.) As a "spin-off" of such observations, we will also be able to detect the presence of Jovian-mass planets without transits using the timing of the eclipse minima. Eclipse minima will drift in time as the binary system is offset by a sufficiently massive planet (i.e., one Jupiter mass) about the binary/giant-planet barycenter, causing a periodic variation in the light travel time to the observer. We present here an outline of present observations taking place at the University of California Lick Observatory using the Crossley 0.9-m telescope in collaboration with other observatories (in South Korea, Crete, France, Canary Islands, and New York) to detect or constrain the existence of terrestrial planets around main sequence eclipsing binary star systems, starting with CM Draconis. We demonstrate the applicability of photometric data to the general detection of gas giant planets via eclipse minima timings in many other small-mass eclipsing binary systems as well.

Observing the Atmospheres of Known Temperate Earth-sized Planets with JWST

NASA Astrophysics Data System (ADS)

Morley, Caroline V.; Kreidberg, Laura; Rustamkulov, Zafar; Robinson, Tyler; Fortney, Jonathan J.

2017-12-01

Nine transiting Earth-sized planets have recently been discovered around nearby late-M dwarfs, including the TRAPPIST-1 planets and two planets discovered by the MEarth survey, GJ 1132b and LHS 1140b. These planets are the smallest known planets that may have atmospheres amenable to detection with the James Webb Space Telescope (JWST). We present model thermal emission and transmission spectra for each planet, varying composition and surface pressure of the atmosphere. We base elemental compositions on those of Earth, Titan, and Venus and calculate the molecular compositions assuming chemical equilibrium, which can strongly depend on temperature. Both thermal emission and transmission spectra are sensitive to the atmospheric composition; thermal emission spectra are sensitive to surface pressure and temperature. We predict the observability of each planet’s atmosphere with JWST. GJ 1132b and TRAPPIST-1b are excellent targets for emission spectroscopy with JWST/MIRI, requiring fewer than 10 eclipse observations. Emission photometry for TRAPPIST-1c requires 5-15 eclipses; LHS 1140b and TRAPPIST-1d, TRAPPIST-1e, and TRAPPIST-1f, which could possibly have surface liquid water, may be accessible with photometry. Seven of the nine planets are strong candidates for transmission spectroscopy measurements with JWST, although the number of transits required depends strongly on the planets’ actual masses. Using the measured masses, fewer than 20 transits are required for a 5σ detection of spectral features for GJ 1132b and six of the TRAPPIST-1 planets. Dedicated campaigns to measure the atmospheres of these nine planets will allow us, for the first time, to probe formation and evolution processes of terrestrial planetary atmospheres beyond our solar system.

Artist Impression of Hot

NASA Image and Video Library

2015-12-14

This image shows an artist's impression of the 10 hot Jupiter exoplanets studied using the Hubble and Spitzer space telescopes. From top left to lower left, these planets are WASP-12b, WASP-6b, WASP-31b, WASP-39b, HD 189733b, HAT-P-12b, WASP-17b, WASP-19b, HAT-P-1b and HD 209458b. The colors of the planets are for illustration purposes only. There is little scientific data on color with the exception of HD 189733b, which became known as the "blue planet." The planets are also depicted with a variety of different cloud properties. The wind patterns shown on these 10 planets, which resemble the visible structures on Jupiter, are based on theoretical models. The illustrations are to scale with each other. HAT-P-12b, the smallest of these planets, is approximately the size of Jupiter, while WASP-17b, the largest one in the sample, is almost twice the size. The hottest planets within the sample are portrayed with a glowing night side. This effect is strongest on WASP-12b, the hottest exoplanet in the sample, but also visible on WASP-19b and WASP-17b. It is also known that several of the planets exhibit strong Rayleigh scattering. This effect causes the blue hue of the daytime sky and the reddening of the sun at sunset on Earth. It is also visible as a blue edge on the planets WASP-6b, HD 189733b, HAT-P-12b and HD 209458b. http://photojournal.jpl.nasa.gov/catalog/PIA20056

Water-rich planets: How habitable is a water layer deeper than on Earth?

NASA Astrophysics Data System (ADS)

Noack, L.; Höning, D.; Rivoldini, A.; Heistracher, C.; Zimov, N.; Journaux, B.; Lammer, H.; Van Hoolst, T.; Bredehöft, J. H.

2016-10-01

Water is necessary for the origin and survival of life as we know it. In the search for life-friendly worlds, water-rich planets therefore are obvious candidates and have attracted increasing attention in recent years. The surface H2O layer on such planets (containing a liquid water ocean and possibly high-pressure ice below a specific depth) could potentially be hundreds of kilometres deep depending on the water content and the evolution of the proto-atmosphere. We study possible constraints for the habitability of deep water layers and introduce a new habitability classification relevant for water-rich planets (from Mars-size to super-Earth-size planets). A new ocean model has been developed that is coupled to a thermal evolution model of the mantle and core. Our interior structure model takes into account depth-dependent thermodynamic properties and the possible formation of high-pressure ice. We find that heat flowing out of the silicate mantle can melt an ice layer from below (in some cases episodically), depending mainly on the thickness of the ocean-ice shell, the mass of the planet, the surface temperature and the interior parameters (e.g. radioactive mantle heat sources). The high pressure at the bottom of deep water-ice layers could also impede volcanism at the water-mantle boundary for both stagnant lid and plate tectonics silicate shells. We conclude that water-rich planets with a deep ocean, a large planet mass, a high average density or a low surface temperature are likely less habitable than planets with an Earth-like ocean.

PLANET HUNTERS. V. A CONFIRMED JUPITER-SIZE PLANET IN THE HABITABLE ZONE AND 42 PLANET CANDIDATES FROM THE KEPLER ARCHIVE DATA

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

Wang, Ji; Fischer, Debra A.; Boyajian, Tabetha S.

We report the latest Planet Hunter results, including PH2 b, a Jupiter-size (R{sub PL} = 10.12 ± 0.56 R{sub ⊕}) planet orbiting in the habitable zone of a solar-type star. PH2 b was elevated from candidate status when a series of false-positive tests yielded a 99.9% confidence level that transit events detected around the star KIC 12735740 had a planetary origin. Planet Hunter volunteers have also discovered 42 new planet candidates in the Kepler public archive data, of which 33 have at least 3 transits recorded. Most of these transit candidates have orbital periods longer than 100 days and 20more » are potentially located in the habitable zones of their host stars. Nine candidates were detected with only two transit events and the prospective periods are longer than 400 days. The photometric models suggest that these objects have radii that range between those of Neptune and Jupiter. These detections nearly double the number of gas-giant planet candidates orbiting at habitable-zone distances. We conducted spectroscopic observations for nine of the brighter targets to improve the stellar parameters and we obtained adaptive optics imaging for four of the stars to search for blended background or foreground stars that could confuse our photometric modeling. We present an iterative analysis method to derive the stellar and planet properties and uncertainties by combining the available spectroscopic parameters, stellar evolution models, and transiting light curve parameters, weighted by the measurement errors. Planet Hunters is a citizen science project that crowd sources the assessment of NASA Kepler light curves. The discovery of these 43 planet candidates demonstrates the success of citizen scientists at identifying planet candidates, even in longer period orbits with only two or three transit events.« less

A STELLAR-MASS-DEPENDENT DROP IN PLANET OCCURRENCE RATES

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

Mulders, Gijs D.; Pascucci, Ilaria; Apai, Dániel

2015-01-10

The Kepler spacecraft has discovered a large number of planets with up to one-year periods and down to terrestrial sizes. While the majority of the target stars are main-sequence dwarfs of spectral type F, G, and K, Kepler covers stars with effective temperatures as low as 2500 K, which corresponds to M stars. These cooler stars allow characterization of small planets near the habitable zone, yet it is not clear if this population is representative of that around FGK stars. In this paper, we calculate the occurrence of planets around stars of different spectral types as a function of planetmore » radius and distance from the star and show that they are significantly different from each other. We further identify two trends. First, the occurrence of Earth- to Neptune-sized planets (1-4 R {sub ⊕}) is successively higher toward later spectral types at all orbital periods probed by Kepler; planets around M stars occur twice as frequently as around G stars, and thrice as frequently as around F stars. Second, a drop in planet occurrence is evident at all spectral types inward of a ∼10 day orbital period, with a plateau further out. By assigning to each spectral type a median stellar mass, we show that the distance from the star where this drop occurs is stellar mass dependent, and scales with semi-major axis as the cube root of stellar mass. By comparing different mechanisms of planet formation, trapping, and destruction, we find that this scaling best matches the location of the pre-main-sequence co-rotation radius, indicating efficient trapping of migrating planets or planetary building blocks close to the star. These results demonstrate the stellar-mass dependence of the planet population, both in terms of occurrence rate and of orbital distribution. The prominent stellar-mass dependence of the inner boundary of the planet population shows that the formation or migration of planets is sensitive to the stellar parameters.« less

Worlds on the Edge Artist Concept

NASA Image and Video Library

2010-08-26

This artist concept illustrates the two Saturn-sized planets discovered by NASA Kepler mission. The star system is oriented edge-on, as seen by Kepler, such that both planets cross in front, or transit, their star, named Kepler-9.

Prospects for detecting decreasing exoplanet frequency with main-sequence age using PLATO

NASA Astrophysics Data System (ADS)

Veras, Dimitri; Brown, David J. A.; Mustill, Alexander J.; Pollacco, Don

2015-10-01

The space mission PLATO will usher in a new era of exoplanetary science by expanding our current inventory of transiting systems and constraining host star ages, which are currently highly uncertain. This capability might allow PLATO to detect changes in planetary system architecture with time, particularly because planetary scattering due to Lagrange instability may be triggered long after the system was formed. Here, we utilize previously published instability time-scale prescriptions to determine PLATO's capability to detect a trend of decreasing planet frequency with age for systems with equal-mass planets. For two-planet systems, our results demonstrate that PLATO may detect a trend for planet masses which are at least as massive as super-Earths. For systems with three or more planets, we link their initial compactness to potentially detectable frequency trends in order to aid future investigations when these populations will be better characterized.

Prospects for detecting decreasing exoplanet frequency with main-sequence age using PLATO

NASA Astrophysics Data System (ADS)

Veras, D.; Brown, D. J. A.; Mustill, A. J.; Pollacco, D.

2017-09-01

The space mission PLATO will usher in a new era of exoplanetary science by expanding our current inventory of transiting systems and constraining host star ages, which are currently highly uncertain. This capability might allow PLATO to detect changes in planetary system architecture with time, particularly because planetary scattering due to Lagrange instability may be triggered long after the system was formed. Here, we utilize previously published instability time-scale prescriptions to determine PLATO's capability to detect a trend of decreasing planet frequency with age for systems with equal- mass planets. For two-planet systems, our results demonstrate that PLATO may detect a trend for planet masses which are at least as massive as super-Earths. For systems with three or more planets, we link their initial compactness to potentially detectable frequency trends in order to aid future investigations when these populations will be better characterized.

Understanding the mass-radius relation for sub-Neptunes: radius as a proxy for composition

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

Lopez, Eric D.; Fortney, Jonathan J.

2014-09-01

Transiting planet surveys like Kepler have provided a wealth of information on the distribution of planetary radii, particularly for the new populations of super-Earth- and sub-Neptune-sized planets. In order to aid in the physical interpretation of these radii, we compute model radii for low-mass rocky planets with hydrogen-helium envelopes. We provide model radii for planets 1-20 M {sub ⊕}, with envelope fractions 0.01%-20%, levels of irradiation 0.1-1000 times Earth's, and ages from 100 Myr to 10 Gyr. In addition we provide simple analytic fits that summarize how radius depends on each of these parameters. Most importantly, we show that atmore » fixed H/He envelope fraction, radii show little dependence on mass for planets with more than ∼1% of their mass in their envelope. Consequently, planetary radius is to a first order a proxy for planetary composition, i.e., H/He envelope fraction, for Neptune- and sub-Neptune-sized planets. We recast the observed mass-radius relationship as a mass-composition relationship and discuss it in light of traditional core accretion theory. We discuss the transition from rocky super-Earths to sub-Neptune planets with large volatile envelopes. We suggest ∼1.75 R {sub ⊕} as a physically motivated dividing line between these two populations of planets. Finally, we discuss these results in light of the observed radius occurrence distribution found by Kepler.« less

Trilogy, an Interplanetary Constellation to Measure the Rate of Mass Loss by the Sun

NASA Astrophysics Data System (ADS)

Zuber, M. T.; Smith, D. E.; Mazarico, E. M.; Genova, A.; Neumann, G. A.; Sun, X.

2017-12-01

As the Sun slowly converts hydrogen into helium it steadily loses mass because the mass of a fused helium atom is less than that of the four original hydrogen atoms. This mass difference is released as energy in the form of electromagnetic and particle radiation. It will also affect the orbits of the planets and other bodies because the Sun's gravity is the central force that determines the sizes of their orbits. This loss of mass, believed to be of order 10-13 solar mass/ year, increases the semi-major axis of Earth's orbit by about 1.5 cm/year, with increasing magnitude with distance, e.g., over 7 cm/year at Jupiter near 5 AU. For the inner planets, where planetary orbital velocities are greatest, the largest effect is in the decrease in angular velocity as a result of the conservation of angular momentum. We will present a mission concept called Trilogy, which would establish geodetic/geophysical spacecraft around several key planetary bodies (i.e., Venus, Mars and Earth's Moon) and measure the ranges between these spacecraft down to centimeter level regularly over a period of years. The required technologies have been demonstrated on missions to the Moon and can now be applied between planets. The observations would enable the accurate determination and monitoring of the trajectories of these masses, from which the rate of decrease in solar mass could be estimated with great precision. Such a dataset would also enable the recovery of parameters key to many scientific fields, from planetary science to heliophysics to astrophysics and relativity.

Migration Processes and Volatiles Inventory to the Inner Planets

NASA Technical Reports Server (NTRS)

Marov, M. Y.; Ipatov, S. I.

2004-01-01

Comets and asteroids colliding with the terrestrial planets can deliver volatiles and organic or prebiotic compounds to the planets, thereby depositing on the planets the fundamental building-blocks for life. The inner planets contain heavier and cosmically less abundant elements in an iron-silicate matrix than the giant planets. This can be caused by the following three mechanisms: uneven fractionation and condensation in the accretionary disk; unequal degree of degassing of the composed matter; and heterogeneous accretion. Asteroid-size bodies consisting of the last low-temperature condensates (similar to most primitive chondritic meteorites, and enriched in hydrated silicates and trapped gases) are believed to have fallen onto the inner planets during the process of the giant planets formation. The relative contribution of either endogenous (i.e. outgassing) or exogenous (i.e. asteroid/comet collisions) sources is difficult to assess, although it is constrained by the pattern of noble gas abundances in the planetary atmospheres.

Worlds Beyond: A Strategy for the Detection and Characterization of Exoplanets

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

Lunine, J; Fischer, D; Hammel, H

2008-06-02

This report is a comprehensive study of the search for and study of planets around other stars (exoplanets). The young but maturing field of exoplanets is perhaps one of the most compelling fields of study in science today--both because of the discoveries made to date on giant planets around other stars, and because the detection of planets just like our Earth ('Earth analogs') is at last within reach technologically. In the Report we outline the need for a vigorous research program in exoplanets to understand our place in the cosmos: whether planets like our home Earth are a common ormore » rare outcome of cosmic evolution. The strategy we developed is intended to address the following fundamental questions, in priority order, within three distinct 5-yr long phases, over a 15 year period: (1) What are the physical characteristics of planets in the habitable zones around bright, nearby stars? (2) What is the architecture of planetary systems? (3) When, how and in what environments are planets formed? The Report recommends a two-pronged strategy for the detection and characterization of planets the size of the Earth. For stars much less massive and cooler than our Sun (M-dwarfs), existing ground-based techniques including radial velocity and transit searches, and space-based facilities both existing and under development such as Spitzer and JWST, are adequate for finding and studying planets close to the mass and size of the Earth. Conducted in parallel with the M-dwarf strategy is one for the more challenging observations of the hotter and brighter F, G, and K stars, some of which are very close in properties to our Sun, in which the frequency of Earth-sized planets is assessed with Corot and Kepler, but new space missions are required for detection and study of specific Earth-mass and Earth-sized objects. Our Task Force concludes that the development of a space-based astrometric mission, narrowly-focused to identify specific nearby stars with Earth-mass planets, followed by direct detection and study via a spaceborne coronagraph/occulter or interferometric mission, is the most robust approach to pursue. Ground and space-based microlensing programs pursued in parallel would provide complementary information on planetary system architectures on galactic scales. The program for F, G, and K stars must be preceded, at the beginning of the strategy, by broad yet detailed technical assessments to determine whether the astrometric and direct detection technologies will be ready in the time frames envisioned (the second and third 5-yr periods, respectively). Also measurement of dust around nearby candidate stars must be undertaken early to determine whether typical systems are clean enough to make direct detection feasible. Alternative strategies are discussed should problems arise in any of these areas. Finally, the Task Force lays out recommended programs in ground-based observations of larger planets, of planet-forming disks, and theoretical and laboratory studies crucial to interpreting and understanding the outcome of the planet search and characterization observations.« less

The nature of the TRAPPIST-1 exoplanets

NASA Astrophysics Data System (ADS)

Grimm, Simon L.; Demory, Brice-Olivier; Gillon, Michaël; Dorn, Caroline; Agol, Eric; Burdanov, Artem; Delrez, Laetitia; Sestovic, Marko; Triaud, Amaury H. M. J.; Turbet, Martin; Bolmont, Émeline; Caldas, Anthony; Wit, Julien de; Jehin, Emmanuël; Leconte, Jérémy; Raymond, Sean N.; Grootel, Valérie Van; Burgasser, Adam J.; Carey, Sean; Fabrycky, Daniel; Heng, Kevin; Hernandez, David M.; Ingalls, James G.; Lederer, Susan; Selsis, Franck; Queloz, Didier

2018-06-01

Context. The TRAPPIST-1 system hosts seven Earth-sized, temperate exoplanets orbiting an ultra-cool dwarf star. As such, it represents a remarkable setting to study the formation and evolution of terrestrial planets that formed in the same protoplanetary disk. While the sizes of the TRAPPIST-1 planets are all known to better than 5% precision, their densities have significant uncertainties (between 28% and 95%) because of poor constraints on the planet's masses. Aims: The goal of this paper is to improve our knowledge of the TRAPPIST-1 planetary masses and densities using transit-timing variations (TTVs). The complexity of the TTV inversion problem is known to be particularly acute in multi-planetary systems (convergence issues, degeneracies and size of the parameter space), especially for resonant chain systems such as TRAPPIST-1. Methods: To overcome these challenges, we have used a novel method that employs a genetic algorithm coupled to a full N-body integrator that we applied to a set of 284 individual transit timings. This approach enables us to efficiently explore the parameter space and to derive reliable masses and densities from TTVs for all seven planets. Results: Our new masses result in a five- to eight-fold improvement on the planetary density uncertainties, with precisions ranging from 5% to 12%. These updated values provide new insights into the bulk structure of the TRAPPIST-1 planets. We find that TRAPPIST-1 c and e likely have largely rocky interiors, while planets b, d, f, g, and h require envelopes of volatiles in the form of thick atmospheres, oceans, or ice, in most cases with water mass fractions less than 5%.

Planetary geodesy. [measurements of sizes, shapes, masses and gravity fields

NASA Technical Reports Server (NTRS)

Anderson, J. D.

1975-01-01

Work related to planetary geodesy conducted during the period from 1971 to 1975 is reviewed, taking into account the traditional subjects of geometrical and physical geodesy. Particular attention is given to the size and shape of the planets and to their masses and gravity fields. Improvements in the principal geodetic parameters of Mercury, Venus, and Mars are considered. Studies of the planets Jupiter, Saturn, Uranus, and Neptune are also discussed.

Characterizing extrasolar terrestrial planets with reflected, emitted and transmitted spectra.

PubMed

Tinetti, Giovanna

2006-12-01

NASA and ESA are planning missions to directly detect and characterize terrestrial planets outside our solar system (nominally NASA-Terrestrial Planet Finder and ESA-DARWIN missions). These missions will provide our first opportunity to spectroscopically study the global characteristics of those planets, and search for signs of habitability and life. We have used spatially and spectrally-resolved models to explore the observational sensitivity to changes in atmospheric and surface properties, and the detectability of surface biosignatures, in the globally averaged spectra and light-curves of the Earth. Atmospheric signatures of Earth-size exoplanets might be detected, in a near future, by stellar occultation as well. Detectability depends on planet's size, atmospheric composition, cloud cover and stellar type. According to our simulations, Earth's land vegetation signature (red-edge) is potentially visible in the disk-averaged spectra, even with cloud cover, and when the signal is averaged over the daily time scale. Marine vegetation is far more difficult to detect. We explored also the detectability of an exo-vegetation responsible for producing a signature that is red-shifted with respect to the Earth vegetation's one.

Forming Giant Planet Cores by Pebble Accretion -- Why Slow and Steady wins the Race

NASA Astrophysics Data System (ADS)

Kretke, Katherine A.; Levison, Harold F.

2014-05-01

In recent years there has been a radical new solution proposed to solve the problem of giant planet core formation. "Pebbles", particles ranging from centimeters to meters in size, have been shown to accrete extremely efficiently due to aerodynamic drag. Large capture cross-sections combined with fast pebble drift rates can allow a single planetesimal to grow from Ceres size to 10s of Earth masses well within the lifetime of gaseous circumstellar disks. However, at large sizes, the the capture-cross section of pebbles goes with the Hill sphere, forcing pebble accretion to becomes a fundamentally "oligarchic-like" process. This makes it difficult to form a few giant planet cores; instead a more generic result is many 10s to 100s of competing oligarchs. In this work, we present a way to get around this oligarchic dilemma If pebbles are assumed to form slowly over a long period of time, then the planetesimal growth rates are slow enough for the planetesimals to dynamically excite each other. As the larger planetisimals/proto-planets stir their smaller companions, these smaller bodies are excited to such a degree that they spend only a small fraction of their orbits embedded in the cooler pebble disk. This allows the larger bodies to starve their neighbors and maintain a relative runaway growth rate to high mass, effectively forming the cores of giant planets.

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

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

Jin, Sheng; Ji, Jianghui; Mordasini, Christoph

2014-11-01

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

On the hypothesis of hyperimpact-induced ejection of asteroid-size bodies from Earth-type planets.

NASA Astrophysics Data System (ADS)

Drobyshevski, E. M.

During the last two decades a number of facts have brought to life a seemingly fantastic idea of ejection of large rocky fragments from planets into space, like for example SNC meteorites or many-km-size fragments of Vesta. The theoretical description of impact processes of this ejection lags behind. Considerable efforts have been spent to show the possibility of ejection of bodies several meters in size from large impact craters on Mars. In general, the possibility of impact self-destruction of inner planets may drastically alter traditional models of the origin of the Solar System. However, non-destructive gasdynamic ejection of large fragments from planets requires a mechanism for fast conversion of shock-wave energy into heat. The extrapolation of data from laboratory impact experiments (≡10 kJ) and nuclear explosions (<1 Mt TNT) in order to describe hyperimpact processes with 105 - 106 Mt TNT energies can hardly be justified, that is why these calculations give relatively small gas production and, consequently, small velocities of fragment ejection from impact craters. It is predicted that at such energies some instabilities may lead to formation of new dissipation channels, that would increase the part of the overheated gas fraction in the hyperimpact ejection products. This would eliminate numerous contradictions in the impact history of planets, asteroids, meteorites etc.

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.

Staring at Saturn

NASA Image and Video Library

2016-09-15

NASA's Cassini spacecraft stared at Saturn for nearly 44 hours on April 25 to 27, 2016, to obtain this movie showing just over four Saturn days. With Cassini's orbit being moved closer to the planet in preparation for the mission's 2017 finale, scientists took this final opportunity to capture a long movie in which the planet's full disk fit into a single wide-angle camera frame. Visible at top is the giant hexagon-shaped jet stream that surrounds the planet's north pole. Each side of this huge shape is slightly wider than Earth. The resolution of the 250 natural color wide-angle camera frames comprising this movie is 512x512 pixels, rather than the camera's full resolution of 1024x1024 pixels. Cassini's imaging cameras have the ability to take reduced-size images like these in order to decrease the amount of data storage space required for an observation. The spacecraft began acquiring this sequence of images just after it obtained the images to make a three-panel color mosaic. When it began taking images for this movie sequence, Cassini was 1,847,000 miles (2,973,000 kilometers) from Saturn, with an image scale of 355 kilometers per pixel. When it finished gathering the images, the spacecraft had moved 171,000 miles (275,000 kilometers) closer to the planet, with an image scale of 200 miles (322 kilometers) per pixel. A movie is available at http://photojournal.jpl.nasa.gov/catalog/PIA21047

Absence of a Metallicity Effect for Ultra-short-period Planets

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

Winn, Joshua N.; Sanchis-Ojeda, Roberto; Isaacson, Howard

Ultra-short-period (USP) planets are a newly recognized class of planets with periods shorter than one day and radii smaller than about 2  R {sub ⊕}. It has been proposed that USP planets are the solid cores of hot Jupiters that have lost their gaseous envelopes due to photo-evaporation or Roche lobe overflow. We test this hypothesis by asking whether USP planets are associated with metal-rich stars, as has long been observed for hot Jupiters. We find the metallicity distributions of USP-planet and hot-Jupiter hosts to be significantly different ( p = 3 × 10{sup −4}) based on Keck spectroscopy ofmore » Kepler stars. Evidently, the sample of USP planets is not dominated by the evaporated cores of hot Jupiters. The metallicity distribution of stars with USP planets is indistinguishable from that of stars with short-period planets with sizes between 2 and 4  R {sub ⊕}. Thus, it remains possible that the USP planets are the solid cores of formerly gaseous planets that are smaller than Neptune.« less

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.

Transitsearch Workshop

NASA Technical Reports Server (NTRS)

Castellano, T.

2004-01-01

The discovery of more than 100 planets around nearby solar-like stars that surpass Jupiter in size yet orbit their stars more quickly than Mercury has heralded a new era in astronomy. These enigmatic 'Hot-Jupiters' are large enough and close enough to their parent stars that their 'transits' can be captured by astronomers equipped with a small computer controlled telescope and a quality electronic CCD camera. The planet reveals its presence through the periodic decrease in brightness as it passes (or transits) in front of the star as seen from Earth. The first known transiting extrasolar planet HD 209458b, in the constellation Pegasus, has been the subject of hundreds of scientific papers since its discovery in 1999. The transit of 8th magnitude HD 209458 has been observed by at least a dozen non-professional astronomers using telescopes as small as 4 inches in aperture. Using equipment already in hand, and armed with target lists, transit time predictions, observing techniques and software procedures developed by astronomers at NASA's Ames Research Center and the University of California at Santa Cruz, non-professional astronomers can contribute significantly to the study of extrasolar planets by carefully measuring the brightness of stars with known Hot-Jupiters. In this way, we may resume (after a two century interruption!) the tradition of planetary discoveries by amateur astronomers begun with William Herschel's 1787 discovery of the 'solar' planet Uranus. In the few years transitsearch has been in existence, investigators Tim Castellano (NASA Ames) and Greg Laughlin (UCSC) have written articles for Sky and Telescope and Astronomy magazines, have been featured in stories by the Reuters News Service, Nature magazine, Science magazine, Space.com, the American Institute of Physics and others and received several hundred thousand total hits on their website www.transitsearch,org.

Simulations of planet migration driven by planetesimal scattering

NASA Astrophysics Data System (ADS)

Kirsh, David R.; Duncan, Martin; Brasser, Ramon; Levison, Harold F.

2009-01-01

Evidence has mounted for some time that planet migration is an important part of the formation of planetary systems, both in the Solar System [Malhotra, R., 1993. Nature 365, 819-821] and in extrasolar systems [Mayor, M., Queloz, D., 1995. Nature 378, 355-359; Lin, D.N.C., Bodenheimer, P., Richardson, D.C., 1996. Nature 380, 606-607]. One mechanism that produces migration (the change in a planet's semi-major axis a over time) is the scattering of comet- and asteroid-size bodies called planetesimals [Fernandez, J.A., Ip, W.-H., 1984. Icarus 58, 109-120]. Significant angular momentum exchange can occur between the planets and the planetesimals during local scattering, enough to cause a rapid, self-sustained migration of the planet [Ida, S., Bryden, G., Lin, D.N.C., Tanaka, H., 2000. Astrophys. J. 534, 428-445]. This migration has been studied for the particular case of the four outer planets of the Solar System (as in Gomes et al. [Gomes, R.S., Morbidelli, A., Levison, H.F., 2004. Icarus 170, 492-507]), but is not well understood in general. We have used the Miranda [McNeil, D., Duncan, M., Levison, H.F., 2005. Astron. J. 130, 2884-2899] computer simulation code to perform a broad parameter-space survey of the physical variables that determine the migration of a single planet in a planetesimal disk. Migration is found to be predominantly inwards, and the migration rate is found to be independent of planet mass for low-mass planets in relatively high-mass disks. Indeed, a simple scaling relation from Ida et al. [Ida, S., Bryden, G., Lin, D.N.C., Tanaka, H., 2000. Astrophys. J. 534, 428-445] matches well with the dependencies of the migration rate: |{da}/{dt}|=aT{4πΣa/M; with T the orbital period of the planet and Σ the surface density of the planetesimal disk. When the planet's mass exceeds that of the planetesimals within a few Hill radii (the unit of the planet's gravitational reach), the migration rate decreases strongly with planet mass. Other trends are identified with the root-mean-squared eccentricity of the planetesimal disk, the mass of the particles dragged by the planet in the corotation region, and the index of the surface density power law. The trends are discussed in the context of an analysis of the scattering process itself, which was performed using a large simulation of massless planetesimals. The scattering process alters semi-major axes, eccentricities and timescales of interaction for the planetesimals. In particular, a bias in scattering timescales on either side of the planet's orbit leads to a very strong tendency for the planet to migrate inwards, towards the star, instead of outwards. The detection of this tendency relies on a level of resolution that may not have been achieved in past studies. The results of this work show that planet migration driven by planetesimal scattering should be a widespread phenomenon, especially for low-mass planets such as still-forming protoplanets.

Searching for and characterising extrasolar Earth-like planets and moons

NASA Astrophysics Data System (ADS)

Schneider, Jean

2002-10-01

The physical bases of the detection and characterisation of extrasolar Earth-like planets and moons in the reflected light and thermal emission regimes are reviewed. They both have their advantages and disadvantages, including artefacts, in the determination of planet physical parameters (mass, size, albedo, surface and atmospheric conditions etc.). After a short panorama of detection methods and the first findings, new perspectives for these different aspects are also presented. Finally brief account of the ground based programmes and space-based projects and their potentialities for Earth-like planets is made and discussed.

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.

Kepler Detects Planet Orbiting Two Stars (Kepler-16b) Reporter Package for TWAN

NASA Image and Video Library

2011-09-19

NASA's Kepler Mission has made the first detection of a planet orbiting two stars. About 200 light years away from our solar system, the planet Kepler-16b is cold, gaseous and about the size of Saturn. Its stars are both smaller than the Sun and about 2 billion years younger than our Solar System. They orbit around each other, so from our vantage point they take turns eclipsing each other about every 41 days. The planet Kepler-16b orbits around both stars every 229 days.

A Bewildering and Dynamic Picture of Exoplanetary Systems Identified by the Kepler Mission (Invited)

NASA Astrophysics Data System (ADS)

Jenkins, J. M.

2013-12-01

Kepler vaulted into the heavens on March 7, 2009, initiating NASA's search for Earth-size planets orbiting Sun-like stars in the habitable zone, where liquid water could exist on a rocky planetary surface. In the 4 years since, a flood of photometric data of unprecedented precision and continuity on more than 190,000 stars has provoked a watershed of 134+ confirmed or validated planets, 3200+ planetary candidates (most sub-Neptune in size and many comparable to or smaller than Earth), and a revolution in asteroseismology and astrophysics. Recent discoveries include Kepler-62 with 5 planets total, of which 2 are in the habitable zone with radii of 1.4 and 1.7 Re. Approximately 500 of the stars in the Kepler survey with planets host multiple transiting planets: 43% of planet candidates have transiting siblings. Many of these multiple transiting planet systems are dynamically packed and are unlikely, therefore, to have formed in situ. These systems experienced strong migration and evolution to arrive at the configurations we observe today, with important implications for the time-variable habitability of these planets over their histories. The half dozen circumbinary transiting planet systems discovered by Kepler to date highlight the dynamic nature of the habitable zone in systems with multiple host stars where the habitable zone may change significantly on timescales commensurate with the orbital period of the binary. While the catalog of circumbinary planets is small at this point, it already possesses at least one example of an exoplanet in the habitable zone. This implies that the majority of habitable zone planets may be circumbinary planets given the high frequency of multiple star systems and the early detection of Kepler-47b. KIC-12557548 is most likely a disintegrating sub-Mercury-sized planet. While it was probably never habitable, it represents a unique example of the dynamic nature of planetary systems. These amazing discoveries challenge our conventional notion of the habitable zone for single stars and static planetary system configurations. This talk will provide an overview of the science results from the Kepler Mission and the work ahead to derive the frequency of Earth-size planets in the habitable zone of solar-like stars from the treasure trove of Kepler data. NASA's quest for exoplanets continues with the Transiting Exoplanet Survey Satellite (TESS) mission, slated for launch in May 2017 by NASA's Explorer Program. TESS will conduct an all- sky transit survey to identify the 1000 best small exoplanets in the solar neighborhood for follow up observations and characterization. TESS's targets will include all F, G, K dwarfs from +4 to +12 magnitude and all M dwarfs known within ~200 light-years. 500,000 target stars will be observed over two years with ~500 square degrees observed continuously for a year in each hemisphere in the James Webb Space Telescopes continuously viewable zones. Since the typical TESS target star is 5 magnitudes brighter than that of Kepler and 10 times closer, TESS discoveries will afford significant opportunities to measure the masses of the exoplanets and to characterize their atmospheres with JWST, ELTs and other exoplanet explorers. TESS' discoveries will raise new questions regarding habitability that will be open to investigation through active efforts to characterize their atmospheres and search for biomarkers. Funding for this mission is provided by NASA's Science Mission Directorate.

Companions in Color: High-Resolution Imaging of Kepler’s Sub-Neptune Host Stars

NASA Astrophysics Data System (ADS)

Ware, Austin; Wolfgang, Angie; Kannan, Deepti

2018-01-01

A current problem in astronomy is determining how sub-Neptune-sized exoplanets form in planetary systems. These kinds of planets, which fall between 1 and 4 times the size of Earth, were discovered in abundance by the Kepler Mission and were typically found with relatively short orbital periods. The combination of their size and orbital period make them unusual in relation to the Solar System, leading to the question of how these exoplanets form and evolve. One possibility is that they have been influenced by distant stellar companions. To help assess the influence of these objects on the present-day, observed properties of exoplanets, we conduct a NIR search for visual stellar companions to the stars around which the Kepler Mission discovered planets. We use high-resolution images obtained with the adaptive optics systems at the Lick Observatory Shane-3m telescope to find these companion stars. Importantly, we also determine the effective brightness and distance from the planet-hosting star at which it is possible to detect these companions. Out of the 200 KOIs in our sample, 42 KOIs (21%) have visual companions within 3”, and 90 (46%) have them within 6”. These findings are consistent with recent high-resolution imaging from Furlan et al. 2017 that found at least one visual companion within 4” for 31% of sampled KOIs (37% within 4" for our sample). Our results are also complementary to Furlan et al. 2017, with only 17 visual companions commonly detected in the same filter. As for detection limits, our preliminary results indicate that we can detect companion stars < 3-5 magnitudes fainter than the planet-hosting star at a separation of ~ 1”. These detection limits will enable us to determine the probability that possible companion stars could be hidden within the noise around the planet-hosting star, an important step in determining the frequency with which these short-period, sub-Neptune-sized planets occur within binary star systems.

Late accretion to the terrestrial planets

NASA Astrophysics Data System (ADS)

Brasser, Ramon; Mojzsis, Stephen; Werner, Stephanie; Matsumura, Soko; Ida, Shigeru

2017-10-01

IntroductionIt is generally accepted that silicate-metal (`rocky') planet formation relies on coagulation from a mixture of sub-Mars sized planetary embryos and (smaller) planetesimals that dynamically emerge from the evolving circum-solar disc in the first few million years of our Solar System. Once the planets have, for the most part, assembled after a giant impact phase, they continue to be bombarded by a multitude of planetesimals left over from accretion. Here we place limits on the mass and evolution of these planetesimals based on constraints from the highly siderophile element (HSE) budget of the Moon. The terrestrial and lunar HSE budgets indicate that Earth’s and Moon’s additions through late accretion were 0.7 wt% and 0.02 wt% respectively. The disproportionate high accretion between the Earth and Moon could be explained by stochastic accretion of a few remaining Ceres-sized bodies that preferentially targeted the Earth.ResultsFrom a combination of N-body and Monte Carlo simulations of planet formation we conclude:1) matching the terrestrial to lunar HSE ratio requires that late accretion on Earth mostly consisted of a single lunar-size impactor striking the Earth before 4.45 Ga2) the flux of terrestrial impactors must have been low avoid wholesale melting of Earth's crust after 4.4 Ga[6], and to simultaneously match the number of observed lunar basins3) after the terrestrial planets have fully formed, the mass in remnant planetesimals was ~0.001 Earth mass, lower than most previous models suggest.4) Mars' HSE budget also requires a colossal impact with a Ceres-sized object before 4.43 Ga, whose visible remnant could be the hemispherical dichotomy.These conclusions lead to an Hadean eon which is more clement than assumed previously. In addition, our dynamically and geochemically self-consistent scenario requires that future N-body simulations of rocky planet formation either directly incorporate collisional grinding or rely on pebble accretion.

Constraining the Properties of Small Stars and Small Planets Observed by K2

NASA Astrophysics Data System (ADS)

Dressing, Courtney D.; Newton, Elisabeth R.; Charbonneau, David; Schlieder, Josh; Hawaii/California/Arizona/Indiana K2 Follow-up Consortium, HARPS-N Consortium

2016-01-01

We are using the results of the NASA K2 mission (the second career of the Kepler spacecraft) to study how the frequency and architectures of planetary systems orbiting M dwarfs throughout the ecliptic plane compare to those of the early M dwarf planetary systems observed by Kepler. In a previous analysis of the Kepler data set, we found that planets orbiting early M dwarfs are common: we measured a cumulative planet occurrence rate of 2.45 +/- 0.22 planets per M dwarf with periods of 0.5-200 days and planet radii of 1-4 Earth radii. Within a conservative habitable zone based on the moist greenhouse inner limit and maximum greenhouse outer limit, we estimated an occurrence rate of 0.15 (+0.18/-0.06) Earth-size planets and 0.09 (+0.10/-0.04) super-Earths per M dwarf HZ. Applying these occurrence rates to the population of nearby stars and assuming that mid- and late-M dwarfs host planets at the same rate as early M dwarfs, we predicted that the nearest potentially habitable Earth-size planet likely orbits an M dwarf a mere 2.6 ± 0.4 pc away. We are now testing the assumption of equal planet occurrence rates for M dwarfs of all types by inspecting the population of planets detected by K2 and conducting follow-up observations of planet candidate host stars to identify false positives and better constrain system parameters. I will present the results of recent observing runs with SpeX on the IRTF to obtain near-infrared spectra of low-mass stars targeted by K2 and determine the radii, temperatures, and metallicities of our target stars using empirical relations. We gratefully acknowledge funding from the NASA XRP Program, the John Templeton Foundation, and the NASA Sagan Fellowship Program.

Kepler Mission: A Search for Habitable Planets

NASA Technical Reports Server (NTRS)

Koch, David; Fonda, Mark (Technical Monitor)

2002-01-01

The Kepler Mission was selected by NASA as one of the next two Discovery Missions. The mission design is based on the search for Earth-size planets in the habitable zone of solar-like stars, but does not preclude the discovery of larger or smaller planets in other orbits of non-solar-like stars. An overview of the mission, the scientific goals and the anticipated results will be presented.

Mapping the Region in the Nearest Star System to Search for Habitable Planets

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; Quarles, B.

2015-01-01

Circumstellar planets within the alpha Centauri AB star system have been suggested through formation models and recent observations, and ACESat (Belikov et al. AAS Meeting #225, #311.01, 2015) is a proposed space mission designed to directly image Earth-sized planets in the habitable zones of both of these stars. The alpha Centauri system is billions of years old, so planets are only expected to be found in regions where their orbits are long-lived. We evaluate the extent of the regions within the alpha Centauri AB star system where small planets are able to orbit for billion-year timescales and we map the positions in the sky plane where planets on stable orbits about either stellar component may appear. We confirm the qualitative results of Wiegert & Holman (Astron. J. 113, 1445, 1997) regarding the approximate size of the regions of stable orbits, which are larger for retrograde orbits relative to the binary than for prograde orbits. Additionally, we find that mean motion resonances with the binary orbit leave an imprint on the limits of orbital stability, and the effects of the Lidov-Kozai mechanism are also readily apparent. Overall, orbits in the habitable zones near the plane of the binary are stable, whereas high-inclination orbits are short-lived.

Prospects for the Detection of Earths Orbiting Other Stars

NASA Technical Reports Server (NTRS)

Bourcki, William J.; Koch, David G.; Jenkins, Jon M.; Lissauer, Jack J.; Dunham, Edward W.; DeVincenzi, Donald L. (Technical Monitor)

2001-01-01

Extrasolar planets have been detected by timing the radio signals from millisecond pulsars, from Doppler velocity changes in the spectra of main sequence stars, and most recently by the white-light transit of HD209458. Detection of Earth-sized planets in and near the habitable zone of main-sequence stars appears to be extremely difficult, if not impossible, from ground-based observatories because of noise introduced by scintillation and transparency changes in the Earth's atmosphere. To overcome these difficulties, several spaceborne photometric missions have been proposed. The COROT mission is a CNES/ESA mission with a 30 cm aperture telescope that will monitor each of several star fields for five months to find short period planets. The Kepler project is a USA effort designed to monitor 100,000 solar-like stars in a single field of view for a period of four years. The long duration enables the reliable detection of planets with orbital periods from a few days to as long as two years. Thus it should be able to determine the frequency of planets in and near the habitable zone and associate them with stellar spectral types. Canadian and Scandinavian missions are also being developed. This paper compares these missions and discusses their expected contribution to our understanding of the frequency of terrestrial-sized planets around other stars.

Prospects for the Detection of Earths Orbiting Other Stars

NASA Technical Reports Server (NTRS)

Borucki, William J.; Koch, David G.; Jenkins, Jon M.; Lissauer, Jack J.; Dunham, Edward W.

2001-01-01

Extrasolar planets have been detected by timing the radio signals from millisecond pulsars, from Doppler velocity changes in the spectra of main sequence stars, and most recently by the white-light transit of HD209458. Detection of Earth-sized planets in and near the habitable zone of main-sequence stars appears to be extremely difficult, if not impossible, from ground-based observatories because of noise introduced by scintillation and transparency changes in the Earth#s atmosphere. To overcome these difficulties, several spaceborne photometric missions have been proposed. The COROT mission is a CNES/ESA mission with a 30 cm aperture telescope that will monitor each of several star fields for five months to find short period planets. The Kepler project is a USA effort designed to monitor 100,000 solar-like stars in a single field of view for a period of four years. The long duration enables the reliable detection of planets with orbital periods from a few days to as long as two years. Thus it should be able to determine the frequency of planets in and near the habitable zone and associate them with stellar spectral types. Canadian and Scandinavian missions are also being developed. This paper compares these missions and discusses their expected contribution to our understanding of the frequency of terrestrial-sized planets around other stars.

Radial pressure in the solar nebula as affecting the motions of planetesimals. [toroidal particle concentration in planetary evolution

NASA Technical Reports Server (NTRS)

Whipple, F. L.

1973-01-01

Growing planetesimals and a range of drag laws depending on the Reynolds number and on the ratio of particle size to mean free path are considered. Particles spiral in the direction of positive gradient, thus being concentrated toward toroidal concentrations of gas. The effect increases with decreasing rates of particle growth, i.e., with increasing time scales of planet formation by accretion. In the outer regions, where evidence suggests that comets were formed and Uranus and Neptune were so accumulated, the effect of the pressure gradient is to clear the forming comets from those regions. The large mass of Neptune may have developed because of this effect, perhaps Neptune's solar distance was reduced from Bode's law, and perhaps no comet belt exists beyond Neptune. In the asteroid belt, on a slow time scale, the effect may have spiraled planetesimals toward Mars and Jupiter, thus contributing to the lack of planet formation in this region.

