[en] We have collected transit times for the TRAPPIST-1 system with the Spitzer Space Telescope over four years. We add to these ground-based, HST and K2 transit time measurements, and revisit an N-body dynamical analysis of the seven-planet system using our complete set of times from which we refine the mass ratios of the planets to the star. We next carry out a photodynamical analysis of the Spitzer light curves to derive the density of the host star and the planet densities. We find that all seven planets' densities may be described with a single rocky mass-radius relation which is depleted in iron relative to Earth, with Fe 21 wt% versus 32 wt% for Earth, and otherwise Earth-like in composition. Alternatively, the planets may have an Earth-like composition, but enhanced in light elements, such as a surface water layer or a core-free structure with oxidized iron in the mantle. We measure planet masses to a precision of 3-5%, equivalent to a radial-velocity (RV) precision of 2.5 cm/sec, or two orders of magnitude more precise than current RV capabilities. We find the eccentricities of the planets are very small; the orbits are extremely coplanar; and the system is stable on 10 Myr timescales. We find evidence of infrequent timing outliers which we cannot explain with an eighth planet; we instead account for the outliers using a robust likelihood function. We forecast JWST timing observations, and speculate on possible implications of the planet densities for the formation, migration and evolution of the planet system.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Agol, Eric
Dorn, Caroline
Grimm, Simon L.
Turbet, Martin
Ducrot, Elsa ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Exotic
Delrez, Laetitia ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Exotic
Gillon, Michaël ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Exotic
Demory, Brice-Olivier
Burdanov, Artem
Barkaoui, Khalid ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Exotic
Benkhaldoun, Zouhair
Bolmont, Emeline
Burgasser, Adam
Carey, Sean
de Wit, Julien
Fabrycky, Daniel
Foreman-Mackey, Daniel
Haldemann, Jonas
Hernandez, David M.
Ingalls, James
Jehin, Emmanuel ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)
Langford, Zachary
Leconte, Jeremy
Lederer, Susan M.
Luger, Rodrigo
Malhotra, Renu
Meadows, Victoria S.
Morris, Brett M.
Pozuelos Romero, Francisco José ; Space Sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Liège, Belgium
Queloz, Didier
Raymond, Sean M.
Selsis, Franck
Sestovic, Marko
Triaud, Amaury H. M. J.
Van Grootel, Valérie ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Astrophysique stellaire théorique et astérosismologie
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