NASA’s robotic rover Perseverance will use a crucial X-ray device to scan for fossils on Mars.
NASA’s Mars 2020 Perseverance rover has a hefty job ahead: Once it survives entry into the Martian atmosphere, and executes the descent and landing phases of the mission on Feb. 18, 2021, it will hunt for microscopic life using a precision X-ray device — called PIXL — powered with artificial intelligence (AI), according to a recent blog post on NASA’s website.
The X-ray device’s name, PIXL, is short for Planetary Instrument for X-ray Lithochemistry. An instrument the size of a lunchbox, PIXL is placed at the end of Perseverance’s 7-foot-long (2-meter-long) robotic arm, according to the NASA blog post.
The rover’s most crucial samples will be collected via a coring drill at the end Perseverance’s arm, and then stored in metal tubes — to be placed on the Martian surface where they will await return to Earth via a future mission.
Nearly every mission that saw a successfull landing on Mars — from the Viking landers to the Curiosity rover — came with an X-ray fluorescence spectrometer. But PIXL differs from its predecessors in numerous ways — for example, it can scan rocks with a powerful, specially-focused X-ray beam to find where chemicals are distributed along the Martian surface, while also noting the quantity, or abundance.
“PIXL’s X-ray beam is so narrow that it can pinpoint features as small as a grain of salt. That allows us to very accurately tie chemicals we detect to specific textures in a rock,” said PIXL’s Principal Investigator Abigail Allwood of NASA’s Jet Propulsion Laboratory in Southern California, in NASA’s blog post.
Analyzing rock textures is critical to deciding which samples should be returned to Earth. Down here, uniquely-warped rocks called stromatolites were forged from ancient layers of bacteria, and are but one example of fossilized ancient life scientists seek on the Red Planet.
To narrow down the best targets, PIXL uses more than just the precision X-ray beam. It also makes use of a hexapod — a device with six mechanical legs joining PIXL to the robotic arm and guided via AI to achieve highly-accurate operation.
Once the rover’s arm is sufficiently close to a notable rock, PIXL uses its state-of-the-art laser and camera to calculate the distance. Then the six legs make minuscule movements — as small as 100 microns, or twice the width of a human hair — to scan the target and analyze underlying chemicals within the area of a postage stamp.
“The hexapod figures out on its own how to point and extend its legs even closer to a rock target,” said Allwood in the blog post. “It’s kind of like a little robot who has made itself at home on the end of the rover’s arm.”
After this, PIXL measures X-rays in short, 10-second bursts from a single point on the rock before the entire instrument turns 100 microns to collect another measurement. To generate one of the postage-stamp-sized chemical maps, the device has to repeat this process thousands of times — which can take eight or nine hours.
This timeframe is part of why PIXL’s microscopic adjustments are so crucial: Mars’ surface temperature changes more than 100 degrees Fahrenheit (38 degrees Celsius) in one day, which causes the metal on Perseverance’s robotic arm to contract and expand up to half of an inch (13 millimeters) — a football field on the scale of a human hair.
To minimize the effects of contractions and expansions, the instrument carries out science work after the Sun sets. “PIXL is a night owl,” said Allwood. “The temperature is more stable at night, and that also lets us work at a time when there’s less activity on the rover.”
As Perseverance — and its X-ray device — continue the journey to Mars, it’s interesting to note the sheer scope of technological advancement accomplished to match the demands of space exploration. While it’s anyone’s guess what we’ll find, scientists are crossing their collective fingers for life signs on the Red Planet.
Mars 2020, Rover, NASA
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