Eeeeeeeek - the sky is falling!!!!

Rogue asteroid heading our way
By Jeff Sommerfeld
December 27, 2004

HOLLYWOOD predictions of a rogue asteroid colliding with Earth and threatening life as we know it has become a real possibility according to a new warning from NASA.

NASA has issued its highest threat warning giving asteroid "2004 MN4" a rating of four on the 10-point Torino Scale used to rate intergalactic threats. The highest previous rating has been one.

The Torino Scale was set up by the International Astronomical Union after concern at too many cases of "crying wolf", where potentially dangerous asteroids were later shown to pose no risk to Earth.

Although the risk from 2004 MN4 was likely to be refined with further measurements, it had already been under observation for 187 days so astronomers were quite confident of their predictions.

The rating for 2004 MN4 means it will have a 1.6 per cent chance of colliding with Earth when it crosses paths on April 13, 2029.

Astronomy educator Paul Floyd said 2004 MN4 was first discovered in March 2004, but contact was lost until it was rediscovered on December 19.

Mr Floyd said it was about 440m in diameter and was significantly larger than many of the asteroids to collide with Earth in its recent history.

He said the danger the asteroid posed would depend on what it was composed of.

If it was a typical "stony type" as most asteroids are, much of it could just vaporise in the atmosphere.

If it was an iron type that remained intact as it passed through the atmosphere, 2004 MN4's size meant it could have an impact equivalent to between 100 to 150 hydrogen bombs.

However, he said it was unlikely to pose a "mass extinction event" such as the one which occurred 65 million years ago. On that occasion a gigantic rock collided with Earth resulting in dust clouds blotting out the sun, destroying most animal and plant life.

A more recent collision with Earth happened 20,000 years ago when an asteroid, 100m in diameter, landed in the US causing a crater one 1km across.

Even if it turns out to be a near miss, Mr Floyd said between now and 2079 there were at least 38 potentially hazardous close encounters.



http://www.news.com.au/common/story_page/0,4057,11787338%255E401,00.html