Uranus’ moon Ariel has a surprising amount of carbon dioxide ice on its trailing hemisphere, despite the moon’s distance from the Sun, where CO2 typically sublimates into gas.

Scientists had hypothesized that radiolysis—breakdown of molecules by ionizing radiation from Uranus’ magnetosphere—might be responsible.

However, a new study published on July 24 in The Astrophysical Journal Letters suggests an alternative: carbon dioxide and other molecules might be emerging from Ariel’s interior, possibly from a subsurface ocean, Phys.org has reported.

Using the James Webb Space Telescope, researchers led by Richard Cartwright from Johns Hopkins Applied Physics Laboratory found that Ariel has some of the most carbon dioxide-rich deposits in the solar system, with thicknesses estimated at 10 millimeters (0.4 inches) on its trailing hemisphere.

The study also detected the first clear signs of carbon monoxide on the moon.

Written by B.C. Begley