Titan’s canyons are flooded with liquid hydrocarbons
Radar data gathered by the Cassini Saturn orbiter have revealed that steep canyons on the planet’s large moon Titan are filled with liquid hydrocarbons. During a close pass over Titan in May 2013, Cassini used its radar as an altimeter, or instrument to measure altitude, to study its canyons up close by pinging radio waves to the moon’s surface to measure its features’ height.
Researchers combined this data with radar images of the same area taken in earlier flybys of Titan and, for the first time, found direct evidence of liquid in the moon’s deep channels and observed canyons running hundreds of meters deep. Cassini had previously seen sunlight glinting off the large moon’s liquid hydrocarbon lakes.
Radar is necessary for imaging Titan because its surface is obscured by a dense atmospheric haze.
The 2013 flyby specifically focused on Ligeia Mare, a large lake in the north, and the channels branching out of it. One such network, known as Vid Flumina, is composed of narrow canyons less than half a mile (slightly under a kilometer) in diameter.
The canyons are steep, with slopes greater than 40 degrees, and have depths ranging from 790 to 1,870 feet (240 to 570 meters).
Like Titan’s methane lakes, the channels appeared dark in the radar images, giving scientists the first clue that they might contain liquid. However, sediment saturated with ice also shows up dark on radar images.
In this case, the way radar signals reflected off the canyons’ bottoms provided another important clue. The radar instrument picked up a glint, confirming a smooth surface like that seen on Titan’s lakes.
By timing the echoes of the radar as it bounced off the edges and bottoms of the canyons, mission scientists were able to accurately measure their depths. The results revealed a landscape with deep gashes, suggesting the geological processes that created them either occurred over a long period of time or erosion in this area was much more rapid than on other locations on Titan’s surface.
According to the researchers, the canyons were likely formed via uplifting of the terrain, sea level changes, or a combination of the two.
Examples of both processes can be seen on Earth. The Grand Canyon, which runs along the Colorado River, was created by the uplifting of terrain over millions of years, increasing that terrain’s altitude while at the same time pushing the river in a downward direction.
The man-made Lake Powell, which also runs along the Colorado River, is another location where changes in water level affect erosion rates.
“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,” explained Valerio Poggiali, an associate of the Cassini radar team and lead author on an article about the findings published in the journal Geophysical Research Letters. “What is clear is that any description of Titan’s geological evolution needs to be able to explain how the canyons got there.”
While some of the liquid hydrocarbons in the canyons of Ligeia Mare are at sea level, others are located tens to hundreds of feet higher. The liquids at higher elevations are likely tributaries that drain into the lower channels.
Mission scientists plan to use the same radar technique to measure the elevations of other channels on Titan’s surface in the hope of better understanding the moon’s geological history.
Alex Hayes of Cornell University in Ithaca, New York, also an associate of the Cassini radar team and co-author of the study, marveled at the similarities of landscapes on Titan and Earth.
“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.”
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.