NASA's Cassini spacecraft has discovered a "mysterious feature" on Saturn's moon Titan. Scientists are working to determine, what, exactly, this feature might be.

NASA reports that the feature is roughly 100 square miles, and it lies in Ligeia Mare, one of Titan's hydrocarbon seas. Cassini's radar has observed the feature twice, but its appearance changed between the two sightings. Scientists suspect the feature's change in appearance could be the result of Titan's changing seasons, which Cassini's current extended mission will monitor.

The feature's first sighting was in July 2013, and the radar images depicted a bright spot, which stood out from the dark sea. Scientists were "perplexed" when the feature couldn't be located with follow-up radar experiments, but they found it again on August 21, 2014.

What is that? @CassiniSaturn sees mysterious feature evolve in sea of Saturn's moon Titan: http://t.co/gRQrPPzYpo pic.twitter.com/gf2ubDEoM0 — NASA (@NASA) September 29, 2014

Though the scientists aren't sure what the feature is, NASA reports that they are "confident" the feature is not a "flaw in their data." Some of their current explanations for the feature include "surface waves, rising bubbles, floating solids, solids suspended just below the surface, or perhaps something more exotic."

Titan's hydrocarbon lakes have long been a source of curiosity for scientists who speculate that life may be able to survive on the moon's surface. "But if life exists on Titan, it would be very different than life on Earth, which is intimately tied to liquid water," Space.com notes.

"Science loves a mystery, and with this enigmatic feature, we have a thrilling example of ongoing change on Titan," Stephen Wall, the deputy team lead of Cassini's radar team, said in a statement. "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." Meghan DeMaria