There's a 10% chance a person will be hit by falling space debris within a decade, researchers calculated.
Experts say controlled reentries, studying fallen debris, and warning systems could lower those odds.
The booster of a 25-ton Long March 5B rocket, which pushed part of China's new space station into orbit in late July, crashed back to Earth on Saturday.
Though some of the booster probably burned up as it plummeted through Earth's atmosphere, reports indicate that parts of the rocket may have survived the fall and crashed near inhabited areas of Borneo, an island in Southeast Asia. Debris was found on both the Malaysian and Indonesian sides of the island, as well as in the ocean near the Philippines. The locations of the debris reports were along the path of the booster's reentry into the atmosphere, previously calculated by orbital-debris experts.
"They sure look like rocket parts to me," Ted Muelhaupt, a consultant for the Aerospace Corporation's Chief Engineer's Office, told Insider, adding, "I've got no reason to dispute that it's pieces of this rocket."
In July, a shepherd in Australia discovered a mysterious piece of debris sticking out of the ground, standing nearly 10 feet tall. On Wednesday, the Australian Space Agency said the giant piece of hardware came from the discarded trunk of a SpaceX Crew Dragon spaceship, which carried astronauts for NASA last year.
Only China and SpaceX can confirm that these pieces come from their spacecraft. But experts like Muelhaupt say they believe the reports.
"There's no doubt in my mind," Jonathan McDowell, a Harvard astronomer who meticulously tracks objects in Earth's orbit, told Insider.
These are just a couple of striking examples of a widespread phenomenon. Every day, multiple man-made objects fall out of orbit and back to Earth, according to Muelhaupt, who works on the Aerospace Corporation's reentry database.
Many space objects burn up in the atmosphere, but chunks of material regularly survive the fall. Experts at the Aerospace Corporation say that up to 40% of the mass of a large space object falling from orbit will reach the ground. About once a week, an object that weighs at least 1 ton falls from orbit and reenters the atmosphere, Muelhaupt said.
In a study published in the journal Nature in July, researchers calculated a roughly 10% chance that debris will strike one or more people within a 10-year period.
"If you roll the dice too many times, someone will get lucky," McDowell said.
Crowded skies mean more falling space debris
Normally, after a launch, rocket boosters push themselves into the remotest part of the Pacific Ocean — a process called "controlled reentry." Smaller discarded objects, like the trunk of a Crew Dragon, are supposed to either burn up in the atmosphere or enter orbit around Earth and stay there.
But in the case of the Long March 5B, China didn't design the rocket booster for controlled reentry. Instead, it fell back to Earth randomly each of the three times it launched. In May 2020, debris from one of those rockets was discovered near two villages in Ivory Coast, reportedly causing property damage.
The Long March 5B boosters are among the largest objects to fall back to Earth, but uncontrolled reentry isn't unique to China. In 1979, NASA's Skylab space station rapidly descended, scattering debris over Australia. Today, though, controlled reentry is standard practice.
Despite the uptick in space activity in recent years, defunct space objects are increasingly being brought down to Earth under control. "Whereas 30 years ago, a rocket stage would have been left in orbit and done an uncontrolled reentry some years later," McDowell said.
Still, Muelhaupt fears there will be more frequent falling-junk incidents — like the chunk of Crew Dragon that landed in Australia — in the future. In spaceflight, the standard acceptable level of risk to human life is one in 10,000. But when companies like SpaceX plan to launch tens of thousands of satellites into orbit, those odds mean a few of them will drop chunks of metal to Earth.
Between multiple companies launching satellite constellations and more space agencies flying spacecraft, there's an increasing chance that debris will land somewhere densely populated.
"You do it often enough, you do it long enough, you're going to get lucky and bring it down in the middle of a city park," Muelhaupt said.
Taking out the space trash
For now, the best way to prevent space-junk disaster is to convince all countries and companies to commit to practicing controlled reentry.
"The People's Republic of China did not share specific trajectory information as their Long March 5B rocket fell back to Earth," Bill Nelson, NASA's administrator, tweeted Saturday, adding that all spacefaring nations should partake in responsible space behavior.
"Doing so is critical to the responsible use of space and to ensure the safety of people here on Earth," Nelson added.
Companies and space agencies can also study space debris to figure out why it fell from orbit, and why certain parts of it didn't burn up along the way. For example, Muelhaupt said the largest piece of suspected SpaceX debris in Australia is a section where metal connects to carbon fiber. Why that attachment broke from the rest of the spacecraft and survived the fiery plummet to Earth, is a question Muelhaupt wants answered.
"I hope they do go collect it and then tell us," Muelhaupt said.
A better understanding of debris falls could help inform real-time warning systems, both for people on the ground and for people flying planes. With passenger planes crisscrossing the planet at all times, there should be a space-debris notice for pilots, Muelhaupt said. A collision is unlikely, but if it did happen the damage would be catastrophic, especially for a commercial flight with passengers.
"The odds of hitting an unprotected individual standing in the open is one thing, but you get an aircraft in flight, now suddenly the consequences are a lot bigger," Muelhaupt said.
He fears it will take a disaster to push regulators and companies to make real change, though.
"I hate to say it: When something bad happens to somebody, that's when we react," Muelhaupt said.
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