By Patrick Gasda
Finding the element boron might not seem exciting, but if you find it on Mars and you’re interested in alien life, it’s a big deal. Like manganese, another element that NASA’s Curiosity rover discovered in surprising abundance on Mars, boron has a lot to say about the habitability of the Red Planet.
Understanding how these elements got there and the implications to our search for life on Mars is part of Curiosity’s mission. A rolling laboratory that has been creeping across Gale Crater for four and a half years, Curiosity bristles with drills, tools and instruments for studying the chemistry of rocks and soil. It’s all about answering a simple question: Could past or present conditions on Mars support life?
To help find out, Los Alamos National Laboratory, in collaboration with the French Space Agency CNES, developed an instrument called ChemCam. Although Los Alamos isn’t often associated with space exploration, the Lab has been building and operating instruments since the early 1960s to monitor the space radiation environment and on other missions, as well.
The lab also developed the nuclear battery, a radioisotope thermoelectric generator, that powers Curiosity. For ChemCam on the Mars rover, it was natural for Los Alamos to draw on its laser-induced breakdown spectroscopy technology developed for national security applications.
Riding high on the rover, ChemCam zaps rocks with a pinpoint infrared laser, then analyzes the light emitted by the resulting superheated plasma that’s hotter than the surface of the sun. Every element emits a unique spectrum, leading to ChemCam’s quick and sure identification of rocks and soil up to 23 feet away. ChemCam team members — or the rover itself—selects the targets, which are spotted through the rover’s mast-mounted cameras.
Early on, Curiosity’s other tools and instruments found clear evidence of ancient streambeds and lakes with all the key conditions required by life (but no life, yet). After that, the discoveries kept coming in. ChemCam revealed manganese oxides in Martian rocks. That was big news. On Earth, manganese oxides form only in an oxygen-rich atmosphere or in the presence of microbes, so Mars likely had an oxygen-rich atmosphere early in its history — the means by which the atmosphere could be enriched in oxygen without life on the planet is still being explored by Curiosity’s scientists.
ChemCam also found boron. Most of us know boron through the mineral compound called borax that’s used in household products. You might even picture the 20 Mule Team Borax brand, which evokes scruffy miners hauling the powdery white stuff out of Death Valley, Calif.
It’s no coincidence that Death Valley and Mars have boron in common. Boron typically occurs in arid locations where water has evaporated. Mars researchers now know Gale Crater once held a lake, but as it evaporated and disappeared, boron, being very water soluble, flowed into a subsurface water system among gaps and cracks in the rock. Then that water dried up. The ChemCam LIBS findings, backed up by clear photos of bright veins of boron-bearing calcium sulfate, indicate that the temperature, alkalinity, and dissolved mineral content of the groundwater were suitable for life. Many terrestrial organisms would be happy living in these groundwater conditions.
There’s more to the story. The sediments that have filled Gale Crater over the eons establish a geologic calendar starting with the formation of the crater 3.8 billion years ago. First the crater filled with deposits from its lake, and then as the lake dried out, the crater filled to its brim with sands before eroding down to the level that we see today on Mars. These processes must have taken hundreds of millions of years to occur. That information helps loosely date the boron deposits and indicates the water, which would have retreated underground after the lake dried out, was active for a very long time, in a range from 3.8 billion to perhaps a little more than 3 billion years ago, extending the timescale of habitability of Mars much longer than previously thought.
Now that scientists know Mars had a hospitable environment for life, the next NASA mission to the Red Planet, in 2020, will blast off with more sophisticated instruments to look for signs of life itself. Just as ChemCam was vital in Curiosity’s discoveries, Los Alamos’s next instrument, SuperCam, which is already being tested at the Laboratory, will play a leading role in Mars 2020.
ChemCam only detects elements, but SuperCam will detect minerals as well as organic compounds — the very stuff of life — in rocks and dirt from a distance. And SuperCam’s new microphone will provide the first audible soundtrack from Mars, including a distinct “zap!” when the laser beam strikes a rock
Until then, ChemCam is only half-way through its 1-million-shot design life, so the team looks forward to fresh data that continue deepening humanity’s knowledge of Earth’s little brother. For now, NASA’s rovers and Los Alamos’s robotic eyes and soon-to-come ears are the next best thing to being there.
Patrick Gasda is a postdoctoral researcher in the Space Science and Applications group at Los Alamos National Laboratory. As a member of the ChemCam team, he works with team leader Roger Wiens to study the geochemistry and astrobiology of Mars.