[meteorite-list] Comet Collision 'Armageddon' Unlikely

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Sep 8 11:52:08 2005
Message-ID: <200509081544.j88FioI05204_at_zagami.jpl.nasa.gov>

http://www.mso.anu.edu.au/news/media_releases/media_release_050907.php

Comet collision 'Armageddon' unlikely

But odds greater than winning Lotto jackpot, ANU astronomer finds
Australian National University
September 7, 2005

The chances of the Earth being hit by a comet from beyond Pluto - a la
Armageddon - are much lower than previously thought, according to new
research by an ANU astronomer.

Using computer simulations and data from an American military telescope,
Dr Paul Francis, from the ANU Research School of Astronomy and
Astrophysics at Mt Stromlo, has found there are seven times fewer comets
in our solar system than previously thought.

'I calculate that small comets, capable of destroying a city, only hit
the Earth once every 40 million years or so," Dr Francis said. "Big
continent-busting comets, as shown in the movies Armageddon and Deep
Impact, are rarer still, only hitting once every 150 million years or
so. So I don't loose sleep over it, but you're still more likely to be
killed by a comet than to win the jackpot at Lotto."

Previous estimates of the number of comets were based on the work of
amateur astronomers, who for hundreds of years have been scanning the
skies, looking for new comets.

Previously, it was believed that these amateur astronomers were only
spotting three per cent of the comets passing close to the Earth: the
rest were thought to be missed because they were in the wrong part of
the sky or were too faint.

But Dr Francis found that the amateurs were doing better than anyone had
realised - they were actually spotting 20 per cent of comets. There are
therefore far fewer undiscovered comets.

"The new data allowed us to count the number of faint and far-away
comets that the amateurs had missed. And we found that they were pretty
rare," Dr Francis said.

These results apply to comets coming from beyond the orbit of Pluto,
which is where most comets live. The Earth is still at risk of being hit
by asteroids, and by so-called short-period comets - ones that come past
repeatedly, like Halley's comet.

"But asteroids and short-period comets come past again and again, so if
we're clever enough we can find them all and predict which, if any, will
hit the Earth," said Dr Francis. "If we find one on a collision course
with the Earth, we would normally have hundreds of years warning in
which to do something about it, like deflecting the asteroid.

"The comets coming from beyond Pluto, so called long-period comets, are
nastier, as they are totally unpredictable, and if we see one on a
collision course we'd have at best one or two years warning - not long
enough to do anything."

Dr Francis' research has been accepted for publication in the
Astrophysical Journal. It was based on computer simulations, published
data from the Lincoln Near Earth Asteroid Research Project at White
Sands Missile Range in New Mexico, and on data from amateur astronomers
around the world.

Further Information

Background material on Dr Francis' research

http://www.mso.anu.edu.au/~pfrancis/comets/
Received on Thu 08 Sep 2005 11:44:50 AM PDT