The team mapped those landforms first, then used a computer program to simulate tidal stress on the surface. As Ariel moves closer to and farther from Uranus during its orbit, its shape shifts from slightly football-like to more spherical, repeatedly stressing the ice.

"First, we mapped out the larger structures that we see on the surface, then we used a computer program to model the tidal stresses on the surface, which result from distortion of Ariel from soccer ball-shaped to slight football-shaped and back," Patthoff said.

To produce fractures of the size observed, the model required either a very thin ice layer over a deep ocean, or a thicker ocean paired with a more elongated orbit.

"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. "Either way, we need an ocean."

Is Uranus hiding multiple ocean worlds?

The researchers calculated that Ariel's past orbital eccentricity, a measure of how much its orbit deviated from circular, reached roughly 0.04. That value is about 40 times greater than Ariel's current eccentricity and roughly four times that of Jupiter's moon Europa, whose icy shell is heavily fractured by tidal stress.

That earlier elongation would have greatly amplified tidal forces on Ariel's ice shell, helping explain the moon's dramatic terrain. It also raises the possibility that Ariel is not alone.

"We are finding evidence that the Uranus system may harbor twin ocean worlds," said Nordheim, principal investigator of the NASA Solar System Workings grant that funded the studies.

The 2025 Miranda paper reported similar evidence: that smaller moon may also have once held a substantial subsurface ocean. Together, the two findings point to a system where hidden liquid layers could have been common rather than exceptional.

What could a future mission reveal?

Scientists still do not know exactly when Ariel's ocean existed or how long it lasted. Existing spacecraft, including Voyager 2, which flew by Uranus in 1986, imaged only the moons' southern hemispheres.

The new models offer predictions for what a future probe might see on Ariel and Miranda's unexplored northern terrain, including the likely locations of fractures and ridges.

Nordheim was direct about what comes next.

"Ultimately, we just need to go back to the Uranus system and see for ourselves," he said.

The North Dakota Space Grant Consortium also supported the work. The paper, "Constraining ocean and ice shell thickness on Ariel from surface geologic structures and stress mapping," appeared in Icarus (DOI: 10.1016/j.icarus.2025.116822).