A study published in Icarus presents evidence that Ariel, a moon orbiting Uranus, may have contained a substantial subsurface ocean beneath its icy crust in the distant past. The research indicates this ocean could have reached depths exceeding 100 miles, substantially deeper than Earth’s Pacific Ocean. Ariel, the brightest of Uranus’ moons and the fourth-largest in the Uranian system, spans approximately 720 miles across and displays a complex surface featuring both ancient impact craters and younger terrain formations, some potentially created through cryovolcanism.
Researchers conducted modeling studies to understand how Ariel’s surface features, including extensive fractures and large-scale structural formations, may have originated. The investigation focused on how changes in the moon’s orbital characteristics and internal structure could generate sufficient tidal stress to produce the observed fractures. Using computational modeling to analyze tidal stress patterns, scientists determined that Ariel’s orbit may have been considerably more eccentric in the past, with an eccentricity value approximately 40 times greater than its current state. Such orbital conditions would have significantly amplified gravitational forces acting on the moon’s icy crust.
The findings suggest that either a thin icy shell overlying a substantial ocean or higher orbital eccentricity combined with a smaller ocean could account for the dramatic surface features visible today. This research follows earlier work examining similar conditions on Miranda, another Uranian moon, suggesting the possibility that multiple moons in the Uranus system may have once harbored subsurface oceans. Scientists acknowledge uncertainty regarding when such an ocean may have existed or its duration.
Researchers note that only the southern hemispheres of Ariel and Miranda have been observed to date. The study’s predictions regarding fracture patterns and surface features could guide future spacecraft missions to the Uranus system, potentially allowing scientists to test their models by imaging unexplored northern hemispheres and searching for predicted geological structures.
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