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12.13.2016

Mars Rock-Ingredient Stew Seen as Plus for Habitability

Color Variations on Mount Sharp, Mars (White Balanced)
The foreground of this scene from the Mastcam on NASA's Curiosity Mars rover shows purple-hued rocks near the rover's late-2016 location. The middle distance includes future destinations for the rover. Variations in color of the rocks hint at the diversity of their composition on lower Mount Sharp. Credit: NASA/JPL-Caltech/MSSS

Fast Facts:

-- NASA's Curiosity Mars rover is finding patterns of change in rock composition at higher, younger layers of a mountain.
-- Ancient Mars sedimentary basins with groundwater were chemically active, a factor favorable for possible life.
-- Curiosity found boron on Mars, a first for this very soluble element.

NASA's Curiosity rover is climbing a layered Martian mountain and finding evidence of how ancient lakes and wet underground environments changed, billions of years ago, creating more diverse chemical environments that affected their favorability for microbial life.

Hematite, clay minerals and boron are among the ingredients found to be more abundant in layers farther uphill, compared with lower, older layers examined earlier in the mission. Scientists are discussing what these and other variations tell about conditions under which sediments were initially deposited, and about how groundwater moving later through the accumulated layers altered and transported ingredients.

Effects of this groundwater movement are most evident in mineral veins. The veins formed where cracks in the layers were filled with chemicals that had been dissolved in groundwater. The water with its dissolved contents also interacted with the rock matrix surrounding the veins, altering the chemistry both in the rock and in the water.

Now and Long Ago at Gale Crater, Mars before Now and Long Ago at Gale Crater, Mars after

"There is so much variability in the composition at different elevations, we've hit a jackpot," said John Grotzinger, of Caltech in Pasadena, California. He and other members of Curiosity's science team presented an update about the mission Tuesday, Dec. 13, in San Francisco during the fall meeting of the American Geophysical Union. As the rover examines higher, younger layers, researchers are impressed by the complexity of the lake environments when clay-bearing sediments were being deposited, and also the complexity of the groundwater interactions after the sediments were buried.

'Chemical Reactor'

Late 2016 Map of NASA's Curiosity Mars Rover Mission
This map shows the route driven by NASA's Curiosity Mars rover from the location where it landed in August 2012 to its location in December 2016, which is in the upper half of a geological unit called the Murray Formation, on lower Mount Sharp. Credit: NASA/JPL-Caltech/Univ. of Arizona
"A sedimentary basin such as this is a chemical reactor," Grotzinger said. "Elements get rearranged. New minerals form and old ones dissolve. Electrons get redistributed. On Earth, these reactions support life." 

Whether Martian life has ever existed is still unknown. No compelling evidence for it has been found. When Curiosity landed in Mars' Gale Crater in 2012, the mission's main goal was to determine whether the area ever offered an environment favorable for microbes.

The crater's main appeal for scientists is geological layering exposed in the lower portion of its central mound, Mount Sharp. These exposures offer access to rocks that hold a record of environmental conditions from many stages of early Martian history, each layer younger than the one beneath it. The mission succeeded in its first year, finding that an ancient Martian lake environment had all the key chemical ingredients needed for life, plus chemical energy available for life. Now, the rover is climbing lower on Mount Sharp to investigate how ancient environmental conditions changed over time.

Curiosity's Rock or Soil Sampling Sites on Mars, Through November 2016
This graphic maps locations of the sites where NASA's Curiosity Mars rover collected its first 19 rock or soil samples for laboratory analysis inside the vehicle. It also presents images of the drilled holes where 15 rock-powder samples were acquired, most recently at "Sebina," on Oct. 20, 2016. Credit: NASA/JPL-Caltech
"We are well into the layers that were the main reason Gale Crater was chosen as the landing site," said Curiosity Deputy Project Scientist Joy Crisp of NASA's Jet Propulsion Laboratory, in Pasadena, California. "We are now using a strategy of drilling samples at regular intervals as the rover climbs Mount Sharp. Earlier we chose drilling targets based on each site's special characteristics. Now that we're driving continuously through the thick basal layer of the mountain, a series of drill holes will build a complete picture."

Four recent drilling sites, from "Oudam" this past June through "Sebina" in October, are each spaced about 80 feet (about 25 meters) apart in elevation. This uphill pattern allows the science team to sample progressively younger layers that reveal Mount Sharp's ancient environmental history.

