Will junk from space fall on my head?
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How did Japan just lose a satellite? Is it going to fall on me? — C.L., Toronto
The Hitomi satellite, an X-ray telescope meant to study objects like black holes and neutron stars, was launched in February 2016 by JAXA, the Japanese space agency. On March 26, something went sideways: The $285-million contraption broke up, lost contact with JAXA (apart from spotty radio signals) and was recorded apparently tumbling end-over-end across the sky.
What happened isn’t clear, but U.S. military experts don’t think it was a collision with a large object. JAXA’s first priority is re-establishing contact; the blame game will follow.
According to UBC astrophysicist Jaymie Matthews, it will likely be years before pieces of Hitomi enter our atmosphere, they’ll be small, and most will land in the ocean. There is a slim chance it could smash into another satellite, but no, it’s not going to fall on you.
It’s more probable, but exceedingly unlikely, you’ll get hit by something else from space. Tonnes of asteroids, meteorites, etc. fall on Earth every day, mostly as dust. The exactly one confirmed case of a direct meteorite hit on a person, in 1954, resulted in a spectacular bruise, not death.
There’s always the chance of a civilization-ending impact from a massive object, but there’s no evidence one is imminent (NASA’s got an eye out) and there’s no point worrying.
This brings up one of my favourite topics in the universe: The difference between hazard and risk. A hazard can cause harm under certain circumstances; a risk is the chance of harm actually happening. Space junk is a hazard, sure. But the risk is infinitesimal.