Helium in Atmosphere of Exoplanet Detected for the First Time

The team made the detection by analysing the infrared spectrum of the atmosphere of WASP-107b [1]. Previous detections of extended exoplanet atmospheres have been made by studying the spectrum at ultraviolet and optical wavelengths; this detection therefore demonstrates that exoplanet atmospheres can also be studied at longer wavelengths.

Credit: ESA/Hubble, M. Kornmesser
“The strong signal from helium we measured demonstrates a new technique to study upper layers of exoplanet atmospheres in a wider range of planets,” says Spake “Current methods, which use ultraviolet light, are limited to the closest exoplanets. We know there is helium in the Earth’s upper atmosphere and this new technique may help us to detect atmospheres around Earth-sized exoplanets – which is very difficult with current technology.”

WASP-107b is one of the lowest density planets known: While the planet is about the same size as Jupiter, it has only 12% of Jupiter’s mass. The exoplanet is about 200 light-years from Earth and takes less than six days to orbit its host star.

The amount of helium detected in the atmosphere of WASP-107b is so large that its upper atmosphere must extend tens of thousands of kilometres out into space. This also makes it the first time that an extended atmosphere has been discovered at infrared wavelengths.

Since its atmosphere is so extended, the planet is losing a significant amount of its atmospheric gases into space — between ~0.1-4% of its atmosphere’s total mass every billion years [2].

As far back as the year 2000, it was predicted that helium would be one of the most readily-detectable gases on giant exoplanets, but until now, searches were unsuccessful.

[1] The measurement of an exoplanet’s atmosphere is performed when the planet passes in front of its host star. A tiny portion of the star’s light passes through the exoplanet’s atmosphere, leaving detectable fingerprints in the spectrum of the star. The larger the amount of an element present in the atmosphere, the easier the detection becomes.

[2] Stellar radiation has a significant effect on the rate at which a planet’s atmosphere escapes. The star WASP-107 is highly active, supporting the atmospheric loss. As the atmosphere absorbs radiation it heats up, so the gas rapidly expands and escapes more quickly into space.
More information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The study was published in the paper

Contacts and sources:
Jessica Spake
University of Exeter

Mathias Jäger
ESA/Hubble