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Shigeru Ida - One of the best experts on this subject based on the ideXlab platform.
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Infall of Planetesimals onto Growing Giant Planets: Onset of Runaway Gas Accretion and Metallicity of Their Gas Envelopes
The Astrophysical Journal, 2008Co-Authors: Masakazu Shiraishi, Shigeru IdaAbstract:We have investigated the planetesimal accretion rate onto giant planets that are growing through Gas accretion, using numerical simulations and analytical arguments. We derived the condition for the opening of a gap in the planetesimal disk, which is determined by a competition between the expansion of the planet's Hill radius due to the planet's growth and the damping of planetesimal eccentricity due to Gas drag. We also derived the semianalytical formula for the planetesimal accretion rate as a function of the ratios of the rates of the Hill radius expansion, the damping, and planetesimal scattering by the planet. The predicted low planetesimal accretion rate due to the opening of the gap in early Gas accretion stages quantitatively shows that "phase 2," which is a long (more than a Myr), slow Gas accretion phase before the onset of runaway Gas accretion, is not likely to occur. In late stages, rapid Hill radius expansion fills the gap, resulting in significant planetesimal accretion, which is as large as several M⊕ for Jupiter and Saturn. The efficient onset of runaway Gas accretion and the late pollution may reconcile the ubiquity of Extrasolar giant planets with the metal-rich envelopes of Jupiter and Saturn inferred from interior structure models. These formulae will give deep insights into the formation of Extrasolar Gas Giants and the diversity in the metallicities of transiting Gas Giants.
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Orbital migration and mass-semimajor axis distributions of Extrasolar planets
Proceedings of the International Astronomical Union, 2007Co-Authors: Shigeru Ida, Douglas N. C. LinAbstract:AbstractHere we discuss the effects of type-I migration of protoplanetary embryos on mass and semimajor axis distributions of Extrasolar planets. We summarize the results of Ida & Lin (2008a, 2008b), in which Monte Carlo simulations with a deterministic planet-formation model were carried out. The strength of type-I migration regulates the distribution of Extrasolar Gas giant planets as well as terrestrial planets. To be consistent with the existing observational data of Extrasolar Gas Giants, the type-I migration speed has to be an order of magnitude slower than that given by the linear theory. The introduction of type-I migration inhibits in situ formation of Gas Giants in habitable zones (HZs) and reduces the probability of passage of Gas Giants through HZs, both of which facilitate retention of terrestrial planets in HZs. We also point out that the effect of magneto-rotational instability (MRI) could lead to trapping of migrating protoplanetary embryos in the regions near an ice line in the disk and it significantly enhances formation/retention probability of Gas Giants against type-I migration.
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Toward a Deterministic Model of Planetary Formation IV: Effects of Type-I Migration
arXiv: Astrophysics, 2007Co-Authors: Shigeru Ida, Douglas N. C. LinAbstract:In a further development of a deterministic planet-formation model (Ida & Lin 2004), we consider the effect of type-I migration of protoplanetary embryos due to their tidal interaction with their nascent disks. During the early embedded phase of protostellar disks, although embryos rapidly emerge in regions interior to the ice line, uninhibited type-I migration leads to their efficient self-clearing. But, embryos continue to form from residual planetesimals at increasingly large radii, repeatedly migrate inward, and provide a main channel of heavy element accretion onto their host stars. During the advanced stages of disk evolution (a few Myr), the Gas surface density declines to values comparable to or smaller than that of the minimum mass nebula model and type-I migration is no longer an effective disruption mechanism for mars-mass embryos. Over wide ranges of initial disk surface densities and type-I migration efficiency, the surviving population of embryos interior to the ice line has a total mass several times that of the Earth. With this reservoir, there is an adequate inventory of residual embryos to subsequently assemble into rocky planets similar to those around the Sun. But, the onset of efficient Gas accretion requires the emergence and retention of cores, more massive than a few M_earth, prior to the severe depletion of the disk Gas. The formation probability of Gas giant planets and hence the predicted mass and semimajor axis distributions of Extrasolar Gas Giants are sensitively determined by the strength of type-I migration. We suggest that the observed fraction of solar-type stars with Gas giant planets can be reproduced only if the actual type-I migration time scale is an order of magnitude longer than that deduced from linear theories.
