Twelve light-years from Earth, a giant planet called Epsilon Indi Ab is covered in something unexpected. Astronomers using the James Webb Space Telescope have discovered water ice clouds high in its atmosphere. This is the first time such clouds have been found on a cold giant exoplanet, and scientists are surprised.
Every theory predicted that this planet should have ammonia clouds, like Jupiter does. However, Elisabeth Matthews and her team at the Max Planck Institute for Astronomy found something different. Using special instruments that block the star's bright light, they compared images taken at different wavelengths. The ammonia signal was weaker than it should have been, which means something is covering it: thick patches of water ice clouds, similar to the thin cirrus clouds we see on Earth.
Epsilon Indi Ab is 7.6 times heavier than Jupiter but roughly the same size. Its atmosphere is between minus 70 and plus 20 degrees Celsius. The planet orbits a star called Epsilon Indi A, located in the southern constellation Indus. This world is the closest super-Jupiter to Earth that astronomers can study directly.
The discovery raises questions about how giant planets form and develop atmospheres. Scientists hope that NASA's Nancy Grace Roman Space Telescope, launching soon, will help them find similar water-ice clouds on other worlds. For now, this strange planetary cousin reminds us how much we still have to learn about the universe.