Ariel, a moon of Uranus, may hide a 100-mile-deep ocean beneath its icy surface

Uranus’ moon Ariel may have hidden a 100-mile-deep ocean beneath its cracked icy shell, according to a new study published in Icarus. The research maps the moon’s surface to trace what its interior and orbit looked like in the past.

Ariel’s Fractured Surface

The second-closest moon to Uranus is Ariel, and it also happens to be the brightest of the planet’s satellites. It spans just 720 miles — roughly the distance between the Planetary Science Institute in Tucson and Salt Lake City, Utah — yet ranks as the fourth-largest moon in the entire Uranian system. Despite its modest dimensions, its surface holds a great deal of complexity.

The surface shows an old crater next to younger features, some of which might have come about through cryovolcanism — eruptions of water, ice, or other materials from beneath the icy crust instead of molten rock. Across the moon, fractures, ridges, and grabens mark places where pieces of the crust have fallen below the land around them.

Tidal Forces and Orbital Shape

To study Ariel’s surface, scientists first charted its biggest features, then turned to a computer model to simulate how the moon gets stretched and squeezed by the gravitational pull of Uranus. That constant flexing may be what creates the major cracks seen across the icy world.

“One key factor is orbital eccentricity, which describes how much an orbit differs from a perfect circle,” Patthoff said. “Changes in Ariel’s interior structure and orbital eccentricity could both influence the amount of tidal stress acting on its icy crust.”

A Much More Eccentric Orbit

Researchers discovered that Ariel might have previously possessed an orbital eccentricity of around 0.04, approximately 40 times larger than what it measures today. Such a change would have significantly increased the tidal forces affecting Ariel, resulting in an orbit roughly four times more stretched than that of Jupiter’s moon Europa, where constant stretching and squeezing have left its icy surface badly broken.

“In order to create those fractures, you have to have either a really thin ice on a really big ocean, or a higher eccentricity and a smaller ocean,” Patthoff said. “But either way, we need an ocean to be able to create the fractures that we are seeing on Ariel’s surface.”

Twin Ocean Worlds in the Uranian System

The previous work by the same group found comparable evidence for Miranda, an icy satellite circling around Uranus. Combined, those discoveries suggest that several moons within the Uranian system might harbor substantial subsurface oceans.

Tom Nordheim, a coauthor and the principal investigator of the NASA Solar System Workings grant that funded the Miranda and Ariel studies, is quoted as saying “We are finding evidence that the Uranus system may harbor twin ocean worlds,”. He works at Johns Hopkins University Applied Physics Laboratory.

What a Future Mission Could Find

Researchers have yet to pinpoint precisely when Ariel’s deep ocean came into being, or how long it endured. The findings provide a key starting point for further work examining how such buried seas arise, change, and might vanish on far-off frozen worlds.

Researchers believe a future mission to Uranus, with its imaging equipment pointed at the unexplored northern hemispheres of Ariel and Miranda, could put their predictions to the test by searching for the fractures and ridges their models suggest should be there.

The North Dakota Space Grant Consortium provided funding for this research.

Key Numbers

What the researchers seek is a return to the Uranus system so that they may witness it for themselves.

Source material: ““We just need to go back” – Uranus’ moon Ariel may have hidden a 100-mile-deep ocean,” ScienceDaily.

Ariel · astrobiology · icy moon · ocean world · solar system · Uranus