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Extrasolar terrestrial planets and possibility of extraterrestrial life
Biological Sciences in Space, 2003Co-Authors: Shigeru IdaAbstract:Recent development of research on Extrasolar planets are reviewed. About 120 Extrasolar Jupiter-mass planets have been discovered through the observation of Doppler shift in the light of their host stars that is caused by acceleration due to planet orbital motions. Although the Extrasolar planets so far observed may be limited to Gas giant planets and their orbits differ from those of giant planets in our Solar system (Jupiter and Saturn), the theoretically predicted probability of existence of Extrasolar terrestrial planets that can have liquid water ocean on their surface is comparable to that of detectable Gas giant planets. Based on the number of Extrasolar Gas Giants detected so far, about 100 life-sustainable planets may exist within a range of 200 light years. Indirect observation of Extrasolar terrestrial planets would be done with space telescopes within several years and direct one may be done within 20 years. The latter can detect biomarkers on these planets as well.
Socrates Aristotle - One of the best experts on this subject based on the ideXlab platform.
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Directly Imaging Tidally Powered Migrating Jupiters
'IOP Publishing', 2014Co-Authors: Dong Subo, Katz Boaz, Socrates AristotleAbstract:Upcoming direct-imaging experiments may detect a new class of long-period, highly luminous, tidally powered Extrasolar Gas Giants. Even though they are hosted by ~ Gyr-"old" main-sequence stars, they can be as "hot" as young Jupiters at ~100 Myr, the prime targets of direct-imaging surveys. They are on years-long orbits and presently migrating to "feed" the "hot Jupiters." They are expected from "high-e" migration mechanisms, in which Jupiters are excited to highly eccentric orbits and then shrink semi-major axis by a factor of ~10-100 due to tidal dissipation at close periastron passages. The dissipated orbital energy is converted to heat, and if it is deposited deep enough into the atmosphere, the planet likely radiates steadily at luminosity L ~ 100-1000 L_Jup(2 x 10-7-2 x 10-6 L_Sun) during a typical ~ Gyr migration timescale. Their large orbital separations and expected high planet-to-star flux ratios in IR make them potentially accessible to high-contrast imaging instruments on 10 m class telescopes. ~10 such planets are expected to exist around FGK dwarfs within ~50 pc. Long-period radial velocity planets are viable candidates, and the highly eccentric planet HD 20782b at maximum angular separation ~0.''08 is a promising candidate. Directly imaging these tidally powered Jupiters would enable a direct test of high-e migration mechanisms. Once detected, the luminosity would provide a direct measurement of the migration rate, and together with mass (and possibly radius) estimate, they would serve as a laboratory to study planetary spectral formation and tidal physics.Comment: Updated to match the published version (with a figure
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Relationship Between Thermal Tides and Radius Excess
2013Co-Authors: Socrates AristotleAbstract:Close-in Extrasolar Gas Giants -- the hot Jupiters -- display departures in radius above the zero-temperature solution, the radius excess, that are anomalously high. The radius excess of hot Jupiters follows a relatively close relation with thermal tidal tidal torques and holds for ~ 4-5 orders of magnitude in a characteristic thermal tidal power in such a way that is consistent with basic theoretical expectations. The relation suggests that thermal tidal torques determine the global thermodynamic and spin state of the hot Jupiters. On empirical grounds, it is shown that theories of hot Jupiter inflation that invoke a constant fraction of the stellar flux to be deposited at great depth are, essentially, falsified.Comment: 5 pages, 1 figure. comments and reference requests welcom
Aristotle Socrates - One of the best experts on this subject based on the ideXlab platform.
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Relationship Between Thermal Tides and Radius Excess
arXiv: Earth and Planetary Astrophysics, 2013Co-Authors: Aristotle SocratesAbstract:Close-in Extrasolar Gas Giants -- the hot Jupiters -- display departures in radius above the zero-temperature solution, the radius excess, that are anomalously high. The radius excess of hot Jupiters follows a relatively close relation with thermal tidal tidal torques and holds for ~ 4-5 orders of magnitude in a characteristic thermal tidal power in such a way that is consistent with basic theoretical expectations. The relation suggests that thermal tidal torques determine the global thermodynamic and spin state of the hot Jupiters. On empirical grounds, it is shown that theories of hot Jupiter inflation that invoke a constant fraction of the stellar flux to be deposited at great depth are, essentially, falsified.
