Apollo asteroids pose a threat to our planet as they routinely cross Earth's orbit.

Now we have 1999 RQ36, a bigger "potentially hazardous" asteroid, with a higher one-in-a-thousand chance of striking Earth in 2182.

"The asteroids in the most Earth-like orbit are the ones that threaten us most, but they're also the ones that are easiest to get to," Yeomans says.