Landing of Martian subsurface probe. Artwork of one of the Deep Space 2 Mars microprobes landing on the surface of Mars. These probes were attached to the Mars Polar Lander that entered the Martian atmosphere on 3 December 1999. Communication was lost at this point, and no further signals have been received. The probes were designed to free- fall into the Martian soil at around 200 metres per second. The impact would have driven the probes about 2 metres into the soil. The probes consisted of an upper part, which was intended to relay information to Earth, connected by flex to the bullet-shaped probe itself. The probes were designed to sample the soil and take physical readings such as temperature, and look for signs of frozen water. It is not known what caused the mission to fail.