Circular features with predictable size on Xanadu region of Titan

NASA Astrophysics Data System (ADS)

Kochemasov, G. G.

2008-09-01

Planets' satellites in the Solar system (rocky and icy) have in common one fundamental property: all of them move simultaneously in two orbits - around Sun and around their planets (planets have only one orbit in the Solar system). As was shown by the wave planetology [1-6] " orbits make structures'. This means that movements in elliptical keplerian orbits imply periodically changing increasing and decreasing accelerations. Multiplied by celestial body mass this produces inertia-gravity forces (Newton: F=m • a). These forces warp celestial bodies in form of standing waves propagating in rotating bodies in four interfering orthogonal and diagonal directions. This interference gives three kinds of regularly disposed tectonic blocks: uprising (+), subsiding (-), neutral (0)(Fig. 1). Their size depends on warping wavelengths. The fundamental wave1 and its first overtone wave2 (and weaker ones) are responsible for ubiquitous tectonic dichotomy - two hemispheres - segments and sectoring. These superimposed global tectonic features are adorned by tectonic granulations size of which is inversely proportional to orbital frequencies: higher frequency - smaller granule, lower frequency - larger granule. A row of the planets granulations is as follows: Mercury πR/16, Venus πR/6, Earth πR/4, Mars πR/2, asteroids πR/1, Jupiter 3πR, Saturn 7.5πR, Uranus 21πR, Neptune 41πR, Pluto 62πR (a granule size is a half of a wavelength; a scale is Earth with πR/4 granule corresponding to 1/1 year orbital frequency; R-radius). So, orbits make structures. They are simpler for planets, but much more complicated for moons. Their surfaces are saturated with granules related to two main frequencies and at least two modulated side frequencies. Two orbits imply a wave modulation. The lower circum-Sun frequency modulates the higher circum-planet frequency by dividing and multiplying it thus producing two side frequencies with corresponding waves and granules. In case of Titan for the first time the larger modulated granules were reported in pre-Cassini era in the Hubble ST images [5] (Fig. 2, 3). Titan rather extensively studied by imaging systems and radar presents now a good example of the wave modulations. It has two orbiting frequencies: around Sun -1/30 years, around Saturn -1/16 days. The corresponding main granule sizes are 7.5πR and πR/91, or 60641 and 88 km, the former size is too large to be directly observed (its wave probably influences only the whole shape of the satellite) and the latter is visible in the near IR image PIA06154 as chains and grids of hollows (about 70 to 100 km across) at intersections of crosscutting tight lineations covering the whole Titan's surface. This mode of granulation is also clearly presented in PIA03567. The modulated side frequencies give granules 662 and 12 km across (πR/12 and πR/667). Both sizes are discernable on Titan's radar image PIA08454. The first as roundish white and dark areas (these granules were discerned and calculated earlier on the Hubble image of Titan in pre-Cassini era [5]). The second size is produced by an intersection of regular wavings-ripples (erroneously interpreted as dunes) with spacing about 10- 20 km covering mainly smooth dark equatorial parts of the satellite. Thus, three granule sizes (662, 88, 12 km) are detected on Titan's surface by imaging from various distances and using different wave diapasons. The Xanadu water ice mountaneous equatorial area was imaged by radar on May 12, 2008 (Fig. 4, PIA10654). Three prominent ridges trending west-to-east are spaced about 25 km apart. In many places of the image are seen not very clear but discernable roundish spots about 10 to 20 km in diameter. Sometimes they are arranged in a row touching each other as in the area between two upper ridges. The best visible darkest spot at bottom center is about 20 km in diameter and shows polygonal outlines as do some other circular spots. Such structures could be interpreted as a manifestation of a wave woven pattern with granules belonging to the modulated ones - πR/667.

True polar wander on convecting planets

NASA Astrophysics Data System (ADS)

Rose, Ian Robert

Rotating planets are most stable when spinning around their maximum moment of inertia, and will tend to reorient themselves to achieve this configuration. Geological activity redistributes mass in the planet, making the moment of inertia a function of time. As the moment of inertia of the planet changes, the spin axis shifts with respect to a mantle reference frame in order to maintain rotational stability. This process is known as true polar wander (TPW). Of the processes that contribute to a planet's moment of inertia, convection in the mantle generates the largest and longest-period fluctuations, with corresponding shifts in the spin axis. True polar wander has been hypothesized to explain several physiographic features on planets and moons in our solar system. On Earth, TPW events have been invoked in some interpretations of paleomagnetic data. Large swings in the spin axis could have enormous ramifications for paleogeography, paleoclimate, and the history of life. Although the existence of TPW is well-verified, it is not known whether its rate and magnitude have been large enough for it to be an important process in Earth history. If true polar wander has been sluggish compared to plate tectonic speeds, then it would be difficult to detect and its consequences would be minor. I investigate rates of true polar wander on convecting planets using scaling, numerics, and inverse problems. I perform a scaling analysis of TPW on a convecting planet, identifying a minimal set of nondimensional parameters which describe the problem. The primary nondimensional numbers that control the rate of TPW are the ratio of centrifugal to gravitational forces m and the Rayleigh number Ra. The parameter m sets the size of a planet's rotational bulge, which determines the amount of work that needs to be done to move the spin axis. The Rayleigh number controls the size, distribution, and rate of change of moment of inertia anomalies, all of which affect the rate of TPW. I find that the characteristic size of moment of inertia anomalies decreases with higher Ra, but that the characteristic response time for TPW also decreases. These two effects approximately cancel. However, the orientation of the principal axes of the moment of inertia becomes less stable to perturbations at high Ra, thereby increasing the rate of TPW. Overall, I find that a more vigorously convecting planet is more likely to experience large TPW events. If early Earth had more vigorous convection, it may have experienced more TPW than present-day Earth. Flow induced by density anomalies in the mantle deflects free surfaces at the surface and the CMB, and the mass anomalies due to these deflections contribute to the moment of inertia. A full accounting of the moment of inertia anomalies must include these surface effects. Numerical models of mantle convection with a free surface have suffered from numerical sloshing instabilities. I analyze the sloshing instability by constructing a generalized eigenvalue problem for the relaxation time spectrum. The minimum relaxation time of the spectrum sets the maximum stable timestep. This analysis gives the first quantitative explanation for why existing techniques for stabilizing geodynamic simulations with a free surface work. I also use this perspective to construct an alternative stabilization scheme based on nonstandard finite differences. This scheme has a single parameter, given by an estimate of the minimum relaxation time, and allows for still larger timesteps. Finally, I develop a new method for analyzing apparent polar wander (APW) paths described by sequences of paleomagnetic poles. Existing techniques, such as spline fits and running means, do not fully account for the uncertainties in the position and timing of paleomagnetic pole paths. Furthermore, they impose regularization on the solution, and the resulting uncertainties are difficult to interpret. Our technique is an extension of paleomagnetic Euler pole (PEP) analysis. I invert for finite Euler pole rotations that can reproduce APW paths within a Bayesian Markov chain Monte Carlo (MCMC) framework. This allows us to naturally include uncertainties in age and position, and provides error estimates on the resulting model parameters. Regularization can be accomplished via physically motivated choices for the parameters' prior probability distributions. I applied the Bayesian PEP technique to the Mesoproterozoic Laurentian APW track, which primarily comes from the Keweenawan Midcontinent Rift. I fit the track with one and two Euler rotations. Both inversions did a good job of reproducing the Keweenawan track, though the two Euler pole inversion has a closer fit. I find that the implied Laurentian plate speeds exceeds 22.9 cm/yr at the 95% confidence level. These speeds are significantly faster than Cenozoic plate speeds, and could be explained by either faster plate speeds in the Proterozoic or a TPW event. (Abstract shortened by ProQuest.).

Commissioning and performance results of the WFIRST/PISCES integral field spectrograph

NASA Astrophysics Data System (ADS)

Saxena, Prabal; Rizzo, Maxime J.; Mejia Prada, Camilo; Llop Sayson, Jorge; Gong, Qian; Cady, Eric J.; Mandell, Avi M.; Groff, Tyler D.; McElwain, Michael W.

2017-09-01

Direct imaging of exoplanets has become a priority in the field of exoplanet discovery and characterization due to its ability to directly obtain evidence about a planet's atmosphere and some bulk properties. Features such as atmospheric composition, structure and clouds are just some of the planetary properties obtainable from directly imaged spectra. However, detecting and observing spectra of exoplanets using direct imaging is challenging due to the combination of extreme star to planet contrast ratios and the relatively small apparent physical separation between a host star and an orbiting planet. Detection of Earth-sized planets in reflected visible light requires contrast ratios of 1010, while even detection of Jupiter-sized planets and large young self-luminous planets requires contrast ratios of 108 and 106, respectively. Consequently, direct detection of exoplanets requires observing strategies which push the boundaries of high contrast imaging. The use of coronagraphy to occult a host star has been combined with adaptive optics (AO) technology to yield a particularly promising means of potentially achieving the required contrast ratios in regions close-in enough to the host star. Ground based adaptive optics systems such as The Gemini Planet Imager (GPI)1 and Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE)2 instrument have been able to achieve contrast ratios nearing 107 using post-processing techniques3, 4 and have yielded a number of direct detections of young self-luminous planets. Advancing these technologies onto a space based platform immune to the difficulties posed by the effects of Earth's atmosphere is the next step in accessing even larger contrast ratios.

XUV-exposed, non-hydrostatic hydrogen-rich upper atmospheres of terrestrial planets. Part I: atmospheric expansion and thermal escape.

PubMed

Erkaev, Nikolai V; Lammer, Helmut; Odert, Petra; Kulikov, Yuri N; Kislyakova, Kristina G; Khodachenko, Maxim L; Güdel, Manuel; Hanslmeier, Arnold; Biernat, Helfried

2013-11-01

The recently discovered low-density "super-Earths" Kepler-11b, Kepler-11f, Kepler-11d, Kepler-11e, and planets such as GJ 1214b represent the most likely known planets that are surrounded by dense H/He envelopes or contain deep H₂O oceans also surrounded by dense hydrogen envelopes. Although these super-Earths are orbiting relatively close to their host stars, they have not lost their captured nebula-based hydrogen-rich or degassed volatile-rich steam protoatmospheres. Thus, it is interesting to estimate the maximum possible amount of atmospheric hydrogen loss from a terrestrial planet orbiting within the habitable zone of late main sequence host stars. For studying the thermosphere structure and escape, we apply a 1-D hydrodynamic upper atmosphere model that solves the equations of mass, momentum, and energy conservation for a planet with the mass and size of Earth and for a super-Earth with a size of 2 R(Earth) and a mass of 10 M(Earth). We calculate volume heating rates by the stellar soft X-ray and extreme ultraviolet radiation (XUV) and expansion of the upper atmosphere, its temperature, density, and velocity structure and related thermal escape rates during the planet's lifetime. Moreover, we investigate under which conditions both planets enter the blow-off escape regime and may therefore experience loss rates that are close to the energy-limited escape. Finally, we discuss the results in the context of atmospheric evolution and implications for habitability of terrestrial planets in general.

KSC-2009-1957

NASA Image and Video Library

2009-03-06

CAPE CANAVERAL, Fla. – The gantry on Launch Pad 17-B at Cape Canaveral Air Force Station in Florida shows the various logos of NASA's Kepler spacecraft launch. Kepler is a spaceborne telescope designed to search the nearby region of our galaxy for Earth-size planets orbiting in the habitable zone of stars like our sun. The habitable zone is the region around a star where temperatures permit water to be liquid on a planet's surface. The challenge for Kepler is to look at a large number of stars in order to statistically estimate the total number of Earth-size planets orbiting sun-like stars in the habitable zone. Kepler will survey more than 100,000 stars in our galaxy. Photo credit: NASA/Jack Pfaller

Kepler-16: a transiting circumbinary planet.

PubMed

Doyle, Laurance R; Carter, Joshua A; Fabrycky, Daniel C; Slawson, Robert W; Howell, Steve B; Winn, Joshua N; Orosz, Jerome A; Prša, Andrej; Welsh, William F; Quinn, Samuel N; Latham, David; Torres, Guillermo; Buchhave, Lars A; Marcy, Geoffrey W; Fortney, Jonathan J; Shporer, Avi; Ford, Eric B; Lissauer, Jack J; Ragozzine, Darin; Rucker, Michael; Batalha, Natalie; Jenkins, Jon M; Borucki, William J; Koch, David; Middour, Christopher K; Hall, Jennifer R; McCauliff, Sean; Fanelli, Michael N; Quintana, Elisa V; Holman, Matthew J; Caldwell, Douglas A; Still, Martin; Stefanik, Robert P; Brown, Warren R; Esquerdo, Gilbert A; Tang, Sumin; Furesz, Gabor; Geary, John C; Berlind, Perry; Calkins, Michael L; Short, Donald R; Steffen, Jason H; Sasselov, Dimitar; Dunham, Edward W; Cochran, William D; Boss, Alan; Haas, Michael R; Buzasi, Derek; Fischer, Debra

2011-09-16

We report the detection of a planet whose orbit surrounds a pair of low-mass stars. Data from the Kepler spacecraft reveal transits of the planet across both stars, in addition to the mutual eclipses of the stars, giving precise constraints on the absolute dimensions of all three bodies. The planet is comparable to Saturn in mass and size and is on a nearly circular 229-day orbit around its two parent stars. The eclipsing stars are 20 and 69% as massive as the Sun and have an eccentric 41-day orbit. The motions of all three bodies are confined to within 0.5° of a single plane, suggesting that the planet formed within a circumbinary disk.

Abstract Concept of TRAPPIST-1 System

NASA Image and Video Library

2017-02-22

This artist's concept appeared on the Feb. 23, 2017 cover of the journal Nature announcing that the TRAPPIST-1 star, an ultra-cool dwarf, has seven Earth-size planets orbiting it. Any of these planets could have liquid water on them. Planets that are farther from the star are more likely to have significant amounts of ice, especially on the side that faces away from the 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. http://photojournal.jpl.nasa.gov/catalog/PIA21421

Kepler Mission: Detecting Earth-sized Planets in Habitable Zones

NASA Technical Reports Server (NTRS)

Kondo, Yoji; Fisher, Richard R. (Technical Monitor)

2001-01-01

The Kepler Mission, which is presently in Phase A, is being proposed for launch in 5 years for a 4-year mission to determine the frequency of Earth-sized or larger planets in habitable zones in our galaxy. Kepler will be placed in an Earth-trailing orbit to provide stable physical environments for the sensitive scientific instruments. The satellite is equipped with a photometric system with the precision of 10E-5, which should be sufficient for detecting the transits of Earth-sized or larger planets in front of dwarf stars similar to the Sun. Approximately 100,000 or more sun-like stars brighter than the 14th apparently magnitude will be monitored continuously for 4 years in a preselected region of the sky, which is about 100 square degrees in size. In addition, Kepler will have a participating scientist program that will enable research in intrinsic variable stars, interacting binaries including cataclysmic stars and X-ray binaries, and a large number of solar analogs in our galaxy. Several ten thousand additional stars may be investigated in the guest observer program open to the whole world.

Giant Planets: Good Neighbors for Habitable Worlds?

NASA Astrophysics Data System (ADS)

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

2018-04-01

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

Views from EPOXI. Colors in Our Solar System as an Analog for Extrasolar Planets

NASA Technical Reports Server (NTRS)

Crow, Carolyn A.; McFadden, L. A.; Robinson, T.; Livengood, T. A.; Hewagama, T.; Barry, R. K.; Deming, L. D.; Meadows, V.; Lisse, C. M.

2010-01-01

With extrasolar planet detection becoming more common place, the frontiers of extrasolar planet science have moved beyond detection to the observations required to determine planetary properties. Once the existing observational challenges have been overcome, the first visible-light studies of extrasolar Earth-sized planets will likely employ filter photometry or low-resolution. spectroscopy to observe disk-integrated radiation from the unresolved planet. While spectroscopy of these targets is highly desirable, and provides the most robust form of characterization. S/N considerations presently limit spectroscopic measurements of extrasolar worlds. Broadband filter photometry will thus serve as a first line of characterization. In this paper we use Extrasolar Observation and Characterization (EPOCh) filter photometry of the Earth. Moon and Mars model spectra. and previous photometric and spectroscopic observations of a range the solar system planets. Titan, and Moon to explore the limitations of using color as a baseline for understanding extrasolar planets

Transit light curves with finite integration time: Fisher information analysis

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

Price, Ellen M.; Rogers, Leslie A.

2014-10-10

Kepler has revolutionized the study of transiting planets with its unprecedented photometric precision on more than 150,000 target stars. Most of the transiting planet candidates detected by Kepler have been observed as long-cadence targets with 30 minute integration times, and the upcoming Transiting Exoplanet Survey Satellite will record full frame images with a similar integration time. Integrations of 30 minutes affect the transit shape, particularly for small planets and in cases of low signal to noise. Using the Fisher information matrix technique, we derive analytic approximations for the variances and covariances on the transit parameters obtained from fitting light curvemore » photometry collected with a finite integration time. We find that binning the light curve can significantly increase the uncertainties and covariances on the inferred parameters when comparing scenarios with constant total signal to noise (constant total integration time in the absence of read noise). Uncertainties on the transit ingress/egress time increase by a factor of 34 for Earth-size planets and 3.4 for Jupiter-size planets around Sun-like stars for integration times of 30 minutes compared to instantaneously sampled light curves. Similarly, uncertainties on the mid-transit time for Earth and Jupiter-size planets increase by factors of 3.9 and 1.4. Uncertainties on the transit depth are largely unaffected by finite integration times. While correlations among the transit depth, ingress duration, and transit duration all increase in magnitude with longer integration times, the mid-transit time remains uncorrelated with the other parameters. We provide code in Python and Mathematica for predicting the variances and covariances at www.its.caltech.edu/∼eprice.« less

A SEARCH FOR ADDITIONAL PLANETS IN FIVE OF THE EXOPLANETARY SYSTEMS STUDIED BY THE NASA EPOXI MISSION

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

Ballard, Sarah; Charbonneau, David; Holman, Matthew J.

We present time series photometry and constraints on additional planets in five of the exoplanetary systems studied by the EPOCh (Extrasolar Planet Observation and Characterization) component of the NASA EPOXI mission: HAT-P-4, TrES-3, TrES-2, WASP-3, and HAT-P-7. We conduct a search of the high-precision time series for photometric transits of additional planets. We find no candidate transits with significance higher than our detection limit. From Monte Carlo tests of the time series using putative periods from 0.5 days to 7 days, we demonstrate the sensitivity to detect Neptune-sized companions around TrES-2, sub-Saturn-sized companions in the HAT-P-4, TrES-3, and WASP-3 systems,more » and Saturn-sized companions around HAT-P-7. We investigate in particular our sensitivity to additional transits in the dynamically favorable 3:2 and 2:1 exterior resonances with the known exoplanets: if we assume coplanar orbits with the known planets, then companions in these resonances with HAT-P-4b, WASP-3b, and HAT-P-7b would be expected to transit, and we can set lower limits on the radii of companions in these systems. In the nearly grazing exoplanetary systems TrES-3 and TrES-2, additional coplanar planets in these resonances are not expected to transit. However, we place lower limits on the radii of companions that would transit if the orbits were misaligned by 2.{sup 0}0 and 1.{sup 0}4 for TrES-3 and TrES-2, respectively.« less

Stellar scattering and the formation of hot Jupiters in binary systems

NASA Astrophysics Data System (ADS)

Martí, J. G.; Beaugé, C.

2015-04-01

Hot Jupiters (HJs) are usually defined as giant Jovian-size planets with orbital periods P<=10 days. Although they lie close to the star, several have finite eccentricities and significant misalignment angle with respect to the stellar equator, leading to ~20% of HJs in retrograde orbits. More than half, however, seem consistent with near-circular and planar orbits. In recent years, two mechanisms have been proposed to explain the excited and misaligned subpopulation of HJs: Lidov-Kozai migration and planet-planet scattering. Although both are based on completely different dynamical phenomena, at first hand they appear to be equally effective in generating hot planets. Nevertheless, there has been no detailed analysis comparing the predictions of both mechanisms, especially with respect to the final distribution of orbital characteristics. In this paper, we present a series of numerical simulations of Lidov-Kozai trapping of single planets in compact binary systems that suffered a close fly-by of a background star. Both the planet and the binary component are initially placed in coplanar orbits, although the inclination of the impactor is assumed random. After the passage of the third star, we follow the orbital and spin evolution of the planet using analytical models based on the octupole expansion of the secular Hamiltonian. We also include tidal effects, stellar oblateness and post-Newtonian perturbations. The present work aims at the comparison of the two mechanisms (Lidov-Kozai and planet-planet scattering) as an explanation for the excited and inclined HJs in binary systems. We compare the results obtained through this paper with results in Beaugé & Nesvorný (2012), where the authors analyse how the planet-planet scattering mechanisms works in order to form this hot Jovian-size planets. We find that several of the orbital characteristics of the simulated HJs are caused by tidal trapping from quasi-parabolic orbits, independent of the driving mechanism (planet-planet scattering or Lidov-Kozai migration). These include both the 3-day pile-up and the distribution in the eccentricity versus semimajor axis plane. However, the distribution of the inclinations shows significant differences. While Lidov-Kozai trapping favours a more random distribution (or even a preference for near polar orbits), planet-planet scattering shows a large portion of bodies nearly aligned with the equator of the central star. This is more consistent with the distribution of known hot planets, perhaps indicating that scattering may be a more efficient mechanism for producing these bodies.

Long Term Planetary Habitability and the Carbonate-Silicate Cycle: The Effect of Planet Size

NASA Astrophysics Data System (ADS)

Rushby, A. J.; Johnson, M.; Mills, B.; Watson, A. J.; Claire, M.

2017-12-01

The potential habitability of exoplanets is traditionally assessed by determining whether or not its orbit falls within the circumstellar `habitable zone' of its star [1]. However, this metric does not readily account readily for changes in the abundance of greenhouse gases and their associated radiative forcing as a result of the action of the carbonate-silicate cycle. We develop a model of the carbon cycle on Earth, coupled with a stellar evolution model and a 1-D radiative-convective climate model with an Earth-like atmospheric water vapour profile [1], to explore the potential changes in the CO2 greenhouse under conditions of varying planet size (0.5 - 2 R⊕) and stellar flux (0.75 to 1.25 S⊕).We find that likely changes in global topography, tectonic outgassing and uplift, and the hydrological cycle on larger planets results in proportionally greater surface temperatures and pCO2 for a given incident flux. For planets between 0.5 and 2 R⊕ the effect of these changes results in average global surface temperature deviations of up to 15 K, which suggests that these relationships be considered in future studies of planetary habitability.Furthermore, by coupling this model with the stellar evolution scheme presented in [2] and setting an upper temperature limit of 343 K, the habitable period of the Earth-sized world around the Sun can be quantified. For a 1 R⊕ planet, this limit is approximately 6.35 Gyr after planet formation, or 1.81 Gyr from present day. Additionally, atmospheric CO2 falls below the limit at which C3 and C4 plants can effectively photosynthesize after 5.38 Gyr and 6.1 Gyr respectively, which may initiate a significant reorganization of the biosphere of the planet well before average surface temperatures render it uninhabitable.References: [1] Kopparapu et al. (2013) The Astrophysical Journal 765(2) [2] Rushby et al. (2013) Astrobiology, 13(9), 833-849.

THE HUNT FOR EXOMOONS WITH KEPLER (HEK). I. DESCRIPTION OF A NEW OBSERVATIONAL PROJECT

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

Kipping, D. M.; Bakos, G. A.; Buchhave, L.

2012-05-10

Two decades ago, empirical evidence concerning the existence and frequency of planets around stars, other than our own, was absent. Since that time, the detection of extrasolar planets from Jupiter-sized to, most recently, Earth-sized worlds has blossomed and we are finally able to shed light on the plurality of Earth-like, habitable planets in the cosmos. Extrasolar moons may also be frequently habitable worlds, but their detection or even systematic pursuit remains lacking in the current literature. Here, we present a description of the first systematic search for extrasolar moons as part of a new observational project called 'The Hunt formore » Exomoons with Kepler' (HEK). The HEK project distills the entire list of known transiting planet candidates found by Kepler (2326 at the time of writing) down to the most promising candidates for hosting a moon. Selected targets are fitted using a multimodal nested sampling algorithm coupled with a planet-with-moon light curve modeling routine. By comparing the Bayesian evidence of a planet-only model to that of a planet-with-moon, the detection process is handled in a Bayesian framework. In the case of null detections, upper limits derived from posteriors marginalized over the entire prior volume will be provided to inform the frequency of large moons around viable planetary hosts, {eta} leftmoon. After discussing our methodologies for target selection, modeling, fitting, and vetting, we provide two example analyses.« less

Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion

PubMed Central

Johansen, Anders; Low, Mordecai-Mark Mac; Lacerda, Pedro; Bizzarro, Martin

2015-01-01

Chondrules are millimeter-sized spherules that dominate primitive meteorites (chondrites) originating from the asteroid belt. The incorporation of chondrules into asteroidal bodies must be an important step in planet formation, but the mechanism is not understood. We show that the main growth of asteroids can result from gas drag–assisted accretion of chondrules. The largest planetesimals of a population with a characteristic radius of 100 km undergo runaway accretion of chondrules within ~3 My, forming planetary embryos up to Mars’s size along with smaller asteroids whose size distribution matches that of main belt asteroids. The aerodynamical accretion leads to size sorting of chondrules consistent with chondrites. Accretion of millimeter-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disc lifetime outside of 25 AU. The contribution of direct planetesimal accretion to the growth of both asteroids and Kuiper belt objects is minor. In contrast, planetesimal accretion and chondrule accretion play more equal roles in the formation of Moon-sized embryos in the terrestrial planet formation region. These embryos are isolated from each other and accrete planetesimals only at a low rate. However, the continued accretion of chondrules destabilizes the oligarchic configuration and leads to the formation of Mars-sized embryos and terrestrial planets by a combination of direct chondrule accretion and giant impacts. PMID:26601169

Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion

NASA Astrophysics Data System (ADS)

Johansen, Anders; Mac Low, Mordecai-Mark; Lacerda, Pedro; Bizzarro, Martin

2015-04-01

Chondrules are millimeter-sized spherules that dominate primitive meteorites (chondrites) originating from the asteroid belt. The incorporation of chondrules into asteroidal bodies must be an important step in planet formation, but the mechanism is not understood. We show that the main growth of asteroids can result from gas drag-assisted accretion of chondrules. The largest planetesimals of a population with a characteristic radius of 100 km undergo runaway accretion of chondrules within ~3 My, forming planetary embryos up to Mars's size along with smaller asteroids whose size distribution matches that of main belt asteroids. The aerodynamical accretion leads to size sorting of chondrules consistent with chondrites. Accretion of millimeter-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disc lifetime outside of 25 AU. The contribution of direct planetesimal accretion to the growth of both asteroids and Kuiper belt objects is minor. In contrast, planetesimal accretion and chondrule accretion play more equal roles in the formation of Moon-sized embryos in the terrestrial planet formation region. These embryos are isolated from each other and accrete planetesimals only at a low rate. However, the continued accretion of chondrules destabilizes the oligarchic configuration and leads to the formation of Mars-sized embryos and terrestrial planets by a combination of direct chondrule accretion and giant impacts.

Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion.

PubMed

Johansen, Anders; Low, Mordecai-Mark Mac; Lacerda, Pedro; Bizzarro, Martin

2015-04-01

Chondrules are millimeter-sized spherules that dominate primitive meteorites (chondrites) originating from the asteroid belt. The incorporation of chondrules into asteroidal bodies must be an important step in planet formation, but the mechanism is not understood. We show that the main growth of asteroids can result from gas drag-assisted accretion of chondrules. The largest planetesimals of a population with a characteristic radius of 100 km undergo runaway accretion of chondrules within ~3 My, forming planetary embryos up to Mars's size along with smaller asteroids whose size distribution matches that of main belt asteroids. The aerodynamical accretion leads to size sorting of chondrules consistent with chondrites. Accretion of millimeter-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disc lifetime outside of 25 AU. The contribution of direct planetesimal accretion to the growth of both asteroids and Kuiper belt objects is minor. In contrast, planetesimal accretion and chondrule accretion play more equal roles in the formation of Moon-sized embryos in the terrestrial planet formation region. These embryos are isolated from each other and accrete planetesimals only at a low rate. However, the continued accretion of chondrules destabilizes the oligarchic configuration and leads to the formation of Mars-sized embryos and terrestrial planets by a combination of direct chondrule accretion and giant impacts.

DETECTION AND CHARACTERIZATION OF EXTRASOLAR PLANETS THROUGH MEAN-MOTION RESONANCES. I. SIMULATIONS OF HYPOTHETICAL DEBRIS DISKS

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

Tabeshian, Maryam; Wiegert, Paul A., E-mail: mtabeshi@uwo.ca

2016-02-20

The gravitational influence of a planet on a nearby disk provides a powerful tool for detecting and studying extrasolar planetary systems. Here we demonstrate that gaps can be opened in dynamically cold debris disks at the mean-motion resonances of an orbiting planet. The gaps are opened away from the orbit of the planet itself, revealing that not all disk gaps need contain a planetary body. These gaps are large and deep enough to be detectable in resolved disk images for a wide range of reasonable disk-planet parameters, though we are not aware of any such gaps detected to date. Themore » gap shape and size are diagnostic of the planet location, eccentricity and mass, and allow one to infer the existence of unseen planets, as well as many important parameters of both seen and unseen planets in these systems. We present expressions to allow the planetary mass and semimajor axis to be calculated from observed gap width and location.« less

Exoplanet habitability.

PubMed

Seager, Sara

2013-05-03

The search for exoplanets includes the promise to eventually find and identify habitable worlds. The thousands of known exoplanets and planet candidates are extremely diverse in terms of their masses or sizes, orbits, and host star type. The diversity extends to new kinds of planets, which are very common yet have no solar system counterparts. Even with the requirement that a planet's surface temperature must be compatible with liquid water (because all life on Earth requires liquid water), a new emerging view is that planets very different from Earth may have the right conditions for life. The broadened possibilities will increase the future chances of discovering an inhabited world.

Photometric Analysis and Transit Times of TRAPPIST-1 B and C

NASA Astrophysics Data System (ADS)

Morris, Brett M.; Agol, Eric; Hawley, Suzanne L.

2018-01-01

TRAPPIST-1 hosts seven Earth-sized planets transiting an M8 star. We observed mid-transit times of each of the inner two planets with the Astrophysical Research Consortium (ARC) 3.5 m Telescope at Apache Point Observatory (APO) to help constrain the planet masses with transit timing variations, and we outline a procedure for analyzing transit observations of late-M stars with APO. The transit times of TRAPPIST-1 b and c are $\\mathrm{BJD}_{\\mathrm{TDB}} = 2457580.87634^{+0.00034}_{-0.00034}$ and $2457558.89477^{+0.00080}_{-0.00085}$, respectively, which will help constrain the planet masses.

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.

Tectonic evolution of the terrestrial planets.

PubMed

Head, J W; Solomon, S C

1981-07-03

The style and evolution of tectonics on the terrestrial planets differ substantially. The style is related to the thickness of the lithosphere and to whether the lithosphere is divided into distinct, mobile plates that can be recycled into the mantle, as on Earth, or is a single spherical shell, as on the moon, Mars, and Mercury. The evolution of a planetary lithosphere and the development of plate tectonics appear to be influenced by several factors, including planetary size, chemistry, and external and internal heat sources. Vertical tectonic movement due to lithospheric loading or uplift is similar on all of the terrestrial planets and is controlled by the local thickness and rheology of the lithosphere. The surface of Venus, although known only at low resolution, displays features both similar to those on Earth (mountain belts, high plateaus) and similar to those on the smaller planets (possible impact basins). Improved understanding of the tectonic evolution of Venus will permit an evaluation of the relative roles of planetary size and chemistry in determining evolutionary style.

Terrestrial Planet and Asteroid Formation in the Presence of Giant Planets. I. Relative Velocities of Planetesimals Subject to Jupiter and Saturn Perturbations

NASA Astrophysics Data System (ADS)

Kortenkamp, Stephen J.; Wetherill, George W.

2000-01-01

We investigate the orbital evolution of 10 13- to 10 25-g planetesimals near 1 AU and in the asteroid belt (near 2.6 AU) prior to the stage of evolution when the mutual perturbations between the planetesimals become important. We include nebular gas drag and the effects of Jupiter and Saturn at their present masses and in their present orbits. Gas drag introduces a size-dependent phasing of the secular perturbations, which leads to a pronounced dip in encounter velocities ( Venc) between bodies of similar mass. Planetesimals of identical mass have Venc ˜1 and ˜10 m s -1 (near 1 and 2.6 AU, respectively) while bodies differing by ˜10 in mass have Venc ˜10 and ˜100 m s -1 (near 1 and 2.6 AU, respectively). Under these conditions, growth, rather than erosion, will occur only by collisions of bodies of nearly the same mass. There will be essentially no gravitational focusing between bodies less than 10 22 to 10 25 g, allowing growth of planetary embryos in the terrestrial planet region to proceed in a slower nonrunaway fashion. The environment in the asteroid belt will be even more forbidding and it is uncertain whether even the severely depleted present asteroid belt could form under these conditions. The perturbations of Jupiter and Saturn are quite sensitive to their semi-major axes and decrease when the planets' heliocentric distances are increased to allow for protoplanet migration. It is possible, though not clearly demonstrated, that this could produce a depleted asteroid belt but permit formation of a system of terrestrial planet embryos on a ˜10 6-year timescale, initially by nonrunaway growth and transitioning to runaway growth after ˜10 5 years. The calculations reported here are valid under the condition that the relative velocities of the bodies are determined only by Jupiter and Saturn perturbations and by gas drag, with no mutual perturbations between planetesimals. If, while subject to these conditions, the bodies become large enough for their mutual perturbations to influence their velocity and size evolution significantly, the problem becomes much more complex. This problem is under investigation.

Terrestrial planet and asteroid formation in the presence of giant planets. I. Relative velocities of planetesimals subject to Jupiter and Saturn perturbations.

PubMed

Kortenkamp, S J; Wetherill, G W

2000-01-01

We investigate the orbital evolution of 10(13)- to 10(25) -g planetesimals near 1 AU and in the asteroid belt (near 2.6 AU) prior to the stage of evolution when the mutual perturbations between the planetesimals become important. We include nebular gas drag and the effects of Jupiter and Saturn at their present masses and in their present orbits. Gas drag introduces a size-dependent phasing of the secular perturbations, which leads to a pronounced dip in encounter velocities (Venc) between bodies of similar mass. Plantesimals of identical mass have Venc approximately 1 and approximately 10 m s-1 (near 1 and 2.6 AU, respectively) while bodies differing by approximately 10 in mass have Venc approximately 10 and approximately 100 m s-1 (near 1 and 2.6 AU, respectively). Under these conditions, growth, rather than erosion, will occur only by collisions of bodies of nearly the same mass. There will be essentially no gravitational focusing between bodies less than 10(22) to 10(25) g, allowing growth of planetary embryos in the terrestrial planet region to proceed in a slower nonrunaway fashion. The environment in the asteroid belt will be even more forbidding and it is uncertain whether even the severely depleted present asteroid belt could form under these conditions. The perturbations of Jupiter and Saturn are quite sensitive to their semi-major axes and decrease when the planets' heliocentric distances are increased to allow for protoplanet migration. It is possible, though not clearly demonstrated, that this could produce a depleted asteroid belt but permit formation of a system of terrestrial planet embryos on a approximately 10(6)-year timescale, initially by nonrunaway growth and transitioning to runaway growth after approximately 10(5) years. The calculations reported here are valid under the condition that the relative velocities of the bodies are determined only by Jupiter and Saturn perturbations and by gas drag, with no mutual perturbations between planetesimals. If, while subject to these conditions, the bodies become large enough for their mutual perturbations to influence their velocity and size evolution significantly, the problem becomes much more complex. This problem is under investigation.

Prevalence and Properties of Planets from Kepler and K2

NASA Astrophysics Data System (ADS)

Petigura, Erik; Marcy, Geoffrey W.; Howard, Andrew; Crossfield, Ian; Beichman, Charles; Sinukoff, Evan

2015-12-01

Discoveries from the prime Kepler mission demonstrated that small planets (< 3 Earth-radii) are common outcomes of planet formation around G, K, and M stars. While Kepler detected many such planets, all but a handful orbit faint, distant stars, which are not amenable to precise follow up measurements. NASA's K2 mission has the potential to increase the number of known small, transiting planets around bright stars by an order of magnitude. I will present the latest results from my team's efforts to detect, confirm, and characterize planets using the K2 mission. I will highlight some of the progress and remaining challenges involved with generating denoised K2 photometry and with detecting planets in the presence of severe instrument systematics. Among our recent discoveries are the K2-3 and K2-21 planetary systems: M dwarfs hosting multiple transiting Earth-size planets with low equilibrium temperatures. These systems offer a convenient laboratory for studying the bulk composition and atmospheric properties of small planets receiving low levels of stellar irradiation, where processes such as mass loss by photo-evaporation could play a weaker role.

RAPID WATER LOSS CAN EXTEND THE LIFETIME OF PLANETARY HABITABILITY

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

Kodama, Takanori; Abe, Yutaka; Genda, Hidenori

Two habitable planetary states are proposed: an aqua planet like the Earth and a land planet that has a small amount of water. Land planets keep liquid water under larger solar radiation compared to aqua planets. Water loss may change an aqua planet into a land planet, and the planet can remain habitable for a longer time than if it had remained an aqua planet. We calculate planetary evolution with hydrogen escape for different initial water inventories and different distances from the central star. We find that there are two conditions necessary to evolve an aqua planet into a land planet: the criticalmore » amount of water on the surface (M{sub ml}) consistent with a planet being a land planet, and the critical amount of water vapor in the atmosphere (M{sub cv}) that defines the onset of the runaway greenhouse state. We find that Earth-sized aqua planets with initial oceans <10% of the Earth's can evolve into land planets if M{sub cv} = 3 m in precipitable water and M{sub ml} = 5% of the Earth's ocean mass. Such planets can keep liquid water on their surface for another 2 Gyr. The initial amount of water and M{sub cv} are shown to be important dividing parameters of the planetary evolution path. Our results indicate that massive hydrogen escape could give a fresh start as another kind of habitable planet rather than the end of its habitability.« less

TRAPPIST-1 Planetary Orbits and Transits

NASA Image and Video Library

2017-02-22

This frame from a video details a system of seven planets orbiting TRAPPIST-1, an ultra-cool dwarf star. Spitzer was able to identify a total of seven rocky worlds, including three in the habitable zone where liquid water might be found. A 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, of these planets are tidally locked, meaning one face of the planet permanently faces their sun. 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. A video is available at http://photojournal.jpl.nasa.gov/catalog/PIA21427

Artist concept of SIM PlanetQuest Artist Concept

NASA Image and Video Library

2002-12-21

Artist's concept of the current mission configuration. SIM PlanetQuest (formerly called Space Interferometry Mission), currently under development, will determine the positions and distances of stars several hundred times more accurately than any previous program. This accuracy will allow SIM to determine the distances to stars throughout the galaxy and to probe nearby stars for Earth-sized planets. SIM will open a window to a new world of discoveries. http://photojournal.jpl.nasa.gov/catalog/PIA04248

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.

KSC-2009-1956

NASA Image and Video Library

2009-03-06

CAPE CANAVERAL, Fla. – The Delta II 7925 rocket stands ready for launch following rollback of the mobile service tower on Launch Pad 17-B at Cape Canaveral Air Force Station. Atop the rocket is NASA's Kepler spacecraft. Kepler is a spaceborne telescope designed to search the nearby region of our galaxy for Earth-size planets orbiting in the habitable zone of stars like our sun. The habitable zone is the region around a star where temperatures permit water to be liquid on a planet's surface. The challenge for Kepler is to look at a large number of stars in order to statistically estimate the total number of Earth-size planets orbiting sun-like stars in the habitable zone. Kepler will survey more than 100,000 stars in our galaxy. Photo credit: NASA/Jack Pfaller

KSC-2009-1961

NASA Image and Video Library

2009-03-06

CAPE CANAVERAL, Fla. – After rollback of the mobile service tower on Cape Canaveral Air Force Station's Launch Pad 17-B, in Florida, NASA's Kepler spacecraft sits poised for launch atop the United Launch Alliance Delta II 7925 rocket. Kepler is a spaceborne telescope designed to search the nearby region of our galaxy for Earth-size planets orbiting in the habitable zone of stars like our sun. The habitable zone is the region around a star where temperatures permit water to be liquid on a planet's surface. The challenge for Kepler is to look at a large number of stars in order to statistically estimate the total number of Earth-size planets orbiting sun-like stars in the habitable zone. Kepler will survey more than 100,000 stars in our galaxy. Photo credit: NASA/Jack Pfaller

KSC-2009-1963

NASA Image and Video Library

2009-03-06

CAPE CANAVERAL, Fla. – After rollback of the mobile service tower on Cape Canaveral Air Force Station's Launch Pad 17-B in Florida, NASA's Kepler spacecraft sits poised for launch atop the United Launch Alliance Delta II 7925 rocket. Kepler is a spaceborne telescope designed to search the nearby region of our galaxy for Earth-size planets orbiting in the habitable zone of stars like our sun. The habitable zone is the region around a star where temperatures permit water to be liquid on a planet's surface. The challenge for Kepler is to look at a large number of stars in order to statistically estimate the total number of Earth-size planets orbiting sun-like stars in the habitable zone. Kepler will survey more than 100,000 stars in our galaxy. Photo credit: NASA/Jack Pfaller

KSC-2009-1972

NASA Image and Video Library

2009-03-06

CAPE CANAVERAL, Fla. – United Launch Alliance's Delta II rocket roars into the night sky carrying NASA's Kepler spacecraft. Liftoff from Launch Pad 17-B at Cape Canaveral Air Force Station in Florida was on time at 10:49 p.m. EST. Kepler is a spaceborne telescope designed to search the nearby region of our galaxy for Earth-size planets orbiting in the habitable zone of stars like our sun. The habitable zone is the region around a star where temperatures permit water to be liquid on a planet's surface. The challenge for Kepler is to look at a large number of stars in order to statistically estimate the total number of Earth-size planets orbiting sun-like stars in the habitable zone. Kepler will survey more than 100,000 stars in our galaxy. Photo credit: NASA/Jack Pfaller

KSC-2009-1962

NASA Image and Video Library

2009-03-06

CAPE CANAVERAL, Fla. – After rollback of the mobile service tower on Cape Canaveral Air Force Station's Launch Pad 17-B in Florida, NASA's Kepler spacecraft sits poised for launch atop the United Launch Alliance Delta II 7925 rocket. Kepler is a spaceborne telescope designed to search the nearby region of our galaxy for Earth-size planets orbiting in the habitable zone of stars like our sun. The habitable zone is the region around a star where temperatures permit water to be liquid on a planet's surface. The challenge for Kepler is to look at a large number of stars in order to statistically estimate the total number of Earth-size planets orbiting sun-like stars in the habitable zone. Kepler will survey more than 100,000 stars in our galaxy. Photo credit: NASA/Jack Pfaller

KSC-2009-1959

NASA Image and Video Library

2009-03-06

CAPE CANAVERAL, Fla. – The Delta II 7925 rocket stands ready for launch following rollback of the mobile service tower on Launch Pad 17-B at Cape Canaveral Air Force Station in Florida. Atop the rocket is NASA's Kepler spacecraft. Kepler is a spaceborne telescope designed to search the nearby region of our galaxy for Earth-size planets orbiting in the habitable zone of stars like our sun. The habitable zone is the region around a star where temperatures permit water to be liquid on a planet's surface. The challenge for Kepler is to look at a large number of stars in order to statistically estimate the total number of Earth-size planets orbiting sun-like stars in the habitable zone. Kepler will survey more than 100,000 stars in our galaxy. Photo credit: NASA/Jack Pfaller

KSC-2009-1958

NASA Image and Video Library

2009-03-06

CAPE CANAVERAL, Fla. – The Delta II 7925 rocket stands ready for launch following rollback of the mobile service tower on Launch Pad 17-B at Cape Canaveral Air Force Station in Florida. Atop the rocket is NASA's Kepler spacecraft. Kepler is a spaceborne telescope designed to search the nearby region of our galaxy for Earth-size planets orbiting in the habitable zone of stars like our sun. The habitable zone is the region around a star where temperatures permit water to be liquid on a planet's surface. The challenge for Kepler is to look at a large number of stars in order to statistically estimate the total number of Earth-size planets orbiting sun-like stars in the habitable zone. Kepler will survey more than 100,000 stars in our galaxy. Photo credit: NASA/Jack Pfaller

KSC-2009-1973

NASA Image and Video Library

2009-03-06

CAPE CANAVERAL, Fla. – On Launch Pad 17-B at Cape Canaveral Air Force Station in Florida, the engines on United Launch Alliance's Delta II rocket carrying NASA's Kepler spacecraft ignite. Liftoff was on time at 10:49 p.m. EST. Kepler is a spaceborne telescope designed to search the nearby region of our galaxy for Earth-size planets orbiting in the habitable zone of stars like our sun. The habitable zone is the region around a star where temperatures permit water to be liquid on a planet's surface. The challenge for Kepler is to look at a large number of stars in order to statistically estimate the total number of Earth-size planets orbiting sun-like stars in the habitable zone. Kepler will survey more than 100,000 stars in our galaxy. Photo credit: NASA/Tony Gray

KSC-2009-1955

NASA Image and Video Library

2009-03-06

CAPE CANAVERAL, Fla. – The Delta II 7925 rocket stands ready for launch following rollback of the mobile service tower on Launch Pad 17-B at Cape Canaveral Air Force Station. Atop the rocket is NASA's Kepler spacecraft. Kepler is a spaceborne telescope designed to search the nearby region of our galaxy for Earth-size planets orbiting in the habitable zone of stars like our sun. The habitable zone is the region around a star where temperatures permit water to be liquid on a planet's surface. The challenge for Kepler is to look at a large number of stars in order to statistically estimate the total number of Earth-size planets orbiting sun-like stars in the habitable zone. Kepler will survey more than 100,000 stars in our galaxy. Photo credit: NASA/Jack Pfaller

A Search for Lost Planets in the Kepler Multi-planet Systems and the Discovery of the Long-period, Neptune-sized Exoplanet Kepler-150 f

NASA Astrophysics Data System (ADS)

Schmitt, Joseph R.; Jenkins, Jon M.; Fischer, Debra A.

