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Soils on Mars are thought to accumulate superoxide radicals, as they are formed continually by UV radiation hits on basalt minerals. Yet, beyond electron paramagnetic resonance (EPR) spectroscopy, no other methods exist that detect and quantify superoxide radicals in soils. This study describes two such assays that are based on the reaction of superoxide radical with hydroethidine and oxidized cytochrome c. They are unique in being able to test unambiguously for the presence of superoxide in a soil matrix with a high level of accuracy. Applications with soils from the Atacama Desert showed that the sensitivity of the assays is equal to or greater than that of EPR spectroscopy.