Scientific confirmation that the NASA Mars rover Curiosity has found a location habitable to Martian microbial life 3 billion years ago is an historic milestone in planetary exploration.

"This is an incredible adventure to get to this point so early in the mission, I feel giddy," said John Grunsfeld NASA associate administrator for science.

The major finding was made in spite of a weak wisp of organics measured by the rover's instruments, except for a major spike in carbon dioxide from the material when heated to 1,535 deg. F (835 deg. C).



The signatures of more than five hundred mass values were sampled during the heating of this drilled sample and analyzed by the SAM instrument. Five are shown in the graph. These traces are diagnostic of water, carbon dioxide, oxygen, and two forms of sulfur, sulfur dioxide, the oxidized form, and hydrogen sulfide, the reduced form. The high deuterium-to-hydrogen ratio in water in the Mars atmosphere is a signature of the lighter hydrogen more rapidly escaping to space over geological time. Credit: NASA/ JPL-Caltech/GSFC.

The new data from the powder drilled from within a rock at Yellowknife Bay indicates that mineralogy, chemistry and abundant fresh water conditions that existed at the time would have supported the existence of prokaryotic organisms.

Such microbes "do not use organics to metabolize, but rather process inorganic compounds for food and energy", said John Grotzinger of Caltech, project scientist for the Mars Science Laboratory.

"There does need to be a source of carbon there somewhere," Grotzinger said. "But if it is just carbon dioxide you can have a "Chemolitho autotrophic organism" that literally feeds on rocks. Such organisms will metabolize and generate organic compounds based on carbon in the carbon dioxide," the project scientist said at a Washington briefing on sample results.



Curiosity's SAM instrument detected the simple carbon-containing compounds chloro- and dichloromethane from the powdered rock sample extracted from the "John Klein" rock on Mars. These species were detected by the gas chromatograph mass spectrometer (GCMS) on Curiosity's Sample Analysis at Mars instrument. The blue peak on the left shows the presence of chloromethane and the two red peaks on the right show the presence of dichloromethane. Credit: NASA/ JPL-Caltech/GSFC

"The fact that Principal Investigator Paul Mahaffy was able to show in the Sample Analysis at Mars instrument that there was a major carbon dioxide spike" that vented from the subsurface rock powder "is what we are really excited about," Grotzinger said. That is because such a spike indicates a key building block for life on Mars.

The main points of the briefing include:

Significance: "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 at NASA Headquarters in Washington. "From what we know now, the answer is yes."

After 50 years of planetary exploration no other location in the solar system beyond Earth has ever been found to be habitable until Curiosity started exploring Yellowknife Bay, Mars.



This set of images shows the results from the rock abrasion tool from NASA's Mars Rover Opportunity (left) and the drill from NASA's Curiosity rover (right).

Scientists were surprised to find a mixture of oxidized, less-oxidized, and even non-oxidized chemicals in the Curiosity sample, providing an energy gradient of the sort many microbes on Earth exploit to live. This partial oxidation was first hinted at when the drill cuttings were revealed to be gray rather than red like with Opportunity's site where high Ph readings means that area is much less desirable for microorganisms. Credit: JPL-Caltech/MSSS

The stuff of life: The rover's instruments found within the gray/green rock sample the elements of carbon, hydrogen, nitrogen, oxygen, phosphors and sulfur, which dominate living cells on Earth. But the science team members said that with the new data they will be able to shift their thinking more to a "Mars paradigm" where the chemistry and mineralogy in the rock samples will align in tune with the Martian environment that existed 3 billion years ago.

Life on Mars and Earth: The habitability finding also raises an interesting comparative planetology question about whether Martian microorganisms could have evolved at about the same time, or even before life developed on Earth as early as 3.8 billion years ago, within 700 million years of the formation of the Solar System 4.5 billion years ago.

Organic molecules: The SAM instrument found simple organic molecules, but not a strong organic signal from past Martian life. Curiosity detected the simple carbon-containing compounds chloro- and dichloromethane from the powdered rock sample extracted from the "John Klein" rock on Mars. These species were detected by the gas chromatograph mass spectrometer (GCMS), one of three instruments that make up SAM.



On the left is "Wopmay" rock, in Endurance Crater, Meridiani Planum, as studied by the Opportunity rover. On the right are the rocks of the "Sheepbed" unit in Yellowknife Bay imaged by Curiosity. The Wopmay environment was acidic and not likely habitable. In the Sheepbed image on the right, these very fine-grained sediments represent the record of an ancient habitable environment. The Sheepbed sediments were likely deposited under fresh water. Scientists think the water cemented the sediments, and also formed concretions. The rock was then fractured and filled with sulfate minerals when water flowed through subsurface fracture networks. Credit: NASA/JPL-Caltech.



