Don't quit your job and sell your house just yet. Astronomers, who have been tracking the asteroid since January 2011, say it is in an elliptical orbit that could bring it somewhere near Earth in 2040. Earth is about 8,000 miles in diameter; the asteroid appears to be about 450 feet across.
The problem is that having watched it for only about half an orbit around the Sun, the scientists cannot say for certain where it will be 28 years from now. So, for the moment, NASA's Near Earth Object Program says the odds are about one in 625 that it could hit us in that still-distant future.
"We have a good opportunity to observe it next year and again in 2015," said Donald Yoemans, who heads the program at NASA's Jet Propulsion Laboratory. "We fully expect that the odds will go way down, most likely to zero, by then."
In the meantime, it was a subject of discussion at a meeting in Vienna of the Scientific and Technical Subcommittee of the United Nations Committee on the Peaceful Uses of Outer Space.
The committee members agreed that 2011 AG5 bears watching, and could be useful as the subject of a "tabletop exercise" in what to do if, anytime soon, there really is an asteroid with our name on it.
"In our Action Team 14 discussions, we thus concluded that it not necessarily can be called a 'real' threat. To do that, ideally, we should have at least one, if not two, full orbits observed," said Detlef Koschny of the European Space Agency in an interview with Space.com
Scientists have discussed all sorts of far-out plans in case a future asteroid truly does turn out to be coming our way. If they have enough lead time, they might send a probe with thruster rockets, or even explosives, to nudge an asteroid into a slightly different orbit. A very small course change, years in advance, could make a big difference by 2040, they say. Even if the asteroid misses Earth by less than a hundred miles, its passing will be a non-event.
There are asteroids wandering around the inner solar system all the time -- one of them, called 2005 YU55, passed within 201,000 miles of Earth in November, closer than the moon is to us.
But about half a dozen times since the planet formed, there have been major for-real impacts with catastrophic results. The last, 65 million years ago, is believed to have killed off the last of the dinosaurs with the dust and ash that darkened the skies after it hit, though there have been scientists who disagree.
Scientists estimate that the asteroid from back then was about nine miles across at its widest, far larger than 2011 AG5. And they point out that they know very little about 2011 AG5; they cannot say whether it is a solid hunk of rock or a loose jumble of debris flying together in space. All they know is that it's in a long, elliptical orbit that takes it almost twice as far from the sun as we are.
"The bottom line is: We have time," Yoemans said. "The sober approach is to make more observations, to wait and see."