The Cassini probe has found evidence that there may be an underground ocean on Saturn's moon Titan. The moon is already an area of tremendous interest to planetary scientists, given its dunes, lakes and mountains. It also has one of the most Earth-like surfaces in the solar system. Now, by using radar measurements to detect changes in the moon's rotation, scientists have gotten more insight into what's below the surface.

This short animation is made up from a sequence of images taken by the Descent Imager/Spectral Radiometer (DISR) instrument on board ESA's Huygens probe, during its successful descent to Titan on Jan. 14, 2005.

The penetrometer was the first thing to hit. The stick-like probe on the bottom of the Huygens lander punched aside a hard pebble made of water ice on the surface of Saturn’s largest moon, Titan, and sliced down through five inches of soft, muddy material. Scientists watching from Earth were ecstatic—the probe was not expected to survive the landing—but at the same time puzzled: If Titan really was, as they suspected, much like a young Earth, where were the liquid oceans predicted to cover the surface?