The International Space Station has been hit by fast-moving debris — but it didn’t cause too much damage. Space junk hurtling towards the station smashed into one of its robotic arms, leaving a hole.

NASA and the Canadian Space Agency first noticed the damage on Canadarm2 on May 12, according to a recent statement. The debris left a gaping hole in a section of the arm boom and thermal blanket.

According to NASA, over 23,000 objects the size of a softball or larger are being tracked by the U.S. Department of Defense at all times to monitor for possible collisions with satellites and the ISS. However, some smaller objects that cannot be tracked still pose a threat, like rocks, dust particles and flecks of paint that chip off of satellites.

“A number of space shuttle windows were replaced because of damage caused by material that was analyzed and shown to be paint flecks,” NASA said. “In fact, millimeter-sized orbital debris represents the highest mission-ending risk to most robotic spacecraft operating in low Earth orbit.”

Space junk, which includes both natural meteoroids and man-made objects, has become a growing area of concern as the region of space immediately surrounding Earth becomes more and more crowded with rocket parts, satellites and other objects. This debris, which travels at approximately 15,700 miles per hour in low-Earth orbit, poses a threat to both spacecraft and astronauts due to their fast speeds.

“Orbital debris is any human-made object in orbit about the Earth that no longer serves a useful function,” NASA says. “Such debris includes nonfunctional spacecraft, abandoned launch vehicle stages, mission-related debris, and fragmentation debris.”

Officials say the nearly 60-foot arm’s capabilities were unaffected by the impact and small hole created by the unknown object. Operations are continuing as planned, while officials continue gathering data on the “lucky strike.”

“The threat of collisions is taken very seriously,” CSA said. “NASA has a long-standing set of guidelines to ensure the safety of Station crew. The safety of astronauts on board the orbiting laboratory remains the top priority of all Station partners.”