JWST spots ice clouds
- JWST observations show water-ice clouds in the atmosphere of the cold, Jupiter-mass exoplanet Epsilon Indi Ab. (sciencedaily.com) - The finding comes from a team led by Elisabeth Matthews of the Max Planck Institute for Astronomy. (spacewar.com) - Researchers say clouds complicate atmospheric models, and they’re asking for more JWST time to study similar “cold Jupiter” worlds. ( )
Clouds on a planet can hide what its air is made of, and James Webb Space Telescope data now point to water-ice clouds on Epsilon Indi Ab, a giant world 12 light-years away. (mpg.de) Epsilon Indi Ab is a gas giant orbiting the nearby star Epsilon Indi A, and Webb first directly imaged it in results released in July 2024. The planet is about 7.6 times Jupiter’s mass, with a similar diameter, making it denser and colder than most directly imaged exoplanets. (esawebb.org; arxiv.org) To study its atmosphere, astronomers used Webb’s Mid-Infrared Instrument, or MIRI, and a coronagraph, which acts like a glare blocker so the telescope can isolate faint light from the planet. They compared brightness at 11.3 micrometers with earlier 10.6 micrometer measurements from 2024 to test for ammonia gas high in the atmosphere. (spacewar.com; arxiv.org) The signal showed less ammonia than cloud-free models predicted for a planet this cold. Elisabeth Matthews of the Max Planck Institute for Astronomy and her team said thick, patchy water-ice clouds are the best fit for that mismatch. (sciencedaily.com; mpg.de) Those clouds matter because most published atmosphere models for giant exoplanets leave clouds out to keep the calculations manageable. This case suggests that shortcut can miss key features even on Jupiter-like planets that should be simpler to read than smaller rocky worlds. (spacewar.com; phys.org) The team framed Epsilon Indi Ab as a test case for studying “solar-system analogue” planets around other stars. Matthews said Webb is now detailed enough that distant observers could, in effect, study Jupiter-like planets around Sun-like stars the way astronomers are beginning to study this one. (mpg.de; indiatoday.in) The result is not yet the end of the story. In a March 2026 preprint, the researchers described the cloud interpretation as the best current explanation, while noting that more wavelength coverage is needed to pin down the planet’s composition and cloud properties. (arxiv.org) More Webb observations are already approved across wavelengths from 3 to 20 micrometers, according to coverage of the release, and the team is also seeking time to observe other cold giant planets. The next data should show whether Epsilon Indi Ab really is wrapped in high, icy clouds—or whether the atmosphere is doing something models still do not capture. (scienceblog.com; sciencedaily.com)
