So the UARS satellite is finally down. After a week hiding under our desks wearing helmets and body armour, we can all safely emerge and go about our business like rational people again.
NASA reports that the decommissioned orbital laboratory burned up over the Pacific Ocean last Saturday at between 3 and 4 in the morning, our time.
Apparently, no one was the wiser of its passing, the ocean being extremely large and human presence on it surpassingly small. There were some earlier reports of debris falling over Canada, but it seems likely that these were either hoaxes or wishful thinking.
So, to summarise for the hard of thinking:
- The satellite came down where it was most likely to, in the water
- In all likelihood, no person was within visual distance
- We may never find the debris, since it is quite small and has probably sunk without a trace
In other words, talk of deaths from falling space debris was premature, if not outright irresponsible. It all comes down to an elementary misreading of the probabilities, and something that science correspondents should have checked as a matter of course.
NASA released a Re-entry and Risk Assessment for the satellite when it became inevitable that it would fall to Earth some time soon. Looking at the top-line statistics could cause you some worry; 26 potentially hazardous objects were expected to survive re-entry, comprising around 500 kilograms of mass. The chance of human casualties was estimated at approximately 1 in 3200.
1 in 3200? The risk is unacceptable! Or at least so went some stories insinuated.
Remember though, probabilities are funny things. That calculation is based on the possibility of debris causing injury to any one of the 6 billion people on the planet. The chance of it hitting any specific person is on the order of several trillion to one.
Despite orbital debris falling to Earth since the beginning of the space programme, and meteors since the formation of this planet, there have been no verified cases of death by falling space debris.
Instead of spending time looking out for objects falling on our heads, we might be better advised to look around us for more credible threats, such as the risk of dying in a car accident, which could reach as high as 1 in 240 for an individual.