Interior Characterization in Multiplanetary Systems: TRAPPIST-1

Dorn, Caroline; Mosegaard, Klaus; Grimm, Simon L.; Alibert, Yann (2018). Interior Characterization in Multiplanetary Systems: TRAPPIST-1. Astrophysical journal, 865(1), p. 20. Institute of Physics Publishing IOP 10.3847/1538-4357/aad95d

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Interior characterization traditionally relies on individual planetary properties, ignoring correlations between different planets of the same system. For multi-planetary systems, planetary data are generally correlated. This is because, the differential masses and radii are better constrained than absolute planetary masses and radii. We explore such correlations and data specific to the multiplanetary-system of TRAPPIST-1 and study their value for our understanding of planet interiors. Furthermore, we demonstrate that the rocky interior of planets in a multi-planetary system can be preferentially probed by studying the most dense planet representing a rocky interior analogue. Our methodology includes a Bayesian inference analysis that uses a Markov chain Monte Carlo scheme. Our interior estimates account for the anticipated variability in the compositions and layer thicknesses of core, mantle, water oceans and ice layers, and a gas envelope. Our results show that (1) interior estimates significantly depend on available abundance proxies and (2) that the importance of inter-dependent planetary data for interior characterization is comparable to changes in data precision by 30 %. For the interiors of TRAPPIST-1 planets, we find that possible water mass fractions generally range from 0-25 %. The lack of a clear trend of water budgets with orbital period or planet mass challenges possible formation scenarios. While our estimates change relatively little with data precision, they critically depend on data accuracy. If planetary masses varied within ±24 %, interiors would be consistent with uniform (~7 %) or an increasing water mass fractions with orbital period (~2-12 %).

Item Type:

Journal Article (Original Article)


08 Faculty of Science > Physics Institute > NCCR PlanetS
08 Faculty of Science > Physics Institute
08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences
10 Strategic Research Centers > Center for Space and Habitability (CSH)

UniBE Contributor:

Grimm, Simon Lukas, Alibert, Y.


500 Science > 530 Physics
500 Science > 520 Astronomy




Institute of Physics Publishing IOP




Danielle Zemp

Date Deposited:

29 May 2019 17:58

Last Modified:

02 Mar 2023 23:31

Publisher DOI:





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