Mars Polar Lander
The Mars Polar Lander and the Mars Climate Orbiter were launched separately on January 3, 1999, to study the Martian weather, climate, water and carbon dioxide. The Polar Lander was planned to touch down on the southern pole region near the CO2 icecap. However, on December 3, the probe was jettisoned, and a planned communcation blackout started that would last until the probe landed. This was the last NASA heard from the Polar Lander. It is assumed it hit the Martian surface at a high rate of speed and disintegrated upon impact.