Two years after reaching Saturn, the Cassini spacecraft is halfway to completing its orbital mission. On July 2, Cassini will perform its 16th flyby of Saturn's largest moon, Titan, at an altitude of 1,906 kms. Cassini will focus on the interactions between Titan's atmosphere and the magnetosphere that surrounds Saturn. Cassini will also study Titan's surface to enable a better understanding of its properties and composition.
What happened to Titan's craters? NASA's Cassini mission should have seen hundreds of impact craters on Saturn's giant moon, but so far it has only spotted a handful. The latest clues in the mystery of the missing craters suggest a conspiracy between volcanoes, rain and settling soot - perhaps aided by an eggshell-thin crust.
Recent radar views of Saturn's moon Titan from the close flyby of the Cassini probe shows a striking variety of surface structures, including a first glimpse of craters formed by meteors. A team led by Steve Wall of NASA's Jet Propulsion Laboratory in Pasadena, California, says it is surprising there are so few craters, compared with the pock-marked face of the bare, icy Saturnian moon Rhea. Wall and colleagues conclude Titan's surface is either geologically active -- so outflows of material from 'cold volcanoes' have covered traces of old craters -- or it has such a thin icy crust over softer material that the craters flatten like dents in soft sand and then become covered by dust. As well as two craters of 280 and 50 miles across, the new images of Titan show a range of other features. The Cassini spacecraft's imaged a long strip of Titan's surface, reaching from high in the southern hemisphere to high in the northern during its third close fly-by of Titan. Cassini passed only about 1,000 miles above the surface, showing features as small as a few hundred feet across. The study appears in this week's issue of the journal Nature.
This image was taken with the Cassini Synthetic Aperture Radar instrument on Oct. 28, 2005.
This was the fourth flyby of Titan during which radar images were obtained, and this pass considerably expanded the coverage of Titan's surface. The swath is about 6,150 kilometres long, extending from 7 degrees north to 18 degrees south latitude and 179 west to 320 west longitude.
The spatial resolution of the radar images ranges from about 300 meters per pixel to about 1.5 kilometres per pixel. It covers the area where the Huygens probe landed (eastern end of the swath), giving geologic context for the landing site. The most ubiquitous features in this swath are "cat scratches," which are interpreted as longitudinal dunes and were first seen in the February 2005 flyby.
Also prominent are long, bright ridges, concentrated near the eastern end of the swath. These may be tectonic in origin, and are seen for the first time here. No impact craters are seen, indicating a young surface.