Editors' Note

Bourrier, Karen; Guest, Kristen; Keep, Christopher; Martín, Daniel; Warne, Vanessa

doi:10.1353/vcr.2017.0021

Cited by 1 publication

(1 citation statement)

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“…The theories describing the recently discovered planet radius gap can be refined through observations of escaping atmospheres, which will lead to a better understanding of the physics of photoevaporation. Atmospheric escape has been detected through observations of hydrogen absorption in the Lyman α line for two hot Jupiters (HD 209458b and HD 189733b;Vidal-Madjar et al 2003Lecavelier Des Etangs et al 2010) and two hot Neptunes (GJ 436b and GJ 3470b;Ehrenreich et al 2015;Bourrier 2018). However, interstellar absorption limits these observations to nearby planets with gas escaping at high velocities.…”

Section: Introductionmentioning

confidence: 99%

Detection of Helium in the Atmosphere of the Exo-Neptune HAT-P-11b

Mansfield

Bean

Oklopčić

et al. 2018

ApJL

107

103

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The helium absorption triplet at a wavelength of 10,833Å has been proposed as a way to probe the escaping atmospheres of exoplanets. Recently this feature was detected for the first time using Hubble Space Telescope (HST ) WFC3 observations of the hot Jupiter WASP-107b. We use similar HST /WFC3 observations to detect helium in the atmosphere of the hot Neptune HAT-P-11b at the 4σ confidence level. We compare our observations to a grid of 1D models of hydrodynamic escape to constrain the thermospheric temperatures and mass loss rate. We find that our data are best fit by models with high mass loss rates ofṀ ≈ 10 9 -10 11 g s −1 . Although we do not detect the planetary wind directly, our data are consistent with the prediction that HAT-P-11b is experiencing hydrodynamic atmospheric escape. Nevertheless, the mass loss rate is low enough that the planet has only lost up to a few percent of its mass over its history, leaving its bulk composition largely unaffected. This matches the expectation from population statistics, which indicate that close-in planets with radii greater than 2 R ⊕ form and retain H/He-dominated atmospheres. We also confirm the independent detection of helium in HAT-P-11b obtained with the CARMENES instrument, making this the first exoplanet with the detection of the same signature of photoevaporation from both ground-and space-based facilities.

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