Last week's launch of the Tianhe space station module was a great leap forward for China's space program—but the Long March 5B rocket used for the launch could cause some major problems back on Earth. The 21-ton core of the rocket is now orbiting Earth and slowly losing altitude. It is expected to crash at an unknown location between May 8 and May 12 in the biggest uncontrolled re-entry in decades, the Guardian reports. Its path can be seen here. Experts say it is most likely to crash into the ocean, though its orbit "passes a little farther north than New York, Madrid and Beijing and as far south as southern Chile and Wellington" and it could crash anywhere in that zone, according to SpaceNews.
"It's potentially not good," Harvard astrophysicist Jonathan McDowell tells the Guardian. He says that if enough of the core survives re-entry, it will be the "equivalent of a small plane crash scattered over 100 miles." McDowell says the uncontrolled re-entry is "negligent" and "unacceptable" by today's standards. "Since 1990 nothing over 10 tons has been deliberately left in orbit to re-enter uncontrolled," he tells the Houston Chronicle. Rockets from the US and other countries "routinely fire their engines to target re-entries over the southern Pacific" to avoid populated areas, notes CBS space consultant William Harwood. US Space Command says it is tracking the rocket but it won't be able to predict a re-entry point until a few hours before re-entry, which Space Command expects to happen on Saturday. (Another Long March rocket core fell to Earth last year.)