On March 4, 2022, a 3-ton rocket booster slammed into the moon at more than 9,330 kilometers (5,800 miles) per hour. This was the first time a piece of space debris—a discarded object left in space by humans—accidentally collided with the moon. Scientists believe it came from a Chinese space mission that launched in 2014.
More than 20,000 pieces of space debris currently circle Earth. Scientists mainly track pieces that orbit close to the planet’s surface. They want to avoid collisions with active spacecraft, like the International Space Station.
The lunar crash demonstrates the need to monitor debris that orbits farther away too, says Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics. As human space activity increases, McDowell says, “we need to work on better air traffic control for the moon.”