N -Body Simulations of Terrestrial Planet Formation Under the Influence of a Hot Jupiter (original) (raw)

On the formation of terrestrial planets in hot-Jupiter systems

Astronomy & Astrophysics, 2007

"Context. There are numerous extrasolar giant planets which orbit close to their central stars. These “hot-Jupiters” probably formed in the outer, cooler regions of their protoplanetary disks, and migrated inward to ∼0.1 AU. Since these giant planets must have migrated through their inner systems at an early time, it is uncertain whether they could have formed or retained terrestrial planets. Aims. We present a series of calculations aimed at examining how an inner system of planetesimals/protoplanets, undergoing terrestrial planet formation, evolves under the influence of a giant planet undergoing inward type II migration through the region bounded between 5–0.1 AU. Methods. We have previously simulated the effect of gas giant planet migration on an inner system protoplanet/planetesimal disk using a N-body code which included gas drag and a prescribed migration rate. We update our calculations here with an improved model that incorporates a viscously evolving gas disk, annular gap and inner-cavity formation due to the gravitational field of the giant planet, and self-consistent evolution of the giant’s orbit. Results. We find that 60% of the solids disk survives by being scattered by the giant planet into external orbits. Planetesimals are scattered outward almost as efficiently as protoplanets, resulting in the regeneration of a solids disk where dynamical friction is strong and terrestrial planet formation is able to resume. A simulation that was extended for a few Myr after the migration of the giant planet halted at 0.1 AU, resulted in an apparently stable planet of ∼2 m⊕ forming in the habitable zone. Migration–induced mixing of volatile-rich material from beyond the “snowline” into the inner disk regions means that terrestrial planets that form there are likely to be water-rich. Conclusions. We predict that hot-Jupiter systems are likely to harbor water-abundant terrestrial planets in their habitable zones. These planets may be detected by 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.

Planet formation models: the interplay with the planetesimal disc

Astronomy & Astrophysics, 2012

Context. According to the sequential accretion model (or core-nucleated accretion model), giant planet formation is based first on the formation of a solid core which, when massive enough, can gravitationally bind gas from the nebula to form the envelope. The most critical part of the model is the formation time of the core: to trigger the accretion of gas, the core has to grow up to several Earth masses before the gas component of the protoplanetary disc dissipates. Aims. We calculate planetary formation models including a detailed description of the dynamics of the planetesimal disc, taking into account both gas drag and excitation of forming planets. Methods. We computed the formation of planets, considering the oligarchic regime for the growth of the solid core. Embryos growing in the disc stir their neighbour planetesimals, exciting their relative velocities, which makes accretion more difficult. Here we introduce a more realistic treatment for the evolution of planetesimals' relative velocities, which directly impact on the formation timescale. For this, we computed the excitation state of planetesimals, as a result of stirring by forming planets, and gas-solid interactions. Results. We find that the formation of giant planets is favoured by the accretion of small planetesimals, as their random velocities are more easily damped by the gas drag of the nebula. Moreover, the capture radius of a protoplanet with a (tiny) envelope is also larger for small planetesimals. However, planets migrate as a result of disc-planet angular momentum exchange, with important consequences for their survival: due to the slow growth of a protoplanet in the oligarchic regime, rapid inward type I migration has important implications on intermediate-mass planets that have not yet started their runaway accretion phase of gas. Most of these planets are lost in the central star. Surviving planets have masses either below 10 M ⊕ or above several Jupiter masses. Conclusions. To form giant planets before the dissipation of the disc, small planetesimals (∼0.1 km) have to be the major contributors of the solid accretion process. However, the combination of oligarchic growth and fast inward migration leads to the absence of intermediate-mass planets. Other processes must therefore be at work to explain the population of extrasolar planets that are presently known.

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."

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.""

