James Webb Space Telescope detects molecules transformed by sunlight in exoplanet’s atmosphere

Astronomers have detected molecules transformed by sunlight in the atmosphere of an alien planet for the first time.

The conversion of molecules by sunlight is seen on many planets in our Solar System, including Earth, where the process creates ozone.

The discovery of molecules of sulphur dioxide in the atmosphere of a big gas giant known as WASP-39b by the James Webb Space Telescope (JWST) shows this process also happens on planets outside our Solar System.

“This is the first time we see concrete evidence of photochemistry — chemical reactions initiated by energetic stellar light — on exoplanets,” Shang-Min Tsai, a researcher at the University of Oxford in the United Kingdom and lead author of a paper explaining the origin of sulphur dioxide in WASP-39b’s atmosphere, said in a statement.

WASP-39b is a “hot Saturn”, a giant gas planet about the size of Jupiter, but with the mass of Saturn.

The atmospheric composition of the hot gas giant exoplanet WASP-39 b.(Supplied: NASA, ESA, CSA, Joseph Olmsted (STScI))

Earlier this year, molecules of carbon dioxide were detected around the exoplanet, which lies some 700 light-years away.

The latest analyses, presented in a suite of five papers on the pre-print website Arxiv, provide the first full picture of the alien world’s atmosphere.

The detection of sulphur dioxide provides hope that similar signatures might be found around smaller Earth-like exoplanets that lie in their star’s habitable zone, commented Nataliea Lowson, an astrophysicist who studies exoplanet atmospheres but is not part of the JWST team.

“This photo chemistry is related to processes on Earth that we know are linked to biosignatures,” said Ms Lowson of the University of Southern Queensland.

How does sunlight make sulphur dioxide?

The JWST detected the molecules using a technique known as spectrography, which breaks down light passing through the planet’s atmosphere as it crosses in front of its Sun. Each wavelength of light corresponds to a different chemical.

The JWST teams detected much more sulphur dioxide than they expected.

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