Surprising carbon dioxide-rich disk challenges planet theory

Surprising carbon dioxide-rich disk challenges planet theory
by Robert Schreiber
Berlin, Germany (SPX) Sep 01, 2025

A team led by Stockholm University has identified a young star surrounded by a disk unusually dominated by carbon dioxide, defying current theories of planet formation. Using the James Webb Space Telescope's MIRI instrument, the researchers found that water vapor is nearly absent in the disk, while carbon dioxide shows up strongly in regions where rocky planets could eventually take shape.

Lead author Jenny Frediani, a PhD student at Stockholm University's Department of Astronomy, said: "Unlike most nearby planet-forming disks, where water vapor dominates the inner regions, this disk is surprisingly rich in carbon dioxide. In fact, water is so scarce in this system that it's barely detectable - a dramatic contrast to what we typically observe."

Ordinarily, models predict that icy pebbles drifting inward from the outer disk would vaporize, creating strong water signatures. The unexpected chemical profile instead suggests that ultraviolet radiation from the host star, or possibly neighboring massive stars, is reshaping the disk's chemistry.

"Such a high abundance of carbon dioxide in the planet-forming zone is unexpected," noted Stockholm University researcher Arjan Bik. "It points to the possibility that intense ultraviolet radiation - either from the host star or neighbouring massive stars - is reshaping the chemistry of the disk."

The team also detected isotopic variants of carbon dioxide, enriched in carbon-13 and oxygen isotopes 17O and 18O. These isotopologues may help explain the unusual isotopic patterns observed in comets and meteorites from the early Solar System.

The disk lies within NGC 6357, a massive star-forming region about 1.7 kiloparsecs (53 trillion kilometers) away. The work is part of the eXtreme Ultraviolet Environments (XUE) collaboration, which examines how radiation alters planet-forming material.

Maria-Claudia Ramirez-Tannus, who leads the XUE project at the Max Planck Institute for Astronomy, emphasized the broader implications: "It reveals how extreme radiation environments - common in massive star-forming regions - can alter the building blocks of planets. Since most stars and likely most planets form in such regions, understanding these effects is essential for grasping the diversity of planetary atmospheres and their habitability potential."

JWST's infrared sensitivity allowed the team to probe the dust-enshrouded disk in detail. By comparing such irradiated environments with quieter star-forming regions, astronomers aim to understand how local conditions drive planetary system diversity. Researchers at Stockholm University and Chalmers played a key role in developing the MIRI camera and spectrograph used in the study.

Research Report:XUE: The CO_2-rich terrestrial planet-forming region of an externally irradiated Herbig disk