2017-04-01

The vast majority of the 4700 confirmed planets (CPs) and planet candidates discovered by the Kepler mission were first found by the Kepler pipeline. In the pipeline, after a transit signal is found, all data points associated with those transits are removed, creating a “Swiss cheese”-like light curve full of holes, which is then used for subsequent transit searches. These holes could render an additional planet undetectable (or “lost”). We examine a sample of 114 stars with 3+ CPs to evaluate the effect of this “Swiss cheesing.” A simulation determines that the probability that a transiting planet is lost due to the transit masking is low, but non-negligible, reaching a plateau at ˜3.3% lost in the period range of P = 400-500 days. We then model all planet transits and subtract out the transit signals for each star, restoring the in-transit data points, and use the Kepler pipeline to search the transit-subtracted (I.e., transit-cleaned) light curves. However, the pipeline did not discover any credible new transit signals. This demonstrates the validity and robustness of the Kepler pipeline’s choice to use transit masking over transit subtraction. However, a follow-up visual search through all the transit-subtracted data, which allows for easier visual identification of new transits, revealed the existence of a new, Neptune-sized exoplanet (Kepler-150 f) and a potential single transit of a likely false positive (FP) (Kepler-208). Kepler-150 f (P = 637.2 days, {R}{{P}}={3.64}-0.39+0.52 R⊕) is confirmed with >99.998% confidence using a combination of the planet multiplicity argument, an FP probability analysis, and a transit duration analysis.

Future Interstellar Travel Destinations: Assessing the Suitability of Nearby Red Dwarf Stars as Hosts to Habitable Life-bearing Planets

NASA Astrophysics Data System (ADS)

Guinan, Edward F.; Engle, S. G.

2013-01-01

As part of our NSF/NASA sponsored “Living with a Red Dwarf Star” program, we are carrying out a comprehensive study of red dwarf stars across the electromagnetic spectrum to assess their suitability as hosts for habitable planets. These cool, dim, long-lived, low mass stars comprise >75% of the stars in our Galaxy. Moreover an increasing number of (potentially habitable) large Earth-size planets are being found hosted by red dwarfs. With intrinsically low luminosities (L < 0.02 Lsun), the habitable zones (HZs) of hosted planets are close to their host stars (typically 0.05 AU < HZ <0.4 AU). Our study indicates red dwarf HZ planets without strong (protective) magnetic fields are especially susceptible to atmospheric erosion & loss by the star’s X-UV and wind fluxes. Also, the frequent flaring of young red dwarf stars and tidal-locking of close-in planets could challenge the development of life. But tidal locking of these planets could have some advantages for the developmenet of life. The long lifetimes of the red dwarfs (> 50 BY) could be favorable for the development of complex (possibly even intelligent) life. We discuss our results in the context of nearby red dwarfs as possible destinations for future interstellar missions program. We illustrate this with examples of the red dwarf exoplanet systems: GJ 581 and HD 85512 (both with large HZ Earth-size planets). Also we discuss the nearest star (4.3 LY) - the red dwarf - Proxima Centauri as a potential destination for future interstellar missions such proposed by Icarus Interstellar and the 100-Year Starship and StarVoyager programs. We gratefully acknowledge the support from NSF-Grant AST-10-09903, Chandra Grants GO1-12124X & GO2-13020X and HST Grant GO-10920.

XUV-Exposed, Non-Hydrostatic Hydrogen-Rich Upper Atmospheres of Terrestrial Planets. Part I: Atmospheric Expansion and Thermal Escape

PubMed Central

Lammer, Helmut; Odert, Petra; Kulikov, Yuri N.; Kislyakova, Kristina G.; Khodachenko, Maxim L.; Güdel, Manuel; Hanslmeier, Arnold; Biernat, Helfried

2013-01-01

Abstract The recently discovered low-density “super-Earths” Kepler-11b, Kepler-11f, Kepler-11d, Kepler-11e, and planets such as GJ 1214b represent the most likely known planets that are surrounded by dense H/He envelopes or contain deep H2O oceans also surrounded by dense hydrogen envelopes. Although these super-Earths are orbiting relatively close to their host stars, they have not lost their captured nebula-based hydrogen-rich or degassed volatile-rich steam protoatmospheres. Thus, it is interesting to estimate the maximum possible amount of atmospheric hydrogen loss from a terrestrial planet orbiting within the habitable zone of late main sequence host stars. For studying the thermosphere structure and escape, we apply a 1-D hydrodynamic upper atmosphere model that solves the equations of mass, momentum, and energy conservation for a planet with the mass and size of Earth and for a super-Earth with a size of 2 REarth and a mass of 10 MEarth. We calculate volume heating rates by the stellar soft X-ray and extreme ultraviolet radiation (XUV) and expansion of the upper atmosphere, its temperature, density, and velocity structure and related thermal escape rates during the planet's lifetime. Moreover, we investigate under which conditions both planets enter the blow-off escape regime and may therefore experience loss rates that are close to the energy-limited escape. Finally, we discuss the results in the context of atmospheric evolution and implications for habitability of terrestrial planets in general. Key Words: Stellar activity—Low-mass stars—Early atmospheres—Earth-like exoplanets—Energetic neutral atoms—Ion escape—Habitability. Astrobiology 13, 1011–1029. PMID:24251443

A Search for Lost Planets in the Kepler Multi-Planet Systems and the Discovery of the Long-Period, Neptune-Sized Exoplanet Kepler-150 f

NASA Technical Reports Server (NTRS)

Schmitt, Joseph R.; Jenkins, Jon M.; Fischer, Debra A.

2017-01-01

The vast majority of the 4700 confirmed planets and planet candidates discovered by the Kepler space telescope were first found by the Kepler pipeline. In the pipeline, after a transit signal is found, all data points associated with those transits are removed, creating a Swiss cheese-like light curve full of holes, which is then used for subsequent transit searches. These holes could render an additional planet undetectable (or lost). We examine a sample of 114 stars with 3+ confirmed planets to see the effect that this Swiss cheesing may have. A simulation determined that the probability that a transiting planet is lost due to the transit masking is low, but non-neglible, reaching a plateau at approximately 3.3% lost in the period range of P = 400 - 500 days. We then model the transits in all quarters of each star and subtract out the transit signals, restoring the in-transit data points, and use the Kepler pipeline to search the transit-subtracted (i.e., transit-cleaned) light curves. However, the pipeline did not discover any credible new transit signals. This demonstrates the validity and robustness of the Kepler pipelines choice to use transit masking over transit subtraction. However, a follow-up visual search through all the transit-subtracted data, which allows for easier visual identification of new transits, revealed the existence of a new, Neptune-sized exoplanet. Kepler-150 f (P = 637.2 days, RP = 3.86 R earth) is confirmed using a combination of false positive probability analysis, transit duration analysis, and the planet multiplicity argument.

A SEARCH FOR LOST PLANETS IN THE KEPLER MULTI-PLANET SYSTEMS AND THE DISCOVERY OF A LONG PERIOD, NEPTUNE-SIZED EXOPLANET KEPLER-150 F.

PubMed

Schmitt, Joseph R; Jenkins, Jon M; Fischer, Debra A

2017-04-01

The vast majority of the 4700 confirmed planets and planet candidates discovered by the Kepler space telescope were first found by the Kepler pipeline. In the pipeline, after a transit signal is found, all data points associated with those transits are removed, creating a "Swiss cheese"-like light curve full of holes, which is then used for subsequent transit searches. These holes could render an additional planet undetectable (or "lost"). We examine a sample of 114 stars with 3+ confirmed planets to see the effect that this "Swiss cheesing" may have. A simulation determined that the probability that a transiting planet is lost due to the transit masking is low, but non-neglible, reaching a plateau at ~3.3% lost in the period range of P = 400 - 500 days. We then model the transits in all quarters of each star and subtract out the transit signals, restoring the in-transit data points, and use the Kepler pipeline to search the transit-subtracted (i.e., transit-cleaned) light curves. However, the pipeline did not discover any credible new transit signals. This demonstrates the validity and robustness of the Kepler pipeline's choice to use transit masking over transit subtraction. However, a follow-up visual search through all the transit-subtracted data, which allows for easier visual identification of new transits, revealed the existence of a new, Neptune-sized exoplanet. Kepler-150 f ( P = 637.2 days, R P = 3.86 R ⊕ ) is confirmed using a combination of false positive probability analysis, transit duration analysis, and the planet multiplicity argument.

A SEARCH FOR LOST PLANETS IN THE KEPLER MULTI-PLANET SYSTEMS AND THE DISCOVERY OF A LONG PERIOD, NEPTUNE-SIZED EXOPLANET KEPLER-150 F

PubMed Central

Schmitt, Joseph R.; Jenkins, Jon M.; Fischer, Debra A.

2018-01-01

The vast majority of the 4700 confirmed planets and planet candidates discovered by the Kepler space telescope were first found by the Kepler pipeline. In the pipeline, after a transit signal is found, all data points associated with those transits are removed, creating a “Swiss cheese”-like light curve full of holes, which is then used for subsequent transit searches. These holes could render an additional planet undetectable (or “lost”). We examine a sample of 114 stars with 3+ confirmed planets to see the effect that this “Swiss cheesing” may have. A simulation determined that the probability that a transiting planet is lost due to the transit masking is low, but non-neglible, reaching a plateau at ~3.3% lost in the period range of P = 400 – 500 days. We then model the transits in all quarters of each star and subtract out the transit signals, restoring the in-transit data points, and use the Kepler pipeline to search the transit-subtracted (i.e., transit-cleaned) light curves. However, the pipeline did not discover any credible new transit signals. This demonstrates the validity and robustness of the Kepler pipeline’s choice to use transit masking over transit subtraction. However, a follow-up visual search through all the transit-subtracted data, which allows for easier visual identification of new transits, revealed the existence of a new, Neptune-sized exoplanet. Kepler-150 f (P = 637.2 days, RP = 3.86 R⊕) is confirmed using a combination of false positive probability analysis, transit duration analysis, and the planet multiplicity argument. PMID:29375142

COAGULATION CALCULATIONS OF ICY PLANET FORMATION AT 15-150 AU: A CORRELATION BETWEEN THE MAXIMUM RADIUS AND THE SLOPE OF THE SIZE DISTRIBUTION FOR TRANS-NEPTUNIAN OBJECTS

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

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

2012-03-15

We investigate whether coagulation models of planet formation can explain the observed size distributions of trans-Neptunian objects (TNOs). Analyzing published and new calculations, we demonstrate robust relations between the size of the largest object and the slope of the size distribution for sizes 0.1 km and larger. These relations yield clear, testable predictions for TNOs and other icy objects throughout the solar system. Applying our results to existing observations, we show that a broad range of initial disk masses, planetesimal sizes, and fragmentation parameters can explain the data. Adding dynamical constraints on the initial semimajor axis of 'hot' Kuiper Beltmore » objects along with probable TNO formation times of 10-700 Myr restricts the viable models to those with a massive disk composed of relatively small (1-10 km) planetesimals.« less

Controls on the Climates of Tidally Locked Terrestrial Planets

NASA Astrophysics Data System (ADS)

Yang, J.; Cowan, N. B.; Abbot, D. S.

2013-12-01

Earth-size planets in the habitable zone of M-dwarf stars may be very common. Due to strong tidal forces, these planets in circulate orbits are expected to be tidally locked, with one hemisphere experiencing perpetual day and the other permanent night. Previous studies on the climates of tidally locked planets were primarily based on complex 3D general circulation models (GCMs). The central question to be answered in this work is: what is the minimum necessary physics needed to understand the climates simulated by GCMs? A two-column model, primarily based on the weak temperature gradient (WTG) approximation (Sobel et al. 2001) and the fixed anvil temperature (FAT) hypothesis (Hartmann and Larson 2002) for the tropical climate of Earth, is developed for understanding the climates of tidally locked planets. This highly idealized model well reproduces fundamental features of the climates obtained in complicated GCMs (Yang et al. 2013), including planetary albedo, longwave cloud forcing, outgoing longwave radiation (OLR), and atmospheric energy transport. This suggests that the WTG approximation and the FAT hypothesis may be good approximations for tidally locked habitable planets, which provides strong constraints on the large-scale circulations, diabatic processes, and cloud behaviour on these planets. Both the simple model and the GCMs predict that (i) convection and planetary albedo on the dayside increase as stellar flux is increased; (ii) longwave cloud radiative forcing increases as stellar flux is increased, due to the cloud top temperature remains nearly constant as the climate changes (FAT hypothesis); (iii) for planets at the inner regions of the habitable zone, the dayside--nightside OLR contrast becomes very weak or even reverses, due to the strong longwave absorption by water vapor and clouds on the dayside; (iv) the dayside--to--nightside atmospheric energy transport (AET) increases as stellar flux is increased, and decreases as oceanic energy transport (OET) is included, although the compensation between AET and OET is incomplete. To summarize, we are able to construct a realistic low-order model for the climate of tidally locked terrestrial planets, including the cloud behavior, using only the two constraints. This bodes well for the interpretation of complex GCMs and future observations of such planets using, for example, the James Webb Space Telescope. Cited papers: [1]. Sobel, A. H., J. Nilsson and L. M. Polvani: The weak temperature gradient approximation and balanced tropical moisture waves, J. Atmos. Sci., 58, 3650-65, 2001. [2]. Hartmann, D. L. and K. Larson, An important constraint on tropical cloud-climate feedback, Geophys. Res. Lett., 29, 1951-54, 2002. [3]. Yang, J., N. B. Cowan and D. S. Abbot: Stabilizing cloud feedback dramatically expands the habitable zone of tidally locked planets, ApJ. Lett., 771, L45, 2013.

Star-planet interactions. IV. Possibility of detecting the orbit-shrinking of a planet around a red giant

NASA Astrophysics Data System (ADS)

Meynet, Georges; Eggenberger, Patrick; Privitera, Giovanni; Georgy, Cyril; Ekström, Sylvia; Alibert, Yann; Lovis, Christophe

2017-06-01

The surface rotations of some red giants are so fast that they must have been spun up by tidal interaction with a close companion, either another star, a brown dwarf, or a planet. We focus here on the case of red giants that are spun up by tidal interaction with a planet. When the distance between the planet and the star decreases, the spin period of the star decreases, the orbital period of the planet decreases, and the reflex motion of the star increases. We study the change rate of these three quantities when the circular orbit of a planet of 15 MJ that initially orbits a 2 M⊙ star at 1 au shrinks under the action of tidal forces during the red giant phase. We use stellar evolution models coupled with computations of the orbital evolution of the planet, which allows us to follow the exchanges of angular momentum between the star and the orbit in a consistent way. We obtain that the reflex motion of the red giant star increases by more than 1 m s-1 per year in the last 40 yr before the planet engulfment. During this phase, the reflex motion of the star is between 660 and 710 m s-1. The spin period of the star increases by more than about 10 min per year in the last 3000 yr before engulfment. During this period, the spin period of the star is shorter than 0.7 yr. During this same period, the variation in orbital period, which is shorter than 0.18 yr, is on the same order of magnitude. Changes in reflex-motion and spin velocities are very small and thus most likely out of reach of being observed. The most promising way of detecting this effect is through observations of transiting planets, that is, through changes of the beginning or end of the transit. For the relatively long orbital periods expected around red giants, long observing runs of typically a few years are needed. Interesting star-planet systems that currently are in this stage of orbit-shrinking would be red giants with fast rotation (above typically 4-5 km s-1), a low surface gravity (log g lower than 2), and having a planet at a distance typically smaller than about 0.4-1 au, depending on log g. A space mission like PLATO might be of great interest for detecting planets that are on the verge of being engulfed by red giants. The discovery of a few systems, even only one, would provide very interesting clues about the physics of tidal interaction between a red giant and a planet.

SpaceSafari

ERIC Educational Resources Information Center

Scarlatos, Tony

2013-01-01

Exploring the Solar System in the elementary school curriculum has traditionally involved activities, such as building scale models, to help students visualize the vastness of space and the relative size of the planets and their orbits. Today, numerous websites provide a wealth of information about the sun and the planets, combining text, photos,…

Chemical composition of Earth, Venus, and Mercury.

PubMed

Morgan, J W; Anders, E

1980-12-01

Model compositions of Earth, Venus, and Mercury are calculated from the premise that planets and chondrites underwent four identical fractionation processes in the solar nebula. Because elements of similar properties stay together in these processes, five constraints suffice to define the composition of a planet: mass of the core, abundance of U, and the ratios K/U, Tl/U, and FeO/(FeO + MgO). Complete abundance tables, and normative mineralogies, are given for all three planets. Review of available data shows only a few gross trends for the inner planets: FeO decreases with heliocentric distance, whereas volatiles are depleted and refractories are enriched in the smaller planets.

Optical Spectra of Extrasolar Giant Planets

NASA Technical Reports Server (NTRS)

Heap, Sara R.; Hubeny, Ivan; Sudarsky, David; Burrows, Adam

2004-01-01

The flux distribution of a planet relative to its host star is a critical quantity for planning space observatories to detect and characterize extrasolar giant planets (EGP's). In this paper, we present optical planet-star contrasts of Jupiter-mass planets as a function of stellar type, orbital distance, and planetary cloud characteristics. As originally shown by Sudarsky et al. (2000, 2003), the phaseaveraged brightness of an EGP does not necessarily decrease monotonically with greater orbital distance because of changes in its albedo and absorption spectrum at lower temperatures. We apply our results to Eclipse, a 1.8-m optical telescope + coronograph to be proposed as a NASA Discovery mission later this year.

Habitable zone limits for dry planets.

PubMed

Abe, Yutaka; Abe-Ouchi, Ayako; Sleep, Norman H; Zahnle, Kevin J

2011-06-01

Most discussion of habitable planets has focused on Earth-like planets with globally abundant liquid water. For an "aqua planet" like Earth, the surface freezes if far from its sun, and the water vapor greenhouse effect runs away if too close. Here we show that "land planets" (desert worlds with limited surface water) have wider habitable zones than aqua planets. For planets at the inner edge of the habitable zone, a land planet has two advantages over an aqua planet: (i) the tropics can emit longwave radiation at rates above the traditional runaway limit because the air is unsaturated and (ii) the dry air creates a dry stratosphere that limits hydrogen escape. At the outer limits of the habitable zone, the land planet better resists global freezing because there is less water for clouds, snow, and ice. Here we describe a series of numerical experiments using a simple three-dimensional global climate model for Earth-sized planets. Other things (CO(2), rotation rate, surface pressure) unchanged, we found that liquid water remains stable at the poles of a low-obliquity land planet until net insolation exceeds 415 W/m(2) (170% that of modern Earth), compared to 330 W/m(2) (135%) for the aqua planet. At the outer limits, we found that a low-obliquity land planet freezes at 77%, while the aqua planet freezes at 90%. High-obliquity land and aqua planets freeze at 58% and 72%, respectively, with the poles offering the last refuge. We show that it is possible that, as the Sun brightens, an aqua planet like Earth can lose most of its hydrogen and become a land planet without first passing through a sterilizing runaway greenhouse. It is possible that Venus was a habitable land planet as recently as 1 billion years ago.

Absence of a Metallicity Effect for Ultra-short-period Planets

NASA Astrophysics Data System (ADS)

Winn, Joshua N.; Sanchis-Ojeda, Roberto; Rogers, Leslie; Petigura, Erik A.; Howard, Andrew W.; Isaacson, Howard; Marcy, Geoffrey W.; Schlaufman, Kevin C.; Cargile, Phillip; Hebb, Leslie

2017-08-01

Ultra-short-period (USP) planets are a newly recognized class of planets with periods shorter than one day and radii smaller than about 2 R ⊕. It has been proposed that USP planets are the solid cores of hot Jupiters that have lost their gaseous envelopes due to photo-evaporation or Roche lobe overflow. We test this hypothesis by asking whether USP planets are associated with metal-rich stars, as has long been observed for hot Jupiters. We find the metallicity distributions of USP-planet and hot-Jupiter hosts to be significantly different (p = 3 × 10-4) based on Keck spectroscopy of Kepler stars. Evidently, the sample of USP planets is not dominated by the evaporated cores of hot Jupiters. The metallicity distribution of stars with USP planets is indistinguishable from that of stars with short-period planets with sizes between 2 and 4 R ⊕. Thus, it remains possible that the USP planets are the solid cores of formerly gaseous planets that are smaller than Neptune. Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology. Keck time was granted by NASA, the University of California, the California Institute of Technology, and the University of Hawaii.

Habitable planets with high obliquities

NASA Technical Reports Server (NTRS)

Williams, D. M.; Kasting, J. F.

1997-01-01

Earth's obliquity would vary chaotically from 0 degrees to 85 degrees were it not for the presence of the Moon (J. Laskar, F. Joutel, and P. Robutel, 1993, Nature 361, 615-617). The Moon itself is thought to be an accident of accretion, formed by a glancing blow from a Mars-sized planetesimal. Hence, planets with similar moons and stable obliquities may be extremely rare. This has lead Laskar and colleagues to suggest that the number of Earth-like planets with high obliquities and temperate, life-supporting climates may be small. To test this proposition, we have used an energy-balance climate model to simulate Earth's climate at obliquities up to 90 degrees. We show that Earth's climate would become regionally severe in such circumstances, with large seasonal cycles and accompanying temperature extremes on middle- and high-latitude continents which might be damaging to many forms of life. The response of other, hypothetical, Earth-like planets to large obliquity fluctuations depends on their land-sea distribution and on their position within the habitable zone (HZ) around their star. Planets with several modest-sized continents or equatorial supercontinents are more climatically stable than those with polar supercontinents. Planets farther out in the HZ are less affected by high obliquities because their atmospheres should accumulate CO2 in response to the carbonate-silicate cycle. Dense, CO2-rich atmospheres transport heat very effectively and therefore limit the magnitude of both seasonal cycles and latitudinal temperature gradients. We conclude that a significant fraction of extrasolar Earth-like planets may still be habitable, even if they are subject to large obliquity fluctuations.

The role of disc self-gravity in circumbinary planet systems - II. Planet evolution

NASA Astrophysics Data System (ADS)

Mutter, Matthew M.; Pierens, Arnaud; Nelson, Richard P.

2017-08-01

We present the results of hydrodynamic simulations examining migration and growth of planets embedded in self-gravitating circumbinary discs. The binary star parameters are chosen to mimic those of the Kepler-16, -34 and -35 systems; the aim of this study is to examine the role of disc mass in determining the stopping locations of migrating planets at the edge of the cavity created by the central binary. Disc self-gravity can cause significant shrinkage of the cavity for disc masses in excess of 5-10 × the minimum mass solar nebula model. Planets forming early in the disc lifetime can migrate through the disc and stall at locations closer to the central star than is normally the case for lower mass discs, resulting in closer agreement between simulated and observed orbital architecture. The presence of a planet orbiting in the cavity of a massive disc can prevent the cavity size from expanding to the size of a lower mass disc. As the disc mass reduces over long time-scales, this indicates that circumbinary planet systems retain memory of their initial conditions. Our simulations produce planetary orbits in good agreement with Keper-16b without the need for self-gravity; Kepler-34 analogue systems produce wide and highly eccentric cavities, and self-gravity improves the agreement between simulations and data. Kepler-35b is more difficult to explain in detail due to its relatively low mass, which results in the simulated stopping location being at a larger radius than that observed.

Survival of habitable planets in unstable planetary systems

NASA Astrophysics Data System (ADS)

Carrera, Daniel; Davies, Melvyn B.; Johansen, Anders

2016-12-01

Many observed giant planets lie on eccentric orbits. Such orbits could be the result of strong scatterings with other giant planets. The same dynamical instability that produces these scatterings may also cause habitable planets in interior orbits to become ejected, destroyed, or be transported out of the habitable zone. We say that a habitable planet has resilient habitability if it is able to avoid ejections and collisions and its orbit remains inside the habitable zone. Here we model the orbital evolution of rocky planets in planetary systems where giant planets become dynamically unstable. We measure the resilience of habitable planets as a function of the observed, present-day masses and orbits of the giant planets. We find that the survival rate of habitable planets depends strongly on the giant planet architecture. Equal-mass planetary systems are far more destructive than systems with giant planets of unequal masses. We also establish a link with observation; we find that giant planets with present-day eccentricities higher than 0.4 almost never have a habitable interior planet. For a giant planet with a present-day eccentricity of 0.2 and semimajor axis of 5 au orbiting a Sun-like star, 50 per cent of the orbits in the habitable zone are resilient to the instability. As semimajor axis increases and eccentricity decreases, a higher fraction of habitable planets survive and remain habitable. However, if the habitable planet has rocky siblings, there is a significant risk of rocky planet collisions that would sterilize the planet.

Variety in planetary systems

NASA Technical Reports Server (NTRS)

Wetherill, George W.

1993-01-01

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

Synergies Between Asteroseismology and Exoplanetary Science

NASA Astrophysics Data System (ADS)

Huber, Daniel

Over the past decade asteroseismology has become a powerful method to systematically characterize host stars and dynamical architectures of exoplanet systems. In this contribution I review current key synergies between asteroseismology and exoplanetary science such as the precise determination of planet radii and ages, the measurement of orbital eccentricities, stellar obliquities and their impact on hot Jupiter formation theories, and the importance of asteroseismology on spectroscopic analyses of exoplanet hosts. I also give an outlook on future synergies such as the characterization of sub-Neptune-size planets orbiting solar-type stars, the study of planet populations orbiting evolved stars, and the determination of ages of intermediate-mass stars hosting directly imaged planets.

A New Probe of the Planet-Forming Region in T Tauri Disks

DTIC Science & Technology

2004-10-20

each object finds the presence of inner disk gaps with sizes of a few AU in each of these young (∼1 Myr) stellar systems. We propose that the...young (≤10 Myr) protoplanetary accretion disks (Beckwith et al. 2000; D’Alessio 2003 and references therein). The onset of this evolution lies in the...Gravitational inter- action between the disk and the forming planet results in the formation of a gap as the mass of the planet increases (Bryden 1

A tunnel and a traffic jam: How transition disks maintain a detectable warm dust component despite the presence of a large planet-carved gap

NASA Astrophysics Data System (ADS)

Pinilla, P.; Klarmann, L.; Birnstiel, T.; Benisty, M.; Dominik, C.; Dullemond, C. P.

2016-01-01

Context. Transition disks are circumstellar disks that show evidence of a dust cavity, which may be related to dynamical clearing by embedded planet(s). Most of these objects show signs of significant accretion, indicating that the inner disks are not truly empty, but that gas is still streaming through to the star. A subset of transition disks, sometimes called pre-transition disks, also shows a strong near-infrared excess, interpreted as an optically thick dusty belt located close to the dust sublimation radius within the first astronomical unit. Aims: We study the conditions for the survival and maintenance of such an inner disk in the case where a massive planet opens a gap in the disk. In this scenario, the planet filters out large dust grains that are trapped at the outer edge of the gap, while the inner regions of the disk may or may not be replenished with small grains. Methods: We combined hydrodynamical simulations of planet-disk interactions with dust evolution models that include coagulation and fragmentation of dust grains over a large range of radii and derived observational properties using radiative transfer calculations. We studied the role of the snow line in the survival of the inner disk of transition disks. Results: Inside the snow line, the lack of ice mantles in dust particles decreases the sticking efficiency between grains. As a consequence, particles fragment at lower collision velocities than in regions beyond the snow line. This effect allows small particles to be maintained for up to a few Myr within the first astronomical unit. These particles are closely coupled to the gas and do not drift significantly with respect to the gas. For lower mass planets (1 MJup), the pre-transition appearance can be maintained even longer because dust still trickles through the gap created by the planet, moves invisibly and quickly in the form of relatively large grains through the gap, and becomes visible again as it fragments and gets slowed down inside of the snow line. Conclusions: The global study of dust evolution of a disk with an embedded planet, including the changes of the dust aerodynamics near the snow line, can explain the concentration of millimetre-sized particles in the outer disk and the survival of the dust in the inner disk if a large dust trap is present in the outer disk. This behaviour solves the conundrum of the combination of both near-infrared excess and ring-like millimetre emission observed in several transition disks.

Super-Earths: Atmospheric Accretion, Thermal Evolution and Envelope Loss

NASA Astrophysics Data System (ADS)

Ginzburg, Sivan; Inamdar, Niraj K.; Schlichting, Hilke E.

Combined mass and radius observations have recently revealed many short-period planets a few times the size of Earth but with significantly lower densities. A natural explanation for the low density of these super Earths super-Earth is a voluminous gas atmosphere that engulfs more compact rocky cores. Planets with such substantial gas atmospheres may be a missing link between smaller planets, that did not manage to obtain or keep an atmosphere, and larger planets, that accreted gas too quickly and became gas giants gas- . In this chapter we review recent advancements in the understanding of low-density low- super-Earth formation and evolution. Specifically, we present a consistent picture of the various stages in the lives of these planets: gas accretion from the protoplanetary disk, possible atmosphere heating and evaporation mechanisms, collisions between planets, and finally, evolution up to the age at which the planets are observed.

A common mass scaling for satellite systems of gaseous planets.

PubMed

Canup, Robin M; Ward, William R

2006-06-15

The Solar System's outer planets that contain hydrogen gas all host systems of multiple moons, which notably each contain a similar fraction of their respective planet's mass (approximately 10(-4)). This mass fraction is two to three orders of magnitude smaller than that of the largest satellites of the solid planets (such as the Earth's Moon), and its common value for gas planets has been puzzling. Here we model satellite growth and loss as a forming giant planet accumulates gas and rock-ice solids from solar orbit. We find that the mass fraction of its satellite system is regulated to approximately 10(-4) by a balance of two competing processes: the supply of inflowing material to the satellites, and satellite loss through orbital decay driven by the gas. We show that the overall properties of the satellite systems of Jupiter, Saturn and Uranus arise naturally, and suggest that similar processes could limit the largest moons of extrasolar Jupiter-mass planets to Moon-to-Mars size.

An Introduction to Exoplanets and the Kepler Mission

NASA Technical Reports Server (NTRS)

Lissauer, Jack

2014-01-01

A quarter century ago, the only planets known to humanity were the familiar objects that orbit our Sun. But improved observational techniques allowed astronomers to begin detecting planets around other stars in the 1990s. The first extrasolar planets (often referred to as exoplanets) to be discovered were quite exotic and unfamiliar objects. Most were giant objects that are hundreds of times as massive as the Earth and orbit so close to their star that they are hotter than pizza ovens. But as observational capabilities improved, smaller and cooler planets were found. The most capable planet-hunting tool developed to date is NASA's Kepler telescope, which was launched in 2009. Kepler has found that planets similar in size to our Earth are quite abundant within our galaxy. Results of Kepler's research will be summarized and placed into context within the new and growing discipline of exoplanet studies.

Capture of terrestrial-sized moons by gas giant planets.

PubMed

Williams, Darren M

2013-04-01

Terrestrial moons with masses >0.1 M (symbol in text) possibly exist around extrasolar giant planets, and here we consider the energetics of how they might form. Binary-exchange capture can occur if a binary-terrestrial object (BTO) is tidally disrupted during a close encounter with a giant planet and one of the binary members is ejected while the other remains as a moon. Tidal disruption occurs readily in the deep gravity wells of giant planets; however, the large encounter velocities in the wells make binary exchange more difficult than for planets of lesser mass. In addition, successful capture favors massive binaries with large rotational velocities and small component mass ratios. Also, since the interaction tends to leave the captured moons on highly elliptical orbits, permanent capture is only possible around planets with sizable Hill spheres that are well separated from their host stars.

Seeing Double with K2: Testing Re-inflation with Two Remarkably Similar Planets around Red Giant Branch Stars

NASA Astrophysics Data System (ADS)

Grunblatt, Samuel K.; Huber, Daniel; Gaidos, Eric; Lopez, Eric D.; Howard, Andrew W.; Isaacson, Howard T.; Sinukoff, Evan; Vanderburg, Andrew; Nofi, Larissa; Yu, Jie; North, Thomas S. H.; Chaplin, William; Foreman-Mackey, Daniel; Petigura, Erik; Ansdell, Megan; Weiss, Lauren; Fulton, Benjamin; Lin, Douglas N. C.

2017-12-01

Despite more than 20 years since the discovery of the first gas giant planet with an anomalously large radius, the mechanism for planet inflation remains unknown. Here, we report the discovery of K2-132b, an inflated gas giant planet found with the NASA K2 Mission, and a revised mass for another inflated planet, K2-97b. These planets orbit on ≈9 day orbits around host stars that recently evolved into red giants. We constrain the irradiation history of these planets using models constrained by asteroseismology and Keck/High Resolution Echelle Spectrometer spectroscopy and radial velocity measurements. We measure planet radii of 1.31 ± 0.11 R J and 1.30 ± 0.07 R J, respectively. These radii are typical for planets receiving the current irradiation, but not the former, zero age main-sequence irradiation of these planets. This suggests that the current sizes of these planets are directly correlated to their current irradiation. Our precise constraints of the masses and radii of the stars and planets in these systems allow us to constrain the planetary heating efficiency of both systems as 0.03{ % }-0.02 % +0.03 % . These results are consistent with a planet re-inflation scenario, but suggest that the efficiency of planet re-inflation may be lower than previously theorized. Finally, we discuss the agreement within 10% of the stellar masses and radii, and the planet masses, radii, and orbital periods of both systems, and speculate that this may be due to selection bias in searching for planets around evolved stars.

Kepler

NASA Technical Reports Server (NTRS)

Howell, Steve B.

2011-01-01

The NASA Kepler mission recently announced over 1200 exoplanet candidates. While some are common Hot Jupiters, a large number are Neptune size and smaller, transit depths suggest sizes down to the radius of Earth. The Kepler project has a fairly high confidence that most of these candidates are real exoplanets. Many analysis steps and lessons learned from Kepler light curves are used during the vetting process. This talk will cover some new results in the areas of stellar variability, solar systems with multiple planets, and how transit-like signatures are vetted for false positives, especially those indicative of small planets.

SIM Lite Detection of Habitable Planets in P-Type Binary-Planetary Systems

NASA Technical Reports Server (NTRS)

Pan, Xiaopei; Shao, Michael; Shaklan, Stuart; Goullioud, Renaud

2010-01-01

Close binary stars like spectroscopic binaries create a completely different environment than single stars for the evolution of a protoplanetary disk. Dynamical interactions between one star and protoplanets in such systems provide more challenges for theorists to model giant planet migration and formation of multiple planets. For habitable planets the majority of host stars are in binary star systems. So far only a small amount of Jupiter-size planets have been discovered in binary stars, whose minimum separations are 20 AU and the median value is about 1000 AU (because of difficulties in radial velocity measurements). The SIM Lite mission, a space-based astrometric observatory, has a unique capability to detect habitable planets in binary star systems. This work analyzed responses of the optical system to the field stop for companion stars and demonstrated that SIM Lite can observe exoplanets in visual binaries with small angular separations. In particular we investigated the issues for the search for terrestrial planets in P-type binary-planetary systems, where the planets move around both stars in a relatively distant orbit.

Vega's hot dust from icy planetesimals scattered inwards by an outward-migrating planetary system

NASA Astrophysics Data System (ADS)

Raymond, Sean N.; Bonsor, Amy

2014-07-01

Vega has been shown to host multiple dust populations, including both hot exozodiacal dust at sub-au radii and a cold debris disc extending beyond 100 au. We use dynamical simulations to show how Vega's hot dust can be created by long-range gravitational scattering of planetesimals from its cold outer regions. Planetesimals are scattered progressively inwards by a system of 5-7 planets from 30 to 60 au to very close-in. In successful simulations, the outermost planets are typically Neptune mass. The back-reaction of planetesimal scattering causes these planets to migrate outwards and continually interact with fresh planetesimals, replenishing the source of scattered bodies. The most favourable cases for producing Vega's exozodi have negative radial mass gradients, with sub-Saturn- to Jupiter-mass inner planets at 5-10 au and outer planets of 2.5 - 20 M⊕ . The mechanism fails if a Jupiter-sized planet exists beyond ˜15 au because the planet preferentially ejects planetesimals before they can reach the inner system. Direct-imaging planet searches can therefore directly test this mechanism.

Planetary Formation and Dynamics in Binary Systems

NASA Astrophysics Data System (ADS)

Xie, J. W.

2013-01-01

As of today, over 500 exoplanets have been detected since the first exoplanet was discovered around a solar-like star in 1995. The planets in binaries could be common as stars are usually born in binary or multiple star systems. Although current observations show that the planet host rate in multiple star systems is around 17%, this fraction should be considered as a lower limit because of noticeable selection effects against binaries in planet searches. Most of the current known planet-bearing binary systems are S-types, meaning the companion star acts as a distant satellite, typically orbiting the inner star-planet system over 100 AU away. Nevertheless, there are four systems with a smaller separation of 20 AU, including the Gamma Cephei, GJ 86, HD 41004, and HD 196885. In addition to the planets in circumprimary (S-type) orbits discussed above, planets in circumbinary (P-type) orbits have been found in only two systems. In this thesis, we mainly study the planet formation in the S-type binary systems. In chapter 1, we first summarize current observational facts of exoplanets both in single-star and binary systems, then review the theoretical models of planet formation, with special attention to the application in binary systems. Perturbative effects from stellar companions render the planet formation process in binary systems even more complex than that in single-star systems. The perturbations from a binary companion can excite planetesimal orbits, and increase their mutual impact velocities to the values that might exceed their escape velocity or even the critical velocity for the onset of eroding collisions. The intermediate stage of the formation process---from planetesimals to planetary embryos---is thus the most problematic. In the following chapters, we investigate whether and how the planet formation goes through such a problematic stage. In chapter 2, we study the effects of gas dissipation on the planetesimals' mutual accretion. We find that in a dissipating gas disk, all the planetesimals eventually converge toward the same forced orbits regardless of their size, leading to the much lower impact velocities. This process progressively increases the net mass accretion and can even trigger the runaway growth for large planetesimals. In chapter 3, for the first time, we adopt a 3-dimensional approach to investigate the planetesimals' mutual accretion in binary systems. We find that the inclusion of a small inclination between the binary orbital plane and the circumstellar disk plane leads to the realization of the differential orbital phasing in 3-dimensional space. In such a case, impacts mainly occur between similar-sized bodies with the impact velocities being significantly reduced, and thus the planetesimal accretion is more favored. In chapter 4, we investigate the planet formation in a specific system, the habitable zone of Alpha Centauri B. For the first time, we develop a scaling method to estimate the planetesimal collisional timescale in binary systems. We find that the accretion-favorable conditions satisfied at 1˜2 AU from Alpha Centauri B after the first 10^5 years. However, the planetesimal accretion is significantly less efficient as compared to the single star case. Our results suggest that the formation of Earth-like planets through the accretion of km-sized planetesimals is possible in Alpha Centauri B, while the formation of gaseous giant planets is not favorable. In chapter 5, we outline a new concept, which we call the ``snowball'' growth mode. In this snowball phase, the isolated planetesimals move in the Keplerian orbits, and grow solely via the direct accretion of subcentimeter-sized dust entrained with the gas in the protoplanetary disk. Using a simplified model in which the planetesimals are progressively produced from the dust, we find that the snowball growth phase can be the dominant mode to transfer mass from the dust to planetesimals. The snowball growth mode could provide an alternative explanation for the turnover point in the size distribution of the present-day asteroid belt. For the specific case of close binaries such as Alpha Centauri, the snowball growth mode provides a safe way for the bodies to grow through the problematic range with a size of 1˜50 km. In chapter 6, we investigate the intermediate stages of the planet formation in highly inclined cases. We find that the gas drag plays a crucial role in the evolution of the planetesimals' semi-major axis, and the results can be generally divided into two categories, i.e., the Kozai-on regime and the Kozai-off regime. For both regimes, a robust outcome over a wide range of parameters is that, the planetesimals migrate/jump inwards and pile up, leading to a severely truncated and dense planetesimal disk around the primary. In this compact and dense disk, the collision rates are high but the relative velocities are low, providing conditions which are favorable for the planetesimal growth, and potentially allow for the subsequent formation of planets. Finally, we summarize this thesis in chapter 7. Many open questions still remain in current research field of planet formation in binary systems, and the current Kepler project provides an unprecedented opportunity for such researches. A comprehensive understanding of planets in binaries requires placing them in a bigger context to include the formation and evolution of stars and/or clusters.

