NASA Mars Rover Adds a New Pet Rock to Its Wheel Hitchhikers Collection

This story is part of Welcome to Mars, our series exploring the red planet.

NASA’s Perseverance rover is turning into a rideshare for Martian rocks. In early 2022, the rover picked up a rock in its left front wheel. That rock is still in residence, but it seems the rover now has a new friend, an even bigger rock that found its way into Percy’s right front wheel.

Astrophotographer Simeon Schmauss noticed the new rock in late February and tweeted a mosaic image of both rocks in the front wheels as seen by Percy’s left and right hazard avoidance cameras mounted low on the rover. 

The HazCams help keep an eye on the terrain the rover traverses, and they’re also useful for monitoring the wheels and, as it turns out, keeping tabs on rocky hitchhikers. The new freeloader seems to have first appeared in a raw image sent back by the rover on Feb. 27. The camera got a closer, though very shadowed, view of the rock on March 1.

Percy’s older pet rock has traveled with the rover for many miles and has witnessed the collection of rock samples and the creation of the first sample depot on another world. One of Perseverance’s main mission goals is help us understand whether Mars once hosted microbial life. Delivering the rover’s sample collection to Earth for closer study via the future Mars Sample Return mission is a key part of this effort.

The new wheel rock may stick around, or it may end up falling out as Perseverance roves through the Jezero Crater. NASA wasn’t worried about the original rock, saying last year that the chunk was “not perceived as a risk.” NASA didn’t immediately respond to a request for comment.

Mars is a notoriously rocky place, as the sibling Curiosity rover and its roughed-up wheels can attest. NASA reworked the design for Percy’s aluminum wheels so they’ll hold up to the rigors of driving across an inhospitable landscape. 

Perhaps the lesson here is that the real treasure in Mars exploration is the rock friends we make along the way.