Curiosity Finds Tantalizing Mineral Clues for Mars Habitability
The mineral, hematite, is formed when another mineral, magnetite, is exposed to Mars' atmosphere and water.
For the first time in its continuing mission to better understand the past habitability of the Red Planet, NASA's Mars rover Curiosity has detected a mineral drilled out of a Martian rock that matches orbital data from NASA's Mars Reconnaissance Orbiter (MRO).
Hematite, an iron-oxide mineral, was detected by the MRO's CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) instrument in 2010 before Curiosity's 2012 landing site was selected. Inside Gale Crater, where mission scientists eventually decided to land Curiosity, hematite was detected, one of the reasons why the mission is studying the geology there.
"This connects us with the mineral identifications from orbit, which can now help guide our investigations as we climb the slope and test hypotheses derived from the orbital mapping," said Curiosity Project Scientist John Grotzinger, of the California Institute of Technology (Caltech) in Pasadena, Calif.
The detection of hematite by Curiosity's on-board chemistry lab - the Chemistry and Mineralogy (CheMin) instrument - not only provides the "ground truth" by connecting orbital data with the mineralogy measured on the ground, it also provides a tool so we can better understand the environmental conditions - potentially habitable conditions - the hematite formed in.
"We've reached the part of the crater where we have the mineralogical information that was important in selection of Gale Crater as the landing site," said Ralph Milliken of Brown University, Providence, Rhode Island, and member of Curiosity's science team. "We're now on a path where the orbital data can help us predict what minerals we'll find and make good choices about where to drill. Analyses like these will help us place rover-scale observations into the broader geologic history of Gale that we see from orbital data."
Hematite is formed when another mineral, magnetite, is exposed to oxidizing conditions. This happens when the mineral is exposed to Mars' atmosphere and water. Interestingly, this tiny CRISM sample contains magnetite, hematite and olivine in a range of oxidization states. This is suggestive of an oxidization gradient through the rock sample, a gradient that may have been used by hypothetical Mars microbes as an energy source.
This latest sample of rock was drilled from a location dubbed "Confidence Hills" at the base of Mount Sharp (a.k.a. Aeolis Mons) at an outcrop called "Pahrump Hills." The drilled rock dust was then dropped into CheMin, which uses X-ray diffraction to detect the chemical fingerprint of minerals locked in the rock.
During Curiosity's first year of operations on the Martian surface, the rover spent much of its time investigating drilled samples from "Yelloknife Bay" located on the plain approaching the base of Mount Sharp. The Yellowknife Bay rock samples are markedly different from this first Mount Sharp sample, suggesting that the two locations had different environmental conditions as the rocks formed. In Yellowknife Bay, which was discovered to be an ancient lake bed, quantities of clay minerals were uncovered inside the rock - minerals that had not been detected by the MRO's CRISM instrument. Its non-detection from orbit was likely caused by a surface layer of dust that coated the rocky surface, obscuring the signal.
The discovery of clays on Mars is an important one as it is further evidence that Mars was once wetter than it is now. The fact that water was much more prevalent in Mars' history bolsters the possibility that Mars may have once hosted microbial life.
The sample drilled from Confidence Hills contains more hematite than the Yellowknife Bay samples. "There's more oxidation involved in the new sample," said CheMin Deputy Principal Investigator David Vaniman of the Planetary Science Institute in Tucson, Ariz.
The study of these minerals at the base of Mount Sharp is a key step in understanding the oxidation levels in Mars' ancient past. NASA's Opportunity rover, which as been exploring Mars' Meridiani Planum since 2004, also discovered hematite spherules that provided more clues about Mars' wet past, but they formed in different conditions to the hematite detected in Confidence Hills.
This latest discovery underlines the need for surface operations on Mars - if we are to truly understand the Red Planet's habitable past, we need wheels, or even boots, on the ground.
This image from NASA's Curiosity rover shows a sample of powdered rock extracted by the rover's drill from the "Confidence Hills" target -- the first rock drilled after Curiosity reached the base of Mount Sharp in September 2014.
The rover's Mars Hand Lens Imager (MAHLI) camera recorded this close-up view of the drill test results during the 180th Martian day, or sol, of the rover's work on Mars.