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

Muñoz-Gutiérrez, M. A.; Pichardo, B.; Peimbert, A., E-mail: mmunoz.astro@gmail.com

We have explored the evolution of a cold debris disk under the gravitational influence of dwarf-planet-sized objects (DPs), both in the presence and absence of an interior giant planet. Through detailed long-term numerical simulations, we demonstrate that when the giant planet is not present, DPs can stir the eccentricities and inclinations of disk particles, in linear proportion to the total mass of the DPs; on the other hand, when the giant planet is included in the simulations, the stirring is approximately proportional to the mass squared. This creates two regimes: below a disk mass threshold (defined by the total massmore » of DPs), the giant planet acts as a stabilizing agent of the orbits of cometary nuclei, diminishing the effect of the scatterers; above the threshold, the giant contributes to the dispersion of the particles.« less

An Exoplanet Spinning Up Its Star

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-11-01

We know that the large masses of stars govern the orbits of the planets that circle them but a large, close-in planet can also influence the rotation of its host star. A recently discovered, unusual hot Jupiter may be causing its star to spin faster than it should.Exotic PlanetsHot Jupiters are gas giants of roughly Jupiters size that orbit close in to their host stars. Though these planets are easy to detect their large sizes and frequent transits mean surveys have a good chance of catching them we havent found many of them, suggesting that planetary systems containing hot Jupiters are fairly unusual.The period-folded light curve of HATS-18, revealing the transit of the hot Jupiter HATS-18b. The period is P=0.8378 days. [Penev et al. 2016]Studying this exotic population of planets, however, can help us to better understand how gas giants form and evolve in planetary systems. New observations of hot Jupiters may also reveal how stars and close-in planets interact through radiation, gravity, and magnetic fields.The recent discovery of a transiting hot Jupiter a little over 2000 light-years away therefore presents an exciting opportunity!A Speeding GiantThe discovery of HATS-18b, a planet of roughly 2 times Jupiters mass and 1.3 times its radius, was announced in a study led by Kaloyan Penev (Princeton University). The planet was discovered using the HATSouth transit survey network, which includes instruments in Chile, Namibia, and Australia, and follow-up photometry and spectroscopy was conducted at a variety of ground-based observatories.HATS-18bs properties are particularly unusual: this hot Jupiter is zipping around its host star which is very similar to the Sun at the incredible pace of one orbit every 0.84 days. HATS-18bs orbit is more than 20 times closer to its host star than Mercurys is to the Sun, bringing it so close it nearly grazes the stars surface!Size of the planetary orbit relative to the stellar radius as a function of the stellar rotation period, for transiting planets with orbital periods shorter than 2 days and masses greater than 0.1 Jupiter masses. HATS-18b is denoted by the red star. [Penev et al. 2016]Tidal InteractionsWhat happens when a massive planet orbits this close to its star? Tidal interactions between the star and the planet cause tidal dissipation in the star, resulting in decay of the planets orbit. But there may be an additional effect of this interaction in the case of HATS-18b, the authors claim: the planet may be transferring some of its angular momentum to the star.As stars age, they should gradually spin slower as they lose angular momentum viastellar winds. But Penev and collaborators note that this exoplanets host star, HATS-18, spins roughly three times as fast asits inferred age suggests it should. The authors conclude that the angular momentum lost by the planet as its orbit shrinks is deposited in the star, causing the star to spin up.HATS-18 is an excellent laboratory for studying how very short-period planets interact with their stars in fact, Penev and collaborators have already used their observations of the system to constrain models of tidal dissipation from Sun-like stars. Additional observations of HATS-18 and other short-period systems should allow us to further test models of how planetary systems form and evolve.CitationK. Penev et al 2016 AJ 152 127. doi:10.3847/0004-6256/152/5/127

Astronomers See First Stages of Planet-Building Around Nearby Star

NASA Astrophysics Data System (ADS)

2005-06-01

Interstellar travelers might want to detour around the star system TW Hydrae to avoid a messy planetary construction site. Astronomer David Wilner of the Harvard-Smithsonian Center for Astrophysics (CfA) and his colleagues have discovered that the gaseous protoplanetary disk surrounding TW Hydrae holds vast swaths of pebbles extending outward for at least 1 billion miles. These rocky chunks should continue to grow in size as they collide and stick together until they eventually form planets. Dust Disk Graphic Artist's Conception of Dusty Disk Around Young Star TW Hydrae CREDIT: Bill Saxton, NRAO/AUI/NSF (Click on image for larger version 1.8 MB) "We're seeing planet building happening right before our eyes," said Wilner. "The foundation has been laid and now the building materials are coming together to make a new solar system." Wilner used the National Science Foundation's Very Large Array to measure radio emissions from TW Hydrae. He detected radiation from a cold, extended dust disk suffused with centimeter-sized pebbles. Such pebbles are a prerequisite for planet formation, created as dust collects together into larger and larger clumps. Over millions of years, those clumps grow into planets. "We're seeing an important step on the path from interstellar dust particles to planets," said Mark Claussen (NRAO), a co-author on the paper announcing the discovery. "No one has seen this before." A dusty disk like that in TW Hydrae tends to emit radio waves with wavelengths similar to the size of the particles in the disk. Other effects can mask this, however. In TW Hydrae, the astronomers explained, both the relatively close distance of the system and the stage of the young star's evolution are just right to allow the relationship of particle size and wavelength to prevail. The scientists observed the young star's disk with the VLA at several centimeter-range wavelengths. "The strong emission at wavelengths of a few centimeters is convincing evidence that particles of about the same size are present," Claussen said. Not only does TW Hydrae show evidence of ongoing planet formation, it also shows signs that at least one giant planet may have formed already. Wilner's colleague, Nuria Calvet (CfA), has created a computer simulation of the disk around TW Hydrae using previously published infrared observations. She showed that a gap extends from the star out to a distance of about 400 million miles - similar to the distance to the asteroid belt in our solar system. The gap likely formed when a giant planet sucked up all the nearby material, leaving a hole in the middle of the disk. Located about 180 light-years away in the constellation Hydra the Water Snake, TW Hydrae consists of a 10 million-year-old star about four-fifths as massive as the Sun. The protoplanetary disk surrounding TW Hydrae contains about one-tenth as much material as the Sun -- more than enough to form one or more Jupiter-sized worlds. "TW Hydrae is unique," said Wilner. "It's nearby, and it's just the right age to be forming planets. We'll be studying it for decades to come." This research was published in the June 20, 2005, issue of the Astrophysical Journal Letters. Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

KSC-2009-1971

NASA Image and Video Library

2009-03-06

CAPE CANAVERAL, Fla. – United Launch Alliance's Delta II rocket, with NASA's Kepler spacecraft aboard, is bathed in light on Launch Pad 17-B at Cape Canaveral Air Force Station in Florida prior to launch. Liftoff is planned for 10:49 p.m. EST. Kepler is a spaceborne telescope designed to search the nearby region of our galaxy for Earth-size planets orbiting in the habitable zone of stars like our sun. The habitable zone is the region around a star where temperatures permit water to be liquid on a planet's surface. The challenge for Kepler is to look at a large number of stars in order to statistically estimate the total number of Earth-size planets orbiting sun-like stars in the habitable zone. Kepler will survey more than 100,000 stars in our galaxy. Photo credit: NASA/Jack Pfaller

KSC-2009-1960

NASA Image and Video Library

2009-03-06

CAPE CANAVERAL, Fla. – Against the backdrop of the Atlantic Ocean, the Delta II 7925 rocket stands ready for launch following rollback of the mobile service tower on Launch Pad 17-B at Cape Canaveral Air Force Station. Atop the rocket is NASA's Kepler spacecraft. Kepler is a spaceborne telescope designed to search the nearby region of our galaxy for Earth-size planets orbiting in the habitable zone of stars like our sun. The habitable zone is the region around a star where temperatures permit water to be liquid on a planet's surface. The challenge for Kepler is to look at a large number of stars in order to statistically estimate the total number of Earth-size planets orbiting sun-like stars in the habitable zone. Kepler will survey more than 100,000 stars in our galaxy. Photo credit: NASA/Jack Pfaller

How many earths are enough?

NASA Astrophysics Data System (ADS)

Beichman, C. A.

2003-10-01

The goals of NASA's Terrestrial Planet Finder (TPF) and ESA's Darwin missions are to find and characterize terrestrial planets in the habitable zones of other stars, and to search for evidence of life in the atmospheres of any planets found. A key issue that must be addressed is the size of the sample of stars that must be searched before the scientific community, the funding agencies, and the public at large will be satisfied that an expensive space observatory will have a high probability of success. This question lies at the heart of the definition of TPF/Darwin. In this paper, I discuss some of the parameters that bound the size of the TPF/Darwin sample and outline a science program to improve our knowledge so that we can make timely decisions about the scope and expense of TPF/Darwin.

Compositional Constraints on the Best Characterized Rocky Exoplanet, Kepler-36 b

NASA Astrophysics Data System (ADS)

Rogers, Leslie; Deck, Katherine; Lissauer, Jack J.; Carter, Joshua A.

2015-01-01

Kepler-36 is an extreme planetary system, consisting of two transiting sub-Neptune-size planets that revolve around a sub-giant star with orbital periods of 13.84 and 16.24 days. Mutual gravitational interactions between the two planets perturb the planets' transit times, allowing the planets' masses to be measured. Despite the similarity of their masses and orbital radii, the planets show a stark contrast in their mean densities; the inner planet (Kepler-36 b) is more than eight times as dense as its outer companion planet (Kepler-36 c). We perform a photo-dynamical analysis of the Kepler-36 system based on more than three years of Kepler photometry. With N-body integrations of initial conditions sampled from the photo-dynamical fits, we further refine the properties of the system by ruling out solutions that show large-scale instability within 5 Giga-days. Ultimately, we measure the planets' masses within 4.2% precision, and the planets' radii with 1.8% precision. Kepler-36 b is currently the rocky exoplanet with the most precisely measured mass and radius. Kepler-36 b's mass and radius are consistent with an Earth-like composition, and an iron-enhanced Mercury-like composition is ruled out.

Compositional Constraints on the Best Characterized Rocky Exoplanet, Kepler-36 b

NASA Astrophysics Data System (ADS)

Rogers, Leslie Anne; Deck, Katherine; Lissauer, Jack; Carter, Joshua

2015-08-01

Kepler-36 is an extreme planetary system, consisting of two transiting sub-Neptune-size planets that revolve around a sub-giant star with orbital periods of 13.84 and 16.24 days. Mutual gravitational interactions between the two planets perturb the planets' transit times, allowing the planets' masses to be measured. Despite the similarity of their masses and orbital radii, the planets show a stark contrast in their mean densities; the inner planet (Kepler-36 b) is more than eight times as dense as its outer companion planet (Kepler-36 c). We perform a photo-dynamical analysis of the Kepler-36 system based on more than three years of Kepler photometry. With N-body integrations of initial conditions sampled from the photo-dynamical fits, we further refine the properties of the system by ruling out solutions that show large scale instability within 5 Giga-days. Ultimately, we measure the planets' masses within 4.2% precision, and the planets' radii with 1.8% precision. Kepler-36 b is currently the rocky exoplanet with the most precisely measured mass and radius. Kepler-36 b’s mass and radius are consistent with a Earth-like composition, and an iron-enhanced Mercury-like composition is ruled out.

Compositional Constraints on the Best Characterized Rocky Exoplanet, Kepler-36 b

NASA Astrophysics Data System (ADS)

Rogers, L.; Deck, K.; Lissauer, J. J.; Carter, J.

2014-12-01

Kepler-36 is an extreme planetary system, consisting of two transiting sub-Neptune-size planets that revolve around a sub-giant star with orbital periods of 13.84 and 16.24 days. Mutual gravitational interactions between the two planets perturb the planets' transit times, allowing the planets' masses to be measured. Despite the similarity of their masses and orbital radii, the planets show a stark contrast in their mean densities; the inner planet (Kepler-36 b) is more than eight times as dense as its outer companion planet (Kepler-36 c). We perform a photo-dynamical analysis of the Kepler-36 system based on more than three years of Kepler photometry. With N-body integrations of initial conditions sampled from the photo-dynamical fits, we further refine the properties of the system by ruling out solutions that show large scale instability within 5 Giga-days. Ultimately, we measure the planets' masses within 4.2% precision, and the planets' radii with 1.8% precision. Kepler-36 b is currently the rocky exoplanet with the most precisely measured mass and radius. Kepler-36 b's mass and radius are consistent with a Earth-like composition, and an iron-enhanced Mercury-like composition is ruled out.

A likely planet-induced gap in the disc around T Cha

NASA Astrophysics Data System (ADS)

Hendler, Nathanial P.; Pinilla, Paola; Pascucci, Ilaria; Pohl, Adriana; Mulders, Gijs; Henning, Thomas; Dong, Ruobing; Clarke, Cathie; Owen, James; Hollenbach, David

2018-03-01

We present high-resolution (0.11 × 0.06 arcsec2) 3 mm ALMA observations of the highly inclined transition disc around the star T Cha. Our continuum image reveals multiple dust structures: an inner disc, a spatially resolved dust gap, and an outer ring. When fitting sky-brightness models to the real component of the 3 mm visibilities, we infer that the inner emission is compact (≤1 au in radius), the gap width is between 18 and 28 au, and the emission from the outer ring peaks at ˜36 au. We compare our ALMA image with previously published 1.6 μm VLT/SPHERE imagery. This comparison reveals that the location of the outer ring is wavelength dependent. More specifically, the peak emission of the 3 mm ring is at a larger radial distance than that of the 1.6 μm ring, suggesting that millimeter-sized grains in the outer disc are located farther away from the central star than micron-sized grains. We discuss different scenarios to explain our findings, including dead zones, star-driven photoevaporation, and planet-disc interactions. We find that the most likely origin of the dust gap is from an embedded planet, and estimate - for a single planet scenario - that T Cha's gap is carved by a 1.2MJup planet.

ARCHITECTURE AND DYNAMICS OF KEPLER'S CANDIDATE MULTIPLE TRANSITING PLANET SYSTEMS

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

Lissauer, Jack J.; Jenkins, Jon M.; Borucki, William J.

About one-third of the {approx}1200 transiting planet candidates detected in the first four months of Kepler data are members of multiple candidate systems. There are 115 target stars with two candidate transiting planets, 45 with three, 8 with four, and 1 each with five and six. We characterize the dynamical properties of these candidate multi-planet systems. The distribution of observed period ratios shows that the vast majority of candidate pairs are neither in nor near low-order mean-motion resonances. Nonetheless, there are small but statistically significant excesses of candidate pairs both in resonance and spaced slightly too far apart to bemore » in resonance, particularly near the 2:1 resonance. We find that virtually all candidate systems are stable, as tested by numerical integrations that assume a nominal mass-radius relationship. Several considerations strongly suggest that the vast majority of these multi-candidate systems are true planetary systems. Using the observed multiplicity frequencies, we find that a single population of planetary systems that matches the higher multiplicities underpredicts the number of singly transiting systems. We provide constraints on the true multiplicity and mutual inclination distribution of the multi-candidate systems, revealing a population of systems with multiple super-Earth-size and Neptune-size planets with low to moderate mutual inclinations.« less

Identifying Exoplanets with Deep Learning: A Five-planet Resonant Chain around Kepler-80 and an Eighth Planet around Kepler-90

NASA Astrophysics Data System (ADS)

Shallue, Christopher J.; Vanderburg, Andrew

2018-02-01

NASA’s Kepler Space Telescope was designed to determine the frequency of Earth-sized planets orbiting Sun-like stars, but these planets are on the very edge of the mission’s detection sensitivity. Accurately determining the occurrence rate of these planets will require automatically and accurately assessing the likelihood that individual candidates are indeed planets, even at low signal-to-noise ratios. We present a method for classifying potential planet signals using deep learning, a class of machine learning algorithms that have recently become state-of-the-art in a wide variety of tasks. We train a deep convolutional neural network to predict whether a given signal is a transiting exoplanet or a false positive caused by astrophysical or instrumental phenomena. Our model is highly effective at ranking individual candidates by the likelihood that they are indeed planets: 98.8% of the time it ranks plausible planet signals higher than false-positive signals in our test set. We apply our model to a new set of candidate signals that we identified in a search of known Kepler multi-planet systems. We statistically validate two new planets that are identified with high confidence by our model. One of these planets is part of a five-planet resonant chain around Kepler-80, with an orbital period closely matching the prediction by three-body Laplace relations. The other planet orbits Kepler-90, a star that was previously known to host seven transiting planets. Our discovery of an eighth planet brings Kepler-90 into a tie with our Sun as the star known to host the most planets.

Supplement to photographic catalog of selected planetary size comparisons

NASA Technical Reports Server (NTRS)

Meszaros, Stephen Paul

1991-01-01

This document updates and extends the photographic catalog of selected planetary size comparisons. It utilizes photographs taken by NASA spacecraft to illustrate size comparisons of planets and moons of the solar system. Global views are depicted at the same scale, within each comparison, allowing size relationships to be studied visually.

A combined transmission spectrum of the Earth-sized exoplanets TRAPPIST-1 b and c.

PubMed

de Wit, Julien; Wakeford, Hannah R; Gillon, Michaël; Lewis, Nikole K; Valenti, Jeff A; Demory, Brice-Olivier; Burgasser, Adam J; Burdanov, Artem; Delrez, Laetitia; Jehin, Emmanuël; Lederer, Susan M; Queloz, Didier; Triaud, Amaury H M J; Van Grootel, Valérie

2016-09-01

Three Earth-sized exoplanets were recently discovered close to the habitable zone of the nearby ultracool dwarf star TRAPPIST-1 (ref. 3). The nature of these planets has yet to be determined, as their masses remain unmeasured and no observational constraint is available for the planetary population surrounding ultracool dwarfs, of which the TRAPPIST-1 planets are the first transiting example. Theoretical predictions span the entire atmospheric range, from depleted to extended hydrogen-dominated atmospheres. Here we report observations of the combined transmission spectrum of the two inner planets during their simultaneous transits on 4 May 2016. The lack of features in the combined spectrum rules out cloud-free hydrogen-dominated atmospheres for each planet at ≥10σ levels; TRAPPIST-1 b and c are therefore unlikely to have an extended gas envelope as they occupy a region of parameter space in which high-altitude cloud/haze formation is not expected to be significant for hydrogen-dominated atmospheres. Many denser atmospheres remain consistent with the featureless transmission spectrum-from a cloud-free water-vapour atmosphere to a Venus-like one.

MINERVA-Red: A telescope dedicated to the discovery of planets orbiting the nearest low-mass stars

NASA Astrophysics Data System (ADS)

Sliski, David; Blake, Cullen; Johnson, John A.; Plavchan, Peter; Wittenmyer, Robert A.; Eastman, Jason D.; Barnes, Stuart; Baker, Ashley

2017-01-01

Results from Kepler and ground-based exoplanet surveys suggest that M-dwarfs host numerous small sized planets. Additionally, the discovery of the Earth-sized exoplanets orbiting Proxima Centauri and Trappist 1 demonstrate that these stars can host terrestrial planets in their habitable zones. Since low-mass stars are intrinsically faint at optical wavelengths, obtaining 1 m/s Doppler resolution to detect their planetary companions remains a challenge for instruments designed for sun-like stars. We describe a novel, high-cadence approach aimed at detecting and characterizing planets orbiting the closest low-mass stars to the Sun. MINERVA-Red is an echelle spectrograph optimized for the 'deep red', between 800 nm and 900 nm, where M-dwarfs are brightest. The spectrograph will be temperature controlled at 20C +/- 10mk and in a vacuum chamber which maintains a pressure below 0.01 mbar while using a Fabry-Perot etalon and U/Ne lamp for wavelength calibration. The spectrometer will operate with a robotic, 0.7-meter telescope at Mt. Hopkins, Arizona. We expect first light in 2017.

HD 89345: a bright oscillating star hosting a transiting warm Saturn-sized planet observed by K2

NASA Astrophysics Data System (ADS)

Van Eylen, V.; Dai, F.; Mathur, S.; Gandolfi, D.; Albrecht, S.; Fridlund, M.; García, R. A.; Guenther, E.; Hjorth, M.; Justesen, A. B.; Livingston, J.; Lund, M. N.; Pérez Hernández, F.; Prieto-Arranz, J.; Regulo, C.; Bugnet, L.; Everett, M. E.; Hirano, T.; Nespral, D.; Nowak, G.; Palle, E.; Silva Aguirre, V.; Trifonov, T.; Winn, J. N.; Barragán, O.; Beck, P. G.; Chaplin, W. J.; Cochran, W. D.; Csizmadia, S.; Deeg, H.; Endl, M.; Heeren, P.; Grziwa, S.; Hatzes, A. P.; Hidalgo, D.; Korth, J.; Mathis, S.; Montañes Rodriguez, P.; Narita, N.; Patzold, M.; Persson, C. M.; Rodler, F.; Smith, A. M. S.

2018-05-01

We report the discovery and characterization of HD 89345b (K2-234b; EPIC 248777106b), a Saturn-sized planet orbiting a slightly evolved star. HD 89345 is a bright star (V = 9.3 mag) observed by the K2 mission with one-minute time sampling. It exhibits solar-like oscillations. We conducted asteroseismology to determine the parameters of the star, finding the mass and radius to be 1.12^{+0.04}_{-0.01} M_⊙ and 1.657^{+0.020}_{-0.004} R_⊙, respectively. The star appears to have recently left the main sequence, based on the inferred age, 9.4^{+0.4}_{-1.3} Gyr, and the non-detection of mixed modes. The star hosts a "warm Saturn" (P = 11.8 days, Rp = 6.86 ± 0.14 R⊕). Radial-velocity follow-up observations performed with the FIES, HARPS, and HARPS-N spectrographs show that the planet has a mass of 35.7 ± 3.3 M⊕. The data also show that the planet's orbit is eccentric (e ≈ 0.2). An investigation of the rotational splitting of the oscillation frequencies of the star yields no conclusive evidence on the stellar inclination angle. We further obtained Rossiter-McLaughlin observations, which result in a broad posterior of the stellar obliquity. The planet seems to conform to the same patterns that have been observed for other sub-Saturns regarding planet mass and multiplicity, orbital eccentricity, and stellar metallicity.

Transit visibility zones of the Solar system planets

NASA Astrophysics Data System (ADS)

Wells, R.; Poppenhaeger, K.; Watson, C. A.; Heller, R.

2018-01-01

The detection of thousands of extrasolar planets by the transit method naturally raises the question of whether potential extrasolar observers could detect the transits of the Solar system planets. We present a comprehensive analysis of the regions in the sky from where transit events of the Solar system planets can be detected. We specify how many different Solar system planets can be observed from any given point in the sky, and find the maximum number to be three. We report the probabilities of a randomly positioned external observer to be able to observe single and multiple Solar system planet transits; specifically, we find a probability of 2.518 per cent to be able to observe at least one transiting planet, 0.229 per cent for at least two transiting planets, and 0.027 per cent for three transiting planets. We identify 68 known exoplanets that have a favourable geometric perspective to allow transit detections in the Solar system and we show how the ongoing K2 mission will extend this list. We use occurrence rates of exoplanets to estimate that there are 3.2 ± 1.2 and 6.6^{+1.3}_{-0.8} temperate Earth-sized planets orbiting GK and M dwarf stars brighter than V = 13 and 16, respectively, that are located in the Earth's transit zone.

A Rocky Planet Forms

NASA Image and Video Library

2018-01-25

An artist's rendition of how a rocky planet forms. As a rocky planet forms, the planet-forming material gathers in a process known as "accretion." It grows larger in size, and increases in temperature, along with the pressure at its core. The energy from this initial planet forming process causes the planet's elements to heat up and melt. Upon melting, layers form and separate. The heavier elements sink to the bottom, the lighter ones float to the top. This material then separates into layers as it cools, which is known as "differentiation." A fully formed planet slowly emerges, with an upper layer known as the crust, the mantle in the middle, and a solid iron core. InSight is short for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport. The InSight mission will help answer key questions about how the rocky planets of the solar system, as well as how rocky exoplanets, formed. So while InSight is a Mars mission, it's also more than a Mars mission. The lander seeks the fingerprints of the processes that formed the rocky planets of the solar system, more than 4 billion years ago. It measures the planet's "vital signs:" its "pulse" (seismology), "temperature" (heat flow) and "reflexes" (precision tracking). https://photojournal.jpl.nasa.gov/catalog/PIA22233

The same frequency of planets inside and outside open clusters of stars.

PubMed

Meibom, Søren; Torres, Guillermo; Fressin, Francois; Latham, David W; Rowe, Jason F; Ciardi, David R; Bryson, Steven T; Rogers, Leslie A; Henze, Christopher E; Janes, Kenneth; Barnes, Sydney A; Marcy, Geoffrey W; Isaacson, Howard; Fischer, Debra A; Howell, Steve B; Horch, Elliott P; Jenkins, Jon M; Schuler, Simon C; Crepp, Justin

2013-07-04

Most stars and their planets form in open clusters. Over 95 per cent of such clusters have stellar densities too low (less than a hundred stars per cubic parsec) to withstand internal and external dynamical stresses and fall apart within a few hundred million years. Older open clusters have survived by virtue of being richer and denser in stars (1,000 to 10,000 per cubic parsec) when they formed. Such clusters represent a stellar environment very different from the birthplace of the Sun and other planet-hosting field stars. So far more than 800 planets have been found around Sun-like stars in the field. The field planets are usually the size of Neptune or smaller. In contrast, only four planets have been found orbiting stars in open clusters, all with masses similar to or greater than that of Jupiter. Here we report observations of the transits of two Sun-like stars by planets smaller than Neptune in the billion-year-old open cluster NGC6811. This demonstrates that small planets can form and survive in a dense cluster environment, and implies that the frequency and properties of planets in open clusters are consistent with those of planets around field stars in the Galaxy.

Passing NASA's Planet Quest Baton from Kepler to TESS

NASA Astrophysics Data System (ADS)

Jenkins, J.

Kepler vaulted into the heavens on March 7, 2009, initiating NASAs search for Earth- size planets orbiting Sun-like stars in the habitable zone, where liquid water could exist on a rocky planetary surface. In the 4 years since Kepler began science operations, a flood of photometric data on upwards of 190,000 stars of unprecedented precision and continuity has provoked a watershed of 134+ confirmed or validated planets, 3200+ planetary candidates (most sub-Neptune in size and many compara- ble to or smaller than Earth), and a resounding revolution in asteroseismology and astrophysics. The most recent discoveries include Kepler-62 with 5 planets total of which 2 are in the habitable zone with radii of 1.4 and 1.7 Re. The focus of the mission is shifting towards how to rapidly vet the 18,000+ threshold crossing events produced with each transiting planet search, and towards those studies that will allow us to understand what the data are saying about the prevalence of planets in the solar neighborhood and throughout the galaxy. This talk will provide an overview of the science results from the Kepler Mission and the work ahead to derive the frequency of Earth-size planets in the habitable zone of solar-like stars from the treasure trove of Kepler data. NASAs quest for exoplanets continues with the Transiting Exoplanet Survey Satel- lite (TESS) mission, slated for launch in May 2017 by NASAs Explorer Program. TESS will conduct an all-sky transit survey to identify the 1000 best small exoplanets in the solar neighborhood for follow up observations and characterization. TESSs targets will include all F, G, K dwarfs from +4 to +12 magnitude and all M dwarfs known within ˜200 light-years. 500,000 target stars will be observed over two years with ˜500 square degrees observed continuously for a year in each hemisphere in the James Webb Space Telescopes continuously viewable zones. Since the typical TESS target star is 5 magnitudes brighter than Kepler’s and 10 times closer, TESS discov- eries will afford significant opportunities to measure the masses of the exoplanets and to characterize their atmospheres with JWST, ELTs and other exoplanet explorers.

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

NASA Astrophysics Data System (ADS)

Chachan, Yayaati; Stevenson, David J.

2018-02-01

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

Potential Habitable Zone Exomoon Candidates and Radial Velocity Estimates for Giant Kepler HZ Candidates.

NASA Astrophysics Data System (ADS)

Hill, M.; Kane, S.; Kopparapu, R.; Seperuelo Duarte, E.; Gelino, D.; Whittenmyer, R.

2017-12-01

The NASA Kepler mission has discovered thousands of new planetary candidates, many of which have been confirmed through follow-up observations. A primary goal of the mission is to determine the occurrence rate of terrestrial-size planets within the Habitable Zone (HZ) of their host stars. A major product of the Habitable Zone Working Group (HZWG) is a list of HZ exoplanet candidates from the Kepler Data Release 24 Q1- Q17 data vetting process [1]. We used a variety of criteria regarding HZ boundaries and planetary sizes to produce complete lists of HZ candidates, including a catalog of 104 candidates within the optimistic HZ. We cross-matched our HZ candidates with the Data Release 25 stellar properties and confirmed planet properties to provide robust stellar parameters and candidate dispositions. We also performed dynamical analysis simulations for multi-planet systems that contain candidates with radii less than two Earth radii as a step toward validation of those systems. From this list we found 39 planet candidates greater than 3 earth radii residing in the Optimistic Habitable Zone of their host star. While giant planets are not favored in the search for eta Earth, they do indicate a potential for large, potentially rocky moons residing in the habitable zone. These giant planets can also provide a potential for a wider range of "habitable" incident flux due to additional energy sources from tidal energy, etc. Thus we analyzed each giant planet, estimating their mass and then calculating the estimated Radial Velocity Semi Amplitudes of each planet for use in follow up observations. We then calculated the planets Hill radius and determined the maximum angular separation of potential moons. This presentation will describe the highlights of the HZ catalog giant planets and the plans for further validation of HZ candidates and follow-up studies. Fig. 1 - Plots both the unconfirmed and confirmed Giant (>3⊕R) Kepler candidates expected Radial Velocity signatures vs the Kepler Magnitude of their host star. References: [1] Kane, S.R., Hill, M.L., Kasting, J.F., et al. 2016, ApJ, 830, 1

First Results of Exoplanet Observations with the Gran Telescopio Canarias: Narrow-Band Transit Photometry Capable of Detecting Super-Earth-size Planets

NASA Astrophysics Data System (ADS)

Ford, Eric B.; Colon, K. D.; Blake, C.; Lee, B.; Mahadevan, S.

2010-01-01

We present the first exoplanet observations from the Gran Telescopio Canarias (GTC) using the OSIRIS tunable filter imager. Our narrow-band transit follow-up observations set a new record for ground-based, narrow-band photometric precision of an exoplanet transit. The demonstrated precision would allow the detection of a transiting super-Earth-sized planet at near-infrared wavelengths. Such high-precision follow-up observations could significantly improve measurements of the size and orbit of transiting super-Earth and Earth-like planets to be discovered by the CoRoT and Kepler space missions (Colon & Ford 2009). OSIRIS is one of two first light instruments for the GTC and features a tunable filter imaging mode. We observed the planet's host star along with several nearby reference stars during each transit, rapidly alternating observations between multiple narrow band-passes. The GTC's large aperture results in small photon noise and minimal scintillation noise, so care must be taken to minimize other potential systematic noise sources. The use of a narrow bandpass (2nm) reduces the effects of differential extinction, and we chose bandpasses that minimize atmospheric absorption and variability. We measure the flux of the target star relative to an ensemble of reference stars, using an aperture photometry algorithm adapted to allow for: 1) the center of the band-pass varying across the field and resulting in sky rings, and 2) a significant defocus to reduce flat fielding uncertainties and increase observing efficiency. We present results from the first tunable filter observations of an exoplanet transit and outline the exciting prospects for future GTC/OSIRIS observations to study super-Earth planets and the atmospheres of giant planets via occultation photometry. Based on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in the island of La Palma.

The Astronomy Workshop

NASA Astrophysics Data System (ADS)

Hamilton, D. P.; Malayeri, M. L.; Pahlevan, K. M. A.; Jacobson, W. C.

2004-05-01

The Astronomy Workshop (http://janus.astro.umd.edu) is a collection of interactive online educational tools developed for use by students, educators, and the general public. The more than 20 tools in the Astronomy Workshop are rated for ease-of-use, and have been extensively tested in large university survey courses, classes for undergraduate majors, and High Schools. Here we briefly describe a few of the more popular tools. The Life of the Sun (New!): The history of the Sun is animated as a movie, showing students how the size and color of our star has evolved and will evolve in time. Animated Orbits of Planets and Moons: The orbital motions of planets, moons, asteroids, and comets are animated at their correct relative speeds in accurate to-scale drawings. Solar System Collisions: This most popular of our applications shows what happens when an asteroid or comet with user-defined size and speed impacts a given planet. The program calculates many effects, including the country of impact (if Earth is the target), energy of explosion, crater size, and magnitude of the ``planetquake'' generated. It also displays a relevant image (e.g. terrestrial crater, lunar crater, etc.). Astronomical Distances: Travel away from the Earth at a chosen speed and see how long it takes to reach other planets, stars and galaxies. This tool helps students visualize astronomical distances in an intuitive way. Funding for the Astronomy Workshop is provided by NSF.

The Astronomy Workshop

NASA Astrophysics Data System (ADS)

Hamilton, D. P.

2005-05-01

The Astronomy Workshop (http://janus.astro.umd.edu) is a collection of interactive online educational tools developed for use by students, educators, and the general public. The more than 20 tools in the Astronomy Workshop are rated for ease-of-use, and have been extensively tested in large university survey courses, classes for undergraduate majors, and High Schools. Here we briefly describe a few of the more popular tools. The Life of the Sun (New!): The history of the Sun is animated as a movie, showing students how the size and color of our star has evolved and will evolve in time. Animated Orbits of Planets and Moons: The orbital motions of planets, moons, asteroids, and comets are animated at their correct relative speeds in accurate to-scale drawings. Solar System Collisions: This most popular of our applications shows what happens when an asteroid or comet with user-defined size and speed impacts a given planet. The program calculates many effects, including the country of impact (if Earth is the target), energy of explosion, crater size, and magnitude of the ``planetquake'' generated. It also displays a relevant image (e.g. terrestrial crater, lunar crater, etc.). Astronomical Distances: Travel away from the Earth at a chosen speed and see how long it takes to reach other planets, stars and galaxies. This tool helps students visualize astronomical distances in an intuitive way. Funding for the Astronomy Workshop is provided by a NASA EPO grant.

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

NASA Astrophysics Data System (ADS)

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

2018-04-01

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

Taxonomy of the extrasolar planet.

PubMed

Plávalová, Eva

2012-04-01

When a star is described as a spectral class G2V, we know that the star is similar to our Sun. We know its approximate mass, temperature, age, and size. When working with an extrasolar planet database, it is very useful to have a taxonomy scale (classification) such as, for example, the Harvard classification for stars. The taxonomy has to be easily interpreted and present the most relevant information about extrasolar planets. I propose an extrasolar planet taxonomy scale with four parameters. The first parameter concerns the mass of an extrasolar planet in the form of units of the mass of other known planets, where M represents the mass of Mercury, E that of Earth, N Neptune, and J Jupiter. The second parameter is the planet's distance from its parent star (semimajor axis) described in a logarithm with base 10. The third parameter is the mean Dyson temperature of the extrasolar planet, for which I established four main temperature classes: F represents the Freezing class, W the Water class, G the Gaseous class, and R the Roasters class. I devised one additional class, however: P, the Pulsar class, which concerns extrasolar planets orbiting pulsar stars. The fourth parameter is eccentricity. If the attributes of the surface of the extrasolar planet are known, we are able to establish this additional parameter where t represents a terrestrial planet, g a gaseous planet, and i an ice planet. According to this taxonomy scale, for example, Earth is 1E0W0t, Neptune is 1N1.5F0i, and extrasolar planet 55 Cnc e is 9E-1.8R1.

Constraints on the Compositions of Small Planets from the HARPS-N Consortium

NASA Astrophysics Data System (ADS)

Charbonneau, David

2015-12-01

HARPS-N is an ultra-stable fiber-fed high-resolution spectrograph optimized for the measurement of very precise radial velocities. The NASA Kepler Mission has demonstrated that planets with radii between 1 - 2.5 that of the Earth are common around Sun-like stars. A chief objective of the HARPS-N Consortium is to measure accurately the masses and infer compositions for a sample of these small worlds. Here I report on our conclusions from the first three years. After analyzing the Kepler light curves to vet potential targets, favoring those with asteroseismic estimates of the stellar properties and excluding those likely to show high RV jitter, we lavished attention on our sample: We typically gathered 100 observations per target, which permitted a mass accuracy of better than 20%. We find that all planets smaller than 1.5 Earth radii are rocky, while we have yet to find a rocky planet larger than this size. I report on the resulting constraints on the planetary compositions, including previously unpublished estimates for several worlds. Comparison of the inferred iron-to-rock ratios to the spectroscopically determined abundances of Fe, Mg, and Si in the stellar atmospheres should provide insight into the formation of terrestrial worlds. I address the transition from rocky planets to Neptune-like worlds, noting that our targets are highly irradiated and hence have likely experienced atmospheric mass loss. The K2 and TESS Missions will provide a list of similarly sized planets around much brighter stars, for which the greater apparent brightness will permit us to measure densities of planets at longer orbital periods, where atmospheric escape will be less important.

A Spitzer search for transits of radial velocity detected super-Earths

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

Kammer, J. A.; Knutson, H. A.; Desert, J.-M.

2014-02-01

Unlike hot Jupiters or other gas giants, super-Earths are expected to have a wide variety of compositions, ranging from terrestrial bodies like our own to more gaseous planets like Neptune. Observations of transiting systems, which allow us to directly measure planet masses and radii and constrain atmospheric properties, are key to understanding the compositional diversity of the planets in this mass range. Although Kepler has discovered hundreds of transiting super-Earth candidates over the past 4 yr, the majority of these planets orbit stars that are too far away and too faint to allow for detailed atmospheric characterization and reliable massmore » estimates. Ground-based transit surveys focus on much brighter stars, but most lack the sensitivity to detect planets in this size range. One way to get around the difficulty of finding these smaller planets in transit is to start by choosing targets that are already known to host super-Earth sized bodies detected using the radial velocity (RV) technique. Here we present results from a Spitzer program to observe six of the most favorable RV-detected super-Earth systems, including HD 1461, HD 7924, HD 156668, HIP 57274, and GJ 876. We find no evidence for transits in any of their 4.5 μm flux light curves, and place limits on the allowed transit depths and corresponding planet radii that rule out even the most dense and iron-rich compositions for these objects. We also observed HD 97658, but the observation window was based on a possible ground-based transit detection that was later ruled out; thus the window did not include the predicted time for the transit detection recently made by the Microvariability and Oscillations of Stars space telescope.« less

Comment on "Minimal size of a barchan dune".

PubMed

Andreotti, B; Claudin, P

2007-12-01

It is now an accepted fact that the size at which dunes form from a flat sand bed as well as their "minimal size" scales on the flux saturation length. This length is by definition the relaxation length of the slowest mode toward equilibrium transport. The model presented by Parteli, Durán, and Herrmann [Phys. Rev. E 75, 011301 (2007)] predicts that the saturation length decreases to zero as the inverse of the wind shear stress far from the threshold. We first show that their model is not self-consistent: even under large wind, the relaxation rate is limited by grain inertia and thus cannot decrease to zero. A key argument presented by these authors comes from the discussion of the typical dune wavelength on Mars (650 m) on the basis of which they refute the scaling of the dune size with the drag length evidenced by Claudin and Andreotti [Earth Planet. Sci. Lett. 252, 30 (2006)]. They instead propose that Martian dunes, composed of large grains (500 microm), were formed in the past under very strong winds. We emphasize that this saltating grain size, estimated from thermal diffusion measurements, is far from straightforward. Moreover, the microscopic photographs taken by the rovers on Martian Aeolian bedforms show a grain size of 87+/-25 microm together with hematite spherules at millimeter scale. As those so-called "blueberries" cannot be entrained more frequently than a few hours per century, we conclude that the saltating grains on Mars are the small ones, which gives a second strong argument against the model of Parteli.

Kepler constraints on planets near hot Jupiters.

PubMed

Steffen, Jason H; Ragozzine, Darin; Fabrycky, Daniel C; Carter, Joshua A; Ford, Eric B; Holman, Matthew J; Rowe, Jason F; Welsh, William F; Borucki, William J; Boss, Alan P; Ciardi, David R; Quinn, Samuel N

2012-05-22

We present the results of a search for planetary companions orbiting near hot Jupiter planet candidates (Jupiter-size candidates with orbital periods near 3 d) identified in the Kepler data through its sixth quarter of science operations. Special emphasis is given to companions between the 21 interior and exterior mean-motion resonances. A photometric transit search excludes companions with sizes ranging from roughly two-thirds to five times the size of the Earth, depending upon the noise properties of the target star. A search for dynamically induced deviations from a constant period (transit timing variations) also shows no significant signals. In contrast, comparison studies of warm Jupiters (with slightly larger orbits) and hot Neptune-size candidates do exhibit signatures of additional companions with these same tests. These differences between hot Jupiters and other planetary systems denote a distinctly different formation or dynamical history.

Theories of the origin and evolution of the giant planets

NASA Technical Reports Server (NTRS)

Pollack, J. B.; Bodenheimer, P.

1989-01-01

Following the accretion of solids and gases in the solar nebula, the giant planets contracted to their present sizes over the age of the solar system. It is presently hypothesized that this contraction was rapid, but not hydrodynamic; at a later stage, a nebular disk out of which the regular satellites formed may have been spun out of the outer envelope of the contracting giant planets due to a combination of total angular momentum conservation and the outward transfer of specific angular momentum in the envelope. If these hypotheses are true, the composition of the irregular satellites directly reflects the composition of planetesimals from which the giant planets formed, while the composition of the regular satellites is indicative of the composition of the less volatile components of the outer envelopes of the giant planets.

The Spiral Wave Instability Induced by a Giant Planet. I. Particle Stirring in the Inner Regions of Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Bae, Jaehan; Nelson, Richard P.; Hartmann, Lee

2016-12-01

We have recently shown that spiral density waves propagating in accretion disks can undergo a parametric instability by resonantly coupling with and transferring energy into pairs of inertial waves (or inertial-gravity waves when buoyancy is important). In this paper, we perform inviscid three-dimensional global hydrodynamic simulations to examine the growth and consequence of this instability operating on the spiral waves driven by a Jupiter-mass planet in a protoplanetary disk. We find that the spiral waves are destabilized via the spiral wave instability (SWI), generating hydrodynamic turbulence and sustained radially alternating vertical flows that appear to be associated with long wavelength inertial modes. In the interval 0.3 {R}{{p}}≤slant R≤slant 0.7{R}{{p}}, where R p denotes the semimajor axis of the planetary orbit (assumed to be 5 au), the estimated vertical diffusion rate associated with the turbulence is characterized by {α }{diff}∼ (0.2{--}1.2)× {10}-2. For the disk model considered here, the diffusion rate is such that particles with sizes up to several centimeters are vertically mixed within the first pressure scale height. This suggests that the instability of spiral waves launched by a giant planet can significantly disperse solid particles and trace chemical species from the midplane. In planet formation models where the continuous local production of chondrules/pebbles occurs over Myr timescales to provide a feedstock for pebble accretion onto these bodies, this stirring of solid particles may add a time constraint: planetary embryos and large asteroids have to form before a gas giant forms in the outer disk, otherwise the SWI will significantly decrease the chondrule/pebble accretion efficiency.

Photographic catalog of selected planetary size comparisons

NASA Technical Reports Server (NTRS)

Meszaros, S. P.

1985-01-01

Photographs taken by NASA spacecraft, and cartographic products based on these photos, are used to illustrate size comparisons of the planets and moons of the solar system. Global views and prominent geographical features are depicted at the same scale, allowing size relationships to be studied visually.

Direct IR Interferometric Detection of Extra Solar Planets

NASA Technical Reports Server (NTRS)

Shao, Michael

1989-01-01

This paper describes a concept for the direct detection of extra solar planets. The concept is based on a decade old idea from Bracewell but expanded. A long baseline interferometer is examined with two three meter telescopes, cooled to 70K and a baseline of 30-50 meters. In space, this instrument would be able to detect an Earth sized planet around a solar like star at 10 parsec in approximately 1 hour of integration (5 sigma). The total number of candidate stars with detectable "Earths" number in the thousands.

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.

High-purity silica reflecting heat shield development

NASA Technical Reports Server (NTRS)

Congdon, W. M.

1974-01-01

A high-purity, fused-silica reflecting heat shield for the thermal protection of outer-planet probes was developed. Factors that strongly influence the performance of a silica heat shield were studied. Silica-bonded silica configurations, each prepared by a different technique, were investigated and rated according to its relative merits. Slip-casting was selected as the preferred fabrication method because it produced good reflectivity and good strength, and is relatively easy to scale up for a full-size outer-planet probe. The slips were cast using a variety of different particle sizes: continuous particle-size slips; monodisperse particle-size slips; and blends of monodisperse particle-size slips were studied. In general, smaller particles gave the highest reflectance. The monodisperse slips as well as the blend slips gave a higher reflectance than the continuous particle-size slips. An upgraded and fused natural quartz was used to study the effects of microstructure on reflectance and as the baseline to ascertain the increase in reflectance obtained from using a higher-purity synthetic material.

SDSS-III MARVELS Planet Candidate RV Follow-up

NASA Astrophysics Data System (ADS)

Ge, Jian; Thomas, Neil; Ma, Bo; Li, Rui; SIthajan, Sirinrat

2014-02-01

Planetary systems, discovered by the radial velocity (RV) surveys, reveal strong correlations between the planet frequency and stellar properties, such as metallicity and mass, and a greater diversity in planets than found in the solar system. However, due to the sample sizes of extant surveys (~100 to a few hundreds of stars) and their heterogeneity, many key questions remained to be addressed: Do metal poor stars obey the same trends for planet occurrence as metal rich stars? What is the distribution of giant planets around intermediate- mass stars and binaries? Is the ``planet desert'' within 0.6 AU in the planet orbital distribution of intermediate-mass stars real? The MARVELS survey has produced the largest homogeneous RV measurements of 3300 V=7.6-12 FGK stars. The latest data pipeline effort at UF has been able to remove long term systematic errors suffered in the earlier data pipeline. 18 high confident giant planet candidates have been identified among newly processed data. We propose to follow up these giant planet candidates with the KPNO EXPERT instrument to confirm the detection and also characterize their orbits. The confirmed planets will be used to measure occurrence rates, distributions and multiplicity of giants planets around F,G,K stars with a broad range of mass (~0.6-2.5 M_⊙) and metallicity ([Fe/H]~-1.5-0.5). The well defined MARVELS survey cadence allows robust determinations of completeness limits for rigorously testing giant planet formation theories and constraining models.

