Helium in the eroding atmosphere of an exoplanet

TL;DR

This study reports the first detection of helium in an exoplanet's atmosphere, revealing an extended, escaping atmosphere on WASP-107b with significant implications for atmospheric loss and evolution.

Contribution

The paper provides the first observational detection of metastable helium in an exoplanet atmosphere, confirming theoretical predictions about atmospheric escape.

Findings

Detected helium absorption at 10,833 Å with high confidence.

Estimated atmospheric escape rate of 10^10 to 3 x 10^11 g/s.

Indicates a highly extended, eroding atmosphere possibly forming a gas tail.

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. Searches for helium, however, have hitherto been unsuccessful. 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 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 10^10 to 3 x 10^11 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.