"Another tiny rock will pass by Earth tonight/tomorrow at around 07:00 UTC (03:00 Eastern US time). Called 2012 KT42, it's probably less than 10 meters across — about the size of a school bus or more likely a minivan. And it'll be a close shave: though the orbit is still not nailed down, the nominal miss distance is about 14,500 kilometers (8900 miles). That's a bit bigger than the diameter of the Earth itself.

Bear in mind, it was only discovered last night, so the current orbit is preliminary. Many small rocks that pass close to Earth are discovered shortly before they breeze past us (and some not until after), so this is nothing out-of-the ordinary.

And since some people tend to get upset about these things, I'll point out that as of right now, it looks like it will miss us. And even if newer observations show it hitting us, this rock is way too small to do any damage. At that size, it'll break up in the atmosphere and make a spectacular light show, but not much else. This has happened countless times with asteroids this size.

Another way to think about this is that rocks this size pass us all the time, but you never hear about them hurting us; that's because they don't! The smaller the asteroid the more common they are, but the less they can do to us. At this size, there's no danger."

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Copied from Discover Magazine.