Search is on for killer asteroids

2004-04-16 12:18

Sydney - Astronomers scanning the universe for giant asteroids that could collide with earth have switched their search to the southern skies where they say they may find the biggest space rocks yet.

They are focussing on rogue asteroids which span more than a kilometre across and would cause massive, continent-wide devastation if they slammed into earth.

Two Australian astronomers have been recruited by Nasa to join the search for what the industry calls Near Earth Objects, or NEOs.

Rob McNaught and Gordon Garradd are using a refurbished 1950s telescope which is the only Nasa-sponsored probe to have a clear view of the southern sky.

They have already been rewarded for their efforts, finding three new asteroids in the first three weeks of the project, named the Siding Spring Survey after their observatory in the mountains of New South Wales state.

"We expect to find quite a few more," McNaught told AFP.

"The ones we've found are relatively small, there's a very large number of these smaller ones," he said.

'Large collisions might occur'

The asteroids located by the team measured between 100 metres and 300 metres across, were travelling at up to 18 kilometres a second and missed earth by between three and 20 million kilometres.

They pass through earth's orbit every year or two.

But it's the large NEOs that are worrying the astronomers most.

"Large collisions might occur every few million years or so but there's nothing to say they're not to going to happen in our lifetime," McNaught said.

It is thought by some experts that an asteroid spanning about 10 kilometres wiped out the dinosaurs when it plunged onto Mexico's Yukatan Peninsula 65 million years ago.

"Anything one kilometre or larger, it's not reasonable to expect humankind to survive unchanged," McNaught said. "Civilisation would be affected by such a collision."

"The global consequences would be in the form of dust thrown into the atmosphere, blanketing the atmosphere, blocking out the sun, affecting agriculture, acid rain and so on," McNaught said.

Colleague Garradd said the earthquake generated by the impact of a giant asteroid would destroy buildings over a large area and molten rock would set everything in its path alight.

Astronomers have already identified around 60% of the 1 000 large asteroids believed to orbit through earth's neighbourhood and none of those pose a threat to our planet.

If any of the remaining 400 are found to be on a collision course, McNaught said we would likely have decades to deal with the crisis.

"Although we have (Hollywood movie) Armageddon which portrays almost immediate impact, that's a very unlikely scenario," McNaught said.

"Typically there would be a long time scale to study the object more closely and decide what sort of technology would be required to do something about it," he said.

- AFP