There was shocking news about a near-miss of an asteroid a couple days back. But how much danger were we really in? According to the linked article, the asteroid passed within 230,000 km. That’s closer than the moon! But for any given object passing that close to the earth, what are the chances we’d actually get hit? Well, without taking the earth’s gravity into account, actually fairly slim:
The 230,000-km-radius circle that the asteroid passed through actually spans an area 1,300 times bigger than the earth. So chances were very slim that we’d actually get hit.
What are the chances that you personally would be affected? Even slimmer. Space.com estimates that the asteroid would have damaged about 2,000 square kilometers. The Earth’s surface is about 510,000,000 square kilometers, so even if the asteroid had hit the Earth, there would be only about a 1 in 250,000 probability of you personally being harmed. Combine the two probabilities, and you’d have a better shot at winning the lottery than getting harmed by that asteroid.
What we don’t know is how common these near-misses are. Perhaps they happen every few years, and astronomers have only just now gotten good enough to start detecting them. If that’s the case, we would expect an earth impact about once every 400 years — still not very likely, and even less likely to affect any given person.