Changing Environments

Detecting a Difference in Clay Minerals at Two Gale Crater Sites
Data graphed here from the Chemistry and Camera (CheMin) instrument on NASA's Mars Curiosity rover show a difference between clay minerals in powder drilled from mudstone outcrops at two locations in Mars' Gale Crater: "Yellowknife Bay" and "Murray Buttes." Credit: NASA/JPL-Caltech
One clue to changing ancient conditions is the mineral hematite. It has replaced less-oxidized magnetite as the dominant iron oxide in rocks Curiosity has drilled recently, compared with the site where Curiosity first found lakebed sediments. "Both samples are mudstone deposited at the bottom of a lake, but the hematite may suggest warmer conditions, or more interaction between the atmosphere and the sediments," said Thomas Bristow of NASA Ames Research Center, Moffett Field, California. He helps operate the Chemistry and Mineralogy (CheMin) laboratory instrument inside the rover, which identifies minerals in collected samples.

Chemical reactivity occurs on a gradient of chemical ingredients' strength at donating or receiving electrons. Transfer of electrons due to this gradient can provide energy for life. An increase in hematite relative to magnetite indicates an environmental change in the direction of tugging electrons more strongly, causing a greater degree of oxidation in iron.

Another ingredient increasing in recent measurements by Curiosity is the element boron, which the rover's laser-shooting Chemistry and Camera (ChemCam) instrument has been detecting within mineral veins that are mainly calcium sulfate. "No prior mission has detected boron on Mars," said Patrick Gasda of the U.S. Department of Energy's Los Alamos National Laboratory, Los Alamos, New Mexico. "We're seeing a sharp increase in boron in vein targets inspected in the past several months." The instrument is quite sensitive; even at the increased level, boron makes up only about one-tenth of one percent of the rock composition.

'Dynamic System'

Boron in Calcium Sulfate Vein at 'Catabola,' Mars
The highest concentration of boron measured on Mars, as of late 2016, is in this mineral vein examined with the ChemCam instrument on NASA's Curiosity rover on Aug, 25, 2016. Orange bars indicate boron content at points in the calcium sulfate vein. The context image is from Curiosity's Mastcam. Credit: NASA/JPL-Caltech/MSSS/LANL/CNES/IRAP/LPGNantes/CNRS/IAS
Boron is famously associated with arid sites where much water has evaporated away -- think of the borax that mule teams once hauled from Death Valley. However, environmental implications of the minor amount of boron found by Curiosity are less straightforward than for the increase in hematite.

Scientists are considering at least two possibilities for the source of boron that groundwater left in the veins. Perhaps evaporation of a lake formed a boron-containing deposit in an overlying layer, not yet reached by Curiosity, then water later re-dissolved the boron and carried it down through a fracture network into older layers, where it accumulated along with fracture-filling vein minerals. Or perhaps changes in the chemistry of clay-bearing deposits, such as evidenced by the increased hematite, affected how groundwater picked up and dropped off boron within the local sediments.

"Variations in these minerals and elements indicate a dynamic system," Grotzinger said. "They interact with groundwater as well as surface water. The water influences the chemistry of the clays, but the composition of the water also changes. We are seeing chemical complexity indicating a long, interactive history with the water. The more complicated the chemistry is, the better it is for habitability. The boron, hematite and clay minerals underline the mobility of elements and electrons, and that is good for life."

Boron, Sodium and Chlorine in Mineral Vein 'Diyogha'
Examination of a calcium sulfate vein called "Diyogha" by the ChemCam instrument on NASA's Curiosity Mars rover found boron, sodium and chlorine. An image from the rover's Mastcam, at left, provides context for the magnified image and composition information from ChemCam, at right. Credit: NASA/JPL-Caltech/MSSS/LANL/CNES/IRAP/LPGNantes/CNRS/IAS

Curiosity is part of NASA's ongoing Mars research and preparation for a human mission to Mars in the 2030s. Caltech manages JPL, and JPL manages the Curiosity mission for NASA's Science Mission Directorate in Washington. For more about Curiosity, visit:

Learn about NASA’s Journey to Mars at:

Laurie Cantillo / Dwayne Brown
NASA Headquarters, Washington
202-358-1077 / 202-358-1726
laura.l.cantillo@nasa.gov / dwayne.c.brown@nasa.gov

Guy Webster / DC Agle
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278 / 818-393-9011
guy.webster@jpl.nasa.gov / agle@jpl.nasa.gov

