"spider" crater on Mercury

A NASA probe that shot past Mercury this month detected a puzzling geological feature that scientists on Wednesday labeled "The Spider" and found evidence of past volcanic activity on the closest planet to the sun.
The U.S. space agency's car-sized MESSENGER spacecraft on January 14 flew past Mercury, whose diameter is just a third the size of Earth's, and its seven scientific instruments gathered new information about the little understood planet.Data collected by MESSENGER showed that a massive impact crater on its surface is larger than previously thought. The probe is due to fly by again this October and in September 2009 before beginning a yearlong orbit of the planet in 2011.
While Mercury looks superficially like Earth's moon with a cratered, rocky surface, scientists said the new findings show they are quite different

Mercury is a mystery in many ways and its proximity to the sun has made it difficult to observe from Earth.
Mercury has been visited by a spacecraft only twice before, in 1974 and 1975 when NASA's Mariner 10 flew past it three times and mapped about 45 percent of its surface. The latest fly-by covered another 30 percent of the surface.
"The Spider" was the most striking feature described by the scientists. It is made up of more than 100 narrow, flat-floored troughs radiating from a central point, much as petals from a daisy or the legs of a spider.
"A REAL MYSTERY"