NASA's Cassini spacecraft first spotted a mysterious island-like feature in Ligeia Mare—a large hydrocarbon sea on Titan, the largest of Saturn's moons—in July 2013. When it faded away during later imaging, some scientists dubbed it "Magic Island." Then last month radar images showed that the island had returned, this time twice as large as when Cassini made the find a year ago—it appears to now be 60 square miles instead of 30, reports Space.com.

"Science loves a mystery, and with this enigmatic feature, we have a thrilling example of ongoing change on Titan," a NASA radar specialist said in an agency statement.

There are four main hypotheses, though NBC News notes that the island is almost definitely not an island. One, it's radar reflections of surface waves on Ligeia Mare; two, gas bubbles are floating out of the sea; three, a solid mass is rising to the surface; or four, it's a grouping of suspended solids, gathering and then dissipating.

Whatever the case, the activity may be due to seasonal changes, with summer approaching in Titan's Northern Hemisphere—though with each year lasting 30 of our own, seasons change slowly when compared to Earth's calendar.

Titan, which is roughly 50% wider than our own moon, is the only body outside of Earth that we know has stable bodies of liquid on its surface.

In fact, it's so cold that methane and ethane exist in liquid form, hence the lakes, rivers, and even rain clouds observed. (Scientists have ranked Titan as the extraterrestrial body that is most capable of supporting life.)

This article originally appeared on Newser: Saturn Moon's 'Magic Island' Reappears, Stumps NASA

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