학술논문
New Mass and Radius Constraints on the LHS 1140 Planets -- LHS 1140 b is Either a Temperate Mini-Neptune or a Water World
Document Type
Working Paper
Author
Cadieux, Charles; Plotnykov, Mykhaylo; Doyon, René; Valencia, Diana; Jahandar, Farbod; Dang, Lisa; Turbet, Martin; Fauchez, Thomas J.; Cloutier, Ryan; Cherubim, Collin; Artigau, Étienne; Cook, Neil J.; Edwards, Billy; Hallatt, Tim; Charnay, Benjamin; Bouchy, François; Allart, Romain; Mignon, Lucile; Baron, Frédérique; Barros, Susana C. C.; Benneke, Björn; Martins, B. L. Canto; Cowan, Nicolas B.; De Medeiros, J. R.; Delfosse, Xavier; Delgado-Mena, Elisa; Dumusque, Xavier; Ehrenreich, David; Hara, Nathan C.; Lafrenière, David; Frensch, Yolanda G. C.; Hernández, J. I. González; Curto, Gaspare Lo; Malo, Lison; Melo, Claudio; Mounzer, Dany; Passeger, Vera Maria; Pepe, Francesco; Poulin-Girard, Anne-Sophie; Santos, Nuno C.; Sosnowska, Danuta; Mascareño, Alejandro Suárez; Thibault, Simon; Vaulato, Valentina; Wade, Gregg A.; Wildi, François
Source
Subject
Language
Abstract
The two-planet transiting system LHS 1140 has been extensively observed since its discovery in 2017, notably with $Spitzer$, HST, TESS, and ESPRESSO, placing strong constraints on the parameters of the M4.5 host star and its small temperate exoplanets, LHS 1140 b and c. Here, we reanalyse the ESPRESSO observations of LHS 1140 with the novel line-by-line framework designed to fully exploit the radial velocity content of a stellar spectrum while being resilient to outlier measurements. The improved radial velocities, combined with updated stellar parameters, consolidate our knowledge on the mass of LHS 1140 b (5.60$\pm$0.19 M$_{\oplus}$) and LHS 1140 c (1.91$\pm$0.06 M$_{\oplus}$) with unprecedented precision of 3%. Transits from $Spitzer$, HST, and TESS are jointly analysed for the first time, allowing us to refine the planetary radii of b (1.730$\pm$0.025 R$_{\oplus}$) and c (1.272$\pm$0.026 R$_{\oplus}$). Stellar abundance measurements of refractory elements (Fe, Mg and Si) obtained with NIRPS are used to constrain the internal structure of LHS 1140 b. This planet is unlikely to be a rocky super-Earth as previously reported, but rather a mini-Neptune with a $\sim$0.1% H/He envelope by mass or a water world with a water-mass fraction between 9 and 19% depending on the atmospheric composition and relative abundance of Fe and Mg. While the mini-Neptune case would not be habitable, a water-abundant LHS 1140 b potentially has habitable surface conditions according to 3D global climate models, suggesting liquid water at the substellar point for atmospheres with relatively low CO$_2$ concentration, from Earth-like to a few bars.
Comment: 31 pages, 18 figures, accepted for publication in ApJL
Comment: 31 pages, 18 figures, accepted for publication in ApJL