Since the Mars rover Curiosity landed in Gale Crater on 6 August 2012, it has sought signs that the Red Planet could once have supported life. Using the rolling robot’s observations, Lanza et al. now suggest that flowing groundwater deposited minerals in Martian sandstone fractures. They also suggest that Mars’s atmosphere was once more Earth-like, with much more oxygen than it has today.
On Earth, rocks record the evolution of the atmosphere. In an oxygen-rich atmosphere, liquid water can deposit manganese oxide minerals; as oxygen levels increased in Earth’s early atmosphere, large deposits of manganese oxides began to appear across the planet. The team believes that a similar process may have occurred on Mars.
In spring of 2014, the researchers examined Martian manganese with Curiosity’s ChemCam, which uses a laser to vaporize materials and determine their composition. The scientists used the instrument to measure concentrations of manganese on rock targets across the rover traverse in Gale Crater. They found that manganese levels were at least 3 times higher than expected in 3% of all sampling locations.
Since then, the team has discovered a new location with high concentrations of manganese in a region called Kimberley. ChemCam’s laser can peel off shallow layers of rock to reveal what lies beneath, and Curiosity can drill into sandstone. Depth data show that patches of concentrated manganese in the Kimberly formation on erosion-resistant fins form thin, uneven layers—typical of water-deposited minerals in fractures on Earth. The overall chemistry suggests the deposits specifically consist of manganese oxides, which require high oxygen concentrations to form.
Altogether, the observations suggest that flowing water on early Mars encountered an oxygen-rich atmosphere and became enriched in oxygen itself. As it flowed through sandstone fractures in Gale Crater, groundwater transported and deposited manganese oxides and other minerals. (Geophysical Research Letters, doi:10.1002/2016GL069109, 2016)
—Sarah Stanley, Freelance Writer