| Issue |
A&A
Volume 660, April 2022
|
|
|---|---|---|
| Article Number | A102 | |
| Number of page(s) | 15 | |
| Section | Planets and planetary systems | |
| DOI | https://doi.org/10.1051/0004-6361/202142374 | |
| Published online | 25 April 2022 | |
Water content trends in K2-138 and other low-mass multi-planetary systems★
1
Aix Marseille Univ, CNRS, CNES, LAM,
Marseille, France
e-mail: lorena.acuna@lam.fr
2
Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Quartier Agora, Allée du 6 Août 19c, Bât. B5C,
4000
Liège, Belgium
3
LATMOS/CNRS/Sorbonne Université/UVSQ,
11 boulevard d'Alembert,
Guyancourt, 78280, France
Received:
5
October
2021
Accepted:
26
January
2022
Context. Both rocky super-Earths and volatile-rich sub-Neptunes have been found simultaneously in multi-planetary systems, suggesting that these systems are appropriate to study different composition and formation pathways within the same environment.
Aims. We perform a homogeneous interior structure analysis of five multi-planetary systems to explore compositional trends and their relation with planet formation. For one of these systems, K2-138, we present revised masses and stellar host chemical abundances to improve the constraints on the interior composition of its planets.
Methods. We conducted a line-by-line differential spectroscopic analysis on the stellar spectra of K2-138 to obtain its chemical abundances and the planetary parameters. We selected multi-planetary systems with five or more low-mass planets (M < 20 M⊕) that have both mass and radius data available. We carried out a homogeneous interior structure analysis on the planetary systems K2-138, TOI-178, Kepler-11, Kepler-102, and Kepler-80. We estimated the volatile mass fraction of the planets in these systems assuming a volatile layer constituted of water in steam and supercritical phases. Our interior-atmosphere model took the effects of irradiation on the surface conditions into account.
Results. K2-138 inner planets present an increasing volatile mass fraction with distance from their host star, while the outer planets present an approximately constant water content. This is similar to the trend observed in TRAPPIST-1 in a previous analysis with the same interior-atmosphere model. The Kepler-102 system could potentially present this trend. In all multi-planetary systems, the low volatile mass fraction of the inner planets could be due to atmospheric escape, while the higher volatile mass fraction of the outer planets can be the result of accretion of ice-rich material in the vicinity of the ice line with later inward migration. Kepler-102 and Kepler-80 present inner planets with high core mass fractions which could be due to mantle evaporation, impacts, or formation in the vicinity of rocklines.
Key words: stars: abundances / stars: individual: K2-138 / planets and satellites: interiors / planets and satellites: composition / planets and satellites: individual: K2-138 / methods: numerical
© L. Acuña et al. 2022
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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