Astronomers utilizing NASA/ESA/CSA’s James Webb Space Telescope have discovered swirling clouds of water ice in the atmosphere of Epsilon Indi Ab, a cold super-Jupiter that challenges current models of giant planetary atmospheres.
An artist’s impression of Epsilon Indi Ab with water clouds above an ammonia-based atmosphere. Image credit: EC Matthews, MPIA / T. Müller, HdA.
Epsilon Indi A, a K5V star located about 12 light-years from Earth in the southern constellation Indus, is home to Epsilon Indi Ab.
This star, also known as HD 209100 or HIP 108870, is estimated to be between 3.7 and 5.7 billion years old.
Slightly less massive and cooler than the Sun, Epsilon Indi A is orbited by Epsilon Indi Ab, a gas giant planet several times more massive than Jupiter.
Epsilon Indi Ab has a surface temperature ranging from 200 to 300 K (approximately -70 to 20 degrees Celsius).
This planet is warmer than Jupiter (140 K, -133 degrees Celsius) due to residual heat from its formation.
Over millions of years, Epsilon Indi Ab is expected to cool further, eventually dropping below Jupiter’s temperature.
“With a mass of 7.6 times that of Jupiter, Epsilon Indi Ab is significantly more massive, yet its diameter is comparable to Jupiter,” stated Dr. Bhavesh Rajput, a student at the Max Planck Institute for Astronomy.
Rajput et al. utilized Webb’s Mid-Infrared Instrument (MIRI) to capture direct images of Epsilon Indi Ab.
They also estimated the ammonia content in its atmosphere.
“For Jupiter, both ammonia gas and clouds dominate the observable upper atmosphere,” the researchers noted.
“Epsilon Indi Ab was presumed to have large amounts of ammonia gas; however, clouds consisting of ammonia were not detected.”
“Intriguingly, our photometric analysis revealed lower ammonia levels than anticipated.”
A likely explanation is the presence of thick yet patchy clouds of water ice, akin to high-altitude cirrus clouds on Earth.
“This discovery poses significant implications and highlights the advancements being made with Webb,” commented Dr. James Mang, an astronomer at the University of Texas at Austin.
“What was once invisible is now within our view, offering insights into atmospheric structures, including cloud formations.”
“This new complexity adds layers to our atmospheric models, allowing for further detailed analyses of these cold, distant exoplanets.”
These findings will be published in the Astrophysics Journal Letter.
_____
Elizabeth C. Matthews et al. 2026. JWST’s second examination of Epsilon Indi Ab: New photometric data confirms ammonia presence and suggests thick cloud layers in the exoplanet’s atmosphere. APJL 1002, L5; doi: 10.3847/2041-8213/ae5823
Source: www.sci.news
