River Networks on Saturn’s Moon Might Have Undergone Erosion Similar to Earth

The geological past of Saturn's largest moon Titan was hidden beneath a thick methane and nitrogen atmosphere and this hazy blanket of gases kept its perplexing terrain unexplored. Saturn's largest moon appeared through telescopes as a hazy orange orbit, in contrast with other heavily-cratered moons in the solar system.

It was in 2004 that Saturn's spacecraft, Cassini Huygens penetrated into Titan's haze, providing scientists with detailed images of the surface. They traced the existence of an icy terrain with the help of radar images. These icy terrains were carved out over millions of years by rivers of liquid methane, similar to how rivers of water have been etched onto the Earth's rocky continents.

With the help of these images, scientists have been able to study the existing landscape, though the geological past still remains a mystery. Based on the images, researchers at MIT and the University of Tennessee at Knoxville have analyzed Titan's river networks and determined that in some regions, rivers have created surprisingly little erosion. The researchers say there are two possible explanations: either erosion on Titan is extremely slow, or some other recent phenomena may have wiped out older riverbeds and landforms.

"It's a surface that should have eroded much more than what we're seeing, if the river networks have been active for a long time," says Taylor Perron, the Cecil and Ida Green Assistant professor of Geology at MIT. "It raises some very interesting questions about what has been happening on Titan in the last billion years."

The study that appeared in the Journal of Geophysical Research-Planets compares Titan, which is four billion years old, to the other moons in the solar system. Titan is described as relatively smooth with a few craters pockmarking its façade. Based on the number of craters they estimate that its surface is much younger, between 100 million and one billion years old.

"We don't have many impact craters on Earth," Perron says. "People flock to them because they're so few, and one explanation is that Earth's continents are always eroding or being covered with sediment. That may be the case on Titan, too."

It is a real challenge for astronomers to identify which of the geological phenomena would have modified Titan's surface, as they assume that processes like tectonic upheaval, icy lava eruptions, erosion and sedimentation by rivers - may be at work.

"It's an interesting challenge," Perron says. "It's almost like we were thrown back a few centuries, before there were many topographic maps, and we only had maps showing where the rivers are."

The team analyzed images taken from Cassini-Huygens, and mapped 52 prominent river networks from four regions on Titan. The researchers compared the images with a model of river network evolution developed by Perron. This model depicts the evolution of a river over time, given variables such as the strength of the underlying material and the rate of flow through the river channels. As a river erodes slowly through the ice, it transforms from a long, spindly thread into a dense, treelike network of tributaries.

They found that the moon's rivers most resembled the early stages of a typical terrestrial river's evolution. The observations indicate that rivers in some regions have caused very little erosion, and hence very little modification of Titan's surface.

"They're more on the long and spindly side," fellow researcher Benjamin Black says. "You do see some full and branching networks, and that's tantalizing, because if we get more data, it will be interesting to know whether there really are regional differences."