Helium has been detected in the atmosphere of an exoplanet for the first time.
The discovery demonstrates that astronomers can analyse the infrared spectrum of starlight to study the extended atmospheres of planets outside our Solar System.
The exoplanet, named WASP-107b, is one of the lowest density planets known.
It is about the same size as Jupiter but has only 12 per cent of the gas giant’s mass.
It is about 200 lightyears from Earth and orbits its host star in just under six days.
“Helium is the second-most common element in the Universe after hydrogen,” says Jessica Spake, a PhD student at the University of Exeter who led the study.
“It is also one of the main constituents of the planets Jupiter and Saturn in our Solar System.
However, up until now helium had not been detected on exoplanets – despite searches for it.”
An animation showing how star light passing through the atmosphere of an exoplanet interacts with the atoms in the atmosphere. As each element blocks a specific wavelength, it leaves a pattern in the spectrum of the star.
Credit: ESA/Hubble, M. Kornmesser
To make the discovery, the team used the Hubble Space Telescope to analyse the infrared spectrum of the atmosphere of WASP-107b.
Previous studies of extended exoplanet atmospheres have been done at ultraviolet and optical wavelengths.
This latest detection shows that exoplanet atmospheres can be studied at longer wavelengths.
The exoplanet’s atmosphere is so extended, between 0.1 – 4 per cent of the atmosphere’s total mass is being lost to space every one billion years.
“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.”