The Curiosity rover has detected intriguing chemical evidence in the form of anomalous amounts of manganese oxide, T pointing to Mars having had not only a habitable environment billions of years ago, but also one possibly inhabited by microbes. NASA’s Curiosity is exploring the giant 154-kilometre (96-mile) diameter Gale crater, where the rover landed in 2012. Curiosity’s discoveries have already established that the crater was at least partially flooded long ago – although the evidence for this has been contested. However, the rover’s latest findings not only strengthen the argument for an ancient lake, but also suggest that conditions within the lake were conducive to life.
The evidence is associated with the compound manganese oxide. Curiosity first found small quantities of manganese oxide in Gale crater in 2016, but now it has discovered much greater abundances of manganese oxide in the sedimentary bedrock of a mudstone geological unit called the Murray Formation. The Murray Formation is found on the flank of Mount Sharp in the middle of the crater. The manganese oxide was identified by Curiosity’s Chemistry and Camera complex (ChemCam), which fires a laser at rocks that scientists wish to study. The laser heats a small patch of a rock’s surface, thereby vaporising it, which results in a small cloud of plasma that ChemCam’s onboard camera and spectrometer can study from a distance to determine the ablated material’s composition. ChemCam discovered mudstone that was enriched in manganese oxide by up to 45 per cent.
On Earth, manganese oxide is commonly found in lakebeds or river deltas where there are high oxidising conditions. Furthermore, microbes that exist in those environments are able to help catalyse the oxidation process. Usually, this process requires a steady stream of oxygen, which is in short supply on Mars.