Spake, JJ and Sing, DK and Evans, TM and Oklopčić, A and Bourrier, V and Kreidberg, L and Rackham, BV and Irwin, J and Ehrenreich, D and Wyttenbach, A and Wakeford, HR and Zhou, Y and Chubb, KL and Nikolov, N and Goyal, JM and Henry, GW and Williamson, MH and Blumenthal, S and Anderson, DR and Hellier, C and Charbonneau, D and Udry, S and Madhusudhan, N (2018) Helium in the eroding atmosphere of an exoplanet. Nature, 557 (7703). 68 -70. ISSN 1476-4687

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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.

Item Type: Article
Additional Information: This is the accepted author manuscript (AAM). The final published version (version of record) is available online via Nature Publishing Group at - please refer to any applicable terms of use of the publisher.
Subjects: Q Science > QB Astronomy > QB460 Astrophysics
Divisions: Faculty of Natural Sciences > School of Chemical and Physical Sciences
Related URLs:
Depositing User: Symplectic
Date Deposited: 17 May 2018 13:39
Last Modified: 17 May 2018 13:42

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