Helium in the eroding atmosphere of an exoplanet

Spake, J. J.; Sing, D. K.; Evans, T. M.; Oklopčić, A.; Bourrier, V.; Kreidberg, L.; Rackham, B. V.; Irwin, J.; Ehrenreich, D.; Wyttenbach, A.; Wakeford, H. R.; Zhou, Y.; Chubb, K. L.; Nikolov, N.; Goyal, J. M.; Henry, G. W.; Williamson, M. H.; Blumenthal, S.; Anderson, D. R.; Hellier, C.; Charbonneau, D.; Udry, S.; Madhusudhan, N.

Helium in the eroding atmosphere of an exoplanet

J. J. Spake (), D. K. Sing, T. M. Evans, A. Oklopčić, V. Bourrier, L. Kreidberg, B. V. Rackham, J. Irwin, D. Ehrenreich, A. Wyttenbach, H. R. Wakeford, Y. Zhou, K. L. Chubb, N. Nikolov, J. M. Goyal, G. W. Henry, M. H. Williamson, S. Blumenthal, D. R. Anderson, C. Hellier, D. Charbonneau, S. Udry and N. Madhusudhan
Additional contact information
J. J. Spake: University of Exeter
D. K. Sing: University of Exeter
T. M. Evans: University of Exeter
A. Oklopčić: Harvard-Smithsonian Center for Astrophysics
V. Bourrier: Observatoire de l’Université de Genève
L. Kreidberg: Harvard Society of Fellows
B. V. Rackham: University of Arizona
J. Irwin: Harvard-Smithsonian Center for Astrophysics
D. Ehrenreich: Observatoire de l’Université de Genève
A. Wyttenbach: Observatoire de l’Université de Genève
H. R. Wakeford: Space Telescope Science Institute
Y. Zhou: University of Arizona
K. L. Chubb: University College London
N. Nikolov: University of Exeter
J. M. Goyal: University of Exeter
G. W. Henry: Tennessee State University
M. H. Williamson: Tennessee State University
S. Blumenthal: University of Exeter
D. R. Anderson: Keele University
C. Hellier: University of Cambridge
D. Charbonneau: Harvard-Smithsonian Center for Astrophysics
S. Udry: Observatoire de l’Université de Genève
N. Madhusudhan: Keele University

Nature, 2018, vol. 557, issue 7703, 68-70

Abstract: 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 atmospheres1. Searches for helium, however, have hitherto been unsuccessful2. 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 giant3 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.

Date: 2018
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DOI: 10.1038/s41586-018-0067-5

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