A meteor and asteroid: 1 in 100 million odds

 Friday was an extremely unusual day, astronomically speaking. Just as scientists were gearing up to witness an asteroid's closest ever approach to Earth in recorded history, a sizeable meteor exploded over Russia, causing thousands of injuries and major damage to buildings.

The asteroid, named DA14, came within 17,000 miles or so, as close as a telecommunication satellite in geosynchronous orbit. DA14 is quite a bit smaller than YU55, the asteroid that passed Earth in November 2011, but DA14 came more than 10 times closer.

These two rare events occurred the same day. Your inner mathematician and your inner prophet of the end times think they should be connected. But scientists say they are not. What gives?

Meg Urry

First, some facts. Meteors are rocky bodies that enter the Earth's atmosphere. Some are leftover debris out of which planets like Earth are formed, while others are the remnants of shattered comets and asteroids. As long as their orbit intersects the Earth's orbit, these rocks can in principle impact the Earth.

Actually, this happens all the time, although usually the impacts occur in unpopulated regions since most of Earth is uninhabited. In fact, most meteors fall into the ocean simply because water covers two-thirds of the planet.