Hot super-Earths and giant planet cores from different migration histories

Cossou, Christophe; Raymond, Sean N.; Hersant, F.; Pierens, A.

doi:10.1051/0004-6361/201424157

Cited by 183 publications

(222 citation statements)

References 150 publications

(292 reference statements)

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“…only rarely become giant planets located at Earth's distance from the Sun and beyond 8,9 , in contrast with observations 10 . Here we report that asymmetries in the temperature rise associated with accreting infalling material 11,12 produce a force (which gives rise to an effect that we call "heating torque") that counteracts inward migration.…”

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confidence: 64%

“…The heating torque has a large efficiency over the mass interval 0.5 − 3 M ⊕ , which is precisely the range of masses where counteracting inward migration is required in order to allow further embryo growth at distances where giant planets are expected to form 9 . Masses smaller than 0.5 M ⊕ , for which the heating torque has a lower efficiency, migrate inward only a negligible fraction of their orbital radius by the time they double their mass.…”

mentioning

confidence: 99%

“…The general picture that now emerges is that embryos with masses in the range 0.3-5 Earth masses are able to avoid inward migration when accretion rates are large. By the time the heating torque efficiency drops, they have entered a regime in which other mechanisms driving outward migration come into play 5,9,15 .…”

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Planet heating prevents inward migration of planetary cores

Benítez-Llambay

Masset

Koenigsberger

et al. 2015

Nature

164

198

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Planetary systems are born in the disks of gas, dust and rocky fragments that surround newly formed stars. Solid content assembles into ever-larger rocky fragments that eventually become planetary embryos. These then continue their growth by accreting leftover material in the disc. Concurrently, tidal effects in the disc cause a radial drift in the embryo orbits, a process known as migration [1][2][3][4] . Fast inward migration is predicted by theory for embryos smaller than three to five Earth masses [5][6][7] . With only inward migration, these embryos can only rarely become giant planets located at Earth's distance from the Sun and beyond 8,9 , in contrast with observations 10 . Here we report that asymmetries in the temperature rise associated with accreting infalling material 11, 12 produce a force (which gives rise to an effect that we call "heating torque") that counteracts inward migration. This provides a channel for the formation of giant planets 8 and also explains the strong planet-metallicity correlation found between the incidence of giant planets and the heavy-element abundance of the host stars 13, 14 .We solve the equations governing the disc hydrodynamics in combination with the equations of radiative transfer. Planets have an angular momentum that increases with their orbital radius. In the case of a nearly circular orbit, the rate of change of angular momentum, or torque, gives the migration rate. Our calculations are performed in three dimensions, yielding a reliable value for the net torque, from which the direction and rate of migration are inferred.Our fiducial computation is one in which a rocky core with 3 Earth masses is located at a distance comparable to that of Jupiter from the Sun and is being bombarded by solid material at a rate that doubles its mass in 100 thousand years. We assume that the gravitational energy of the infalling solid material is transformed entirely into heat and ultimately radiated by the planet 11 . A second computation is performed with the same set up, but without the planet's radiation, in order to distinguish the effects of the heating torque from other torques. We find that the heating torque (defined as the torque difference between cases with accretion turned respectively on and off) has a positive sign (figure 1), which enables it to counteract the effect of the standard, negative torque.The latter includes all torque components of the non-heating case, and is always negative for small 2 mass embryos (typically smaller than 5 M ⊕ , where M ⊕ is the Earth's mass). Thus, the effect of the heating torque is to either slow down the inward migration, cancel it, or reverse its direction.The most important factors governing the strength of the heating torque and thus, the direction of migration, are the accretion rate of the embryo, its mass and the opacity of the disc. For our fiducial values of opacity, disc structure and embryo mass, we find that outward migration occurs for accretion rates corresponding to a mass doubling time less than approximately 60 t...

