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Radar beams from NASA’s Cassini spacecraft pierce the cloudy haze of Titan to reveal what’s underneath. What they revealed about Saturn’s intriguing moon during a May 2013 flyby is a first. Deep canyons flooded with liquid hydrocarbons.
A network of canyons named Vid Flumina appear dark in the radar image below.
Titan’s methane-rich seas also appear dark. But scientists couldn’t just assume the dark color meant liquids were present. Saturated sediment could also be responsible for the dark color. And at Titan’s icy temperatures, it would be ice instead of rock.
So, how can Cassini’s team figure out exactly what the dark colors represent? Scientists paid close attention to how the radar signals reflected off the bottom of the canyons. Cassini’s radar detected a glint off the bottom of the canyon. The same feature is seen in Titan’s hydrocarbon seas and indicates a very smooth surface. Too smooth to be saturated sediments.
With the discovery of liquid hydrocarbons within the canyons locked down, it was time to figure out how deep they are. That’s another great thing about radar. It can be used as an altimeter to figure out the heights (or in this case, depth) of surface features on the moon.
The canyons making up Vid Flumina are narrow. Most are less than a half mile wide. But they are deep. The ones Cassini could measure ranged from 790 to 1,870 feet. And their walls are steep at more than 40 degrees.
NASA describes the network of canyons as a ‘Nile-like River Valley.’ It stretches more than 200 miles and empties into Ligeria Mare, one of three large seas in the northern latitudes of Saturn’s moon. It’s relatively straight path suggests it could be tracing at least one fault.
How Titan’s rivers carved these canyons
Cassini’s radar team point to two possible scenarios. Uplifting terrain or changes in sea level. Chances are it’s both. Here’s what Valerio Poggiali, a member of the Cassini radar team and lead author of the study, had to say.
“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. What is clear is that any description of Titan’s geological evolution needs to be able to explain how the canyons got there,” says Poggiali.
We can turn closer to home to see what this pair of processes looks like. Just look at the Colorado River in Arizona. The Grand Canyon is a perfect example of uplifting terrain. As the terrain around the river rose, the water etched deeper. Several million years later, the canyon reaches depths of over a mile.
For an example of changes in sea level, look at Lake Powell. As water levels drop in the lake, the river’s rate of erosion increases according to NASA.
“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 Alex Hayes. He’s another Cassini radar team associate and co-author of the study.
Future research will expand the search to many more canyons. One thing is for sure. Whatever process etched these canyons was either active for a long time or worked quickly. Further study should help scientists pin down which.
What Cassini is doing these days
Yesterday, the spacecraft soared past Titan again at just 994 miles above the moon’s surface. It was the final gravity science flyby of the mission. Using the High Gain Antenna Radio, Cassini analyzed Titan’s deep structure. Data from this flyby will build on data gathered from previous flybys to understand how the icy crust of Titan flows.
Cassini has just over one year left traveling around the Saturn system. Soon the spacecraft will begin what NASA is dubbing the ‘Grand Finale.’ It’s a series of orbits taking the spacecraft between Saturn’s upper atmosphere and its innermost ring. On September 15, 2017, the spacecraft is expected to enter Saturn’s atmosphere, and its mission will come to an end.
But it won’t be the last we hear about Cassini. The data gathered in its decade-plus visit to Saturn and its moons will be studied for years to come.