Thursday, October 8, 2009
US space agency Nasa has sharply downgraded the threat that a massive asteroid could slam into Earth in 2036.
Apophis was discovered in 2004 and is two-and-a-half times the size of an American football field.
It captured widespread attention after calculations suggested it might pose a threat to the planet.
There is now a one-in-250,000 chance of a collision with Earth in 2036, according to new calculations by Nasa's Jet Propulsion Laboratory (JPL) in California.
This was sharply down from an earlier estimate of a one-in-45,000 chance.
At first, astronomers feared the 885ft (270-metre) asteroid had a 2.7% chance of colliding with Earth in 2029.
Later calculations ruled out a collision in that year, leaving 2036 as the encounter posing the greatest danger.
Apophis is now expected to sail about 18,300 miles (29,450km) above Earth's surface on April 13, 2029 - closer than some satellites.
Even though scientists are certain it will not hit the Earth, the Los Angeles Times said they are less sure about how the close approach will affect the asteroid's orbit.
"The deflection caused by the 2029 encounter will be significant," Steve Chesley, of JPL's Near-Earth Object Programme office, told the paper.
"We're not worried about 2029. We're worried about its future trajectory."
JPL is to present its results at the conference of the American Astronomical Society in Puerto Rico on October 8.
"The refined orbital determination further reinforces that Apophis is an asteroid we can look to as an opportunity for exciting science and not something that should be feared," Near-Earth office manager Don Yeomans said.
Sumber: Yahoo. (http://uk.news.yahoo.com/5/20091008/...r-3fd0ae9.html)