An international team of researchers has found that Saturn's largest moon Titan has deep canyons filled with liquid hydrocarbons, making the alien moon look a lot like Earth, but with rivers of methane instead of water.
"Earth is warm and rocky, with rivers of water, while Titan is cold and icy, with rivers of methane. And yet it's remarkable that we find such similar features on both worlds," said team member Alex Hayes, from Cornell University.
The team says these channels and canyons form a river network they're calling Vid Flumina. Each of these canyons are about 0.8 kilometres (0.5 miles) wide and somewhere between 244 metres (800 feet) and 579 metres (1,900 feet) deep.
All of these rivers appear to flow into the moon's largest sea, Ligeia Mare, which is full of liquid methane hydrocarbons, but further research is needed to understand the flow and current of the rivers.
The team was able to make these observations thanks to data collected by NASA's Cassini spacecraft back in 2013 that measured Titan's topography, but the funny thing is that – despite having all of these new data to work off – the canyons are still quite a mystery.
"The canyons found in Titan's north are even more surprising, as we have no idea how they formed. Their narrow width and depth imply rapid erosion, as sea levels rise and fall in the nearby sea," said Hayes.
"This brings up a host of questions, such as where did all the eroded material go?"
On Earth, canyon formation is a simple, yet lengthy process that involves rivers slowly carving into the Earth's surface, carrying away layer after layer of river bed until canyons eventually form. The sediment that is scraped off the riverbed simply washes downstream to larger bodies of water like lakes or oceans.
On Titan, though, it remains unclear how these canyons came to be. Did they form thanks to erosion like Earth's? Or did they form from impacts or geological activities beneath the surface?
"It's likely that a combination of … forces contributed to the formation of the deep canyons, but at present, it's not clear," said team leader Valerio Poggiali, from the Sapienza University of Rome.
"What is clear is that any description of Titan's geological evolution needs to be able to explain how the canyons got there."
While understanding how methane rivers work on Titan will give us a better understanding of how this moon of Saturn formed, other scientists say that Titan could be home to microorganisms that thrive in methane-based atmospheres.
In fact, Titan is such a promising place for potential alien life, NASA is planning on sending an autonomous submarine there to explore these rivers and seas after Cassini finishes its mission.
So far, the Cassini mission – which is about to celebrate its 20th birthday – has provided researchers with unique pictures and observations of Titan and Saturn that have led to a plethora of scientific discoveries.
The mission will continue to run for another 10 months, with the hope that it will shine a light on the possibility of life at some point in its history, though there's still a long road ahead.
The team's work was published in Geophysical Research Letters.