Abigail Tabor
Ames Research Center, Moffett Field, Calif.
650-604-0643
abigail.s.tabor@nasa.gov

Laura Mullane
Los Alamos National Research Laboratory, Los Alamos, N.M.
505-667-6012
mullane@lanl.gov


All Related Images
  • This map shows the route driven by NASA's Curiosity Mars rover from the location where it landed in August 2012 to its location in December 2016, which is in the upper half of a geological unit called the Murray formation, on lower Mount Sharp.
    Late 2016 Map of NASA's Curiosity Mars Rover Mission
  • This graphic depicts aspects of the driving distance, elevation, geological units and time intervals of NASA's Curiosity Mars rover mission, as of late 2016. The vertical dimension is exaggerated 14-fold compared with the horizontal dimension, for presentation-screen proportions.
    Curiosity Rover's Martian Mission, Exaggerated Cross Section
  • This series of pie charts shows similarities and differences in the mineral composition of mudstone at 10 sites where NASA's Curiosity Mars rover collected rock-powder samples and analyzed them with the rover's Chemistry and Mineralogy (CheMin) instrument.
    Mudstone Mineralogy from Curiosity's CheMin, 2013 to 2016
  • Data graphed here from the Chemistry and Camera (CheMin) instrument on NASA's Mars Curiosity rover show a difference between clay minerals in powder drilled from mudstone outcrops at two locations in Mars' Gale Crater: "Yellowknife Bay" and "Murray Buttes."
    Detecting a Difference in Clay Minerals at Two Gale Crater Sites
  • This graphic illustrates how dimensions of clay minerals' crystal structure are affected by which ions are present in the mineral. The CheMin instrument on NASA's Curiosity Mars rover identified different clay minerals this way at two sites in Gale Crater: "Murray Buttes" and "Yellowknife Bay."
    Clay Mineral Crystal Structure Tied to Composition
  • This graphic shows proportions of minerals identified by the Curiosity Mars rover's CheMin instrument in mudstone outcrops at "Yellowknife Bay" in 2013 and at "Murray Buttes" in 2016. For example, the rover found more hematite and less magnetite at Murray Buttes, compared with Yellowknife Bay.
    Mineral Content Comparison at Two Gale Crater Sites
  • This map shows the route driven by NASA's Curiosity Mars rover (blue line) and locations where the rover's ChemCam instrument detected the element boron (dots, colored by abundance of boron according to the key at right). The inset is a blowup of the most recent portion of the traverse.
    Where's Boron? Mars Rover Detects It
  • The highest concentration of boron measured on Mars, as of late 2016, is in this mineral vein examined with the ChemCam instrument on NASA's Curiosity rover on Aug, 25, 2016. Orange bars indicate boron content at points in the calcium sulfate vein. The context image is from Curiosity's Mastcam.
    Boron in Calcium Sulfate Vein at 'Catabola,' Mars
  • Examination of a calcium sulfate vein called "Diyogha" by the ChemCam instrument on NASA's Curiosity Mars rover found boron, sodium and chlorine. An image from the rover's Mastcam, at left, provides context for the magnified image and composition information from ChemCam, at right.
    Boron, Sodium and Chlorine in Mineral Vein 'Diyogha'
  • This graphic portrays two hypotheses about how the element boron ended up in calcium sulfate veins found within mudstone layers of Mars' lower Mount Sharp.
    Two Possible Ways Boron Got into Veins on Mount Sharp
  • This graphic maps locations of the sites where NASA's Curiosity Mars rover collected its first 19 rock or soil samples for laboratory analysis inside the vehicle. It also presents images of the drilled holes where 15 rock-powder samples were acquired, most recently at "Sebina," on Oct. 20, 2016.
    Curiosity's Rock or Soil Sampling Sites on Mars, Through November 2016
  • The foreground of this scene from the Mastcam on NASA's Curiosity Mars rover shows purple-hued rocks near the rover's late-2016 location. The middle distance includes future destinations for the rover. Variations in color of the rocks hint at the diversity of their composition on lower Mount Sharp.
    Color Variations on Mount Sharp, Mars (White Balanced)
  • This pair of drawings depicts the same location at Gale Crater on at two points in time: now and billions of years ago. Water moving beneath the ground, as well as water above the surface in ancient rivers and lakes, provided favorable conditions for microbial life, if Mars has ever hosted life.
    Now and Long Ago at Gale Crater, Mars


Credit: NASA/JPL-Caltech


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