Scientists have long been intrigued by Miranda, Uranus’s fifth-largest moon. Images captured by Voyager 2 in 1986 revealed a chaotic, icy surface, scarred by massive fault systems and enigmatic regions known as “coronae.” New research published in the Planetary Science Journal delves deeper into Miranda’s mysteries, suggesting the moon may have harbored a vast subsurface ocean in its recent geological past and experienced tectonic activity far longer than previously thought.

“Miranda’s surface is like a jigsaw puzzle, with pieces that don’t seem to fit,” says Caleb Strom, lead author of the study and a researcher at the University of North Dakota. “Our work suggests that these features tell a story of a dramatically changing world, with a potential ocean playing a key role.”

Strom and his team meticulously mapped Miranda’s craters, ridges, and valleys, comparing their distribution to models of stress caused by tidal forces, ice shell thickening, and even true polar wander — a phenomenon where the moon’s spin axis shifts due to internal mass redistribution. Their findings paint a picture of a moon undergoing intense geological upheaval.

“We found that Miranda’s ice shell, the solid outer layer, would have needed to be incredibly thin, perhaps only 30 kilometers thick, to experience the level of tectonic activity we see,” explains Strom. “This thin shell points to a massive, 100-kilometer deep ocean lurking beneath, possibly within the last 500 million years.”

The implications of a recent ocean on Miranda are significant. It places this small moon in the same league as Enceladus and Europa, icy moons of Saturn and Jupiter, respectively, known for their potentially habitable subsurface oceans. While no evidence of active plumes or cryovolcanism was detected on Miranda by Voyager 2, scientists haven’t ruled out the possibility of these features.

“Miranda may have been, or could still be, an ocean world,” Strom speculates. “The presence of ammonia on its surface hints at recent geological activity that may have brought material up from the depths.”
The study also suggests that Miranda’s geological activity may have been driven by a combination of factors. Obliquity tides, caused by the moon’s tilted spin axis, and true polar wander, likely contributed to the unique distribution of tectonic features.

“Miranda’s story is far from over,” Strom concludes. “Our findings highlight the need for a dedicated mission to Uranus and its moons. Only then can we truly unravel the secrets of this fascinating and dynamic world.”

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