“Fluffy” exoplanet filled with water, sulphur and sand rain

Astronomers have used the James Webb Space Telescope (JWST) to identify clouds of water vapour, sulphur dioxide and silicates on a nearby exoplanet.

European researchers found the compounds on WASP-107b, an exoplanet some 200 light-years from Earth.

With the mass of Neptune and the size of Jupiter, WASP-107b is not a dense planet – in fact, it’s “fluffy”. This lets astronomers peer about 50 times further into its atmosphere than they might for a Jupiter-like density.

WASP-107, the star the exoplanet orbits, is slightly cooler, and a little smaller, than our own Sun. WASP-107b zooms around it in a very tight orbit, taking only 5.7 Earth days to complete one rotation.  This also makes it super hot, with temperatures of around 500°C in its fluffy atmosphere.

James Webb’s Mid-Infrared Instrument (MIRI) let the researchers identify components of the planet’s atmosphere, including water vapour and clouds of silicate particles – essentially, sand.

“JWST is revolutionising exoplanet characterisation, providing unprecedented insights at remarkable speed,” says lead author Professor Leen Decin, from KU Leuven, Belgium.

“The discovery of clouds of sand, water, and sulphur dioxide on this exoplanet by JWST’s MIRI instrument is a pivotal milestone.

“It reshapes our understanding of planetary formation and evolution, shedding new light on our own Solar System.”

The researchers couldn’t find any methane on the planet, which suggests that the planet’s interior is very warm. They also believe that the silicate clouds, which sit at very high altitudes, form a “rain cycle” made of sand.

“The fact that we see these sand clouds high up in the atmosphere must mean that the sand rain droplets evaporate in deeper, very hot layers and the resulting silicate vapour is efficiently moved back up, where they recondense to form silicate clouds once more,” says lead author Dr Michiel Min, an astronomer at the University of Amsterdam, Netherlands.

“This is very similar to the water vapour and cloud cycle on our own Earth but with droplets made of sand.”

The researchers have published their findings in Nature.

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