On the formation of hot Neptunes and super-Earths

McNeil, D. S.; Nelson, Richard P.

doi:10.1111/j.1365-2966.2009.15805.x

Cited by 87 publications

(54 citation statements)

References 69 publications

(166 reference statements)

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“…As such, a suitable model would involve a domain ranging from as far in as 0.1 au out to approximately 50 au. Such a simulation is beyond current modelling techniques because of the required numbers of protoplanets and planetesimals, even for the method presented by McNeil & Nelson (2009, 2010) which utilizes multiple time‐steps in a parallel symplectic integrator. Instead, such global models of planetary formation are probably going to require efficient use of modern GPU technology. Gas disc model .…”

Section: Discussionmentioning

confidence: 99%

“…Terquem & Papaloizou (2007) examined the formation of hot‐super‐Earths and hot‐Neptunes using N ‐body simulations with type I migration. McNeil & Nelson (2009, 2010) carried out large‐scale simulations of oligarchic growth to explore the formation of systems of hot‐Neptunes and super‐Earths, such as those around the stars Gliese 581 and HD 698433, using a novel symplectic integrator with multiple time‐steps. An alternative to these approaches has been planetary population synthesis modelling, as presented by Ida & Lin (2008, 2010), Mordasini, Alibert & Benz (2009b), Mordasini et al (2009a) and Miguel, Guilera & Brunini (2011).…”

Section: Introductionmentioning

confidence: 99%

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Global models of planetary system formation in radiatively-inefficient protoplanetary discs

Hellary

Nelson

2011

Monthly Notices of the Royal Astronomical Society

107

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We present the results of N‐body simulations of planetary system formation in radiatively‐inefficient disc models, where positive corotation torques may counter the rapid inward migration of low‐mass planets driven by Lindblad torques. The aim of this work is to examine the nature of planetary systems that arise from oligarchic growth in such discs. We adapt the commonly used Mercury‐6 symplectic integrator by including simple prescriptions for planetary migration (types I and II), planetary atmospheres that enhance the probability of planetesimal accretion by protoplanets, gas accretion on to forming planetary cores, and gas disc dispersal. We perform a suite of simulations for a variety of disc models with power‐law surface density and temperature profiles, with a focus on models in which unsaturated corotation torques can drive outward migration of protoplanets. In some models, we account for the quenching of corotation torques which arises when planetary orbits become eccentric. Approximately half of our simulations lead to the successful formation of gas giant planets with a broad range of masses and semimajor‐axes. Giant planetary masses range from being approximately equal to that of Saturn up to approximately twice that of Jupiter. The semimajor‐axes of these range from being ∼0.2 au up to ∼75 au, with disc models that drive stronger outward migration favouring the formation of longer period giant planets. Out of a total of 20 giant planets being formed in our simulation suite, we obtain three systems that contain two giants. No super‐Earth or Neptune‐mass planets were present in the final stages of our simulations, in contrast to the large abundance of such objects being discovered in observation surveys. This result arises because of rapid inward migration suffered by massive planetary cores that form early in the disc lifetime (for which the corotation torques saturate), combined with gas accretion on to massive cores which leads them to become gas giants. Numerous low‐mass planets are formed and survive in the simulations, with masses ranging from a few tenths of an Earth mass up to ∼3 Earth masses. Simulations in which the quenching of corotation torques for planets on modestly eccentric orbits was included failed to produce any giant planets, apparently because Lindblad torques induce rapid inward migration of planetary cores in these systems. We conclude that convergent migration induced by corotation torques operating during planetary formation can enhance the growth rate of planetary cores, but these often migrate into the central star because corotation torques saturate. Outward migration of planetary cores of modest mass can lead to the formation of gas giant planets at large distances from the central star, similar to those observed recently through direct imaging surveys. The excitation of planetary eccentricities through planet–planet scattering during oligarchic growth may quench the effects of corotation torques, however, such that inward migration is driven by Lindblad torques.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Global models of planetary system formation in radiatively-inefficient protoplanetary discs

