MASSIVE ASTEROID TO HIT EARTH IN 2040?

-The 460 feet (140 meter) wide space rock may pose a hazard in 2040, so researchers are calling for deflection plan discussions.

-Asteroid 2011 AG5 was discovered in January 2011 by Mount Lemmon Survey astronomers in Tucson, Ariz.

-Although it is currently considered "high risk," we've only been watching it for half an orbit, so more observations are needed.

Scientists are keeping a close eye on a big asteroid that may pose an impact threat to Earth in a few decades. The space rock, which is called 2011 AG5, is about 460 feet (140 meters) wide. It may come close enough to Earth in 2040 that some researchers are calling for a discussion about how to deflect it.

Talk about the asteroid was on the agenda during the 49th session of the Scientific and Technical Subcommittee of the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS), held earlier this month in Vienna.

A UN Action Team on near-Earth objects (NEOs) noted the asteroid's repeat approaches to Earth and the possibility -- however remote -- that 2011 AG5 might smack into our planet 28 years from now.

The object was discovered in January 2011 by Mount Lemmon Survey observers in Tucson, Ariz. While scientists have a good bead on the space rock's size, its mass and compositional makeup are unknown at present.

An Asteroid Desktop Exercise

"2011 AG5 is the object which currently has the highest chance of impacting the Earth ... in 2040. However, we have only observed it for about half an orbit, thus the confidence in these calculations is still not very high," said Detlef Koschny of the European Space Agency's Solar System Missions Division in Noordwijk, The Netherlands.

"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," Koschny told SPACE.com.

Koschny added that the Action Team did recommend to the NEO Working Group of COPUOS to use 2011 AG5 as a "desktop exercise" and link ongoing studies to the asteroid.

"We are currently also in the process of making institutions like the European Southern Observatory aware of this object," Koschny said. "We hope to make the point that this object deserves the allocation of some special telescope time."

Non-Zero Impact Probability

The near-Earth asteroid 2011 AG5 currently has an impact probability of 1 in 625 for Feb. 5, 2040, said Donald Yeomans, head of the Near-Earth Object Observations Program at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

This impact probability isn't set in stone, however. So far, researchers have been able to watch the asteroid for just a short time -- the first nine months of 2011 -- and the numbers may change after further observation, Yeomans told SPACE.com.

"Fortunately, this object will be observable from the ground in the 2013-2016 interval," Yeomans said. In the very unlikely scenario that its impact probability does not significantly decrease after processing these additional observations, "there would be time to mount a deflection mission to alter its course before the 2023 keyhole," he added.

Keyholes are small regions in space near Earth through which a passing NEO's orbit may be perturbed due to gravitational effects, possibly placing it onto a path that would impact Earth.