National Aeronautics and Space Administration Planetary Protection Office

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Solar System Missions

Missions That Explore Our Solar System

Mars Exploration Rovers
Illustration of a Mars Exploration Rover in operation on the surface.
Illustration of a Mars Exploration Rover in operation on the surface – NASA/JPL

NASA’s Mars Exploration Rover spacecraft – Spirit and Opportunity – were launched in June and July 2003, respectively, and landed on Mars in January 2004. Mars is considered a prime site for astrobiological investigation, and MER mission science is focused on how past water activity on Mars has influenced the planet’s environment over time. Mars has surface water ice, and many scientists believe that liquid water may still exist beneath the surface of the planet.

This mission is classified Category IVa for planetary protection purposes. Planetary protection policy dictated evaluating that the rovers met the biological requirements set forth by the requirements for Category IVa missions. Both rovers were developed by NASA’s Jet Propulsion Laboratory. Final assembly of the rovers took place at the Kennedy Space Center, where they underwent bioload reduction and biological contamination prevention techniques.

Spacecraft parts with large surface areas (e.g., the airbags used during landing) that could tolerate high temperatures were subjected to dry microbial heat reduction processes to reduce bioload. High-efficiency particulate arrestor (HEPA) filters were used to protect electronic boxes and other sensitive areas from external biological contamination, and techniques such as alcohol wiping were used during assembly to maintain the cleanliness of each rover. Planetary protection technicians sampled spacecraft surfaces during assembly and prior to encapsulation in the aeroshell to check for microbial spores. Testing showed that the total spore count on both Spirit and Opportunity was well below the allowable level.

For more information on the Mars Exploration Rovers, see Mission Project Home Page at the Jet Propulsion Laboratory website. Also, please visit the pages for Spirit and Opportunity at the Science Mission Directorate website.