Geochemical observations on Mars
With the LIBS instrument in place the rover can measure the Martian surface within a circumference of up to about six meters. This is where the project can really benefit from the key strengths of the LIBS technology.
“We can get a good LIBS measurement on rocks and soil on the Martian surface. And we can do it without driving there, simply by shooting the laser from wherever the rover ends up. It's a quick observation, at least compared to any other geochemical observation we could make. An observation typically lasts around 15 minutes, and then we move on to the next target or drive on, whatever we’re up for on that particular day on Mars.”
The ability to shoot the laser and make analytical observations from a distance, means that it is possible to get a high volume of LIBS measurements. “That allows us to really track how the geochemical evolution varies as we as we drive across the Martian surface,” says Jens Frydenvang.
“Our ability to perform a lot of observations means that ChemCam and SuperCam can be used as a scout to decide if we need to drive up to a specific outcrop and utilize our arm. We can drill into the sample and get much more detailed observations, look at the mineralogy and so on if the Chemcam LIBS instrument measurements tell us that this is truly interesting,” he adds.
Another part of the work involves continuous tracking. “We have the power, the resources, and the range to find relevant rocks to investigate and see, did anything change compared to where we were the last time. So, we have a fantastic sort of tracking of how the geochemistry has evolved as we climb up through the geological layers of a mountain on Mars.”
In terms of power, the LIBS instrument doesn't need that much, which is also an advantage.
Why LIBS?
The question arises, why LIBS? Is there another method available that could provide the same measurements? According to Jens Frydenvang the short answer is no. There are other technologies available such as X-ray fluorescence (XRF), but it requires longer analysis time or that you get very close to the sample.
“We do have a version of X-ray fluorescence on both rovers that also provides geochemical observations. On Curiosity it is a particle induced fluorescence instrument called APXS, and on the Perseverance rover we have a micro-XRF instrument called PIXL. For both, the time it requires to get an observation is typically much greater than a single LIBS observation, and it also requires that the arm can be deployed on the target,” he explains. “Compared to X-ray fluorescence, the LIBS instrument is faster and much more flexible,” he adds.
“In addition to that, we have the benefit that because an integral part of LIBS is that we create those explosions on the surface, it means that we quite effectively blow away dust which otherwise covers all parts of the Martian surface. So, due to the inherent concept of LIBS, we actually have a unique way of getting to the underneath rocks without being affected by the ubiquitous surficial dust.”
Getting a clean sample surface is otherwise a pretty big issue in the case of X-ray fluorescence. On the Curiosity rover, good APXS observations typically require the use of a brush to remove dust, and on the Perseverance rover, PIXL observations are often preceded by abrading the rock with the rover drill in order to get a fresh surface. “So, there are multiple benefits where LIBS really has become a very powerful tool for planetary exploration,” concludes Jens Frydenvang.
