Washington (CNN)The large Chinese rocket that is out of control and set to reenter Earth’s atmosphere this weekend has brought about an alarming but not unprecedented situation.
Space debris has crashed into Earth on a number of occasions, including last year.
The good news is that debris plunging toward Earth — while unnerving — generally poses very little threat to personal safety. As Jonathan McDowell, an astrophysicist at the Astrophysics Center at Harvard University, told CNN: “This is not the end of days.”
Still, the episode has fueled fresh questions about space debris, uncontrolled reentry and what precautions might need to be taken, if any.
Here’s what you need to know:
How often does uncontrolled space debris crash into Earth?
Most pieces will burn up in the Earth’s atmosphere before having a chance to make an impact on the surface. But parts of larger objects, like rockets, can survive reentry and potentially reach populated areas.
Last year, one of the largest pieces of uncontrolled space debris ever passed directly over Los Angeles and Central Park in New York City before landing in the Atlantic Ocean.
Weighing in at nearly 20 tons, the debris — an empty core stage from a Chinese rocket — was the largest piece of space junk to fall uncontrolled back to Earth since 1991 and the fourth biggest ever.
The only larger pieces were from NASA’s Skylab space station in 1979, Skylab’s rocket stage in 1975 and the Soviet Union’s Salyut 7 space station in 1991. The space shuttle Columbia from 2003 could be added to that list since NASA lost control of it on its descent back to Earth.
This doesn’t happen more often because space agencies around the world have generally tried to avoid leaving big objects in orbit that have the potential to reenter Earth’s atmosphere and that they cannot control.
“Norms have been established,” McDowell said. “There’s no international law or rule — nothing specific — but the practice of countries around the world has been: ‘Yeah, for the bigger rockets, let’s not leave our trash in orbit in this way.'”
The Chinese rocket set to enter Earth’s atmosphere this weekend, however, is designed in a way that “leaves these big stages in low orbit,” McDowell said.
“It’s really not best practice compared to what other space agencies do. They go to quite fair lengths to avoid doing this.”
How much debris is floating around in space?
Above us there is a cloud of more than 9,000 tons of space junk — equivalent to the weight of 720 school buses.
This amounts to hundreds of thousands — possibly millions — of objects whirling around in orbit uncontrolled, including spent rocket boosters, dead satellites and detritus from military anti-satellite missile demonstrations.
The junk is heavily concentrated in areas of orbit closest to the Earth’s surface. And, though it doesn’t pose much of a risk to humans on the ground, it does threaten hoards of active satellites that provide all sorts of services, including tracking the weather, studying the Earth’s climate and providing telecom services.
The debris also threatens the International Space Station, where crews of astronauts have lived since 2000 and which had to adjust its own orbit multiple times last year due to
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