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Titan has a huge ice belt near its equator, and we don’t know how it got there. Most of the surface is covered in organic sediment that constantly rains from the sky, but one corridor 6300 kilometres long – about 40 per cent of the frigid moon’s circumference – seems to be bare ice.

On many of the cold worlds in the outer solar system, water ice acts as bedrock. Titan, Saturn’s largest moon, also has seas of methane and a thick atmosphere full of organic molecules. That thick atmosphere makes it extraordinarily difficult to see down to the surface.

There are just a few wavelengths of light that can penetrate the haze. Caitlin Griffith at the University of Arizona and her colleagues used data from the Cassini spacecraft to look for signs of exposed water ice on the surface using those wavelengths.

They found one particularly icy area surrounding a 500-metre high mountain called Doom Mons (which is named after Mount Doom, from Lord of the Rings) and a neighbouring pit that’s 1500 metres deep.

These areas have previously been noted for possible signs of cryovolcanism, which could bring ice up from under the surface, but there is also a long, straight line of ice that is more difficult to explain. Its 6300 kilometre length should be buried under hundreds of metres of organic sediment.

“It’s possible that we are seeing something that’s a vestige of a time when Titan was quite different,” says Griffith. “It can’t be explained by what we see there now.” Titan is probably not geologically active now, but the exposed ice could be a sign of the moon’s crust shifting or quaking in the past.

The ice may be embedded in the side of cliff faces exposed by erosion, rather than flat on the ground, Griffith says – so don’t get your hopes up for ice skating. “It would be one of the worst moons in the outer solar system to ice skate on anyway, because you have all this gunk that’s coming down from the atmosphere that might be sticky and gooey.”

Figuring out the distribution of that sediment could help us learn not only about Titan’s surface, but also about the history of its atmosphere, because the organic molecules on the surface were once part of the moon’s signature orange haze.