The Search for Life on MarsThe Viking program of the 1970's was the first to return data that there is currently no evidence of life on Mars.
As part of a more thorough search, the Mars Surveyor Program was put in place.
Five spacecraft in all were to be sent to Mars between 1996 and 2005. Those spacecraft were to include the Mars Global Surveyor, and the Mars Climate Orbiter and Polar Lander. Unfortunately, the Mars Climate Orbiter and Polar Lander have been lost. Scientists still hope that after all the information is gathered, they might know more about the evolution of Mars and its potential to harbor life.