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There's water in the atmosphere of a Goldilocks exoplanet

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There's water vapour in the atmosphere of exoplanet K2-18b - a planet eight times as heavy, and twice as large as earth - which orbits within the habitable zone of its star, according to international researchers. Although they can't be certain of the exact percentages of chemicals in the atmosphere, the team analysed data from the Hubble Space Telescope to obtain an estimate. They suggest that it may be up to 50 per cent water with a significant amount of hydrogen as well. The team suggest that K2-18b is a great target for the new James Webb Space Telescope, which may be able to give more information about the planetary climate.

Journal/conference: Nature Astronomy

DOI: 10.1038/s41550-019-0878-9

Organisation/s: University College London, UK

Funder: This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreements 758892, ExoAI; 776403/ExoplANETS A) and under the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement numbers 617119 (ExoLights) and 267219 (ExoMol). We further acknowledge funding by the Science and Technology Funding Council (STFC) grants ST/K502406/1 and ST/P000282/1. The data used here were obtained by the Hubble Space Telescope as part of the 13665 and 14682 GO proposals (PI: B. Benneke).

Media Release

From: Springer Nature

Planetary science: Atmospheric water vapour on a habitable-zone exoplanet *PRESS BRIEFING*

Water vapour has been detected in the atmosphere of an exoplanet lying within the habitable zone of its star, reports a paper published in Nature Astronomy. This finding may improve our understanding of the atmospheric evolution of potentially temperate planets.

Exoplanet K2-18 b has a mass eight-times that of Earth and is twice as large. It was first discovered in 2015 and could either be a rocky planet with an extended atmosphere or an icy planet with a high concentration of water in its interior. Most of the exoplanets with atmospheres previously detected and characterized have been gas giants. Observing the atmospheres of smaller, rocky or icy planets is an essential step towards our understanding of terrestrial bodies.

Angelos Tsiaras and colleagues analysed exoplanet K2-18 b using spectroscopic data obtained by the Hubble Space Telescope. The authors found strong evidence of water vapour in its atmosphere. They also suggest that the planet may have a significant amount of hydrogen in its envelope. Although the precise composition of the atmosphere cannot be extracted, the authors modelled different scenarios that indicate that up to 50% of the atmosphere of K2-18 b could be water.

The authors conclude that K2-18 b provides an excellent target for follow-up observations to provide further insights into the composition and climate of habitable-zone planets.

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