Approaching doom? The view from an asteroid as it hurtles toward earth, according to an artist's conception.

The Sky is Falling!

It's Friday the 13th, and a huge chunk of space rock is hurling towards Earth. A new Hollywood disaster movie? Not this time. Twenty-four years from now, a 320-meter wide asteroid known as 2004 MN4 will rapidly be closing in on our planet, carrying with it a potential impact of 15 hydrogen bombs. But don't build that spaceship yet. New evidence indicates that this disaster movie will have a happy ending.

When astronomers discovered 2004 MN4 in December, it was immediately clear that the object would have a close encounter with the Earth in 2029. Based on initial observations, NASA scientists estimated the probability of an impact at 2.7 percent. Days later, astronomers discovered older archived images of the asteroid, enabling them to calculate its orbit much more precisely and to rule out an impact. Now, radar observations from the giant, 300-meter radio telescope of Arecibo, Puerto Rico, made at the end of last month reveal for the first time how close the asteroid flyby will be.

The closest approach of 2004 MN4 to earth will occur at 30,000 kilometers above the surface, just below the orbits of many communications satellites, according to new orbital calculations announced on 4 February by the International Astronomical Union. To observers in Asia, Europe, and Africa, the asteroid will appear as a slow shooting star. Professional astronomers will have a unique opportunity to study an asteroid up close without the need for an expensive space probe.

"Out of all the asteroid close approaches we are able to predict with any degree of confidence, this is the closest," says to Paul Chodas of NASA's Jet Propulsion Laboratory in Pasadena, California. Chodas, who was part of the team that made the flyby calculations, notes that during the 2029 encounter, 2004 MN4 will be strongly tugged by Earth's gravity, making future orbital predictions difficult. In 2035, 2036, and 2037, the object will again visit our cosmic neighborhood, but the chances of impact are negligible, he says.

Which is not to say that Earth is safe, says David Morrison of NASA's Ames Research Center in Mountain View, California: "We could be struck at any time, without warning, by an asteroid hundreds of meters in diameter. Of course, the probabilities are low, but until we conduct a comprehensive survey of asteroids this small, we will not be able to predict the next such impact."

Related sites
Risk analysis for 2004 MN4
Arecibo Observatory