Washington: NASA’s Cassini spacecraft has captured some dramatic views of Saturn’s second largest moon Rhea.
Pictures reveal fractures cutting through craters on the moon’s surface, revealing a history of tectonic rumbling.
“These recent, high-resolution Cassini images help us put Saturn’s moon in the context of the moons’ geological family tree,” said Paul Helfenstein, Cassini imaging team associate, based at Cornell University, Ithaca, New York.
“Since NASA’s Voyager mission visited Saturn, scientists have thought of Rhea and Dione as close cousins, with some differences in size and density. The new images show us they’re more like fraternal twins, where the resemblance is more than skin deep. This probably comes from their nearness to each other in orbit,” he added.
During the March flyby, Cassini made its closest approach to Rhea’s surface so far, swooping within 100 kilometers (62 miles) of the moon.
Other pictures show a web of bright, “wispy” fractures resembling some that were first spotted on another part of Rhea by the two Voyager spacecraft in 1980 and 1981.
Since July 2004, Cassini’s imaging cameras have captured pictures the trailing hemispheres of both satellites several times at much higher resolution – revealing that the wispy markings are actually exposures of bright ice along the steep walls of long scarps, or lines of cliffs.
This means that tectonic activity produced the features rather than cryovolcanism.
Images of densely cratered plains indicate that Rhea has not experienced much internal activity but suggest that some regions have ruptured in response to tectonic stress more recently.
The side of the moon that faces Saturn a slightly bluer area, possibly due to different surface compositions or to different sizes and fine-scale textures of the grains making up the moon’s icy soil.
In future, Cassini will continue to chart the terrain of this and other Saturn moons.
“The 11th of January 2011 will be especially exciting, when Cassini flies just 76 kilometers [47 miles] above the surface of Rhea,” said Thomas Roatsch, a Cassini imaging team scientist based at the German Aerospace Center Institute of Planetary Research in Berlin.
“These will be by far the best images we’ve ever had of Rhea’s surface -- details down to just a few meters will become recognizable.”