A study published in Icarus presents evidence that Ariel, a moon orbiting Uranus, may have contained a substantial subsurface ocean in its past. The research indicates this hidden ocean could have exceeded 100 miles in depth, substantially deeper than Earth’s Pacific Ocean. Ariel, the brightest of Uranus’ moons and fourth-largest in the Uranian system, spans approximately 720 miles across and displays an unusually complex geological surface for its size.
The moon’s landscape features ancient impact craters alongside younger terrain, with some smooth regions potentially formed through cryovolcanism. Notably, Ariel is covered with extensive fractures, ridges, and grabens, some occurring at scales rarely seen elsewhere in the Solar System. These dramatic surface features prompted researchers to investigate what Ariel’s interior structure and orbital characteristics might have been historically to explain the present-day geology.
The research team employed computer modeling to analyze tidal stresses on Ariel’s surface resulting from gravitational forces as the moon orbits Uranus. By mapping surface structures and simulating how tidal forces would deform the moon from spherical to slightly football-shaped and back, the scientists inferred past orbital eccentricity and ocean depth. Findings suggest Ariel’s orbit may have been approximately 40 times more eccentric than today, roughly four times more eccentric than Jupiter’s moon Europa, which experiences substantial tidal fracturing.
This investigation represents the second in a series examining subsurface oceans on Uranus’ moons, following a similar study on Miranda last year. The combined findings suggest multiple moons in the Uranian system may have once hosted substantial subsurface oceans. Researchers emphasize that future spacecraft missions to the Uranus system could test these predictions by imaging the unexplored northern hemispheres of both Ariel and Miranda and verifying predicted fracture and ridge patterns. The exact timeline of when these oceans existed remains undetermined, but the results provide a foundation for understanding how subsurface oceans form and evolve on distant icy worlds.
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