Cassini Finds Flooded Canyons on Titan

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Cassini Finds Flooded Canyons on Titan
Jet Propulsion Laboratory
August 10, 2016

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, as well as the first observation of canyons hundreds of meters
deep.

A new paper in the journal Geophysical Research Letters describes how
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 -- in particular, a
network of them named Vid Flumina -- 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 -- those measured are
790 to 1,870 feet (240 to 570 meters) from top to bottom.

The branching channels appear dark in radar images, much like Titan's
methane-rich seas. This suggested to scientists that the channels might
also be filled with liquid, but a direct detection had not been made until
now. 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.
But during this pass, the radar was used as an altimeter, sending pings
of radio waves to the moon's surface to measure the height of features
there. The researchers combined the altimetry data with previous radar
images of the region to make their discovery.

Key to understanding the nature of the channels was the way Cassini's
radar signal reflected off the bottoms of the features. The radar instrument
observed a glint, indicating an extremely smooth surface like that observed
from Titan's hydrocarbon seas. The timing of the radar echoes, as they
bounced off the canyons' edges and floors, provided a direct measure of
their depths.

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. The researchers' proposed scenarios
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. What is clear is that any description of Titan's geological
evolution needs to be able to explain how the canyons got there," said
Valerio Poggiali of the University of Rome, a Cassini radar team associate
and lead author of the study.

Earthly 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.

While the altimeter data also showed that the liquid in some of the canyons
around Ligeia Mare is at sea level -- the same altitude as the liquid
in the sea itself -- in others it sits tens to hundreds of feet (tens
of meters) higher in elevation. The researchers interpret the latter to
be tributaries that drain into the main channels below.

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. NASA's Jet Propulsion Laboratory,
a division of Caltech in Pasadena, manages the mission for NASA's Science
Mission Directorate, Washington. JPL designed, developed and assembled
the Cassini orbiter. The radar instrument was built by JPL and the Italian
Space Agency, working with team members from the US and several European
countries.

More information about Cassini:

http://www.nasa.gov/cassini

http://saturn.jpl.nasa.gov

News Media Contact
Preston Dyches
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-7013
preston...@jpl.nasa.gov

2016-207