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DIRECTLY IMAGING TIDALLY POWERED MIGRATING JUPITERS
The Astrophysical Journal, 2012Co-Authors: Subo Dong, Boaz Katz, Aristotle SocratesAbstract:Upcoming direct-imaging experiments may detect a new class of long-period, highly luminous, tidally powered Extrasolar Gas Giants. Even though they are hosted by {approx} Gyr-'old' main-sequence stars, they can be as 'hot' as young Jupiters at {approx}100 Myr, the prime targets of direct-imaging surveys. They are on years-long orbits and presently migrating to 'feed' the 'hot Jupiters'. They are expected from 'high-e' migration mechanisms, in which Jupiters are excited to highly eccentric orbits and then shrink semimajor axis by a factor of {approx}10-100 due to tidal dissipation at close periastron passages. The dissipated orbital energy is converted to heat, and if it is deposited deep enough into the atmosphere, the planet likely radiates steadily at luminosity L {approx} 100-1000 L{sub Jup}(2 Multiplication-Sign 10{sup -7}-2 Multiplication-Sign 10{sup -6} L{sub Sun }) during a typical {approx} Gyr migration timescale. Their large orbital separations and expected high planet-to-star flux ratios in IR make them potentially accessible to high-contrast imaging instruments on 10 m class telescopes. {approx}10 such planets are expected to exist around FGK dwarfs within {approx}50 pc. Long-period radial velocity planets are viable candidates, and the highly eccentric planet HD 20782b at maximum angular separation {approx}0.''08 is a promising candidate. Directly imagingmore » these tidally powered Jupiters would enable a direct test of high-e migration mechanisms. Once detected, the luminosity would provide a direct measurement of the migration rate, and together with mass (and possibly radius) estimate, they would serve as a laboratory to study planetary spectral formation and tidal physics.« less
Douglas N. C. Lin - One of the best experts on this subject based on the ideXlab platform.
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Orbital migration and mass-semimajor axis distributions of Extrasolar planets
Proceedings of the International Astronomical Union, 2007Co-Authors: Shigeru Ida, Douglas N. C. LinAbstract:AbstractHere we discuss the effects of type-I migration of protoplanetary embryos on mass and semimajor axis distributions of Extrasolar planets. We summarize the results of Ida & Lin (2008a, 2008b), in which Monte Carlo simulations with a deterministic planet-formation model were carried out. The strength of type-I migration regulates the distribution of Extrasolar Gas giant planets as well as terrestrial planets. To be consistent with the existing observational data of Extrasolar Gas Giants, the type-I migration speed has to be an order of magnitude slower than that given by the linear theory. The introduction of type-I migration inhibits in situ formation of Gas Giants in habitable zones (HZs) and reduces the probability of passage of Gas Giants through HZs, both of which facilitate retention of terrestrial planets in HZs. We also point out that the effect of magneto-rotational instability (MRI) could lead to trapping of migrating protoplanetary embryos in the regions near an ice line in the disk and it significantly enhances formation/retention probability of Gas Giants against type-I migration.
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Toward a Deterministic Model of Planetary Formation IV: Effects of Type-I Migration
arXiv: Astrophysics, 2007Co-Authors: Shigeru Ida, Douglas N. C. LinAbstract:In a further development of a deterministic planet-formation model (Ida & Lin 2004), we consider the effect of type-I migration of protoplanetary embryos due to their tidal interaction with their nascent disks. During the early embedded phase of protostellar disks, although embryos rapidly emerge in regions interior to the ice line, uninhibited type-I migration leads to their efficient self-clearing. But, embryos continue to form from residual planetesimals at increasingly large radii, repeatedly migrate inward, and provide a main channel of heavy element accretion onto their host stars. During the advanced stages of disk evolution (a few Myr), the Gas surface density declines to values comparable to or smaller than that of the minimum mass nebula model and type-I migration is no longer an effective disruption mechanism for mars-mass embryos. Over wide ranges of initial disk surface densities and type-I migration efficiency, the surviving population of embryos interior to the ice line has a total mass several times that of the Earth. With this reservoir, there is an adequate inventory of residual embryos to subsequently assemble into rocky planets similar to those around the Sun. But, the onset of efficient Gas accretion requires the emergence and retention of cores, more massive than a few M_earth, prior to the severe depletion of the disk Gas. The formation probability of Gas giant planets and hence the predicted mass and semimajor axis distributions of Extrasolar Gas Giants are sensitively determined by the strength of type-I migration. We suggest that the observed fraction of solar-type stars with Gas giant planets can be reproduced only if the actual type-I migration time scale is an order of magnitude longer than that deduced from linear theories.
