Testing Rocks on Earth to Help NASA's Work on Mars

When NASA’s Perseverance Mars rover tried to collect its first rock core sample last August, the outcome presented a puzzle for the mission team: The rover’s sample tube came up empty. But why?

Not long after, Perseverance successfully gathered a sample the size of a piece of chalk from a different rock. The team concluded that the first rock they had chosen was so crumbly that the rover’s percussive drill likely pulverized it.

But engineers at NASA’s Jet Propulsion Laboratory in Southern California, which manages the mission, want to understand why that first sample, nicknamed “Roubion,” turned to dust. The mission’s scientists and engineers had run extensive test campaigns on dozens of rock types prior to launch, but they hadn’t seen any react exactly like Roubion. So a new test campaign was started – one that would include a field trip, a duplicate of Perseverance’s drill, and JPL’s unique Extraterrestrial Materials Simulation Lab. Answers remain elusive, but here’s a closer look at the process.

Remembering Roubion

Re-creating the unique physical properties of Roubion would be key to the test campaign.

“Of the rocks we’ve seen, Roubion had the most evidence of interaction with water,” said Ken Farley of Caltech, Perseverance’s project scientist. “That’s why it fell apart.”

Rocks altered by water can be more susceptible to falling apart; they’re also highly valuable to Perseverance’s scientists. Water is one of the keys to life – at least on Earth – which is why Perseverance is exploring Jezero Crater. Billions of years ago, Jezero contained a river-fed lake, making it an ideal spot to look for signs of ancient microscopic life now. Perseverance is collecting samples that future missions could bring back to Earth to be studied in labs with powerful equipment too large to be sent to Mars.

To find Roubion stand-ins, a handful of rover team members were granted permission to hunt rocks in the Santa Margarita Ecological Reserve, a two-hour drive from JPL. The team was searching for rocks that filled a geological sweet spot: weathered enough to be Roubion-like, but not so fragile that they would fall apart at the slightest touch. They eventually selected a half-dozen rocks.

Field Trip

“It was very physical work,” said JPL’s Louise Jandura, chief engineer for sampling and caching, who has been leading the test campaign. “We were chipping away with rock hammers and crowbars. A couple rocks were big enough that it took all five of us holding on to a stretched-out canvas to get it into the bed of our truck.”

Next step: testing at JPL. One of the places where that happens is the Extraterrestrial Materials Simulation Lab, a kind of service center that prepares materials for testing elsewhere at JPL.

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