So why do scientists bother to keep track of all those potentially hazardous objects? It's not because they're very likely to pose a danger, but because if they were to crash into us, the effects could be catastrophic. An object just one kilometer (just over half a mile) in diameter would put a quarter of the planet's population at risk. Researchers keep talking about how to prepare for an asteroid collision because they know that an impact of some kind, somehow, is basically inevitable. There are too many potentially hazardous objects for it to never happen. But that doesn't mean that every flyby is dangerous. Most aren't.