As I mentioned in my last post, asteroids come in a range of sizes. A few are big, maybe a thousand miles across. Most are small. The smaller you go, the more there are. And there's no formal lower limit on the size of an asteroid, so rocks just a few feet across could be called asteroids.
I mention this so that when I say the next sentence, you don't worry (because there is no need to worry). But, in just a few hours an asteroid is going to hit the Earth.
Don't worry, this is not one of those dinosaur-murdering, ten-mile-wide monsters. No, this rock is probably about 30 feet across, which is so small that it is likely to explode and burn up in Earth's atmosphere.
The asteroid, with the exciting name of 2008 TC3 was discovered last night by astronomers at the Mount Lemmon Observatory outside of Tucson, Arizona. It was quickly confirmed by other observers. The size of the rock is estimated from how bright the object appears and how far away it is. For being on a track to hit the Earth, it is still very faint, over 10,000 times fainter than what your unaided eye can see.
That will change tonight, though, when the rock enters Earth atmosphere over Sudan. Friction from the atmosphere will cause the rock to heat up and start to burn away, producing a brilliant fireball. The fireball could explode, which could create a loud sonic boom. And all of this while the fireball passes over a war zone...
We have no clue whether this asteroid will survive its trip, reaching the Earth's surface as a shower of meteorites, or whether it will completely disintegrate in the atmosphere. At any rate, people in northern Africa and the Arabian Peninsula all have a good chance of seeing a fireball tonight (at 02:46 UT, or about 10:46pm Eastern Daylight time).
Asteroids this size probably hit somewhere over the Earth every few months. The difference with 2008 TC3 is that we know it is coming. And, for the first time, we might be able to train scientific instruments on the fireball and learn something about it, like its composition, whether it is a solid rock or a conglomeration of even smaller rocks, and perhaps even where in the Solar System it came from (though this article from New Scientist says there probably won't be any time for an official observing expedition to be put together).
So, again, no need to panic. I'm not fleeing for the hills; in fact, I'm a bit disappointed that I will miss out on the show. I look forward to seeing pictures and video of this event!