A small (10 meter wide) asteroid will pass by the Earth Wednesday, at 12:47 UT. This tiny rock, called 2010 AL30, will pass us at a safe distance of 130,000 km (80,000 miles). As cosmic encounters go, this is a hair's breadth, but in human terms it's a long way off; as this graphic makes clear. It's about a third of the way to the Moon.
2010 AL30 was only discovered on Monday. It's escaped our previous notice because it's dinky. Even when it passes you'll need a telescope to see it. There has been some speculation that this was a man-made object like a rocket booster, since it's about the right size, and sometimes near-Earth objects turn out to be space junk. But in this case the orbit doesn't really match any rocket trajectory, so it's probably a natural rock.
And since I know someone would ask, if this were aimed at us, it would probably explode high up in the atmosphere and not hit the ground. It would be quite a show, but most likely wouldn't do any damage on the ground (even if it were iron, at that size it's unlikely it would make it to the ground, and instead would tear itself to pieces on the way in).
And one last thing: note what I titled this post. Now look around the web to see how other articles are titled. Just sayin'.
Tip o' the Whipple Shield to Mike Murray for putting that graphic together and letting me know about it.