TOI-1235 b: a keystone super-earth for testing radius valley emergence models around early M dwarfs

Ryan Cloutier, Joseph E. Rodriguez, Jonathan Irwin, David Charbonneau, Keivan G. Stassun, Annelies Mortier, David W. Latham, Howard Isaacson, Andrew W. Howard, Stéphane Udry, Thomas G. Wilson, Christopher A. Watson, Matteo Pinamonti, Florian Lienhard, Paolo Giacobbe, Pere Guerra, Karen A. Collins, Allyson Beiryla, Gilbert A. Esquerdo, Elisabeth MatthewsRachel A. Matson, Steve B. Howell, Elise Furlan, Ian J. M. Crossfield, Jennifer G. Winters, Chantanelle Nava, Kristo Ment, Eric D. Lopez, George Ricker, Roland Vanderspek, Sara Seager, Jon M. Jenkins, Eric B. Ting, Peter Tenenbaum, Alessandro Sozzetti, Lizhou Sha, Damien Ségransan, Joshua E. Schlieder, Dimitar Sasselov, Arpita Roy, Paul Robertson, Ken Rice, Ennio Poretti, Giampaolo Piotto, David Phillips, Joshua Pepper, Francesco Pepe, Emilio Molinari, Teo Mocnik, Giuseppina Micela, Michel Mayor, Aldo F. Martinez Fiorenzano, Franco Mallia, Jack Lubin, Christophe Lovis, Mercedes López-Morales, Molly R. Kosiarek, John F. Kielkopf, Stephen R. Kane, Eric L. N. Jensen, Giovanni Isopi, Daniel Huber, Michelle L. Hill, Avet Harutyunyan, Erica Gonzales, Steven Giacalone, Adriano Ghedina, Andrea Ercolino, Xavier Dumusque, Courtney D. Dressing, Mario Damasso, Paul A. Dalba, Rosario Cosentino, Dennis M. Conti, Knicole D. Colón, Kevin I. Collins, Andrew Collier Cameron, David Ciardi, Jessie Christiansen, Ashley Chontos, Massimo Cecconi, Douglas A. Caldwell, Christopher Burke, Lars Buchhave, Charles Beichman, Aida Behmard, Corey Beard, Joseph M. Akana Murphy

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32 Citations (Scopus)


Small planets on close-in orbits tend to exhibit envelope mass fractions of either effectively zero or up to a few percent depending on their size and orbital period. Models of thermally driven atmospheric mass loss and of terrestrial planet formation in a gas-poor environment make distinct predictions regarding the location of this rocky/nonrocky transition in period-radius space. Here we present the confirmation of TOI-1235 b (P = 3.44 days, rp = 1.738-0.076+0.087 R⊕), a planet whose size and period are intermediatebetween the competing model predictions, thus making the system animportant test case for emergence models of the rocky/nonrockytransition around early M dwarfs (Rs = 0.630 ± 0.015 R⊙, Ms = 0.640 ± 0.016 M⊙). We confirm the TESS planet discovery using reconnaissance spectroscopy, ground-based photometry, high-resolution imaging, and aset of 38 precise radial velocities (RVs) from HARPS-N and HIRES. We measure a planet mass of 6.91-0.85+0.75 M⊕, which implies an iron core mass fraction of 20-12+15% in the absence of a gaseous envelope. The bulk composition of TOI-1235 b is therefore consistent with being Earth-like, and we constrain an H/He envelope mass fraction to be <0.5% at 90% confidence. Our results are consistent with model predictions from thermally driven atmospheric mass loss but not with gas-poor formation, suggesting that the former class of processes remains efficient at sculpting close-in planets around early M dwarfs. Our RV analysis also reveals a strong periodicity close to the first harmonic of the photometrically determined stellar rotation period that we treat as stellar activity, despite other lines of evidence favoring a planetary origin (P = 21.8-0.8+0.8 days, mp sin i = 13.0-5.3+3.8 M⊕) that cannot be firmly ruled out by our data.
Original languageEnglish
Article number22
JournalAstronomical Journal
Issue number1
Early online date12 Jun 2020
Publication statusPublished - Jul 2020


  • Radial velocity
  • M dwarf stars
  • Transit photometry
  • Exoplanet formation
  • Exoplanet structure


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