Cassini maps depths of Titan’s seas

Methane lakes extend more than 200 meters below surface of Saturnian moon

Ligeia Mare, sea on Titan

DEEP DOWN  One of the largest seas on Titan, Ligeia Mare, seen in this false-color radar image taken by the Cassini spacecraft, extends more than 200 meters below the moon’s surface. 

JPL-Caltech/NASA, ASI, Cornell

TUCSON — Planetary scientists have for the first time mapped the depths of three methane seas on Saturn’s moon Titan. The second-largest of these, Ligeia Mare, contains enough liquid methane to fill three Lake Michigans.

The sea bottoms showed up in radar observations from NASA’s Cassini spacecraft, which arrived at Saturn in 2004. Researchers directed the probe to bounce radar off of Titan’s seas to see how choppy they are. A closer look at the data showed a second, weaker reflection after the first, indicating that the radar penetrated the sea and reflected off the bottom.

The eastern part of Ligeia Mare averages from 20 to 40 meters in depth, says Alexander Hayes, a Cornell University planetary scientist who reported the discovery November 10 at the American Astronomical Society’s Division for Planetary Sciences meeting. Elsewhere in Ligeia Mare, Cassini did not detect a second reflection, suggesting that the seafloor drops below Cassini’s range of 200 meters.

Hayes also presented the discovery of a second “magic island” — ephemeral radar reflections first reported in June (SN Online: 6/22/14). The new observations from Kraken Mare, the largest of Titan’s seas, confirm that the mysterious features sit on top of the sea and are most likely wind-driven waves or flotsam stirred from somewhere below.

Christopher Crockett is an Associate News Editor. He was formerly the astronomy writer from 2014 to 2017, and he has a Ph.D. in astronomy from the University of California, Los Angeles.

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