How real is the threat of an asteroid hitting Earth, and is there anything we can do to prevent it from happening? Asteroid impacts are nothing new. Only last year, one exploded over the city of Chelyabinsk in Russia injuring 1500 people and damaging some 7,000 buildings.

"It was a pretty nasty event, luckily nobody was killed, but it just shows the sort of force that these things have," says Alan Harris, Senior Scientist, DLR Institute of Planetary Research Berlin.

While there was surprise nobody saw it coming, the asteroid itself wasn't that big, measuring no more than 20 metres across. It was tricky to spot, arriving into Earth's atmosphere backlit by the Sun.

In fact, much bigger threats lurk out in space. Just a few days ago another asteroid 270 metres wide passed near Earth. That kind of object could cause much more damage.

"Something with the size of a hundred metres for instance, which still isn't very big, you're talking about something that would fit into a football field, and that could actually completely destroy an urban area in the worst case. So those are the things that we're really looking out for, and that we're trying to find ways to tackle," says Harris.

Action to address the asteroid threat is already underway. Earlier in February, space scientists and policy experts from all the major space-faring nations held talks to create a framework for action....