Last year, the Messenger probe--the first mission to Mercury since the 1970s--returned crystal-clear views of the 960-mile-wide Caloris impact basin, here seen in false color as yellow-orange. Messenger settled doubts about the planet's volcanic past, confirming that its smooth plains seem to be the result of ancient eruptions. The small orange specks visible at the basin's rim are thought to be volcanic features. The bright spiderlike formation in the center of Caloris, with troughs radiating outward from a central crater, has yet to be explained. Messenger will next fly past the planet in September 2009, and will begin orbiting Mercury in 2011.