01 January 2010

Giant asteroid to pass earth at close range 270-metre rock will swing by in 2029 — and it could be back after that

from: http://www.thestar.com/news/sciencetech/article/744268--giant-asteroid-to-pass-earth-at-close-range
The head of Russia's space agency called on Wednesday for a massive planetary effort to deflect a massive asteroid as it skips by the Earth in 2029.

"People's lives are at stake," Anatoly Perminov told Voice of Russia radio. "We should pay several hundred million dollars and build a system that would allow us to prevent a collision, rather than sit and wait for it to happen and kill hundreds of thousands of people."
Perminov said that Russia will consider building a spacecraft designed to nudge the Apophis asteroid away from the Earth, and invited NASA, the European Space Agency and the Chinese space agency to join him.
The Apophis asteroid, the size of just under three football fields, was first spotted heading towards Earth five years ago. At that time, it was suggested that there was a 2.7 per cent chance it would strike our planet in 2029. That alarming initial estimate has been seriously downgraded since, but continues to hold the attention of expert observers.
Apophis will first pass us at close range in just under twenty years. It may graze the Earth, missing us by only 30,000 km, less than the distance between the earth and the moon. But, at this point, astronomers have ruled out the possibility that it will hit us.
However, there is a very small chance that it will pass through a 600 metre-wide "gravitational keyhole" as it swings by. That would alter the course of the rock and cause it to slingshot back and hit the Earth in 2036. New NASA calculations released in October put the chances of impact during the second pass at 1-in-250,000.
That doesn't sound too terribly alarming, but as Dr. William Ailor, of California's Aerospace Corporation said Wednesday, "That's a pretty high probability if you're betting the planet."
In April, Ailor chaired the bi-annual Planetary Defense Conference that brings together the world's leading asteroid experts.
"There are still issues around how great does the risk have to be before you start planning a mission like this. But ultimately, everyone agrees that we will have to do this sooner or later," Ailor said.
Prof. Donald K. Yeomans, manager of NASA's Near-Earth Object Program Office, says the time to make a decision on Apophis is in late 2012 and early 2013, when it makes another close approach, within about nine million miles of Earth.
"The additional optical and radar data taken then will almost certainly remove any possibility of an Earth collision in April 2036. To my mind it would make sense to wait until 2013, refine the orbit and in the very unlikely event that the impact probability increases, then begin planning possible deflection options.
"While Apophis is almost certainly not a problem, I am encouraged that the Russian science community is willing to study the various deflection options that would be available in the event of a future Earth threatening encounter by an asteroid. We haven't found one yet but it does make sense to study deflection options in advance."
A variety of deflection methods have been suggested in past: gravitational tractors, landing a manned mission on Apophis, knocking it off target by ramming it or striking it with nuclear weapons. There is no broad consensus on what might work best.
"There's also the question of how you design the 'campaign' to attack the asteroid. You'd probably have to launch multiple vehicles, in case some failed," Ailor said.
Five years ago, Ailor said, the Aerospace Corp. ballparked the cost of such a mission at $80 billion (U.S.). NASA's current annual budget is a little over $17 billion. Perminov, sounding less than expert on the whole subject, got the year of impact wrong (2032), couldn't cite the latest estimates accurately and seriously underestimated the potential cost. But he's right about the risk.
Ailor points out that the asteroid which exploded over Tunguska, Russia in 1908 was only 30 metres across. It devastated more than 2,000 square kilometres of forest. Apophis is 270 metres in diameter.
What if it hit the Earth directly?
"That'd be a very bad day," Ailor said. "Probably not the end of all life as we know it. But a bad day."

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