Perseverance collects first rock samples from Mars

NASA’s Mars Rover Perseverance successfully collected its first two rock samples from Mars in early September 2021, a month after an initial failed attempt. The rocks were collected from Jezero Crater, a wide Martian basin where scientists posit water flowed billions of years ago. As part of a planned ongoing mission, the precious samples have been sealed within airtight titanium tubes and will be cached first onboard Perseverance, then on the planet’s surface until a later mission to Mars will collect them and return them to Earth for full analysis. These samples will be the first from another planet to be returned to Earth. 

Perseverance made its first sample collection attempt in early August which unfortunately resulted in the sample being turned to dust. This time, on a different rock sample nicknamed ‘Rochette’ a few hundred metres away, Perseverance was successful. 

After collecting its first sample, named ‘Montdenier’, on 6 September, the rover collected a second sample, ‘Montagnac’, from the same rock, two days later.

Analysis of both the rocks from which the samples were taken and from the rover’s previous sampling attempt may help scientists piece together the area’s past, which was marked by both volcanic activity and periods of persistent water.

“It looks like our first rocks reveal a potentially habitable sustained environment,” said Ken Farley of Caltech, project scientist for the mission, which is led by NASA’s Jet Propulsion Laboratory (JPL) in Southern California. “It’s a big deal that the water was there a long time.”

Along with identifying and collecting samples of rock and regolith (broken rock and dust) while searching for signs of ancient microscopic life, Perseverance’s mission includes studying the Jezero region to understand the geology and ancient habitability of the area.

The rock that provided the mission’s first core samples is basaltic in composition and potentially the result of lava flows. The volcanic origin of the rock including the crystalline minerals could help scientists accurately date when it formed. Some of those events include the formation of Jezero Crater, the emergence and disappearance of Jezero’s lake, and changes to the planet’s climate in the ancient past.

“For all of NASA science, this is truly a historic moment,” said Thomas Zurbuchen, associate administrator for science at NASA Headquarters in Washington. “Just as the Apollo Moon missions demonstrated the enduring scientific value of returning samples from other worlds for analysis here on our planet, we will be doing the same with the samples Perseverance collects as part of our Mars Sample Return program. 

“Using the most sophisticated science instruments on Earth, we expect jaw-dropping discoveries across a broad set of science areas, including exploration into the question of whether life once existed on Mars.”

In the quest to search for microscopic life from billions of years ago, Perseverance has an array of hi-tech instruments, including the Planetary Instrument for X-ray Lithochemistry, aka PIXL. PIXL is a lunchbox-size instrument located on the end of Perseverance's 2-meter-long robotic arm.  

Australian Dr. Abigail Allwood is the inventor and the principal investigator of the PIXL aboard NASA's Perseverance Mars rover, based at NASA’s JPL in Southern California. Originally from Brisbane, Dr. Allwood is the first woman, and first Australian, to lead an investigation on the Mars Rover mission. She studied Geoscience at the Queensland University of Technology before completing her Ph.D. Earth Science at Macquarie University in Sydney. 

"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 Dr Allwood. 

Rock textures are an essential clue when deciding which samples are worth returning to Earth. On Earth, distinctively warped rocks called stromatolites were made from ancient layers of bacteria, and they are just one example of fossilized ancient life that scientists will be looking for on Mars.

A major way PIXL differs from its predecessors is in its ability to scan rock using a powerful, finely-focused X-ray beam to discover where – and in what quantity – chemicals are distributed across the surface.

To help find the best targets, PIXL relies on more than a precision X-ray beam alone. It also needs a hexapod - a device featuring six mechanical legs connecting PIXL to the robotic arm and guided by artificial intelligence to get the most accurate aim. After the rover's arm is placed close to an interesting rock, PIXL uses a camera and laser to calculate its distance. The hexapod’s legs can make minute movements of just 100 microns, or about twice the width of a human hair so that PIXL can scan the target, and map the chemicals found within a postage-stamp-size area.

"The hexapod figures out on its own how to point and extend its legs even closer to a rock target," Dr Allwood said. "It's kind of like a little robot who has made itself at home on the end of the rover's arm."

Then PIXL measures X-rays in 10-second bursts from a single point on a rock before the instrument tilts 100 microns and takes another measurement. This process is repeated thousands of times over eight or nine hours to produce a chemical map of the rock about the size of a postage stamp. 

The temperature on Mars changes by more than 38 degrees Celsius over a day causing the metal on Perseverance to expand and contract by as much as 13 millimetres. To minimize the impact of this movement on PIXL’s microscopic adjustments, it operates during the Martian night. 

"PIXL is a night owl," Allwood said. "The temperature is more stable at night, and that also lets us work at a time when there's less activity on the rover."

When asked by Macquarie Uni interview, ‘The Lighthouse’, what success looks like in relation to the Mars Mission, Dr Allwood responded, “Success doesn’t mean to me, finding life. It means doing the best possible analysis we can of the geology we’re presented with. To modify the famous quote from Forest Gump, ‘Geology is like a box of chocolates, you never know what you’re going to get.’. 

“Whatever it is that the geology hands us, whether it’s evidence of life or something else, I think being able to do a really rigorous, defensible interpretation of what we’re presented with and making (thorough) field notes for what we bring back to Earth so that future sample analysis scientists who look at them, can use them as a really faithful reliable set of data and observations to back up what they find in the samples. I think that sort of multi-generational view of your science, and your contribution as a scientist is important.”

While it may be ten years before the samples return to Earth, through the use of PIXL mapping out chemistry in rock textures, perhaps these samples are the ones that contain fossilised microbes. Proof of life on Mars, albeit billions of years ago.