The joint NASA-ESA Cassini space probe, exploring Saturn and its moons, has revealed extraordinary lakes and seas of liquid methane around the north pole of Saturnian moon Titan. Scientists associated with the Cassini mission described a strange rectangular area of large seas, picked out by imaging instruments aboard the probe.

Elongated lakes and narrow channels linking two large seas are apparent in the new image. It’s reminiscent of the topographic depressions in the basin and range region of the western US. Those are shaped by the movements of tectonic plates on America’s fringe, which suggests that the large lakes seen on Titan may be shaped by tectonic forces.

“Scientists have been wondering why Titan’s lakes are where they are. These images show us that the bedrock and geology must be creating a particularly inviting environment for lakes,” said Randolph Kirk, part of the Cassini RADAR team and based at the US Geological Survey. “We think it may be something like the formation of the prehistoric lake called Lake Lahontan near Lake Tahoe in Nevada and California, where deformation of the crust created fissures that could be filled up with liquid.”

Scientists described the observations of huge polar lakes called Ligeia and Kraken on Titan at the meeting of the American Geophysical Union here in San Francisco today, the world’s largest gathering of Earth scientists.

Alongside the two large liquid bodies, there are a myriad of smaller lakes scattered around the pole of Titan. Their origins are unclear, with speculations ranging from volcanic craters to giant sinkholes formed because parts of Titan’s crust dissolved.

Cassini’s radar has charted the areas of the lakes and seas near the pole but has also bounced signals off the lake beds in the first depth soundings of an extraterrestrial sea. Marco Mastrogiuseppe from Sapienza University in Rome noted just how rare this is: “For the first time we were able to observe the topography of the subsurface of an extraterrestrial sea.”

“Ligeia Mare turned out to be just the right depth for radar to detect a signal back from the sea floor, which is a signal we didn’t think we’d be able to get,” said Mastrogiuseppe. A maximum depth of around 170 meters, similar to Lake Michigan, was determined.

The total volume of Ligeia is put at 9,000 cubic kilometers, but that volume is filled not with water, but with hydrocarbons. The total volume of the hydrocarbons in Titanic seas corresponds to around 300 times that of Earth’s oil reserves—all on a body smaller than Earth.

The radar reflectivity suggests that the lakes are mainly filled with methane, mixed with a few other heavier hydrocarbons, including ethane and nitrogen-containing compounds. Alongside Ligeia sits another sea, Kraken. Comparable in size to the Caspian Sea here on Earth, Kraken is four or more times the area of Ligeia. Cassini will return to carry out bathymetry of it in August of 2014.

Jeffrey Kargel of the University of Arizona pointed out that the presence of extensive methane seas and lakes adds to an existing problem: there aren’t as many heavy hydrocarbons as we’d expect from our models of Titan’s chemistry. Among these heavier compounds are ethane, ethylene, propylene, acetylene, and benzene—they’re expected to be generated as sunlight causes chemical reactions in Titan’s soup of natural gas. Yet so far, we haven’t seen very much of them.

Using visible wavelengths, Cassini has also revealed a world that is difficult to imagine. Titan has a northern polar cap larger than Greenland, and there are suggestions of huge dune fields of solid hydrocarbon sand around the equator. These equatorial “rocks” are saturated in ethane, while the polar regions appear to be made of methane. Underneath it all are crystallized heavy hydrocarbons, which form Titan’s crust.

Cassini first arrived at Saturn in 2004, yet it continues to produce surprises. Only four percent of its propulsion is left, and future maneuvers will largely be powered by the gravitational fields of Saturn and its moons. The probe’s final journey, planned for September 2017, will skirt Saturn’s innermost ring and touch its atmosphere before finally succumbing to the giant planet’s grasp.

This article was originally published at The Conversation. This is an edited form of it.