New data from NASA’s Curiosity rover suggests that the mineral content of Mars’ fine soil is not unlike weathered basalts found in Hawaii. The wheeled spacecraft, which touched down on the surface of the Red Planet in early August – following an adrenaline-pumping descent through the atmosphere and emplacement within Gale Crater by the first rocket-propelled ‘Sky Crane’ – is presently hard at work processing its first sample of alien soil. Curiosity’s Chemistry and Mineralogy (CheMin) instrument employed X-ray diffraction for the first time on Mars to accurately ‘read’ a sample’s mineralogical content.
Launched in November 2011, Curiosity touched down on the surface of the Red Planet in the small hours of 6 August, beside the 18,000-foot peak of Aeolis Mons (‘Mount Sharp’) in the yawning bowl of Gale Crater. Its primary mission is expected to last two Earth-years and will encompass a full geological and mineralogical investigation of the 96-mile-wide crater, whose layers are already revealing fundamental details about the region’s long history of environmental change and the possible presence of organic molecules. Two weeks after touching down, Curiosity’s landing site was named ‘Bradbury Landing’, in honour of the late science fiction writer Ray Bradbury, who died earlier this year.
Since then, the rover has crept in an east-southeasterly direction across the ochre-hued landscape toward Glenelg, a geologically significant area, marked by a natural intersection of three terrain types, including layered bedrock. On 28 September, partway toward this destination, Curiosity encountered a patch of dust and sand which investigators have nicknamed ‘Rocknest’. It resides slightly downslope from a cluster of dark rocks and covers an area of about 5 feet by 16 feet. At Rocknest, the rover performed the first-ever demonstration of X-ray diffraction analysis of a soil sample on the surface of Mars; this technique is commonly used by geologists on Earth to accurately ‘read’ a mineral’s internal structure by recording how its crystals distinctively interact with X-ray excitation.
CheMin processed a small quantity of soil through a sieve to exclude particles greater than 0.006 inches across – about the thickness of a single human hair – and identified the presence of feldspar, pyroxenes and olivine. The sample contained dust distributed globally in dust storms and fine sand which had originated in the locality of Bradbury Landing. Unlike the ‘conglomerate’ rocks recently observed by the rover, which are several billion years old, the soil material analysed at Rocknest is thought to be more representative of ongoing geophysical processes in today’s Mars.
“Our team is elated with these first results from our instrument,” said David Blake, the CheMin principal investigator, based at NASA’s Ames Research Center in Moffett Field, California. “They heighten our anticipation for future CheMin analyses in the months and miles ahead for Curiosity.” The qualitative results obtained at Rocknest also provide “refined and in some cases new identifications” of Mars’ mineralogical composition. CheMin works by having samples of rocks and soils delivered by Curiosity’s 7-foot-long manipulator arm and it is a central tenet in the primary goal of the mission to assess past and present environmental conditions on Mars and address the question of whether Gale Crater ever supported a favourable situation for the evolution of microbial life. This search encompasses not only the possibility of ancient habitable environments on the Red Planet, but also potential mineral biosignatures and the detection of life-enabling energy sources.
“Much of Mars is covered with dust, and we had an incomplete understanding of its mineralogy,” said David Bish, a CheMin co-investigator from Indiana University in Bloomington. “We now know it is mineralogically similar to basaltic material, with significant amounts of feldspar, pyroxene and olivine, which was not unexpected. Roughly half the soil is non-crystalline material, such as volcanic glass or products from weathering of the glass.” Summing up the Rocknest findings, Bish added that the results are consistent with predictions of Gale Crater recording a transition through time from a ‘wet’ to a ‘dry’ environment. “The ancient rocks, such as the conglomerates, suggest flowing water,” he said, “while the minerals in the younger soil are consistent with limited interaction with water.”