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In 2016, China announced that its first human station, Tiangong-1, would make an uncontrolled reentry into Earth’s atmosphere, and given the module’s large size and density, some big pieces might survive all the way to the ground. It’s predictably garnered a lot of attention, and the panic just won’t go away.

Of course, there have been the standard frantic articles about the “doomed” station “spiraling out of control.” Some stories have insinuated that the station will fall in New Zealand’s backyard — though it’s far too early to know where it’s going to reenter. Others have hyped up the idea that toxic debris will rain down on Earth. It’s all hogwash.

“Even a small chance of being killed by space debris seems like too much.”

As a space reporter, I find this frustrating because I know how often objects fall to Earth without us being able to control them. The truth is Tiangong-1 is the last thing anyone needs to worry about. Yes, the module is a bit bigger than most satellites that fall back to Earth, but the odds of any pieces falling on your head are minuscule — less than your chances of getting hit by lightning. In fact, you can read all the reasons why you shouldn’t be scared of the space station in our article. A lot of other reporters have done some great reporting on this topic, too. But despite all of the information that’s available, I’ve run into an interesting problem: people are still scared when I tell them the odds.

It’s something that’s baffled me. Multiple people have asked about this, and even after I explain the situation, they still seem uneasy. Earlier this year, for instance, my co-worker Russell Brandom sent me an article about Tiangong-1’s demise. I pointed him to our article, and told him everything was going to be fine. His panic didn’t subside. “Even a small chance of being killed by space debris seems like too much,” he told me.

Russell technically has a small chance of being hit by space debris all the time — well, an infinitesimal one. A person’s lifetime risk of being hit by reentering space debris is about one in a trillion, according to the Aerospace Corporation, a nonprofit research organization that provides guidance on space missions. Tiangong-1 isn’t going to drastically increase those odds.

So why is the space station still scaring people? I think most of the problem began with the first reports in 2016 that Tiangong-1 was “out of control.” It’s true: China doesn’t have the ability to maneuver the space station from Earth anymore, and its orbit is slowly decaying. But this idea of an uncontrollable space station probably inspired visions of a huge chunk of metal spiraling wildly toward Earth. Plus, US companies nowadays often come up with ways to safely de-orbit larger pieces of metal they send to orbit. “There are a lot more controlled reentries than 20 years ago, and for more massive objects, [companies and countries] take more care,” says Jonathan McDowell, an astrophysicist at Harvard and spaceflight expert.

Still, uncontrolled reentries happen all the time. The upper stages of SpaceX’s Falcon 9, Russia’s Soyuz, or Europe’s Ariane 5 rockets don’t always do a controlled de-orbit after every launch. Those pieces range from two to four tons, so they’re not quite as massive as Tiangong-1. But a rocket piece about the same mass as the Chinese space station made an uncontrolled fall to Earth this year. The upper stage of a Russian Zenit rocket fell over Peru in January, and it’s about eight tons, close to the size of Tiangong-1. A tank or two made it to the ground, but no injuries were reported.

Granted, the Zenit upper stage is mostly comprised of empty fuel tanks, and Tiangong-1 is denser. “It’s got a lot of heavy equipment, so it’s not like a rocket stage that’s a big empty tank,” says McDowell. “People are worried more [about if] it might reach the ground.” That may be the other piece of the puzzle, too: the idea of a space station falling to Earth is more menacing than a piece of a rocket or an average satellite.

I’ve started to wonder if this isn’t just another example of how our brains aren’t very good at assessing real-world risks. Our brains are very sensitive to risk. That’s what kept us alive back when everything around us was a legitimate risk to ourselves. This backfires today because we hear about all sorts of things that seem dangerous but aren’t likely to harm us at all.

Novelty definitely plays a role. This is the same reason many people are far more worried about plane crashes (which aren’t common anymore) than car crashes (which happen all the time). Plane crashes seem rare and terrible, and so they stick in our minds more; car crashes, while tragic, don’t grab our attention. It’s easy to feel frightened by terrorist attacks, which seem catastrophic, but we’re actually more likely to be killed by falling furniture.

“Are fears ever rational?”

The Nobel Prize-winning psychologist Daniel Kahneman is famous for suggesting that our brain runs two systems: System 1 and System 2. System 1 is your quick, intuitive, emotional responses, like being afraid when you hear that a space station could fall on your head. System 2 is the deliberate, reasonable response that takes a lot of cognitive energy, like slowing down to calculate the probability that the space station will actually fall on your head. You can’t stop System 1 from running, and emotions are powerful. Unfortunately, not a lot of people take the time to do the calculations, and so they remain afraid.

So, Russell’s fear of even a small chance of space debris falling on him is a great example of System 1 out of control. I told him this. “Are fears ever rational?” he asked. “I feel like you’re just afraid of the things you’re afraid of.” It’s a good point. Every time I pass over the Queensboro Bridge in New York, I think about our car swerving and plunging into the East River. It’s not likely to happen, but I’ll forever worry about it even if someone tells me the odds.

The good news about Tiangong-1 is that people won’t have to worry for much longer. The European Space Agency estimates that the station will likely come down sometime between March 29th and April 9th, though those dates are still subject to change. Once it falls, the risk will be eliminated. But if you want to scare yourself with space debris, there’s always NASA’s Hubble Space Telescope: unless NASA sends another mission to Hubble, the observatory will have to come down at some point, too — and it’s even heavier than Tiangong-1.

Angela Chen contributed to this report.
https://www.theverge.com/2018/3/11/17100434/china-falling-space-station-tiangong-1-risk-assessment
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