Space is full of mysteries, and now we can add one more to the list. A mysterious feature recently appeared on Titan, one of Saturn's moons, and scientists, as of yet, have no real explanation for it.

NASA's Cassini spacecraft originally spotted this mystery in July 2013 during a flyby of Titan. The feature appeared again after a flyby in August 2013, and images show that the feature has grown and changed in a month's time.

"NASA tells the full story, including the team's recovery of the feature in the Titan flyby just this August," says NASA spokesperson Preston Dyches. "So it's no longer a disappearing feature, but an evolving one."

This mysterious thing, found in one of Titan's seas called Ligeia Mare, takes up about 100 square miles in that ocean.

In radar imagery, Ligeia Mare appears dark, while the mysterious feature, whatever it is, appears bright against that dark sea. Before the feature showed up, there was no sign of anything like this in the region.

Of course, at first, scientists thought that the brighter area might be a flaw with the equipment, but they ruled that possibility out. Whatever the feature is, it is real.

Scientists also determined that this isn't happening from sea evaporation, because Ligeia Mare's shoreline has not changed.

So exactly what is this thing? NASA's team thinks it could be something simple, such as surface waves or rising bubbles. Perhaps it's something solid floating on the surface or just underneath the surface of the sea. Or it could be related to the changing seasons on Titan, something that happens when the moon's northern hemisphere enters its summer phase.

However, there is a possibility that it's something else entirely, and that's the most exciting prospect of all.

"Science loves a mystery, and with this enigmatic feature, we have a thrilling example of ongoing change on Titan," says Stephen Wall, the deputy team lead of Cassini's radar team at NASA's Jet Propulsion Laboratory. "We're hopeful that we'll be able to continue watching the changes unfold and gain insights about what's going on in that alien sea."

Titan, which is larger than Earth's moon, fascinates scientists, particularly because it's the only other celestial body, in addition to Earth, that we know of with stable water on its surface. Unlike Earth, though, its lakes and seas contain ethane and methane, suggesting that the moon could potentially sustain life, albeit unlike the kind of life found on Earth.