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European astronomers have found water vapour, sulphur dioxide, and sand clouds in the atmosphere of an exoplanet using the James Webb Space Telescope, describing it as a “crucial” discovery.

Exoplanets are planets found beyond our solar system, with many orbiting other stars.

The new study, led by astronomers at KU Leuven, looked at an exoplanet named WASP-107b, which is a Neptune-like gas giant that was discovered in 2017.

It is more than 200 light-years away from Earth and is orbiting a star slightly smaller than the Sun. Its “thin atmosphere” allows astronomers to study its chemical composition.

The astronomers were surprised to detect sulphur dioxide, which smells like burning matches, in the atmosphere but no methane. Methane is a greenhouse gas and its absence indicates that the exoplanet has a warm core, they said.

The James Webb Space Telescope “is bringing about a scientific revolution in the field of exoplanet characterisation at an unprecedented pace,” Leen Decin, a professor from KU Leuven and one of the study’s lead authors, said in a statement.

“The discovery of sand clouds, water vapour and sulphur dioxide in the tenuous atmosphere of this exoplanet by James Webb’s MIRI instrument is a crucial milestone,” Decin said.

She added that it also sheds light on our solar system. The astronomers’ findings were published in the journal Nature.

Droplets made of sand

The clouds in the exoplanet’s atmosphere are made up of silicon, which is the main component of sand, the astronomers found.

Michiel Min, from the Netherlands Institute for Space Research, said in a statement that the sand clouds high in the atmosphere have a similar cycle to the water vapour and cloud cycle on Earth but with “droplets made of sand”.

The researchers say the observations provide important insights into the chemistry of this exoplanet.

The James Webb Space Telescope is a space science observatory and an international programme led by the US National Aeronautics and Space Administration (NASA), the European Space Agency (ESA) and the Canadian Space Agency.