Thursday, March 20, 2008

Didn't see this one coming

You know how so much of the speculation and anticipation of the Cassini mission to Saturn focused on the possible methane oceans on Titan's surface? Looks like we might have set our sights too high. By about 62 miles, to be precise:
Cassini Spacecraft Finds Ocean May Exist Beneath Titan's Crust

PASADENA, Calif. - 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.

"With its organic dunes, lakes, channels and mountains, Titan has one of the most varied, active and Earth-like surfaces in the solar system," said Ralph Lorenz, lead author of the paper and Cassini radar scientist at the Johns Hopkins Applied Physics Laboratory in Laurel, Md., "Now we see changes in the way Titan rotates, giving us a window into Titan's interior beneath the surface."

Members of the mission's science team used Cassini's Synthetic Aperture Radar to collect 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.

Using data from the radar's early observations, the scientists and radar engineers established the locations of 50 unique landmarks on Titan's surface. They 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.

"We believe that about 62 miles beneath the ice and organic-rich surface is an internal ocean of liquid water mixed with ammonia," said Bryan Stiles of NASA's Jet Propulsion Laboratory (JPL) in, Pasadena, Calif. Stiles also is a contributing author to the paper.

Okay, that's fascinating just on the face of it. Because of temperature and chemical differences, this water-ice-ammonia ocean is functioning as an outer-system analog of the molten magma of the Earth's mantle, upon which the Earth's crust lies, thus allowing plate tectonics to occur. Albeit at a much faster rate than what we see terrestrially. Can you imagine the San Andreas fault slipping by as much as 19 miles over a 5 year period?

Of course, for us writers of speculative fiction, the potential presence of a sub-surface ocean conjures images of Europa and the inevitable speculation regarding extant life. And sure enough, a few graphs down comes the money shot:
"The combination of an organic-rich environment and liquid water is very appealing to astrobiologists," Lorenz said. "Further study of Titan's rotation will let us understand the watery interior better, and because the spin of the crust and the winds in the atmosphere are linked, we might see seasonal variation in the spin in the next few years."

Nifty. What's the over/under on the first appearance of a "subsurface Titan ocean" in the pages of Analog?

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