NASA's Curiosity Mars rover has discovered a rock outcropping that may have been a suitable habitat for microbes in ancient times. Based on a sample collected by unmanned rover’s drill at the John Klein area in Gale Crater and analyzed using the Sample Analysis at Mars (SAM) and Chemistry and Mineralogy (CheMin) instruments, the findings contribute to Curiosity's primary mission of seeking out areas of the Red Planet where life may have once or still could exist.
The minerals uncovered by the drilling operation were sedimentary rock of fine-grained mudstone containing clay minerals, sulfate minerals and other chemicals identified as sulfur, nitrogen, hydrogen, oxygen, phosphorus and carbon formed at a time when Mars was much wetter and water flowed regularly across the bottom of Gale Crater. The clay is the product of the reaction of fresh water on igneous rock, such as the olivine also found at the site, and could have occurred at the site or elsewhere and the clay washed downstream by flowing water.
"Clay minerals make up at least 20 percent of the composition of this sample," said David Blake, principal investigator for the CheMin instrument at NASA's Ames Research Center in Moffett Field, California.
Mars is very hostile to organic molecules – and life in general. The lack of water, extremely thin atmosphere and abundance of hard UV radiation have turned the soil into an extremely reactive form of iron oxide and other compounds. This is destructive for organic molecules while providing only a very shallow chemical energy gradient, so there isn’t much left to power living organisms.
An exciting feature of Curiosity’s fist drilling operation was that beneath the dead, reddish surface of the John Klein rock there was a gray interior that it is not harshly oxidizing, acidic or extremely salty. The presence of calcium sulfate indicates that the rocks are neutral or mildly alkaline. Furthermore, the lack of oxidizing chemicals indicates that the interior of the rocks have a much steeper energy gradient, which could power life.
"The range of chemical ingredients we have identified in the sample is impressive, and it suggests pairings such as sulfates and sulfides that indicate a possible chemical energy source for microorganisms," said Paul Mahaffy, principal investigator of the SAM suite of instruments at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
Analyzing the samples is the job of Curiosity's Sample Analysis at Mars (SAM) instrument suite. To do this, the sample, which had been sieved and processed by the rover’s robotic hand, is heated in a quartz oven to 1,535⁰ Fahrenheit (835⁰ Celsius). This bakes off gases, which are sent through SAM’s quadrupole mass spectrometer (QMS). The QMS weighs the masses of the elements in the gas and the characteristic signatures for various compounds are produced.
Next, some of the gas is sent to the tunable laser spectrometer (TLS) to measure isotopes of carbon, oxygen and hydrogen with the isotope ratios allowing scientists to date the sample. This is because lighter hydrogen isotopes escape over time, leaving behind heavier ones. Measuring heavier hydrogen against lighter isotopes gives some idea of how old the deposit is.
The final step in the analysis is to take some of the sample gas and pass it to the gas chromatograph spectroscope to look for organic compounds – the key indicator of life chemistry.
"A fundamental question for this mission is whether Mars could have supported a habitable environment," said Michael Meyer, lead scientist for NASA's Mars Exploration Program. "From what we know now, the answer is yes."
The announcement of the findings comes on the tail of a minor problem for the nuclear-powered explorer. There was a glitch in Curiosity’s A-side computer indicating a corrupting memory location, so mission control at the Jet Propulsion Laboratory (JPL) in Pasadena, California, switched to the redundant B-side computer, which put the rover into safe mode until it could be safely restarted.
This was followed by a large solar flare on March 5 that subsequently struck Mars and mission control put Curiosity put to sleep for 22 hours. Curiosity’s electronics are made out of hardened components and shielded with the computers sealed in a lead box, but the computer glitch combined with the flare made NASA’s engineers opt for a conservative approach.
The JPL video below explains why the search for organic molecules on Mars is important.