Rocket debris from China's space station launch is hurtling back to Earth — and scientists aren't sure where it will land

A huge piece of space junk is about to make an uncontrolled re-entry back into Earth's atmosphere, threatening to drop debris on a number of cities around the world in the coming days. It's leftover from China's first module for its new Tianhe space station — and no one knows where it will land. 

The 46,000-pound Chinese rocket Long March-5B recently launched the first module for the country's new space station into orbit. After the core separated from the rest of the rocket, it should have followed a predetermined flight path into the ocean. But now, scientists have little idea where it will land as it orbits the planet unpredictably every 90 minutes, at about 17,324 miles per hour. As it soars through the atmosphere, appearing to tumble, it is slowly losing altitude.