Exoplanets & Exomoons

A Reanalysis Of The LHS 1140 b Atmosphere Observed With The Hubble Space Telescope

By Keith Cowing
Status Report
April 1, 2024
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A Reanalysis Of The LHS 1140 b Atmosphere Observed With The Hubble Space Telescope
Comparison between the observed planetary spectrum (black dots) and the best fit for a secondary atmosphere dominated by H2O (blue) and one dominated by CH4 (red), without clouds. The green line represents the flat model. — astro-ph.EP

The super-Earth LHS 1140 b is an interesting target for atmospheric observations since it is close to the habitable zone of its star and falls in the gap of the radius distribution of small exoplanets, in the region thought to correspond to the transition between planets with and without atmospheres.

Observations of the primary transit with WFC3 on board of the Hubble Space Telescope (HST) revealed a modulation in the planet transmission spectrum compatible with the presence of water; however this modulation may be also due to stellar activity-related phenomena. Here we present a detailed analysis of the WFC3/HST observations to probe the nature of this modulation and to understand if it can be attributable to the presence of unocculted spots on the stellar surface.

Our analysis strongly suggests that LHS1140 is a rather quiet star with subsolar [Fe/H] and enriched in alpha elements. Therefore, we rule out the possibility that the planetary spectrum is affected by the presence of spots and faculae. This analysis shows the importance of a proper modelling of the stellar spectrum when analyzing transit observations. Finally, we modelled the planetary atmosphere of LHS1140 b to retrieve its atmospheric composition.

However, the low resolution and the narrow spectral range of HST observations prevented us from definitively determining whether the spectral features are attributable to the presence of water or of other molecules in the planetary atmosphere.

Alfredo Biagini, Gianluca Cracchiolo, Antonino Petralia, Jesús Maldonado, Claudia Di Maio, Giuseppina Micela

Comments: 12 pages, 10 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2403.20285 [astro-ph.EP] (or arXiv:2403.20285v1 [astro-ph.EP] for this version)
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Submission history
From: Alfredo Biagini Mr.
[v1] Fri, 29 Mar 2024 16:54:29 UTC (3,402 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) 🖖🏻