Curiosity rover detects boron, more evidence of past habitability on Mars
This pair of drawings (animated) depicts the same location (Curiosity’s current position) 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. Credits: NASA/JPL-Caltech
As NASA’s Curiosity Mars rover climbs the slopes of Mount Sharp, the layered mountain at the center of Gale crater, it is finding patterns of change in rock composition in the mountain’s higher, younger layers. The rover has also detected the chemical element boron for the first time on the surface of Mars. Scientists with the Curiosity mission discussed some of their recent findings on Tuesday, Dec. 13, at the Fall Meeting of the American Geophysical Union (AGU) in San Francisco, California.
Ingredients such as hematite, clay minerals, and boron have been found to be more abundant in layers further uphill, compared with lower, older layers studied earlier in Curiosity’s mission. These and other variations are providing scientists with clues about the conditions under which sediments were initially deposited and about how groundwater moving later through the accumulated layers altered and transported ingredients.
The effects of 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 and its dissolved contents also interacted with the rock matrix surrounding the veins, changing the chemistry both in the rock and in the water.
‘Chemical reactor’
“There is so much variability in the composition at different elevations, we’ve hit a jackpot,” said John Grotzinger, of Caltech in Pasadena, California. “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.”
The foreground of this scene from the Mastcam on NASA’s Curiosity Mars rover shows purple-hued rocks near the rover’s late-2016 (sol 1516) 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. (Click to enlarge) Photo & Caption Credit: NASA/JPL-Caltech/MSSS
Gale Crater’s main appeal for researchers is geological layering exposed in the lower slopes of Mount Sharp. These exposures allow access to rocks that contain a record of environmental conditions from many distinct periods of early Martian history, each layer more recent than the one beneath it. During its first year, the Curiosity mission succeeded in discovering that an ancient Martian lake environment had all of the key chemical ingredients needed for life, plus an available source of chemical energy for life. The rover is now climbing lower Mount Sharp on an extended mission to study how ancient environmental conditions changed over time.
“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 of the rover’s recent drilling sites are spaced about 80 feet (about 25 meters) apart in elevation. This uphill pattern allows researchers to study progressively younger layers of Mount Sharp that reveal the mountain’s ancient environmental history.
Environmental change
The mineral hematite is an important clue to changing ancient conditions on Mars. In the rocks Curiosity has drilled recently, hematite has replaced the less oxidized magnetite as the dominant form of iron oxide, compared with the site where the rover 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.
This HiRISE image 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. Image & Caption Credit: NASA/JPL-Caltech/Univ. of Arizona
Another component recently measured in increasing amounts is the element boron, which has been found within mineral veins containing mostly calcium sulfate by the rover’s laser-firing Chemistry and Camera instrument (ChemCam). The instrument is very sensitive – even at the increased levels found at higher elevations, boron only makes up about one-tenth of one percent of the rock composition.
“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.”
‘Dynamic system’
Researchers are considering two possibilities for the source of boron that groundwater left in the veins. It is possible that 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 network of fractures into older layers, where it accumulated along with fracture-filling vein minerals. An alternative possibility is that changes in the chemistry of clay-bearing deposits, 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.”
Video courtesy of Los Alamos National Laboratory
Jim Sharkey
Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.
