A Caltech Library Service

The nature of the TRAPPIST-1 exoplanets

Grimm, Simon L. and Carey, Sean and Ingalls, James G. (2018) The nature of the TRAPPIST-1 exoplanets. Astronomy & Astrophysics, 613 . Art. No. A68. ISSN 0004-6361. doi:10.1051/0004-6361/201732233.

[img] PDF - Published Version
See Usage Policy.

[img] PDF - Accepted Version
See Usage Policy.


Use this Persistent URL to link to this item:


Context. The TRAPPIST-1 system hosts seven Earth-sized, temperate exoplanets orbiting an ultra-cool dwarf star. As such, it represents a remarkable setting to study the formation and evolution of terrestrial planets that formed in the same protoplanetary disk. While the sizes of the TRAPPIST-1 planets are all known to better than 5% precision, their densities have significant uncertainties (between 28% and 95%) because of poor constraints on the planet’s masses. Aims. The goal of this paper is to improve our knowledge of the TRAPPIST-1 planetary masses and densities using transit-timing variations (TTV). The complexity of the TTV inversion problem is known to be particularly acute in multi-planetary systems (convergence issues, degeneracies and size of the parameter space), especially for resonant chain systems such as TRAPPIST-1. Methods. To overcome these challenges, we have used a novel method that employs a genetic algorithm coupled to a full N-body integrator that we applied to a set of 284 individual transit timings. This approach enables us to efficiently explore the parameter space and to derive reliable masses and densities from TTVs for all seven planets. Results. Our new masses result in a five- to eight-fold improvement on the planetary density uncertainties, with precisions ranging from 5% to 12%. These updated values provide new insights into the bulk structure of the TRAPPIST-1 planets. We find that TRAPPIST-1 c and e likely have largely rocky interiors, while planets b, d, f, g, and h require envelopes of volatiles in the form of thick atmospheres, oceans, or ice, in most cases with water mass fractions less than 5%.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Carey, Sean0000-0002-0221-6871
Ingalls, James G.0000-0003-4714-1364
Additional Information:© 2018 ESO. Article published by EDP Sciences. Received 3 November 2017; Accepted 21 January 2018; Published online 04 June 2018. We are grateful to the referee for an helpful review that improved the manuscript. We thank Robert Hurt for suggesting the inclusion of Figure 13 as well as Yann Alibert, Gavin Coleman, Apurva Oza and Christoph Mordasini for insightful discussions on the TRAPPIST-1 system. B.-O.D. acknowledges support from the Swiss National Science Foundation (PP00P2-163967). This work has been carried out within the frame of the National Centre for Competence in Research PlanetS supported by the Swiss National Science Foundation. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 679030/WHIPLASH), and FP/2007-2013 grant agreement No. 336480, as well as from the ARC grant for Concerted Research Actions, financed by the Wallonia-Brussels Federation. M. Gillon, and V. Van Grootel are Belgian F.R.S.-FNRS Research Associates, E. Jehin is F.R.S.-FNRS Senior Research Associate. S.N.R. thanks the Agence Nationale pour la Recherche for support via grant ANR-13-BS05-0003-002 (grant MOJO). This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. E.A. acknowledges NSF grant AST-1615315, NASA grant NNX14AK26G and from the NASA Astrobiology Institute’s Virtual Planetary Laboratory Lead Team, funded through the NASA Astrobiology Institute under solicitation NNH12ZDA002C and Cooperative Agreement Number NNA13AA93A This paper includes data collected by the K2 mission. Funding for the K2 mission is provided by the NASA Science Mission directorate. Calculations were performed on UBELIX (, the HPC cluster at the University of Bern.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Swiss National Science Foundation (SNSF)PP00P2-163967
European Research Council (ERC)679030
European Research Council (ERC)336480
Communauté française de Belgique - Actions de recherche concertée - Académie universitaire Wallonie-EuropeUNSPECIFIED
Fonds de la Recherche Scientifique (FNRS)UNSPECIFIED
Agence Nationale pour la Recherche (ANR)ANR-13-BS05-0003-002
Subject Keywords:Planets and satellites – Techniques: photometric – Methods: numerical
Record Number:CaltechAUTHORS:20180208-164218383
Persistent URL:
Official Citation:The nature of the TRAPPIST-1 exoplanets. Simon L. Grimm, Brice-Olivier Demory, Michaël Gillon, Caroline Dorn, Eric Agol, Artem Burdanov, Laetitia Delrez, Marko Sestovic, Amaury H. M. J. Triaud, Martin Turbet, Émeline Bolmont, Anthony Caldas, Julien de Wit, Emmanuël Jehin, Jérémy Leconte, Sean N. Raymond, Valérie Van Grootel, Adam J. Burgasser, Sean Carey, Daniel Fabrycky, Kevin Heng, David M. Hernandez, James G. Ingalls, Susan Lederer, Franck Selsis and Didier Queloz. A&A, 613 (2018) A68. DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84753
Deposited By: George Porter
Deposited On:09 Feb 2018 23:52
Last Modified:15 Nov 2021 20:22

Repository Staff Only: item control page