Veil Lifts on Titan's Great Secrets
A composite of several Cassini images shows Titan's varied surface, including possibly a remnant of an old impact basin (large circular feature near the center of Titan's disk). Mountain ranges to the southeast of the circular feature, and the dark linear feature to the northwest of the circular impact scar may be evidence of past tectonic activity.
Credit: NASA/JPL/University of Arizona.

When the Cassini spacecraft reached Saturn?s largest moon Titan and deployed its Huygens probe to study the surface, it lifted a shroud that had hung over a world possibly containing conditions for life?s building blocks.

Now a planetary scientist and an astronomy writer have laid out Cassini?s findings and Titan?s enduring mysteries in a new book, ?Titan Unveiled? (Princeton University Press, 2008).

As Cassini entered Saturn's orbit in 2004 and began snapping images during flybys of Titan later that year, scientists realized that Titan has sand dunes not unlike those in the Sahara desert. They had assumed little sand would exist at the moon because of a lack of erosion processes, and that Titan?s winds lacked the strength to create dune patterns.

"Both hypotheses were wrong for interesting reasons," said Ralph Lorenz, co-author and planetary scientist on the Cassini-Huygens mission at Johns Hopkins University Applied Physics Lab in Maryland.

The sand had originated not from erosion pounding rocks into small grains, but instead from chemicals that drizzled down from Titan?s clouds. Cassini also found powerful near-surface winds at Titan due to the gravitational influence of Saturn on the atmosphere.

Another surprise arose from ?just how glaring the influence of rainfall and rivers was in the Huygens landing,? Lorenz told Titan?s surface and atmosphere contain methane, which acts like liquid water under the frigid temperatures of roughly -290 degrees F (-179 degrees C) on the surface.

Falling and flowing methane may only form a temporary feature on Titan?s surface, but Cassini also detected larger bodies of liquid such as lakes, using optical cameras and radar. However, the south polar region of Titan appears to have fewer lakes ? just one of the differences between the north and south poles that has become an ?emerging mystery,? Lorenz said.

An added bombshell came from the discovery that Titan?s icy surface slides around like cheese on pizza sauce. That suggests the moon harbors a hidden ocean that may consist of water and ammonia.

Yet one of Titan?s most noticeable features remains a mystery. An orange shroud of methane has long hidden the moon?s surface from astronomers' eyes, but remains despite getting steadily destroyed by the sun?s harsh ultraviolet rays and making up just 5 percent of the mainly nitrogen atmosphere. Scientists suspect the methane may get replenished by underground lakes or volcanic vents.

Strangeness aside, Titan still astounds scientists who "didn?t expect it to be so Earth-like and varied," Lorenz noted. The dunes, lakes, rivers and rain all appear strikingly familiar and suggest a constantly changing climate that goes with Titan?s seasons.

Cassini will continue to map Titan and explore its surface as the probe swings by during the course of its extended Saturn mission. But Lorenz and other scientists eagerly await a dedicated Titan mission that can thoroughly examine the moon ? although it may have to compete with Europa as an attractive destination.