Astronomy

NASA’s Cassini spacecraft has discovered evidence that points to the existence of an underground ocean of water and ammonia on Saturn’s moon Titan. The findings made using radar measurements of Titan’s rotation will appear in the March 21 issue of the journal Science.

According to Ralph Lorenz, lead author of the paper and Cassini radar scientist at the Johns Hopkins Applied Physics Laboratory in Laurel, Md., Titan has one of the most varied, active and Earth-like surfaces in the solar system with its organic dunes, lakes, channels and mountains.

Scientists and radar engineers at Cassini’s Synthetic Aperture Radar have collected imaging data during 19 separate passes over Titan between October 2005 and May 2007. The radar can see through Titan’s dense, methane-rich atmospheric haze, detailing never-before-seen surface features and establishing their locations on the moon’s surface. They believe that about 62 miles beneath the ice and organic-rich surface is an internal ocean of liquid water mixed with ammonia.

Using data from the radar’s early observations, they established the locations of 50 unique landmarks on Titan’s surface, and then searched for these same lakes, canyons and mountains in the reams of data returned by Cassini in its later flybys of Titan. They found prominent surface features had shifted from their expected positions by up to 19 miles. A systematic displacement of surface features would be difficult to explain unless the moon’s icy crust was decoupled from its core by an internal ocean, making it easier for the crust to move.

The study of Titan is a major goal of the Cassini-Huygens mission because it may preserve, in deep-freeze, many of the chemical compounds that preceded life on Earth. Titan is the only moon in the solar system that possesses a dense atmosphere. The moon’s atmosphere is 1.5 times denser than Earth’s. Titan is also known as the largest of Saturn’s moons. It actually bigger than the planet Mercury!

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