EXOPLANETS • JAMES WEBB SPACE TELESCOPE • OCTOBER 2026
Just 12 Light-Years Away: Webb Investigates a Super-Jupiter With Possible Water-Ice Clouds
Evidence status: Peer-reviewed direct-imaging and mid-infrared photometry. Atmospheric ammonia is supported by measurements; thick water-ice clouds are a favored model-based interpretation, not directly photographed clouds.
Meet Epsilon Indi Ab
Epsilon Indi Ab orbits the nearby K-type star Epsilon Indi A, approximately 12 light-years from Earth. It is a cold gas giant with a mass estimated at 7.6 ± 0.7 Jupiter masses in the 2026 analysis, although its diameter is roughly Jupiter-sized. Its atmosphere is estimated at about 200–300 kelvin, warmer than Jupiter's upper atmosphere despite receiving little starlight. Internal heat left from formation contributes to its temperature.
How Webb studied it
Scientists used the James Webb Space Telescope's Mid-Infrared Instrument (MIRI) and a coronagraph to suppress the glare of the host star. The team combined new 11.3-micrometer observations with earlier measurements at 10.6 micrometers and other wavelengths. This is direct imaging of the planet as a faint infrared source, not a detailed photograph of its cloud patterns.
What the measurements reveal
The planet was 0.88 ± 0.08 magnitudes brighter at 11.3 micrometers than at 10.6 micrometers, consistent with absorption from ammonia. However, the ammonia feature was shallower than expected in simple atmospheric models. The researchers favor thick water-ice clouds as an explanation because clouds could mute ammonia features and suppress near-infrared emission. Alternative explanations include an atmosphere with lower heavy-element abundance or depleted nitrogen.
Why the possible ice clouds matter
Cold giant planets are a test of how atmospheric chemistry, temperature, clouds and radiation interact. If clouds are common in this class of worlds, cloud-free models may systematically misinterpret their brightness and composition. The findings also help refine the observing and modeling techniques needed for future studies of smaller, potentially rocky exoplanets.
What remains uncertain?
Researchers have not directly resolved the planet's individual clouds or established their exact altitude, thickness or coverage. More wavelength measurements and comparisons with other cold giant planets are needed to distinguish cloud effects from differences in chemical composition. Epsilon Indi Ab is a giant gas planet; the possible presence of water-ice clouds does not imply an ocean or habitability.
Sources
Matthews et al. (2026), The Astrophysical Journal Letters, “A Second Visit to Eps Ind Ab with JWST”
Max Planck Institute for Astronomy, research announcement (April 22, 2026)
NASA Exoplanet Archive: Epsilon Indi A system
Editorial note: The dramatic full-disk planet illustration circulated with news coverage is an artist's impression, not a Webb photograph. Research published May 2026; MKP summary added October 25, 2026.