Ocean worlds, such as Europa around Jupiter and Enceladus around Saturn, are recent and fascinating discoveries. These moons hide, far beneath their icy crusts, a deep liquid ocean. Other moons and dwarf planets also hide liquid oceans underneath, and the latest candidate is Miranda – the smallest of Uranus’s five round moons.
Miranda might be the smallest round object in the Solar System. It has a diameter of just 470 kilometers (290 miles). Its surface area is just about the area of Texas. Still, it is a complex world. Its surface is among the most extreme we have observed anywhere and features the tallest cliff in the Solar System: Verona Rupes, which has a drop of about 20 kilometers (12 miles). An equivalent cliff on Earth would have to be over 270 kilometers tall.
It was these and many other interesting features that suggested the presence of an ocean. Once the surface structures are plugged into computer models, the enigmatic geology is best matched by the presence of a vast ocean that formed between 100 and 500 million years ago.
“To find evidence of an ocean inside a small object like Miranda is incredibly surprising,” co-author Tom Nordheim, from Johns Hopkins Applied Physics Laboratory (APL), said in a statement. “It helps build on the story that some of these moons at Uranus may be really interesting – that there may be several ocean worlds around one of the most distant planets in our Solar System, which is both exciting and bizarre.”
The ocean would be at least 100 kilometers (62 miles deep) under a crust of no more than 30 kilometers (19 miles). Given the small size of the moon, the ocean would occupy half of its total volume.
The team believed it formed due to a gravitational resonance with another moon, squishing Miranda until its interior got warm enough to liquefy. The cosmic dance is not over, but the ocean has not completely frozen over. If it had, there would be cracks on the surface: water ice has a larger volume than liquid water. If Miranda has a truly liquid ocean, it would be truly remarkable.
That alone would warrant a mission there, as we discussed with Professor Brian Cox a few weeks back. There is so much more to the ice giants, Uranus and Neptune, that we do not know.
The study is published in The Planetary Science Journal.
