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Nature. 2018 May;557(7703):68-70. doi: 10.1038/s41586-018-0067-5. Epub 2018 May 2.

Helium in the eroding atmosphere of an exoplanet.

Author information

1
Department of Physics and Astronomy, University of Exeter, Exeter, UK. jspake@astro.ex.ac.uk.
2
Department of Physics and Astronomy, University of Exeter, Exeter, UK.
3
Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA.
4
Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA.
5
Observatoire de l'Université de Genève, 51 chemin des Maillettes, Versoix, Switzerland.
6
Harvard Society of Fellows, Cambridge, MA, USA.
7
Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA.
8
Department of Astronomy/Steward Observatory, University of Arizona, Tucson, AZ, USA.
9
Space Telescope Science Institute, Baltimore, MD, USA.
10
Department of Physics and Astronomy, University College London, London, UK.
11
Center of Excellence in Information Systems, Tennessee State University, Nashville, TN, USA.
12
Astrophysics Group, Keele University, Keele, UK.
13
Institute of Astronomy, University of Cambridge, Cambridge, UK.

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.

PMID:
29720632
DOI:
10.1038/s41586-018-0067-5

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