In 2016, China announced that its first human station, Tiangong-1, would make an uncontrolled reentry into Earth's atmosphere, and given the large size and density of the module, some large pieces could survive all the way to the ground. It is foreseeable that it attracts a lot of attention, and the panic simply will not disappear.
Of course, there have been standard frenetic articles about the "doomed" station "spiraling out of control". Some stories have hinted that the station will fall in New Zealand's backyard, although it is too early to know where it will re-enter. Others have promoted the idea that toxic waste will fall on Earth. It's all nonsense.
"Even a small chance of dying from space debris seems 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 that Tiangong-1 is the last thing anyone should worry about. Yes, the module is a bit larger than most satellites that fall back to Earth, but the chances of a piece falling on your head are tiny, less than your chances of being struck by lightning. In fact, you can read all the reasons why you should not be afraid of the space station in our article. Many other reporters have also made great reports on this subject. But despite all the information available, I came across an interesting problem: people are still afraid when I tell them the odds.
It is something that baffles me. Several people have asked about this, and even after explaining the situation, they still seem uncomfortable. Earlier this year, for example, my co-worker Russell Brandom sent me an article about the disappearance of Tiangong-1. I pointed to our article and told him that everything would be fine. His panic did not diminish. "Even a small chance of being killed by space debris seems too much," he told me.
Russell technically has a small chance of being hit by space debris all the time, well, an infinitesimal one. According to Aerospace Corporation, a nonprofit research organization that provides guidance on space missions, a person's risk of impact upon re-entry into space debris is approximately one in a trillion. Tiangong-1 is not going to drastically increase those probabilities.
So, why is the space station still scaring people? I think most of the problem started with the first reports in 2016 that Tiangong-1 was "out of control". It's true: China no longer has the ability to maneuver the space station from Earth, and its orbit is slowly decaying. But this idea of an uncontrollable space station probably inspired the visions of a large piece of metal spiraling wildly towards Earth. In addition, companies in the United States often find ways to safely deorb larger metal parts that they send to orbits. "There are much more controlled re-entries than 20 years ago, and for more massive objects, [companies and countries] take more care," says Jonathan McDowell, a Harvard astrophysicist and space flight expert.
Even so, uncontrolled reentries happen all the time. The superior stages of SpaceX's Falcon 9 rockets, Russian Soyuz or Ariane 5 rockets from Europe do not always make a controlled desorption after each launch. Those pieces vary from two to four tons, so they are not as massive as Tiangong-1. But a rocket of the same mass as the Chinese space station made an uncontrolled fall this year on Earth. The upper stage of a Russian zenith rocket landed on Peru in January, and has about eight tons, about the size of Tiangong-1. A tank or two reached the ground, but no injuries were reported.
An object of the second stage of a Delta rocket that re-entered Texas. Image: NASA
Okay, the Zenit upper stage is mostly composed of empty fuel tanks, and Tiangong-1 is denser. "It has a lot of heavy equipment, so it's not like a rocket that is a big empty tank," says McDowell. "People are more worried [about if] than they can get to the ground." That may be the other piece of the puzzle: the idea of a space station falling to Earth is more threatening than a piece of a rocket or an average satellite.
I began to wonder if this is not just another example of how our brains are not very good at assessing real-world risks. Our brains are very sensitive to risk. That's what kept us alive when everything around us was a legitimate risk to ourselves. This is counterproductive today because we hear all kinds of things that seem dangerous but that can not harm us at all.
The novelty definitely plays a role. This is the same reason why many people are more concerned about plane crashes (which are no longer common) than car crashes (which happen all the time). Air accidents seem strange and terrible, and that's why they stay in our minds more; Car accidents, although tragic, do not attract our attention. It is easy to feel scared by terrorist attacks, which seem catastrophic, but in reality we are more prone to die because of the furniture that falls.
"Are fears always rational?"
Nobel Prize-winning psychologist Daniel Kahneman is famous for suggesting that our brain uses two systems: System 1 and System 2. System 1 is your quick and intuitive emotional response, like being afraid when you hear that a space station could fall on your head . System 2 is the deliberate and reasonable response that requires a large amount of cognitive energy, such as slowing down to calculate the probability that the space station actually falls on your head. You can not stop the execution of System 1, and the emotions are powerful. Unfortunately, not many people take the time to do the calculations, so they are afraid.
So, Russell's fear that there is a small chance that space debris will fall on him is a great example of System 1 being out of control. I told him this. "Are fears always rational?" He asked. "I feel like you only fear the things you fear." It is a good point. Every time I pass through the Queensboro Bridge in New York, I think of our car that deviates and sinks in the East River. It's not likely to happen, but I'll always worry if someone tells me the odds.
The good news about Tiangong-1 is that people will not have to worry about much longer. The European Space Agency estimates that the station will probably fall sometime between March 29 and April 9, although those dates are still subject to change. Once it falls, the risk will be eliminated. But if you want to be scared with space debris, there's always the NASA 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.