Webb reveals carbon rich disc around giant exoplanet

Webb reveals carbon rich disc around giant exoplanet
by Erica Marchand
Paris, France (SPX) Sep 30, 2025

NASA's James Webb Space Telescope has captured the first detailed measurements of a circumplanetary disc that may serve as a birthplace for moons around a massive exoplanet. The discovery, involving the companion world CT Cha b located 625 light years away, sheds light on how Jupiter's Galilean satellites may have emerged more than four billion years ago.

The international team used Webb's Mid-Infrared Instrument (MIRI) to probe the system and revealed a carbon-rich disc encircling CT Cha b. While no moons have yet been detected, the disc demonstrates conditions that could support moon formation. Researchers emphasize that such structures offer a living laboratory to compare with early Solar System processes.

CT Cha b orbits a two-million-year-old star still surrounded by its own circumstellar disc. Webb observations revealed that the planet's disc is not linked to the star's accretion material, with the two systems separated by 74 billion kilometers. This independence allows astronomers to study its chemistry directly.

High-contrast spectrography enabled scientists to isolate the faint light of CT Cha b from its host star. The team identified seven carbon-bearing molecules, including acetylene and benzene, marking a striking contrast to the star's water-rich but carbon-poor disc. Such rapid chemical diversification within only two million years highlights the dynamism of young planetary systems.

Lead author Gabriele Cugno of the University of Zurich said, "We want to learn more about how our Solar System formed moons. This means that we need to look at other systems that are still under construction. We're trying to understand how it all works."

Co-lead Sierra Grant of Carnegie Science added, "We can see evidence of the disc 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."

Future Webb campaigns will extend the survey to other young exoplanets with circumplanetary discs, offering a broader view of the diversity of moon-forming environments. These findings will also support upcoming missions such as ESA's Jupiter Icy Moons Explorer (Juice) and future exploration of Saturn's moon Enceladus.

Research Report:A Carbon-rich Disk Surrounding a Planetary-mass Companion