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Planetesimal Accretion onto Growing Proto-Gas Giant Planets
The Astrophysical Journal, 2007Co-Authors: Ji-lin Zhou, Douglas N. C. LinAbstract:The solar and Extrasolar Gas Giants appear to have diverse internal structure and metallicities. We examine a potential cause for these dispersions in the context of the conventional sequential accretion formation scenario. In principle, Gas accretion onto cores with masses below several times that of the Earth is suppressed by the energy released from the bombardment of residual planetesimals. Due to their aerodynamical and tidal interaction with the nascent Gas disk, planetesimals on eccentric orbits undergo slow orbital decay. We show that these planetesimals generally cannot pass through the mean motion resonances of the cores, and the suppression of planetesimal bombardment rate enables the cores to accrete Gas with little interruption, thus shortening the timescale of Gas giant formation. During growth from the cores to protoplanets, resonances overlap with each other, which strongly enhances the eccentricity excitation of the trapped planetesimals. Subsequent Gas drag induces the planetesimals to migrate to the proximity of the protoplanets and collide with them. This process leads to the resumption and a surge of planetesimal bombardment during the advanced stage of the protoplanet growth. Intruder planetesimals with different masses can either be resolved in the envelope or reach the core of the protoplanets. This mechanism may account for the diversity of the core-envelope structure between Jupiter, Saturn, and the metallicity dispersion inferred from the transiting Extrasolar planets. During the final formation stage of the proto-Gas Giants, gap opening in Gas disk leads to the accumulation of planetesimals outside the feeding zone of the protoplanets. The surface density enhancement promotes the subsequent buildup of cores for secondary Gas giant planets outside the orbit of the first-born protoplanets and the formation of eccentric multiple planet systems.
Komacek, Thaddeus David - One of the best experts on this subject based on the ideXlab platform.
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The Atmospheric Circulation and Evolution of Close-In Extrasolar Gas Giant Planets
The University of Arizona., 2018Co-Authors: Komacek, Thaddeus DavidAbstract:The atmospheres of Extrasolar Gas Giants that receive strong stellar irradiation, or “hot Jupiters,” are beginning to be characterized as a population. Spectro- photometric full-phase light curves of hot Jupiters allow for basic inferences of their atmospheric circulation, providing two key observables. First, they measure the amplitude of brightness variation, which has shown that the fractional brightness temperature difference between the dayside and nightside in the atmospheres of these tidally locked planets can approach unity. Additionally, each planet has a significant observed offset of the brightest point in their light curve, and offsets in the infrared ubiquitously occur before secondary eclipse. These infrared offsets are best explained by strong (~ a few km/s) eastward winds in hot Jupiter atmospheres. Motivated by these observations, I have developed a first-principles analytic theory that predicts dayside-nightside temperature differences and horizontal and vertical wind speeds as a function of incident stellar flux, rotation rate, frictional drag strength, and atmospheric pressure level. To complement and compare with this theory, I have performed a hierarchy of three-dimensional numerical simulations of the atmospheric circulation to explore changes with incident stellar flux, rotation rate, and drag strength. Both the theory and numerical simulations predict that the dayside-nightside temperature differences of hot Jupiters and their wind speeds should increase with increasing incident stellar flux and decrease with increasing drag strength. So far, this has been hinted at in the observed sample of hot Jupiter phase curves, but I predict that these broad trends will be robust with a larger observed population. I extend this theory to estimate vertical mixing rates, which is critical for understanding the impact of clouds and disequilibrium chemistry on observations of hot Jupiters. I find good agreement between numerically simulated vertical mixing rates and analytic theory, allowing one to use these theoretically predicted vertical mixing rates as input for one-dimensional models of cloud formation and disequilibrium chemistry in hot Jupiter atmospheres. I use this same suite of simulations to diagnose observable time-variability in the atmospheres of hot Jupiters, finding that purely hydrodynamic mechanisms induce significant variability in phase curve offset, amplitude, and secondary eclipse depth. Lastly, as many hot Jupiters are “inflated,” with radii larger than those in standard irradiated evolution models, I use one-dimensional planetary structure modeling to determine the effect that the atmospheric circulation has on the evolution of the planet by transporting heat toward the interior. I find that if the atmospheric circulation can deposit heat at pressures ??greater than 100 bars and if this heat is applied early (within ~ 10 Myr of formation) and persists throughout their evolution, then atmospheric circulation can explain the inflated radii of the bulk of the hot Jupiter sample
