NASA's Mars missions over the past four decades, listed by launch date:
November 1964, Mariner 3: Spacecraft loses contact after takeoff. Mariner 4 launches three weeks later and in July 1965 becomes the world's first spacecraft to take close-up pictures of Mars, returning 21 photos.
February 1969, Mariner 6: Spacecraft flies past Mars in July 1969 and returns 75 photos.
March 1969, Mariner 7: Spacecraft flies past Mars in August 1969 and returns 126 photos.
May 1971, Mariner 8: Orbiter fails on launch. Mariner 9 orbiter arrives at Mars in November and operates until October 1972.
August 1975, Viking 1: Orbiter reaches Mars in June 1976 followed by Viking 1 lander the next month. Orbiter operates until 1980; lander lasts until 1982.
September 1975, Viking 2: Orbiter arrives at Mars in August 1976, and Viking 2 lander touches down the following month. Lander lasts until 1980; orbiter operates until 1987.
September 1992, Mars Observer: Craft loses communication in August 1993 just before going into orbit around Mars.
November 1996, Mars Global Surveyor: Orbiter reaches Mars in September 1997. Continues to operate.
December 1996, Mars Pathfinder: Lander and Sojourner rover land on Mars in July 1997. Last transmission September 1997.
December 1998, Mars Climate Orbiter: Lost on arrival in September 1999.
January 1999 Mars Polar Lander: Spacecraft and accompanying Deep Space 2 microprobes lose contact during arrival at south pole of Mars in December 1999.
March 2001, Mars Odyssey: Spacecraft reaches orbit October 2001. Continues to operate.
June 2003, Mars rover Spirit: Craft sets down in the Gusev Crater region in January 2004. It has been examining rocks that suggest a wet and violent history in Mars' early life. Continues to operate.
July 2003, Mars rover Opportunity: Craft parachutes to Meridiani plains three weeks after Spirit's touchdown. It has also found geological evidence of past water activity. Continues to operate.
Aug. 10, 2005, Mars Reconnaissance Orbiter: Craft entered orbit in March 2006. It has sent back more than 25,000 images and 3,500 radar observations. Continues to operate.