Issue Date: April 6, 2008

Meet the NASA guy who tracks the asteroids like Apophis headed our way.

By Martin Mazloom

On June 30, 1908, an asteroid fragment -- roughly 50 meters in diameter -- shot toward Earth and exploded over a desolate region of Siberia known as Tunguska. Within seconds, the explosion scorched and felled millions of trees over about 1,600 square miles. If the fragment had hit a few hours later, a half-million people could have died in St. Petersburg, Russia.

What can we puny earthlings do in the face of asteroids and comets that are hurtling at more than 40,000 mph near and sometimes exactly at our precious planet? Fortunately, in 1998, NASA decided to take action and established a program to monitor these potentially hazardous objects.

Recently, I sat down with Donald Yeomans, head of NASA's Near-Earth Object Program at the Jet Propulsion Laboratory in Pasadena, Calif., to discuss close encounters of the worst kind:

What is the mission of the Near-Earth Object Program?
The NASA goal is to discover 90% of the large, near-Earth objects [asteroids and comets] larger than 1 kilometer in diameter by the end of this year. There are more than 900 of them in the total population, we think. We've discovered about 80% of them to date.

Why 1 kilometer or larger objects?
The reason 1 kilometer [about the length of 10 football fields] was picked was because if one of those objects hit, it would be a global problem. Those kinds of hits happen only once every half a million years, but if one of those things should hit, it would be an explosive event on the order of 50,000 megatons of TNT. To put that in perspective, large nuclear weapons are around 3 megatons. It wouldn't bea civilization-ending event, but it would be catastrophicfor Third World countries and many of the economies of the world.

Any particular objects we should be worried about?
There's Apophis. It's about 270 meters in diameter, and it's going to make a very close approach to Earth on April 13, 2029. It turns out to be Friday the 13th. Very strange.

Great.
For a while there, we thought it had a chance of hitting Earth in 2029, but then, when we got additional data, we were able to rule out the 2029 impact. And there are at least two other asteroids heading our risk list.

How do we stop an object headed toward Earth?
If you find an object 20 or 30 years before it's going to hit the Earth, all you would need to do is run into it with a spacecraft and slow it downa millimeter per second or so and then it would miss the Earth in 20 or 30 years.

Where would be the safest place for an object to hit?
If it's a small object, it would be best to hit in the ocean or in an unpopulated area. If it's larger -- a kilometer or so -- then it doesn't really matter where it hits. It creates a global problem.

Do you ever freak out thinking about what might happen to Earth if we get hit?
No, actually, because I know we're doing something about it. It's the only natural disaster we can do something about. The Near-Earth Object Program is a fairly modest program within NASA ÐÐ it's only about $4 million a year, but it's a nice insurance policy.

Martin Mazloom last gave us a quiz about WD-40.