Disk-Planet Interactions During Planet Formation, 2007

The discovery of close orbiting extrasolar giant planets led to extensive studies of disk planet interactions and the forms of migration that can result as a means of accounting for their location. Early work established the type I and type II migration regimes for low mass embedded planets and high mass gap forming planets respectively. While providing an attractive means of accounting for close orbiting planets intially formed at several AU, inward migration times for objects in the earth mass range were found to be disturbingly short, making the survival of giant planet cores an issue. Recent progress in this area has come from the application of modern numerical techniques wich make use of up to date supercomputer resources. These have enabled higher resolution studies of the regions close to the planet and the initiation of studies of planets interacting with disks undergoing MHD turbulence. This work has led to indications of how the inward migration of low to intermediate mass planets could be slowed down or reversed. In addition, the possibility of a new very fast type III migration regime, that can be directed inwards or outwards, that is relevant to partial gap forming planets in massive disks has been investigated.

Disk-Planet Interactions During Planet Formation

Protostars and Planets V, 2007

The discovery of close orbiting extrasolar giant planets led to extensive studies of diskplanet interactions and the forms of migration that can result as a means of accounting for their location. Early work established the type I and type II migration regimes for low-mass embedded planets and high-mass gap-forming planets respectively. While providing an attractive means of accounting for close orbiting planets initially formed at several AU, inward migration times for objects in the Earth-mass range were found to be disturbingly short, making the survival of giant planet cores an issue. Recent progress in this area has come from the application of modern numerical techniques that make use of up-to-date supercomputer resources. These have enabled higher-resolution studies of the regions close to the planet and the initiation of studies of planets interacting with disks undergoing magnetohydrodynamic turbulence. This work has led to indications of how the inward migration of low- to intermediate-mass planets could be slowed down or reversed. In addition, the possibility of a new very fast type III migration regime, which can be directed inward or outward, that is relevant to partial gap-forming planets in massive disks has been investigated.

Crowding-Out of Giants by Dwarfs: An Origin for the Lack of Companion Planets in Hot Jupiter Systems

The Astrophysical Journal, 2013

We investigate formation of close-in terrestrial planets from planetary embryos under the influence of a hot Jupiter (HJ) using gravitational N -body simulations that include gravitational interactions between the gas disk and the terrestrial planet (e.g., type I migration). Our simulations show that several terrestrial planets efficiently form outside the orbit of the HJ, making a chain of planets, and all of them gravitationally interact directly or indirectly with the HJ through resonance, which leads to inward migration of the HJ. We call this mechanism of induced migration of the HJ as "crowding out." The HJ is eventually lost by collision with the central star, and only several terrestrial planets remain. We also find that the efficiency of the crowding-out effect depends on model parameters; for example, the heavier the disk is, the more efficient the crowding out is. When planet formation occurs in a massive disk, the HJ can be lost to the central star and is never observed. On the other hand, for a less massive disk, the HJ and terrestrial planets can coexist; however, the companion planets can be below the detection limit of current observations. In both cases, systems with the HJ and terrestrial planets have little chance for detection. Therefore, our model naturally explains the lack of companion planets in HJ systems regardless of the disk mass. In effect, our model provide a theoretical prediction for future observations; additional planets can be discovered just outside the HJ, and their masses should generally be small. Subject headings: planets and satellites: formation -planets and satellites: terrestrial planets -planet-disk interactions

Exploring the architectures of planetary systems that form in thermally evolving viscous disc models

2016

The diversity in observed planets and planetary systems has raised the question of whether they can be explained by a single model of planet formation or whether multiple models are required. The work presented in this thesis aims to examine the oligarchic growth scenario, to determine whether the core accretion model, where planets form bottom-up, can recreate the observed diversity. I begin by exploring how changing model parameters such as disc mass and metallicity influence the types of planetary systems that emerge. I show that rapid inward migration leads to very few planets with masses mp > 10M⊕ surviving, with surviving planetary systems typically containing numerous low-mass planets. I examine what conditions are required for giant planets to form and survive migration, finding that for a planet similar to Jupiter to form and survive, it must form at an orbital radius rp > 10 au. In the second project in this thesis, I update the physical models before examining wheth...

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.