Perseverance Has a Pet Rock! But It’s No Ordinary Rock…

Perseverance has been on Mars for more than a year, beaming back pictures from the Red Planet all the while. We’ve seen Jezero Crater itself, along with thousands of shots of the Martian landscape and sky. Perseverance also takes periodic selfies, to check its condition and calibrate its sensors. But it’s lonely out there on the Red Planet. So, a few months ago, the rover picked up a companion. Tucked inside one of its wheels, Perseverance has a pet rock.

It’s no AIBO or K-9, but sure enough, this rock has tumbled along at Perseverance’s heel for months. Mission scientists believe that the rock came from debris the rover kicked up during its travels through Jezero. In a blog post, Perseverance team member Eleni Ravanis said the rock may come from lava flows in the “Máaz” formation of Jezero Crater. But that’s not all that makes it special.

This is not the first time a rock has hitched a ride on a Mars rover mission. Spirit and Curiosity have both had their own traveling companions. But this is the longest we’ve ever seen a rover hang on to the same rock. “While it’s unclear exactly how long these rocks stuck around, they tended to hop off after a few weeks,” said Ravanis. “Perseverance’s current companion is therefore on its way to setting Mars hitch-hiking records!”

Perseverance first caught its pet rock on camera in February. “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,” a JPL spokesperson explained. “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.”

Since Perseverance picked up its pet rock, the pair has covered more than five miles (8 km). We don’t know whether the rock will fall out or stay with the rover. But if it does depart, it will fall among rocks very different than itself. Perseverance is currently navigating Hawksbill Gap, one route to the top of the Three Forks river delta. But the rocks it sampled on May 29, 2022 (Sol 452) looks like sedimentary rock. A lava rock would be far from the Shire indeed.

So far, the Perseverance rover has collected eight rock core samples. The rover has now entered its Delta Front science campaign. And it recently got permission from NASA to “pick its own targets to zap.” But it seems that Perseverance got its pet rock by pure serendipity. In the blog post, Ravanis quipped, “How do you choose a rock on Mars? Sometimes you don’t— it chooses you.”