Venus is actually known for being quite uninhabitable due to its high surface temperatures, while Mars is known for its rusty red horizons. Even some of the outer planets’ moons have fascinating environments, with Europa and Enceladus having subsurface oceans.

Recent observations by the James Webb Space Telescope suggest that Uranus’ moon Ariel is also a strong candidate for a subsurface ocean. How did you come to this conclusion? JWST detected carbon dioxide ice on the surface at the trailing edge of the extraorbital features. A subsurface ocean is one possible reason!

Uranus is the seventh planet of the solar system and has five moons. Ariel is one of them and is known for its icy surface and fascinating geological features. It was discovered in 1851 by William Lassell, who financed his love of astronomy with his beer-making business!

Ariel’s surface is a veritable mixture of canyons, ridges, faults, and valleys, mostly caused by tectonic activity. Cryovolcanism is a major surface process that results in continuous surface renewal, giving Ariel the brightest surface of all Uranus’ moons.

Close examination of Ariel reveals that the surface is covered in significant amounts of carbon dioxide ice. Ariel’s trailing hemisphere appears particularly ice-covered, much to the community’s surprise. With the Uranus system’s average distance from the Sun of 2.9 billion kilometers, carbon dioxide is usually lost directly to space by turning into gas, and is not expected to freeze!

Until recently, the most popular theory for supplying carbon dioxide to Ariel’s surface was interaction between its surface and charged particles in Uranus’ magnetosphere, a process known as radiolysis, which breaks down molecules through ionization.

A new study recently published in the Astrophysical Journal Letters suggests an intriguing alternative: Carbon dioxide molecules are being expelled from Ariel, likely from a subsurface liquid ocean!

A team of astronomers using JWST performed a spectral analysis of Ariel and compared the results with laboratory results. The results showed that Ariel has some of the most carbon-rich deposits in the Solar System.

This deposit is not just debris and traces, but also about 10 millimeters in size in the back hemisphere. The results also showed signals from carbon monoxide, which should not be present given the average temperatures.

It remains possible that radiolysis is responsible for at least some of the deposits, but recharge from the subsurface ocean is thought to be the main factor. This hypothesis was supported by the discovery of signals from carbonate minerals, which are salts that can only exist through the interaction between rock and water.

Ariel is covered in canyons, cracks, and grooves, and these are suspected to be openings into its interior. A robotic explorer in the Uranus system could determine the origin of carbon oxides in Ariel. Given that Voyager 2 only imaged 35% of the lunar surface, we are still in the dark without such a mission.