They test the self-driving Rover Perseverance on Mars 1:09
(CNN) --
The Perseverance rover befriended a rock about four months ago, and they've been inseparable ever since.
A rock got into the rover's left front wheel in early February while it was cruising the Red Planet, according to Perseverance's left hazard-avoidance camera.
In four months, the rock has traveled more than 8.5 kilometers through the rugged terrain.
He joined the mission during the Jezero Crater exploration campaign, the site of an ancient lake and river delta, where NASA scientists studied rocks from a formation the team refers to as "Maaz."
The Mars Perseverance rover gained a new travel companion when a rock got into its wheel four months ago while it was exploring Jezero Crater.
The boulder accompanied Perseverance north to the Octavia E. Butler landing platform, before turning west toward the remnants of a delta scientists call "Kodiak," and then to the western Jezero delta.
The current goal of the Mars rover is to drill cores and examine the sedimentary rocks around the delta area.
These rocks were created billions of years ago, when there was water in the area, according to NASA.
Perseverance's pet rock, which moves on the vehicle's wheel, does not affect operations and it remains to be seen how long the robotic explorer's new friend will stick around.
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If the rock falls off and says goodbye to the rover, it will be far from home, surrounded by strange and unknown rocks.
The Perseverance rover observes the eclipse of the "pope" moon of Mars doomed to die
Spirit and Curiosity's pet rocks
Curiosity isn't the first Mars rover to adopt a pet rock.
The Spirit rover, which was active from 2004 to 2010, had a potato-sized rock in its right rear wheel early in its journey.
The stone blocked the wheel, so NASA scientists had to unlock it.
The Curiosity rover is no stranger to rocks looking for a ride and has had several rocks lodged in its right front wheel for weeks.
The rover began roaming the red planet in mid-2012 and is still in operation.
Perseverance Rover