Explaining meteors: are we in danger?

The dinosaurs didn't get on with them, but there are things we can do to avert an impact
Even small meteors can cause significant damage. Photograph: Niyazz /Alamy

In February, a meteor exploded over the Russian city of Chelyabinsk, causing significant damage. A recent study in Nature suggests that there are more of these potentially threatening small meteors than we previously thought. We ask expert Dr Hugh Lewis from the University of Southampton to explain how we can tackle meteors, big and small.

Which asteroids can we detect?

We've been looking now for a number of years to try to identify all the objects that are larger than 1km in size – objects that size are going to cause a lot of damage should they hit the Earth. When you get down to smaller size, we can only see some of those objects, basically because they are darker – we rely on them reflecting light from the sun to see them in telescopes and so the smaller they get, the less sunlight they are going to be reflecting.

How much damage can a small meteor cause?

As you saw with the event over Chelyabinsk, an object that was probably less then 20m in size can have quite a significant impact on the ground. The meteor itself broke up before it hit the ground but the airburst caused all the damage — the broken windows, throwing people across rooms, and structural damage.

How can we get better at spotting potential threats?

We have the Spaceguard Survey and there are people now who are advocating the use of space-based missions to look for asteroids.

The B612 Foundation is proposing a mission called "Sentinel", where a spacecraft will be launched into a Venus-like orbit to look for objects larger than 140m. If an asteroid is coming to us from the direction of the Sun, we can't observe it easily with a telescope.

The Sentinel spacecraft will look out from the sun and will see a greater range of objects. But it will need to have very sensitive detectors – it is planning to use an infrared detector.

How do we avoid devastation from a large meteor?

We may have decades of warning for objects that we are able to track. An asteroid threat is a natural hazard that we could probably do something about now with the technology we already have.

All we need to do is make it miss Earth, but in such a way that it doesn't then come back some years later and collide with the Earth. A big nuclear bomb going off in orbit is probably not the way you want to do it. Nasa has already demonstrated something that you could use to deflect an asteroid, it was its "Deep Impact" mission — it basically flew a spacecraft into the asteroid and hit it at high speed. If you nudge it 30 years before it is due to hit the Earth then that little nudge is enough.

What can we do if a small meteor reaches Earth?

We don't have time to deflect it, we probably don't have time to evacuate an area, but what we can do is start to educate people. If you see something like this — bright flash in the sky, huge smoke trail that's formed, [then] the last thing you want to do is be standing next to a window.