Collision course transcript
Don Yeomans: On November 8, 2011 we have a 400m sized object coming within the orbit of the moon.
ALEX CULLEN: 400m? That's a big asteroid.
Don Yeomans: It is indeed.
ALEX CULLEN: If that hit, we'd be in a lot of trouble.
Don Yeomans: We would indeed, yes.
ALEX CULLEN: The asteroid goes by the unromantic name of 2005 YU55. It's the size of an aircraft carrier and on Wednesday it will pass between the earth and moon.
Don Yeomans: There's no reason to panic.
ALEX CULLEN: Here's what the impact of an asteroid a fraction of that size — just 50 metres in diameter — did 50,000 years ago. It's big but this is the result of only a small asteroid impact. It hit travelling at almost 42,000km/h and left this crater about 1.5km wide. Out here in the Arizona desert, it didn't do much damage but just imagine what it would have done to a big city.
ALEX CULLEN: What if one of these was to hit a city, for instance...
Don Yeomans: It would be lights out. If an object of that size were to explode over a city, it would cause devastation.
ALEX CULLEN: Don Yeomans runs NASA's JPL Spaceguard program. Last month, his team of asteroid trackers calculated there were nearly 20,000 near-earth asteroids - some one kilometre in size. The largest could wipe out the world. What sort of damage are we talking about?
Don Yeomans: An impact by a large asteroid has the capability of taking out our civilisation and not many worrisome threats can make that claim so it is worth some effort. And I think the effort is well under way to find these objects, to track them for 100 years into the future and see whether any of them represent a threat.
Ed Beshore: NASA and the US Congress became a bit concerned several years ago that an object of one kilometre size or larger that might hit the Earth could have global catastrophic consequences.
ALEX CULLEN: In the Catalina mountains north of Tucson Arizona, I'm travelling with Ed Beshore who tracks comets and asteroids for NASA using telescopes in the US and in Australia. Is there a situation where you could find one the day before it gets here?
Ed Beshore: Absolutely. Actually, we did that. With the observatory that we're going to right now, we found an object in October of 2006 that we discovered and it actually hit the earth the next day. Fortunately it was only 3m in size, about the size of a car. So it came in over the Sudan desert, broke up harmlessly.
ALEX CULLEN: Luckily it was only 3m.
Ed Beshore: That's right.
ALEX CULLEN: About 70 percent of new asteroid discoveries are made here.
Ed Beshore: In this particular case the object is moving relatively fast.
ALEX CULLEN: Ed and the other astronomers scan outer space for moving objects.
Ed Beshore: Every night we turn in about 6,000 observations of asteroids.
About 10 or 12 of them on a good night are near-earth objects, and about three or four a week are what we call potentially hazardous asteroids -
asteroids that get close enough to the earth that we have to maintain
a watch over them. A 1km asteroid could throw up hundreds of billions of tonnes of soil into the upper atmosphere. That would effectively shade the earth and change the climate and it would make it very difficult to grow food.
ALEX CULLEN: Should we be concerned?
Ed Beshore: We should be cautious. But like anything else we should take prudent measures to try and eliminate as much of the risk as we can.
ALEX CULLEN: 65 million years ago in the age of the dinosaurs, an asteroid about the size of Sydney Harbour crashed into central America. It turned day into night for a year and almost everything on Earth died. The biggest threat now is an asteroid called Apophis. In 2029 it will pass so close to Earth, we'll be able to see it with the naked eye. What worries astronomers most is Apophis passing through a small corridor in space called a key hole where our gravity would change its orbit, sending it on a collision course with us seven years later.
Dr Bruce Betts: It really would be truly catastrophic if an object the size of Apophis hit. It would be a disaster for millions of people.
ALEX CULLEN: Which is why Dr Bruce Betts at the Planetary Society in Los Angeles is keeping a close eye on Apophis. So what are the chances of a big one hitting the earth?
Dr Bruce Betts: The chances of a big one hitting the earth are 100 percent. The key question is time frame.
ALEX CULLEN: In the movie 'Armageddon' Bruce Willis blew up an approaching asteroid with a nuclear weapon. But in reality, that's the worst thing to do because the blast would create smaller asteroids that could smash into Earth. So what, if anything, can we do to protect our planet?
Dr Tom Jones: One way of knocking an asteroid off its orbit and making it miss the earth would be to slam into it with a hyper-velocity bullet, a big space craft that hits it at tens of kilometres per second.
ALEX CULLEN: Dr Tom Jones is a former NASA astronaut. He fears nowhere near enough is being done to prepare for a doomsday asteroid.
Dr Tom Jones: We should have a book on the shelf that tells us the procedures for deciding when to deflect an asteroid, when it's going to be done, how much it costs, what kind of space craft has to be built. And then the world can then pull that plan off the shelf when it's necessary.
ALEX CULLEN: Whose problem is this?
Dr Tom Jones: Well, it is everyone's problem, it's a global threat. Because when we're confronted but a future asteroid impact, which is a certainty, the process of deflecting that asteroid and moving it off its target - let's say it's Sydney, Australia - would be to drag it at its end point across the globe until you miss the earth entirely. And as you move that aim point, it's going to cross other major cities and regions and countries of the world. So it becomes everyone's concern.
ALEX CULLEN: The clearest reminder of that danger is the imminent arrival of 2005 YU55 on Wednesday. Scientists around the world will be keenly watching this close encounter. Then all they have to do is learn to talk to each other. The future of the Earth may one day depend on it. Who's responsible for deflecting an asteroid?
Don Yeomans: If we do find an object that's on an earth-threatening trajectory, then we have to ask the question, who do you call? Would the US be in charge? I don't know. Would the European space agency be in charge? Would the Russian space agency be in charge?
ALEX CULLEN: So we don't know who's in charge?
Don Yeomans: Not yet. We're working on it.
