Phil Plait writes in Slate:
…Another big impact like Chelyabinsk may not occur again for 500 years, or another may come in tonight. There are billions of such rocks in space, and they are simply too small and faint to track. We can only talk about them statistically. The same is true, more or less, with DA14-sized rocks as well, but most likely there are a million or so of them, with 10,000 having been spotted. That’s 1 percent.
When people think asteroid impacts, they think dinosaur killers. But we have most of the 10-km asteroids mapped out, and we know we’re pretty safe from them. But watch those videos from Russia again, and remember that a rock smaller than an average hill did that.
We need to take this threat seriously. Congress has called for an investigation into the issue, and I applaud that. I hope something comes out of it. Specifically, cash for NASA, cash for observatories, and cash for private endeavors to build more telescopes, to launch space missions, and to map the volume of space around the Earth’s orbit where these rocks lurk.
While I don’t lie awake at night in fear of this, I also know that if we wait long enough doing nothing, something the size of Chelyabinsk will hit us again, or it might be bigger. Or it might be made of metal and survive entry into our atmosphere, dumping its megaton of energy into a city instead of high in the atmosphere.
As science fiction author Larry Niven said, dinosaurs aren’t around because they didn’t have a space program. We do. Now we just have to be intelligent enough to fund it, and to use it.