Boron, a metalloid chemical element with properties intermediate between those of carbon and aluminum, has been identified for the first time on the Martian surface, indicating the potential for habitable groundwater in the ancient past.
The highest concentration of boron measured on Mars is in this mineral vein, called ‘Catabola,’ examined with the ChemCam instrument on NASA’s Curiosity rover on Aug, 25, 2016, during Sol 1441 of the mission. This two-part illustration shows the context of the erosion-resistant, raised vein, in an image from Curiosity’s Mast Camera (Mastcam), and a detailed inset image from ChemCam’s remote micro-imager. The inset includes indicators of the boron content measured at 10 points along the vein that were analyzed with ChemCam’s laser-firing spectrometer. The vein’s main component is calcium sulfate. The highest boron content identified is less than one-tenth of one percent. The heights of the orange bars at each point indicate relative abundance of boron, compared with boron content at other points. Scale bar – 0.36 inches (9.2 mm). Image credit: NASA/ JPL-Caltech / MSSS / LANL / CNES-IRAP / William Rapin.
The boron was identified by the Chemistry and Camera (ChemCam) instrument on NASA’s Curiosity rover in calcium sulfate mineral veins in Gale Crater.
“No prior mission to Mars has found boron,” said Dr. Patrick Gasda, a researcher at Los Alamos National Laboratory.
“The ChemCam instrument provides quantitative elemental compositions of targets in Gale Crater using laser-induced breakdown spectroscopy,” the scientists explained.
“We observed boron lines in 23 calcium sulfate veins: 3 in Yellowknife Bay and 20 in the Murray lacustrine mudstone and the Stimson eolian sandstone units since sol 727, as Curiosity arrived at the base of Mt. Sharp, a 5 km sedimentary mound in the center of Gale Crater.”
The team’s preliminary results show that the Gale Crater veins have between 10–100 ppm boron.
“If the boron that we found on Mars is similar to what we see on Earth, it would indicate that the groundwater of ancient Mars that formed these veins would have been 32-140 degrees Fahrenheit (0-60 degrees Celsius) and neutral-to-alkaline pH,” Dr. Gasda said.
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 boron found by the rover are still open to debate.
Dr. Gasda and co-authors are considering at least two possibilities for the source of boron that groundwater left in the veins:
(i) it could be that the drying out of part of Gale lake resulted in a boron-containing deposit in an overlying layer, not yet reached by Curiosity; some of the material from this layer could have later been carried by groundwater down into fractures in the rocks;
(ii) or perhaps changes in the chemistry of clay-bearing deposits and groundwater affected how boron was picked up and dropped off within the local sediments.
“ChemCam cannot directly determine mineralogy, but boron is likely present as borax as the dominate borate phase in the Gale Crater veins, based on previous estimates of vein fluid temperature,” the researchers said.
“Borates forming in this environment tend to precipitate from mildly alkaline fluids. The fluid temperature and pH implies these veins were potentially habitable environments.”
Dr. Gasda and colleagues reported their findings yesterday at the 2016 American Geophysical Union Fall Meeting in San Francisco, CA.
_____
Patrick James Gasda et al. First Observations of Boron on Mars and Implications for Gale Crater Geochemistry. 2016 AGU Fall Meeting, abstract # P21D-04
This article is based on a press-release from Los Alamos National Laboratory.
