Why NASA’s Mars rover failed to collect its first rock core

After drilling into its first rock on Mars but failing to capture it in a storage tube on 6 August, NASA’s Perseverance rover is rolling onwards. Rather than make a second attempt now at drilling in the same geologically interesting area in Mars’s Jezero Crater, it will instead drill into different terrain next month, in the hope that those rocks will be more amenable to coring.

After a few days assessing what went wrong during the first attempt, NASA announced on 11 August that the rover had pulverized the sampled rock into powder and small fragments. They fell to the crater floor rather than sliding into the tube, as an intact core would have done.

“It took a few minutes for this reality to sink in,” wrote Louise Jandura, the chief engineer for sampling and caching at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, which operates the rover, in an 11 August update.

Perseverance is attempting to become the first mission to drill and collect a suite of rock cores from the Martian surface. It is planned that other spacecraft will eventually retrieve the samples and bring them back to Earth, where scientists can study them. “This is just another reminder that there are still a lot of unknowns about Mars,” says Meenakshi Wadhwa, a planetary scientist at Arizona State University in Tempe who is NASA’s principal scientist for the sample-retrieval effort. “This planet still has the capacity to surprise us when we least expect it.”

Researchers were particularly excited about the rover’s first drilling attempt. They had selected one of the flat rocks that make up much of the floor of Jezero Crater, where the rover landed in February, and which it has been exploring since then. Preliminary exploration of those flat rocks — dubbed the ‘cratered floor fractured rough’ — suggested that they might be volcanic in origin, perhaps even from an ancient lava flow. Collecting a volcanic rock from Mars and returning it to Earth would allow geologists to date its formation precisely, and thus pin down a chronology for much of Mars’s geological history.

But despite initial images suggesting that Perseverance had successfully drilled 7 centimetres into the surface and extracted a slim cylinder of intact rock, NASA later discovered that the sampling tube that had been automatically sealed and stored inside the rover’s belly was empty.

The rock was crumblier than engineers had expected, says Jennifer Trosper, the mission’s project manager at the JPL. Perhaps there was a hard layer of rock hiding looser material beneath it, or perhaps there were large voids in the rock that caused it to collapse. “There wasn’t anything obvious,” she says, to suggest “that this might disintegrate or be pulverized when we cored it”.

Taking a step back

Rather than try again with the cratered floor fractured rough, Perseverance has already departed the area and is heading towards a region named South Séítah, which probably contains layered sedimentary rocks that are more like the Earth rocks that engineers drilled during tests before the mission’s launch. “We are going to step back and do something we are more confident of,” says Trosper. The rover will try to drill a core there, perhaps in early September. When it does, engineers will pause the automated drilling process to check whether a core has been extracted before the rover takes the next steps of sealing the tube and storing it away.

The empty tube it stored on 6 August will serve as a sample of the Martian atmosphere, which the Perseverance team intended to collect at some point during the mission, although not so soon. The rover carries 43 sampling tubes, so 42 remain. The ultimate goal is to fill about 35 tubes with Martian rock and soil, from various parts of Jezero Crater. They would return to Earth no earlier than 2031.

Engineers tested the Perseverance drilling system more than 100 times on a range of rocks on Earth, to prepare for everything the rover might encounter on Mars. But the cratered floor fractured rough proved beyond the system’s experience.

Perseverance isn’t the first spacecraft to run into problems with Mars rock and soil. NASA’s InSight lander deployed a probe known as the mole, which tried for nearly two years to bury itself up to 5 metres deep in the Martian soil to measure heat flow. The team finally gave up in January, after the probe was unable to build up enough friction against the soil to hammer itself into the ground. And NASA’s Curiosity rover, which has been exploring Gale Crater since 2012, has occasionally and unexpectedly broken rocks apart while drilling into them.

Curiosity and Perseverance are similar in many respects — Perseverance was actually built using much of the leftover hardware from Curiosity — but there is one major difference in how they drill into the Martian surface. Curiosity intentionally grinds rock into powder, which it then places inside onboard analytical instruments for scientific studies. NASA designed Perseverance to extract intact cores that slide into its sampling tubes. So crumbly rocks are good for Curiosity, but not for Perseverance.

‘We’ll figure it out’

After its second attempt to collect a core, at South Séítah, Perseverance will head back in the direction it came from, once again crossing the cratered floor fractured rough — which it might try sampling again if the engineering team can find a more promising drilling site, with rocks that look like they will hold together better. “Anomalies like this are what we’re created to solve,” says Trosper. “I’m a little disappointed, but I think we’ll figure it out.”

Perseverance will then loop around a region of sand dunes on its way to its ultimate destination, an ancient river delta in Jezero that might contain traces of Martian life.


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