Masses and compositions of three small planets orbiting the nearby M dwarf L231-32 (TOI-270) and the M dwarf radius valley
Journal article, 2021

We report on precise Doppler measurements of L231-32 (TOI-270), a nearby M dwarf (d = 22 pc, M = 0.39 M, R = 0.38 R), which hosts three transiting planets that were recently discovered using data from the Transiting Exoplanet Survey Satellite (TESS). The three planets are 1.2, 2.4, and 2.1 times the size of Earth and have orbital periods of 3.4, 5.7, and 11.4 d. We obtained 29 high-resolution optical spectra with the newly commissioned Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) and 58 spectra using the High Accuracy Radial velocity Planet Searcher (HARPS). From these observations, we find the masses of the planets to be 1.58 ± 0.26, 6.15 ± 0.37, and 4.78 ± 0.43 M, respectively. The combination of radius and mass measurements suggests that the innermost planet has a rocky composition similar to that of Earth, while the outer two planets have lower densities. Thus, the inner planet and the outer planets are on opposite sides of the 'radius valley'-a region in the radius-period diagram with relatively few members-which has been interpreted as a consequence of atmospheric photoevaporation. We place these findings into the context of other small close-in planets orbiting M dwarf stars, and use support vector machines to determine the location and slope of the M dwarf (Teff < 4000 K) radius valley as a function of orbital period. We compare the location of the M dwarf radius valley to the radius valley observed for FGK stars, and find that its location is a good match to photoevaporation and core-powered mass-loss models. Finally, we show that planets below the M dwarf radius valley have compositions consistent with stripped rocky cores, whereas most planets above have a lower density consistent with the presence of a H-He atmosphere.

planets and satellites: formation

planets and satellites: fundamental parameters

planets and satellites: composition

planets and satellites: individual: L231-32

Author

Vincent Van Eylen

University College London (UCL)

Princeton University

N. Astudillo-Defru

Universidad Catolica de la Santisima Concepcion

X. Bonfils

Grenoble Alpes University

J.H. Livingston

University of Tokyo

T. Hirano

Tokyo Institute of Technology

R. Luque

University of La Laguna

Instituto de Astrofísica de Canarias

K. W.F. Lam

Technische Universität Berlin

A.B. Justesen

Aarhus University

J. N. Winn

Princeton University

D. Gandolfi

University of Turin

G. Nowak

University of La Laguna

Instituto de Astrofísica de Canarias

Enric Palle

Instituto de Astrofísica de Canarias

University of La Laguna

Simon Albrecht

Aarhus University

Fei Dai

California Institute of Technology (Caltech)

B. Campos Estrada

Imperial College London

James E. Owen

Imperial College London

D. Foreman-Mackey

Flatiron Institute

Malcolm Fridlund

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

Leiden University

Judith Korth

University of Cologne

S. Mathur

University of La Laguna

Instituto de Astrofísica de Canarias

T. Forveille

Grenoble Alpes University

T. Mikal-Evans

Massachusetts Institute of Technology (MIT)

H. L.M. Osborne

University College London (UCL)

C. S.K. Ho

University College London (UCL)

J. M. Almenara

Grenoble Alpes University

E. Artigau

Université de Montréal

O. Barragán

University of Oxford

S.C.C. Barros

University of Porto

F. Bouchy

University of Geneva

J. Cabrera

German Aerospace Center (DLR)

D. A. Caldwell

SETI Institute

D. Charbonneau

Harvard-Smithsonian Center for Astrophysics

Priyanka Chaturvedi

Thüringer Landessternwarte Tautenburg

William D. Cochran

The University of Texas at Austin

Szilard Csizmadia

German Aerospace Center (DLR)

Mario Damasso

Istituto nazionale di astrofisica (INAF)

X. Delfosse

Grenoble Alpes University

J. R. De Medeiros

Federal University of Rio Grande do Norte

R. F. Diaz

Consejo Nacional de Investigaciones Cientificas y Tecnicas

René Doyon

Université de Montréal

M. Esposito

Thüringer Landessternwarte Tautenburg

G. Furész

Massachusetts Institute of Technology (MIT)

P. Figueira

European Southern Observatory Santiago

University of Porto

Iskra Georgieva

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Extragalactic Astrophysics

E. Goffo

University of Turin

S. Grziwa

Massachusetts Institute of Technology (MIT)

E. W. Guenther

Thüringer Landessternwarte Tautenburg

A. Hatzes

Thüringer Landessternwarte Tautenburg

Jon M. Jenkins

NASA Ames Research Center

Petr Kabath

Czech Academy of Sciences

E. Knudstrup

Aarhus University

D. W. Latham

Harvard-Smithsonian Center for Astrophysics

B. Lavie

University of Geneva

C. Lovis

University of Geneva

R. E. Mennickent

University of Concepcion

S. E. Mullally

Space Telescope Science Institute (STScI)

F. Murgas

University of La Laguna

Instituto de Astrofísica de Canarias

Norio Narita

Astrobiology Center, Japan

University of Tokyo

University of La Laguna

Japan Science and Technology Agency

Francesco Pepe

University of Geneva

Carina Persson

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

S. Redfield

Wesleyan University

George R. Ricker

Massachusetts Institute of Technology (MIT)

N. C. Santos

University of Porto

S. Seager

Massachusetts Institute of Technology (MIT)

L. M. Serrano

University of Turin

Alexis M. S. Smith

German Aerospace Center (DLR)

A. Suárez Mascareño

Instituto de Astrofísica de Canarias

J. Šubjak

NASA Ames Research Center

J. D. Twicken

NASA Ames Research Center

SETI Institute

S. Udry

University of Geneva

Roland K. Vanderspek

Massachusetts Institute of Technology (MIT)

M. Zapatero-Osorio

Centro de Astrobiologia (CAB)

Monthly Notices of the Royal Astronomical Society

0035-8711 (ISSN) 1365-2966 (eISSN)

Vol. 507 2 2154-2173

Subject Categories

Meteorology and Atmospheric Sciences

Astronomy, Astrophysics and Cosmology

Geophysics

DOI

10.1093/mnras/stab2143

More information

Latest update

10/18/2021