On the formation of terrestrial planets in hot-Jupiter systems (original) (raw)
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The effect of type I migration on the formation of terrestrial planets in hot-Jupiter systems
Astronomy & Astrophysics, 2007
"Context. Our previous models of a giant planet migrating through an inner protoplanet/planetesimal disk find that the giant shepherds a portion of the material it encounters into interior orbits, whilst scattering the rest into external orbits. Scattering tends to dominate, leaving behind abundant material that can accrete into terrestrial planets. Aims. We add to the possible realism of our model by simulating type I migration forces which cause an inward drift, and strong eccentricity and inclination damping of protoplanetary bodies. This extra dissipation might be expected to enhance shepherding at the expense of scattering, possibly modifying our previous conclusions. Methods. We employ an N-body code that is linked to a viscous gas disk algorithm capable of simulating: gas accretion onto the central star; gap formation in the vicinity of the giant planet; type II migration of the giant planet; type I migration of protoplanets; and the effect of gas drag on planetesimals. We use the code to re-run three scenarios from a previous work where type I migration was not included. Results. The additional dissipation introduced by type I migration enhances the inward shepherding of material but does not severely reduce scattering. We find that >50% of the solids disk material still survives the migration in scattered exterior orbits: most of it well placed to complete terrestrial planet formation at <3 AU. The shepherded portion of the disk accretes into hot-Earths, which survive in interior orbits for the duration of our simulations. Conclusions. Water-rich terrestrial planets can form in the habitable zones of hot-Jupiter systems and hot-Earths and hot-Neptunes may also be present. These systems should be targets of future planet search missions."
On the possibility of terrestrial planet formation in hot-Jupiter systems
International Journal of Astrobiology, 2006
About a fifth of the exoplanetary systems that have been discovered contain a so-called hot-Jupiter – a giant planet orbiting within 0.1 AU of the central star. Since these stars are typically of the F/G spectral type, the orbits of any terrestrial planets in their habitable zones at y1 AU should be dynamically stable. However, because hot-Jupiters are thought to have formed in the outer regions of a protoplanetary disc, and to have then migrated through the terrestrial planet zone to their final location, it is uncertain whether terrestrial planets can actually grow and be retained in these systems. In this paper we review attempts to answer this question. Initial speculations, based on the assumption that migrating giant planets will clear planet-forming material from their swept zone, all concluded that hot-Jupiter systems should lack terrestrial planets. We show that this assumption may be incorrect, for when terrestrial planet formation and giant planet migration are simulated simultaneously, abundant solid material is predicted to remain from which terrestrial planet growth can resume.
Terrestrial planet formation in low-eccentricity warm-Jupiter systems
Astronomy & Astrophysics, 2009
""Context. Extrasolar giant planets are found to orbit their host stars with a broad range of semi-major axes 0.02 ≤ a ≤ 6 AU. Current theories suggest that giant planets orbiting at distances between 0.02−2 AU probably formed at larger distances and migrated to their current locations via type II migration, disturbing any inner system of forming terrestrial planets along the way. Migration probably halts because of fortuitously-timed gas disk dispersal. Aims. The aim of this paper is to examine the effect of giant planet migration on the formation of inner terrestrial planet systems. We consider situations in which the giant planet halts migration at semi-major axes in the range 0.13−1.7 AU due to gas disk dispersal, and examine the effect of including or neglecting type I migration forces on the forming terrestrial system. Methods. We employ an N-body code that is linked to a viscous gas disk algorithm capable of simulating gas loss via accretion onto the central star and photoevaporation, gap formation by the giant planet, type II migration of the giant, optional type I migration of protoplanets, and gas drag on planetesimals. Results. Most of the inner system planetary building blocks survive the passage of the giant planet, either by being shepherded inward or scattered into exterior orbits. Systems of one or more hot-Earths are predicted to form and remain interior to the giant planet, especially if type II migration has been limited, or where type I migration has affected protoplanetary dynamics. Habitable planets in low-eccentricity warm-Jupiter systems appear possible if the giant planet makes a limited incursion into the outer regions of the habitable zone (HZ), or traverses its entire width and ceases migrating at a radial distance of less than half that of the HZ’s inner edge. Conclusions. Type II migration does not prevent terrestrial planet formation. A wide variety of planetary system architectures exists that can potentially host habitable planets.""
