Soil deep in a crater dating to some 3.7 billion years ago contains evidence that Mars was once much warmer and wetter, says University of Oregon geologist Gregory Retallack, based on images and data captured by the rover Curiosity.
Recent images from Curiosity from the impact Gale Crater, Retallack said, reveal Earth-like soil profiles with cracked surfaces lined with sulfate, ellipsoidal hollows and concentrations of sulfate comparable with soils in Antarctic Dry Valleys and Chile’s Atacama Desert.
“The key to this discovery has been the superb chemical and mineral analytical capability of the Curiosity Rover, which is an order of magnitude improvement over earlier generations of rovers. The new data show clear chemical weathering trends, and clay accumulation at the expense of the mineral olivine, as expected in soils on Earth. Phosphorus depletion within the profiles is especially tantalizing, because it attributed to microbial activity on Earth.”
The ancient soils, he said, do not prove that Mars once contained life, but they do add to growing evidence that an early wetter and warmer Mars was more habitable than the planet has been in the past 3 billion years.
For a record of older life and soils on Mars, Retallack said, new missions will be needed to explore older and more clayey terrains. The newly discovered soils provide more benign and habitable soil conditions than known before on Mars.
In an email, Malcolm Walter of the Australian Centre for Astrobiology, who was not involved in the research, said the potential discovery of these fossilized soils in the Gale Crater dramatically increases the possibility that Mars has microbes.