The fourth planet, Mars, is the most Earth-like planet in terms of temperature and length of day. It even has a similar tilt on it's axis which gives it seasons, a very noticeable summer and winter. When mankind begins to colonize other planets, Mars will be first.

• Mars M1 s/n 1 (Marsnik 1, Korabl 4, Mars 1960A) (USSR)  10 October 1960. First Soviet attempt at a planetary probe. Mission objectives were to investigate interplanetary space, return surface images of Mars from a flyby trajectory, and provide radio communications from long distances. Failed to reach Earth orbit when the third stage pumps were unable to develop enough thrust to commence ignition.
• Mars M1 s/n 2 (Marsnik 2, Korabl 5, Mars 1960B) (USSR)  14 October 1960. Identical to Marsnik 1in design and mission. Failed to reach Earth orbit when the third stage pumps were unable to develop enough thrust to commence ignition.
• Sputnik 22 (Korabl 11, Mars 1962A, Sputnik 29) (USSR)  24 October 1962. This was an attempted Mars flyby. Final rocket stage exploded and trying to leave Earth orbit.
• Mars 1 (Sputnik 23, 1962 Beta Nu 1, Mars 2MV-4) (USSR)  1 November 1962. Intended to blyby Mars at a distance of about 11,000 km. Communications failed on 21 March 1963 after 106 million km. Closest approach to Mars occurred on 19 June 1963 at a distance of approximately 193,000 km. Mars 1 then entered a heliocentric orbit.
• Sputnik 24 (Beta Xi 1, Korabl 13, Mars 1962B, Sputnik 31) (USSR)  4 November 1962. This was an attempted Mars lander mission. Failed to leave Earth orbit, broke up during the Mars transfer burn.
• Mariner 3 (USA)  5 November 1964. Attempted Mars flyby. A protective shield failed to eject. The instruments remained covered and the added weight prevented the proper trajectory. Now in solar orbit.
• Mariner 4 (Mariner-Mars 1964) (USA)  28 November 1964. Passed within 9,920 km of Mars on 14-15 July 1965, returned photos. Now in solar orbit.
• Zond 2 (USSR)  30 November 1964. Intended to be a flyby with a descent module. One solar panel failed and contact was lost in early May 1965. Zond 2 flew by Mars on 6 August 1965 at a distance of 1500 km.
• Zond 3 (USSR)  18 July 1965. Originally intended as a companion to Zond 2, the launch opportunity was missed and Zond 3 ended up doing a lunar flyby instead. It did reach the distance of the orbit of Mars and is in heliocentric orbit. There was no contact with Mars.
• Mariner 6 (Mariner F, Mariner Mars 69A) (USA)   24 February 1969. Passed within 3,431 km on 31 July 1969. Took measurements and did imaging. Now in solar orbit.
• Mariner 7 (USA)  27 March 1969. Passed within 3,430 km on 5 August 1969. Took measurements and did imaging. Now in solar orbit.
• Mars 1969A (Mars 69A) (USSR)  27 March 1969. Attempted Mars orbiter. Third stage exploded 439 seconds after liftoff.
• Mars 1969B (Mars 69B) (USSR)  2 April 1969.   Attempted Mars orbiter. First stage exploded less than 1 second after liftoff.
• Mariner 8 (Mariner-H) (USA) 8 May 1971. Attempted Mars orbiter. Failed to reach Earth orbit when upper stage began to oscillate and tumbled out of control.
• Cosmos 419 (USSR)  10 May 1971. Attempted Mars orbiter. Failed to leave Earth orbit due to an incorrect ignition timer setting.
• Mars 2 (Mars 2 Orbiter) (USSR)  19 May 1971. Lander portion failed and crashed on November 27, 1971. Orbiter was a success. Transmissions continued until August 1972.
• Mars 3 (USSR)  28 May 1971. Lander made it to the Martian surface on 2 December 1971, but only returned 20 seconds of data. A low fuel condition caused the orbiter to be put into a different orbit than planned. Transmissions continued until August 1972.
• Mariner 9 (Mariner-I, Mariner Mars '71) (USA)   30 May 1971. Went into Martian orbit 14 November 1971, returned photos of the surface and the two Martian moons. About 70% of the Martian surface was mapped. Mariner 9 was turned off 27 October 1972. It's orbit should last about 50 years before entering the Martian atmosphere.
• Mars 4 (USSR)  21 July 1973. Attempted orbiter. Failed to insert into Martian orbit on 10 February 1974 when the retro-rockets did not ignite.
• Mars 5 (USSR)  25 July 1973. Orbiter. Succeeded going into Martian orbit on 12 February 1974. Loss of pressurization in the transmitter module ended the mission after 22 orbits.
