There’s a big rock stuck inside one of Perseverance’s wheels

It looks like the Perseverance rover has an unwanted passenger, a rock stuck inside one of its wheels. The image of the stone was selected by public input as the “Image of the Week” for Week 54 (Feb. 20–26, 2022) of the Perseverance mission. Perseverance captured this image on February 25, 2022.

The rover’s Front Left Hazard Avoidance Camera A captured the image. When the rover is driving, it makes periodic stops to let the Hazard Cameras survey the immediate surroundings. The Hazard Cameras help evaluate the hazards in front of and behind the rover, like large boulders, deep trenches, or dunes. The cameras create 3D views of the surroundings that help the rover make its own decisions without consulting with the rover team on Earth on every move.

The rock’s been there for a few days, based on images from March 2. It’s difficult to tell from the picture for sure, but it doesn’t appear to be wedged in. Will it fall out during normal operations?

The rock doesn’t appear to be causing any damage or hindering the rover’s operations. And it’s not the first time a stone got stuck in a rover’s wheel. MSL Curiosity also had a rocky hitchhiker in one of its wheels.

NASA thinks rovers can get rocks stuck in their wheels when traversing slopes. They can also get in there as the rover moves over loose terrain and as the rover’s weight breaks rocks into pieces. In a 2017 article at Mashable, Curiosity Project Scientist Ashwin Vasavada said, “We don’t exactly know how the rocks get in the wheels, but it’s likely that they can hop in as the wheels (and heavy rover) break rocks and sink into the soil around loose rocks.”

They’ve said that rocks in rover wheels haven’t been a problem in the past. The rocks are pretty soft and tend to fall out on their own. The only potential problem is if the rocks somehow interfere with cables running to the motor on each wheel.

NASA doesn’t seem worried about it, though; otherwise, they would’ve changed the design to prevent it.

At least one Mars rover mission ended due to problems with its wheels, but not because a rock got stuck. In 2009, NASA’s Spirit Rover got one of its wheels stuck in soft soil. After months of carefully planned maneuvers and extrication attempts, NASA announced that the rover was stuck. In May 2011, they ended the mission.

Perseverance’s mission was planned to last at least one Mars year or 687 Earth days. It’s a little over halfway through its planned mission at 373 sols on March 8.

But rover missions to Mars tend to last longer than planned. Spirit and Opportunity were supposed to last about 90 sols, but Spirit lasted 2208 sols, and Opportunity lasted 5,352 sols. MSL Curiosity has been active on Mars for more than nine years, and its primary mission was set at only 687 days.

Perseverance’s planned mission length is at least one full Martian year. And its Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) could last 10 years or more. Hopefully, Perseverance will complete its mission and cache samples for later retrieval and even find preserved biosignatures.

Eventually, the mission will end. But it probably won’t be because of a rock in its wheel.