SECULAR BEHAVIOR OF EXOPLANETS: SELF-CONSISTENCY AND COMPARISONS WITH THE PLANET-PLANET SCATTERING HYPOTHESIS

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

Timpe, Miles; Barnes, Rory; Kopparapu, Ravikumar

2013-09-15

If mutual gravitational scattering among exoplanets occurs, then it may produce unique orbital properties. For example, two-planet systems that lie near the boundary between circulation and libration of their periapses could result if planet-planet scattering ejected a former third planet quickly, leaving one planet on an eccentric orbit and the other on a circular orbit. We first improve upon previous work that examined the apsidal behavior of known multiplanet systems by doubling the sample size and including observational uncertainties. This analysis recovers previous results that demonstrated that many systems lay on the apsidal boundary between libration and circulation. We thenmore » performed over 12,000 three-dimensional N-body simulations of hypothetical three-body systems that are unstable, but stabilize to two-body systems after an ejection. Using these synthetic two-planet systems, we test the planet-planet scattering hypothesis by comparing their apsidal behavior, over a range of viewing angles, to that of the observed systems and find that they are statistically consistent regardless of the multiplicity of the observed systems. Finally, we combine our results with previous studies to show that, from the sampled cases, the most likely planetary mass function prior to planet-planet scattering follows a power law with index -1.1. We find that this pre-scattering mass function predicts a mutual inclination frequency distribution that follows an exponential function with an index between -0.06 and -0.1.« less

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

Self-Stirring of Debris Discs by Planetesimals Formed by Pebble Concentration

NASA Astrophysics Data System (ADS)

Krivov, Alexander V.; Booth, Mark

2018-06-01

When a protoplanetary disc looses gas, it leaves behind planets and one or more planetesimal belts. The belts get dynamically excited, either by planets ("planet stirring") or by embedded big planetesimals ("self-stirring"). Collisions between planetesimals become destructive and start to produce dust, creating an observable debris disc. Following Kenyon & Bromley (2008), it is often assumed that self-stirring starts to operate as soon as the first ˜1000 km-sized embedded "Plutos" have formed. However, state-of-the-art pebble concentration models robustly predict planetesimals between a few km and ˜200 km in size to form in protoplanetary discs rapidly, before then slowly growing into Pluto-sized bodies. We show that the timescale, on which these planetesimals excite the disc sufficiently for fragmentation, is shorter than the formation timescale of Plutos. Using an analytic model based on the Ida & Makino (1993) theory, we find the excitation timescale to be T_excite ≈ 100 x_m^{-1} M_\\star ^{-3/2} a^3 Myr, where xm is the total mass of a protoplanetary disc progenitor in the units of the Minimum-Mass Solar Nebula, a its radius in the units of 100 AU, and M⋆ is the stellar mass in solar masses. These results are applied to a set of 23 debris discs that have been well resolved with ALMA or SMA. We find that the majority of these discs are consistent with being self-stirred. However, three large discs around young early-type stars do require planets as stirrers. These are 49 Cet, HD 95086, and HR 8799, of which the latter two are already known to have planets.

KSC-2009-1975

NASA Image and Video Library

2009-03-06

CAPE CANAVERAL, Fla. – On Launch Pad 17-B at Cape Canaveral Air Force Station in Florida, United Launch Alliance's Delta II rocket carrying NASA's Kepler spacecraft rises through the exhaust cloud created by the firing of the rocket’s engines. Liftoff was on time at 10:49 p.m. EST. Kepler is a spaceborne telescope designed to search the nearby region of our galaxy for Earth-size planets orbiting in the habitable zone of stars like our sun. The habitable zone is the region around a star where temperatures permit water to be liquid on a planet's surface. The challenge for Kepler is to look at a large number of stars in order to statistically estimate the total number of Earth-size planets orbiting sun-like stars in the habitable zone. Kepler will survey more than 100,000 stars in our galaxy. Photo credit: NASA/Regina Mitchell-Ryall, Tom Farrar

KSC-2009-1974

NASA Image and Video Library

2009-03-06

CAPE CANAVERAL, Fla. – On Launch Pad 17-B at Cape Canaveral Air Force Station in Florida, exhaust clouds cascade around the base of United Launch Alliance's Delta II rocket carrying NASA's Kepler spacecraft as the rocket’s engines ignite. Liftoff was on time at 10:49 p.m. EST. Kepler is a spaceborne telescope designed to search the nearby region of our galaxy for Earth-size planets orbiting in the habitable zone of stars like our sun. The habitable zone is the region around a star where temperatures permit water to be liquid on a planet's surface. The challenge for Kepler is to look at a large number of stars in order to statistically estimate the total number of Earth-size planets orbiting sun-like stars in the habitable zone. Kepler will survey more than 100,000 stars in our galaxy. Photo credit: NASA/Sandra Joseph, Kevin O'Connell

Ceres and the terrestrial planets impact cratering record

NASA Astrophysics Data System (ADS)

Strom, R. G.; Marchi, S.; Malhotra, R.

2018-03-01

Dwarf planet Ceres, the largest object in the Main Asteroid Belt, has a surface that exhibits a range of crater densities for a crater diameter range of 5-300 km. In all areas the shape of the craters' size-frequency distribution is very similar to those of the most ancient heavily cratered surfaces on the terrestrial planets. The most heavily cratered terrain on Ceres covers ∼15% of its surface and has a crater density similar to the highest crater density on <1% of the lunar highlands. This region of higher crater density on Ceres probably records the high impact rate at early times and indicates that the other 85% of Ceres was partly resurfaced after the Late Heavy Bombardment (LHB) at ∼4 Ga. The Ceres cratering record strongly indicates that the period of Late Heavy Bombardment originated from an impactor population whose size-frequency distribution resembles that of the Main Belt Asteroids.

Detection of extrasolar planets by the large deployable reflector

NASA Technical Reports Server (NTRS)

Hollenbach, D. J.; Takahashi, T.

1984-01-01

The best wavelength for observing Jupiter-size planetary companions to stars other than the Sun is one at which a planet's thermal emission is strongest; typically this would occur in the far-infrared region. It is assumed that the orbiting infrared telescope used is diffraction-limited so that the resolution of the planet from the central star is accomplished in the wings of the star's Airy pattern. Proxima Centauri, Barnard's Star, Wolf 359, and Epsilon Eridani are just a few of the many nearest main-sequence stars that could be studied with the large deployable relfector (LDR). The detectability of a planet improves for warmer planets and less luminous stars; therefore, planets around white dwarfs and those young planets which have sufficient internal gravitational energy release so as to cause a significant increase in their temperatures are considered. If white dwarfs are as old as they are usually assumed to be (5-10 billion yr), then only the nearest white dwarf (Sirius B) is within the range of LDR. The Ursa Major cluster and Perseu cluster are within LDR's detection range mainly because of their proximity and young age, respectively.

TWO SMALL PLANETS TRANSITING HD 3167

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

Vanderburg, Andrew; Bieryla, Allyson; Latham, David W.

2016-09-20

We report the discovery of two super-Earth-sized planets transiting the bright (V = 8.94, K = 7.07) nearby late G-dwarf HD 3167, using data collected by the K2 mission. The inner planet, HD 3167 b, has a radius of 1.6 R {sub ⊕} and an ultra-short orbital period of only 0.96 days. The outer planet, HD 3167 c, has a radius of 2.9 R {sub ⊕} and orbits its host star every 29.85 days. At a distance of just 45.8 ± 2.2 pc, HD 3167 is one of the closest and brightest stars hosting multiple transiting planets, making HD 3167more » b and c well suited for follow-up observations. The star is chromospherically inactive with low rotational line-broadening, ideal for radial velocity observations to measure the planets’ masses. The outer planet is large enough that it likely has a thick gaseous envelope that could be studied via transmission spectroscopy. Planets transiting bright, nearby stars like HD 3167 are valuable objects to study leading up to the launch of the James Webb Space Telescope .« less

Long-Term Stability of Planets in the Alpha Centauri System

NASA Technical Reports Server (NTRS)

Lissauer, Jack; Quarles, Billy

2015-01-01

The alpha Centauri system is billions of years old, so planets are only expected to be found in regions where their orbits are long-lived. We evaluate the extent of the regions within the alpha Centauri AB star system where small planets are able to orbit for billion-year timescales, and we map the positions in the sky plane where planets on stable orbits about either stellar component may appear. We confirm the qualitative results of Wiegert & Holman (Astron. J. 113, 1445, 1997) regarding the approximate size of the regions of stable orbits of a single planet, which are larger for retrograde orbits relative to the binary than for pro-grade orbits. Additionally, we find that mean motion resonances with the binary orbit leave an imprint on the limits of orbital stability, and the effects of the Lidov-Kozai mechanism are also readily apparent. Overall, orbits of a single planet in the habitable zones near the plane of the binary are stable, whereas high-inclination orbits are short-lived. However, even well within regions where single planets are stable, multiple planet systems must be significantly more widely-spaced than they need to be around an isolated star in order to be long-lived.

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.

TRAPPIST-1 System - Artist Concept

NASA Image and Video Library

2017-08-11

This illustration shows what the TRAPPIST-1 system might look like from a vantage point near planet TRAPPIST-1f (at right). 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. https://photojournal.jpl.nasa.gov/catalog/PIA21751

Flow of Planets, Not Weak Tidal Evolution, Produces the Short-Period Planet Distribution with More Planets than Expected

NASA Astrophysics Data System (ADS)

Taylor, Stuart F.

2013-01-01

The most unexpected planet finding is arguably the number of those with shorter periods than theorists had expected, because most such close planets had been expected to migrate into the star in shorter timescales than the ages of the stars. Subsequent effort has been made to show how tidal dissipation in stars due to planets could be weaker than expected, but we show how the occurrence distribution of differently-sized planets is more consistent with the explanation that these planets have more recently arrived as a flow of inwardly migrating planets, with giant planets more likely to be found while gradually going through a short period stage. This continual ``flow'' of new planets arriving from further out is presumably supplied by the flow likely responsible for the short period pileup of giant planets (Socrates+ 2011). We have previously shown that the shortest period region of the exoplanet occurrence distribution has a fall-off shaped by inward tidal migration due to stellar tides, that is, tides on the star caused by the planets (Taylor 2011, 2012). The power index of the fall-off of giant and intermediate radius planet candidates found from Kepler data (Howard+ 2011) is close to the index of 13/3 which is expected for planets in circular orbits undergoing tidal migration. However, there is a discrepancy of the strength of the tidal migration determined using fits to the giant and medium planets distributions. This discrepancy is best resolved by the explanation that more giant than medium radii planets migrate through these short period orbits. We also present a correlation between higher eccentricity of planetary orbits with higher Fe/H of host stars, which could be explained by high eccentricity planets being associated with recent episodes of other planets into stars. By the time these planets migrate to become hot Jupiters, the pollution may be mixed into the star. The clearing of other planets by migrating hot giant planets may result in hot Jupiters being anti-correlated with additional planets. We present results from our study of inward migration.

Towards an initial mass function for giant planets

NASA Astrophysics Data System (ADS)

Carrera, Daniel; Davies, Melvyn B.; Johansen, Anders

2018-07-01

The distribution of exoplanet masses is not primordial. After the initial stage of planet formation, gravitational interactions between planets can lead to the physical collision of two planets, or the ejection of one or more planets from the system. When this occurs, the remaining planets are typically left in more eccentric orbits. In this report we demonstrate how the present-day eccentricities of the observed exoplanet population can be used to reconstruct the initial mass function of exoplanets before the onset of dynamical instability. We developed a Bayesian framework that combines data from N-body simulations with present-day observations to compute a probability distribution for the mass of the planets that were ejected or collided in the past. Integrating across the exoplanet population, one can estimate the initial mass function of exoplanets. We find that the ejected planets are primarily sub-Saturn-type planets. While the present-day distribution appears to be bimodal, with peaks around ˜1MJ and ˜20M⊕, this bimodality does not seem to be primordial. Instead, planets around ˜60M⊕ appear to be preferentially removed by dynamical instabilities. Attempts to reproduce exoplanet populations using population synthesis codes should be mindful of the fact that the present population may have been depleted of sub-Saturn-mass planets. Future observations may reveal that young giant planets have a more continuous size distribution with lower eccentricities and more sub-Saturn-type planets. Lastly, there is a need for additional data and for more research on how the system architecture and multiplicity might alter our results.

Toward an initial mass function for giant planets

NASA Astrophysics Data System (ADS)

Carrera, Daniel; Davies, Melvyn B.; Johansen, Anders

2018-05-01

The distribution of exoplanet masses is not primordial. After the initial stage of planet formation, gravitational interactions between planets can lead to the physical collision of two planets, or the ejection of one or more planets from the system. When this occurs, the remaining planets are typically left in more eccentric orbits. In this report we demonstrate how the present-day eccentricities of the observed exoplanet population can be used to reconstruct the initial mass function of exoplanets before the onset of dynamical instability. We developed a Bayesian framework that combines data from N-body simulations with present-day observations to compute a probability distribution for the mass of the planets that were ejected or collided in the past. Integrating across the exoplanet population, one can estimate the initial mass function of exoplanets. We find that the ejected planets are primarily sub-Saturn type planets. While the present-day distribution appears to be bimodal, with peaks around ˜1MJ and ˜20M⊕, this bimodality does not seem to be primordial. Instead, planets around ˜60M⊕ appear to be preferentially removed by dynamical instabilities. Attempts to reproduce exoplanet populations using population synthesis codes should be mindful of the fact that the present population may have been been depleted of sub-Saturn-mass planets. Future observations may reveal that young giant planets have a more continuous size distribution with lower eccentricities and more sub-Saturn type planets. Lastly, there is a need for additional data and for more research on how the system architecture and multiplicity might alter our results.

Habitable zones exposed: astrosphere collapse frequency as a function of stellar mass.

PubMed

Smith, David S; Scalo, John M

2009-09-01

Stellar astrospheres--the plasma cocoons carved out of the interstellar medium by stellar winds--are one of several buffers that partially screen planetary atmospheres and surfaces from high-energy radiation. Screening by astrospheres is continually influenced by the passage of stars through the fluctuating density field of the interstellar medium (ISM). The most extreme events occur inside dense interstellar clouds, where the increased pressure may compress an astrosphere to a size smaller than the liquid-water habitable-zone distance. Habitable planets then enjoy no astrospheric buffering from exposure to the full flux of galactic cosmic rays and interstellar dust and gas, a situation we call "descreening" or "astrospheric collapse." Under such conditions the ionization fraction in the atmosphere and contribution to radiation damage of putative coding organisms at the surface would increase significantly, and a series of papers have suggested a variety of global responses to descreening. These possibilities motivate a more careful calculation of the frequency of descreening events. Using a ram-pressure balance model, we compute the size of the astrosphere in the apex direction as a function of parent-star mass and velocity and ambient interstellar density, emphasizing the importance of gravitational focusing of the interstellar flow. The interstellar densities required to descreen planets in the habitable zone of solar- and subsolar-mass stars are found to be about 600(M/M[middle dot in circle])(-2) cm(-3) for the Sun's velocity relative to the local ISM. Such clouds are rare and small, indicating that descreening encounters are rare. We use statistics from two independent catalogues of dense interstellar clouds to derive a dependence of descreening frequency on the parent-star mass that decreases strongly with decreasing stellar mass, due to the weaker gravitational focusing and smaller habitable-zone distances for lower-mass stars. We estimate an uncertain upper limit to the absolute frequency of descreening encounters as 1-10 Gyr(-1) for solar-type stars and 10(2) to 10(9) times smaller for stars between 0.5 and 0.1 M[middle dot in circle]. Habitable-zone planets orbiting late-K to M stars are virtually never exposed to the severe consequences that have been proposed for astrospheric descreening events, but descreening events at a moderate rate may occur for stars with the Sun's mass or larger.

A Distant Solar System Artist Concept

NASA Image and Video Library

2004-12-09

This artist concept depicts a distant hypothetical solar system, similar in age to our own. Looking inward from the system outer fringes, a ring of dusty debris can be seen, and within it, planets circling a star the size of our Sun. This debris is all that remains of the planet-forming disk from which the planets evolved. Planets are formed when dusty material in a large disk surrounding a young star clumps together. Leftover material is eventually blown out by solar wind or pushed out by gravitational interactions with planets. Billions of years later, only an outer disk of debris remains. These outer debris disks are too faint to be imaged by visible-light telescopes. They are washed out by the glare of the Sun. However, NASA's Spitzer Space Telescope can detect their heat, or excess thermal emission, in infrared light. This allows astronomers to study the aftermath of planet building in distant solar systems like our own. http://photojournal.jpl.nasa.gov/catalog/PIA07096

Kepler’s DR25 Most Earth-like Planet Candidates: What To Know Before You Go

NASA Astrophysics Data System (ADS)

Thompson, Susan E.; Kepler Team

2018-01-01

The Kepler mission’s latest catalog of planet candidates (data release 25 KOI catalog at the NASA exoplanet archive) was released in June of 2017. The catalog contains 4034 candidates including a significant population of terrestrial-size planets in the habitable zone of FGK dwarf stars. I will highlight what we know about these planet candidates in the DR25 catalog and discuss some of the caveats when working with these detections. Specifically, I will discuss how the noise in the Kepler light curves (from both the instrument and the stars) is known to occasionally produce weak, transit-like signals. We use simulations of this noise to measure how often these signals sneak into the catalog. I will also demonstrate ways to select a high-reliability sample using information available in the catalog. Such considerations may prove useful for anyone planning to use these planet candidates for occurrence rate calculations, choosing targets for follow-up, or deciding which planet to visit on his/her next holiday.

Probing LSST's Ability to Detect Planets Around White Dwarfs

NASA Astrophysics Data System (ADS)

Cortes, Jorge; Kipping, David

2018-01-01

Over the last four years more than 2,000 planets outside our solar system have been discovered, motivating us to search for and characterize potentially habitable worlds. Most planets orbit Sun-like stars, but more exotic stars can also host planets. Debris disks and disintegrating planetary bodies have been detected around white dwarf stars, the inert, Earth-sized cores of once-thriving stars like our Sun. These detections are clues that planets may exist around white dwarfs. Due to the faintness of white dwarfs and the potential rarity of planets around them, a vast survey is required to have a chance at detecting these planetary systems. The Large Synoptic Survey Telescope (LSST), scheduled to commence operations in 2023, will image the entire southern sky every few nights for 10 years, providing our first real opportunity to detect planets around white dwarfs. We characterized LSST’s ability to detect planets around white dwarfs through simulations that incorporate realistic models for LSST’s observing strategy and the white dwarf distribution within the Milky Way galaxy. This was done through the use of LSST's Operations Simulator (OpSim) and Catalog Simulator (CatSim). Our preliminary results indicate that, if all white dwarfs were to possess a planet, LSST would yield a detection for every 100 observed white dwarfs. In the future, a larger set of ongoing simulations will help us quantify the number of planets LSST could potentially find.

Little Black Spot on the Star Today Artist Concept

NASA Image and Video Library

2015-07-30

This artist's conception shows the silhouette of a rocky planet, dubbed HD 219134b, as it passes in front of its star. At 21 light-years away, the planet is the closest outside of our solar system that can be seen crossing, or transiting, its star -- a bonus for astronomers because transiting planets make ideal specimens for detailed studies of their atmospheres. It was discovered using the HARPS-North instrument on the Italian 3.6-meter National Galileo Telescope in the Canary Islands, and NASA's Spitzer Space Telescope. The planet, which is about 1.6 times the size of Earth, is also the nearest confirmed rocky planet outside our solar system. It orbits a star that is cooler and smaller than our sun, whipping closely around it in a mere three days. The proximity of the planet to the star means that it would be scorching hot and not habitable. Transiting planets are ideal targets for astronomers wanting to know more about planetary compositions and atmospheres. As a planet passes in front of its star, it causes the starlight to dim, and telescopes can measure this effect. If molecules are present in the planet's atmosphere, they can absorb certain wavelengths of light, leaving imprints in the starlight. This type of technique will be used in the future to investigate potentially habitable planets and search for signs of life. http://photojournal.jpl.nasa.gov/catalog/PIA19831

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.

PROBING TRAPPIST-1-LIKE SYSTEMS WITH K2

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

Demory, Brice-Olivier; Queloz, Didier; Gillen, Ed

2016-07-10

The search for small planets orbiting late M dwarfs holds the promise of detecting Earth-size planets for which their atmospheres could be characterized within the next decade. The recent discovery of TRAPPIST-1 entertains hope that these systems are common around hosts located at the bottom of the main sequence. In this Letter, we investigate the ability of the repurposed Kepler mission ( K2 ) to probe planetary systems similar to TRAPPIST-1. We perform a consistent data analysis of 189 spectroscopically confirmed M5.5 to M9 late M dwarfs from Campaigns 1–6 to search for planet candidates and inject transit signals withmore » properties matching TRAPPIST-1b and c. We find no transiting planet candidates across our K2 sample. Our injection tests show that K2 is able to recover both TRAPPIST-1 planets for 10% of the sample only, mainly because of the inefficient throughput at red wavelengths resulting in Poisson-limited performance for these targets. Increasing injected planetary radii to match GJ 1214b’s size yields a recovery rate of 70%. The strength of K2 is its ability to probe a large number of cool hosts across the different campaigns, out of which the recovery rate of 10% may turn into bona fide detections of TRAPPIST-1-like systems within the next two years.« less

The Habitable Exoplanet Imaging Mission (HabEx)

NASA Astrophysics Data System (ADS)

Gaudi, B. Scott; Habitable Exoplanet Imaging Mission Science and Technology Definition Team

2018-01-01

The Habitable Exoplanet Imaging Mission (HabEx) is a candidate flagship mission being studied by NASA and the astrophysics community in preparation of the 2020 Decadal Survey. The HabEx mission concept is a large (~4 to 6.5m) diffraction-limited optical space telescope, providing unprecedented resolution and contrast in the optical, with likely extensions into the near UV and near infrared domains. We discuss the primary science goals of HabEx. First, HabEx will survey a large sample of stars to search for planets potentially habitable planets: roughly Earth-sized planets with separations consistent with being in the habitable zones of their parent stars. Promising candidates will be followed up in detail, in order to characterize their orbits and atmospheres, and so confirm that they are indeed terrestrial-sized planets in the habitable zones of their parent stars, and search for signatures of habitability and potentially biosignatures. Second, HabEx will perform a ‘deep dive’ survey of roughly a dozen of the nearest and most promising stellar systems, providing the first complete “family portraits” of planets around our nearest Sun-like neighbors, and placing the solar system in the context of a diverse set of these planetary systems. Additionally, HabEx will enable a wide range of other astrophysical investigations, including detailed characterization of the properties of nearby stars and galaxies.

The Hydrogen Content of a Rocky Earth-Size Exoplanet

NASA Astrophysics Data System (ADS)

Berta-Thompson, Zach

2016-10-01

The composition of a terrestrial planet's atmosphere results from a complex interplay of accretion, escape, and outgassing. We have little data on how such processes proceed for planets around stars other than our Sun. The warm, Earth-size planet GJ1132b transits a late M dwarf and offers a unique opportunity for studying the atmospheric composition of a rocky exoplanet. Thanks to this transiting planet's proximity (12pc) and large transit depth (0.3%), possible scenarios for GJ1132b's atmospheric transmission spectrum can be observed with the Hubble Space Telescope. Here, we propose to use WFC3/IR to observe five transits of GJ1132b, to search for absorption features from a cloud-free, hydrogen-rich atmosphere. Such an atmosphere could potentially arise from late outgassing of volatiles from the planetary interior. The detection of molecular absorption in GJ1132b's atmosphere is an important step toward the long-term goal of characterizing the atmospheres of cooler habitable planets, and GJ1132b is a favorable target for JWST observations. The results of this Hubble/WFC3 investigation would inform the optimal strategy to observe GJ1132b with JWST. If we detect deep absorption features with WFC3, JWST should observe GJ1132b across its entire wavelength range. If we do not, JWST may first need to focus more intensely on smaller individual wavelength windows. This planet provides the first chance for WFC3 to study the atmosphere of an exoplanet that almost resembles terrestrial worlds in our own Solar System.

Exoplanet Biosignatures: Observational Prospects.

PubMed

Fujii, Yuka; Angerhausen, Daniel; Deitrick, Russell; Domagal-Goldman, Shawn; Grenfell, John Lee; Hori, Yasunori; Kane, Stephen R; Pallé, Enric; Rauer, Heike; Siegler, Nicholas; Stapelfeldt, Karl; Stevenson, Kevin B

2018-06-01

Exoplanet hunting efforts have revealed the prevalence of exotic worlds with diverse properties, including Earth-sized bodies, which has fueled our endeavor to search for life beyond the Solar System. Accumulating experiences in astrophysical, chemical, and climatological characterization of uninhabitable planets are paving the way to characterization of potentially habitable planets. In this paper, we review our possibilities and limitations in characterizing temperate terrestrial planets with future observational capabilities through the 2030s and beyond, as a basis of a broad range of discussions on how to advance "astrobiology" with exoplanets. We discuss the observability of not only the proposed biosignature candidates themselves but also of more general planetary properties that provide circumstantial evidence, since the evaluation of any biosignature candidate relies on its context. Characterization of temperate Earth-sized planets in the coming years will focus on those around nearby late-type stars. The James Webb Space Telescope (JWST) and later 30-meter-class ground-based telescopes will empower their chemical investigations. Spectroscopic studies of potentially habitable planets around solar-type stars will likely require a designated spacecraft mission for direct imaging, leveraging technologies that are already being developed and tested as part of the Wide Field InfraRed Survey Telescope (WFIRST) mission. Successful initial characterization of a few nearby targets will be an important touchstone toward a more detailed scrutiny and a larger survey that are envisioned beyond 2030. The broad outlook this paper presents may help develop new observational techniques to detect relevant features as well as frameworks to diagnose planets based on the observables. Key Words: Exoplanets-Biosignatures-Characterization-Planetary atmospheres-Planetary surfaces. Astrobiology 18, 739-778.

ALMA observations of protoplanetary disks

NASA Astrophysics Data System (ADS)

Hogerheijde, Michiel

2015-08-01

The Universe is filled with planetary systems, as recent detections of exo-planets have shown. Such systems grow out of disks of gas and dust that surround newly formed stars. The ground work for our understanding of the structure, composition, and evolution of such disks has been laid with infrared telescopes in the 1980's, 1990's, and 2000's, as well as with millimeter interferometers operating in the United States, France, and Japan. With the construction of the Atacama Large Millimeter / submillimeter Array, a new era of studying planet-forming disks has started. The unprecedented leap in sensitivity and angular resolution that ALMA offers, has truely revolutionized our understanding of disks. No longer featureless objects consisting of gas and smalll dust, they are now seen to harbor a rich structure and chemistry. The ongoing planet-formation process sculpts many disks into systems of rings and arcs; grains grown to millimeter-sizes collect in high-pressure areas where they could grow out to asteroids or comets or further generations of planets. This wealth of new information directly addresses bottlenecks in our theoretical understanding of planet formation, such as the question how grains can grow past the 'meter-sized' barrier or overcome the 'drift barrier', and how gas and ice evolve together and ultimately determine the elemental compositions of both giant and terrestrial planets. I will review the recent ALMA results on protoplanetary disks, presenting results on individual objects and from the first populations studies. I will conclude with a forward look, on what we might expect from ALMA in this area for the years and decades to come.

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

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.

Exoplanet Classification and Yield Estimates for Direct Imaging Missions

NASA Astrophysics Data System (ADS)

Kopparapu, Ravi Kumar; Hébrard, Eric; Belikov, Rus; Batalha, Natalie M.; Mulders, Gijs D.; Stark, Chris; Teal, Dillon; Domagal-Goldman, Shawn; Mandell, Avi

2018-04-01

Future NASA concept missions that are currently under study, like the Habitable Exoplanet Imaging Mission (HabEx) and the Large Ultra-violet Optical Infra Red Surveyor, could discover a large diversity of exoplanets. We propose here a classification scheme that distinguishes exoplanets into different categories based on their size and incident stellar flux, for the purpose of providing the expected number of exoplanets observed (yield) with direct imaging missions. The boundaries of this classification can be computed using the known chemical behavior of gases and condensates at different pressures and temperatures in a planetary atmosphere. In this study, we initially focus on condensation curves for sphalerite ZnS, {{{H}}}2{{O}}, {CO}}2, and {CH}}4. The order in which these species condense in a planetary atmosphere define the boundaries between different classes of planets. Broadly, the planets are divided into rocky planets (0.5–1.0 R ⊕), super-Earths (1.0–1.75 R ⊕), sub-Neptunes (1.75–3.5 R ⊕), sub-Jovians (3.5–6.0 R ⊕), and Jovians (6–14.3 R ⊕) based on their planet sizes, and “hot,” “warm,” and “cold” based on the incident stellar flux. We then calculate planet occurrence rates within these boundaries for different kinds of exoplanets, η planet, using the community coordinated results of NASA’s Exoplanet Program Analysis Group’s Science Analysis Group-13 (SAG-13). These occurrence rate estimates are in turn used to estimate the expected exoplanet yields for direct imaging missions of different telescope diameters.

Earth-based planet finders power up

NASA Astrophysics Data System (ADS)

Clery, Daniel

2018-01-01

NASA's Kepler spacecraft has racked up thousands of exoplanet discoveries since its launch in 2009, but before Kepler, the workhorses of exoplanet identification were ground-based instruments that measure tiny stellar wobbles caused by the gravity of an orbiting planet. They are now undergoing a quiet renaissance. The new generation of these devices may be precise enough to find a true Earth twin: a planet with the same mass as ours, orbiting a sunlike star once a year. That's something Kepler—sensitive to planet size, but not mass—can't do. Over the past few months, two new third-generation instruments have opened their eyes to the sky and nearly two dozen others are either under construction or have recently begun service.

The Impact of Clouds and Hazes in Substellar Atmospheres

NASA Astrophysics Data System (ADS)

Morley, Caroline; Fortney, Jonathan J.; Marley, Mark S.

2016-01-01

The formation of clouds significantly alters the spectra of cool substellar atmospheres from terrestrial planets to brown dwarfs. In cool planets like Earth and Jupiter, volatile species like water and ammonia condense to form ice clouds. In hot planets and brown dwarfs, iron and silicates instead condense, forming dusty clouds. Irradiated methane-rich planets may have substantial hydrocarbon hazes. During my thesis, I have studied the impact of clouds and hazes in a variety of substellar objects. First, I present results for cool brown dwarfs including clouds previously neglected in model atmospheres. Model spectra that include sulfide and salt clouds can match the spectra of T dwarf atmospheres; water ice clouds will alter the spectra of the newest and coldest brown dwarfs, the Y dwarfs. These sulfide/salt and ice clouds potentially drive spectroscopic variability in these cool objects, and this variability should be distinguishable from variability caused by hot spots.Next, I present results for small, cool exoplanets between the size of Earth and Neptune, so-called super Earths. They likely have sulfide and salt clouds and also have photochemical hazes caused by stellar irradiation. Vast resources have been dedicated to characterizing the handful of super Earths accessible to current telescopes, yet of the planets smaller than Neptune studied to date, all have radii in the near-infrared consistent with being constant in wavelength, likely showing that these small planets are consistently enshrouded in thick hazes and clouds. Very thick, lofted clouds of salts or sulfides in high metallicity (1000× solar) atmospheres create featureless transmission spectra in the near-infrared. Photochemical hazes with a range of particle sizes also create featureless transmission spectra at lower metallicities. I show that despite these challenges, there are promising avenues for understanding this class of small planets: by observing the thermal emission and reflectivity of small planets, we can break the degeneracies and better constrain the atmospheric compositions. These observations may provide rich diagnostics of molecules and clouds in small planets, in contrast to the limited success to date.

From the Exoplanetary Bestiary to the Exoplanetary Zoo

NASA Astrophysics Data System (ADS)

Unterborn, C. T.; Panero, W. R.; Stixrude, L. P.; Kellogg, L. H.; Lithgow-Bertelloni, C. R.; Diamond, M. R.

2014-12-01

While much attention has been focused on the exoplanetary "bestiary" of super-Earths, lava worlds, and diamond planets, habitable planets are more likely to be found in a more similar exoplanetary "zoo." Many planet-hosting stars are similar in composition to the Sun, with moderate variations in metal abundances. Even for those stars with O and Fe abundances similar to the Sun, many have 100% variations in the refractory, rock-forming elements such as Si, Mg, Al and Ca. For an Earth sized planet, this variation creates planets with drastically different mantle mineral assemblages and variable melting, elastic, and viscous properties, leading to variable dynamical behavior. This dynamical behavior dictates the dominant mode of heat extraction, be it through a conducting rigid lid or via plate tectonics. Without tectonics, there is no mechanism known with which to create a deep water and carbon cycle, thus creating a long-lived habitable surface. We present the results of integrated modeling in which we consider the effects of variations in bulk mantle composition on Earth-mass planets. To explore the variations expected in this planetary zoo, we present condensation sequence calculations for stars of varying refractory element abundances. These calculations constrain the potential refractory mineral reservoir from which Earth-mass terrestrial planets will form. As planets of this size inevitably will convect, the thermal structure of the mantle is controlled by surface melting temperature and the first crust can be estimated from decompression melting of a convecting mantle. The thermodynamic code HeFESTo determines the mineralogy and resulting thermoelastic properties of both the mantle and potential foundering of crustal material. Finally, with parameterized convection modeling and 2- and 3-D convection modeling, we determine terrestrial mantle's convective regime as a function of bulk composition. We therefore consider a planet's potential for Earth-like plate tectonics by applying compositional perturbations from the Earth. Aspects affecting this potential include the location of the basalt-eclogite transition in the upper mantle and the density contrast, and thus negative buoyancy, between the foundering crust and mantle. Portions of this work were initiated at the CIDER 2014 program.

Beyond Proxima b: Investigating the next nearest Potentially Habitable Exoplanets: Kapteyn b (13 LY) and Wolf 1061 c (14 LY) - Assessing their Suitabilty for Life

NASA Astrophysics Data System (ADS)

Guinan, Edward F.; Engle, Scott G.

2017-01-01

The discovery of an Earth-size (~1.3 Me) planet, Proxima b, orbiting in the Habitable Zone (HZ) of the nearest star (d = 4.25 LY), has provided great impetus for the study of the potential habitability of other nearby HZ planets. Ribas et al. (2016, A&A in press) have shown, that in spite of the relatively high levels of magnetic-dynamo generated X-ray & UV radiation from its M5.5 V host star that the planet endures, there are pathways for the Proxima b to possess an atmosphere, water and climate conditions to be potentially habitable. At a distance of 13 LY, the old (11.5 Gyr) Pop II M1.5 star, Kapteyn Star, has been found to hosts two large earth mass planets, one of which - Kapteyn b (M= 4.8 Me; a = 0.17 AU) is located near the mid-HZ of host star (see Englada-Escude’ et al. 2014). Unlike Proxima b, the Kapteyn b planet receives significantly less high energy radiation from its host star due the star’s lower magnetic activity and the planet’s greater distance from its host star (see Guinan et al. 2016). Recently three large earth size planets have been found orbiting the nearby (14 LY) solar-age M3 V star - Wolf 1061 (Wright et al. 2016). One of these planets, Wolf 1061 c (M = 4.6 Me; a = 0.084 AU) is located in the star’s HZ. As in the case of Kapteyn b, Wolf 1061 appears to receive less high energy radiation than Proxima b. Here we provide preliminary assessments of the effects of the host star’s high energy X-ray and UV photo-ionization radiation on the atmospheres and water inventories of the hosted planets. We compare the suitability of these three nearest planets for potential habitability and suitability for life.This research is supported by grants from NSF (RUI) and NASA.

Kepler Mission: Current Status

NASA Astrophysics Data System (ADS)

Borucki, William J.; Koch, D. G.; Lissauer, J. J.; Bryson, S.; Natalie, B.; Caldwell, D. A.; DeVore, E.; Jenkins, J. M.; Christensen-Dalsgaard, J.; Cochran, W. D.; Dunham, E. W.; Gautier, T. N.; Geary, J. C.; Latham, D. W.; Sasselov, D.; Gilliland, R. L.; Gould, A.; Howell, S. B.; Monet, D. G.

2007-12-01

Kepler is a Discovery-class mission designed to determine the frequency of Earth-size planets in and near the habitable zone of solar-like stars. The instrument consists of a high precision photometer with Schmidt-type optics and a focal plane containing 95 million pixels to monitor over 100,000 stars to search for patterns of transits generated by planets as small as Mars. The recent reduction in the mission duration is discussed with regard to the impact on the expected science product and null statistics. Both terrestrial and giant planets discoveries will be followed up with ground-based Doppler-velocity observations to determine mass and density. The first meeting of Kepler Asteroseismic Science Consortium was held in Paris to organize an international team to analyze the Kepler data to determine the characteristics of the brighter target stars including their size and age. Stellar size determinations accurate to a few percent are expected. These will allow very accurate planet sizes to be determined from the depth of the transit signals. NASA HQ received thirty six proposals for the Participating Scientist Program and chose several new members to join the Science Team. Both the 0.95 m Schmidt corrector and 1.4 m aperture primary mirror have been completed and delivered for integration into the photometer. The focal plane with forty-two science CCD detectors and their processing electronics has been assembled and tested. The spacecraft assembly has begun with the mounting of the reaction control system, reaction wheels, attitude determination & control system, and power systems. Both the photometer and spacecraft are nearing final assembly with all subsystems having passed their environmental and performance testing. The photometer to spacecraft integration will begin this spring. The Mission is on schedule for a launch in February 2009. The Kepler Mission is funded by the NASA Astrophysics Division, Science Mission Directorate.

Lunar and Planetary Science XXXV: Origin of Planetary Systems

NASA Technical Reports Server (NTRS)

2004-01-01

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

An Earth-mass planet orbiting α Centauri B.

PubMed

Dumusque, Xavier; Pepe, Francesco; Lovis, Christophe; Ségransan, Damien; Sahlmann, Johannes; Benz, Willy; Bouchy, François; Mayor, Michel; Queloz, Didier; Santos, Nuno; Udry, Stéphane

2012-11-08

Exoplanets down to the size of Earth have been found, but not in the habitable zone--that is, at a distance from the parent star at which water, if present, would be liquid. There are planets in the habitable zone of stars cooler than our Sun, but for reasons such as tidal locking and strong stellar activity, they are unlikely to harbour water-carbon life as we know it. The detection of a habitable Earth-mass planet orbiting a star similar to our Sun is extremely difficult, because such a signal is overwhelmed by stellar perturbations. Here we report the detection of an Earth-mass planet orbiting our neighbour star α Centauri B, a member of the closest stellar system to the Sun. The planet has an orbital period of 3.236 days and is about 0.04 astronomical units from the star (one astronomical unit is the Earth-Sun distance).

The Kepler Mission: A Mission to Determine the Frequency of Inner Planets Near the Habitable Zone of a Wide Range of Stars

NASA Technical Reports Server (NTRS)

Borucki, W. J.; Koch, D. G.; Dunham, E. W.; Jenkins, J. M.

1997-01-01

The surprising discovery of giant planets in inner orbits around solar-like stars has brought into question our understanding of the development and evolution of planetary systems, including our solar system. To make further progress, it is critical to detect and obtain data on the frequency and characteristics of Earth-class planets. The Kepler Mission is designed to be a quick, low-cost approach to accomplish that objective. Transits by Earth-class planets produce a fractional change. in stellar brightness of 5 x 10(exp -5) to 40 x 10(exp -5) lasting for 4 to 16 hours. From the period and depth of the transits, the orbit and size of the planets can be calculated. The proposed instrument is a one-meter aperture photometer with a 12 deg. field-of-view (FOV). To obtain the required precision and to avoid interruptions caused by day-night and seasonal cycles, the photometer will be launched into a heliocentric orbit. It will continuously and simultaneously monitor the flux from 80,000 dwarf stars brighter than 14th magnitude in the Cygnus constellation. The mission tests the hypothesis that the formation of most stars produces Earth-class planets in inner orbits. Based on this assumption and the recent observations that 2% of the stars have giant planets in inner orbits, several types of results are expected from the mission: 1. From transits of Earth-class planets, about 480 planet detections and 60 cases where two or more planets are found in the same system. 2. From transits of giant planets, about 160 detections of inner-orbit planets and 24 detections of outer-orbit planets. 3. From the phase modulation of the reflected light from giant planets, about 1400 planet detections with periods less than a week, albedos for 160 of these giant planets, and densities for seven planets.

The Kepler Mission: A Mission to Determine the Frequency of Inner Planets Neat the Habitable Zone of a Wide Range of Stars

NASA Technical Reports Server (NTRS)

Borucki, W. J.; Koch, D. G.; Dunham, E. W.; Jenkins, J. M.; Young, Richard E. (Technical Monitor)

1997-01-01

The surprising discovery of giant planets in inner orbits around solar-like stars has brought into question our understanding of the development and evolution of planetary systems, including our solar system. To make further progress, it is critical to detect and obtain data on the frequency and characteristics of Earth-class planets. The Kepler Mission is designed to be a quick, low-cost approach to accomplish that objective. Transits by Earth-class planets produce a fractional change in stellar brightness of 5 x 10(exp -5) to 40 x 10(exp -5) lasting for 4 to 16 hours, From the period and depth of the transits, the orbit and size of the planets can be calculated. The proposed instrument is a one-meter aperture photometer with a 12 deg field-of-view (FOV). To obtain the required precision and to avoid interruptions caused by day-night and seasonal cycles, the photometer will be launched into a heliocentric orbit. It will continuously and simultaneously monitor the flux from 80,000 dwarf stars brighter than 14th magnitude in the Cygnus constellation. The mission tests the hypothesis that the formation of most stars produces Earth-class planets in inner orbits. Based on this assumption and the recent observations that 2% of the stars have giant planets in inner orbits, several types of results are expected from the mission: 1. From transits of Earth-class planets, about 480 planet detections and 60 cases where two or more planets are found in the same system. 2. From transits of giant planets, about 160 detections of inner-orbit planets and 24 detections of outer-orbit planets. 3. From the phase modulation of the reflected light from giant planets, about 1400 planet detections with periods less than a week, albedos for 160 of these giant planets, and densities for seven planets.

Architectural and chemical insights into the origin of hot Jupiters

NASA Astrophysics Data System (ADS)

Schlaufman, Kevin C.

2015-10-01

The origin of Jupiter-mass planets with orbital periods of only a few days is still uncertain. This problem has been with us for 20 years, long enough for significant progress to have been made, and also for a great deal of ``lore" to have accumulated about the properties of these planets. Among this lore is the widespread belief that hot Jupiters are less likely to be in multiple giant planet systems than longer-period giant planets. I will show that in this case the lore is not supported by the best data available today: hot Jupiters are not lonely. I will also show that stellar sodium abundance is inversely proportional to the probability that a star hosts a short-period giant planet. This observation is best explained by the effect of decreasing sodium abundance on protoplanetary disk structure and reveals that planetesimal-disk or planet-disk interactions are critical for the existence of short-period giant planets.

CHROMOSPHERIC EMISSION OF PLANET CANDIDATE HOST STARS: A WAY TO IDENTIFY FALSE POSITIVES

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

Karoff, Christoffer; Knudsen, Mads Faurschou; Albrecht, Simon

2016-10-10

It has been hypothesized that the presence of closely orbiting giant planets is associated with enhanced chromospheric emission of their host stars. The main cause for such a relation would likely be enhanced dynamo action induced by the planet. We present measurements of chromospheric emission in 234 planet candidate systems from the Kepler mission. This ensemble includes 37 systems with giant-planet candidates, which show a clear emission enhancement. The enhancement, however, disappears when systems that are also identified as eclipsing binary candidates are removed from the ensemble. This suggests that a large fraction of the giant-planet candidate systems with chromosphericmore » emission stronger than the Sun are not giant-planet systems, but false positives. Such false-positive systems could be tidally interacting binaries with strong chromospheric emission. This hypothesis is supported by an analysis of 188 eclipsing binary candidates that show increasing chromospheric emission as function of decreasing orbital period.« less

Polarized scattered light from self-luminous exoplanets. Three-dimensional scattering radiative transfer with ARTES

NASA Astrophysics Data System (ADS)

Stolker, T.; Min, M.; Stam, D. M.; Mollière, P.; Dominik, C.; Waters, L. B. F. M.

2017-11-01

Context. Direct imaging has paved the way for atmospheric characterization of young and self-luminous gas giants. Scattering in a horizontally-inhomogeneous atmosphere causes the disk-integrated polarization of the thermal radiation to be linearly polarized, possibly detectable with the newest generation of high-contrast imaging instruments. Aims: We aim to investigate the effect of latitudinal and longitudinal cloud variations, circumplanetary disks, atmospheric oblateness, and cloud particle properties on the integrated degree and direction of polarization in the near-infrared. We want to understand how 3D atmospheric asymmetries affect the polarization signal in order to assess the potential of infrared polarimetry for direct imaging observations of planetary-mass companions. Methods: We have developed a three-dimensional Monte Carlo radiative transfer code (ARTES) for scattered light simulations in (exo)planetary atmospheres. The code is applicable to calculations of reflected light and thermal radiation in a spherical grid with a parameterized distribution of gas, clouds, hazes, and circumplanetary material. A gray atmosphere approximation is used for the thermal structure. Results: The disk-integrated degree of polarization of a horizontally-inhomogeneous atmosphere is maximal when the planet is flattened, the optical thickness of the equatorial clouds is large compared to the polar clouds, and the clouds are located at high altitude. For a flattened planet, the integrated polarization can both increase or decrease with respect to a spherical planet which depends on the horizontal distribution and optical thickness of the clouds. The direction of polarization can be either parallel or perpendicular to the projected direction of the rotation axis when clouds are zonally distributed. Rayleigh scattering by submicron-sized cloud particles will maximize the polarimetric signal whereas the integrated degree of polarization is significantly reduced with micron-sized cloud particles as a result of forward scattering. The presence of a cold or hot circumplanetary disk may also produce a detectable degree of polarization (≲1%) even with a uniform cloud layer in the atmosphere.