Terrestrial Planet Formation in Exoplanetary Systems
2008
Many giant exoplanets are thought to have formed in the outer regions of a protoplanetary disk, and to have then migrated close to the central star. Hence, it is uncertain whether terrestrial planets can grow and be retained in these `hot-Jupiter' systems. Previous speculations, based on the assumption that migrating giant planets will clear planet-forming material from their swept zone, have concluded that such systems should lack terrestrial planets. This thesis presents a succession of four planet formation models, of increasing sophistication, aimed at examining how an inner system of solid bodies, undergoing terrestrial planet formation, evolves under the inuence of a giant planet undergoing inward type II migration. Protoplanetary growth is handled by an N+N'-body code, capable of simulating the accretion of a two-phase protoplanetplanetesimal population, and tracking their volatiles content. Gas dynamics and related dissipative processes are calculated with a linked viscous gas disk algorithm capable of simulating: gas accretion onto the central star and photoevaporation; type II migration of the giant planet; type I migration of protoplanets; and the effect of gas drag on planetesimals. In all simulations, a large fraction of the inner system material survives the passage of the giant, either by accreting into massive planets shepherded inward of the giant (reminiscent of the short-period `hot-Earths' discovered recently), or by being scattered into external orbits. Typically, sufcient mass is scattered outward to provide for the eventual accretion of a set of terrestrial planets in external orbits. The results of this thesis lead to the prediction that hot-Jupiter systems are likely to harbor water-rich terrestrial planets in their habitable zones and hot-Earths may also be present. These planets may be detected by future planet search missions.
N -Body Simulations of Terrestrial Planet Formation Under the Influence of a Hot Jupiter
The Astrophysical Journal, 2014
We investigate the formation of multiple-planet systems in the presence of a hot Jupiter using extended N -body simulations that are performed simultaneously with semi-analytic calculations. Our primary aims are to describe the planet formation process starting from planetesimals using highresolution simulations, and to examine the dependences of the architecture of planetary systems on input parameters (e.g., disk mass, disk viscosity). We observe that protoplanets that arise from oligarchic growth and undergo type I migration stop migrating when they join a chain of resonant planets outside the orbit of a hot Jupiter. The formation of a resonant chain is almost independent of our model parameters, and is thus a robust process. At the end of our simulations, several terrestrial planets remain at around 0.1 AU. The formed planets are not equal-mass; the largest planet constitutes more than 50 percent of the total mass in the close-in region, which is also less dependent on parameters. In the previous work of this paper (Ogihara et al. 2013), we have found a new physical mechanism of induced migration of the hot Jupiter, which is called a crowding-out. If the hot Jupiter opens up a wide gap in the disk (e.g., owing to low disk viscosity), crowding-out becomes less efficient and the hot Jupiter remains. We also discuss angular momentum transfer between the planets and disk.
Outward Migration of Jupiter and Saturn in Evolved Gaseous Disks
Astrophysical Journal, 2012
The outward migration of a pair of resonant-orbit planets, driven by tidal interactions with a gas-dominated disk, is studied in the context of evolved solar nebula models. The planets' masses, M 1 and M 2, correspond to those of Jupiter and Saturn. Hydrodynamical calculations in two and three dimensions are used to quantify the migration rates and analyze the conditions under which the outward migration mechanism may operate. The planets are taken to be fully formed after 106 and before 3 × 106 years. The orbital evolution of the planets in an evolving disk is then calculated until the disk's gas is completely dissipated. Orbital locking in the 3:2 mean motion resonance may lead to outward migration under appropriate conditions of disk viscosity and temperature. However, resonance locking does not necessarily result in outward migration. This is the case, for example, if convergent migration leads to locking in the 2:1 mean motion resonance, as post-formation disk conditions seem to suggest. Accretion of gas on the planets may deactivate the outward migration mechanism by raising the mass ratio M 2/M 1 and/or by reducing the accretion rate toward the star, and hence depleting the inner disk. For migrating planets locked in the 3:2 mean motion resonance, there are stalling radii that depend on disk viscosity and on stellar irradiation, when it determines the disk's thermal balance. Planets locked in the 3:2 orbital resonance that start moving outward from within 1-2 AU may reach beyond ≈5 AU only under favorable conditions. However, within the explored space of disk parameters, only a small fraction—less than a few percent—of the models predict that the interior planet reaches beyond ≈4 AU.
