Close Encounter 
A tiny neighbor will pay Earth a visit this evening. It'll pass about 200,000 miles away -- less than the distance to the Moon. It's so tiny, though, that we won't be able to see it.
2009 BD is an asteroid -- a chunk of rock that's about the size of a house. It's a member of a group of asteroids known as Apollos, after a large member of the group that was discovered in the 1930s.
All of the Apollos follow orbits that cross Earth's orbit around the Sun. In fact, the orbit of 2009 BD is almost identical to Earth's.
We pay special attention to the Apollos because there's a chance they could hit us. An Apollo about the size of an SUV slammed into Earth's atmosphere in 2008. It exploded high above Sudan. It didn't cause any damage, but it did rain tiny bits of debris across the desert.
2009 BD is larger, but probably not large enough to hit the ground. Instead, as it plunged into the atmosphere, the pressure would either break it into big chunks, or cause it to explode with the force of a small atom bomb. The odds are that the blast would happen over the oceans or uninhabited land. And even if it did happen over a city, if it were high enough in the atmosphere there likely wouldn't be any damage.
Even if it doesn't hit Earth -- or the Moon -- 2009 BD isn't a long-term visitor to this region of the solar system. Gravitational interactions with Earth will kick it away from us -- thinning out our cosmic neighborhood.
Script by Damond Benningfield, Copyright 2011