A seven-planet resonant chain in TRAPPIST-1

Luger, Rodrigo, Sestovic, Marko, Kruse, Ethan, Grimm, Simon L., Demory, Brice-Olivier, Agol, Eric, Bolmont, Emeline, Fabrycky, Daniel, Fernandes, Catarina S. et al (2017) A seven-planet resonant chain in TRAPPIST-1. Nature Astronomy, 1 (0129). ISSN 2397-3366

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Official URL: https://doi.org/10.1038/s41550-017-0129


The TRAPPIST-1 system is the first transiting planet system found orbiting an ultra-cool dwarf star1. At least seven planets similar to Earth in radius were previously found to transit this host star2. Subsequently, TRAPPIST-1 was observed as part of the K2 mission and, with these new data, we report the measurement of an 18.77 d orbital period for the outermost transiting planet, TRAPPIST-1h, which was unconstrained until now. This value matches our theoretical expectations based on Laplace relations3 and places TRAPPIST-1h as the seventh member of a complex chain, with three-body resonances linking every member. We find that TRAPPIST-1h has a radius of 0.727 R⊕ and an equilibrium temperature of 169 K. We have also measured the rotational period of the star at 3.3 d and detected a number of flares consistent with a low-activity, middle-aged, late M dwarf.

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