Effectively zero. That's the chance of you being hit by a falling satellite.
Although the number of satellites in orbit has risen exponentially, modern satellites have manoeuvring capabilities to control their re-entry trajectory and are constructed from low-density materials so that they’ll burn up as they fall through the atmosphere.
Space debris does still reach the ground though – spent rocket stages from China’s Long March rockets being a recent example.
But over the last 50 years, NASA has only recorded an average of one piece of space debris reaching the ground per day and there are currently no known incidents of death or serious injury.
One piece per day sounds like a lot, but to put it in perspective, there are at least three plane crashes a day (mostly involving non-commercial, light aircraft), and the deaths of people being hit by falling planes are still extremely rare.
When a plane crashes, it usually remains in one piece until the moment of impact and is often full of fuel. That makes a falling aircraft much more deadly than a typical piece of space debris, which may just be a small titanium shim or a piece of carbon-fibre panelling.
The extra altitude that the space debris has fallen from makes no difference here though, since it will have reached its terminal velocity long before it hits the ground, so falling from 300km (approx 186 miles) is effectively the same as 10km (6.2 miles).
Aircraft also tend to fly near densely populated areas, whereas spacecraft are distributed much more evenly over the globe. If everyone in the world went outside and spread out, they would only cover about 0.0002 per cent of Earth’s surface.
So even if every piece of falling space debris was lethal, they would miss 99.9998 per cent of the time, translating to one death every 1,300 years.
This article is an answer to the question (asked by Charlie Bond, via email) 'What are the chances I'll be hit by a falling satellite?'
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