A NASA space probe, launched in 1996 December, that landed in a lowland area on Mars, Ares Vallis, in 1997 July. It deployed a micro-rover called Sojourner that roamed the surface, analysing the composition of Martian rocks. The lander and rover operated for nearly three months until communication was lost in 1997 September.
http://mars.jpl.nasa.gov/MPF/index1.html Official mission website.
Subjects: astronomy and cosmology.