The nature of the TRAPPIST-1 exoplanets.

By S. Grimm, B. Demory, M. Gillon, C. Dorn, E. Agol, A. Burdanov, L. Delrez, M. Sestovic, A. Triaud, M. Turbet and 16 more. 2018

255 citations recorded by the source corpus.

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%.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/123e721beffe0f5ade9730a61ef4aa0a4c384730

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Citations in the corpus

• The CARMENES search for exoplanets around M dwarfs (2018, background): “Furthermore, the TRAPPIST-1 system was detected by transit search and the planet’s dynamical masses have been inferred from transit timing variations (Gillon et al. 2017; Grimm et al. 2018).”
• The Detectability and Characterization of the TRAPPIST-1 Exoplanet Atmospheres with JWST (2019, methodology): “For target exposure times per transit, we use the median transit durations for the TRAPPIST-1 planets from Grimm et al. (2018), and for photometry and spectroscopy noise calculations, we assume that an equal amount of time is spent observing in transit/eclipse versus out of transit/eclipse.”
• Disentangling the Planet from the Star in Late-Type M Dwarfs: A Case Study of TRAPPIST-1g (2018, methodology): “This was followed by long-term TTV analysis using both Spitzer and K2 photometry to provide precise constraints on the masses, and therefore the densities, of each planet in the system (Grimm et al. 2018).”
• Evolved Climates and Observational Discriminants for the TRAPPIST-1 Planetary System (2018, methodology): “Here we adopt the current best-fit orbital periods,radii, and masses of the TRAPPIST-1 planets (see Table 1 and Gillon et al. 2016, 2017; Luger et al. 2017b; Grimm et al. 2018).”
• A Framework for Prioritizing the TESS Planetary Candidates Most Amenable to Atmospheric Characterization (2018, methodology): “The TSM values and planet parameters for the top 10 simulated planets are given in Table 2, benchmarked against the known planets LHS 1140b (Dittmann et al. 2017) and TRAPPIST1f (Gillon et al. 2017; Grimm et al. 2018).”