NASA’s Cassini Solstice Mission released a statement Monday detailing the observations of a mysterious feature in one of the largest seas on Saturn’s largest moon, Titan.

The feature, which is approximately 100 square miles (260 square kilometers) and located in the Ligeia Mare sea of Titan, was first observed in radar images during a July 2013 Titan surveillance by the Cassini spacecraft. According to the statement, no reports of this feature were ever previously recorded, and the feature disappeared over the next several months from Cassini’s infrared imager. During a recent fly-by on Aug. 21, however, the feature reappeared with a noticeably altered appearance.

Scientists believe that the feature is not a flaw in their data and suggest that it could be surface waves, rising bubbles, or even floating solids similar to Earth’s icebergs. “For a bit of background, on Earth, it’s quite a simple situation because ice floats in water,” said Jason Hofgartner, member of the Cassini Radar Science Team, in a recent statement to MailOnline. “On Titan, it’s more complicated because you have a methane and ethane mixture, we think, and there’s nitrogen from the atmosphere that also gets dissolved.”

“So when you freeze it, it undergoes complicated composition changes. Whether you can get icebergs that can float is a matter for debate, but it’s possible. When it warms, those icebergs could switch from sinking to floating.”

The researchers believe that changing seasons on Titan could play a role in the feature’s reappearance. “That’s sort of an ongoing theme for a lot of the Cassini results; a lot of things depend on the season at Saturn as it moves in orbit,” said Emma Bunce, who is also a member of the Cassini mission team. “Because this lake itself is actually near to Titan’s northern pole, perhaps it is something to do with illumination conditions”

According to the statement by Cassini, a major goal of the current mission is to monitor all these possibly seasonal changes on Titan. “Science loves a mystery, and with this enigmatic feature, we have a thrilling example of ongoing change on Titan,” said Stephen Wall, deputy team lead of Cassini’s radar team. “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.”