The vast oceans and lakes of liquid methane on Saturn's moon Titan have garnered a lot of attention from scientists, but a new study has zeroed in on the root-like network of channels that crisscross the surface. The findings provide the first direct evidence that those canyons – some as deep as 1,870 ft (570 m) – are also flooded with liquid hydrocarbons.
Titan's many canals have long appeared dark on radar images, leading scientists to suspect they were filled with liquid, but they couldn't rule out the possibility that the effect was caused by saturated sediment at the bottom. Using data gathered by NASA's Cassini spacecraft during a close pass in May 2013, the researchers were able to confirm the presence of liquid in Vid Flumina, a network of channels that branch out from Titan's large northern sea, Ligeia Mare.
On this particular pass, Cassini used its radar instrument as an altimeter, blasting the surface with radio waves to measure the height and depth of the landscape's features. The researchers combined this data with radar images of the same region to paint a more complete picture. Liquid was confirmed thanks to the radar instrument detecting a glint reflecting off the bottom of the canyons, in a manner much like that given off by the rest of the moon's oceans.
The channels that make up Vid Flumina are quite narrow, mostly around half a mile wide, and between 790 and 1,870 ft (241 and 570 m) deep, with sides sloping in at around a 40-degree angle. With that much variation in depth, different pockets of liquid were found at different elevations: in some areas it sat at sea level, while in others it could be as much as hundreds of feet higher, forming tributaries that feed into the oceans and lakes.
"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," says Alex Hayes, a co-author of the study published in the journal Geophysical Research Letters.
How exactly Titan's canyons came to be so deep is still a mystery, but scientists suspect forces similar to those that create canyons here on Earth – the terrain may have been uplifted, the sea level may have changed over time, or of course, a bit of both.
"It's likely that a combination of these forces contributed to the formation of the deep canyons, but at present it's not clear to what degree each was involved," says Valerio Poggiali, lead author of the study. "What is clear is that any description of Titan's geological evolution needs to be able to explain how the canyons got there."
Helping to develop those theories is the next step for the researchers, with future work expected to apply the methods from this study to other channels, in order to expand the picture and history of Titan's fascinating landscape.