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Planet heating prevents inward migration of planetary cores

Benítez-Llambay

Masset

Koenigsberger

et al. 2015

Nature

164

198

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“…It is also pointed out that the mass dependence of planet traps can originate from a unique feature of the corotation torque -saturation (Kretke & Lin 2012;Hellary & Nelson 2012;Bitsch et al 2013;Cossou et al 2014;Dittkrist et al 2014). In principle, the corotation torque is characterized by the gas motion at the socalled horse-shoe orbit (e.g., Ward 1991;Masset 2002).…”

Section: Planet Trapsmentioning

confidence: 99%

Super-Earths as Failed Cores in Orbital Migration Traps

Hasegawa

2016

ApJ

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We explore whether close-in super-Earths were formed as rocky bodies that failed to grow fast enough to become the cores of gas giants before the natal protostellar disk dispersed. We model the failed cores' inward orbital migration in the low-mass or type I regime, to stopping points at distances where the tidal interaction with the protostellar disk applies zero net torque. The three kinds of migration traps considered are those due to the dead zone's outer edge, the ice line, and the transition from accretion to starlight as the disk's main heat source. As the disk disperses, the traps move toward final positions near or just outside 1 au. Planets at this location exceeding about 3 M ⊕ open a gap, decouple from their host trap, and migrate inward in the high-mass or type II regime to reach the vicinity of the star. We synthesize the population of planets formed in this scenario, finding that some fraction of the observed super-Earths can be failed cores. Most super-Earths formed this way have more than 4 M ⊕ , so their orbits when the disk disperses are governed by type II migration. These planets have solid cores surrounded by gaseous envelopes. Their subsequent photoevaporative mass loss is most effective for masses originally below about 6 M ⊕ . The failed core scenario suggests a division of the observed super-Earth mass-radius diagram into five zones according to the inferred formation history.

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“…Paardekooper et al (2011) revised the torque formula by taking into account the effects of viscous and thermal diffusion on the corotation torque, which indicates that only planets with a limited range of masses can experience the non-linear corotation torque due to saturation effects. In fact, planets with masses smaller than a few Earth masses are not affected by the nonlinear corotation torque (the horseshoe torque) and they migrate inward under the influence of the Lindblad torque (e.g., Kretke & Lin 2012;Hellary & Nelson 2012;Cossou et al 2014), which means that the solar system's terrestrial planets still have the problem of inward migration. However, if the slope of the gas surface density becomes large enough, the positive linear corotation torque can reverse the migration.…”

Section: Introductionmentioning

confidence: 99%

Formation of terrestrial planets in disks evolving via disk winds and implications for the origin of the solar system’s terrestrial planets

Ogihara

Kobayashi

Inutsuka

et al. 2015

A&A

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Context. Recent three-dimensional magnetohydrodynamical simulations have identified a disk wind by which gas materials are lost from the surface of a protoplanetary disk, which can significantly alter the evolution of the inner disk and the formation of terrestrial planets. A simultaneous description of the realistic evolution of the gaseous and solid components in a disk may provide a clue for solving the problem of the mass concentration of the terrestrial planets in the solar system. Aims. We simulate the formation of terrestrial planets from planetary embryos in a disk that evolves via magnetorotational instability and a disk wind. The aim is to examine the effects of a disk wind on the orbital evolution and final configuration of planetary systems. Methods. We perform N-body simulations of sixty 0.1 Earth-mass embryos in an evolving disk. The evolution of the gas surface density of the disk is tracked by solving a one-dimensional diffusion equation with a sink term that accounts for the disk wind. Results. We find that even in the case of a weak disk wind, the radial slope of the gas surface density of the inner disk becomes shallower, which slows or halts the Type I migration of embryos. If the effect of the disk wind is strong, the disk profile is significantly altered (e.g., positive surface density gradient, inside-out evacuation), leading to outward migration of embryos inside ∼1 AU. Conclusions. Disk winds play an essential role in terrestrial planet formation inside a few AU by changing the disk profile. In addition, embryos can undergo convergent migration to ∼1 AU in certainly probable conditions. In such a case, the characteristic features of the solar system's terrestrial planets (e.g., mass concentration around 1 AU, late giant impact) may be reproduced.

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Hot super-Earths and giant planet cores from different migration histories

Cited by 183 publications

References 150 publications

Planet heating prevents inward migration of planetary cores

Planet heating prevents inward migration of planetary cores

Super-Earths as Failed Cores in Orbital Migration Traps

Formation of terrestrial planets in disks evolving via disk winds and implications for the origin of the solar system’s terrestrial planets

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