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GJ 367b: A dense, ultrashort-period sub-Earth planet transiting a nearby red dwarf star

K. W. F. Lam, Sz. Csizmadia, N. Astudillo-Defru, X. Bonfils, D. Gandolfi, P. Padovani, M. Esposito, C. Hellier, T. Hirano, J. H. Livingston, F. Murgas, A. M. S. Smith, K. A. Collins, S. Mathur, R. A. Garcia, S. B. Howell, N. C. Santos, F. Dai, G. R. Ricker, R. K. Vanderspek, D. W. Latham, S. Seager, J. N. Winn, J. M. Jenkins, S. Albrecht, J.-M. Almenara, E. Artigau, O. Barragán, F. Bouchy, J. Cabrera, D. Charbonneau, P. Chaturvedi, A. Chaushev, J. L. Christiansen, W. D. Cochran, J. R. De Meideiros, X. Delfosse, R. F. Díaz, R. Doyon, P. Eigmüller, P. Figueira, T. Forveille, M. Fridlund, G. Gaisné, E. Goffo, I. Georgieva, S. Grziwa, E. W. Guenther, A. Hatzes, M. C. Johnson, P. Kabáth, E. Knudstrup, J. Korth, P. Lewin, J. J. Lissauer, C. Lovis, R. Luque, C. Melo, E. H. Morgan, R. L. Morris, M. Mayor, N. Narita, H. L. M. Osborne, E. Palle, F. Pepe, C. M. Persson, S. N. Quinn, H. Rauer, S. Redfield, J. E. Schlieder, D. Ségransan, L. M. Serrano, J. C. Smith, J. ¦ubjak, J. D. Twicken, S. Udry, V. Van Eylen, M. Vezie

Abstract
Ultrashort-period (USP) exoplanets have orbital periods shorter than 1 day. Precise masses and radii of USP exoplanets could provide constraints on their unknown formation and evolution processes. We report the detection and characterization of the USP planet GJ 367b using high-precision photometry and radial velocity observations. GJ 367b orbits a bright (V-band magnitude of 10.2), nearby, and red (M-type) dwarf star every 7.7 hours. GJ 367b has a radius of 0.718 ± 0.054 Earth-radii and a mass of 0.546 ± 0.078 Earth-masses, making it a sub-Earth planet. The corresponding bulk density is 8.106 ± 2.165 grams per cubic centimeter—close to that of iron. An interior structure model predicts that the planet has an iron core radius fraction of 86 ± 5%, similar to that of Mercury’s interior.

Keywords
Astronomy; Planetary Sciences; Astrophysics - Earth and Planetary Astrophysics

Science
Volume 374, Number 6572, Page 1271
2021 December

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia