While you were working: An asteroid just flew by

CNN News Wire | 2/15/2013, 9:52 a.m.

It was hardly a doomsday event, but at 2:24 p.m. ET, an asteroid came pretty close to Earth.

And it was only one of thousands of objects that are destined to one day enter our neighborhood in space.

"There are lots of asteroids that we're watching that we haven't yet ruled out an Earth impact (for), but all of them have an impact probability that is very, very low," Don Yeomans, manager of the Near-Earth Object Program Office at NASA's Jet Propulsion Laboratory, said at a press briefing.

This particular asteroid is called 2012 DA14.

The asteroid is thought to be 45 meters--about half a football field--long. It came no closer than 17,100 miles to our planet's surface.

An object the size of 2012 DA14 appears to hit Earth about once every 1,200 years, Yeomans said.

"There really hasn't been a close approach that we know about for an object of this size," he added.

On its close approach to Earth, it was predicted the asteroid would travel at 7.8 kilometers per second, roughly eight times the speed of a bullet from a high-speed rifle, he said.

If it had hit our planet--which was impossible--it would have done so with the energy of 2.4 megatons of TNT, Yeomans said. This is comparable to the event in Tunguska, Russia, in 1908. That asteroid entered the atmosphere and exploded, leveling trees over an area of 820 square miles--about two-thirds the size of Rhode Island. Like that rock, 2012 DA14 would likely not have left a crater.

What else is out there?

So, we knew that this particular asteroid wasn't going to hit us, but how about all of those other giant rocks floating nearby beyond our atmosphere?

NASA says 9,672 objects have been classified as near-Earth objects, or NEOs, as of February 5. Near-Earth objects are comets or asteroids in orbits that allow them to enter Earth's neighborhood.

There's an important distinction between these two types of objects: Comets are mostly water, ice and dust, while asteroids are mostly rock or metal. Both comets and asteroids have hit Earth in the past.

More than 1,300 near-Earth objects have been classified as potentially hazardous to Earth, meaning that someday they may come close or hit our home planet. NASA is monitoring these objects and updating their locations as new information comes in. Right now, scientists aren't warning of any imminent threats.

Yeomans and colleagues are using telescopes on the ground and in space to nail down the precise orbit of objects that might threaten Earth and predict whether the planet could be hit.

Observatories around the world send their findings to the NASA-funded Minor Planet Center, which keeps a database of all known asteroids and comets in our solar system.

NASA also has a space probe tracking asteroids to learn more about them. The Dawn probe was launched in 2007 and has already sent back dramatic pictures from the giant asteroid Vesta.

The spacecraft is now heading to the dwarf planet Ceres. Vesta and Ceres are the two most massive objects in the main asteroid belt.