One of Saturn's moons, Mimas, just turned up a new mystery: It may contain an underground ocean that could be "life-friendly."

Using images of Mimas from NASA's Cassini spacecraft, scientists studied the wobble of the moon as it orbits around Saturn. This orbit is elliptical, rather than spherical, creating a deviation. This wobble is similar to that of the Earth's moon and is called "libration."

"Observing libration can provide useful insights about what is going on inside a body," says Radwan Tajeddine, a Cassini research associate. "In this case, it is telling us that this cratered little moon may be more complex than we thought."

Tajeddine compared it to spinning an egg to see if it's hard-boiled or raw.

Until now, the most unique feature of Mimas was its cratered appearance, making it resemble the Death Star from Star Wars fame. However, Mimas is slowly becoming more intriguing with this new finding.

One of the theories about this libration is that Mimas has a deep underground ocean, about 15 miles beneath its surface. This would put it in a category with other ocean worlds, such as Saturn moons Enceladus and Titan.

"If Mimas does have an ocean, this would definitely be another interesting body in the solar system to be added to list of potential 'life-friendly' environments," says Tajeddine.

At first, the ocean theory seems unlikely, as Mimas' small size prevents it from holding onto heat left over from its birth. However, models showed that liquid water underneath it's surface is still possible. The gravitational pull of Saturn as its moons orbit around it could create enough heat through friction to melt the ice inside of Mimas, resulting in liquid water. Scientists believe that Mimas' orbit was even more stretched out at one point, which would have made this effect even more pronounced.

Another theory is that Mimas has a core shaped like a football. Scientists first thought its core was spherical, because they estimate its age is more than 4 billion years old, but instead, it might be oblong, telling a new story about how the moon originally formed.

In this scenario, the same gravitational pull from Saturn could have created this odd-shaped core, covered in ice. Models showed that the low temperature of Mimas might keep the shape from becoming spherical over time.

Whatever the case, Mimas just became more interesting to scientists, who will spend more time examining it in hopes of unveiling its secrets.