Alert to contamination: Both chloro- and dichloromethane were also detected earlier by SAM at the "Rocknest" sand drift. It is possible that these simple carbon-containing compounds were produced by the reaction between Martian carbon and chlorine released when this sample was heated in the SAM oven.

However, analysis of an additional drilled sample is required to help scientists understand if instead any residual terrestrial carbon from the drill, or perhaps chlorine left over from the Rocknest sample, is responsible for the generation of some or all of these compounds.

Strategy forward: Curiosity will remain at Yellowknife Bay well into May or even June to drill for a second subsurface rock sample in a somewhat different location in the bay. Once that second sample is processed 2-3 times through SAM and CheMin, the rover will be started on its about 5 month traverse toward Mt. Sharp.



Diagram shows Curiosity's landing site in relation to major water features. A stream sweeping down from crater wall formed alluvial fan. The red signature indicates high thermal inertia of an area that does not cool as quickly as surrounding area. This is the Yellowknife Bay area. Credit: NASA/JPL-Caltech.

Second rock drilling: Curiosity's engineering team continues to restore the rover's A-side computer to full health for its new backup role after a significant malfunction in late February. Some science operations will resume through the end of March, including the possible run of a triple dose of the original sample in SAM to boost an organic signal if it is there.



But Mars, now 221 million mi. (356 million km.) from Earth will move behind the Sun in April, making it difficult for Earth to communicate with the rover. Curiosity will remain quiescent during April, but in May the science team will select a new site where a second sample will be drilled and run two or more times through SAM and CheMin for comparison with the original subsurface rock data.

The second run should also benefit from decreased contamination, if any, from the original use of the drill and the highly oxidized Rocknest sample processed last fall. Some red Rocknest sample was noticed in the scoop that handled the rock sample after drilling.



Image (left) shows dry lakebed in Australia similar to Yellowknife Bay on Mars. Image (right) shows a core sample of the Australian site showing how bands of clays form in the sediment. Credit: NASA/JPL-Caltech

Electricity is in the air: Scientists were surprised to find a mixture of oxidized, less-oxidized, and even non-oxidized chemicals, providing an energy gradient of the sort many microbes on Earth exploit to live. This partial oxidation was first hinted at when the drill cuttings were revealed to be gray rather than red.

"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 micro-organisms," said Paul Mahaffy, principal investigator of the SAM suite of instruments at NASA's Goddard Space Flight Center in Greenbelt, Md.



These images, made from data obtained by Curiosity's Chemistry and Mineralogy instrument (CheMin), show the patterns obtained from a drift of windblown dust and sand called "Rocknest" (left) and from a powdered rock sample drilled from the "John Klein" bedrock. (right). The presence of abundant clay minerals in the John Klein drill powder and the lack of abundant salt suggest a fresh water environment. The presence of calcium sulfates rather than magnesium or iron sulfates suggests a neutral to mildly alkaline pH environment in a lacustrine (lakebed) environment with high water activity. Credit: NASA/JPL-Caltech/Ames

Impressive Clays: "Clay minerals make up 20-30 percent of the composition of this sample," said David Blake, principal investigator for the CheMin instrument at NASA's Ames Research Center.

These clay minerals are a product of the reaction of relatively fresh water with igneous minerals, such as olivine, also present in the sediment. The reaction could have taken place within the sedimentary deposit, during transport of the sediment, or in the source region of the sediment. The presence of calcium sulfate along with the clay suggests the soil is neutral or mildly alkaline.

But the Mars meteorite community believes that the analysis of meteorites from Mars found similar reactions between the flow of water through clays (known as smectites) found in a number of Martian meteorites years before Curiosity reported its clay findings. Clays are important because they are the most likely to preserve organics as a tip off to the existence of past life.



Awards: Members of the rover team also won two major awards this week. The 2013 Smithsonian National Air & Space Museum Trophy for Current Achievement will be awarded to the Mars Science Laboratory Entry, Descent, and Landing Team. They will be presented their award April 24 at a black-tie dinner at the Smithsonian Air and Space Museum building in downtown Washington, D.C.

In addition, the Jet Propulsion Laboratory Social Media Team for Curiosity has captured the 2013 South by Southwest (SXSW) Interactive Award for best social media campaign for turning the Mars Science Laboratory mission into an internet sensation. The award was presented March 12 in Austin, Texas to Veronica McGregor, Stephanie L. Smith and Courtney O'Connor of JPL.

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