The rocket, a Long March 5B, launched on April 29 to place the first part of China’s Tianhe space station in orbit around the Earth.

It did so successfully, but the 20-ton rocket has since remained in space and is slowly getting closer and closer to Earth. Scientists do not know exactly when or where it will return, and due to its size it is also unknown whether it will completely burn up on re-entry.

The U.S. Space Command said in a statement Tuesday: “U.S. Space Command is aware of and tracking the location of the Chinese Long March 5B in space, but its exact entry point into the Earth’s atmosphere cannot be pinpointed until within hours of its re-entry, which is expected around May 8.”

Jonathan McDowell is an astrophysicist at Harvard University’s Astrophysics Center. He told Newsweek he thinks the rocket is not designed to de-orbit in a controlled way because it is now the second time this situation has occurred. Newsweek contacted the Chinese government for comment earlier this week and has not yet received a response.

McDowell added: “Obviously the precedent is the last time, when the debris landed in Cote d’Ivoire—a populated area, but not urban.”

On May 5, 2020 China launched the same model of rocket in a mission that was intended to test out an experimental crew capsule for future manned missions in space.

The crew capsule reached a height of around 5,000 miles before returning to Earth in a controlled way. But it emerged that the rocket would undergo an uncontrolled re-entry.

The U.S. 18th Space Control Squadron confirmed the rocket re-entered the atmosphere over the Atlantic Ocean at around 11:33 a.m. EDT on May 11, 2020. It had passed directly over New York City shortly before it did so.

Afterwards, reports began to surface that debris from the rocket had landed in Africa’s Côte d’Ivoire.

On May 12, 2020 McDowell posted a photo of what was allegedly a “12 meter-long object” that had landed in the village of Mahounou.

He said in a tweet that same day that, in his opinion, some of the objects “are very likely part of the Chinese rocket stage,” but added other bits of metal found by locals may have been unrelated.

Also on May 12, 2020, a Côte d’Ivoire infrasound station detected “signals of rocket debris” travelling faster than the speed of sound through the atmosphere around 37 miles away from the station, according to Lassina Zerbo, Executive Secretary of the Comprehensive Nuclear Test Ban Treaty Organization.

Uncontrolled de-orbits are not unheard of. One of the largest ever was NASA’s 77-ton Skylab de-orbit which occurred in 1979. NASA was not able to prevent it from sinking out of orbit, and it eventually came down over the Indian Ocean but also over populated areas of Western Australia. No-one was injured.