Image: 2011 AG5
Gemini Observatory
Asteroid 2011 AG5, highlighted in this photo with a yellow circle, is not on a collision course with Earth in the year 2040, scientists say. Earlier this year, experts had said there was a 1-in-500 chance of a collision.
updated 12/26/2012 7:34:42 PM ET 2012-12-27T00:34:42

A new study confirms that a huge asteroid will pass harmlessly by Earth in 28 years.

New observations of the asteroid 2011 AG5 now give astronomers complete confidence that the 460–foot-wide (140-meter-wide) space rock won't hit Earth in the year 2040. When it was discovered last year, scientists said that 2011 AG5 had a 1-in-500 chance of impact with our planet.

Astronomers solidified the asteroid's harmless status during an observation campaign in October, using the Gemini North telescope in Hawaii. The finding added more support to a NASA study that came to a similar conclusion in June based on months of observations of asteroid 2011 AG5.

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The researchers behind the latest study say the asteroid shouldn't get any closer than 550,000 miles (890,000 kilometers) — about twice the distance between Earth and the moon.

"These were extremely difficult observations of a very faint object," the University of Hawaii's Richard Wainscoat, a member of the team of researchers monitoring 2011 AG5, said in a statement. "We were surprised by how easily the Gemini telescope was able to recover such a faint asteroid so low in the sky."

Just because it is a large asteroid doesn't mean it's easy to see, scientists said. Researchers used the Gemini North to photograph the asteroid three times in October.

NASA astronomers and other scientists regularly monitor the sky for asteroids that could pose a potential impact threat to Earth. About 9,000 such near-Earth asteroids have been discovered to date, though up to a million or more could exist, NASA scientists say.

Nearly 95 percent of the largest near-Earth asteroids, those larger than 1 kilometer (0.6 miles) in size, have been identified, NASA scientists say. The space agency's Asteroid Watch program to monitor nearby space rocks is based at the Jet Propulsion Laboratory in Pasadena, Calif.

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