Today, space rocks are being taken seriously.

No matter how remote, the danger from celestial objects is gradually prompting an international response, unlocking resources and setting the basis for a coordinated planetary defence against a faceless enemy.

Dozens of observatories around the world now scour the skies nightly for any threat from space. The United States has a dedicated deep-space telescope on asteroid duty, and Japan is building one. The British government last week set up a three-man task force to evaluate any peril from the skies.

Each day, several thousand tonnes of cosmic debris fall to Earth, says Jean-Eudes Arlot, director of the Institute of Celestial Mechanics at the Paris Observatory.

Most of it consists of minute specks of dust released from passing comets, or fragments of asteroids that smashed into each other millions of years ago.

Objects of this size are harmless. Larger ones, about the size of a pebble, provide an entertaining "shooting star," burning up from friction with the Earth's atmosphere.

What worries space watchers are the bigger celestial wanderers -- brutes that measure several metres (yards) or more and race through the heavens at up to 30 kilometers (20 miles) per second.

As was shown in 1994, when the tail of the comet Shoemaker-Levy 9 rammed dramatically into Jupiter, these release catastrophic energy on impact.

An asteroid or comet measuring at least a kilometer (half a mile) that slammed into Mexico's Yucatan peninsula around 65 million years ago is believed to have caused the dinosaurs to die out.

It unleashed a firestorm and kicked up such huge volumes of dust that vegetation could no longer get adequate light from the Sun. Plants withered, and the impact resounded up the food chain.

Scientists agree that the risk of doomsday is very remote.

Yet every 100 years or so an object measuring 50 metres (165 feet) smacks into the Earth, inflicting local devastation, according to NASA's Jet Propulsion Laboratory (JPL).

A comet about 60 metres (200 feet) wide exploded over Siberia in 1908 with a force the equivalent of 600 times the Hiroshima bomb, reducing a 40-kilometer (25-mile wide) patch of forest to matchwood.

Cities the size of London or New York would be reduced to cinders by such an impact. If the object hit the sea, it could trigger a giant tidal wave, swamping low-lying areas.

The good news is that resources, ideas and organisation are quickly improving mankind's knowledge of the threat.

Governments are allocating more and more funds, equipment and personnel to monitor the skies. Data and watch duties are being shared among astronomers and space agencies through a loose cooperative effort, Spaceguard Foundation.

An international measurement of risk assessment, called the Torino Scale, was agreed last year. The International Astronomical Union (IAU), based in Paris, has been placed in charge of vetting any warning to ensure the size of the danger and avoid any false alarm.

Big technical strides are also being made.

In less than two years, a deep space telescope operating at the White Sands Missile Range in New Mexico has discovered more than 200 of the 700 or so known Near-Earth Objects (NEO), as these dangerous itinerants are called.

A second large telescope is scheduled to start operating at the same site.

"It'll be another 10 or 15 years before we've detected most objects more than a kilometer across," says Hans Rickman, the IAU's deputy secretary-general.

"Enormous progress has been made in plotting the trajectories of NEOs," says Arlot.

"Ten years ago, the margin of error would have been in the thousands of kilometers, up to 10,000 kilometers (6,000 miles).

"Today, that margin is several dozen kilometers (miles), mainly thanks to satellite technology that uses the stars as a measuring point when the asteroid passes near by."

That sort of finessing is vital.

It helped to tone down a scare about the the most dangerous identified NEO -- a kilometer- (half-mile) -sized asteroid, 1999 AN10, which is due to skim past the Earth on August 7, 2027.

The latest arithmetic says 1999 AN10 could run as close as 37,000 kms (19,000 miles) -- but no closer -- to the Earth.

"The probability of a collision in 2027 is essentially zero," JPL's NEO Program says.

But, it adds, there is "about one chance in 10 million" that the asteroid will hit the Earth when it returns on its orbit around the Sun in 2039.

Such observations could give the Earth years of warning about impending danger.

Yet what could be done if the alarm sounded?

Experts caution against Hollywood heroics of blasting the asteroid into smithereens with nuclear bombs, as this could merely cause it to split into chunks that could rain down over a larger area.

"It could be possible to land a probe on to it and use solar power to nudge it out of its orbit," said Arlot.

"But the interception would have to be done over a great distance and the operation would have to be unfold over several months or years. In theory, it's possible, but at the moment, despite the progress, that remains in the realm of science fiction."

The Torino Scale Asteroid and Comet Impact Hazard Predictions in the 21st Century Events Having No Likely Consequences 0 The likelihood of a collision is zero or well below the chance that a random object of the sale size will strike the Earth within the few decades. This designation also applies to any small object that, in the event of a collision, is unlikely to reach the Earth surface intact. Events Meriting Careful Monitoring 1 The chance of collision is extremely unlikely, about the same as a random object of the same size striking the Earth within the next few decades. 2 A somewhat close, but not unusual encounter. Collision is very unlikely. Events Meriting Concern 3 A close encounter, 1% or greater chance of a collision capable of causing localized destruction. 4 A close encounter, 1% or greater chance of a collision capable of causing regional destruction. 5 A close encounter, with a significant threat of a collision capable of causing regional devastation. Threatening Events 6 A close encounter, with a significant threat of a collision capable of causing global catastrophe. 7 A close encounter, with a extremely significant threat of a collision capable of causing global catastrophe. 8 A collision capable of causing localized destruction. Such events occur somewhere on Earth between once per 50 years and once per 1000 years. Certain Collisions 9 A collision capable of causing regional devastation. Such events occur somewhere between once per 1000 years and once per 100,000 years. 10 A collision capable of causing a global climatic catastrophe. Such events occur somewhere once per 100,000 years or less often. HTML Chart Copyright SpaceDaily.com

SPACE SCIENCE
The Solar Trojans of Earth
London - October, 26 1999 - We will never see it but the Earth has at least one other natural satellite. In discovering several new types of orbital motion, a team of British scientists has shown that the gravitational forces of our planet and of the Sun allow our planet to capture passing asteroids. One of them is named 'Cruithne', and can be considered -- at least for the next 5000 years -- as 'Earth's second Moon'.