Q&A ON ASTEROIDS AND THE THREAT TO EARTH

Duncan Steel,
Vice president of Spaceguard

Q: Is the threat of an asteroid hitting Earth exaggerated?

A: No, it's not exaggerated. Compared to other hazards we face, it turns out to be a very real risk. Based on recent evidence, we estimate the chances of an asteroid doing catastrophic damage in the next century are approximately one in 5,000.

Q: If we find an asteroid on a collision course with Earth, is there an international plan?

A: No, there is no international plan. This is an area of which governments are sadly ignorant. What we really need to do is to carry out a surveillance programme first of all, and this is simply not being done. In essence, the only country doing anything in this area is the United States. There is no southern hemisphere asteroid search programme.

Q: What is the difference between an asteroid and a comet?

A: The difference between an asteroid and a comet is defined by what they are made of. Asteroids are lumps of rock and metal. Comets are basically dirty snowballs, and part of the ice of which they are made evaporates as they come closer to the Sun, giving them their fuzzy appearance.

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The amount of water vapour around a comet makes it appear very bright, because it reflects a great deal of sunlight. Asteroids, however, are very dark and small and this makes them much more difficult to spot.

Q: Could we blow up an asteroid if it was a threat to Earth?

A: It's unlikely that we'll need to do this within our lifetimes. That's because we probably won't find an asteroid on a collision course with Earth.

However, if we did find one which was due to hit us in 10 or 20 years, it might be possible to divert it so it misses.

Unfortunately, the only way we know of to accomplish this would involve using nuclear weapons. But it's not like in the movies. We would need to use a nuclear weapon in a 'gentle' way.

We would want to give it a nudge so that it remained intact. Blasting it on its surface would simply shatter it into pieces. We would still be hit by the fragments. But it should be possible to give the object a sufficient shove with an explosion to get it to miss the Earth.

The essential thing is we need lots of warning time, and that means many years. This is why a diligent search programme is necessary now. And it must be global.

Q: Could we attach sails to an asteroid and use the solar wind to nudge it off course?

A: This has been suggested, but the reality is that if we did find one which was threatening us, we would surely use a proven technique. The solar sail idea is nice in theory. But in practice we wouldn't be able to gamble with the chance that it might not work.

Dealing with asteroids is like dealing with cancer. The first step is a screening programme and it's unlikely that you will develop a particular type of cancer. But if you do, none of the solutions are pleasant. It's the same with asteroids. We wouldn't want to use nuclear weapons in space, but I believe it would be essential.

Find out about solar sails

Q: How can we spot asteroids from Earth?

A: It's impossible to see asteroids coming from the day side of the Earth using ground-based telescopes. But we could see them using telescopes in space.

The problem is that this is very expensive. At the current time, the money isn't even available to carry out the research on the ground. It's much cheaper to use ground-based telescopes. But in some ways, space-based telescopes would be much better.

Q: What can ordinary people do to help?

A: I would urge anybody concerned about this to write both to their own MP and also the Prime Minister. The letter could also be sent to the Science Minister, Lord Sainsbury.

However, having said that, one must realise that this isn't a science programme. It's a defence programme. Civilian scientists, such as myself, might advise defence scientists on what needs to be done. But it's not really our job to search for these things. In the United States, the vast majority of the asteroid discoveries are made using telescopes which belong to the US Air Force.

Let me just urge all concerned people to try to convince others that we are not joking. This is a serious hazard. It must be taken seriously.

Q: What is the biggest asteroid yet detected?

A: The largest Earth-approaching asteroid is called Eros which a NASA spacecraft landed on last year. It is about 20 miles across. However, it cannot hit the Earth.

The largest Earth-crossing asteroid is about five miles across. The largest asteroid in the main belt between Mars and Jupiter is about 600 miles in diameter. However, in the past year, a couple of larger asteroids have been found out beyond the orbit of the planet Neptune.

Explore asteroids further

Q: How can you calculate the future path of an asteroid?

A: It's easy to tell that an asteroid will be Earth-crossing many years from now, even just after it is discovered.

Asteroids remain on the same orbit around the Sun unless something happens to divert them, such as coming too close to one of the planets. Our computer programmes take all these things into account.

The real difficulty is when we find an asteroid which will come very close to the Earth but we don't have enough data to be sure it'll miss. This is what leads to the occasional scares in the media.

Most often, a few weeks of observations, or a few months, will give us enough accurate measurements of the asteroid's orbit to prove that it won't hit the Earth. But it does take time.

Unfortunately, a lot of this asteroid tracking is still left to the enthusiasm of amateur astronomers spread around the world. If there is an asteroid due to hit us next week, most likely we will be unaware of it until it actually hits.

Q: Where's the best place in space to look for asteroids?

A: Search programmes concentrate upon the part of the sky which we call 'opposition'. That is, the place directly overhead at midnight (in the opposite direction to the Sun). It happens that it's easiest to find asteroids in that direction because they are reflecting sunlight straight back to our telescopes.

Obviously we would like to be able to scan all of the night sky, every night, so that we don't miss any asteroids. But the current search programmes fall a long way short of that. We must do better.

We need more larger telescopes because currently we are only spotting big asteroids. To see the smaller ones we need telescopes which cover a larger area of the sky, not just tiny spots like most astronomical telescopes.

Q: Should we be panicking?

A: No. This is a hazard we can deal with and we must deal with. And remember, you are much less likely to die in an asteroid impact than you are in a car accident.

Lembit Öpik
Member of Parliament

Q: What is the UK government doing?

A: The Department of Trade and Industry [DTI] has accepted that there is a clear and present danger of a major impact. They have provided £250,000 for public information services about this matter

Q: What do we need to do next?

A: The next big step I'm determined to achieve is the forging of a serious degree of international political co-operation between the UK and the USA. We need to kick start an international 'Track and Whack' programme for incoming asteroids. In effect, I'm campaigning for a global insurance policy.

Q: How much would it cost for a defence plan?

I suspect it may take a few more scare stories from space itself to get the money we need – about £80 million for the entire tracking project over 10 years.

We have enough of a shared sense of survival to find the money. We should also share the effort to save billions of lives and trillions of pounds that would be lost in a serious impact.

Q: Haven't the government got better things to spend their money on?

A large space rock can do far more damage than any dictator. And, ironically, a large space rock may actually be rather cheaper and easier to stop!