Part of a Chinese Rocket Weighing 18 Tons and Measuring 100 Feet Just Crashed Into the Atlantic in Uncontrolled Descent

A large segment of a Chinese rocket weighing nearly 18 tonnes crashed into the Atlantic Ocean on Monday—representing one of the largest pieces of space debris to have fallen to Earth uncontrolled.

The nearly 100-foot-long rocket segment passed directly over Los Angeles and New York City before eventually smashing into the ocean off the west coast of Mauritania in West Africa, according to Jonathan McDowell, an astronomer from the Harvard-Smithsonian Center for Astrophysics.

The space debris was the empty core stage from China's Long March 5B rocket, which launched on May 5 from the Wenchang Space Launch Center carrying an unmanned prototype spacecraft that has now landed back on Earth, CNN reported.

After being launched into space, the rocket core stage began a planned, albeit uncontrolled descent, with the United States Air Force's 18th Space Control Squadron confirming the reentry of the rocket at 8:33 a.m. PDT UTC (11:33 a.m. ET.)

The core stage of the Chinese rocket is the largest piece of space debris to make an uncontrolled descent back to Earth since 1991, aside from the space shuttle Columbia, which became uncontrolled after disintegrating as it reentered the atmosphere in February, 2003, killing all seven crew members.

#18SPCS has confirmed the reentry of the CZ-5B R/B (#45601, 2020-027C) at 08:33 PDT on 11 May, over the Atlantic Ocean. The #CZ5B launched China’s test crew capsule on 5 May 2020. #spaceflightsafety

— 18 SPCS (@18SPCS) May 11, 2020

"At 17.8 tonnes, [the core stage] is the most massive object to make an uncontrolled reentry since the 39-tonne Salyut-7 in 1991, unless you count OV-102 Columbia in 2003," McDowell tweeted.

In fact, the core stage is the fourth largest piece of space debris ever to make an uncontrolled descent, after Salyut-7 (a Soviet space station,) Skylab (the first U.S. space station) in 1979 and the rocket stage of Skylab in 1975.

And the TIP message is out, showing reentry at 1534 UTC at location 20W 20N, just before the ground track passed over Nouakchott. pic.twitter.com/wcQ7BmJblk

— Jonathan McDowell (@planet4589) May 11, 2020

Tracking space objects as they fall to Earth is a difficult task given their high speeds and relatively small sizes.

"The problem is that it is traveling very fast horizontally through the atmosphere and it's hard to predict when it will finally come down," McDowell told CNN. "The Air Force's final prediction was plus or minus half an hour, during which time it went 3/4 of the way around the world. It's pretty hard to do any better."

Long March 5B rocket
A Long March 5B rocket lifts off from the the Wenchang launch site on China's southern Hainan island on May 5, 2020. STR/AFP via Getty Images

As an example of this difficulty, those who track space objects falling to Earth were only able to narrow down a potential reentry point to somewhere in or near Australia, the United States or Africa.

It is feasible that some of the core stage could have survived the descent, although much of the rocket will likely have burnt up in the atmosphere. Any remaining pieces could have potentially caused some localized damage on the ground if it struck a populated area. However, the chances of this happening are very small given that the majority of the Earth's surface is uninhabited.

And a new prediction: between 1443 and 1555 UTC. Finally we can narrow down potential reentry areas in Australia, US, Africa pic.twitter.com/0dxRX02QfP

— Jonathan McDowell (@planet4589) May 11, 2020

"For a large object like this, dense pieces like parts of the rocket engines could survive reentry and crash to Earth," McDowell told CNN. "Once they reach the lower atmosphere they are traveling relatively slowly, so worst case is they could take out a house."

Nevertheless, McDowell said that the descent of the Chinese rocket core stage was intriguing because of the path that it took.

"I've never seen a major reentry pass directly over so many major conurbations!" he tweeted.