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arXiv · 1812.02189

Spectrally resolved helium absorption from the extended atmosphere of a warm Neptune-mass exoplanet

R. Allart·V. Bourrier·C. Lovis·D. Ehrenreich·J. J. Spake·A. Wyttenbach·L. Pino·F. Pepe·D. K. Sing·A. Lecavelier des Etangs
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Abstract

Stellar heating causes atmospheres of close-in exoplanets to expand and escape. These extended atmospheres are difficult to observe because their main spectral signature - neutral hydrogen at ultraviolet wavelengths - is strongly absorbed by interstellar medium. We report the detection of the near-infrared triplet of neutral helium in the transiting warm Neptune-mass exoplanet HAT-P-11b using ground-based, high-resolution observations. The helium feature is repeatable over two independent transits, with an average absorption depth of 1.08+/-0.05%. Interpreting absorption spectra with 3D simulations of the planet's upper atmosphere suggests it extends beyond 5 planetary radii, with a large scale height and a helium mass loss rate =< 3x10^5 g/s. A net blue-shift of the absorption might be explained by high-altitude winds flowing at 3 km/s from day to night-side.

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R. Allart, V. Bourrier, C. Lovis, D. Ehrenreich, J. J. Spake, A. Wyttenbach, L. Pino, F. Pepe, D. K. Sing, A. Lecavelier des Etangs. 2018-12-05. Spectrally resolved helium absorption from the extended atmosphere of a warm Neptune-mass exoplanet. https://doi.org/10.1126/science.aat5879

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