Launched in 1992 at a price of nearly a billion dollars, the Mars Observer was designed for a mission to orbit and observe for one Martian year (about 1 Earth year and 10 and a half months), intended for observation of the movement of ice, frost and dust across the surface of the Red Planet.
In 1993 NASA's Mars Observer mysteriously disappeared just as it was about to enter orbit around Mars. The most probable cause of the loss of Mars Observer was a rupture of the fuel pressurization side of the spacecraft's propulsion system. The resulting asymmetrical gas leak would have caused the spacecraft to go into a high speed spin which would not have let its transmitter be turned on. Or perhaps the electrical system failed, or there was the loss of some function that prevented both of the main and backup computers from controlling the spacecraft.
We may never know what happened to Mars Observer.
Photos. Two Viking orbiter photos are shown here: on the left, the terraced terrain at the Mars's north pole, which is made up of frozen water; on the right, Mars's south pole, which contains frozen carbon dioxide. Courtesy of NASA, JPL
Mission to Mars. An educational site created for the ThinkQuest contest.