Webb finds signs of water-ice clouds on Epsilon Indi Ab

The Max Planck Institute for Astronomy said on 22 April 2026 that Epsilon Indi Ab appears to have water-ice clouds in its atmosphere. The peer-reviewed results appeared in The Astrophysical Journal Letters the same day, the institute said. Researchers had expected ammonia gas to dominate the planet's upper atmosphere, so the cloud evidence was a surprise.

The ammonia that was not there

The team found ammonia, but less than anticipated, according to the institute. Its best explanation, based on an analysis of the atmosphere, is water-ice clouds high in the atmosphere, similar to high-altitude cirrus clouds on Earth. Most current theoretical models of exoplanet atmospheres include no clouds at all, because clouds make computing the data more complicated. That has a practical consequence: because astronomers may not be looking for clouds, clouds could be missed in observations even when they are there.

A cold Jupiter-like planet

Futura reported that Epsilon Indi Ab is about 12 light-years from Earth and the first planet identified orbiting Epsilon Indi A, a star in the southern constellation Indus. The host star is somewhat less massive and cooler than the Sun and is classified as an orange K-type main-sequence star, K5 V.

The same report said the planet's mass is estimated at 7.6 times Jupiter's, with an uncertainty of about 0.7 Jupiter masses, while its diameter is thought to be comparable to Jupiter's. It orbits about 30 AU from its star, close to Neptune's distance from the Sun and about four times farther out than Jupiter orbits. One lap takes 180 Earth years; Jupiter needs 12, and Neptune needs 165.

The same report added that infrared observations put its atmospheric temperature at about 200 to 300 Kelvin, or about minus 70 to 20 degrees Celsius. That is warmer than Jupiter's upper atmosphere, which has a characteristic temperature of about 140 Kelvin, or minus 133 degrees Celsius. Part of the warmth comes from internal heat left from the planet's formation, and over the next several billion years the planet is expected to cool gradually and eventually become colder than Jupiter.

What the result means

Co-author James Mang of the University of Texas at Austin said what once seemed impossible to detect is now within reach, including the presence of clouds. He said the result reveals new layers of complexity that models are now beginning to capture and opens the door to more detailed characterization of cold, distant worlds.

Lead author Elisabeth Matthews of the Max Planck Institute for Astronomy said JWST is finally allowing astronomers to study solar-system analog planets in detail. She said that if aliens several light-years away looked back at the Sun, JWST would be the first telescope able to study Jupiter in detail, while studying Earth in detail would require much more advanced telescopes.

Most Jupiter-like worlds found so far are hot Jupiters, which orbit close to their stars and are extremely hot, making them easier to detect and study. Jupiters farther from their stars are cooler and harder to find, and cooler planets require more sensitive instruments and longer observation times. Finding water-ice clouds on an exo-Jupiter is a step toward studying smaller, earthlike planets, though such clouds on those worlds might require more powerful telescopes.

By May 2026, the Extrasolar Planets Encyclopaedia listed more than 8,190 exoplanets.