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A Mars Rock Appears to Be Stuck in Perseverance Rover’s Wheel

Unwanted rocks won't leave NASA's six-wheeled rover alone.

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The stone sitting inside the interior of one of Percy’s six aluminum wheels, in an image captured on February 25, 2022.
The stone sitting inside the interior of one of Percy’s six aluminum wheels, in an image captured on February 25, 2022.
Image: NASA/JPL-Caltech

NASA’s Perseverance rover has involuntarily adopted a traveling companion, in the form of a stone that’s lodged in one of its six aluminum wheels.

An image captured by Perseverance’s Onboard Front Left Hazard Avoidance Camera, or Hazcam for short, shows the interloper sitting on the interior of a wheel. The rover must’ve kicked up the rock while exploring Jezero Crater, where it’s been operating since it landed on Mars in February 2021.

The picture was taken on February 25, 2022, but a similar image taken five days later showed the rock still firmly in place. The stone, it would appear, is now a stubborn fixture of the $2.2 billion rover. It’s not known when the rock managed to hop aboard, but sleuthing by C|Net reporter Amanda Kooser suggests it’s been there since at least February 6, 2021.

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A Hazcam image taken on March 2, 2022 shows the rock still firmly in place.
A Hazcam image taken on March 2, 2022 shows the rock still firmly in place.
Image: NASA/JPL-Caltech

The rock appears to be a cosmetic annoyance and not anything that’s currently hindering the rover’s progress. At least we hope. I reached out to NASA’s Jet Propulsion Laboratory to confirm that the rock isn’t currently posing a problem.

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“It’s not perceived as a risk. We’ve seen these kinds of rocks get ‘caught’ in Curiosity’s wheels from time to time, too,” explained a JPL spokesperson in an email. “They occur during cross-slope drives, and tend to fall out entirely on their own after a while (there’s no particular way to get this rock out of our ‘shoe’). These kinds of rocks don’t impact driving other than making it a bit noisier.”

The spokesperson said the rock appears to have been picked up in early February, “likely when we did our first long AutoNav drive,” which involved a “significant amount of cross-slope driving.”

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That Perseverance’s 20.7-inch-wide (52.2-centimeter) wheels are able to withstand this unexpected intrusion is not a huge surprise. The rover was fitted with upgraded wheels to prevent the wear-and-tear seen on NASA’s Curiosity rover. Each aluminum wheel is fitted with 48 cleats that improve traction and curved titanium spokes that provide bouncy support. The upgraded wheels are also narrower, with a thicker and more robust thread, as Morten Bo Madsen, a Mars 2020 project scientist and astrophysicist at the Niels Bohr Institute, told Gizmodo in 2020.

Perseverance is currently backtracking toward the Octavia E. Butler landing site, and it’s driving longer distances than at any other time during the mission. Mission planners are hoping to collect more surface samples before the rover reaches Jezero’s delta, where it will use its Mastcam-Z and SuperCam instruments to study its structure and mineralogy.

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This isn’t Percy’s first pebble problem: In January, debris got into the rover’s machinery following a rock sample extraction. Thankfully, the rover managed to dislodge those pebbles, which were clogging its sample cache system.

This article has been updated with comments from the NASA spokesperson.