NASA has just made a significant discovery on the surface of Mars that could prove to be a hurdle for the agency as it seeks to explore the Red Planet. Cracks have appeared in the wheels of the Mars Curiosity rover after 10 miles of trekking across Mars since it landed on the planet back in 2012.

While wear and tear is to be expected, NASA has seen noticeable breaks during their routine check of the wheels on March 19, as compared to the last check on Jan. 27. It’s a sign that Curiosity is showing its age, and it could put a cap on its missions.

NASA engineers are confident that all six wheels have enough lifespan to get the vehicle to its remaining destinations planned over its life, but it’s a sign that time may be running out for the plucky rover, which is currently at the Murray formation near Mount Sharp.

“All six wheels have more than enough working lifespan remaining to get the vehicle to all destinations planned for the mission,” said Curiosity Project Manager Jim Erickson at NASA’s Jet Propulsion Laboratory, Pasadena, California. “While not unexpected, this damage is the first sign that the left middle wheel is nearing a wheel-wear milestone.”

The NASA statement adds: “The monitoring of wheel damage on Curiosity, plus a program of wheel-longevity testing on Earth, was initiated after dents and holes in the wheels were seen to be accumulating faster than anticipated in 2013. Testing showed that at the point when three grousers on a wheel have broken, that wheel has reached about 60 percent of its useful life. Curiosity already has driven well over that fraction of the total distance needed for reaching the key regions of scientific interest on Mars’ Mount Sharp.”