Webb Space Telescope has detected water-ice clouds in the atmosphere of Epsilon Indi Ab, a Jupiter-like exoplanet 12 light-years from Earth, revealing atmospheric complexity not predicted by current models.
The discovery, led by Elisabeth Matthews of the Max Planck Institute for Astronomy, used JWST’s mid-infrared instrument MIRI to directly image the planet, which orbits its K-type star at roughly 30 astronomical units — similar to Neptune’s distance from the Sun.
Epsilon Indi Ab has an estimated temperature of 275 Kelvin (2°C), warmer than Jupiter’s 140 Kelvin, suggesting it is younger and still cooling from formation, while its mass is about 7.6 times that of Jupiter despite a similar radius.
Although ammonia was previously detected in its atmosphere, the planet’s observed brightness exceeded expectations at certain wavelengths, prompting researchers to re-analyze data with higher sensitivity.
This excess brightness, unexplained by ammonia alone, was attributed to water-ice clouds — a feature not included in most exoplanet atmospheric models due to computational simplification.
The finding challenges long-standing assumptions in planetary science, particularly the neglect of cloud formation in simulations of cold gas giants, and suggests models must be revised to reflect observed complexity.
Studying such Jupiter analogs is difficult because most transiting exoplanets are hot and close to their stars; direct imaging, as used here, offers a rare window into cooler, more solar-system-like worlds.
For more on this story, see Webb detects water-ice clouds on cold super-Jupiter exoplanet 12 light-years away.
Matthews noted that JWST now enables detailed study of solar-system analogs in a way previously impossible, comparing it to how alien observers might study Jupiter from afar.
James Mang of the University of Texas emphasized that the detection of structural features like clouds brings researchers closer to probing exoplanet atmospheres in ways once deemed unattainable.
The presence of ammonia-rich atmospheres, noted by The Daily Beast as giving the planet a urine-like odor, coexists with water-ice clouds, indicating a chemically layered and dynamic environment.
This detection marks a step toward characterizing temperate exoplanets, though direct biosignature searches on Earth-like worlds will require more advanced telescopes than JWST.
The study was published in The Astrophysical Journal Letters, underscoring its relevance to ongoing efforts to understand planetary formation and atmospheric evolution beyond our solar system.
This follows our earlier report, James Webb Space Telescope Reveals Missing Massive Stars May Collapse Into Black Holes or Be Hidden by Dust.
How far is Epsilon Indi Ab from Earth?
Epsilon Indi Ab is located approximately 12 light-years from Earth.
Why were water-ice clouds not expected in Epsilon Indi Ab’s atmosphere?
Existing exoplanet atmospheric models often exclude clouds to simplify calculations, so their detection challenges current assumptions about cold gas giant atmospheres.
What makes Epsilon Indi Ab a useful analog for studying Jupiter?
Its temperature, mass, and orbital distance resemble Jupiter’s, allowing researchers to study a solar-system-like gas giant in detail using JWST.
