Uranus holds many mysteries – that’s why scientists are so enthusiastic about probing it in the future. But a new study suggests that the planet’s moons might also harbour some secrets of their own. Specifically, Miranda, one of Uranus’ five major moons (there’s 28 in total), recently surprised researchers with evidence that it might host an underground ocean, which would make it a strong candidate for finding alien life beyond Earth.

Tom Nordheim, a planetary scientist at Maryland’s Johns Hopkins Applied Physics Laboratory, analysed the obscure moon using imagery captured in 1968 by Voyager 2, a spacecraft launched into the depths of our solar system all the way back in 1977. Researchers earmarked this cosmic body because of the erratic patterns on its surface, which seem to be the product of tidal forces and temperature fluctuations within the moon itself.

The question is: is there still something going on inside Uranus’s moon? To answer that all-important question, the researchers – also including Caleb Strom (University of North Dakota) and Alex Patthoff (the Planetary Science Institute in Arizona) – attempted to reverse-engineer Miranda’s surface patterns, working backwards to figure out what they say about the evolution of the moon’s core.

Using an extensive map of the surface, combined with a specialised computer model, the team determined that the most likely story is that there was a massive ocean beneath the icy surface of Miranda some 100 million to 500 million years ago. Apparently, it could have been around 100 kilometres deep, making up almost half of the moon’s body (by comparison, Earth’s ocean measures about 11 kilometres at its deepest point).

Uranus is much further from the Sun than Earth, though, and temperatures on Miranda can get as low as -187 celsius. So how did the ocean not freeze up completely? According to the study, Miranda might have been locked in a “dance” with nearby moons, and their gravitational pull caused friction, warming its interior. If the theory is correct, though, iit fell out of this “dance” at some point, and its insides will have been cooling ever since.

If the ocean had completely frozen over, though, the water would have expanded as it turned to ice, and caused cracking on the surface of Miranda. The team didn’t find any evidence of this, so they’ve concluded that the ocean must still be at least partially liquid. Nordheim describes the finding as “incredibly surprising” and says: “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.”

At the end of the day, we’re still not sure what we’ll find if we travel to Uranus’s moons and take a look inside. Thanks to the new research, though, Miranda joins icy moons like Europa and Enceladus as just a few of the potential hotspots for alien life in our solar system.