A Mars rover is a motor vehicle designed to travel on the surface of Mars. Rovers have several advantages over stationary landers: they examine more territory, they can be directed to interesting features, they can place themselves in sunny positions to weather winter months, and they can advance the knowledge of how to perform very remote robotic vehicle control. They serve a different purpose than orbital spacecraft like Mars Reconnaissance Orbiter. A more recent development is the Mars helicopter.
As of May 2021[update], there have been six successful robotically operated Mars rovers; the first five, managed by the American NASA Jet Propulsion Laboratory, were (by date of Mars landing): Sojourner (1997–1997), Opportunity (2004–2018), Spirit (2004–2010), Curiosity (2012–), and Perseverance (2021–). The sixth, managed by the China National Space Administration, is Zhurong (2021–).
On January 24, 2016, NASA reported that then current studies on Mars by Opportunity and Curiosity would be searching for evidence of ancient life, including a biosphere based on autotrophic, chemotrophic or chemolithoautotrophic microorganisms, as well as ancient water, including fluvio-lacustrine environments (plains related to ancient rivers or lakes) that may have been habitable.[1][2][3][4][5] The search for evidence of habitability, taphonomy (related to fossils), and organic carbon on Mars is now a primary NASA objective.[1][6]
The Soviet probes, Mars 2 and Mars 3, were physically tethered probes; Sojourner was dependent on the Mars Pathfinder base station for communication with Earth; Opportunity, Spirit and Curiosity were on their own. As of July 2022, Curiosity is still active, while Spirit, Opportunity, and Sojourner completed their missions before losing contact. On February 18, 2021, Perseverance, the newest American Mars rover, successfully landed. On May 14, 2021, China's Zhurong became the first non-American rover to successfully operate on Mars.
Multiple rovers have been dispatched to Mars:
Curiosity of the Mars Science Laboratory (MSL) mission by NASA, was launched November 26, 2011[7][8] and landed at the Aeolis Palus plain near Aeolis Mons (informally "Mount Sharp")[9][10][11][12] in Gale Crater on August 6, 2012.[13][14][15] The Curiosity rover is still operational as of July 2022. Perseverance, NASA rover based on the successful Curiosity design. Launched with the Mars 2020 mission on July 30, 2020, it landed on February 18, 2021.[16] It carried the Mars Helicopter Ingenuity attached to its belly.
Zhurong launched with the Tianwen-1 CNSA Mars mission on July 23, 2020, landed on May 14, 2021 in the southern region of Utopia Planitia, and deployed on May 22, 2021, while dropping a remote selfie camera on 1 June, 2021.[17][18]
Mars 3, PrOP-M rover, landed successfully on December 2, 1971. 4.5 kilograms (9.9 lb) rover tethered to the Mars 3 lander. Lost when the Mars 3 lander stopped communicating about 14.5 seconds after landing.[19] The loss of communication may have been due to the extremely powerful Martian dust storm taking place at the time or an issue with the Mars 3 orbiter's ability to relay communications. Sojourner rover, Mars Pathfinder, landed successfully on July 4, 1997. Communications were lost on September 27, 1997. Sojourner had traveled a distance of just over 100 meters (330 ft).[20] Spirit (MER-A), Mars Exploration Rover (MER), launched on June 10, 2003,[21] and landed on January 4, 2004. Nearly 6 years after the original mission limit, Spirit had covered a total distance of 7.73 km (4.80 mi) but its wheels became trapped in sand.[22] The last communication received from the rover was on March 22, 2010, and NASA ceased attempts to re-establish communication on May 25, 2011.[23] Opportunity (MER-B), Mars Exploration Rover, launched on July 7, 2003[21] and landed on January 25, 2004. Opportunity surpassed the previous records for longevity at 5,352 sols (5498 Earth days from landing to mission end; 15 Earth years or 8 Martian years) and covered 45.16 km (28.06 mi). The rover sent its last status on 10 June 2018 when a global 2018 Mars dust storm blocked the sunlight needed to recharge its batteries.[24] After hundreds of attempts to reactivate the rover, NASA declared the mission complete on February 13, 2019. Mars 2, PrOP-M rover, 1971, Mars 2 landing failed taking Prop-M with it. The Mars 2 and 3 spacecraft from the Soviet Union had identical 4.5 kg Prop-M rovers. They were to move on skis while connected to the landers with cables.[19]
The European-Russian ExoMars rover Rosalind Franklin was confirmed technically ready for launch in March 2022 and planned to launch in September 2022, but due to the suspension of cooperation with Roscosmos this is delayed and a fast-track study was started to determine alternative launch options.[25]
The JAXA Melos rover was supposed to be launched in 2022. JAXA has not given an update since 2015. NASA Mars Geyser Hopper
Examples of instruments onboard landed rovers include:
Interactive image map of the global topography of Mars, overlain with locations of Mars Lander and Rover sites. Hover your mouse over the image to see the names of over 60 prominent geographic features, and click to link to them. Coloring of the base map indicates relative elevations, based on data from the Mars Orbiter Laser Altimeter on NASA's Mars Global Surveyor. Whites and browns indicate the highest elevations (+12 to +8 km); followed by pinks and reds (+8 to +3 km); yellow is 0 km; greens and blues are lower elevations (down to −8 km). Axes are latitude and longitude; Polar regions are noted. 
Circa the 2010s, NASA had established certain goals for the rover program.
NASA distinguishes between "mission" objectives and "science" objectives. Mission objectives are related to progress in space technology and development processes. Science objectives are met by the instruments during their mission in space.
The science instruments are chosen and designed based on the science objectives and goals. The primary goal of the Spirit and Opportunity rovers was to investigate "the history of water on Mars".[34]
The four science goals of NASA's long-term Mars Exploration Program are:
