Did Uranus’ Moon Miranda once hold a 100-kilometre-deep ocean? See what new study suggests

Miranda does not look like a typical small moon. The surface, seen in detail only once during Voyager 2’s flyby in 1986, carries scars that seem out of scale with its size. Wide fault systems cut across older cratered ground. Three large regions known as coronae interrupt the terrain with ridges and grooves that appear younger than their surroundings. A new peer-reviewed study in The Planetary Science Journal takes another look at those structures. Using geological mapping and computer stress models, researchers tested how thick Miranda’s ice shell may be and whether a subsurface ocean could have existed in the recent geological past. Their results suggest a thin outer shell and the possible presence of deep liquid water long after the moon first formed.Ridges, furrows, and craters were detected by the team in Miranda's southern hemisphere. Arden Corona and Elsinore Corona, which were situated on opposite sides of the moon, were the primary focus of attention. The two regions do not appear to be identical. Furrows and terrace-like scarps, which are frequently associated with extension, are the distinguishing features of Arden. The topography of Elsinore is characterised by folded and ridged features, which are more consistent with compression. That contrast is important. When mapped structures were compared to expected stress patterns, certain interior models aligned better than others. Some stress patterns were consistent with the fractures' broad layout. Others were not. Computer simulations tested tidal forces caused by orbital eccentricity and possible shifts in spin axis, along with stress from ice shell thickening. Across many scenarios, a consistent pattern emerged. If Miranda’s brittle ice shell was around 30 kilometres thick or less, tidal stress could reach levels high enough to fracture surface ice, creating fault lines, deep canyons and patchwork terrain similar to what spacecraft images have revealed.Thicker shells reduced the stress below likely failure strength. In those cases, the observed scale of tectonic disruption became harder to explain, suggesting the moon’s outer layer was once thinner and far more dynamic than it appears today.The same models predict that a subsurface ocean more than 100 kilometres thick might have existed between 100 and 500 million years ago. In terms of time on the planet, this is recent. Evidence remains indirect. Voyager 2 observed only one hemisphere. Still, the combination of documented geology and stress modelling lends credence to the theory that Miranda was not always frozen solid. It may have held heat for longer than previously thought, given its small size, distance, and outward quietness.