Dawes Review 7: The Tidal Downsizing Hypothesis of Planet Formation

Nayakshin, Sergei

doi:10.1017/pasa.2016.55

Cited by 88 publications

(70 citation statements)

References 274 publications

(814 reference statements)

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“…It can be argued that this approach, which does not rely on unknown or improperly modeled physics, is less prone to bias the estimation of the planet frequency. However, it puts an equal statistical weight on planets at all masses and separations, which is in contradiction with all models of planet formation, either based on CA (Mordasini et al 2009;Ida & Lin 2004;Ida et al 2013) or GI (Forgan & Rice 2013;Forgan et al 2015;Nayakshin 2017), which all agree that the formation of very massive companions at large orbital separation occurs much less frequently than less massive, closer-in planets. Although based on models, this information is important to take into account prior to the analysis.…”

Section: Discussioncontrasting

confidence: 64%

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The VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits

Vigan

Bonavita

Biller

et al. 2017

A&A

129

136

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Understanding the formation and evolution of giant planets (≥1 M Jup ) at wide orbital separation (≥5 AU) is one of the goals of direct imaging. Over the past 15 yr, many surveys have placed strong constraints on the occurrence rate of wide-orbit giants, mostly based on non-detections, but very few have tried to make a direct link with planet formation theories. In the present work, we combine the results of our previously published VLT/NaCo large program with the results of 12 past imaging surveys to constitute a statistical sample of 199 FGK stars within 100 pc, including three stars with sub-stellar companions. Using Monte Carlo simulations and assuming linear flat distributions for the mass and semi-major axis of planets, we estimate the sub-stellar companion frequency to be within 0.75-5.70% at the 68% confidence level (CL) within 20-300 AU and 0.5-75 M Jup , which is compatible with previously published results. We also compare our results with the predictions of state-of-the-art population synthesis models based on the gravitational instability (GI) formation scenario with and without scattering. We estimate that in both the scattered and non-scattered populations, we would be able to detect more than 30% of companions in the 1-75 M Jup range (95% CL). With the three sub-stellar detections in our sample, we estimate the fraction of stars that host a planetary system formed by GI to be within 1.0-8.6% (95% CL). We also conclude that even though GI is not common, it predicts a mass distribution of wide-orbit massive companions that is much closer to what is observed than what the core accretion scenario predicts. Finally, we associate the present paper with the release of the Direct Imaging Virtual Archive (DIVA), a public database that aims at gathering the results of past, present, and future direct imaging surveys.

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Section: Discussioncontrasting

confidence: 64%

“…If the contraction of the fragment is slow enough, and the migration and sedimentation fast enough, then the fragment may be stripped of gas by tidal interactions with the host star and this process could in principle form both close-in, and wide orbit, planets (Nayakshin 2017).…”

Section: Planet Population Synthesis Modelsmentioning

confidence: 99%

The VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits

Vigan

Bonavita

Biller

et al. 2017

A&A

129

136

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“…To better understand the diversity of planetary composition in this size regime, a larger sample of exoplanets with well-constrained mass and radius is needed. A better insight into planetary composition will also make it possible to constrain planetary formation processes, since the two alternative planetary formation theories, namely core accretion (Lissauer 1993) and gravitational instability models (Nayakshin 2017), predict different metal-gas ratio compositions.…”

Section: Introductionmentioning

confidence: 99%

Precise masses for the transiting planetary system HD 106315 with HARPS

Barros

Gosselin

Lillo-Box

et al. 2017

A&A

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Context. The multi-planetary system HD 106315 was recently found in K2 data . The planets have periods of P b ∼ 9.55 and P c ∼ 21.06 days, and radii of r b = 2.44±0.17 R ⊕ and r c = 4.35±0.23 R ⊕ . The brightness of the host star (V=9.0 mag) makes it an excellent target for transmission spectroscopy. However, to interpret transmission spectra it is crucial to measure the planetary masses. Aims. We obtained high precision radial velocities for HD 106315 to determine the mass of the two transiting planets discovered with Kepler K2. Our successful observation strategy was carefully tailored to mitigate the effect of stellar variability. Methods. We modelled the new radial velocity data together with the K2 transit photometry and a new ground-based partial transit of HD 106315c to derive system parameters. Results. We estimate the mass of HD 106315b to be 12.6 ± 3.2 M ⊕ and the density to be 4.7 ± 1.7 g cm −3 , while for HD 106315c we estimate a mass of 15.2 ± 3.7 M ⊕ and a density of 1.01 ± 0.29 g cm −3 . Hence, despite planet c having a radius almost twice as large as planet b, their masses are consistent with one another. Conclusions. We conclude that HD 106315c has a thick hydrogen-helium gaseous envelope. A detailed investigation of HD 106315b using a planetary interior model constrains the core mass fraction to be 5-29%, and the water mass fraction to be 10-50%. An alternative, not considered by our model, is that HD 106315b is composed of a large rocky core with a thick H-He envelope. Transmission spectroscopy of these planets will give insight into their atmospheric compositions and also help constrain their core compositions.

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“…If clumps do not accrete gas and contract slowly, then they are tidally disrupted (Boley et al 2010;Nayakshin 2010a) after they migrate too close to the host star, leaving behind a solid core (if grain sedimentation within the clump was sufficiently rapid; see Boss 1997;Helled & Schubert 2008;Helled, Podolak & Kovetz 2008;Nayakshin 2011). This channel of clump evolution is the base for the tidal downsizing scenario of planet formation (see the recent review in Nayakshin 2017).…”

Section: Introductionmentioning

confidence: 99%

A desert of gas giant planets beyond tens of au: from feast to famine

Nayakshin

2017

Monthly Notices of the Royal Astronomical Society

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It is argued that frequency of gravitational fragmentation of young massive discs around FGK stars may be much higher than commonly believed. Numerical simulations presented here show that survival of gas giant planets at large separations from their host stars is very model dependent. Low-mass clumps in slowly cooling discs are found to accrete gas very slowly and migrate inward very rapidly in the well-known type I regime (no gap open). They are either tidally disrupted or survive as planets inwards of about 10 au. In this regime, probability of clump survival at large separations is extremely low, perhaps as low as 0.001, requiring up to a dozen clumps per star early on to explain the observed population. In contrast, initially massive clumps or low-mass clumps born in rapidly cooling discs accrete gas rapidly. Opening deep gaps in the disc, they migrate in the much slower type II regime and are more likely to survive beyond tens of au. The frequency of disc fragmentation in this case is at the per cent level if the clump growth saturates at brown dwarf masses but may be close to 100 per cent if clumps evolve into low stellar mass companions. Taking these theoretical uncertainties into account, current observations limit the number of planet mass clumps hatched by young massive discs around FGK stars to between 0.01 and ∼10. A deeper theoretical understanding of such discs is needed to narrow this uncertainty down.

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Dawes Review 7: The Tidal Downsizing Hypothesis of Planet Formation

Cited by 88 publications

References 274 publications

The VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits

The VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits

Precise masses for the transiting planetary system HD 106315 with HARPS

A desert of gas giant planets beyond tens of au: from feast to famine

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