Astronomers have identified something surprising on a distant gas giant: water ice clouds. The invention was made by a team led by Elisabeth Matthews on the Max Planck Institute for Astronomy (MPIA), and it challenges many existing models of how exoplanet atmospheres behave. The planet, often called Epsilon Indi Ab, is comparable to Jupiter, yet its atmosphere appears more complex than expected. The observing method utilized in this study also marks a very important step toward the long run goal of finding and studying Earth like planets.
The seek for planets beyond our solar system has evolved over a long time. Scientists ultimately hope to detect signs of life on distant worlds, possibly inside the subsequent few a long time. Early efforts, from 1995 through about 2022, focused mainly on discovering latest exoplanets. Researchers relied on indirect techniques that would reveal a planet’s mass, size, or sometimes each.
The launch of the James Webb Space Telescope (JWST) in 2022 marked the start of a brand new phase. For the primary time, astronomers could study the atmospheres of many exoplanets intimately, gaining insights into their composition and structure. Even so, this stage continues to be a step away from directly trying to find life, which can likely require more advanced telescopes in the longer term.
The newest research pushes these techniques further, even though it doesn’t yet goal Earth like planets. Elisabeth Matthews (Max Planck Institute for Astronomy), the study’s lead creator, explains: “JWST is finally allowing us to check solar-system analogue planets intimately. If we were aliens, several light years away, and looking out back on the Sun, JWST is the primary telescope that may allow us to check Jupiter intimately. For studying Earth intimately, we would want rather more advanced telescopes, though.”
Why Jupiter Like Exoplanets Are Hard to Study
Despite JWST’s capabilities, studying planets much like Jupiter has been difficult. Most gas giants observed thus far are much hotter than Jupiter. It is because essentially the most common approach to studying exoplanet atmospheres requires the planet to pass in front of its star from Earth’s perspective. Planets closer to their stars usually tend to align this manner, but also they are much hotter.
To get around this limitation, Matthews and her team used a distinct approach. Their work provides one among the closest looks yet at a real Jupiter analogue, and it revealed an unexpected feature.
Using JWST’s mid infrared instrument MIRI, the team directly imaged Epsilon Indi Ab. This planet orbits the star Epsilon Indi A within the constellation Indus (within the southern sky). Based on Bhavesh Rajpoot, a PhD student at MPIA who contributed to the research, “This planet has a considerably greater mass than Jupiter — the brand new study fixes its mass at 7.6 Jupiter masses — however the diameter is concerning the same as for its solar-system cousin.”
A Cold Giant With Lingering Heat
Epsilon Indi Ab orbits about 4 times farther from its star than Jupiter does from the Sun. Its host star is barely smaller and cooler than the Sun, which keeps the planet’s temperature relatively low. Its surface temperature is estimated to be between 200 and 300 Kelvin (between -70 and +20 degrees Celsius).
Even so, the planet is warmer than Jupiter, which has a temperature of about 140 K. Scientists imagine this extra warmth comes from heat left over from the planet’s formation. Over billions of years, Epsilon Indi Ab is anticipated to chill and eventually turn out to be even colder than Jupiter.
To look at the planet, astronomers used a coronagraph on the MIRI instrument to dam out the intense light from the host star. This allowed them to detect the faint glow of the planet itself. They captured images using a filter at 11.3 μm, which sits just outside a wavelength related to ammonia molecules NH3. By comparing these observations with earlier images taken at 10.6 μm in 2024, the team was in a position to estimate how much ammonia is present. (Incidentally, each the mechanical filter wheels placing the coronagraph and the filter in front of the MIRI camera were constructed at MPIA, one among the German contributions to the JWST.)
Evidence Points to Water Ice Clouds
In Jupiter’s atmosphere, ammonia gas and ammonia clouds dominate the visible upper layers. Based on its properties, Epsilon Indi Ab was expected to contain large amounts of ammonia gas as well, but not ammonia clouds. As a substitute, the observations revealed less ammonia than predicted.
The more than likely explanation is the presence of thick but uneven water ice clouds, much like cirrus clouds high in Earth’s atmosphere — an unexpected complication.
Astronomers typically interpret such data by comparing observations with computer models of planetary atmospheres. Nonetheless, many existing models don’t include clouds because they’re difficult to simulate. This discovery highlights the necessity to improve those models. James Mang (University of Texas at Austin), a co creator of the study, notes: “It’s an awesome problem to have, and it speaks to the immense progress we’re making due to JWST. What once seemed not possible to detect is now nearby, allowing us to probe the structure of those atmospheres, including the presence of clouds. This reveals latest layers of complexity that our models are actually starting to capture, and opens the door to much more detailed characterization of those cold, distant worlds.”
Looking Ahead With Future Telescopes
Future observations could provide even clearer views of those clouds. NASA’s Nancy Grace Roman Space Telescope, where MPIA is a partner, is anticipated to launch in 2026-2027 and needs to be well suited to directly detecting reflective water ice clouds.
Within the meantime, Matthews and her colleagues are in search of additional JWST remark time to check more cold Jupiter like planets. As researchers proceed refining their techniques, they’re constructing the inspiration for studying Earth like worlds in the longer term and, ultimately, trying to find signs of life beyond our solar system.
Background Information
The outcomes described here have been published as E. C. Matthews et al., “A second visit to Eps Ind Ab with JWST: latest photometry confirms ammonia and suggests thick clouds within the exoplanet atmosphere of the closest super-Jupiter” within the Astrophysical Journal Letters.
The MPIA researchers involved are Elisabeth Matthews and Bhavesh Rajpoot, in collaboration with James Mang and Caroline Morley (University of Texas at Austin), Aarynn Carter and Mathilde Mâlin (Space Telescope Science Institute), and others.