WASHINGTON, Aug. 5 (Xinhua) -- NASA's Mars rover Curiosity is set to touch down in the Gale Crater area of Mars early Monday. The mission will study whether the Red Planet has evidence of past and present habitable environments. The following is a brief introduction to NASA's past Mars missions:
Mariner 3: launched on Nov. 5, 1964. However, soon after its launch, the shroud encasing the spacecraft atop its rocket failed to open properly and the mission was unsuccessful.
Mariner 4: launched on Nov. 18, 1964. It made its first successful Mars flyby in July 1965 and returned 21 photos.
Mariner 6: launched on Feb. 24, 1969. It flew past Mars in July 1969 and returned 75 photos.
Mariner 7: launched on March 27, 1969. It flew past Mars in August 1969 and returned 126 photos.
Mariner 8: failed during launch on May 8, 1971.
Mariner 9: launched on May 30, 1971 and became the first artificial satellite of Mars when it arrived at and went into orbit in November 1971. It operated till October 1972 and returned 7,329 photos.
Viking 1: The complex of Mars orbiter and lander was launched on Aug. 20, 1975 and arrived at Mars orbit in June 1976. The lander touched down on Mars in July 1976. Orbiter operated till 1980, and lander till 1982.
Viking 2: The second complex of Mars orbiter and lander was launched on Sept. 9, 1975 and arrived at Mars orbit in August 1976. The lander touched down in September 1976. Orbiter operated till 1987, and lander till 1980. Combined, the Viking orbiters and landers returned more than 50,000 photos.
Mars Observer: launched on Sept. 25, 1992 and lost just before Mars arrival in August 1993.
Mars Global Surveyor: launched on Nov. 7, 1996. This orbiter arrived at Mars orbit in September 1997 and conducted a high-detail mapping to Mars. Its last communication to Earth occurred in November 2006.
Mars Pathfinder: launched on Dec. 2, 1996, it landed in July 1997. Its last transmission occurred in September 1997.
Mars Climate Orbiter: launched on Dec. 11, 1998 and lost upon arrival in September 1999.
Mars Polar Lander: launched on Jan. 3, 1999. The lander and two probes lost just on arrival in December 1999.
Mars Odyssey: launched on April 7, 2001, it arrived at Mars orbit in October 2001, currently holding the record of the longest-surviving and continually active spacecraft in orbit around a planet other than the Earth.
Mars Exploration Rover Spirit: one of two rovers launched in 2003 to explore Mars and search for signs of past life, Spirit outlasted its planned 90-day mission. Among her myriad discoveries, Spirit found evidence that Mars was once much wetter than it is today and helped scientists better understand the Martian wind. The mission ended on May 25, 2011.
Mar Exploration Rover Opportunity: landing following Spirit in January 2004 for 90-day prime mission in Meridiani Planum region, it is currently conducting extended mission.
Mars Reconnaissance Orbiter: launched on Aug. 12, 2005, it began orbiting in March 2006. Its primary mission ended on Dec. 31, 2010, and it will serve as a relay satellite for Curiosity's landing.
Phoenix Mars Lander: landing in May 2008, it ended operations due to severe ice damage to its solar panels in May 2010. The mission's biggest surprise was the discovery of perchlorate, an oxidizing chemical on Earth that is food for some microbes and potentially toxic for others.