Planetary mass–radius relations across the galaxy

Michel, Arnaud; Haldemann, Jonas; Mordasini, Christoph; Alibert, Yann

doi:10.1051/0004-6361/201936916

Cited by 13 publications

(9 citation statements)

References 60 publications

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“…This model lacks some of the relevant physical processes, and the approximation given in Mordasini (2020) does not allow to form TOI-421 b with 0.5-0.7 of its mass in the atmosphere within the snow line. However, Michel et al (2020) predicts that beyond the snow line, planets can be formed with a significant fraction of their mass being water ice (up to ∼ 70%), which would be compatible with the initial parameters we constrained here.…”

Section: Discussionsupporting

confidence: 79%

Atmospheric mass loss and stellar wind effects in young and old systems – II. Is TOI-942 the past of TOI-421 system?

Kubyshkina

Vidotto

D’Angelo

et al. 2021

Monthly Notices of the Royal Astronomical Society

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The two planetary systems TOI-942 and TOI-421 share many similar characteristics, apart from their ages (50 Myr and 9 Gyr). Each of the stars hosts two sub-Neptune-like planets at similar orbits and in similar mass ranges. In this paper, we aim to investigate whether the similarity of the host stars and configuration of the planetary systems can be taken as proof that the two systems were formed and evolved in a similar way. In paper I of this series, we performed a comparative study of these two systems using 3D modeling of atmospheric escape and its interaction with the stellar wind, for the four planets. We demonstrated that though the strong wind of the young star has a crucial effect on observable signatures, its effect on the atmospheric mass loss is minor in the evolutionary context. Here, we use atmosphere evolution models to track the evolution of planets in the younger system TOI-942 and also to constrain the past of the TOI-421 system. We demonstrate that despite all the similarities, the two planetary systems are on two very different evolutionary pathways. The inner planet in the younger system, TOI-942, will likely lose all of its atmosphere and become a super-Earth-like planet, while the outer planet will become a typical sub-Neptune. Concerning the older system, TOI-421, our evolution modeling suggests that they must have started their evolution with very substantial envelopes, which can be a hint of formation beyond the snow line.

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Section: Discussionsupporting

confidence: 79%

Atmospheric mass loss and stellar wind effects in young and old systems – II. Is TOI-942 the past of TOI-421 system?

Kubyshkina

Vidotto

D’Angelo

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…As this has now been quantified in III, it suggests that, despite different host stars and stellar neighbourhoods, small, close-in exoplanet cores all attain a very similar core density. Whilst there exist strong degeneracies in core composition, which allow different fractions to equate to the same bulk core density, it still raises the question of why such fine-tuning of bulk density would arise in a stochastic core assembly process (Michel et al 2020).…”

Section: Core Composition Spreadmentioning

confidence: 99%

Unveiling the planet population at birth

Rogers

Owen

2021

Monthly Notices of the Royal Astronomical Society

133

117

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The radius distribution of small, close-in exoplanets has recently been shown to be bimodal. The photoevaporation model predicted this bimodality. In the photoevaporation scenario, some planets are completely stripped of their primordial H/He atmospheres, whereas others retain them. Comparisons between the photoevaporation model and observed planetary populations have the power to unveil details of the planet population inaccessible by standard observations, such as the core mass distribution and core composition. In this work, we present a hierarchical inference analysis on the distribution of close-in exoplanets using forward-models of photoevaporation evolution. We use this model to constrain the planetary distributions for core composition, core mass and initial atmospheric mass fraction. We find that the core-mass distribution is peaked, with a peak-mass of ∼4 M⊕. The bulk core-composition is consistent with a rock/iron mixture that is ice-poor and “Earth-like”; the spread in core-composition is found to be narrow ($\lesssim 16\%$ variation in iron-mass fraction at the 2σ level) and consistent with zero. This result favours core formation in a water/ice poor environment. We find the majority of planets accreted a H/He envelope with a typical mass fraction of $\sim 4\%$; only a small fraction did not accrete large amounts of H/He and were “born-rocky”. We find four-times as many super-Earths were formed through photoevaporation, as formed without a large H/He atmosphere. Finally, we find core-accretion theory over-predicts the amount of H/He cores would have accreted by a factor of ∼5, pointing to additional mass-loss mechanisms (e.g. “boil-off”) or modifications to core-accretion theory.

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“…We therefore refrained from making any decisive claim regarding the details of the effect of stellar α-enhancement on planets. However, we do suggest that α-enhancement can serve more than just a proxy for age, but it might also be an important factor that could affect the types (Santos et al 2017;Michel et al 2020) and occurrence rates of planets around thick-disk stars.…”

Section: Discussionmentioning

confidence: 70%

Exoplanets in the Galactic context: Planet occurrence rates in the thin disk, thick disk and stellar halo of Kepler stars

Bashi,

Zucker

2021

Preprint

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In order to gain a better understanding of planet formation and evolution, it is important to examine the statistics of exoplanets in the Galactic context. By combining information on stellar elemental abundances and kinematics, we constructed separate samples of Kepler stars according to their affiliation to the Galactic components of thin disk, thick disk and stellar halo. Using a Bayesian analysis with conjugate priors, we then investigated how planet occurrence rates differ in different regions of planet properties. We find that young, slow and metal-rich stars, associated mainly with the thin disk, host on average more planets (especially close-in super Earths) compared to the old, fast and metal-poor thick disk stars. We further assess the dependence between stellar properties such as spectral type and metallicity, and planet occurrence rates. The trends we find agree with those found by other authors as well. We argue that in the Galactic context, these are probably not the main properties that affect planet occurrence rates, but rather the dynamical history of stars, and especially stellar age and kinematics, impact the current distribution of planets in the Galaxy.

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Planetary mass–radius relations across the galaxy

Cited by 13 publications

References 60 publications

Atmospheric mass loss and stellar wind effects in young and old systems – II. Is TOI-942 the past of TOI-421 system?

Atmospheric mass loss and stellar wind effects in young and old systems – II. Is TOI-942 the past of TOI-421 system?

Unveiling the planet population at birth

Exoplanets in the Galactic context: Planet occurrence rates in the thin disk, thick disk and stellar halo of Kepler stars

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