Astronomers spot carbon-heavy disk around young star, challenging planet formation models

An image of the star-forming region NGC 6357 highlights the young star XUE 10. Using JWST/MIRI, scientists detected a planet-forming disk rich in four distinct forms of carbon dioxide but with little water, offering fresh insights into the chemical conditions where planets are beginning to form. (Image: Stockholm University (SU) and María Claudia Ramírez-Tannus, Max Planck Institute for Astronomy (MPIA))

Astronomers studying a young star system have found something unexpected: a planet-forming disk unusually rich in carbon dioxide, but with hardly any water. The finding, made with the James Webb Space Telescope, challenges long-held ideas about how planets are born.

What did scientists discover in the planet-forming disk?
A team led by Jenny Frediani at Stockholm University found strikingly high amounts of carbon dioxide in regions where rocky planets might one day emerge. “Unlike most planet-forming disks, where water dominates, this one is surprisingly carbon dioxide rich,” Frediani said. “Water is so scarce it is barely detectable.”

NGC 6357 with the star XUE 10 (Image: Stockholm University (SU) and María Claudia Ramírez-Tannus, Max Planck Institute for Astronomy (MPIA))

Conventional models predict water vapour in a disk’s inner regions, as icy pebbles drift inward and vaporise. But Webb’s MIRI instrument revealed a strong carbon dioxide signal instead. “This challenges current models because such high levels of carbon dioxide compared with water cannot be explained easily,” Frediani explained.

Researcher Arjan Bik suggested the chemistry may be shaped by powerful ultraviolet radiation, either from the central star or nearby massive stars. This could be rewriting the chemistry of the disk in unexpected ways.

Where was the unusual disk found?
The carbon dioxide-rich system lies within NGC 6357, a star-forming region about 53 quadrillion kilometres from Earth. It was observed by the eXtreme Ultraviolet Environments collaboration, which studies how intense radiation affects planet-forming disks.

The team also detected rare isotopic forms of carbon dioxide containing carbon-13 and oxygen-17 or oxygen-18. These isotopes may explain unusual chemical fingerprints found in meteorites and comets within our own Solar System.

What does this mean for future studies?
Maria-Claudia Ramirez-Tannus of the Max Planck Institute for Astronomy said the discovery shows how extreme environments shape the building blocks of planets. “Since most stars and likely most planets form in such regions, this is essential for understanding planetary diversity and habitability,” she said.

Thanks to Webb’s advanced infrared instruments, scientists can now study dusty disks with unmatched clarity, comparing turbulent star-forming zones with calmer regions. This is helping astronomers understand how the environments where stars are born can ultimately shape the planets that orbit them.

The findings appear in Astronomy & Astrophysics.