Free Astronomy Magazine January-February 2026

23 JANUARY-FEBRUARY 2026 the planet’s disk, including acety- lene (C 2 H 2 ) and benzene (C 6 H 6 ). This carbon-rich chemistry is in stark con- trast to the chemistry seen in the disk around the host star, where the researchers found water but no car- bon. The difference between the two disks offers evidence for their rapid chemical evolution over only 2 million years. A circumplanetary disk has long been hypothesized as the birth- place of Jupiter’s four major moons. These Galilean satellites must have condensed out of such a flattened disk billions of years ago, as evident in their co-planar orbits about Jupiter. The two outermost Galilean moons, Ganymede and Callisto, are 50% water ice. But they presum- ably have rocky cores, perhaps ei- ther of carbon or silicon. “We want to learn more about how our solar system formed moons. This means that we need to look at other sys- tems that are still under construc- tion. We’re trying to understand how it all works,” said Cugno. “How do these moons come to be? What are their ingredients? What physical processes are at play, and over what timescales? Webb allows us to witness the drama of moon for- mation and investigate these ques- tions observationally for the first time.” In the coming year, the team will use Webb to perform a compre- hensive survey of similar objects, to better understand the diversity of physical and chemical properties in the disks around young planets. A n artistic rendering of a dust and gas disk encircling the young exoplanet CT Cha b, 625 light-years from Earth. Spec- troscopic data from NASA’s James Webb Space Telescope sug- gests the disk contains the raw materials for moon formation: diacetylene, hydrogen cyanide, propyne, acetylene, ethane, car- bon dioxide, and benzene. The planet appears at lower right, while its host star and surrounding circumstellar disk are visible in the background. [NASA, ESA, CSA, STScI, Gabriele Cugno (Uni- versity of Zürich, NCCR PlanetS), Sierra Grant (Carnegie Institu- tion for Science), Joseph Olmsted (STScI), Leah Hustak (STScI)] The two objects are 46 billion miles apart. Observing planet and moon formation is fundamental to under- standing the evolution of planetary systems across our galaxy. Moons likely outnumber planets, and some might be habitats for life as we know it. But we are only now enter- ing an era where we can witness their formation. This discovery fos- ters a better understanding of plan- et and moon formation, say re- searchers. Webb’s data is invaluable for mak- ing comparisons to our solar sys- tem's birth over 4 billion years ago. “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 forma- tion,” said co-lead author Sierra Grant of the Carnegie Insti- tution for Science in Washington. “We are seeing what material is accreting to build the planet and moons,” added main lead author Gabriele Cugno of the University of Zürich and member of the National Cen- ter of Competence in Research PlanetS. In- frared observations of CT Cha b were made with Webb’s MIRI (Mid-In- frared Instrument) using its medium resolution spectrograph. An initial look into Webb’s archival data re- vealed signs of molecules within the circumplanetary disk, which moti- vated a deeper dive into the data. Because the planet’s faint signal is buried in the glare of the host star, the researchers had to disentangle the light of the star from the planet using high-contrast methods. “We saw molecules at the location of the planet, and so we knew that there was stuff in there worth digging for and spending a year trying to tease out of the data. It really took a lot of perseverance,” said Grant. Ulti- mately, the team discovered seven carbon-bearing molecules within !