Rover uses laser to understand the chemistry of Mars rocks

A study conducted by Erin Gibbons, a PhD student in Earth and Planetary Sciences at McGill University in Canada, made use of the SuperCam instrument on NASA’s Perseverance rover, applying its laser beams to “zap” rocks on Mars and determine their chemistry.

Image captured by the Perseverance rover as it scrapes Martian rocks. The equipment’s laser-sensing camera can reveal clues about the chemistry of Martian rocks. Image: NASA / JPL-Caltech

As is known, the color palette of the surface of Mars is of soft warm tones, such as burnt orange, which reflect soil minerals, especially iron, which oxidize under the atmosphere, while a soft gray characterizes non-rusted rocks. Now, the Perseverance rover is adding another color to the regular Mars landscape: purple.

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Over the past year, we’ve seen prominent patches of purple speckled on top of the rocks. The stains range from thin veneers to thick smudges and usually have a smooth, opaque texture. Other Mars rovers such as Curiosity and Opportunity have also seen purple-colored rocks, but not with this kind of mottled texture and certainly not in such abundance.

“We are eager to understand what these enigmatic rock linings reveal about the history of Jezero Crater,” Erin said, referring to the Perseverance rover’s landing site on Mars. “Did they form when ancient waters reacted with rocks? Or did they form over millions of years of dust accumulating and cementing an already barren world? We need more details on her makeup to be sure.”

Radiation is used to understand the composition of rocks on Mars

Erin says that SuperCam’s zapping process is very intense. “On impact, the laser heats the rock to nearly 10,000 degrees Celsius, vaporizing a small amount of material and converting it to plasma.

According to the researcher, when the laser stops firing, the plasma cools and emits radiation at wavelengths that correspond to the chemical constituents of the vaporized material.

“We record this radiation and use it to interpret what rocks are made of. An added benefit of this technique is that we can use vaporization to effectively pierce a target: by repeatedly firing the laser at the same location, we vaporize more and more material and penetrate deeper, allowing us to study the interior,” Erin explained.

To understand the purple spots on Jezero’s rocks, the scientists aimed the laser at a small blur and fired it 150 times (“5x longer than our typical operation,” Erin said). “The goal is to vaporize through the purple material and into the rock below, thus revealing how the chemistry changes between the two layers.”

Erin says the laser drill hole will be less than 1mm deep – however, she says, it could reveal clues about environmental evolution in Jezero Crater as a whole. “Understanding how and when these purple coatings formed will help unravel how Jezero transitioned from a lake to a dust basin,” Erin said.

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