Water vapour in the atmosphere of the habitable-zone eight Earth-mass planet K2-18 b
Angelos Tsiaras, Ingo P. Waldmann, Giovanna Tinetti, Jonathan Tennyson, and Sergey N. Yurchenko

TL;DR
This study reports the first detection of water vapour in the atmosphere of a habitable-zone super-Earth, K2-18 b, using Hubble Space Telescope observations, providing insights into its composition and potential habitability.
Contribution
First spectroscopic detection of water vapour in a habitable-zone super-Earth's atmosphere, demonstrating the feasibility of studying such planets with current telescopes.
Findings
Water vapour detected with high confidence (∼3.6σ).
Atmosphere likely contains some hydrogen.
Provides insights into habitable-zone exoplanet atmospheres.
Abstract
In the past decade, observations from space and ground have found HO to be the most abundant molecular species, after hydrogen, in the atmospheres of hot, gaseous, extrasolar planets. Being the main molecular carrier of oxygen, HO is a tracer of the origin and the evolution mechanisms of planets. For temperate, terrestrial planets, the presence of HO is of great significance as an indicator of habitable conditions. Being small and relatively cold, these planets and their atmospheres are the most challenging to observe, and therefore no atmospheric spectral signatures have so far been detected. Super-Earths -- planets lighter than ten M -- around later-type stars may provide our first opportunity to study spectroscopically the characteristics of such planets, as they are best suited for transit observations. Here we report the detection of an HO spectroscopic…
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