Near-Earth objects dangerous, general says

Could a stray one of these start a nuclear exchange

By Dr David Whitehouse BBC News Online science editor

This summer, as India and Pakistan faced-off over the disputed Kashmir region, US early warning satellites detected an explosion in the Earth's atmosphere with an energy of 12 kilotonnes of explosive.

The detonation, equivalent to the blast that destroyed Hiroshima, fortunately occurred over the Mediterranean Sea.

But according to US Brig Gen Simon Worden, if it had occurred at the same latitude a few hours earlier, the result could have been much worse.

Had the explosion occurred over India or Pakistan, the resulting panic could have sparked a nuclear war, Worden says.

Could have killed millions

Although US scientists quickly determined that a meteor caused the explosion, neither India nor Pakistan have the sophisticated sensors that can tell the difference between a natural near-Earth object impact and a nuclear detonation, Worden says.

"This is one of many threats posed by Near Earth Objects (Neo's) especially as more and more nations acquire nuclear weapons," he warns.

More warning needed

In recent years, the US Department of Defense has been providing data about asteroid strikes to nations potentially under missile attack. However, it takes several weeks for the data to be released since much of it is gathered from classified sources.

Worden suggests that a Neo warning centre be established that can assess and release this data to all parties while ensuring sensitive data is safeguarded.

"Just about everyone knows of the 'dinosaur killer' asteroids," Worden says. "These are objects, a few kilometres across, that strike on time scales of tens of millions of years."

Worden: Focus our energies

"While the prospect of such strikes grabs people's attention and makes great catastrophe movies, too much focus on these events has been counterproductive. We need to focus our energies on the smaller, more immediate threats."

The smaller strikes, while not exactly commonplace, have occurred on several occasions over the past century, with potentially devastating results, he said.

"An object probably less than 100 metres in diameter struck Tunguska in Siberia in 1908, releasing the energy equivalent to a 10-megaton nuclear blast," says Worden.

"In 1996, our satellite sensors detected a burst over Greenland equal to a 100-kiloton yield. Had any of these struck over a populated area, perhaps hundreds of thousands might have perished.

"We know the orbits of just a few. New space-surveillance systems capable of scanning the entire sky every few days are needed."

"I believe various aspects related to Neo impacts, including the possibility that an impact would be misidentified as a nuclear attack, are critical national and international security issues," he adds.