Exoplanets & Exomoons

Warm Terrestrial Planet With Half The Mass Of Venus Transiting A Nearby Star

By Keith Cowing
August 10, 2021
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Warm Terrestrial Planet With Half The Mass Of Venus Transiting A Nearby Star
Mass-radius diagram of the small-planet population. Each point represents a confirmed exoplanet for which the mass and radius are measured with a relative precision better than 50 %. These data have been extracted from exoplanet.eu (Schneider et al. 2011). The shape of the points indicates the technique used to measure the mass of the planet: circles for RV, and squares for transit timing variations. The color of the point reflects the intensity of the incident flux. The level of transparency of the error bars indicates the relative precision of the planetary bulk density. The better the precision, the more opaque the error bars. The three transiting planets in the L 98-59 system are labeled and appear circled in black. The labeled blue stars indicate the Solar System planets. The colored dashed lines are the mass-radius models from Zeng et al. (2016). The gray region indicates the maximum collision stripping of the mantle. The shaded horizontal blue line represent the radius gap (Fulton et al. 2017). L 98-59 b is in a sparsely populated region of the parameter space and currently the lowest-mass planet with a mass measured through RV. Lower planetary masses have all been measured through transit-timing variation, e.g., for Trappist-1 h (Gillon et al. 2017) to the left of L 98-59 b. This plot has been produced using the code available at <a href="https://github.com/odemangeon/mass-radius_diagram">https://github.com/odemangeon/mass-radius_diagram</a>.

The advent of a new generation of radial velocity instruments has allowed us to break the one Earth-mass barrier. We report a new milestone in this context with the detection of the lowest-mass planet measured so far using radial velocities: L 98-59 b, a rocky planet with half the mass of Venus.

It is part of a system composed of three known transiting terrestrial planets (planets b to d). We announce the discovery of a fourth nontransiting planet with a minimum mass of 3.06_{-0.37}^{+0.33} MEarth and an orbital period of 12.796_{-0.019}^{+0.020} days and report indications for the presence of a fifth nontransiting terrestrial planet. With a minimum mass of 2.46_{-0.82}^{+0.66} MEarth and an orbital period 23.15_{-0.17}^{+0.60} days, this planet, if confirmed, would sit in the middle of the habitable zone of the L 98-59 system.

L 98-59 is a bright M dwarf located 10.6 pc away. Positioned at the border of the continuous viewing zone of the James Webb Space Telescope, this system is destined to become a corner stone for comparative exoplanetology of terrestrial planets. The three transiting planets have transmission spectrum metrics ranging from 49 to 255, which makes them prime targets for an atmospheric characterization with the James Webb Space Telescope, the Hubble Space Telescope, Ariel, or ground-based facilities such as NIRPS or ESPRESSO.

With an equilibrium temperature ranging from 416 to 627 K, they offer a unique opportunity to study the diversity of warm terrestrial planets.
L 98-59 b and c have densities of 3.6_{-1.5}^{+1.4} and 4.57_{-0.85}^{+0.77} this http URL^{-3}, respectively, and have very similar bulk compositions with a small iron core that represents only 12 to 14 % of the total mass, and a small amount of water. However, with a density of 2.95_{-0.51}^{+0.79} this http URL^{-3} and despite a similar core mass fraction, up to 30 % of the mass of L 98-59 d might be water.

Olivier D. S. Demangeon, M. R. Zapatero Osorio, Y. Alibert, S. C. C. Barros, V. Adibekyan, H. M. Tabernero, A. Antoniadis-Karnavas, J. D. Camacho, A. Suárez Mascareño, M. Oshagh, G. Micela, S. G. Sousa, C. Lovis, F. A. Pepe, R. Rebolo, S. Cristiani, N. C. Santos, R. Allart, C. Allende Prieto, D. Bossini, F. Bouchy, A. Cabral, M. Damasso, P. Di Marcantonio, V. D’Odorico, D. Ehrenreich, J. Faria, P. Figueira, R. Génova Santos, J. Haldemann, N. Hara, J. I. González Hernández, B. Lavie, J. Lillo-Box, G. Lo Curto, C. J. A. P. Martins, D. Mégevand, A. Mehner, P. Molaro, N. J. Nunes, E. Pallé, L. Pasquini, E. Poretti, A. Sozzetti, S. Udry

Comments: 38 pages, 23 figures, Accepted for publication in Astronomy & Astrophysics
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
DOI: 10.1051/0004-6361/202140728
Cite as: arXiv:2108.03323 [astro-ph.EP] (or arXiv:2108.03323v1 [astro-ph.EP] for this version)
Submission history
From: Olivier D. S. Demangeon
[v1] Fri, 6 Aug 2021 22:33:50 UTC (6,084 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