JB: How will this be implemented?

MADDOX: There are lots of very interesting problems that people haven't really thought about; for example, the best way of avoiding an impact is to explode a nuclear weapon near the projectile. If you can catch it early enough, shall we say several days before it's going to hit the earth, then a quite small nuclear weapon, shall we say 100 megatons, would be enough to nudge it in one direction or the other, but the most efficient way is actually to slow it down; to explode the thing in front of the asteroid. There are a number of associated hazards - if the explosion were not absolutely accurately timed, it might blow the asteroid up, and that might seem good news except there would then be several fragments, and one of those would certainly hit the earth, and it might still be quite big. So the best thing is a carefully controlled explosion to nudge the thing away.

The trouble with that is that the Russians and the United States are now against the deployment of nuclear weapons in space; the Chinese are probably against the development of other people's nuclear weapons in space; nobody has talked about the question anyway. So the idea that it might be announced there's going to be an impact a year from now wouldn't actually leave enough time for people to get around the table and decide what best to do about it. My own opinion is that there's going to have to be rather formal negotiation quite soon on what would happen if there were an impending impact. There would have to be arrangements that would make sure that no nuclear weapon authorized for use under this program could be used to divert an asteroid onto some sensitive part of the world, like China or Russia - and so on. All kinds of problems.

JB: How much time would we have?

MADDOX: It depends. In the worst case there would be hardly any warning at all - a couple of days. A couple of days is too little time to do anything. And the chance that a large object, ten-kilometer object, would arrive with only two or three days' warning is probably about ten percent. No program that one can think of devising is going to avoid the worst case - you can't get absolute security - but you could at least hope to get rid of ninety percent of the big impacts.

In the case of asteroids, the warning probably would be quite long, possibly even two or three years, because these asteroids make circuits about the sun just like the planets do, but they go in eccentric orbits, which is why they can hit the earth. This means that if you pick one up on a particular orbit, you might be able to figure out that on its next orbit, or its next but one, it's going to hit the earth. You've got quite some time to plan what to do in that case. And the feasibility of doing something will of course improve as time passes, so in that case one could begin by hoping to avoid half the large objects, quite soon, and, maybe in a hundred years, to avoid ninety percent of the large objects. However, we'll still be stuck with the problem of the ten percent.

JB: How do these ten percent sneak in?

MADDOX: They begin as comets and the thing about comets is that nobody is entirely clear how they find their way into the inner solar system. The theory - and there's no confirmation of this at all - is that right at the edge of the solar system, roughly at the place where the sun's gravitation field is comparable with the gravitational field due to external objects, like molecular clouds, other stars, and so on - there's a cloud of cometary material called the Oort Cloud, named after the Dutch astronomer Van Oort. What's said to happen is that these objects are either deflected into the solar system by a passing star, or attracted in by some conjunction of one of the outer planets with Jupiter, so that they start drifting into the solar system.

They spend some time with Neptune, and some time with Saturn, some time with Jupiter, and either they become asteroids, in which case there's relatively little problems, or in some extreme cases they start heading in from the outer region of the solar system, and they just make one pass at the sun. That's the most dangerous case, because these hyperbolic comets, as they are called, are traveling very fast, and they haven't been seen before, and they will only make one pass at the sun anyway. In that case it would really be quite hard to be sure that one could spot them many days in advance of an impact. That would be curtains.MADDOX: They begin as comets and the thing about comets is that nobody is entirely clear how they find their way into the inner solar system. The theory - and there's no confirmation of this at all - is that right at the edge of the solar system, roughly at the place where the sun's gravitation field is comparable with the gravitational field due to external objects, like molecular clouds, other stars, and so on - there's a cloud of cometary material called the Oort Cloud, named after the Dutch astronomer Van Oort. What's said to happen is that these objects are either deflected into the solar system by a passing star, or attracted in by some conjunction of one of the outer planets with Jupiter, so that they start drifting into the solar system.

They spend some time with Neptune, and some time with Saturn, some time with Jupiter, and either they become asteroids, in which case there's relatively little problems, or in some extreme cases they start heading in from the outer region of the solar system, and they just make one pass at the sun. That's the most dangerous case, because these hyperbolic comets, as they are called, are traveling very fast, and they haven't been seen before, and they will only make one pass at the sun anyway. In that case it would really be quite hard to be sure that one could spot them many days in advance of an impact. That would be curtains.

JB: Ok, we've talked about data handling, infection, cloning, and impact. Going beyond cloning, let's talk about the stability of the human genome.

MADDOX: I dealt with that in the case of the sheep but let me add this to it, because I think it's important. Up until now it's been the assumption of most generations living on the surface of the earth, that the ideal condition of human beings is that in which we recognize that we're a part of the natural world, and our goal is harmony with the natural world. If you think of it, what natural selection, Darwinian natural selection, does, is precisely to make the successful species, those that survive, fit for the environment at the time. It's a device for making sure that everything is in harmony with the natural world. We have accepted, I think, as the human race, that this is indeed the case, that we must accept our dependence on the natural world and our need to be in harmony with it.

What happens, then, if we learn that we are one of those many species destined to become extinct because for some reason or another our genome hasn't worked out to be quite as stable as it might have been. In those circumstances we would have a nasty choice. We would have to decide, would we not, whether or not we let ourselves become extinct, as part of our dependence on nature, part of our being a part of nature, or whether we actually struggle against it; do something about it.

My guess is that if the question of human extinction is ever posed clearly, people will say that it's all very well to say we've been a part of nature up to now, but at this turning point in the human race's history, it is surely essential that we do something about it; that we fix the genome, to get rid of the disease that's causing the instability, if necessary we clone people known to be free from the risk, because that's the only way in which we can keep the human race alive. A still, small voice may at that stage ask, but what right does the human race have to claim precedence for itself. To which my guess is the full-throated answer would be, sorry, the human race has taken a decision, and that decision is to survive. And, if you like, the hell with the rest of the ecosystem.