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; N Madhusudhan

doi:10.1038/s41586-018-0067-5

Helium in the eroding atmosphere of an exoplanet

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

Authors

J J Spake¹, D K Sing^{2

3}, T M Evans², A Oklopčić⁴, V Bourrier⁵, L Kreidberg^{6

7}, B V Rackham⁸, J Irwin⁷, D Ehrenreich⁵, A Wyttenbach⁵, H R Wakeford⁹, Y Zhou⁸, K L Chubb¹⁰, N Nikolov², J M Goyal², G W Henry¹¹, M H Williamson¹¹, S Blumenthal², D R Anderson¹², C Hellier¹³, D Charbonneau⁷, S Udry⁵, N Madhusudhan¹²

Affiliations

¹ Department of Physics and Astronomy, University of Exeter, Exeter, UK. [email protected].
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.

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

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.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.