This fall, Chinese officials lost communication with an orbiting space lab called Tiangong-1. The 8-ton station will fall to Earth—perhaps sometime next year—but no one knows exactly when or where.

Tiangong-1 is one of tens of thousands of large pieces of space debris circling Earth. The junk includes defunct satellites, rocket parts, and even a wrench lost by astronauts. Experts track larger pieces of space debris to avoid collisions with working spacecraft and determine whether the junk will ultimately fall to Earth.

When Tiangong-1 falls, it will most likely burn up in Earth’s atmosphere, says space engineering expert John Crassidis of the University at Buffalo in New York.