The Mars Perseverance rover has had an "unexpected traveling companion" since last February, when a rock found its way into the rover's front left wheel. According to a NASA release, the rock has done no damage to Perseverance's wheel in the four months since it first hitched a ride. Oddly, this is not the only time a rock has made it onto a Mars rover. Curiosity also had a rock hitchhiker in its front wheel, and 18 years ago the Spirit rover had its own rock companion find its way into that vehicle's rear right wheel. These rocks usually dislodge themselves after a few weeks, but Perseverance's rock companion seems to be going for a new record.