Tracking dangerous asteroids

MARINA BROZOVIC, NASA/JPL Physicist: On what kind of odds would you risk the future of mankind?

TITLE: Watcher of the unseen

BROZOVIC: At this point, we know about 14,000 what we call near-Earth asteroids. There were impacts in the past, there will definitely be impacts in the future, the question is when, and will we be ready?

I work for the solar system dynamics group at JPL. We're kind of the flight control for the solar system. Anything that moves, we want to know the orbit of it. From near-Earth asteroids, main belt asteroids, planets, satellites, comets, so... it really is a true kind of traffic centre.

My first memory of really being interested in space was ... let me start rambling and then you guys can cut. (Laughs off-camera)

TITLE: Split, Croatia

BROZOVIC: You know, when I was a child, I can say that the meaning of the universe was very important to me. My first memory of being intrigued by space was when Carl Sagan's Cosmos was on TV. Carl Sagan was such a kind of natural talent to talk about these mysteries of the universe, and you understand the basic concepts. But then also, you know, that at the same time inspired me, because I wanted to understand much more. I wanted to understand the details.

So there is a very large reservoir of asteroids that are between the orbits of Mars and Jupiter. You probably have billions of objects there. So what happens is that because of the gravitational influence of Jupiter and Saturn, some of these objects get kind of nudged, and they migrate into the inner solar system. And that is what we call near-Earth objects.

Discovering near-Earth objects, it's very important, because they have changed the history of the Earth. There were many many large impacts on Earth's history. Asteroids definitely brought some organic material. The question is whether they brought water. We know that asteroids affected life on Earth. 66 million years ago, a very large asteroid about 10 kilometres in diameter hit on the Yucatán Peninsula in Mexico. To the best of our knowledge, besides immediate obliteration in the radius of hundreds of kilometres, the impact kicked out enough dust that the Earth would be engulfed in darkness for several years. And that could have been the main cause for the extinction of 75 per cent of species on Earth, including the dinosaurs.

So this is something very profound for us. It's kind of our responsibility as a species to understand the risk involved.

The way that you discover near-Earth asteroids is with large telescopes. There was a mandate by Congress for NASA to discover all the near-Earth asteroids that are larger than 1 kilometre, and by now we know about 95 per cent of these objects. But that is not going to be enough, because something the size of probably 50 metres can cause like a city-level devastation. There are millions of these objects, and we can only guess that we maybe know, maybe one percent. I mean, we got hit just in 2013.

TITLE: On February 2015, 2013, a very small asteroid (17 metres) fell unexpectedly over the remote Russian city of Chelyabinsk.

BROZOVIC: Chelyabinsk was a demonstration of what a small asteroid can do. It was not even something that reached the surface.

TITLE: The asteroid exploded approximately 97,000 feet in the air. The force of the explosion was 20 to 30 times greater than that of the nuclear bomb that destroyed Hiroshima. Over 1,400 people were injured. Damage was estimated at one billion rubles.

BROZOVIC: So you see how even these small ones can still potentially be dangerous.

If we find something with some chance of impact, we would probably have at least several years to prepare. So in that case, there would probably be a deflection mission. That basically means that you have a spacecraft that kind of rams into the asteroid and changes its velocity and you end up completely missing the Earth.

We did have a little mini-trial. It was a spacecraft called Deep Impact that rammed into Comet Tempel. So this is not science fiction. Asteroids larger than 30 metres impact Earth about once every few centuries. Larger than 300 metres, once every hundred thousand years. So it is very wise to keep watch.

We're born curious. We are all born explorers, and we just kind of started looking out and really understanding what is our place in the solar system. We try to understand the small things, and then, hopefully, during your career, you're going to work on much more complex projects that really can address some of the fundamental questions of the universe. Our real love: is there somebody out there?