Astronomers have uncovered new insights into planet formation after detecting complex hydrocarbon molecules in the circumstellar disk of a young Sun-like star, T Chamaeleontis, located about 350 light-years from Earth. The discovery sheds light on how planetary systems evolve and how early chemical building blocks of life can survive in planet-forming environments.
Scientists from the Indian Institute of Astrophysics (IIA), an autonomous institute under the Department of Science and Technology, analysed archival data from NASA’s James Webb Space Telescope (JWST) using its Mid-Infrared Instrument (MIRI). The study focused on polycyclic aromatic hydrocarbons (PAHs)—flat, carbon-rich molecules considered precursors to complex organic chemistry.
T Chamaeleontis is surrounded by a circumstellar disk featuring a large gap believed to be carved by a forming planet. Normally, dense inner regions of such disks block ultraviolet radiation from reaching the outer disk, making PAHs difficult to detect around low-mass stars. However, observations revealed that a partial collapse of the disk’s inner wall during a high accretion event allowed ultraviolet radiation to illuminate the outer regions, triggering strong PAH emission.
JWST observations from 2022 showed significantly brighter PAH signatures compared to earlier data from NASA’s Spitzer Space Telescope collected in 2002. A comparison of the two datasets confirmed that while the intensity of the emission increased, the intrinsic properties of the molecules—such as size and charge—remained stable over two decades.
“This is one of the lowest-mass stars where PAHs have been clearly detected in a circumstellar disk,” said Arun Roy, post-doctoral fellow at IIA and lead researcher of the study. He explained that the sudden illumination acted like a curtain lifting, revealing chemical processes that had remained hidden for years.
The study, published in The Astronomical Journal, reports that the detected PAHs are relatively small molecules, containing fewer than 30 carbon atoms. Researchers believe the findings provide valuable clues about the interaction between young planets and their natal disks during early stages of planetary evolution.