• Mars 6 (USSR)  5 August 1973. attempted lander. Lander failed on descent on 12 March 1974. Data was transmitted from the lander for 224 seconds.
• Mars 7 (USSR)  9 August 1971. Attempted lander. Failed to insert into Martian orbit on 9 March 1974 when the lander separated prematurely and missed the planet. Now in solar orbit.
• Viking 1 (USA)  20 August 1975. Made successful landing on 20 July 1976. Communications ended 13 November 1982. The Vikung 1 and 2 orbiters imaged the entire Martian surface.
• Viking 2 (USA)  9 September 1975. Made successful landing on 3 September 1976. Communications ended 11 April 1980. The Vikung 1 and 2 orbiters imaged the entire Martian surface.
• Phobos 1 (USSR)  7 July 1988. Failed en route to Mars when a software error caused a loss of communication on 2 September 1988.
• Phobos 2 (USSR)  12 July 1988. Made it to Martian orbit, moved to within 800 km of Phobos, then failed shortly before the release of two landers when a computer malfunction ended communications. Contact was not resored and the mission ended 27 March 1989.
• Mars Observer (MGCO,  Mars Geoscience/Climatology Orbiter) (USA)  25 September 1992. Planned orbiter. Communication was lost on August 21, 1993 just 3 days before Martian orbit insertion. The cause was never determined
• Mars Global Surveyor  (USA) 7 November 1996. Successful insertion into Martian orbit on 12 September 1997. Objectives involve high resolution imaging, topographic and gravity studies, the role of water and dust on the surface and in the atmosphere of Mars, the weather and climate of Mars, the composition of the surface and atmosphere, and the existence and evolution of the Martian magnetic field.
• Mars-96 (Mars 8) (Russia)  16 November 1996. Attempted orbiter and lander. Reached Earth orbit, but failed during insertion into a Mars trajectory and reentered the atmosphere 17 November 1996.
• Mars Pathfinder (Mars Environmental Survey, MESUR, Pathfinder) (USA)  4 December 1996. Survived an impact with Mars on 4 July 1997, dispatched a rover named Sojourner, returned data for over 2 ˝ months.
• Nozomi (Planet-B) (Japan)  3 July 1998. Japanese spacecraft with a hoped for orbital insertion in January 2004. Failure to resolve fuel consumption problems during the first year, then damage from a solar flare in April 2002 finally forced the off-course probe to be abandoned on 10 December 2003.
• Mars Climate Orbiter (Mars '98 Orbiter,  Mars Surveyor 98 Orbiter) (USA)  11 December 1998. The orbiter was probably lost in the Martian atmosphere on 23 September 1999 during the orbital insertion maneuver due to a programming error.
• Mars Polar Lander (MPL,  Mars Surveyor '98 Lander) (USA)  3 January 1999. Reached Mars orbit on 3 December 1999. All contact was lost during the landing descent. The engines shut down too early and the probe crashed to the surface.
  Deep Space 2 ( Amundsen, Scott, DS2,  Mars Microprobe,  New Millenium DS2) Attempted Mars penetrators. These were part of the Mars Polar Lander package, also lost 3 December 1999.
• Mars Odyssey ( Mars Surveyor 2001 Orbiter) (USA)   7 April 2001. Went into Mars orbit on 24 October 2001 for a 2 ˝ year geological study. The orbiter is acting as a communications relay for the Mars 2003 Rovers (Spirit and Opportunity).
• Mars Express (ESA)  2 June 2003. Consists of an orbiter and a lander (Beagle 2) which was slated to land on 25 December 2003. While orbital insertion went as planned, nothing further was heard from the lander. (Mars from 5.5 km, 1 December 2003, Credit ESA )
• Mars Exploration Rover-A ("Spirit") (USA)   10 June 2003. This is a six wheeled rover which successfully landed in the Gusev Crater on 4 January 2004. The task is to search for evidence of water. After 19 days on the surface, computer problems arose. The cause of the problem was found and corrected. By the beginning of February, full functionality had been restored.
• Mars Exploration Rover-B ("Opportunity") (USA)  8 July 2003. The second six wheeled rover successfully landed about 9600 km away from the MER-A in an area known as Meridiani Planum on 25 January 2004. It is to study sites of geological importance on the Red Planet.
• Mars Reconnaissance Rover (USA)  12 August 2005. Mars orbiter entered Mars orbit 10 March 2006.
• Phoenix Mars Lander (USA)  4 August 2007. Mars lander with a robotic arm, scheduled to reach Mars 25 May 2008.