Earlier this year, it has been identified a mysterious “ghost” object that had suddenly appeared and then disappeared on Saturn’s largest moon, Titan. Now, new observations by the Cassini team show this elusive feature is back again. Titan just got a little more mysterious.
NASA’s Cassini spacecraft has spotted an odd islandlike feature in Ligeia Mare, one of Titan’s largest hydrocarbon seas. Scientists don’t know what to make of the feature, which has apparently doubled in size over the past year or so, from about 30 square miles to 60 square miles (78 to 155 square kilometers).
The mysterious 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.
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 low-resolution radar and Cassini’s infrared imager.
This led some team members to suggest it might have been a transient feature. But during Cassini’s flyby on August 21, 2014, the feature was again visible, and its appearance had changed during the 11 months since it was last seen.
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.
“Science loves a mystery, and with this enigmatic feature, we have a thrilling example of ongoing change on Titan,” said 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.”
The monitoring of Titan’s changing climate and surface features is a primary goal of Cassini’s ongoing, and twice-extended, mission.
Further studies may confirm or eliminate explanations that have been presented to date – or they may lead to completely new hypotheses about mysteries held within and below Titan’s seas.
Possible explanations for the feature include solids floating on or just below the sea’s surface, rising bubbles, or waves on the sea’s surface. The presence of the feature could be tied to Titan’s seasons, which are transitioning into summer now in the northern hemisphere. Cassini will continue to monitor Ligeia Mare as the seasons shift.