Kepler constraints on planets near hot Jupiters

PubMed Central

Steffen, Jason H.; Ragozzine, Darin; Fabrycky, Daniel C.; Carter, Joshua A.; Ford, Eric B.; Holman, Matthew J.; Rowe, Jason F.; Welsh, William F.; Borucki, William J.; Boss, Alan P.; Ciardi, David R.; Quinn, Samuel N.

2012-01-01

We present the results of a search for planetary companions orbiting near hot Jupiter planet candidates (Jupiter-size candidates with orbital periods near 3 d) identified in the Kepler data through its sixth quarter of science operations. Special emphasis is given to companions between the 2∶1 interior and exterior mean-motion resonances. A photometric transit search excludes companions with sizes ranging from roughly two-thirds to five times the size of the Earth, depending upon the noise properties of the target star. A search for dynamically induced deviations from a constant period (transit timing variations) also shows no significant signals. In contrast, comparison studies of warm Jupiters (with slightly larger orbits) and hot Neptune-size candidates do exhibit signatures of additional companions with these same tests. These differences between hot Jupiters and other planetary systems denote a distinctly different formation or dynamical history. PMID:22566651

NanoRocks: Design and performance of an experiment studying planet formation on the International Space Station

NASA Astrophysics Data System (ADS)

Brisset, Julie; Colwell, Joshua; Dove, Adrienne; Maukonen, Doug

2017-07-01

In an effort to better understand the early stages of planet formation, we have developed a 1.5U payload that flew on the International Space Station (ISS) in the NanoRacks NanoLab facility between September 2014 and March 2016. This payload, named NanoRocks, ran a particle collision experiment under long-term microgravity conditions. The objectives of the experiment were (a) to observe collisions between mm-sized particles at relative velocities of < 1 cm/s and (b) to study the formation and disruption of particle clusters for different particle types and collision velocities. Four types of particles were used: mm-sized acrylic, glass, and copper beads and 0.75 mm-sized JSC-1 lunar regolith simulant grains. The particles were placed in sample cells carved out of an aluminum tray. This tray was attached to one side of the payload casing with three springs. Every 60 s, the tray was agitated, and the resulting collisions between the particles in the sample cells were recorded by the experiment camera. During the 18 months the payload stayed on ISS, we obtained 158 videos, thus recording a great number of collisions. The average particle velocities in the sample cells after each shaking event were around 1 cm/s. After shaking stopped, the inter-particle collisions damped the particle kinetic energy in less than 20 s, reducing the average particle velocity to below 1 mm/s, and eventually slowing them to below our detection threshold. As the particle velocity decreased, we observed the transition from bouncing to sticking collisions. We recorded the formation of particle clusters at the end of each experiment run. This paper describes the design and performance of the NanoRocks ISS payload.

NanoRocks: Design and performance of an experiment studying planet formation on the International Space Station.

PubMed

Brisset, Julie; Colwell, Joshua; Dove, Adrienne; Maukonen, Doug

2017-07-01

In an effort to better understand the early stages of planet formation, we have developed a 1.5U payload that flew on the International Space Station (ISS) in the NanoRacks NanoLab facility between September 2014 and March 2016. This payload, named NanoRocks, ran a particle collision experiment under long-term microgravity conditions. The objectives of the experiment were (a) to observe collisions between mm-sized particles at relative velocities of < 1 cm/s and (b) to study the formation and disruption of particle clusters for different particle types and collision velocities. Four types of particles were used: mm-sized acrylic, glass, and copper beads and 0.75 mm-sized JSC-1 lunar regolith simulant grains. The particles were placed in sample cells carved out of an aluminum tray. This tray was attached to one side of the payload casing with three springs. Every 60 s, the tray was agitated, and the resulting collisions between the particles in the sample cells were recorded by the experiment camera. During the 18 months the payload stayed on ISS, we obtained 158 videos, thus recording a great number of collisions. The average particle velocities in the sample cells after each shaking event were around 1 cm/s. After shaking stopped, the inter-particle collisions damped the particle kinetic energy in less than 20 s, reducing the average particle velocity to below 1 mm/s, and eventually slowing them to below our detection threshold. As the particle velocity decreased, we observed the transition from bouncing to sticking collisions. We recorded the formation of particle clusters at the end of each experiment run. This paper describes the design and performance of the NanoRocks ISS payload.

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.

Observing the Spectra of MEarth and TRAPPIST Planets with JWST

NASA Astrophysics Data System (ADS)

Morley, Caroline; Kreidberg, Laura; Rustamkulov, Zafar; Robinson, Tyler D.; Fortney, Jonathan J.

2017-10-01

During the past two years, nine planets close to Earth in radius have been discovered around nearby M dwarfs cooler than 3300 K. These planets include the 7 planets in the TRAPPIST-1 system and two planets discovered by the MEarth survey, GJ 1132b and LHS 1140b (Dittmann et al. 2017; Berta-Thompson et al. 2015; Gillon et al. 2017). These planets are the smallest planets discovered to date that will be amenable to atmospheric characterization with JWST. They span equilibrium temperatures from ˜130 K to >500 K, and radii from 0.7 to 1.43 Earth radii. Some of these planets orbit as distances potentially amenable to surface liquid water, though the actual surface temperatures will depend strongly on the albedo of the planet and the thickness and composition of its atmosphere. The stars they orbit also vary in activity levels, from the quiet LHS 1140b host star to the more active TRAPPIST-1 host star. This set of planets will form the testbed for our first chance to study the diversity of atmospheres around Earth-sized planets. Here, we will present model spectra of these 9 planets, varying the composition and the surface pressure of the atmosphere. We base our elemental compositions on three outcomes of planetary atmosphere evolution in our own solar system: Earth, Titan, and Venus. We calculate the molecular compositions in chemical equilibrium. We present both thermal emission spectra and transmission spectra for each of these objects, and make predictions for the observability of these spectra with different instrument modes with JWST.

On volcanism and thermal tectonics on one-plate planets

NASA Technical Reports Server (NTRS)

Solomon, S. C.

1978-01-01

For planets with a single global lithospheric shell or 'plate', the thermal evolution of the interior affects the surface geologic history through volumetric expansion and the resultant thermal stress. Interior warming of such planets gives rise to extensional tectonics and a lithospheric stress system conductive to widespread volcanism. Interior cooling leads to compressional tectonics and lithospheric stresses that act to shut off surface volcanism. On the basis of observed surface tectonics, it is concluded that the age of peak planetary volume, the degree of early heating, and the age of youngest major volcanism on the one-plate terrestrial planets likely decrease in the order Mercury, Moon, Mars.

Do planets remember how they formed?

NASA Astrophysics Data System (ADS)

Kipping, David

2018-01-01

One of the most directly observable features of a transiting multiplanet system is their size-ordering when ranked in orbital separation. Kepler has revealed a rich diversity of outcomes, from perfectly ordered systems, like Kepler-80, to ostensibly disordered systems, like Kepler-20. Under the hypothesis that systems are born via preferred formation pathways, one might reasonably expect non-random size-orderings reflecting these processes. However, subsequent dynamical evolution, often chaotic and turbulent in nature, may erode this information and so here we ask - do systems remember how they formed? To address this, we devise a model to define the entropy of a planetary system's size-ordering, by first comparing differences between neighbouring planets and then extending to accommodate differences across the chain. We derive closed-form solutions for many of the microstate occupancies and provide public code with look-up tables to compute entropy for up to 10-planet systems. All three proposed entropy definitions exhibit the expected property that their credible interval increases with respect to a proxy for time. We find that the observed Kepler multis display a highly significant deficit in entropy compared to a randomly generated population. Incorporating a filter for systems deemed likely to be dynamically packed, we show that this result is robust against the possibility of missing planets too. Put together, our work establishes that Kepler systems do indeed remember something of their younger years and highlights the value of information theory for exoplanetary science.

Architectural and Chemical Insights into the Origin of Hot Jupiters

NASA Astrophysics Data System (ADS)

Schlaufman, Kevin C.

2015-08-01

The origin of Jupiter-mass planets with orbital periods of only a few days is still uncertain. This problem has been with us for 20 years, long enough for significant progress to have been made, and also for a great deal of "lore" to have accumulated about the properties of these planets. Among this lore are the widespread beliefs that hot Jupiters are less likely be in multiple giant planet systems than longer-period giant planets, and that there is an excess of close-in giant planets with orbital periods near three days. I will show that in these cases the lore is not supported by the best data available today: hot Jupiters are not lonely and there is no evidence of a three-day pile-up. I will also show that stellar sodium abundance is inversely proportional to the probability that a star hosts a short-period giant planet. This observation is best explained by the effect of decreasing sodium abundance on protoplanetary disk structure and reveals that planet-disk interactions are critical for the existence of short-period giant planets. Collectively, these results support the importance of disk migration for the origin of short-period giant planets.

Pinning Down Properties of TRAPPIST-1

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2018-02-01

TRAPPIST-1, a nearby ultracool dwarf star, was catapulted into the public eye roughly a year ago when it was determined to host seven transiting, Earth-sized planets three of which are located in its habitable zone. But how correct are the properties weve measured for this system?TRAPPIST-1 is a very small, dim star its only 11% the diameter of the Sun which makes it easier for us to learn about its planets from transit data. [ESO]Intrigue of TRAPPIST-1One reason the TRAPPIST-1 system is of particular interest to scientists is that its small star (roughly the size of Jupiter) means that the system has a very favorable planet-to-star ratio. This makes it possible to learn a great deal about the properties of the planets using current and next-generation telescopes.The observations we expect to be able to make of TRAPPIST-1 exoplanets of the planet atmospheres, surface conditions, and internal compositions, for example will allow us to test planet formation and evolution theories and assess the prospects of habitability for Earth-sized planets orbiting cool M dwarfs.Why Stellar Measurements MatterThe parallax motion of TRAPPIST-1 in dec (top) and R.A. (bottom) as a function of day. Observations were made between 2013 and 2016 and then folded over a year. [Van Grootel et al. 2018]In order to make these measurements, however, we first need very precise measurements of the host stars parameters. This is because transiting exoplanet parameters are generally determined relative to those of the host. A few examples:Determining how much irradiation a planet receives requires knowing the luminosity of the host star and planets orbit size. The latter is calculated based on the host stars mass.Determining the planets radius requires knowing the host stars radius, as the planets transit depth tells us only the star-to-planet radius ratio.Determining whether or not the planet is able to retain an atmosphere and therefore whether it has exhibited long-term habitability requires knowing the time the host star takes to contract onto the main sequence, which depends on the stars mass.When the TRAPPIST-1 planetary system was discovered, measurements of TRAPPIST-1s properties were made to the best of our abilities at the time. Now, in a new study led by Valrie Van Grootel (University of Lige, Belgium), a team of scientists has used new observations and analysis techniques to refine our measurements of the star.Stellar luminosity for evolution models for various masses and metallicities. The green dashed horizontal lines bracket the authors observed value for TRAPPIST-1s luminosity. A stellar mass of 0.09 M is needed to account for the old age and luminosity of the star. [Van Grootel et al. 2018]New EstimatesUsing 188 epochs of observations of TRAPPIST-1 from multiple telescopes between 2013 and 2016, Van Grootel and collaborators obtained a very precise measurement for TRAPPIST-1s parallax. This allowed them to refine the estimate of its luminosity now measured at (5.22 0.19) x 10-4that of the Sun to twice the precision of the previous estimate.The team then produced a new estimate for TRAPPIST-1s mass using new stellar evolution modeling and analysis, combined with empirical mass derived for similar ultracool dwarfs in astrometric binaries. This approach produces a final mass for TRAPPIST-1 of 0.089 0.006 M which is nearly 10% higher than the previous estimate and significantly more precise. Finally, the authors use these values to obtain new estimates of TRAPPIST-1s radius (0.121 0.003 R) and effective temperature (2516 41 K).These new, refined measurements will ensure that our future observations of the TRAPPIST-1 planets are being interpreted correctly which is criticalfor a system that will be so thoroughly scrutinized in coming years. Keep an eye out for new results about TRAPPIST-1 in the future!CitationValrie Van Grootel et al 2018 ApJ 853 30. doi:10.3847/1538-4357/aaa023

The Dynamical Imprint of Lost Protoplanets on the Trans-Neptunian Populations, and Limits on the Primordial Size Distribution of Trans-Neptunian Objects at Pluto and Larger Sizes.

NASA Astrophysics Data System (ADS)

Shannon, Andrew Brian; Dawson, Rebekah

2018-04-01

Planet formation remains a poorly understood process, in part because of our limited access to the intermediate phases of planetesimal and protoplanet growth. Today, the vast majority of the accessible remaining planetesimals and protoplanets reside within the Hot Trans-Neptunian Object population. This population has been depleted by 99% - 99.9% over the course of the Solar system's history, and as such the present day size-number distribution may be incomplete at the large size end. We show that such lost protoplanets would have left signatures in the dynamics of the present-day Trans-Neptunian Populations, and their primordial number can thus be statistically limited by considering the survival of ultra-wide binary TNOs, the Cold Classical Kuiper belt, and the resonant populations. We compare those limits to the predicted size-number distribution of various planetesimal and proto-planet growth models.

Climate evolution on the terrestrial planets

NASA Technical Reports Server (NTRS)

Kasting, J. F.; Toon, O. B.

1989-01-01

The present comparative evaluation of the long-term evolution of the Venus, earth, and Mars climates suggests that the earth's climate has remained temperate over most of its history despite a secular solar luminosity increase in virtue of a negative-feedback cycle based on atmospheric CO2 levels and climate. The examination of planetary climate histories suggests that an earth-sized planet should be able to maintain liquid water on its surface at orbital distances in the 0.9-1.5 AU range, comparable to the orbit of Mars; this, in turn, implies that there may be many other habitable planets within the Galaxy.

Comparison of the distribution of large magmatic centers on Earth, Venus, and Mars

NASA Technical Reports Server (NTRS)

Crumpler, L. S.

1993-01-01

Volcanism is widely distributed over the surfaces of the major terrestrial planets: Venus, Earth, and Mars. Anomalous centers of magmatic activity occur on each planet and are characterized by evidence for unusual concentrations of volcanic centers, long-lived activity, unusual rates of effusion, extreme size of volcanic complexes, compositionally unusual magmatism, and evidence for complex geological development. The purpose of this study is to compare the characteristics and distribution of these magmatic anomalies on Earth, Venus, and Mars in order to assess these characteristics as they may relate to global characteristics and evolution of the terrestrial planets.

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.

Atmospheric Characterization of Giant Exoplanets in Extreme Environments

NASA Astrophysics Data System (ADS)

Wilkins, Ashlee

The study of planets around other stars has entered a science-rich era of characterization, in which detailed information about individual planets can be inferred from observations beyond discovery and confirmation, which only yield bulk properties like mass or radius. Characterization probes more revealing quantities such as chemical abundances, albedo, and temperature/pressure profiles, allowing us to address larger questions of planet formation mechanisms, planetary evolution, and, eventually, presence of biosignature gases. The primary method for characterization of close-in planets is transit spectroscopy. My dissertation comprises transiting exoplanet case studies using the Hubble Space Telescopes Wide-Field Camera-3 (HST/WFC3) as a tool of exoplanet characterization in a near-infrared band dominated by broad water absorption. Much of my efforts went toward a characterization of the WFC3 systematic effects that must be mitigated to extract the incredibly small (tens to 200 parts per million) signals. The case study subjects in this dissertation are CoRoT-2b (in emission), WASP-18b (in transmission and emission), and HATS-7b (in transmission), along with some partial/preliminary analyses of HAT-p-3b and HD 149026b (both in transmission). I also present an analysis of transit timing of WASP-18b with HST and other observatories as another clue to its evolution as a close-in, extremely massive planet purported to be spiraling in to its host star. The five planets range from super Neptunes to Super-Jupiter in size/mass. The observability of such planets--i.e. giants across a continuum of mass/size in extreme local environments close to their respective host stars,--is a unique opportunity to probe planet formation and evolution, as well as atmospheric structures in a high-irradiation environment. This genre of observations reveal insights into aerosols in the atmosphere; clouds and/or hazes can significantly impact atmospheric chemistry and observational signatures, and the community must better understand the phenomenon of aerosols in advance of the next generation of space observatories, including JWST and WFIRST. In conducting these case studies as part of larger collaborations and HST observing campaigns, my work aids in the advancement of exoplanet atmosphere characterization from single, planetby-planet, case studies, to an understanding of the large, hot, gaseous planets as a population.

Comment on ``Minimal size of a barchan dune''

NASA Astrophysics Data System (ADS)

Andreotti, B.; Claudin, P.

2007-12-01

It is now an accepted fact that the size at which dunes form from a flat sand bed as well as their “minimal size” scales on the flux saturation length. This length is by definition the relaxation length of the slowest mode toward equilibrium transport. The model presented by Parteli, Durán, and Herrmann [Phys. Rev. E 75, 011301 (2007)] predicts that the saturation length decreases to zero as the inverse of the wind shear stress far from the threshold. We first show that their model is not self-consistent: even under large wind, the relaxation rate is limited by grain inertia and thus cannot decrease to zero. A key argument presented by these authors comes from the discussion of the typical dune wavelength on Mars (650 m) on the basis of which they refute the scaling of the dune size with the drag length evidenced by Claudin and Andreotti [Earth Planet. Sci. Lett. 252, 30 (2006)]. They instead propose that Martian dunes, composed of large grains (500μm) , were formed in the past under very strong winds. We emphasize that this saltating grain size, estimated from thermal diffusion measurements, is far from straightforward. Moreover, the microscopic photographs taken by the rovers on Martian Aeolian bedforms show a grain size of 87±25μm together with hematite spherules at millimeter scale. As those so-called “blueberries” cannot be entrained more frequently than a few hours per century, we conclude that the saltating grains on Mars are the small ones, which gives a second strong argument against the model of Parteli

Collisional disruption of gravitational aggregates in the tidal environment

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

Hyodo, Ryuki; Ohtsuki, Keiji

2014-05-20

The degree of disruption in collisions in free space is determined by specific impact energy, and the mass fraction of the largest remnant is a monotonically decreasing function of impact energy. However, it has not been shown whether such a relationship is applicable to collisions under the influence of a planet's tidal force, which is important in ring dynamics and satellite accretion. Here we examine the collisional disruption of gravitational aggregates in the tidal environment by using local N-body simulations. We find that outcomes of such a collision largely depend on the impact velocity, the direction of impact, and themore » radial distance from the planet. In the case of a strong tidal field corresponding to Saturn's F ring, collisions in the azimuthal direction are much more destructive than those in the radial direction. Numerical results of collisions sensitively depend on the impact velocity, and a complete disruption of aggregates can occur even in impacts with velocity much lower than their escape velocity. In such low-velocity collisions, the deformation of colliding aggregates plays an essential role in determining collision outcomes, because the physical size of the aggregate is comparable to its Hill radius. On the other hand, the dependence of collision outcomes on impact velocity becomes similar to the case in free space when the distance from the planet is sufficiently large. Our results are consistent with Cassini observations of the F ring, which suggest ongoing creation and disruption of aggregates within the ring.« less

BIRTH LOCATIONS OF THE KEPLER CIRCUMBINARY PLANETS

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

Silsbee, Kedron; Rafikov, Roman R., E-mail: ksilsbee@astro.princeton.edu

2015-07-20

The Kepler mission has discovered about a dozen circumbinary planetary systems, all containing planets on ∼1 AU orbits. We place bounds on the locations in the circumbinary protoplanetary disk, where these planets could have formed through collisional agglomeration starting from small (kilometer-sized or less) planetesimals. We first present a model of secular planetesimal dynamics that accounts for the (1) perturbation due to the eccentric precessing binary, as well as the (2) gravity and (3) gas drag from a precessing eccentric disk. Their simultaneous action leads to rich dynamics, with (multiple) secular resonances emerging in the disk. We derive analytic resultsmore » for size-dependent planetesimal eccentricity and demonstrate the key role of the disk gravity for circumbinary dynamics. We then combine these results with a simple model for collisional outcomes and find that in systems like Kepler-16, planetesimal growth starting with 10–100 m planetesimals is possible outside a few AU. The exact location exterior to which this happens is sensitive to disk eccentricity, density, and precession rate, as well as to the size of the first generation of planetesimals. Strong perturbations from the binary in the inner part of the disk, combined with a secular resonance at a few AU, inhibit the growth of kilometer-sized planetesimals within 2–4 AU of the binary. In situ planetesimal growth in the Kepler circumbinary systems is possible only starting from large initial planetesimals (few-kilometer-sized even assuming favorable disk properties, i.e., low surface density)« less

Overview and Status of the Kepler Mission

NASA Technical Reports Server (NTRS)

Koch, D.; Borucki, W.; Dunham, E.; Geary, J.; Gilliland, R.; Jenkins, J.; Latham, D.; Mayer, D.; Sobeck, C.; Duren, R.

2003-01-01

The Kepler Mission is a search for terrestrial planets with the design optimized for detecting Earth-size planets in the habitable zone (HZ) of solar-like stars. In addition, the mission has a broad detection capability for a wide range of planetary sizes, planetary orbits and spectral types of stars. The mission is in the midst of the development phase with good progress leading to the preliminary design review later this year. Long lead procurements are well under way. An overview in all areas is presented including both the flight system (photometer and spacecraft) and the ground system. Launch is on target for 2007 on a Delta II.

The Leonard Award Address: On the Difficulties of Making Earth-Like Planets

NASA Astrophysics Data System (ADS)

Taylor, Stuart Ross

1999-05-01

Here I discuss the series of events that led to the formation and evolution of our planet to examine why the Earth is unique in the solar system. A multitude of factors are involved. These begin with the initial size and angular momentum of the fragment that separated from a molecular cloud. These are crucial in determining whether a planetary system or a double star develops from the resulting nebula. Another requirement is that there must be an adequate concentration of heavy elements to provide the two percent 'rock' and 'ice' components of the original nebula. An essential step in forming rocky planets in the inner nebula is loss of gas and depletion of volatile elements due to early solar activity, that is linked to the mass of the central star. The lifetime of the gaseous nebula controls the formation of gas giants. In our system, fine timing was needed to form the gas giant, Jupiter before the gas in the nebula was depleted. Although Uranus and Neptune eventually formed cores large enough to capture gas, they missed out and ended as ice giants The early formation of Jupiter is responsible for the existence of the asteroid belt (and our supply of meteorites) and the small size of Mars while the gas giant now acts as a gravitational shield for the terrestrial planets. The Earth and the other inner planets accreted long after the giant planets in a gas-free inner nebula from volatile-depleted planetesimals that were probably already differentiated into metallic cores and silicate mantles. The accumulation of the Earth from such planetesimals was essentially a stochastic process, accounting for the differences among the four rocky inner planets including the startling contrast between those two apparent twins, Earth and Venus. Impact history and accretion of a few more or less planetesimals were apparently crucial. The origin of the Moon by a single massive impact with a body larger than Mars accounts for the obliquity (and its stability) and spin of the Earth in addition to explaining the angular momentum, orbital characteristics and unique composition of the Moon. Plate tectonics, unique among the terrestrial planets, led to the development of the continental crust on the Earth, an essential platform for the evolution of Homo sapiens. Random major impacts have punctuated the geological record, accentuating the directionless course of evolution. Thus a massive asteroidal impact terminated the Cretaceous Period, resulted in the extinction of at least 70% of species living at that time and led to the rise of mammals. This sequence of events that resulted in the formation and evolution of our planet were thus unique within our system. The individual nature of the eight planets is repeated among the 60-odd satellites: no two seem identical. This survey of our solar system raises the question whether the random sequence of events that led to the formation of the Earth are likely to be repeated in detail elsewhere. Preliminary evidence from the 'new planets' is not reassuring. The discovery of other planetary systems has removed the previous belief that they would consist of a central star surrounded by an inner zone of rocky planets and an outer zone of giant planets beyond a few AU. Jupiter-sized bodies in close orbits around other stars probably formed in a similar manner to our giant planets at several AU from their parent star and subsequently migrated inwards becoming stranded in close but stable orbits as 'hot Jupiters', when the nebula gas was depleted. Such events would prevent the formation of terrestrial-type planets in such systems.

A Neptune-sized transiting planet closely orbiting a 5–10-million-year-old star.

PubMed

David, Trevor J; Hillenbrand, Lynne A; Petigura, Erik A; Carpenter, John M; Crossfield, Ian J M; Hinkley, Sasha; Ciardi, David R; Howard, Andrew W; Isaacson, Howard T; Cody, Ann Marie; Schlieder, Joshua E; Beichman, Charles A; Barenfeld, Scott A

2016-06-30

Theories of the formation and early evolution of planetary systems postulate that planets are born in circumstellar disks, and undergo radial migration during and after dissipation of the dust and gas disk from which they formed. The precise ages of meteorites indicate that planetesimals—the building blocks of planets—are produced within the first million years of a star’s life. Fully formed planets are frequently detected on short orbital periods around mature stars. Some theories suggest that the in situ formation of planets close to their host stars is unlikely and that the existence of such planets is therefore evidence of large-scale migration. Other theories posit that planet assembly at small orbital separations may be common. Here we report a newly born, transiting planet orbiting its star with a period of 5.4 days. The planet is 50 per cent larger than Neptune, and its mass is less than 3.6 times that of Jupiter (at 99.7 per cent confidence), with a true mass likely to be similar to that of Neptune. The star is 5–10 million years old and has a tenuous dust disk extending outward from about twice the Earth–Sun separation, in addition to the fully formed planet located at less than one-twentieth of the Earth–Sun separation.

M2K Planet Search: Spectroscopic Screening and Transit Photometry

NASA Astrophysics Data System (ADS)

Mann, Andrew; Gaidos, E.; Fischer, D.; Lepine, S.

2010-10-01

The M2K project is a search for planets orbiting nearby early M and late K dwarf drawn from the SUPERBLINK catalog. M and K dwarfs are highly attractive targets for finding low-mass and habitable planets because (1) close-in planets are more likely to orbit within their habitable zone, (2) planets orbiting them induce a larger Doppler signal and have deeper transits than similar planets around F, G, and early K type stars, (3) planet formation models predict they hold an abundance of super-Earth sized planets, and (4) they represent the vast majority of the stars close enough for direct imaging techniques. In spite of this, only 10% of late K and early M dwarfs are being monitored by current Doppler surveys. As part of the M2K project we have obtained low-resolution spectra for more than 2000 of our sample of 10,000 M and K dwarfs. We vet our sample by screening these stars for high metallicity and low chromospheric activity. We search for transits on targets showing high RMS Doppler signal and photometry candidates provided by SuperWASP project. By using "snapshot” photometry have been able to achieve sub-millimag photometry on numerous transit targets in the same night. With further follow-up observations we will be able to detect planets smaller than 10 Earth masses.

Data Validation in the Kepler Science Operations Center Pipeline

NASA Technical Reports Server (NTRS)

Wu, Hayley; Twicken, Joseph D.; Tenenbaum, Peter; Clarke, Bruce D.; Li, Jie; Quintana, Elisa V.; Allen, Christopher; Chandrasekaran, Hema; Jenkins, Jon M.; Caldwell, Douglas A.;

Accretion of Rocky Planets by Hot Jupiters

NASA Astrophysics Data System (ADS)

Ketchum, Jacob A.; Adams, Fred C.; Bloch, Anthony M.

2011-11-01

The observed population of Hot Jupiters displays a stunning variety of physical properties, including a wide range of densities and core sizes for a given planetary mass. Motivated by the observational sample, this Letter studies the accretion of rocky planets by Hot Jupiters, after the Jovian planets have finished their principal migration epoch and become parked in ~4 day orbits. In this scenario, rocky planets form later and then migrate inward due to torques from the remaining circumstellar disk, which also damps the orbital eccentricity. This mechanism thus represents one possible channel for increasing the core masses and metallicities of Hot Jupiters. This Letter determines probabilities for the possible end states for the rocky planet: collisions with the Jovian planets, accretion onto the star, ejection from the system, and long-term survival of both planets. These probabilities depend on the mass of the Jovian planet and its starting orbital eccentricity, as well as the eccentricity damping rate for the rocky planet. Since these systems are highly chaotic, a large ensemble (N ~ 103) of simulations with effectively equivalent starting conditions is required. Planetary collisions are common when the eccentricity damping rate is sufficiently low, but are rare otherwise. For systems that experience planetary collisions, this work determines the distributions of impact velocities—both speeds and impact parameters—for the collisions. These velocity distributions help determine the consequences of the impacts, e.g., where energy and heavy elements are deposited within the giant planets.

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.

Born dry in the photoevaporation desert: Kepler's ultra-short-period planets formed water-poor

NASA Astrophysics Data System (ADS)

Lopez, Eric D.

2017-11-01

Recent surveys have uncovered an exciting new population of ultra-short-period (USP) planets with orbital periods less than a day. These planets typically have radii ≲1.5 R⊕, indicating that they likely have rocky compositions. This stands in contrast to the overall distribution of planets out to ∼100 d, which is dominated by low-density sub-Neptunes above 2 R⊕, which must have gaseous envelopes to explain their size. However, on the USP orbits, planets are bombarded by intense levels of photoionizing radiation and consequently gaseous sub-Neptunes are extremely vulnerable to losing their envelopes to atmospheric photoevaporation. Using models of planet evolution, I show that the rocky USP planets can easily be produced as the evaporated remnants of sub-Neptunes with H/He envelopes and that we can therefore understand the observed dearth of USP sub-Neptunes as a natural consequence of photoevaporation. Critically however, planets on USP orbits could often retain their envelopes if they are formed with very high-metallicity water-dominated envelopes. Such water-rich planets would commonly be ≳2 R⊕ today, which is inconsistent with the observed evaporation desert, indicating that most USP planets likely formed from water-poor material within the snow-line. Finally, I examine the special case of 55 Cancri e and its possible composition in the light of recent observations, and discuss the prospects for further characterizing this population with future observations.

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.

The Effects of Metallicity and Grain Size on Gravitational Instabilities in Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Cai, Kai; Durisen, Richard H.; Michael, Scott; Boley, Aaron C.; Mejía, Annie C.; Pickett, Megan K.; D'Alessio, Paola

2006-01-01

Observational studies show that the probability of finding gas giant planets around a star increases with the star's metallicity. Our latest simulations of disks undergoing gravitational instabilities (GIs) with realistic radiative cooling indicate that protoplanetary disks with lower metallicity generally cool faster and thus show stronger overall GI activity. More importantly, the global cooling times in our simulations are too long for disk fragmentation to occur, and the disks do not fragment into dense protoplanetary clumps. Our results suggest that direct gas giant planet formation via disk instabilities is unlikely to be the mechanism that produced most observed planets. Nevertheless, GIs may still play an important role in a hybrid scenario, compatible with the observed metallicity trend, where structure created by GIs accelerates planet formation by core accretion.

The Effects of Metallicity and Grain Size on Gravitational Instabilities in Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Cai, K.; Durisen, R. H.; Michael, S.; Boley, A. C.; Mejía, A. C.; Pickett, M. K.; D'Alessio, P.

Observational studies show that the probability of finding gas giant planets around a star increases with the star's metallicity. Our latest simulations of disks undergoing gravitational instabilities (GIs) with realistic radiative cooling indicate that protoplanetary disks with lower metallicity generally cool faster and thus show stronger overall GI-activity. More importantly, the global cooling times in our simulations are too long for disk fragmentation to occur, and the disks do not fragment into dense protoplanetary clumps. Our results suggest that direct gas giant planet formation via disk instabilities is unlikely to be the mechanism that produced most observed planets. Nevertheless, GIs may still play an important role in a hybrid scenario, compatible with the observed metallicity trend, where structure created by GIs accelerates planet formation by core accretion.

KOI-676: An active star with two transiting planets and a third possible candidate detected with TTV

NASA Astrophysics Data System (ADS)

Ioannidis, P.; Schmitt, J.; Avdellidou, C.; von Essen, C.; Eric, A.

2013-09-01

We report the detection and characterization of two short period, Neptune sized planets, around the active star KOI-676. The orbital elements of both planets are not the expected ones, as they lead to miscalculation of the stellar parameters. We discuss various scenarios which could cause that discrepancy and we suggest that the reason is most probably the high eccentricities of the orbits. We use the Transit Timing Variations, detected in both planets' O-C diagrams to support our theory, while due to the lack of autocorrelation in their pattern we suggest the existence of a third, more massive, mutual inclined, outer perturber. To clarify our suggestions we use n-body simulations to model the TTVs and check the stability of the system.

TRAPPIST-1 Planet Lineup - Updated Feb. 2018

NASA Image and Video Library

2018-02-05

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, as of February 2018. This image represents an updated version of PIA21422, which was created in 2017. The planets' appearances were re-imagined based on a 2018 study using additional observations from NASA's Spitzer and Kepler space telescopes, in addition to previous data from Spitzer, the ground-based TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) telescope and other ground-based observatories. The system was named for the TRAPPIST telescope. The new analysis concludes that the seven planets of TRAPPIST-1 are all rocky, and some could contain significant amounts of water. TRAPPIST-1 is an ultra-cool dwarf star in the constellation Aquarius, and its planets orbit very close to it. The form that water would take on TRAPPIST-1 planets would depend on the amount of heat they receive from their star, which is a mere 9 percent as massive as our Sun. Planets closest to the star are more likely to host water in the form of atmospheric vapor, while those farther away may have water frozen on their surfaces as ice. TRAPPIST-1e is the rockiest planet of them all, but still is believed to have the potential to host some liquid water. In this illustration, the relative sizes of the planets and their host star, an ultracool dwarf, are all shown to scale. An annotated image is available at https://photojournal.jpl.nasa.gov/catalog/PIA22093

Photometric Observations of 6000 Stars in the Cygnus Field

NASA Technical Reports Server (NTRS)

Borucki, W.; Caldwell, D.; Koch, D.; Jenkins, J.; Ninkov, Z.

1999-01-01

A small photometer to detect transits by extrasolar planets has been assembled and is being tested at Lick Observatory on Mt. Hamilton, California. The Vulcan photometer is constructed from a 30 cm focal length, F/2.5 AeroEktar reconnaissance lens and Photometrics PXL16800 CCD camera. A spectral filter is used to confine the pass band from 480 to 763 mn. It simultaneously monitors 6000 stars brighter than 12th magnitude within a single star field in the galactic plane. When the data are folded and phased to discover low amplitude transits, the relative precision of one-hour samples is about 1 part per thousand (10 x l0(exp -3)) for many of the brighter stars. This precision is sufficient to find jovian-size planets orbiting solar-like stars, which have signal amplitudes from 5 to 30 x l0(exp -3) depending on the inflation of the planet and the size of the star. Based on the frequency of giant inner-planets discovered by Doppler-velocity method, one or two planets should be detectable in a rich star field. The goal of the observations is to obtain the sizes of giant extrasolar planets in short-period orbits and to combine these with masses determined from Doppler velocity measurements to determine the densities of these planets. A further goal is to compare the measured planetary diameters with those predicted from theoretical models. From August 10 through September 30 of 1998, a forty nine square degree field in the Cygnus constellation centered at RA and DEC of 19 hr 47 min, +36 deg 55 min was observed. Useful data were obtained on twenty-nine nights. Nearly fifty stars showed some evidence of transits with periods between 0.3 and 8 days. Most had amplitudes too large to be associated with planetary transits. However, several stars showed low amplitude transits. The data for several transits of each of these two stars have been folded and been folded into 30 minute periods. Only Cygl433 shows any evidence of a flattened bottom that is expected when a small object transits a much larger primary. However when high-resolution spectra were obtained for both stars, the stars were found to be double-lined binaries so similar in size as to have indistinguishable transit depths. The low amplitude of the transits is explained if the stellar orbital planes are tipped approximately 5 degrees from the line of sight causing both binaries to show grazing transits. The two absorption lines, due to the H(sub beta) feature in each star, are apparent and indicate the presence of a binary system with similar components.

Runaway greenhouse effect on exomoons due to irradiation from hot, young giant planets

NASA Astrophysics Data System (ADS)

Heller, R.; Barnes, R.

2015-04-01

The Kepler space telescope has proven capable of detecting transits of objects almost as small as the Earth's Moon. Some studies suggest that moons as small as 0.2 Earth masses can be detected in the Kepler data by transit timing variations and transit duration variations of their host planets. If such massive moons exist around giant planets in the stellar habitable zone (HZ), then they could serve as habitats for extraterrestrial life. While earlier studies on exomoon habitability assumed the host planet to be in thermal equilibrium with the absorbed stellar flux, we here extend this concept by including the planetary luminosity from evolutionary shrinking. Our aim is to assess the danger of exomoons to be in a runaway greenhouse state due to extensive heating from the planet. We apply pre-computed evolution tracks for giant planets to calculate the incident planetary radiation on the moon as a function of time. Added to the stellar flux, the total illumination yields constraints on a moon's habitability. Ultimately, we include tidal heating to evaluate a moon's energy budget. We use a semi-analytical formula to parameterize the critical flux for the moon to experience a runaway greenhouse effect. Planetary illumination from a 13-Jupiter-mass planet onto an Earth-sized moon at a distance of ten Jupiter radii can drive a runaway greenhouse state on the moon for about 200 million years (Myr). When stellar illumination equivalent to that received by Earth from the Sun is added, then the runaway greenhouse holds for about 500 Myr. After 1000 Myr, the planet's habitable edge has moved inward to about six Jupiter radii. Exomoons in orbits with eccentricities of 0.1 experience strong tidal heating; they must orbit a 13-Jupiter-mass host beyond 29 or 18 Jupiter radii after 100 Myr (at the inner and outer boundaries of the stellar HZ, respectively), and beyond 13 Jupiter radii (in both cases) after 1000 Myr to be habitable. If a roughly Earth-sized, Earth-mass moon would be detected in orbit around a giant planet, and if the planet-moon duet would orbit in the stellar HZ, then it will be crucial to recover the orbital history of the moon. If, for example, such a moon around a 13-Jupiter-mass planet has been closer than 20 Jupiter radii to its host during the first few hundred million years at least, then it might have lost substantial amounts of its initial water reservoir and be uninhabitable today.

The Kepler Project: Mission Update

NASA Technical Reports Server (NTRS)

Borucki, William J.; Koch, David G.

2009-01-01

Kepler is a Discovery-class mission designed to determine the frequency of Earth-size planets in and near the habitable zone of solar-like stars. The instrument consists of a 0.95 m aperture photometer designed to obtain high precision photometric measurement of > 100,000 stars to search for patterns of transits. The focal plane of the Schmidt-telescope contains 42 CCDs with at total of 95 mega pixels that cover 116 square degrees of sky. The photometer was launched into an Earth-trailing heliocentric orbit on March 6, 2009, finished its commissioning on May 12, and is now in the science operations mode. During the commissioning of the Kepler photometer, data were obtained at a 30 minute cadence for 53,000 stars for 9.7 days. Although the data have not yet been corrected for the presence of systematic errors and artifacts, the data show the presence of hundreds of eclipsing binary stars and variable stars of amazing variety. To provide some estimate of the capability of the photometer, a quick analysis of the photometric precision was made. Analysis of the commissioning data also show transits, occultations and light emitted from the known exoplanet HAT-P7b. The data show a smooth rise and fall of light: from the planet as it orbits its star, punctuated by a drop of 130 +/- 11 ppm in flux when the planet passes behind its star. We interpret this as the phase variation of the dayside thermal emission plus reflected light from the planet as it orbits its star and is occulted. The depth of the occultation is similar in amplitude to that expected from a transiting Earth-size planet and demonstrates that the Mission has the precision necessary to detect such planets.

Validation of Small Kepler Transiting Planet Candidates in or near the Habitable Zone

NASA Astrophysics Data System (ADS)

Torres, Guillermo; Kane, Stephen R.; Rowe, Jason F.; Batalha, Natalie M.; Henze, Christopher E.; Ciardi, David R.; Barclay, Thomas; Borucki, William J.; Buchhave, Lars A.; Crepp, Justin R.; Everett, Mark E.; Horch, Elliott P.; Howard, Andrew W.; Howell, Steve B.; Isaacson, Howard T.; Jenkins, Jon M.; Latham, David W.; Petigura, Erik A.; Quintana, Elisa V.

2017-12-01

A main goal of NASA’s Kepler Mission is to establish the frequency of potentially habitable Earth-size planets ({η }\\oplus ). Relatively few such candidates identified by the mission can be confirmed to be rocky via dynamical measurement of their mass. Here we report an effort to validate 18 of them statistically using the BLENDER technique, by showing that the likelihood they are true planets is far greater than that of a false positive. Our analysis incorporates follow-up observations including high-resolution optical and near-infrared spectroscopy, high-resolution imaging, and information from the analysis of the flux centroids of the Kepler observations themselves. Although many of these candidates have been previously validated by others, the confidence levels reported typically ignore the possibility that the planet may transit a star different from the target along the same line of sight. If that were the case, a planet that appears small enough to be rocky may actually be considerably larger and therefore less interesting from the point of view of habitability. We take this into consideration here and are able to validate 15 of our candidates at a 99.73% (3σ) significance level or higher, and the other three at a slightly lower confidence. We characterize the GKM host stars using available ground-based observations and provide updated parameters for the planets, with sizes between 0.8 and 2.9 R ⊕. Seven of them (KOI-0438.02, 0463.01, 2418.01, 2626.01, 3282.01, 4036.01, and 5856.01) have a better than 50% chance of being smaller than 2 R ⊕ and being in the habitable zone of their host stars.

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

Exoplanet Biosignatures: Observational Prospects

PubMed Central

Angerhausen, Daniel; Deitrick, Russell; Domagal-Goldman, Shawn; Grenfell, John Lee; Hori, Yasunori; Kane, Stephen R.; Pallé, Enric; Rauer, Heike; Siegler, Nicholas; Stapelfeldt, Karl; Stevenson, Kevin B.

2018-01-01

Abstract Exoplanet hunting efforts have revealed the prevalence of exotic worlds with diverse properties, including Earth-sized bodies, which has fueled our endeavor to search for life beyond the Solar System. Accumulating experiences in astrophysical, chemical, and climatological characterization of uninhabitable planets are paving the way to characterization of potentially habitable planets. In this paper, we review our possibilities and limitations in characterizing temperate terrestrial planets with future observational capabilities through the 2030s and beyond, as a basis of a broad range of discussions on how to advance “astrobiology” with exoplanets. We discuss the observability of not only the proposed biosignature candidates themselves but also of more general planetary properties that provide circumstantial evidence, since the evaluation of any biosignature candidate relies on its context. Characterization of temperate Earth-sized planets in the coming years will focus on those around nearby late-type stars. The James Webb Space Telescope (JWST) and later 30-meter-class ground-based telescopes will empower their chemical investigations. Spectroscopic studies of potentially habitable planets around solar-type stars will likely require a designated spacecraft mission for direct imaging, leveraging technologies that are already being developed and tested as part of the Wide Field InfraRed Survey Telescope (WFIRST) mission. Successful initial characterization of a few nearby targets will be an important touchstone toward a more detailed scrutiny and a larger survey that are envisioned beyond 2030. The broad outlook this paper presents may help develop new observational techniques to detect relevant features as well as frameworks to diagnose planets based on the observables. Key Words: Exoplanets—Biosignatures—Characterization—Planetary atmospheres—Planetary surfaces. Astrobiology 18, 739–778. PMID:29938537

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.

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.

Spitzer's window onto the evolution of young planets

NASA Astrophysics Data System (ADS)

Newton, Elisabeth; Mann, Andrew; Rizzuto, Aaron; Vanderburg, Andrew

2018-05-01

Exoplanets in young associations provide an otherwise inaccessible window into how planetary systems form and evolve. We expect to discover 19 young exoplanets around bright stars through our TESS GI programs, which will provide a critical data set for studying planet formation and evolution into the next decade. Here, we propose to obtain transit observations of these young planets with Spitzer. We seek to use Spitzer because it enables us is to obtain precise photometric observations at wavelengths that will also mitigate the impact of stellar activity, which is expected to be high for these young stars. Using data from Spitzer, we will directly address two questions: how do the atmospheres of sub-Neptune sized planets evolve? And what is the mechanism by which planets migrate onto short orbits? We will do this by measuring minimum eccentricities via the photoeccentric effect and by accurately and precisely constraining the planetary properties. We will additionally improve transit ephemerides, ensuring that the transits of these planets are not lost as the community prepares for future observations with JWST, HST, and ground-based facilities. This is a target of opportunity program.