Astronomy & Astrophysics, 2005
Giant planets found orbiting close to their central stars, the so called “hot Jupiters”, are thought to have originally formed in the cooler outer regions of a protoplanetary disk and then to have migrated inward via tidal interactions with the nebula gas. We present the results of N-body simulations which examine the effect such gas giant planet migration has on the formation of terrestrial planets. The models incorporate a 0.5 Jupiter mass planet undergoing type II migration through an inner protoplanet-planetesimal disk, with gas drag included. Each model is initiated with the inner disk being at successively increased levels of maturity, so that it is undergoing either oligarchic or giant impact style growth as the gas giant migrates. In all cases, a large fraction of the disk mass survives the passage of the giant, either by accreting into massive terrestrial planets shepherded inward of the giant, or by being scattered into external orbits. Shepherding is favored in younger disks where there is strong dynamical friction from planetesimals and gas drag is more influential, whereas scattering dominates in more mature disks where dissipation is weaker. In each scenario, sufficient mass is scattered outward to provide for the eventual accretion of a set of terrestrial planets in external orbits, including within the system’s habitable zone. This scattering, however, significantly reduces the density of solid material, indicating that further accretion will occur over very long time scales. A particularly interesting result is the generation of massive, short period, terrestrial planets from compacted material pushed ahead of the giant. These planets are reminiscent of the short period Neptune-mass planets discovered recently, suggesting that such “hot Neptunes” could form locally as a by product of giant planet migration.
The dynamics of Jupiter and Saturn in the gaseous protoplanetary disk
Icarus, 2007
We study the possibility that the mutual interactions between Jupiter and Saturn prevented Type II migration from driving these planets much closer to the Sun. Our work extends previous results by , by exploring a wider set of initial conditions and disk parameters, and by using a new hydrodynamical code that properly describes for the global viscous evolution of the disk. Initially both planets migrate towards the Sun, and Saturn's migration tends to be faster. As a consequence, they eventually end up locked in a mean motion resonance. If this happens in the 2:3 resonance, the resonant motion is particularly stable, and the gaps opened by the planets in the disk may overlap.
The formation and habitability of terrestrial planets in the presence of close-in giant planets
2005
'Hot jupiters,'giant planets with orbits very close to their parent stars, are thought to form farther away and migrate inward via interactions with a massive gas disk. If a giant planet forms and migrates quickly, the planetesimal population has time to re-generate in the lifetime of the disk and terrestrial planets may form [PJ Armitage, A reduced efficiency of terrestrial planet formation following giant planet migration, Astrophys. J. 582 (2003) L47–L50].
Shaping of the Inner Solar System by the Gas-Driven Migration of Jupiter
Proceedings of the International Astronomical Union, 2012
A persistent difficulty in terrestrial planet formation models is creating Mars analogs with the appropriate mass: Mars is typically an order of magnitude too large in simulations. Some recent work found that a small Mars can be created if the planetesimal disk from which the planets form has an outermost edge at 1.0 AU. However, that work and no previous work could produce a truncation of the planetesimal disk while also explaining the mass and structure of the asteroid belt. We show that gas-driven migration of Jupiter inward to 1.5 AU, before its subsequent outward migration, can truncate the disk and repopulate the asteroid belt. This dramatic migration history of Jupiter suggests that the dynamical behavior of our giant planets was more similar to that inferred for extra-solar planets than previously thought, as both have been characterised by substantial radial migration.