Two identical NASA Mars rovers, named Spirit and Opportunity, launched in 2003 June and July. They landed on opposite sides of the planet, in Gusev crater and on Meridiani Planum, in 2004 January to explore the surrounding surface. Each carried a panoramic camera (Pancam), instruments to analyse selected rocks, and a Rock Abrasion Tool (RAT) for grinding away the weathered surfaces of rocks to expose their interiors.
http://marsrovers.jpl.nasa.gov/home/index.html Official mission website.
Subjects: astronomy and cosmology.