A small rock has been hitching a ride on NASA's Perseverance rover on the surface of Mars for four months without falling off. The rock attached itself on the Perseverance's wheel in February and has since been transported more than 5.3 miles (8.5 km) aboard the rover, NASA has said. he photos of the rock were taken by the rover's front cameras used to navigate hazards, called 'Hazcams'. NASA said the 'unexpected traveling companion' isn't doing any damage to the wheel, although it could drop off at any time.