Washington, Sep 30 (IANS): NASA's Cassini spacecraft is closely monitoring the evolution of a mysterious feature in a large hydrocarbon sea on Saturn's moon Titan.

The enigmatic feature, which appears bright in radar images against the dark background of the liquid sea, was first spotted during Cassini's July 2013 Titan flyby.

The feature covers an area of about 260 square km in Ligeia Mare - one of the largest seas on Titan.

The appearance of this feature could be related to changing seasons on Titan, as summer draws near in the moon's northern hemisphere.

"Science loves a mystery and with this feature, we have a thrilling example of ongoing change on Titan," said Stephen Wall, leader of Cassini's radar team based at NASA's Jet Propulsion Laboratory in Pasadena, California.

Previous observations showed no sign of bright features in that part of Ligeia Mare.

Scientists were perplexed to find the feature had vanished when they looked again, over several months, with a low-resolution radar and Cassini's infrared imager.

Scientists on the radar team are confident that the feature is not an artifact, or flaw, in their data, which would have been one of the simplest explanations.

They also do not see evidence that its appearance results from evaporation in the sea, as the overall shoreline of Ligeia Mare has not changed noticeably.

The team has suggested the feature could be surface waves, rising bubbles, floating solids, solids suspended just below the surface or perhaps something more exotic.

"We are hopeful that we will be able to continue watching the changes unfold and gain insights about what is going on in that alien sea," Wall added.