Asteroids less threat to Earth than thought

Posted by Emma Woollacott

Good news: we're not likely to get wiped out in the same way as the dinosaurs, at least not any time soon.

NASA says it's managed to identify over 90 percent of the biggest near-Earth asteroids, and there's nothing that size headed our way.

There were almost as many of the largest near-Earth asteroids - 3,300 feet and larger - as expected. These are about the size of a small mountain and would have global consequences if they were to strike Earth.

But NASA's now identified 93 percent of them, and says none represents a threat to Earth in the next few centuries. It believes it's spotted everything six miles across or more, or as big as the one thought to have wiped out the dinosaurs.

"The risk of a really large asteroid impacting the Earth before we could find and warn of it has been substantially reduced," says Tim Spahr, director of the Minor Planet Center at the Harvard Smithsonian Center for Astrophysics.

The new observations by NASA's Wide-field Infrared Survey Explorer (WISE) revises the total number of large asteroids from about 1,000 down to 981, of which 911 already have been found.

They also show there are far fewer middle-sized asteroids in our vicinity than previously thought - around 19,500 rather than 35,000.

However, lots of these remain uncharted, meaning there's still a risk of one hitting us sometime, and one could destroy a metropolitan area if it was to impact in the wrong place.

So far, the Spaceguard effort has found and is tracking more than 5,200 near-Earth asteroids 330 feet or larger, leaving more than an estimated 15,000 still to discover.

In addition, scientists estimate there are more than a million unknown smaller near-Earth asteroids that could cause damage if they were to hit Earth. It may not be time to throw away your hard hat just yet.