Grandiose Canyons on a Saturn Moon, Filled With Liquid Methane

Deep, narrow canyons on Titan, Saturn’s largest moon, are flooded with liquid methane and other hydrocarbons, radar data from NASA’s Cassini spacecraft has found.

Titan, the Saturn moon with a diameter one and a half times that of Earth’s moon, is a surprisingly complex world. It has three large seas, a thick covering of haze and clouds, and surface contours carved by erosion — despite temperatures of about minus 300 degrees Fahrenheit (minus 184 Celsius).

“For many things, it is similar to our planet,” said Valerio Poggiali of the University of Rome, and a member of the Cassini spacecraft mission’s radar team. “That is why we consider Titan really a laboratory for a deeper understanding of our home planet.”

On Earth, the dynamics of climate arise from the transformations of water between its liquid, ice and vapor phases. On Titan, the chilly conditions are close to where methane can similarly coexist as liquid, ice and vapor, and that generates similar climate and geological phenomena.

The newly described canyons in Titan’s north polar regions are about half a mile wide and 790 to 1,870 feet deep, with slopes greater than 40 degrees. Earlier observations by Cassini had spotted channels branching off Ligeia Mare, the second largest of Titan’s seas, adding to the exotic features observed on the moon’s surface.

In synthetic aperture radar images, the channels were dark, just like the sea that is mostly liquid methane. That suggested the channels, too, were filled with liquid methane and other hydrocarbons, but it was also possible that the dark areas were hydrocarbon-saturated sediments.

Mr. Poggiali, an engineering graduate student, turned to data that Cassini collected in 2013, when the radar was used to measure elevations as it passed over this region.

In an article published Tuesday in the journal Geophysical Research Letters, Mr. Poggiali and his colleagues reported that they had spotted three reflections from the radar signal. The first came from the radar bouncing off the edges of the canyon.

The second was a bright reflection, like a glint off a mirror. This they interpreted as the liquid surface, and tellingly the height of the surface in the main channels was the same as that of the sea, even more than 100 miles away. For the dark material to be that flat and that reflective, it almost certainly had to be the same liquid as in the sea. (The smaller tributaries were at higher elevations, suggesting that they were flowing downhill into the larger rivers.)

This was the first direct detection of a liquid flooding the channels, Mr. Poggiali said.

The third reflection, a faint echo, came from the bottom of the canyon. The timing of the reflections provided a measure of the canyons’ depths, and how much of them was filled with liquid.