May 11th saw one of the largest pieces of space debris crash back down to Earth in an uncontrolled manner, landing into the Atlantic Ocean off the North-West African coast, for another time after a similar incident in April.
The debris was a huge chunk part of the Chinese Long March 5B rocket, which successfully launched into orbit on May 5th from Wenchang Space Center in South Hainan province, China.
Crashing back down to Earth
A few tense hours passed as part of the rocket commenced its re-entry path and started its descent towards an unknown site on our planet. That chunk of rocket weighs roughly 18 tonnes, making it the largest piece of space debris to fall uncontrollably back to Earth in decades.
"At 17.8 tonnes, it 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," explained Jonathan McDowell, astronomer at the Harvard-Smithsonian Center for Astrophysics over Twitter.
The descent was confirmed by the 18th Space Control Squadron, a U.S. Air Force unit, on Twitter.
"For a large object like this, dense pieces like parts of the rocket engines could survive re-entry 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."
Something falling down to Earth slowly could be relatively easily localized, keeping the damage to a minimum. However, when something is speeding rapidly down to Earth in an uncontrolled manner, it's hard to know where it'll have impact, and how much potential damage it could create.
For future reference note that DoD's announcement of the reentry time came about 1.5 hours after the event - by historical standards pretty fast. In the absence of eyewitness reports, the info always comes with a delay which is why I kept saying "if the thing is still up.."— Jonathan McDowell (@planet4589) May 11, 2020
As per McDowell's comments on Twitter "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. 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."
If CZ-5B is still in orbit, its next landfall is over Nouakchott (Mauritania) at 1535 UTC.— Jonathan McDowell (@planet4589) May 11, 2020
Luckily, the landing site was into the Atlantic Ocean, off the west coast of Africa, where no humans were injured.