Water Ocean on Titan

Titan is the oddity among themoons and this is an effort to sort it all out. It is a reservoir of volatiles that may be of actual economic interestin the distant future.

In the meantime we are still atleast a generation away from actually landing on it and looking around. 

This work at least shows us thatthe upper crustal layer is floating on something that is liquid.

A Water Ocean on Titan

by Charles Q. Choi

for Astrobiology Magazine

Moffett Field CA (SPX) May 06, 2011

This artist's illustration shows the likely interior structure ofSaturn's moon Titan.The cool and sluggish interior failed to separate into completelydifferentiated layers of ice and rock. In addition to the hazy surface of Titan(yellow), the layers in the cutaway show an ice layer starting near the surface(light gray), an internal ocean (blue), another layer of ice (light gray) andthe mix of rock and ice in the interior (dark gray). In the background are theCassini spacecraft andSaturn, not to scale. Image credit: NASA/JPL

http://www.saturndaily.com/reports/A_Water_Ocean_on_Titan_999.html

Oddities in the rotation of Saturn's largest moon Titan might add to growingevidence that it harbors an underground ocean, researchers suggest. Titan,which is larger than Mercury, is the only world besides Earth known to haveliquid on its surface. Its seas, made of liquid methane instead of water, haveoften led to speculation as to whether or not they could host life.

In addition to its seas on its surface, scientists recently alsodiscovered hints that Titan possesses an internal ocean, one of water andammonia. Using radar to peer through Titan's dense atmosphere, NASA's Cassini spacecraftfound that over time, a number of prominent surface features hadshifted from their expected positions by up to 19 miles (30 kilometers),showing that the crust was moving and suggesting that it rested on liquid.

Now Cassini's gravity and radar observations of Titan have discoveredmore clues that it might have an underground sea.

Titan apparently has an orbit very similar to our moon's - forinstance, it always presents the same face toward its planet.

However, they noted that Titan's axis of rotation was tilted by about0.3 degrees. This tilt, or obliquity, seems high, given the estimate of Titan'smoment of inertia, or its resistance to changes to its rotation.

One implausible reason for these findings is that Titan is a solid bodythat is denser near the surface than at its center. "This is incontradiction with all we know about others planets and satellites andplanetary formation processes," said researcher Rose-Marie Baland, aplanetary scientist at the Royal Observatory of Belgiumin Brussels.

Another more likely explanation is that Titan is not solid all the waythrough, but has an icy shell overlying a liquid water ocean, an icy mantle andan icy, rocky core. The research team's models can give a wide range ofthicknesses for the liquid ocean, anywhere from three to 265 miles (five to 425km), as well as for the icy shell, anywhere from 90 to 125 miles (150 to 200km).

"We found it very exciting to use some measurements that seem incontradiction and to try to reconcile them," Baland said. "It was likeputting together pieces of a puzzle."

Still, the case for Titan having an underground ocean is not closedyet. Its orbit and rotation might also be explained by a recent disturbance,such as a collision with a comet or asteroid.

"Our analysis strengthens the possibility that Titan has asubsurface ocean, but it does not prove it undoubtedly," Baland toldAstrobiology Magazine. "So there is still work to do."

Since life as we know it needs liquid water, if Titan does have asubsurface water ocean that may increase the chances the moon could harboralien life.

In the future, Baland noted that she and her colleagues would like touse this method to analyze Jupiter's four largest satellites, the Galileanmoons - Io, Europa, Ganymede and Callisto.

"The measurement of the obliquity of Europeor Ganymede could bring additional evidence for subsurface liquid layers,"Baland said.

Baland and her colleagues will detail their findings in a forthcomingissue of the journal Astronomy and Astrophysics.