Small Comets Bring Big Trouble -- U.S. scientists

ALBUQUERQUE, N.M., April 16 (Reuter) - A small comet slamming into earth would cause tidal waves as high as New York's World Trade Centre and climate changes that could wipe out world agriculture, according to a computer simulation unveiled on Wednesday.

Under the model, developed by scientists at Sandia National Laboratories in New Mexico, a half-mile (1 km) wide comet -- smaller than the Hale-Bopp comet now passing by Earth -- would destroy anything within 60 to 120 miles (96 to 192 km) of the impact point and could bring on a nuclear winter.

``Something of this size could potentially kill a billion people,'' said Mark Boslough, one of the Sandia scientists who worked on the simulation. He said it was the first realistic computer simulation ever of a comet impact.

The Hale-Bopp comet is about 24 miles (40 km) in diameter, but even a small comet like that in the simulation would hit Earth with the power of 30,000 megatons, or about 10 times the power of all nuclear weapons on earth at the height of the arms race, Boslough said.

Those killed by tidal waves from an ocean impact would probably be the lucky ones. Most people would die of starvation as dust or water vapour rose into the atmosphere, shrouding the sun, he said.

``A lot of people would die a slow death just like a lot of dinosaurs died 65 million years ago,'' said Boslough.

Scientists are working to identify any space objects that could approach Earth and to determine when one could slam into the planet. The hope is that some kind of defence system could be built to deflect comets or asteroids.

``If we have enough time, say 50 years, we can do something about it,'' said Boslough.

But right now, he said, no technology existed that could turn away a speeding comet.