Liquid methane-filled canyons hundreds to thousands of feet deep etch the surface of Saturn’s largest moon, according to researchers with NASA’s Cassini mission.
Cassini pinged the surface of Titan with microwaves, finding that some channels are deep canyons filled with liquid hydrocarbons. One such feature is Vid Flumina, the branching network of narrow lines in the upper-left quadrant of the image. Image credit: NASA / JPL-Caltech / ASI.
Cassini radar observations of Titan’s north pole depict cavernous gorges a little less than half a mile (< 1 km) wide, with slopes steeper than 40 degrees.
The eight canyons branch off from Vid Flumina, a 250-mile (400 km) long river flowing into Ligeia Mare, Titan’s second-largest hydrocarbon sea.
The canyons are quite deep – 790 to 1,870 feet (240 to 570 m) from top to bottom – and appear dark in radar images, much like Titan’s seas.
The new Cassini data confirm the canyons are filled with flowing methane – a feature planetary scientists had suspected but not directly observed.
The new findings suggest the canyons were likely carved by liquid methane draining into Vid Flumina, a process similar to the carving of river gorges on Earth.
“These are processes we need to totally understand because they can shed deeper light on our own planet,” said co-author Dr. Valerio Poggiali, from the La Sapienza University of Rome in Italy.
“Titan is the only planetary body in our Solar System, other than Earth, to have a surface actively eroding on a large scale,” added Dr. Rosaly Lopes of NASA’s Jet Propulsion Laboratory.
“We have seen some canyons elsewhere, such as Vallis Marineris on Mars. However, on Titan, this study shows evidence that some canyons are still filled with liquid and presumably in the process of carving canyons.”
This image from Cassini shows Ligeia Mare, the second largest known body of liquid on Titan. The image is a false-color mosaic of synthetic aperture radar images obtained by Cassini between February 2006 and April 2007. Dark areas (low radar return) are colored black while bright regions (high radar return) are colored yellow to white. In this color scheme, liquids, which are dark to the radar, end up appearing black and the solid surface of Titan, which appears bright to the radar, ends up appearing yellow. Image credit: NASA / JPL-Caltech / ASI / Cornell.
Scientists first observed seas on Titan in 2006 during one of Cassini’s early flybys. Six years later the spacecraft spied Vid Flumina and its branching channels.
Researchers suspected those channels, some of which appeared canyon-like, were filled with flowing methane. Other clues like icy pebbles rounded by river-flow affirmed their suspicions, but they lacked direct evidence the channels were liquid-filled – until now.
“What we didn’t know was whether some channels still contained liquids, i.e., whether these rivers of methane were still flowing,” Dr. Lopes said.
Studying the geologic processes on Titan can help scientists tease apart the moon’s origins and conditions on early Earth.
Titan allows them to see how these processes change under varying conditions, like changes in temperature.
“On Earth we can’t vary the conditions like surface temperature and atmospheric density to see how geologic processes would behave. But by turning to Titan, scientists can see how familiar processes could change when those conditions are altered,” Dr. Lopes said.
“Although the term is overused, Titan is really a ‘natural laboratory’ for understanding geological processes.”
“Many more small canyons may line Titan’s surface, possibly hidden just below the resolution of Cassini’s instruments,” she added.
“Future missions could reveal those and other features, which may further color our understanding of Titan’s origins.”
The findings were published this week in the journal Geophysical Research Letters.
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V. Poggiali et al. Liquid-filled canyons on Titan. Geophysical Research Letters, published online August 9, 2016; doi: 10.1002/2016GL069679
