Using the James Webb Space Telescope (JWST), astronomers have discovered a strange disk of gas and dust around an infant star that could challenge current models of planet formation.
The protoplanetary disk has an odd chemical composition. It features a surprisingly high concentration of carbon dioxide in the region in which rocky planets like Earth are expected to form and is also unexpectedly low in water content.
The protoplanetary disk investigated by JWST surrounds the infant star XUE 10, which is located around 5,550 light-years from Earth in the vast star-forming region known as NGC 6357. The new discovery was made by the eXtreme Ultraviolet Environments (XUE) collaboration, a research team that focuses on how intense fields of radiation impact the chemistry of protoplanetary disks.
“Unlike most nearby planet-forming disks, where water vapor dominates the inner regions, this disk is surprisingly rich in carbon dioxide,” XUE collaboration team member Jenny Frediani, of Stockholm University in Sweden, said in a statement.
“In fact, water is so scarce in this system that it’s barely detectable — a dramatic contrast to what we typically observe,” Frediani added. “This challenges current models of disk chemistry and evolution, since the high carbon dioxide levels relative to water cannot be easily explained by standard disk evolution processes.”
Strange chemistry
Stars form when overdense patches clump together in vast clouds of gas and dust, eventually gathering enough mass to undergo gravitational collapse. What remains of the material that birthed this still-growing protostar swirls around it, flattening out and eventually forming a protoplanetary disk in which planets can be born.
Scientists currently theorize that planet formation occurs when “pebbles” rich in water ice drift from the colder outer regions of a protoplanetary disk to its warmer inner regions. These higher temperatures cause solid ice to transform directly into gas, a process known as sublimation.
This usually also results in telescopes like JWST spotting strong signals from water vapor in protoplanetary disks. The disk around XUE 10, however, showed strong carbon dioxide signals.
“Such a high abundance of carbon dioxide in the planet-forming zone is unexpected,” said XUE Collaboration member and Stockholm University researcher Arjan Bik. “It points to the possibility that intense ultraviolet radiation — either from the host star or neighboring massive stars — is reshaping the chemistry of the disk.”
This wasn’t the only surprise that JWST delivered to the team with regard to XUE 10 and its protoplanetary disk. Data from the disk revealed molecules of carbon dioxide, enriched with the carbon isotopes carbon-13 and the oxygen isotopes oxygen-17 and oxygen-18.
The presence of these isotopes could help explain why certain unusual isotopes are left in fragments of the early solar system in the formation of meteorites and comets.
The research demonstrates JWST’s impressive ability to detect chemical fingerprints in distant protoplanetary disks during crucial eras of planet formation.
“It reveals how extreme radiation environments — common in massive star-forming regions — can alter the building blocks of planets,” said team leader Maria-Claudia Ramirez-Tannus from the Max Planck Institute for Astronomy in Germany. “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.”
The team’s research was published on Friday (Aug. 29) in the journal Astronomy & Astrophysics.
