A Mars rover is a motor vehicle that travels across the surface of the planet Mars upon arrival. 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.
As of May 2021, there have been six successful robotically operated Mars rovers, the first five managed by the American NASA Jet Propulsion Laboratory: Sojourner, Opportunity, Spirit, Curiosity, and Perseverance. The sixth is Zhurong, managed by the China National Space Administration.
On January 24, 2016, NASA reported that current studies on Mars by Curiosity and Opportunity 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 that may have been habitable. The search for evidence of habitability, taphonomy, and organic carbon on Mars is now a primary NASA objective.