Enlarge Image

Planetary scientists have gathered additional evidence that hydrocarbons rain down on Titan, Saturn’s methane-shrouded moon, filling lakes on its frigid surface. Comparing infrared images of Titan’s south pole taken 11 months apart by the Cassini spacecraft, researchers found intriguing changes.

The image at left (unlabeled and labeled) was recorded July 3, 2004. The right image, recorded June 6, 2005, shows new dark areas (circled) along with low-lying bright clouds.

Researchers suggest that the hydrocarbon-laden clouds generated a rainstorm over the region, resupplying lakes with liquid hydrocarbons and creating new dark areas in the process.

Elizabeth Turtle of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., and her colleagues describe the images in the Jan. 29 Geophysical Research Letters. The team predicts that as Titan’s northern hemisphere moves into summer, large cloud systems will form there, creating an even greater rainfall than in the south and enlarging dark patches believed to be northern lakes. — Ron Cowen