This set of images compares rocks seen by NASA’s Opportunity rover and Curiosity rover at two different parts of Mars. 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, in Gale Crater, as seen by Curiosity.
Scientists identified sulfur, nitrogen, hydrogen, oxygen, phosphorus and carbon — some of the key chemical ingredients for life — in the powder Curiosity drilled out of a sedimentary rock near an ancient stream bed in Gale Crater on the Red Planet last month.
“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 the agency’s headquarters in Washington. “From what we know now, the answer is yes.”
The image merges topographic data with thermal inertia data that record the ability of the surface to hold onto heat. Red indicates a surface material that retains its heat longer into the evening than other areas, suggesting differences relative to its surroundings. Curiosity crossed the boundary from lower thermal inertia values to higher values on Sol 121 (the 121st Martian day of operations, which was Dec. 8, 2012, on Earth) while driving down into an area known as “Yellowknife Bay”. The black oval indicates the targeted landing area for the rover, known as the “landing ellipse,” and the black cross shows where the rover actually touched down at what has since been named the Bradbury Landing site. The blue circle indicates where the John Klein drill site is within the Yellowknife Bay area.
An alluvial fan, or fan-shaped deposit where debris spread out downslope, has been highlighted in lighter colors for better viewing. On Earth, alluvial fans often are formed by water flowing downslope. The John Klein outcrop is part of a geologic layer, known as “Sheepbed,” which is a mudstone with abundant evidence for ancient aqueous processes. It seems likely that sediments were transported downhill from the eroding crater rim and became part of alluvial fan systems. The materials then flowed out where water and sediments accumulated to form a habitable environment represented by the Sheepbed mudstone.
This image was obtained by the Thermal Emission Imaging System on NASA’s Odyssey orbiter.
Clues to this habitable environment come from data returned by the rover’s Sample Analysis at Mars (SAM) and Chemistry and Mineralogy (CheMin) instruments. The data indicate the Yellowknife Bay area the rover is exploring was the end of an ancient river system or an intermittently wet lake bed that could have provided chemical energy and other favorable conditions for microbes. The rock is made up of a fine-grained mudstone containing clay minerals, sulfate minerals and other chemicals. This ancient wet environment, unlike some others on Mars, was not harshly oxidizing, acidic or extremely salty.
The patch of bedrock where Curiosity drilled for its first sample lies in an ancient network of stream channels descending from the rim of Gale Crater. The bedrock also is fine-grained mudstone and shows evidence of multiple periods of wet conditions, including nodules and veins.
Curiosity’s drill collected the sample at a site just a few hundred yards away from where the rover earlier found an ancient streambed in September 2012.
“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, Calif.
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.
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 (as found at Meridiani Planum by NASA’s Mars Exploration Rover Opportunity) suggests a neutral to mildly alkaline pH environment. The Rocknest sand shadow mineralogy suggests a dry, aeolian (wind-shaped) environment with low water activity. The John Klein mineralogy suggests a lacustrine (lakebed) environment with high water activity.
As seen on the left, the Rocknest data reveal abundant plagioclase feldspar, pyroxene and olivine minerals. The data also indicate reveal small amounts of magnetite and anhydrite. In addition, the Rocknest sample contains 25 to 35 percent amorphous, or non-crystalline, material.
X-ray diffraction analysis of the John Klein drill powder reveals abundant phyllosilicate (a class of clay minerals called smectites that form by the action of relatively pure and neutral pH water on source minerals), plagioclase feldspar, pyroxene, magnetite and olivine. Alternatively, the clay minerals could have been transported by water from sources higher up the sediment fan to form the John Klein mineral assemblage. The region of the pattern indicating the phyllosilicates is labeled in the annotated version of this image. The data also show minor amounts of anhydrite and bassanite. The John Klein sample also contains about 20 percent amorphous material.
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.
An additional drilled sample will be used to help confirm these results for several of the trace gases analyzed by the SAM instrument.
“We have characterized a very ancient, but strangely new ‘gray Mars’ where conditions once were favorable for life,” said John Grotzinger, Mars Science Laboratory project scientist at the California Institute of Technology in Pasadena, Calif. “Curiosity is on a mission of discovery and exploration, and as a team we feel there are many more exciting discoveries ahead of us in the months and years to come.”
Scientists plan to work with Curiosity in the “Yellowknife Bay” area for many more weeks before beginning a long drive to Gale Crater’s central mound, Mount Sharp. Investigating the stack of layers exposed on Mount Sharp, where clay minerals and sulfate minerals have been identified from orbit, may add information about the duration and diversity of habitable conditions.
NASA’s Mars Science Laboratory Project has been using Curiosity to investigate whether an area within Mars’ Gale Crater ever has offered an environment favorable for microbial life. Curiosity, carrying 10 science instruments, landed seven months ago to begin its two-year prime mission. NASA’s Jet Propulsion Laboratory in Pasadena, Calif., manages the project for NASA’s Science Mission Directorate in Washington.
Contacts and sources:
Jet Propulsion Laboratory, Pasadena, Calif.