NASA's James Webb Space Telescope has observed a carbon-rich disk surrounding the exoplanet CT Cha b, 625 light-years from Earth, potentially serving as a moon factory. The disk, separate from the star's own disk, offers insights into early planet and moon formation. The young star system is just 2 million years old.
The James Webb Space Telescope has provided the first direct measurements of the chemical composition and physical conditions in a possible moon-forming disk around the massive exoplanet CT Cha b. Located 625 light-years away, this carbon-rich disk encircles the planet, which orbits a star only 2 million years old. Although no moons were detected, the environment suggests a birthplace for future moons, shedding light on how natural satellites form.
The study, published in The Astrophysical Journal Letters, highlights that the planet and its star are 46 billion miles apart, indicating separate disks of activity. The star continues to gather material from its larger disk, while CT Cha b's disk shows a distinct composition. Researchers used Webb's Mid-Infrared Instrument (MIRI) and a medium-resolution spectrograph, applying high-contrast imaging to isolate the planet's faint glow from the star's brightness.
Analysis revealed seven carbon-bearing molecules in the disk, including acetylene (C2H2) and benzene (C6H6). This contrasts sharply with the star's disk, which contains water but lacks carbon, illustrating rapid chemical evolution over 2 million years. "We can see evidence of the disk around the companion, and we can study the chemistry for the first time. We're not just witnessing moon formation -- we're also witnessing this planet's formation," said co-lead author Sierra Grant of the Carnegie Institution for Science.
"We are seeing what material is accreting to build the planet and moons," added lead author Gabriele Cugno of the University of Zürich. The findings draw parallels to Jupiter's large moons—Io, Europa, Ganymede, and Callisto—which likely formed from a similar disk billions of years ago. "We want to learn more about how our solar system formed moons... Webb allows us to witness the drama of moon formation," Cugno noted.
The team plans further Webb observations of young planetary systems to explore disk diversity and moon formation processes.