Astronomers have identified an unusual bright feature on the surface of Saturn's largest moon that has now disappeared. They are calling it a "magic island".

Rather than magic, they are however actually putting it down to some kind of "transient geological feature" that could help us better understand Titan's weather, as well as liquid bodies here on Earth, since it was spotted in the moon's second-largest sea.

The anomaly was picked up from data captured by Nasa's Cassini spacecraft, which first arrived at Saturn in 2004, during its northern winter. Titan has incredibly long seasons, and is only now heading towards a summer solstice that will take place in 2017. This, believes the team from Cornell writing in Nature Geoscience, may be what is behind the disappearing act pulled in Ligeia Mare, Titan's northern sea, which spans for kilometres. The team suggests it may have been caused by "surface waves, rising bubbles, and suspended or floating solids".

"This discovery tells us that the liquids in Titan's northern hemisphere are not simply stagnant and unchanging, but rather that changes do occur," commented lead author on the paper and Cornell planetary sciences graduate Jason Hofgartner. "We don't know precisely what caused this 'magic island' to appear, but we'd like to study it further."

Ligeia Mare, the second largest sea on the Saturn moon Titan, sports its usual coastline in this image.
Ligeia Mare, the second largest sea on the Saturn moon Titan, sports its usual coastline in this image.NASA/JPL-Caltech/Cornell
A mysteriously bright object appears on Ligeia Mare.
A mysteriously bright object appears on Ligeia Mare.NASA/JPL-Caltech/Cornell

Titan's surface is covered in liquid methane and ethane, which make up vast lakes and rivers across the moon's surface. Like an iceberg breaking off and floating out to sea in the summer months, the unidentified object on Titan's surface could be a clue about the changing seasons and how it affects the moon's landscape. "We suggest that our observations are an initial glimpse of dynamic processes that are commencing in the northern lakes and seas as summer nears in the northern hemisphere," write the authors.

The team came upon the change on Titan's surface in particularly mundane fashion, "flipping" back and forth between older images, more recent ones and those captured in between on 10 July 2013. Before this date, not only had there been no "magic island" in the picture, there was not even a hint of any geological movement in the body of water -- even waves were nowhere to be found. Suddenly, a white area appeared in the sea, around 20km long and 10km wide.

The team speculates that the object might have been caused by winds in the north creating waves; gases coming up from the seabed to the surface; sunken solids formed in winter become buoyant as Titan nears summer (kind of like an iceberg); or suspended solids that behave like "silt". It would indicate the weather during winter and spring is particularly placid. 

Hofgartner speculates: "Likely, several different processes -- such as wind, rain and tides -- might affect the methane and ethane lakes on Titan. We want to see the similarities and differences from geological processes that occur here on Earth. Ultimately, it will help us to understand better our own liquid environments here on the Earth."

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