TOI-1695 b: A Water World Orbiting an Early-M Dwarf in the Planet Radius Valley

Collin Cherubim*, Ryan Cloutier, David Charbonneau, Chris Stockdale, Keivan G. Stassun, Richard P. Schwarz, Boris Safonov, Annelies Mortier, Pablo Lewin, David W. Latham, Keith Horne, Raphaëlle D. Haywood, Erica Gonzales, Maria V. Goliguzova, Karen A. Collins, David R. Ciardi, Allyson Bieryla, Alexandre A. Belinski, Bill Wohler, Christopher A. WatsonRoland Vanderspek, Stéphane Udry, Alessandro Sozzetti, Damien Ségransan, Dimitar Sasselov, George R. Ricker, Ken Rice, Ennio Poretti, Giampaolo Piotto, Francesco Pepe, Emilio Molinari, Giuseppina Micela, Michel Mayor, Christophe Lovis, Mercedes López-Morales, Jon M. Jenkins, Zahra Essack, Xavier Dumusque, John P. Doty, Knicole D. Colón, Andrew Collier Cameron, Lars A. Buchhave

*Corresponding author for this work

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Characterizing the bulk compositions of transiting exoplanets within the M dwarf radius valley offers a unique means to establish whether the radius valley emerges from an atmospheric mass-loss process or is imprinted by planet formation itself. We present the confirmation of such a planet orbiting an early-M dwarf (T mag = 11.0294 ± 0.0074, M s = 0.513 ± 0.012 M , R s = 0.515 ± 0.015 R , and T eff = 3690 ± 50 K): TOI-1695 b (P = 3.13 days and R p = 1.90 − 0.14 + 0.16 R ⊕ ). TOI-1695 b’s radius and orbital period situate the planet between model predictions from thermally driven mass loss versus gas depleted formation, offering an important test case for radius valley emergence models around early-M dwarfs. We confirm the planetary nature of TOI-1695 b based on five sectors of TESS data and a suite of follow-up observations including 49 precise radial velocity measurements taken with the HARPS-N spectrograph. We measure a planetary mass of 6.36 ± 1.00 M , which reveals that TOI-1695 b is inconsistent with a purely terrestrial composition of iron and magnesium silicate, and instead is likely a water-rich planet. Our finding that TOI-1695 b is not terrestrial is inconsistent with the planetary system being sculpted by thermally driven mass loss. We present a statistical analysis of seven well-characterized planets within the M dwarf radius valley demonstrating that a thermally driven mass-loss scenario is unlikely to explain this population.

Original languageEnglish
Article number167
JournalAstronomical Journal
Issue number4
Number of pages17
Publication statusPublished - 2023


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