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

Planet formation in binary systems: simulating coagulation using analytically determined collision velocities.

NASA Astrophysics Data System (ADS)

Silsbee, Kedron; Rafikov, Roman

2017-06-01

The existence of planets in tight binary systems presents an interesting puzzle. It is thought that cores of giant planets form via agglomeration of planetesimals in mutual collisions. However, in tight binary systems, one would naïvely expect the collision velocities between planetesimals to be so high that even 100 km bodies would be destroyed, rather than growing in mutual collisions. In these systems, planetesimals are perturbed by gravity from the companion star, and gravity and gas drag from a massive eccentric gas disk. There is a damaging secular resonance that occurs due to the combination of disk gravity and gravity from the binary companion, however the disk gravity can also create locations of low relative eccentricity between planetesimals of different sizes that would not exist if the disk gravity were ignored. Because the gas drag acts more strongly on smaller planetesimals, orbital eccentricity and apsidal angle depend on planetesimal size. Consequently, planetesimal collision velocities depend on the sizes of the collision partners. Same-size bodies collide at low velocity because their orbits are apsidally aligned. Therefore, often in a given environment some collisions will lead to planetesimal growth, and some to erosion or destruction. This variety of collisional outcomes makes it difficult to determine whether any planetesimals can grow to large sizes. We run a multi-annulus coagulation/fragmentation simulation that also includes the effect of size-dependent radial drift of planetesimals to determine the minimum size of initial planetesimal necessary for growth to large sizes in collisions. The minimum initial size of planetesimal necessary for growth depends greatly on the disk mass, eccentricity and the degree of apsidal alignment with the binary. We find that in a wide variety of situations, it is a reasonable approximation that growth occurs as long as there are no collisions capable of completely destroying a planetesimal, but erosion by moderately damaging collisions can also prevent growth from occurring.

Celestial Exoplanet Survey Occulter: A Concept for Direct Imaging of Extrasolar Earth-like Planets from the Ground

NASA Astrophysics Data System (ADS)

Janson, M.

2007-02-01

We present a new concept for detecting and characterizing extrasolar planets down to Earth size or smaller through direct imaging. The New Worlds Observer (NWO) occulter developed by Cash and coworkers is placed in a particular geometrical setup in which fuel requirements are small and the occulter is used in combination with ground-based telescopes, presumably leading to an extreme cost efficiency compared to other concepts with similar science goals. We investigate the various aspects of the given geometry, such as the dynamics and radiation environment of the occulter, and construct a detailed example target list to ensure that an excellent science case can be maintained despite the limited sky coverage. It is found that more than 200 systems can be observed with two to three visits per system, using only a few tons of fuel. For each system, an Earth-sized planet with an Earth-like albedo can be found in the habitable zone in less than 2 hr.

Exo-Transmit: An Open-Source Code for Calculating Transmission Spectra for Exoplanet Atmospheres of Varied Composition

NASA Astrophysics Data System (ADS)

Kempton, Eliza M.-R.; Lupu, Roxana; Owusu-Asare, Albert; Slough, Patrick; Cale, Bryson

2017-04-01

We present Exo-Transmit, a software package to calculate exoplanet transmission spectra for planets of varied composition. The code is designed to generate spectra of planets with a wide range of atmospheric composition, temperature, surface gravity, and size, and is therefore applicable to exoplanets ranging in mass and size from hot Jupiters down to rocky super-Earths. Spectra can be generated with or without clouds or hazes with options to (1) include an optically thick cloud deck at a user-specified atmospheric pressure or (2) to augment the nominal Rayleigh scattering by a user-specified factor. The Exo-Transmit code is written in C and is extremely easy to use. Typically the user will only need to edit parameters in a single user input file in order to run the code for a planet of their choosing. Exo-Transmit is available publicly on Github with open-source licensing at https://github.com/elizakempton/Exo_Transmit.

Clouds and hazes in exoplanets and brown dwarfs

NASA Astrophysics Data System (ADS)

Morley, Caroline Victoria

The formation of clouds significantly alters the spectra of cool substellar atmospheres from terrestrial planets to brown dwarfs. In cool planets like Earth and Jupiter, volatile species like water and ammonia condense to form ice clouds. In hot planets and brown dwarfs, iron and silicates instead condense, forming dusty clouds. Irradiated methane-rich planets may have substantial hydrocarbon hazes. During my dissertation, I have studied the impact of clouds and hazes in a variety of substellar objects. First, I present results for cool brown dwarfs including clouds previously neglected in model atmospheres. Model spectra that include sulfide and salt clouds can match the spectra of T dwarf atmospheres; water ice clouds will alter the spectra of the newest and coldest brown dwarfs, the Y dwarfs. These sulfide/salt and ice clouds potentially drive spectroscopic variability in these cool objects, and this variability should be distinguishable from variability caused by hot spots. Next, I present results for small, cool exoplanets between the size of Earth and Neptune. They likely have sulfide and salt clouds and also have photochemical hazes caused by stellar irradiation. Vast resources have been dedicated to characterizing the handful of super Earths and Neptunes accessible to current telescopes, yet of the planets smaller than Neptune studied to date, all have radii in the near-infrared consistent with being constant in wavelength, likely showing that these small planets are consistently enshrouded in thick hazes and clouds. For the super Earth GJ 1214b, very thick, lofted clouds of salts or sulfides in high metallicity (1000x solar) atmospheres create featureless transmission spectra in the near-infrared. Photochemical hazes also create featureless transmission spectra at lower metallicities. For the Neptune-sized GJ 436b, its thermal emission and transmission spectra combine indicate a high metallicity atmosphere, potentially heated by tides and affected by disequilibrium chemistry. I show that despite the challenges, there are promising avenues for understanding small planets: by observing thermal emission and reflected light, we can break the degeneracies and con- strain the atmospheric compositions. These future observations will provide rich diagnostics of molecules and clouds in small planets.

Planetesimal-driven planet migration in the presence of a gas disk

NASA Astrophysics Data System (ADS)

Capobianco, Christopher C.; Duncan, Martin; Levison, Harold F.

2011-01-01

We report here on an extension of a previous study by Kirsh et al. (Kirsh, D.R., Duncan, M., Brasser, R., Levison, H.F. [2009]. Icarus 199, 197-209) of planetesimal-driven migration using our N-body code SyMBA (Duncan, M.J., Levison, H.F., Lee, M.H. [1998]. Astron. J. 116, 2067-2077). The previous work focused on the case of a single planet of mass Mem, immersed in a planetesimal disk with a power-law surface density distribution and Rayleigh distributed eccentricities and inclinations. Typically 10 4-10 5 equal-mass planetesimals were used, where the gravitational force (and the back-reaction) on each planetesimal by the Sun and planet were included, while planetesimal-planetesimal interactions were neglected. The runs reported on here incorporate the dynamical effects of a gas disk, where the Adachi et al. (Adachi, I., Hayashi, C., Nakazawa, K. [1976]. Prog. Theor. Phys. 56, 1756-1771) prescription of aerodynamic gas drag is implemented for all bodies. In some cases the Papaloizou and Larwood (Papaloizou, J.C.B., Larwood, J.D. [2000]. Mon. Not. R. Astron. Soc. 315, 823-833) prescription of Type-I migration for the planet are implemented, as well as a mass distribution. In the gas-free cases, rapid planet migration was observed - at a rate independent of the planet's mass - provided the planet's mass was not large compared to the mass in planetesimals capable of entering its Hill sphere. In such cases, both inward and outward migrations can be self-sustaining, but there is a strong propensity for inward migration. When a gas disk is present, aerodynamic drag can substantially modify the dynamics of scattered planetesimals. For sufficiently large or small mono-dispersed planetesimals, the planet typically migrates inward. However, for a range of plausible planetesimal sizes (i.e. 0.5-5.0 km at 5.0 AU in a minimum mass Hayashi disk) outward migration is usually triggered, often accompanied by substantial planetary mass accretion. The origins of this behaviour are explained in terms of a toy model. The effects of including a size distribution and torques associated with Type-I migration are also discussed.

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

Zhu Zhaohuan; Dong Ruobing; Nelson, Richard P.

By carrying out two-dimensional two-fluid global simulations, we have studied the response of dust to gap formation by a single planet in the gaseous component of a protoplanetary disk-the so-called dust filtration mechanism. We have found that a gap opened by a giant planet at 20 AU in an {alpha} = 0.01, M-dot =10{sup -8} M{sub Sun} yr{sup -1} disk can effectively stop dust particles larger than 0.1 mm drifting inward, leaving a submillimeter (submm) dust cavity/hole. However, smaller particles are difficult to filter by a gap induced by a several M{sub J} planet due to (1) dust diffusion andmore » (2) a high gas accretion velocity at the gap edge. Based on these simulations, an analytic model is derived to understand what size particles can be filtered by the planet-induced gap edge. We show that a dimensionless parameter T{sub s} /{alpha}, which is the ratio between the dimensionless dust stopping time and the disk viscosity parameter, is important for the dust filtration process. Finally, with our updated understanding of dust filtration, we have computed Monte Carlo radiative transfer models with variable dust size distributions to generate the spectral energy distributions of disks with gaps. By comparing with transitional disk observations (e.g., GM Aur), we have found that dust filtration alone has difficulties depleting small particles sufficiently to explain the near-IR deficit of moderate M-dot transitional disks, except under some extreme circumstances. The scenario of gap opening by multiple planets studied previously suffers the same difficulty. One possible solution is to invoke both dust filtration and dust growth in the inner disk. In this scenario, a planet-induced gap filters large dust particles in the disk, and the remaining small dust particles passing to the inner disk can grow efficiently without replenishment from fragmentation of large grains. Predictions for ALMA have also been made based on all these scenarios. We conclude that dust filtration with planet(s) in the disk is a promising mechanism to explain submm observations of transitional disks but it may need to be combined with other processes (e.g., dust growth) to explain the near-IR deficit of some systems.« less

Selections from 2017: Atmosphere Around an Earth-Like Planet

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-12-01

Editors note:In these last two weeks of 2017, well be looking at a few selections that we havent yet discussed on AAS Nova from among the most-downloaded paperspublished in AAS journals this year. The usual posting schedule will resume in January.Detection of the Atmosphere of the 1.6 M Exoplanet GJ 1132 bPublished March2017Main takeaway:An atmosphere was detected around the roughly Earth-size exoplanet GJ 1132 b using a telescope at the European Southern Observatory in Chile. A team of scientists led byJohn Southworth (Keele University) found features indicating the presence of an atmosphere in theobservationsof this 1.6-Earth-mass planet as it transits an M-dwarf host star. This is the lowest-mass planet with a detected atmosphere thus far.Why its interesting:M dwarfs are among the most common stars in our galaxy, and weve found manyEarth-sizeexoplanets in or near the habitable zones around M-dwarf hosts. But M dwarfs are also more magnetically active than stars like our Sun, suggesting that the planets in M-dwarfhabitable zones may not be able to support life due to stellar activity eroding their atmospheres. The detection of an atmosphere around GJ 1132 b suggests that some planets orbiting M dwarfsare able to retain their atmospheres which meansthat these planetsmay be an interesting place to search for life after all.How the atmosphere was detected:The measured planetary radius for GJ 1132 b as a function of the wavelength used to observe it. [Southworth et al. 2017]When measuring the radius of GJ 1132 b based on its transits, the authors noticed that the planet appeared to be largerwhen observed in some wavelengths than in others. This can beexplained if the planet has asurface radius of 1.4 Earth radii, overlaid by an atmosphere that extends out another few tenths of an Earth radius. The atmosphere, which may consist of water vapor or methane, is transparent to some wavelengths and absorbs others which is why the apparent size of the planet changes acrosswavelength bands.CitationJohn Southworth et al 2017 AJ 153 191. doi:10.3847/1538-3881/aa6477

Dust coagulation and magnetic field strength in a planet-induced gap subject to MRI turbulence

NASA Astrophysics Data System (ADS)

Carballido, Augusto; Matthews, Lorin; Hyde, Truell

2017-01-01

We investigate the coagulation of dust particles in and around a gap opened by a Jupiter-mass planet. To this end, we carry out a high-resolution magnetohydrodynamic (MHD) simulation of the gap environment, which is turbulent due to the magneto rotational instability. From the MHD simulation, we obtain values of the gas velocities, densities and turbulent stresses close to the gap edge, in one of the two gas streams that accrete onto the planet, and inside the low-density gap. The MHD values are then supplied to a Monte Carlo dust coagulation algorithm, which models grain sticking, compaction and bouncing. We consider two dust populations for each region: one whose initial size distribution is monodisperse, with monomer radius equal to 1 micron, and another one whose initial size distribution follows the Mathis-Rumpl-Nordsieck distribution for interstellar dust grains, with an initial range of monomer radii between 0.5 and 10 microns. Without bouncing, our Monte Carlo calculations show steady growth of dust aggregates in all regions, and the mass-weighted (MW) average porosity of the initially mono disperse population reaches extremely high final values of 98%. The final MW porosities in all other cases without bouncing range from 30% to 82%. The efficiency of compaction is due to high turbulent relative speeds between dust particles. When bouncing is introduced, growth is slowed down in the planetary wake and inside the gap.We also analyze the strength of the magnetic field threading the gaps opened by planets of different sub-Jovian masses. Preliminary results show that, in a gap opened by a large-mass planet (~ 1 MJ), the time-averaged radial profile of the vertical component of the field (Bz) increases sharply inside the gap, and less sharply in the case of less massive planets. In gaps opened by intermediate-mass planets (~ 0.5 — 0.75 MJ), the radial profile of Bz exhibits local maxima in the vicinity of the planet, but not at the gap center.

Super-Earth and Sub-Neptune Exoplanets: a First Look from the MEarth Project

NASA Astrophysics Data System (ADS)

Berta, Zachory K.

Exoplanets that transit nearby M dwarfs allow us to measure the sizes, masses, and atmospheric properties of distant worlds. Between 2008 and 2013, we searched for such planets with the MEarth Project, a photometric survey of the closest and smallest main-sequence stars. This thesis uses the first planet discovered with MEarth, the warm 2.7 Earth radius exoplanet GJ1214b, to explore the possibilities that planets transiting M dwarfs provide. First, we perform a broad reconnaissance of the GJ1214b planetary system to refine the system's physical properties. We fit many transits to improve the planetary parameters, use starspots to measure GJ1214's rotation period (>50 days), and search for additional transiting planets, placing strong limits on habitable-zone Neptune-sized exoplanets in the system. We present Hubble Space Telescope observations of GJ1214b's atmosphere. We find the transmission spectrum to be flat between 1.1 and 1.7 microns, ruling out at 8 sigma the presence of a clear hydrogen-rich envelope that had been proposed to explain GJ1214b's large radius. Additional observations will determine whether the absence of deep absorption features in GJ1214b's transmission spectrum is due to the masking influence of high altitude clouds or to the presence of a compact, hydrogen-poor atmosphere. We describe a new algorithm to find transiting planets in light curves plagued by stellar variability and systematic noise sources. This Method to Include Starspots and Systematics in the Marginalized Probability of a Lone Eclipse (MISS MarPLE) reliably assesses the significance of individual transit events, a necessary requirement for detecting habitable zone planets from the ground with MEarth. We compare MEarth's achieved sensitivity to planet occurrence statistics from the NASA Kepler Mission, and find that MEarth's single discovery of GJ1214b is consistent with expectations. We find that warm Neptunes are rare around mid-to-late M dwarfs (<0.15 planets/star). Capitalizing on knowledge from Kepler, we propose a new strategy to boost MEarth's sensitivity to smaller and cooler exoplanets, and increase the expected yield of the survey by 2.5x.

RAYLEIGH SCATTERING IN THE ATMOSPHERE OF THE WARM EXO-NEPTUNE GJ 3470B

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

Dragomir, Diana; Benneke, Björn; Pearson, Kyle A.

2015-12-01

GJ 3470b is a warm Neptune-size planet transiting an M dwarf star. Like the handful of other small exoplanets for which transmission spectroscopy has been obtained, GJ 3470b exhibits a flat spectrum in the near- and mid-infrared. Recently, a tentative detection of Rayleigh scattering in its atmosphere has been reported. This signal manifests itself as an observed increase of the planetary radius as a function of decreasing wavelength in the visible. We set out to verify this detection and observed several transits of this planet with the LCOGT network and the Kuiper telescope in four different bands (Sloan g, Sloanmore » i, Harris B, and Harris V). Our analysis reveals a strong Rayleigh scattering slope, thus confirming previous results. This makes GJ 3470b the smallest known exoplanet with a detection of Rayleigh scattering. We find that the most plausible scenario is a hydrogen/helium-dominated atmosphere covered by clouds which obscure absorption features in the infrared and hazes which give rise to scattering in the visible. Our results demonstrate the feasibility of exoplanet atmospheric characterization from the ground, even with meter-class telescopes.« less

Effects of Water Amount on the Surface Environment of Terrestrial Planets: High Pressure Ice and Carbon Cycle

NASA Astrophysics Data System (ADS)

Nakayama, Akifumi; Abe, Yutaka

2015-12-01

Terrestrial planets with several wt% of H2O in extrasolar planetary systems are theoretically predicted in the habitable zone [Raymond et al., 2004]. Such planets are expected to be covered by an ocean entirely (called as “ocean planets”). Amount of atmospheric CO2 (PCO2) is important for surface environment because CO2 is a strong greenhouse gas. PCO2 is determined by a race between degassing and sink through weathering on carbon cycle. On an ocean planet, seafloor weathering is important because continental weathering can’t work [Abbot et al., 2012]. In addition, ocean planets with large water amount may have high-pressure (HP) ice on the seafloor [Leger et al., 2004]. Since the ocean floor is covered by ice in such case, it has been thought that any weathering processes will not work and PCO2 will be extremely high. When plate tectonics works, heat flow from oceanic crust decreases with distance from the mid ocean ridge. Therefore, HP ice near the mid ocean ridge will be kept solid-liquid coexistent state at the melting point because of high heat flow. Seafloor weathering works in this region. The seafloor weathering under this condition efficiently works because weathering temperature is kept melting point regardless of surface temperature. Thus, our aim is to clarify the relationship between water amount and surface environment focusing seafloor environment. We develop a carbon cycle model considering the seafloor weathering. Our major assumptions are following; 1) Earth-sized ocean planets with various water amount, 2) Degassing rate is depended on the total amount of carbon and total carbon inventory is proportional to the surface water amount. We investigated thermal state of HP ice and determined effective weathering region where HP ice is coexistent with water, then we investigated the PCO2 in equilibrium state where degassing and regassing are balanced. As a result, forming of HP ice may cause snowball state due to high weathering rate. When solar incident flux and heat flow from mantle are the present Earth’s value and a ratio of CO2 / H2O inventory is carbonaceous chondrite composition, a planet with large ocean which is larger than 90 Earth’s ocean mass lapses into snowball state. It was previously believed that forming of HP ice supports warm climate; rather, forming of HP ice could cause snowball state.

Searching for Life: Early Earth, Mars and Beyond

NASA Technical Reports Server (NTRS)

DesMarais, David J.; Chang, Sherwood (Technical Monitor)

1996-01-01

We might be entering a golden age for exploring life throughout time and space. Rapid gene sequencing will better define our most distant ancestors. The earliest geologic evidence of life is now 3.8 billion years old. Organic matter and submicron-sized morphologies have been preserved in the martian crust for billions of years. Several new missions to Mars are planned, with a high priority on the search for life, past or present. The recent discovery of large extrasolar planets has heightened interest in spacecraft to detect small, earth-like planets. A recent workshop discussed strategies for life detection on such planets. There is much to anticipate in the near future.

Planetary plasma waves

NASA Technical Reports Server (NTRS)

Gurnett, Donald A.

1993-01-01

The primary types of plasma waves observed in the vicinity of the planets Venus, Mars, Earth, Jupiter, Saturn, Uranus, and Neptune are described. The observations are organized according to the various types of plasma waves observed, ordered according to decreasing distance from the planet, starting from the sunward side of the planet, and ending in the region near the closest approach. The plasma waves observed include: electron plasma oscillations and ion acoustic waves; trapped continuum radiation; electron cyclotron and upper hybrid waves; whistler-mode emissions; electrostatic ion cyclotron waves; and electromagnetic ion cyclotron waves.

Kepler's Final Survey Catalog

NASA Astrophysics Data System (ADS)

Mullally, S. E.

2017-12-01

The Kepler mission was designed to detect transiting exoplanets and has succeeded in finding over 4000 candidates. These candidates include approximately 50 terrestrial-sized worlds near to the habitable zone of their GKM dwarf stars (shown in figure against the stellar temperature). However not all transit detections are created equal. False positives, such as background eclipsing binaries, can mimic the signal of a transiting planet. Additionally, at Kepler's detection limit noise, either from the star or from the detector, can create signals that also mimic a transiting planet. For the data release 25 Kepler catalog we simulated these false alarms and determined how often known false alarms are called candidates. When this reliability information is combined with our studies of catalog completeness, this catalog can be used to understand the occurrence rate of exoplanets, even for the small, temperate planet candidates found by Kepler. I will discuss the automated methods we used to create and characterize this latest catalog, highlighting how we balanced the completeness and reliability of the long period candidates. While Kepler has been very successful at detecting transiting terrestrial-sized exoplanets, many of these detections are around stars that are too dim for successful follow-up work. Future missions will pick up where Kepler left off and find small planets around some of the brightest and smallest stars.

Transiting Exoplanet Survey Satellite (TESS)

NASA Technical Reports Server (NTRS)

Ricker, G. R.; Clampin, M.; Latham, D. W.; Seager, S.; Vanderspek, R. K.; Villasenor, J. S.; Winn, J. N.

2012-01-01

The Transiting Exoplanet Survey Satellite (TESS) will discover thousands of exoplanets in orbit around the brightest stars in the sky. In a two-year survey, TESS will monitor more than 500,000 stars for temporary drops in brightness caused by planetary transits. This first-ever spaceborne all-sky transit survey will identify planets ranging from Earth-sized to gas giants, around a wide range of stellar types and orbital distances. No ground-based survey can achieve this feat. A large fraction of TESS target stars will be 30-100 times brighter than those observed by Kepler satellite, and therefore TESS . planets will be far easier to characterize with follow-up observations. TESS will make it possible to study the masses, sizes, densities, orbits, and atmospheres of a large cohort of small planets, including a sample of rocky worlds in the habitable zones of their host stars. TESS will provide prime targets for observation with the James Webb Space Telescope (JWST), as well as other large ground-based and space-based telescopes of the future. TESS data will be released with minimal delay (no proprietary period), inviting immediate community-wide efforts to study the new planets. The TESS legacy will be a catalog of the very nearest and brightest main-sequence stars hosting transiting exoplanets, thus providing future observers with the most favorable targets for detailed investigations.

Kepler Planet Detection Mission: Introduction and First Results

NASA Technical Reports Server (NTRS)

Borucki, William; Koch, David; Basri, Gibor; Batalha, Natalie; Brown, Timothy; Lissauer, Jack J.; Morrison, David; Rowe, Jason; Bryson, Stephen T.; Dotson, Jessie;

The California- Kepler Survey. II. Precise Physical Properties of 2025 Kepler Planets and Their Host Stars

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

Johnson, John Asher; Cargile, Phillip A.; Sinukoff, Evan

We present stellar and planetary properties for 1305 Kepler Objects of Interest hosting 2025 planet candidates observed as part of the California- Kepler Survey. We combine spectroscopic constraints, presented in Paper I, with stellar interior modeling to estimate stellar masses, radii, and ages. Stellar radii are typically constrained to 11%, compared to 40% when only photometric constraints are used. Stellar masses are constrained to 4%, and ages are constrained to 30%. We verify the integrity of the stellar parameters through comparisons with asteroseismic studies and Gaia parallaxes. We also recompute planetary radii for 2025 planet candidates. Because knowledge of planetarymore » radii is often limited by uncertainties in stellar size, we improve the uncertainties in planet radii from typically 42% to 12%. We also leverage improved knowledge of stellar effective temperature to recompute incident stellar fluxes for the planets, now precise to 21%, compared to a factor of two when derived from photometry.« less

An opening criterion for dust gaps in protoplanetary discs

NASA Astrophysics Data System (ADS)

Dipierro, Giovanni; Laibe, Guillaume

2017-08-01

We aim to understand under which conditions a low-mass planet can open a gap in viscous dusty protoplanetary discs. For this purpose, we extend the theory of dust radial drift to include the contribution from the tides of an embedded planet and from the gas viscous forces. From this formalism, we derive (I) a grain-size-dependent criterion for dust gap opening in discs, (II) an estimate of the location of the outer edge of the dust gap and (III) an estimate of the minimum Stokes number above which low-mass planets are able to carve gaps that appear only in the dust disc. These analytical estimates are particularly helpful to appraise the minimum mass of a hypothetical planet carving gaps in discs observed at long wavelengths and high resolution. We validate the theory against 3D smoothed particle hydrodynamics simulations of planet-disc interaction in a broad range of dusty protoplanetary discs. We find a remarkable agreement between the theoretical model and the numerical experiments.

On the ability of synchronously rotating planets to support atmospheres

NASA Astrophysics Data System (ADS)

Joshi, Manoj M.; Haberle, Robert M.

1997-01-01

Planets within the habitable zones of M stars are likely to be synchronous rotators, i.e., one side is permanently illuminated while the other side is in perpetual darkness. For such planets to be habitable, horizontal atmospheric motions must be capable of transporting enough heat from the day side to the night side to prevent the atmosphere from freezing out. Simple calculations have shown that the equivalent of approximately 150 mb of CO2 is required to prevent atmospheric condensation on the dark side. We now use a 3D global circulation model in order to better assess the ability of these planets to sustain an atmosphere. The results of this work show that for an Earth-sized planet, 100 mb of CO2 is required to support an atmosphere, while 1-2 bars are sufficient to allow liquid water everywhere. Planetary systems associated with M stars should therefore not be ruled out in the search for life in the universe.

Spectroscopy of Kepler Exo-planet Transit Candidate Stars

NASA Astrophysics Data System (ADS)

Howell, Steve B.; Everett, Mark; Silva, David; Rowe, Jason; Szkody, Paula; Mighell, Ken; Ciardi, David

2012-02-01

We propose a long term spectroscopic follow-up program in support of the NASA Kepler exo-planet mission. The Kepler project is now focusing on exo-planet candidates which are smaller in radius (down to Earth- size), have longer period orbits and many of which orbit fainter stars. Our program will spend 85% of the time on our primary goal, spectroscopy of the host stars of exoplanet candidates, and 15% of the time on investigation of other astrophysically interesting stars discovered by Kepler. Our prime goal is to obtain reconnaissance spectra of newly discovered exo-planet stars yielding model fits to T_eff and log g. Secondary goals are to obtain velocity information on EBs with a third component aimed toward discovery of circumbinary planets (such as Kepler 16b) and identification spectra of U-band selected targets in order to find more white dwarfs for Kepler focal plane calibration purposes. All of these tasks can be accomplished using the Kitt Peak 4-m telescope and RCspec as shown by our previous time allocations.

Superflares and Giant Planets

NASA Astrophysics Data System (ADS)

Rubenstein, Eric P.

2001-02-01

Nine solar analogues, stars similar in size and composition to the Sun, are known to have produced enormous flares. These outbursts, which were from 100 to 10 million times the size of even the largest solar flares, have puzzled astronomers, because sunlike stars should in theory vary little in brightness. A likely explanation is that these stars have unseen planetary companions circling in close orbits. Giant planets with large magnetic fields would, over time, entangle the magnetic fields of the parent stars. Eventually, the stretched and twisted magnetic-field lines would break and reattach themselves in a less complicated arrangement. This process, called magnetic reconnection, neatly explains how vast amounts of energy can be released so suddenly from superflaring solar analogues.

Biases in Planet Occurrence Caused by Unresolved Binaries in Transit Surveys

NASA Astrophysics Data System (ADS)

Bouma, L. G.; Masuda, Kento; Winn, Joshua N.

2018-06-01

Wide-field surveys for transiting planets, such as the NASA Kepler and TESS missions, are usually conducted without knowing which stars have binary companions. Unresolved and unrecognized binaries give rise to systematic errors in planet occurrence rates, including misclassified planets and mistakes in completeness corrections. The individual errors can have different signs, making it difficult to anticipate the net effect on inferred occurrence rates. Here, we use simplified models of signal-to-noise limited transit surveys to try and clarify the situation. We derive a formula for the apparent occurrence rate density measured by an observer who falsely assumes all stars are single. The formula depends on the binary fraction, the mass function of the secondary stars, and the true occurrence of planets around primaries, secondaries, and single stars. It also takes into account the Malmquist bias by which binaries are over-represented in flux-limited samples. Application of the formula to an idealized Kepler-like survey shows that for planets larger than 2 R ⊕, the net systematic error is of order 5%. In particular, unrecognized binaries are unlikely to be the reason for the apparent discrepancies between hot-Jupiter occurrence rates measured in different surveys. For smaller planets the errors are potentially larger: the occurrence of Earth-sized planets could be overestimated by as much as 50%. We also show that whenever high-resolution imaging reveals a transit host star to be a binary, the planet is usually more likely to orbit the primary star than the secondary star.

Constraints on the Obliquities of Kepler Planet-hosting Stars

NASA Astrophysics Data System (ADS)

Winn, Joshua N.; Petigura, Erik A.; Morton, Timothy D.; Weiss, Lauren M.; Dai, Fei; Schlaufman, Kevin C.; Howard, Andrew W.; Isaacson, Howard; Marcy, Geoffrey W.; Justesen, Anders Bo; Albrecht, Simon

2017-12-01

Stars with hot Jupiters have obliquities ranging from 0° to 180°, but relatively little is known about the obliquities of stars with smaller planets. Using data from the California-Kepler Survey, we investigate the obliquities of stars with planets spanning a wide range of sizes, most of which are smaller than Neptune. First, we identify 156 planet hosts for which measurements of the projected rotation velocity (v\\sin i) and rotation period are both available. By combining estimates of v and v\\sin i, we find nearly all the stars to be compatible with high inclination, and hence, low obliquity (≲20°). Second, we focus on a sample of 159 hot stars ({T}{eff}> 6000 K) for which v\\sin i is available but not necessarily the rotation period. We find six stars for which v\\sin i is anomalously low, an indicator of high obliquity. Half of these have hot Jupiters, even though only 3% of the stars that were searched have hot Jupiters. We also compare the v\\sin i distribution of the hot stars with planets to that of 83 control stars selected without prior knowledge of planets. The mean v\\sin i of the control stars is lower than that of the planet hosts by a factor of approximately π /4, as one would expect if the planet hosts have low obliquities. All these findings suggest that the Kepler planet-hosting stars generally have low obliquities, with the exception of hot stars with hot Jupiters.

Dependence of the Onset of the Runaway Greenhouse Effect on the Latitudinal Surface Water Distribution of Earth-Like Planets

NASA Astrophysics Data System (ADS)

Kodama, T.; Nitta, A.; Genda, H.; Takao, Y.; O'ishi, R.; Abe-Ouchi, A.; Abe, Y.

2018-02-01

Liquid water is one of the most important materials affecting the climate and habitability of a terrestrial planet. Liquid water vaporizes entirely when planets receive insolation above a certain critical value, which is called the runaway greenhouse threshold. This threshold forms the inner most limit of the habitable zone. Here we investigate the effects of the distribution of surface water on the runaway greenhouse threshold for Earth-sized planets using a three-dimensional dynamic atmosphere model. We considered a 1 bar atmosphere whose composition is similar to the current Earth's atmosphere with a zonally uniform distribution of surface water. As previous studies have already showed, we also recognized two climate regimes: the land planet regime, which has dry low-latitude and wet high-latitude regions, and the aqua planet regime, which is globally wet. We showed that each regime is controlled by the width of the Hadley circulation, the amount of surface water, and the planetary topography. We found that the runaway greenhouse threshold varies continuously with the surface water distribution from about 130% (an aqua planet) to 180% (the extreme case of a land planet) of the present insolation at Earth's orbit. Our results indicate that the inner edge of the habitable zone is not a single sharp boundary, but a border whose location varies depending on planetary surface condition, such as the amount of surface water. Since land planets have wider habitable zones and less cloud cover, land planets would be good targets for future observations investigating planetary habitability.

The magnetic field inside a protoplanetary disc gap opened by planets of different masses

NASA Astrophysics Data System (ADS)

Carballido, Augusto; Matthews, Lorin S.; Hyde, Truell W.

2017-12-01

We perform magnetohydrodynamic simulations of protoplanetary disc gaps opened by planets of various masses, with the aim of calculating the strength of the vertical magnetic field threading such gaps. We introduce a gravitational potential at the centre of a shearing box to compute the tidal interaction between the planets and the disc gas, which is turbulent due to the magnetorotational instability. Two types of simulations are executed: 1) In type 'Z', the initial magnetic field has only a uniform, vertical component, and ten planet masses between 0.66 and 6.64 thermal masses are used; 2) In type 'YZ', the initial magnetic field has both toroidal and vertical components, and five planet masses covering the same mass range are used. Our results show that, for low planet masses, higher values of the vertical magnetic field occur inside the gaps than outside, in agreement with the previous work. However, for massive planets, we find that the radial profiles of the field show dips near the gap centre. The interior of the Hill sphere of the most massive planet in the Z runs contains more low-plasma β values (i.e. high magnetic pressure) compared to lower-mass planets. Values of β at a distance of one Hill radius from each planet show a moderate decrease with planet mass. These results are relevant for the magnetic structure of circumplanetary discs and their possible outflows, and may be refined to aid future observational efforts to infer planet masses from high-resolution polarimetric observations of discs with gaps.

Internal constitution of Mars.

NASA Technical Reports Server (NTRS)

Anderson, D. L.

1972-01-01

Models of the internal structure of Mars consistent with the mass, radius and moment of inertia of the planet are constructed. The models assume that the radius of the core is between 0.36 and 0.60 of the radius of the planet, that the zero-pressure density of the mantle is between 3.54 and 3.49 g/cu cm, and that the planet contains 25 to 28% iron. Meteorite models of Mars containing 25 wt % iron and 12 wt % core are also proposed. It is maintained that Mars in contrast to the earth is an incompletely differentiated planet with a core substantially richer in sulfur than the core of the earth. The absence of a magnetic field on Mars is possibly linked with lack of lunar precessional torque and the small size and high resistivity of the Martian core.

Comparing TRAPPIST-1 to the Solar System

NASA Image and Video Library

2018-02-05

This graph presents known properties of the seven TRAPPIST-1 exoplanets (labeled b through h), showing how they stack up to the inner rocky worlds in our own solar system. The horizontal axis shows the level of illumination that each planet receives from its host star. TRAPPIST-1 is a mere 9 percent the mass of our Sun, and its temperature is much cooler. But because the TRAPPIST-1 planets orbit so closely to their star, they receive comparable levels of light and heat to Earth and its neighboring planets. The vertical axis shows the densities of the planets. Density, calculated based on a planet's mass and volume, is the first important step in understanding a planet's composition. The plot shows that the TRAPPIST-1 planet densities range from being similar to Earth and Venus at the upper end, down to values comparable to Mars at the lower end. The relative sizes of the planets are indicated by the circles. The masses and densities of the TRAPPIST-1 planets were determined by careful measurements of slight variations in the timings of their orbits using extensive observations made by NASA's Spitzer and Kepler space telescopes, in combination with data from Hubble and a number of ground-based telescopes. These measurements are the most precise to date for any system of exoplanets. By comparing these measurements with theoretical models of how planets form and evolve, researchers have determined that they are all rocky in overall composition. Estimates suggest the lower-density planets could have large quantities of water -- as much as 5 percent by mass for TRAPPIST-1d. Earth, in comparison, has only about 0.02 percent of its mass in the form of water. https://photojournal.jpl.nasa.gov/catalog/PIA22095

Rocky Worlds Limited to ∼1.8 Earth Radii by Atmospheric Escape during a Star’s Extreme UV Saturation

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

Lehmer, Owen R.; Catling, David C., E-mail: info@lehmer.us

Recent observations and analysis of low-mass (<10 M {sub ⊕}) exoplanets have found that rocky planets only have radii up to 1.5–2 R {sub ⊕}. Two general hypotheses exist for the cause of the dichotomy between rocky and gas-enveloped planets (or possible water worlds): either low-mass planets do not necessarily form thick atmospheres of a few wt.%, or the thick atmospheres on these planets easily escape, driven by X-ray and extreme ultraviolet (XUV) emissions from young parent stars. Here, we show that a cutoff between rocky and gas-enveloped planets due to hydrodynamic escape is most likely to occur at amore » mean radius of 1.76 ± 0.38 (2 σ ) R {sub ⊕} around Sun-like stars. We examine the limit in rocky planet radii predicted by hydrodynamic escape across a wide range of possible model inputs, using 10,000 parameter combinations drawn randomly from plausible parameter ranges. We find a cutoff between rocky and gas-enveloped planets that agrees with the observed cutoff. The large cross-section available for XUV absorption in the extremely distended primitive atmospheres of low-mass planets results in complete loss of atmospheres during the ∼100 Myr phase of stellar XUV saturation. In contrast, more-massive planets have less-distended atmospheres and less escape, and so retain thick atmospheres through XUV saturation—and then indefinitely as the XUV and escape fluxes drop over time. The agreement between our model and exoplanet data leads us to conclude that hydrodynamic escape plausibly explains the observed upper limit on rocky planet size and few planets (a “valley”, or “radius gap”) in the 1.5–2 R {sub ⊕} range.« less

K2-155: A Bright Metal-poor M Dwarf with Three Transiting Super-Earths

NASA Astrophysics Data System (ADS)

Hirano, Teruyuki; Dai, Fei; Livingston, John H.; Fujii, Yuka; Cochran, William D.; Endl, Michael; Gandolfi, Davide; Redfield, Seth; Winn, Joshua N.; Guenther, Eike W.; Prieto-Arranz, Jorge; Albrecht, Simon; Barragan, Oscar; Cabrera, Juan; Cauley, P. Wilson; Csizmadia, Szilard; Deeg, Hans; Eigmüller, Philipp; Erikson, Anders; Fridlund, Malcolm; Fukui, Akihiko; Grziwa, Sascha; Hatzes, Artie P.; Korth, Judith; Narita, Norio; Nespral, David; Niraula, Prajwal; Nowak, Grzegorz; Pätzold, Martin; Palle, Enric; Persson, Carina M.; Rauer, Heike; Ribas, Ignasi; Smith, Alexis M. S.; Van Eylen, Vincent

2018-03-01

We report on the discovery of three transiting super-Earths around K2-155 (EPIC 210897587), a relatively bright early M dwarf (V = 12.81 mag) observed during Campaign 13 of the NASA K2 mission. To characterize the system and validate the planet candidates, we conducted speckle imaging and high-dispersion optical spectroscopy, including radial velocity measurements. Based on the K2 light curve and the spectroscopic characterization of the host star, the planet sizes and orbital periods are {1.55}-0.17+0.20 {R}\\oplus and 6.34365 ± 0.00028 days for the inner planet; {1.95}-0.22+0.27 {R}\\oplus and 13.85402 ± 0.00088 days for the middle planet; and {1.64}-0.17+0.18 {R}\\oplus and 40.6835 ± 0.0031 days for the outer planet. The outer planet (K2-155d) is near the habitable zone, with an insolation 1.67 ± 0.38 times that of the Earth. The planet’s radius falls within the range between that of smaller rocky planets and larger gas-rich planets. To assess the habitability of this planet, we present a series of three-dimensional global climate simulations, assuming that K2-155d is tidally locked and has an Earth-like composition and atmosphere. We find that the planet can maintain a moderate surface temperature if the insolation proves to be smaller than ∼1.5 times that of the Earth. Doppler mass measurements, transit spectroscopy, and other follow-up observations should be rewarding, as K2-155 is one of the optically brightest M dwarfs known to harbor transiting planets.

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.

The Water Content of Exo-earths in the Habitable Zone around Low-mass Stars

NASA Astrophysics Data System (ADS)

Mulders, Gijs Dirk; Ciesla, Fred; Pascucci, Ilaria; apai, Daniel

2015-08-01

Terrestrial planets in the habitable zones of low-mass M dwarf stars have become the focus of many astronomical studies: they are more easily accessible to detection and characterization than their counterparts around sunlike stars. The habitability of these planets, however, faces a number of challenges, including inefficient or negligible water delivery during accretion. To understand the water content of planets in and around the habitable zone, simulations of the final stages of planet formation are necessary.We present detailed accretion simulations of wet and dry planetary embryos around a range of stellar masses. We focus on different pathways of delivering water from beyond the snow line to terrestrial planets in the habitable zone. We explore the impact of using either asteroid-like or comet-like bodies, and the effects of a dispersion in snow line locations. We derive the probability distribution of water abundances for terrestrial sized planets in the habitable zone.While these models predict that the bulk of terrestrial planets in the habitable zones of M stars will be dry, a small fraction receives earth-like amounts of water. Given their larger numbers and higher planet occurrence rates, this population of water-enriched worlds in the habitable zone of M stars may equal that around sun-like stars in numbers.References:Ciesla, Mulders et al. 2015Mulders et al. ApJ subm.

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

Heller, René; Zuluaga, Jorge I., E-mail: rheller@physics.mcmaster.ca, E-mail: jzuluaga@fisica.udea.edu.co

With most planets and planetary candidates detected in the stellar habitable zone (HZ) being super-Earths and gas giants rather than Earth-like planets, we naturally wonder if their moons could be habitable. The first detection of such an exomoon has now become feasible, and due to observational biases it will be at least twice as massive as Mars. However, formation models predict that moons can hardly be as massive as Earth. Hence, a giant planet's magnetosphere could be the only possibility for such a moon to be shielded from cosmic and stellar high-energy radiation. Yet, the planetary radiation belt could alsomore » have detrimental effects on exomoon habitability. Here we synthesize models for the evolution of the magnetic environment of giant planets with thresholds from the runaway greenhouse (RG) effect to assess the habitability of exomoons. For modest eccentricities, we find that satellites around Neptune-sized planets in the center of the HZ around K dwarf stars will either be in an RG state and not be habitable, or they will be in wide orbits where they will not be affected by the planetary magnetosphere. Saturn-like planets have stronger fields, and Jupiter-like planets could coat close-in habitable moons soon after formation. Moons at distances between about 5 and 20 planetary radii from a giant planet can be habitable from an illumination and tidal heating point of view, but still the planetary magnetosphere would critically influence their habitability.« less

Kepler Mission to Detect Earth-like Planets

NASA Technical Reports Server (NTRS)

Kondo, Yoji

2003-01-01

Kepler Mission to detect Earth-like planets in our Milky Way galaxy was approved by NASA in December 2001 for a 4-5 year mission. The launch is planned in about 5 years. The Kepler observatory will be placed in an Earth-trailing orbit. The unique feature of the Kepler Mission is its ability to detect Earth-like planets orbiting around solar-type stars at a distance similar to that of Earth (from our Sun); such an orbit could provide an environment suitable for supporting life as we know it. The Kepler observatory accomplishes this feat by looking for the transits of planetary object in front of their suns; Kepler has a photometric precision of 10E-5 (0.00001) to achieve such detections. Other ongoing planetary detection programs (based mostly on a technique that looks for the shifting of spectral lines of the primary star due to its planetary companions' motions around it) have detected massive planets (with masses in the range of Jupiter); such massive planets are not considered suitable for supporting life. If our current theories for the formation of planetary systems are valid, we expect to detect about 50 Earth-like planets during Kepler's 4-year mission (assuming a random distribution of the planetary orbital inclinations with respect to the line of sight from Kepler). The number of detection will increase about 640 planets if the planets to be detected are Jupiter-sized.

Kepler Mission to Detect Earth-like Planets

NASA Technical Reports Server (NTRS)

Kondo, Yoji

2002-01-01

Kepler Mission to detect Earth-like planets in our Milky Way galaxy was approved by NASA in December 2001 for a 4-5 year mission. The launch is planned in about 5 years. The Kepler observatory will be placed in an Earth-trailing orbit. The unique feature of the Kepler Mission is its ability to detect Earth-like planets orbiting around solar-type stars at a distance similar to that of Earth (from our Sun); such an orbit could provide an environment suitable for supporting life as we know it. The Kepler observatory accomplishes this feat by looking for the transits of planetary object in front of their suns; Kepler has a photometric precision of 10E-5 (0.00001) to achieve such detections. Other ongoing planetary detection programs (based mostly on a technique that looks for the shifting of spectral lines of the primary star due to its planetary companions' motions around it) have detected massive planets (with masses in the range of Jupiter); such massive planets are not considered suitable for supporting life. If our current theories for the formation of planetary systems are valid, we expect to detect about 50 Earth-like planets during Kepler's 4-year mission (assuming a random distribution of the planetary orbital inclinations with respect to the line of sight from Kepler). The number of detection will increase about 640 planets if the planets to be detected are Jupiter-sized.