Hellary

Nelson

2011

Monthly Notices of the Royal Astronomical Society

107

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“…Ikoma & Genda (2006)), and volatiles (a.k.a "ices") (e.g. McNeil & Nelson (2010)). Given the present extreme stellar irradiation, one would expect volatiles, if present on the planet, Corot-7b's Mass Fig.…”

Section: Description and Possible Originmentioning

confidence: 99%

Composition and fate of short-period super-Earths

Valencia¹,

Ikoma

Guillot³

et al. 2010

A&A

234

294

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Context. The discovery of CoRoT-7b, a planet of a radius 1.68 ± 0.09 R ⊕ , a mass 4.8 ± 0.8 M ⊕ , and an orbital period of 0.854 days demonstrates that small planets can orbit extremely close to their star. Aims. Several questions arise concerning this planet, in particular concerning its possible composition, and fate. Methods. We use knowledge of hot Jupiters, mass loss estimates and models for the interior structure and evolution of planets to understand its composition, structure and evolution. Results. The inferred mass and radius of CoRoT-7b are consistent with a rocky planet that would be significantly depleted in iron relative to the Earth. However, a one sigma increase in mass (5.6 M ⊕ ) and one sigma decrease in size (1.59 R ⊕ ) would make the planet compatible with an Earth-like composition (33% iron, 67% silicates). Alternatively, it is possible that CoRoT-7b contains a significant amount of volatiles. For a planet made of an Earth-like interior and an outer volatile-rich vapour envelope, an equally good fit to the measured mass and radius is found for a mass of the vapour envelope equal to 3% (and up to 10% at most) of the planetary mass. Because of its intense irradiation and small size, we determine that the planet cannot possess an envelope of hydrogen and helium of more than 1/10 000 of its total mass. We show that a relatively significant mass loss ∼10 11 g s −1 is to be expected and that it should prevail independently of the planet's composition. This is because to first order, the hydrodynamical escape rate is independent of the mean molecular mass of the atmosphere, and because given the intense irradiation, even a bare rocky planet would be expected to possess an equilibrium vapour atmosphere thick enough to capture stellar UV photons. Clearly, this escape rate rules out the possibility that a hydrogen-helium envelope is present, as it would escape in only ∼1 Ma. A water vapour atmosphere would escape in ∼1 Ga, indicating that this is a plausible scenario. The origin of CoRoT-7b cannot be inferred from the present observations: It may have always had a rocky composition; it may be the remnant of a Uranus-like ice giant, or a gas giant with a small core that has been stripped of its gaseous envelope. Conclusions. With high enough sensitivity, spectroscopic transit observations of CoRoT-7 should constrain the composition of the evaporating flow and therefore allow us to distinguish between a rocky planet and a volatile-rich vapour planet. In addition, the theoretical tools developed in this study are applicable to any short-period transiting super-Earth and will be important to understanding their origins.

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“…However, it can be quite difficult to concentrate planets close to the host star to the degree observed in STIPs (McNeil & Nelson 2010). Also, migrating planets tend to become trapped in orbits of low-order mean motion resonances, which is not a particular feature of STIPs (Baruteau et al 2014;Fabrycky et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Inside-out Planet Formation. IV. Pebble Evolution and Planet Formation Timescales

Tan

Zhu

et al. 2018

ApJ

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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 e yr −1 and relatively low viscosity conditions in the DZIB region, i.e., a Shakura-Sunyaev parameter of α∼10 .

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On the formation of hot Neptunes and super-Earths

Cited by 87 publications

References 69 publications

Global models of planetary system formation in radiatively-inefficient protoplanetary discs

Global models of planetary system formation in radiatively-inefficient protoplanetary discs

Composition and fate of short-period super-Earths

Inside-out Planet Formation. IV. Pebble Evolution and Planet Formation Timescales

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