New research suggests that Ariel, one of Uranus’ moons, may have once contained a subsurface ocean more than 100 miles (170 kilometers) deep. This finding, published in *Icarus*, indicates that the distant Uranian system could harbor multiple hidden ocean worlds. Ariel is the brightest and second-closest of Uranus' moons. It measures 720 miles (1,159 kilometers) across.
Planetary Science Institute senior scientist Alex Patthoff, a co-author, noted Ariel's unique characteristics among icy moons. Despite its size, Ariel has a complex surface. This includes ancient impact craters and younger terrain. Some smooth regions may have formed through cryovolcanism, where water or ice erupts from the moon's interior.
Ariel's surface also features large fractures, ridges, and grabens. These are areas where the crust has dropped. Researchers investigated how Ariel's past interior and orbit could have created these structures. They modeled tidal stresses on the surface. These stresses result from gravitational forces as Ariel orbits Uranus. The moon is repeatedly stretched and squeezed.
The study found Ariel may have had a higher orbital eccentricity in the past. This means its orbit was less circular. This increased tidal forces on the moon. These forces could have caused the large fractures observed today. The presence of an ocean is necessary to create these surface fractures. This research builds on previous findings for Miranda, another Uranian moon, suggesting it also had a subsurface ocean.
Tom Nordheim of Johns Hopkins University Applied Physics Laboratory, a co-author, stated that the Uranus system may contain twin ocean worlds. Scientists do not yet know when Ariel's deep ocean existed or for how long. Future missions to Uranus could test these predictions. They could image Ariel's unexplored northern hemisphere. This research was funded by a National Aeronautics and Space Administration (NASA) Solar System Workings grant and the North Dakota Space Grant Consortium.
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