After more than a year together on the Red Planet, NASA's Perseverance rover and its hitchhiking "pet rock" have finally parted ways. The stone had been lodged in one of the rover's wheels for more than half of its mission on Mars.
Perseverance accidentally picked up the pet rock in its front left wheel on Feb. 4, 2022 or Sol 341 — the 341st Martian day of the mission. The rock posed no danger to the rover's scientific mission but did manage to periodically photobomb images and cling on despite several vigorous maneuvers across the planet's surface. Mission scientists previously likened the situation to "having a pebble stuck in your shoe."
On April 18 (Sol 768), NASA released an image (opens in new tab) of the rover's front left wheel showing the rock had been dislodged. In total, the rock remained in the rover's wheel for around 439 days (427 Sols) — around 55% of the time Perseverance has spent on Mars since landing there on Feb 18, 2021. During that time, the pair traveled around 6.2 miles (10 kilometers) together. (A sol, or Martian day, is 37 minutes longer than an Earth day.)
"Farewell 'Rock Friend,' you will be missed," Perseverance mission scientist Gwénaël Caravaca (opens in new tab), wrote on Twitter (opens in new tab).
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During its mission, Perseverance has picked up several other smaller rocks in its other wheels. But these all fell out within a couple of days or weeks of getting stuck, and posed no threat to the wandering robot. However, rocks lodged in other places have previously caused problems for the rover.
A bunch of small pebbles fell into part of Perseverance's inner machinery in December 2021, causing the rover to shut down for almost a week before mission scientists could figure out a way to safely remove them.
Hitchhiking rocks have also caused issues on other Mars rovers. Operators of NASA's Spirit rover — which roamed the Red Planet between January 2004 and March 2010 — had to perform a sharp turn to shake out a "potato-sized" stone from its right-rear wheel in December 2004. Mission scientists, performed this maneuver because they feared it would cause significant damage to the rover, according to NASA (opens in new tab).