A Study on the Characteristics of the Structure of Vega's Debris Disk

NASA Astrophysics Data System (ADS)

Lu, Tao; Ji, Jiang-hui

2013-10-01

The clumpy structure in the Vega's debris disk was reported at millimeter wavelengths previously, and attributed to the concentration of dust grains trapped in resonances with a potential high-eccentricity planet. However, current imaging at multi-wavelengths with higher sensitivity indicates that the Vega's debris disk has a smooth structure. But a planet orbiting Vega could not be neglected, and the present-day observations may place a severe constraint on the orbital parameters for the potential planet. Herein, we utilize the modi- fied MERCURY codes to numerically simulate the Vega system, which consists of a debris disk and a planet. In our simulations, the initial inner and outer boundaries of the debris disk are assumed to be 80 AU and 120 AU, respectively. The dust grains in the disk have the sizes from 10 μm to 100 μm, and the nearly coplanar orbits. From the outcomes, we show that the evolution of debris disk is consistent with recent observations, if there is no planet orbiting Vega. However, if Vega owns a planet with a high eccentricity (e.g., e = 0.6), the planet's semi- major axis cannot be larger than 60 AU, otherwise, an aggregation phenomenon will occur in the debris disk due to the existence of the postulated planet. In addition, the 2:1 mean motion resonances may play a significant role in forming the structure of debris disk.

How rare is complex life in the Milky Way?

PubMed

Bounama, Christine; von Bloh, Werner; Franck, Siegfried

2007-10-01

An integrated Earth system model was applied to calculate the number of habitable Earth-analog planets that are likely to have developed primitive (unicellular) and complex (multicellular) life in extrasolar planetary systems. The model is based on the global carbon cycle mediated by life and driven by increasing stellar luminosity and plate tectonics. We assumed that the hypothetical primitive and complex life forms differed in their temperature limits and CO(2) tolerances. Though complex life would be more vulnerable to environmental stress, its presence would amplify weathering processes on a terrestrial planet. The model allowed us to calculate the average number of Earth-analog planets that may harbor such life by using the formation rate of Earth-like planets in the Milky Way as well as the size of a habitable zone that could support primitive and complex life forms. The number of planets predicted to bear complex life was found to be approximately 2 orders of magnitude lower than the number predicted for primitive life forms. Our model predicted a maximum abundance of such planets around 1.8 Ga ago and allowed us to calculate the average distance between potentially habitable planets in the Milky Way. If the model predictions are accurate, the future missions DARWIN (up to a probability of 65%) and TPF (up to 20%) are likely to detect at least one planet with a biosphere composed of complex life.

Planet-driven Spiral Arms in Protoplanetary Disks. II. Implications

NASA Astrophysics Data System (ADS)

Bae, Jaehan; Zhu, Zhaohuan

2018-06-01

We examine whether various characteristics of planet-driven spiral arms can be used to constrain the masses of unseen planets and their positions within their disks. By carrying out two-dimensional hydrodynamic simulations varying planet mass and disk gas temperature, we find that a larger number of spiral arms form with a smaller planet mass and a lower disk temperature. A planet excites two or more spiral arms interior to its orbit for a range of disk temperatures characterized by the disk aspect ratio 0.04≤slant {(h/r)}p≤slant 0.15, whereas exterior to a planet’s orbit multiple spiral arms can form only in cold disks with {(h/r)}p≲ 0.06. Constraining the planet mass with the pitch angle of spiral arms requires accurate disk temperature measurements that might be challenging even with ALMA. However, the property that the pitch angle of planet-driven spiral arms decreases away from the planet can be a powerful diagnostic to determine whether the planet is located interior or exterior to the observed spirals. The arm-to-arm separations increase as a function of planet mass, consistent with previous studies; however, the exact slope depends on disk temperature as well as the radial location where the arm-to-arm separations are measured. We apply these diagnostics to the spiral arms seen in MWC 758 and Elias 2–27. As shown in Bae et al., planet-driven spiral arms can create concentric rings and gaps, which can produce a more dominant observable signature than spiral arms under certain circumstances. We discuss the observability of planet-driven spiral arms versus rings and gaps.

HIDING IN THE SHADOWS. II. COLLISIONAL DUST AS EXOPLANET MARKERS

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

Dobinson, Jack; Leinhardt, Zoë M.; Lines, Stefan

Observations of the youngest planets (∼1–10 Myr for a transitional disk) will increase the accuracy of our planet formation models. Unfortunately, observations of such planets are challenging and time-consuming to undertake, even in ideal circumstances. Therefore, we propose the determination of a set of markers that can preselect promising exoplanet-hosting candidate disks. To this end, N-body simulations were conducted to investigate the effect of an embedded Jupiter-mass planet on the dynamics of the surrounding planetesimal disk and the resulting creation of second-generation collisional dust. We use a new collision model that allows fragmentation and erosion of planetesimals, and dust-sized fragmentsmore » are simulated in a post-process step including non-gravitational forces due to stellar radiation and a gaseous protoplanetary disk. Synthetic images from our numerical simulations show a bright double ring at 850 μm for a low-eccentricity planet, whereas a high-eccentricity planet would produce a characteristic inner ring with asymmetries in the disk. In the presence of first-generation primordial dust these markers would be difficult to detect far from the orbit of the embedded planet, but would be detectable inside a gap of planetary origin in a transitional disk.« less

Aeolian Grain Evolution on Mars: Implications for Regolith Origins

NASA Astrophysics Data System (ADS)

Sullivan, R. J.; Cabrol, N. A.; Golombek, M.; Herkenhoff, K. E.; Landis, G.; Mer Athena Science Team

2010-12-01

Early wind tunnel experiments and the Viking Lander experience led to concepts of grain evolution and regolith development on Mars. Wind tunnel experiments showed that 100-150 μm grains are easiest to entrain on Mars, but at 10 times higher wind speeds than on Earth. Even if trajectory speeds of martian saltating grains achieve smaller fractions of entraining wind speeds than on Earth, kinetic energies of these grains would be much higher, with greater potential for damage to the grains during return collisions with the particle bed. On this basis Sagan et al. [1977] JGR 82, 28, 4430 proposed that aeolian grain evolution on Mars followed a “kamikaze” pattern in which an initially coarse grain, entrained only relatively rarely by the strongest winds, would be abraded by high kinetic energy impacts and migrate through successively smaller size-frequencies at an ever-increasing rate (as entrainment became easier and thus more likely) until the grain was essentially turned to dust. On this basis it was proposed that sand-sized grains might be relatively short-lived and perhaps rare on Mars. MER observations motivate adjustments to these concepts, with implications for origins of martian regolith reworked by wind. Along both MER traverses, on opposite sides of the planet, regolith is volumetrically dominated by very fine sand mixed with unresolved finer grains. Sorting probably is poor, based on weakly cohesive remolding by rover wheel cleats. The size-frequency of this material, even if not precisely known, is consistent with grains that have evolved by attrition to sizes smaller than the most easily-moved 100-150 μm interval, to where entrainment becomes more difficult due to the increasing relative importance of inter-particle surface forces. At these smaller sizes also, kinetic energies have been reduced proportionally by the cube of the particle radius, so grain-to-grain attrition is less effective for further evolution to even smaller grain sizes. Characteristics of the most ubiquitous, volumetrically dominant regolith component at both MER sites are consistent with a residuum of grains developed by aeolian grain-to-grain collisions. At both MER sites also: (1) there is a paucity of grains between 300 and 850 μm; and (2) grains >850 μm have participated in creep movements (driven by saltation of finer grains) during past migrations of coarse-grained ripples. These and other observations suggest aeolian grain evolution in which (1) the coarsest grains initially would be driven in creep only, where attrition efficiency might be limited; (2) probability of saltation increases when grain size evolves somewhere below ~900 μm, accelerating further grain evolution to smaller sizes until slowed by decreasing susceptibility to entrainment and (more importantly) decreased collisional effectiveness at grain sizes of <100 μm. We speculate that on a planet where aeolian working of surface materials is common, this grain evolution scenario could have widespread applicability and that regolith grain size-frequency characteristics encountered at both MER sites might be common in many regolith units across the martian surface that have been processed by wind.

CONSTRAINTS ON PLANET OCCURRENCE AROUND NEARBY MID-TO-LATE M DWARFS FROM THE MEARTH PROJECT

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

Berta, Zachory K.; Irwin, Jonathan; Charbonneau, David, E-mail: zberta@cfa.harvard.edu

The MEarth Project is a ground-based photometric survey intended to find planets transiting the closest and smallest main-sequence stars. In its first four years, MEarth discovered one transiting exoplanet, the 2.7 R{sub ⊕} planet GJ1214b. Here, we answer an outstanding question: in light of the bounty of small planets transiting small stars uncovered by the Kepler mission, should MEarth have found more than just one planet so far? We estimate MEarth's ensemble sensitivity to exoplanets by performing end-to-end simulations of 1.25 × 10{sup 6} observations of 988 nearby mid-to-late M dwarfs, gathered by MEarth between 2008 October and 2012 June.more » For 2-4 R{sub ⊕} planets, we compare this sensitivity to results from Kepler and find that MEarth should have found planets at a rate of 0.05-0.36 planets yr{sup –1} in its first four years. As part of this analysis, we provide new analytic fits to the Kepler early M dwarf planet occurrence distribution. When extrapolating between Kepler's early M dwarfs and MEarth's mid-to-late M dwarfs, we find that assuming the planet occurrence distribution stays fixed with respect to planetary equilibrium temperature provides a good match to our detection of a planet with GJ1214b's observed properties. For larger planets, we find that the warm (600-700 K), Neptune-sized (4 R{sub ⊕}) exoplanets that transit early M dwarfs like Gl436 and GJ3470 occur at a rate of <0.15 star{sup –1} (at 95% confidence) around MEarth's later M dwarf targets. We describe a strategy with which MEarth can increase its expected planet yield by 2.5 × without new telescopes by shifting its sensitivity toward the smaller and cooler exoplanets that Kepler has demonstrated to be abundant.« less

Modeling collisions in circumstellar debris disks

NASA Astrophysics Data System (ADS)

Nesvold, Erika

2015-10-01

Observations of resolved debris disks show a spectacular variety of features and asymmetries, including inner cavities and gaps, inclined secondary disks or warps, and eccentric, sharp-edged rings. Embedded exoplanets could create many of these features via gravitational perturbations, which sculpt the disk directly and by generating planetesimal collisions. In this thesis, I present the Superparticle Model/Algorithm for Collisions in Kuiper belts and debris disks (SMACK), a new method for simultaneously modeling, in 3-D, the collisional and dynamical evolution of planetesimals in a debris disk with planets. SMACK can simulate azimuthal asymmetries and how these asymmetries evolve over time. I show that SMACK is stable to numerical viscosity and numerical heating over 107 yr, and that it can reproduce analytic models of disk evolution. As an example of the algorithm's capabilities, I use SMACK to model the evolution of a debris ring containing a planet on an eccentric orbit and demonstrate that differential precession creates a spiral structure as the ring evolves, but collisions subsequently break up the spiral, leaving a narrower eccentric ring. To demonstrate SMACK's utility in studying debris disk physics, I apply SMACK to simulate a planet on a circular orbit near a ring of planetesimals that are experiencing destructive collisions. Previous simulations of a planet opening a gap in a collisionless debris disk have found that the width of the gap scales as the planet mass to the 2/7th power (alpha = 2/7). I find that gap sizes in a collisional disk still obey a power law scaling with planet mass, but that the index alpha of the power law depends on the age of the system t relative to the collisional timescale t coll of the disk by alpha = 0.32(t/ tcoll)-0.04, with inferred planet masses up to five times smaller than those predicted by the classical gap law. The increased gap sizes likely stem from the interaction between collisions and the mean motion resonances near the chaotic zone. I investigate the effects of the initial eccentricity distribution of the disk particles and find a negligible effect on the gap size at Jovian planet masses, since collisions tend to erase memory of the initial particle eccentricity distributions. I also find that the presence of Trojan analogs is a potentially powerful diagnostic of planets in the mass range ˜1--10MJup. I apply my model to place new upper limits on planets around Fomalhaut, HR 4796 A, HD 202628, HD 181327, and beta Pictoris. Finally, to show how SMACK can be used to analyze a single debris disk in detail, I present a new model of the beta Pictoris disk and planet system that, for the first time, combines simulations of the colliding planetesimals and the dynamics of the dust grains, allowing me to model features and asymmetries in both submillimeter and scattered light images of the disk. I combine a 100,000 superparticle SMACK simulation with N-body integrations of the dust produced by the simulated collisions. I find that secular perturbations of the planet's measured inclination and eccentricity can explain the observed warp and planetesimal ring, while collisions between planetesimals shape the disk by eroding close-in material. The complex 3D structure of the disk due to the perturbations from the planet creates an azimuthally asymmetric spatial distribution of collisions, which could contribute to the observed azimuthal clump of CO gas seen with ALMA. My simulations of the small dust grains produced by collisions demonstrate that the "birth ring" approximation for beta Pictoris fails to account for the ˜54% of dust mass produced outside of the planetesimal ring. I also reproduce the gross morphology of high-resolution scattered light images of the disk, including the two-disk "x"-pattern seen in scattered light, which has not been replicated by previous dust dynamics models.

Constraining the mass of the planet(s) sculpting a disk cavity. The intriguing case of 2MASS J16042165-2130284

NASA Astrophysics Data System (ADS)

Canovas, H.; Hardy, A.; Zurlo, A.; Wahhaj, Z.; Schreiber, M. R.; Vigan, A.; Villaver, E.; Olofsson, J.; Meeus, G.; Ménard, F.; Caceres, C.; Cieza, L. A.; Garufi, A.

2017-02-01

Context. The large cavities observed in the dust and gas distributions of transition disks may be explained by planet-disk interactions. At 145 pc, 2MASS J16042165-2130284 (J1604) is a 5-12 Myr old transitional disk with different gap sizes in the mm- and μm-sized dust distributions (outer edges at 79 and at 63 au, respectively). Its 12CO emission shows a 30 au cavity. This radial structure suggests that giant planets are sculpting this disk. Aims: We aim to constrain the masses and locations of plausible giant planets around J1604. Methods: We observed J1604 with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) at the Very Large Telescope (VLT), in IRDIFS_EXT, pupil-stabilized mode, obtaining YJH-band images with the integral field spectrograph (IFS) and K1K2-band images with the Infra-Red Dual-beam Imager and Spectrograph (IRDIS). The dataset was processed exploiting the angular differential imaging (ADI) technique with high-contrast algorithms. Results: Our observations reach a contrast of ΔK,ΔYH 12 mag from 0".15 to 0".80 ( 22 to 115 au), but no planet candidate is detected. The disk is directly imaged in scattered light at all bands from Y to K, and it shows a red color. This indicates that the dust particles in the disk surface are mainly ≳0.3 μm-sized grains. We confirm the sharp dip/decrement in scattered light in agreement with polarized light observations. Comparing our images with a radiative transfer model we argue that the southern side of the disk is most likely the nearest. Conclusions: This work represents the deepest search yet for companions around J1604. We reach a mass sensitivity of ≳2-3 MJup from 22 to 115 au according to a hot start scenario. We propose that a brown dwarf orbiting inside of 15 au and additional Jovian planets at larger radii could account for the observed properties of J1604 while explaining our lack of detection. Based on observations made with the VLT, program 095.C-0673(A).The reduced images (FITS files) are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/598/A43

Formation of TRAPPIST-1

NASA Astrophysics Data System (ADS)

Ormel, C. W.; Liu, B.; Schoonenberg, D.

2017-09-01

We present a model for the formation of the recently-discovered TRAPPIST-1 planetary system. In our scenario planets form in the interior regions, by accretion of mm to cm-size particles (pebbles) that drifted from the outer disk. This scenario has several advantages: it connects to the observation that disks are made up of pebbles, it is efficient, it explains why the TRAPPIST-1 planets are ˜Earth mass, and it provides a rationale for the system's architecture.

VERITAS: a Discovery-Class Venus Surface Geology and Geophysics Mission

NASA Technical Reports Server (NTRS)

Freeman, Anthony; Smrekar, Suzanne E.; Hensley, Scott; Wallace, Mark; Sotin, Christophe; Darrach, Murray; Xaypraseuth, Peter; Helbert, Joern; Mazarico, Erwan

2016-01-01

Our understanding of solar system evolution is limited by a great unanswered question: How Earthlike is Venus? We know that these "twin" planets formed with similar bulk composition and size. Yet the evolutionary path Venus followed has diverged from Earth's, in losing its surface water and becoming hotter than Mercury. What led to this? The answer has profound implications for how terrestrial planets become habitable and the potential for life in the universe.

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

NASA Astrophysics Data System (ADS)

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

2017-11-01

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

Remote sensing of planetary properties and biosignatures on extrasolar terrestrial planets

NASA Technical Reports Server (NTRS)

Des Marais, David J.; Harwit, Martin O.; Jucks, Kenneth W.; Kasting, James F.; Lin, Douglas N C.; Lunine, Jonathan I.; Schneider, Jean; Seager, Sara; Traub, Wesley A.; Woolf, Neville J.

2002-01-01

The major goals of NASA's Terrestrial Planet Finder (TPF) and the European Space Agency's Darwin missions are to detect terrestrial-sized extrasolar planets directly and to seek spectroscopic evidence of habitable conditions and life. Here we recommend wavelength ranges and spectral features for these missions. We assess known spectroscopic molecular band features of Earth, Venus, and Mars in the context of putative extrasolar analogs. The preferred wavelength ranges are 7-25 microns in the mid-IR and 0.5 to approximately 1.1 microns in the visible to near-IR. Detection of O2 or its photolytic product O3 merits highest priority. Liquid H2O is not a bioindicator, but it is considered essential to life. Substantial CO2 indicates an atmosphere and oxidation state typical of a terrestrial planet. Abundant CH4 might require a biological source, yet abundant CH4 also can arise from a crust and upper mantle more reduced than that of Earth. The range of characteristics of extrasolar rocky planets might far exceed that of the Solar System. Planetary size and mass are very important indicators of habitability and can be estimated in the mid-IR and potentially also in the visible to near-IR. Additional spectroscopic features merit study, for example, features created by other biosignature compounds in the atmosphere or on the surface and features due to Rayleigh scattering. In summary, we find that both the mid-IR and the visible to near-IR wavelength ranges offer valuable information regarding biosignatures and planetary properties; therefore both merit serious scientific consideration for TPF and Darwin.

A Comparison of Simulated JWST Observations Derived from Equilibrium and Non-equilibrium Chemistry Models of Giant Exoplanets

NASA Astrophysics Data System (ADS)

Blumenthal, Sarah D.; Mandell, Avi M.; Hébrard, Eric; Batalha, Natasha E.; Cubillos, Patricio E.; Rugheimer, Sarah; Wakeford, Hannah R.

2018-02-01

We aim to see if the difference between equilibrium and disequilibrium chemistry is observable in the atmospheres of transiting planets by the James Webb Space Telescope (JWST). We perform a case study comparing the dayside emission spectra of three planets like HD 189733b, WASP-80b, and GJ 436b, in and out of chemical equilibrium at two metallicities each. These three planets were chosen because they span a large range of planetary masses and equilibrium temperatures, from hot and Jupiter-sized to warm and Neptune-sized. We link the one-dimensional disequilibrium chemistry model from Venot et al. (2012), in which thermochemical kinetics, vertical transport, and photochemistry are taken into account, to the one-dimensional, pseudo line-by-line radiative transfer model, Pyrat bay, developed especially for hot Jupiters, and then simulate JWST spectra using PandExo for comparing the effects of temperature, metallicity, and radius. We find the most significant differences from 4 to 5 μm due to disequilibrium from CO and CO2 abundances, and also H2O for select cases. Our case study shows a certain “sweet spot” of planetary mass, temperature, and metallicity where the difference between equilibrium and disequilibrium is observable. For a planet similar to WASP-80b, JWST’s NIRSpec G395M can detect differences due to disequilibrium chemistry with one eclipse event. For a planet similar to GJ 436b, the observability of differences due to disequilibrium chemistry is possible at low metallicity given five eclipse events, but not possible at the higher metallicity.

Remote sensing of planetary properties and biosignatures on extrasolar terrestrial planets.

PubMed

Des Marais, David J; Harwit, Martin O; Jucks, Kenneth W; Kasting, James F; Lin, Douglas N C; Lunine, Jonathan I; Schneider, Jean; Seager, Sara; Traub, Wesley A; Woolf, Neville J

2002-01-01

The major goals of NASA's Terrestrial Planet Finder (TPF) and the European Space Agency's Darwin missions are to detect terrestrial-sized extrasolar planets directly and to seek spectroscopic evidence of habitable conditions and life. Here we recommend wavelength ranges and spectral features for these missions. We assess known spectroscopic molecular band features of Earth, Venus, and Mars in the context of putative extrasolar analogs. The preferred wavelength ranges are 7-25 microns in the mid-IR and 0.5 to approximately 1.1 microns in the visible to near-IR. Detection of O2 or its photolytic product O3 merits highest priority. Liquid H2O is not a bioindicator, but it is considered essential to life. Substantial CO2 indicates an atmosphere and oxidation state typical of a terrestrial planet. Abundant CH4 might require a biological source, yet abundant CH4 also can arise from a crust and upper mantle more reduced than that of Earth. The range of characteristics of extrasolar rocky planets might far exceed that of the Solar System. Planetary size and mass are very important indicators of habitability and can be estimated in the mid-IR and potentially also in the visible to near-IR. Additional spectroscopic features merit study, for example, features created by other biosignature compounds in the atmosphere or on the surface and features due to Rayleigh scattering. In summary, we find that both the mid-IR and the visible to near-IR wavelength ranges offer valuable information regarding biosignatures and planetary properties; therefore both merit serious scientific consideration for TPF and Darwin.

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

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

TRAPPIST-1 Statistics Table

NASA Image and Video Library

2017-02-22

This chart shows, on the top row, artist concepts of the seven planets of TRAPPIST-1 with their orbital periods, distances from their star, radii and masses as compared to those of Earth. On the bottom row, the same numbers are displayed for the bodies of our inner solar system: Mercury, Venus, Earth and Mars. The TRAPPIST-1 planets orbit their star extremely closely, with periods ranging from 1.5 to only about 20 days. This is much shorter than the period of Mercury, which orbits our sun in about 88 days. The artist concepts show what the TRAPPIST-1 planetary system may look like, based on available data about their 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. http://photojournal.jpl.nasa.gov/catalog/PIA21425

Core-powered mass-loss and the radius distribution of small exoplanets

NASA Astrophysics Data System (ADS)

Ginzburg, Sivan; Schlichting, Hilke E.; Sari, Re'em

2018-05-01

Recent observations identify a valley in the radius distribution of small exoplanets, with planets in the range 1.5-2.0 R⊕ significantly less common than somewhat smaller or larger planets. This valley may suggest a bimodal population of rocky planets that are either engulfed by massive gas envelopes that significantly enlarge their radius, or do not have detectable atmospheres at all. One explanation of such a bimodal distribution is atmospheric erosion by high-energy stellar photons. We investigate an alternative mechanism: the luminosity of the cooling rocky core, which can completely erode light envelopes while preserving heavy ones, produces a deficit of intermediate sized planets. We evolve planetary populations that are derived from observations using a simple analytical prescription, accounting self-consistently for envelope accretion, cooling and mass-loss, and demonstrate that core-powered mass-loss naturally reproduces the observed radius distribution, regardless of the high-energy incident flux. Observations of planets around different stellar types may distinguish between photoevaporation, which is powered by the high-energy tail of the stellar radiation, and core-powered mass-loss, which depends on the bolometric flux through the planet's equilibrium temperature that sets both its cooling and mass-loss rates.

Photo by Voyager 1 (JPL) The spacecraft took this photo of the planet Jupiter on Jan 24, while still

NASA Technical Reports Server (NTRS)

1979-01-01

Photo by Voyager 1 (JPL) The spacecraft took this photo of the planet Jupiter on Jan 24, while still more than 25 million miles (40 million kilometers) away. As the spacecraft draws closer to the planet (about 1 million kilometers a day) more details are emergng in the turbulent clouds. The Great Red Spot shows prominently below center, surrounded by what scientists call a remarkably complex region of the giant planet's atmosphere. An elongated yellow cloud within the Great Red Spot is swirling around the spot's interior boundary in a counterclockwise direction with a period of a little less than six days, confirming the whirlpool-like circulation that astronomers have suspected from ground-based photographs. Ganymede, Jupiter's largest satellite, can be seen to the lower left of the planet. Ganymede is a planet-sized body larger than Mercury. This color photo was assembled at Jet Propulsion Laboratory's Image Processing Lab from there black and white images taken through filters. The Voyagers are managed for NASA's Office of Space Science by Jet Propulsion Laboratory. (ref: P-20945C Mission Image 1-9)

The Dynamics of Orbit-Clearing for Planets on Eccentric Orbits

NASA Astrophysics Data System (ADS)

Hastings, Danielle; Margot, Jean-Luc

2016-10-01

The third requirement in the 2006 International Astronomical Union (IAU) definition of a planet is that the object has cleared the neighborhood around its orbit. Margot (2015) proposed a metric that quantitatively determines if an object has enough mass to clear an orbital zone of a specific extent within a defined time interval. In this metric, the size of the zone to be cleared is given by CRH, where C is a constant and RH is the Hill Radius. Margot (2015) adopts C=2*31/2 to describe the minimum extent of orbital clearing on the basis of the planet's feeding zone. However, this value of C may only apply for eccentricities up to about 0.3 (Quillen & Faber 2006). Here, we explore the timescales and boundaries of orbital clearing for planets over a range of orbital eccentricities and planet-star mass ratios using the MERCURY integration package (Chambers 1999). The basic setup for the integrations includes a single planet orbiting a star and a uniform distribution of massless particles extending beyond CRH. The system is integrated for at least 106 revolutions and the massless particles are tracked in order to quantify the timescale and extent of the clearing.

Characterising Hot-Jupiters' atmospheres with observations and modelling

NASA Astrophysics Data System (ADS)

Tinetti, G.

2007-08-01

Exoplanet transit photometry and spectroscopy are currently the best techniques to probe the atmospheres of extrasolar worlds. The best targets to be observed with these methods, are the planets that orbit very close to their parent star, both because their probability to transit grows and their atmospheres are warmer and more expanded, hence easier to probe. These characteristics are met by the so called Hot-Jupiters, massive low-density gaseous planets orbiting very close-in. Phase-curves allow to observe the change in brightness in the combined light of the planet-star system, also for non-transiting exoplanets. We review here the most crucial observations performed with the Hubble and Spitzer Space Telescopes at multiple wavelenghts, and the most successful models proposed in the literature to plan and interpret those observations. In particular we will focus on most recent observations and modelling claiming the detection of water vapour in the atmospheres of these planets. Further into the future, the JamesWebb Space Telescope will allow to probe the atmospheres of smaller size-planets with the same techniques. We briefly report here the results expected for hot and warm Neptunes, or transiting terrestrial planets.

Exchange of meteorites (and life?) between stellar systems.

PubMed

Melosh, H J

2003-01-01

It is now generally accepted that meteorite-size fragments of rock can be ejected from planetary bodies. Numerical studies of the orbital evolution of such planetary ejecta are consistent with the observed cosmic ray exposure times and infall rates of these meteorites. All of these numerical studies agree that a substantial fraction (up to one-third) of the ejecta from any planet in our Solar System is eventually thrown out of the Solar System during encounters with the giant planets Jupiter and Saturn. In this paper I examine the probability that such interstellar meteorites might be captured into a distant solar system and fall onto a terrestrial planet in that system within a given interval of time. The overall conclusion is that it is very unlikely that even a single meteorite originating on a terrestrial planet in our solar system has fallen onto a terrestrial planet in another stellar system, over the entire period of our Solar System's existence. Although viable microorganisms may be readily exchanged between planets in our solar system through the interplanetary transfer of meteoritic material, it seems that the origin of life on Earth must be sought within the confines of the Solar System, not abroad in the galaxy.

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.

Radii and Orbits of Hot Jupiters

NASA Astrophysics Data System (ADS)

Wu, Yanqin

2011-09-01

Hot jupiters suffer extreme external (stellar) and internal (tidal, Ohmic and wind-power) heating. These lead to peculiar thermal evolution, which is potentially self-destrutive. For instance, the amount of energy deposited during tidal dissipation far exceeds the planets' binding energy. If this energy is mostly deposited in shallow layers, it does little damage to the planet. However, the presence of stellar insolation changes the picture, and Ohmic/wind-power heating further modifies the subsequent evolution of these jupiters. A diversity of planetary sizes results. We tie these thermodynamical processes together with the migration history of hot jupiters to explain the orbital distribution and physical radii of hot jupiters. Moreover, we constrain the location of tidal heating inside the planet.

KSC-08pd4058

NASA Image and Video Library

2008-12-17

CAPE CANAVERAL, Fla. -- On Complex 17-B at Cape Canaveral Air Force Station in Florida, the second stage has been mated to the first stage of the Delta 2 rocket that will launch NASA's Kepler spacecraft. The Kepler mission is specifically designed to survey our region of the Milky Way galaxy to discover hundreds of Earth-size and smaller planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets. Results from this mission will allow us to place our solar system within the continuum of planetary systems in the Galaxy. NASA's planet-hunting Kepler mission is scheduled to launch no earlier than March 5, 2009. Photo credit: NASA/Jim Grossmann

Dimensionality and integrals of motion of the Trappist-1 planetary system

NASA Astrophysics Data System (ADS)

Floß, Johannes; Rein, Hanno; Brumer, Paul

2018-04-01

The number of isolating integrals of motion of the Trappist-1 system - a late M-dwarf orbited by seven Earth-sized planets - was determined numerically, using an adapted version of the correlation dimension method. It was found that over the investigated time-scales of up to 20 000 years the number of isolating integrals of motion is the same as one would find for a system of seven non-interacting planets - despite the fact that the planets in the Trappist-1 system are strongly interacting. Considering perturbed versions of the Trappist-1 system shows that the system may occupy an atypical part of phase-space with high stability. These findings are consistent with earlier studies.

Magma ocean formation due to giant impacts

NASA Technical Reports Server (NTRS)

Tonks, W. B.; Melosh, H. J.

1992-01-01

The effect of giant impacts on the initial chemical and thermal states of the terrestrial planets is just now being explored. A large high speed impact creates an approximately hemispherical melt region with a radius that depends on the projectile's radius and impact speed. It is shown that giant impacts on large planets can create large, intact melt regions containing melt volumes up to a few times the volume of the projectile. These large melt regions are not created on asteroid sized bodies. If extruded to the surface, these regions contain enough melt to create a magma ocean of considerable depth, depending on the impact speed, projectile radius, and gravity of the target planet.

Dimensionality and integrals of motion of the Trappist-1 planetary system

NASA Astrophysics Data System (ADS)

Floß, Johannes; Rein, Hanno; Brumer, Paul

2018-07-01

The number of isolating integrals of motion of the Trappist-1 system - a late M-dwarf orbited by seven Earth-sized planets - was determined numerically, using an adapted version of the correlation dimension method. It was found that over the investigated time-scales of up to 20 000 yr the number of isolating integrals of motion is the same as one would find for a system of seven non-interacting planets - despite the fact that the planets in the Trappist-1 system are strongly interacting. Considering perturbed versions of the Trappist-1 system shows that the system may occupy an atypical part of phase-space with high stability. These findings are consistent with earlier studies.

Vital signs of life on distant worlds

NASA Astrophysics Data System (ADS)

2003-01-01

Ozone in a planet's spectrum may indicate the presence of life hi-res Size hi-res: 673 kb Credits: ESA 2001. Illustration by Medialab Ozone in a planet's spectrum may indicate the presence of life Darwin will most probably look for the spectral signature of ozone, which is unlikely to exist in any quantity for any length of time in the atmosphere of a planet that is not home to life. The background image is a view of Earth seen by the Apollo 17 crew as they traveled toward the Moon. The white patch at the bottom is Antarctica. Unobscured by clouds, Africa and the Arabian Peninsula are visible at the top of this image. The large island off the coast of Africa is the Malagasy Republic. Looking for Earth-like planets hi-res Size hi-res: 2106 Kb Credits: ESA 2002. Illustration by Medialab Looking for Earth-like planets Darwin has six telescopes that analyse the atmospheres of Earth-like planets Darwin's flotilla hi-res Size hi-res: 902 Kb Credits: ESA 2002. Illustration by Medialab Darwin's flotilla Darwin's six telescopes, a central view-combining spacecraft, and communication satellite (shown bottom left) Our radio and television broadcasts have been leaking into space since the 1930s, when the first powerful emitters were constructed. However, you can do things the other way around as well. The Search for Extraterrestrial Intelligence (SETI) has used radio telescopes to listen to the cosmos for similar signals. Nowadays, astrobiologists are pinpointing more subtle signs that all life, not just intelligent life, might radiate into space. They call these telltale signatures 'biomarkers'. When ESA's Darwin mission begins sending back data in the next decade, biomarkers will help indicate whether neighbouring planets are inhabited. If we only used radio waves as markers of life, this would exclude all forms of life that have not yet developed the means to emit radio waves. Life has been around for thousands of millions of years, but human beings have used radio waves for less than a century. Malcolm Fridlund, Project Scientist for ESA's Darwin mission says, "If other planets follow the Earth's pattern, it is much more likely that they will be inhabited by dinosaurs or even bacteria than by something that can count." In the 1970s, the British scientist James Lovelock pointed out that, just by breathing, life affects the composition of the Earth's atmosphere. He suggested looking for similar effects as a way to search with telescopes for life on other planets. You can study the composition of an atmosphere by splitting a planet's light into a rainbow of colours. This 'spectrum' will contain dark lines made by various chemicals in the planet's atmosphere. Darwin's strategy is to look for oxygen because oxygen is used by some life forms and produced as waste by others. Scientists believe that without life, all free oxygen in a planet's atmosphere would disappear within just four million years, because it reacts so easily with other chemicals. "The best estimates suggest that Darwin will be able to detect the build-up of oxygen caused within a few hundred million years of life's origin," says Fridlund. Although Darwin will not detect oxygen directly, it will 'see' ozone, a form of oxygen. It will also see carbon dioxide, water, and, in certain cases, methane. Fridlund says, "The general consensus is that if we find ozone, liquid water, and carbon dioxide simultaneously, it will be a very strong indicator of life's presence." The work will not stop once Darwin completes its survey of the nearest several thousand star-planet systems. Once it finds a living planet, the race will be on to understand the nature of its life forms. That means searching for more specific biomarkers. In future space missions, for example, scientists may use chlorophyll as a biomarker. This molecule allows plants and certain bacteria to use light as an energy source. "Finding the next generation of biomarkers is a very active field of research at the moment," says Fridlund. He can see a future in which space telescopes look for intelligent civilisations by searching for industrial pollution in a planet's atmosphere. This may sound like science fiction but for now, oxygen, carbon dioxide, and water will be good enough as indicators of life.

Effect of the tidal-seismic resonance

NASA Astrophysics Data System (ADS)

Tian, Y.; Zheng, Y.

2017-12-01

For a moon spiraling inward to its planet, the tidal force frequency of a moon is increasing. When the distance of the moon to the planet is close enough, the tidal force frequency can intrude into the frequency range of planet normal modes. Usually the football mode, also known as 0S2, has the lowest frequency. This mode is most likely to be excited and coupled first. When the tidal force has the same frequency with the normal modes, the resonance can happen. The existence of the topography or internal heterogeneities of the planet can have mode coupling. So the energy of gravity force with higher spatial frequencies can be transferred to the low spatial 0S2 mode. The resonant mode 0S2 can exert a negative torque to the rotating moon so its orbit decays. With our 3D numerical boundary element method which takes into account planet surface topography (i.e., Mars as example), we found that the closer the moon is to the planet, the greater falling rate of the moon would be. We applied our method to a planet with equal size of Mars and elastic constants in possible range. The vibration amplitude on the planet surface can reach to the scale of meters when as the moon drop down to about 1.04 radius of the planet to achieve resonance with the 0S2 mode. Our modeling showed that the influence of tidal force caused resonance could not be neglected in the process of moon falling. On the other hand, the resonance may also be able to speed up the accretion of the early forming planet by absorbing the dust of small asteroid nearby by the tidal-seismic resonance.

Optimal survey strategies and predicted planet yields for the Korean microlensing telescope network

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

Henderson, Calen B.; Gaudi, B. Scott; Skowron, Jan

2014-10-10

The Korean Microlensing Telescope Network (KMTNet) will consist of three 1.6 m telescopes each with a 4 deg{sup 2} field of view (FoV) and will be dedicated to monitoring the Galactic Bulge to detect exoplanets via gravitational microlensing. KMTNet's combination of aperture size, FoV, cadence, and longitudinal coverage will provide a unique opportunity to probe exoplanet demographics in an unbiased way. Here we present simulations that optimize the observing strategy for and predict the planetary yields of KMTNet. We find preferences for four target fields located in the central Bulge and an exposure time of t {sub exp} = 120more » s, leading to the detection of ∼2200 microlensing events per year. We estimate the planet detection rates for planets with mass and separation across the ranges 0.1 ≤ M{sub p} /M {sub ⊕} ≤ 1000 and 0.4 ≤ a/AU ≤ 16, respectively. Normalizing these rates to the cool-planet mass function of Cassan et al., we predict KMTNet will be approximately uniformly sensitive to planets with mass 5 ≤ M{sub p} /M {sub ⊕} ≤ 1000 and will detect ∼20 planets per year per dex in mass across that range. For lower-mass planets with mass 0.1 ≤ M{sub p} /M {sub ⊕} < 5, we predict KMTNet will detect ∼10 planets per year. We also compute the yields KMTNet will obtain for free-floating planets (FFPs) and predict KMTNet will detect ∼1 Earth-mass FFP per year, assuming an underlying population of one such planet per star in the Galaxy. Lastly, we investigate the dependence of these detection rates on the number of observatories, the photometric precision limit, and optimistic assumptions regarding seeing, throughput, and flux measurement uncertainties.« less

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

LIFETIME AND SPECTRAL EVOLUTION OF A MAGMA OCEAN WITH A STEAM ATMOSPHERE: ITS DETECTABILITY BY FUTURE DIRECT IMAGING

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

Hamano, Keiko; Kawahara, Hajime; Abe, Yutaka

2015-06-20

We present the thermal evolution and emergent spectra of solidifying terrestrial planets along with the formation of steam atmospheres. The lifetime of a magma ocean and its spectra through a steam atmosphere depends on the orbital distance of the planet from the host star. For a Type I planet, which is formed beyond a certain critical distance from the host star, the thermal emission declines on a timescale shorter than approximately 10{sup 6} years. Therefore, young stars should be targets when searching for molten planets in this orbital region. In contrast, a Type II planet, which is formed inside themore » critical distance, will emit significant thermal radiation from near-infrared atmospheric windows during the entire lifetime of the magma ocean. The K{sub s} and L bands will be favorable for future direct imaging because the planet-to-star contrasts of these bands are higher than approximately 10{sup −7}–10{sup −8}. Our model predicts that, in the Type II orbital region, molten planets would be present over the main sequence of the G-type host star if the initial bulk content of water exceeds approximately 1 wt%. In visible atmospheric windows, the contrasts of the thermal emission drop below 10{sup −10} in less than 10{sup 5} years, whereas those of the reflected light remain 10{sup −10} for both types of planets. Since the contrast level is comparable to those of reflected light from Earth-sized planets in the habitable zone, the visible reflected light from molten planets also provides a promising target for direct imaging with future ground- and space-based telescopes.« less

KSC-2009-1129

NASA Image and Video Library

2009-01-13

CAPE CANAVERAL, Fla. -- Ball Aerospace and Technology workers conduct a light test on the solar array panels of NASA's Kepler spacecraft. A NASA Discovery mission, Kepler is specifically designed to survey our region of the Milky Way galaxy to discover hundreds of Earth-size and smaller planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets. Kepler will hunt for planets using a specialized one-meter diameter telescope called a photometer to measure the small changes in brightness caused by the transits. Results from this mission will allow us to place our solar system within the continuum of planetary systems in the Galaxy. After processing at Astrotech, Kepler will be carried to its launch pad at Cape Canaveral Air Force Station. NASA's planet-hunting Kepler mission is scheduled to launch no earlier than March 5 atop a United Launch Alliance Delta II rocket. Photo credit: NASA/Kim Shiflett

KSC-2009-1124

NASA Image and Video Library

2009-01-13

CAPE CANAVERAL, Fla. -- Lights are reflected on the solar array panels of NASA's Kepler spacecraft during illumination testing. A NASA Discovery mission, Kepler is specifically designed to survey our region of the Milky Way galaxy to discover hundreds of Earth-size and smaller planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets. Kepler will hunt for planets using a specialized one-meter diameter telescope called a photometer to measure the small changes in brightness caused by the transits. Results from this mission will allow us to place our solar system within the continuum of planetary systems in the Galaxy. After processing at Astrotech, Kepler will be carried to its launch pad at Cape Canaveral Air Force Station. NASA's planet-hunting Kepler mission is scheduled to launch no earlier than March 5 atop a United Launch Alliance Delta II rocket. Photo credit: NASA/Kim Shiflett

KSC-2009-1125

NASA Image and Video Library

2009-01-13

CAPE CANAVERAL, Fla. -- Ball Aerospace and Technology workers conduct a light test on the solar array panels of NASA's Kepler spacecraft. A NASA Discovery mission, Kepler is specifically designed to survey our region of the Milky Way galaxy to discover hundreds of Earth-size and smaller planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets. Kepler will hunt for planets using a specialized one-meter diameter telescope called a photometer to measure the small changes in brightness caused by the transits. Results from this mission will allow us to place our solar system within the continuum of planetary systems in the Galaxy. After processing at Astrotech, Kepler will be carried to its launch pad at Cape Canaveral Air Force Station. NASA's planet-hunting Kepler mission is scheduled to launch no earlier than March 5 atop a United Launch Alliance Delta II rocket. Photo credit: NASA/Kim Shiflett

KSC-2009-1126

NASA Image and Video Library

2009-01-13

CAPE CANAVERAL, Fla. -- Ball Aerospace and Technology workers conduct a light test on the solar array panels of NASA's Kepler spacecraft. A NASA Discovery mission, Kepler is specifically designed to survey our region of the Milky Way galaxy to discover hundreds of Earth-size and smaller planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets. Kepler will hunt for planets using a specialized one-meter diameter telescope called a photometer to measure the small changes in brightness caused by the transits. Results from this mission will allow us to place our solar system within the continuum of planetary systems in the Galaxy. After processing at Astrotech, Kepler will be carried to its launch pad at Cape Canaveral Air Force Station. NASA's planet-hunting Kepler mission is scheduled to launch no earlier than March 5 atop a United Launch Alliance Delta II rocket. Photo credit: NASA/Kim Shiflett

K2-137 b: an Earth-sized planet in a 4.3-h orbit around an M-dwarf

NASA Astrophysics Data System (ADS)

Smith, A. M. S.; Cabrera, J.; Csizmadia, Sz; Dai, F.; Gandolfi, D.; Hirano, T.; Winn, J. N.; Albrecht, S.; Alonso, R.; Antoniciello, G.; Barragán, O.; Deeg, H.; Eigmüller, Ph; Endl, M.; Erikson, A.; Fridlund, M.; Fukui, A.; Grziwa, S.; Guenther, E. W.; Hatzes, A. P.; Hidalgo, D.; Howard, A. W.; Isaacson, H.; Korth, J.; Kuzuhara, M.; Livingston, J.; Narita, N.; Nespral, D.; Nowak, G.; Palle, E.; Pätzold, M.; Persson, C. M.; Petigura, E.; Prieto-Arranz, J.; Rauer, H.; Ribas, I.; Van Eylen, V.

2018-03-01

We report the discovery in K2's Campaign 10 of a transiting terrestrial planet in an ultra-short-period orbit around an M3-dwarf. K2-137 b completes an orbit in only 4.3 h, the second shortest orbital period of any known planet, just 4 min longer than that of KOI 1843.03, which also orbits an M-dwarf. Using a combination of archival images, adaptive optics imaging, radial velocity measurements, and light-curve modelling, we show that no plausible eclipsing binary scenario can explain the K2 light curve, and thus confirm the planetary nature of the system. The planet, whose radius we determine to be 0.89 ± 0.09 R⊕, and which must have an iron mass fraction greater than 0.45, orbits a star of mass 0.463 ± 0.052 M⊙ and radius 0.442 ± 0.044 R⊙.