Disentangling atmospheric compositions of K2-18 b with next generation facilities

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Disentangling atmospheric compositions of K2-18 b with next generation facilities

Changeat, Q; Edwards, B; Al-Refaie, AF; Tsiaras, A; Waldmann, IP; Tinetti, G; (2021) Disentangling atmospheric compositions of K2-18 b with next generation facilities. Experimental Astronomy 10.1007/s10686-021-09794-w. (In press). Green open access

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Abstract

Recent analysis of the planet K2-18 b has shown the presence of water vapour in its atmosphere. While the H_{2}O detection is significant, the Hubble Space Telescope (HST) WFC3 spectrum suggests three possible solutions of very different nature which can equally match the data. The three solutions are a primary cloudy atmosphere with traces of water vapour (cloudy sub-Neptune), a secondary atmosphere with a substantial amount (up to 50% Volume Mixing Ratio) of H_{2}O (icy/water world) and/or an undetectable gas such as N2 (super-Earth). Additionally, the atmospheric pressure and the possible presence of a liquid/solid surface cannot be investigated with currently available observations. In this paper we used the best fit parameters from Tsiaras et al. (Nat. Astron. 3, 1086, 2019) to build James Webb Space Telescope (JWST) and Ariel simulations of the three scenarios. We have investigated 18 retrieval cases, which encompass the three scenarios and different observational strategies with the two observatories. Retrieval results show that twenty combined transits should be enough for the Ariel mission to disentangle the three scenarios, while JWST would require only two transits if combining NIRISS and NIRSpec data. This makes K2-18 b an ideal target for atmospheric follow-ups by both facilities and highlights the capabilities of the next generation of space-based infrared observatories to provide a complete picture of low mass planets.

Type:	Article
Title:	Disentangling atmospheric compositions of K2-18 b with next generation facilities
Open access status:	An open access version is available from UCL Discovery
DOI:	10.1007/s10686-021-09794-w
Publisher version:	https://doi.org/10.1007/s10686-021-09794-w
Language:	English
Additional information:	© 2021 Springer Nature Switzerland AG. This article is licensed under a Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/).
Keywords:	Radiative transfer, Techniques: spectroscopic, Telescopes, Occultations
UCL classification:	UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI:	https://discovery.ucl.ac.uk/id/eprint/10134973