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Helium in the eroding atmosphere of an exoplanet

Hellier

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Abstract

Helium is the second-most abundant element in the Universe after hydrogen and is one of the main constituents of gas-giant planets in our Solar System. Early theoretical models predicted helium to be among the most readily detectable species in the atmospheres of exoplanets, especially in extended and escaping atmospheres 1 . Searches for helium, however, have hitherto been unsuccessful 2 . Here we report observations of helium on an exoplanet, at a confidence level of 4.5 standard deviations. We measured the near-infrared transmission spectrum of the warm gas giant 3 WASP-107b and identified the narrow absorption feature of excited metastable helium at 10,833 angstroms. The amplitude of the feature, in transit depth, is 0.049?±?0.011 per cent in a bandpass of 98 angstroms, which is more than five times greater than what could be caused by nominal stellar chromospheric activity. This large absorption signal suggests that WASP-107b has an extended atmosphere that is eroding at a total rate of 1010 to 3?×?1011 grams per second (0.1-4 per cent of its total mass per billion years), and may have a comet-like tail of gas shaped by radiation pressure.

Acceptance Date Mar 9, 2018
Publication Date May 2, 2018
Publicly Available Date Mar 29, 2024
Journal Nature
Print ISSN 1476-4687
Publisher Nature Publishing Group
Pages 68 -70
DOI https://doi.org/10.1038/s41586-018-0067-5
Publisher URL http://doi.org/10.1038/s41586-018-0067-5

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