Published : Thursday, August 11, 2016 | 1:16 PM
Pasadena’s Jet Propulsion Laboratory announced Wednesday that NASA’s Cassini spacecraft has found deep, steep-sided canyons on Saturn’s moon Titan that are flooded with liquid hydrocarbons. The finding represents the first direct evidence of the presence of liquid-filled channels on Titan and the first observation of canyons hundreds of meters deep.
A new paper in the journal Geophysical Research Letters describes how JPL scientists analyzed Cassini data from a close pass the spacecraft made over Titan in May 2013. During the flyby, Cassini’s radar instrument focused on channels that branch out from the large, northern sea Ligeia Mare.
The Cassini observations reveal that the channels are narrow canyons, generally less than half a mile (a bit less than a kilometer) wide, with slopes steeper than 40 degrees. The canyons also are quite deep – anywhere from 790 to 1,870 feet, or 240 to 570 meters, from top to bottom.
Previous observations show the branching channels appearing dark in radar images, much like Titan’s methane-rich seas. To scientists, this suggested that the channels might also be filled with liquid, but it was only now that a direct detection had been made. Previously it wasn’t clear if the dark material was liquid or merely saturated sediment – which at Titan’s frigid temperatures would be made of ice, not rock.
Cassini’s radar is often used as an imager, providing a window to peer through the dense haze that surrounds Titan to reveal the surface below. During this particular pass, the radar was used as an altimeter, sending pings of radio waves to the moon’s surface to measure the height of features of the canyons on Titan. The researchers combined the altimetry data with previous radar images of the region to make their discovery.
The presence of such deep cuts in the landscape indicates that whatever process created them was active for a long time or eroded down much faster than other areas on Titan’s surface. Some of the scenarios the researchers look at include uplift of the terrain and changes in sea level, or perhaps both.
“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,” said Valerio Poggiali of the University of Rome, a Cassini radar team associate at JPL and lead author of the study. “What is clear is that any description of Titan’s geological evolution needs to be able to explain how the canyons got there.”
On Earth, examples of both of these types of canyon-carving processes are found along the Colorado River in Arizona. An example of uplift powering erosion is the Grand Canyon, where the terrain’s rising altitude caused the river to cut deeply downward into the landscape over the course of several million years. For canyon formation driven by variations in water level, look to Lake Powell. When the water level in the reservoir drops, it increases the river’s rate of erosion.
“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, a Cassini radar team associate at Cornell University, Ithaca, New York, and a co-author of the study.
Future work will extend the methods used in this study to all other channels Cassini’s radar altimeter has observed on Titan. The researchers expect their continued work to produce a more comprehensive understanding of forces that have shaped the Saturnian moon’s landscape.
The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory manages the mission for NASA’s Science Mission Directorate, Washington.
The Cassini orbiter was designed, developed and assembled by JPL personnel. JPL also built the radar instrument with the Italian Space Agency working with team members from the U.S. and several other European countries.
For more information about the Cassini project, visit www.nasa.gov/cassini.