London Observer 
Monday, Dec 08, 2008
A group of the world’s leading scientists has urged the United Nations to establish an international network to search the skies for asteroids on a collision course with Earth. The spaceguard system would also be responsible for deploying spacecraft that could destroy or deflect incoming objects.
The group – which includes the Royal Society president Lord Rees and environmentalist Crispin Tickell – said that the UN needed to act as a matter of urgency. Although an asteroid collision with the planet is a relatively remote risk, the consequences of a strike would be devastating.
An asteroid that struck the Earth 65 million years ago wiped out the dinosaurs and 70 per cent of the species then living on the planet. The destruction of the Tunguska region of Siberia in 1908 is known to have been caused by the impact of a large extraterrestrial object.
‘The international community must begin work now on forging three impact prevention elements – warning, deflection technology and a decision-making process – into an effective defence against a future collision,’ said the International Panel on Asteroid Threat Mitigation, which is chaired by former American astronaut Russell Schweickart. The panel made its presentation at the UN’s building in Vienna.
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The risk of a significantly sized asteroid – defined by the panel as being more than 45 metres in diameter – striking the Earth has been calculated at two or three such events every 1,000 years, a rare occurrence, though such a collision would dwarf all other natural disasters in recent history.
The panel added that developments in telescope design mean that, by 2020, it should be possible to pinpoint about 500,000 asteroids in orbit round the Sun and study their movements. Of these, several dozen will be revealed to pose threats to Earth, the panel added.