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Image: Asteroid encounter
P. Carril / ESA
Asteroids zip past Earth in this artist's conception. If an asteroid known as 2011 AG5 happens to pass through a particular region of space called a "keyhole" in 2023, it would be on track to hit Earth during a later encounter in 2040.
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updated 2/27/2012 1:52:39 PM ET 2012-02-27T18:52:39

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, or COPUOS, held earlier this month in Vienna.

A UN Action Team on near-Earth objects 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.

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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. [The 7 Strangest Asteroids in the Solar System]

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 the Dutch city of Noordwijk.

"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. [Photos: Asteroids in Deep Space]

"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.

Prudent course of action
2011 AG5 may zip through such a keyhole on its close approach to Earth in February 2023, which will bring the asteroid within 0.02 astronomical units (1.86 million miles, or 2.99 million kilometers) of Earth.

One astronomical unit is the average distance between Earth and sun, which is approximately 93 million miles (150 million kilometers).

According to a JPL estimate, the 2023 keyhole — through which 2011 AG5 must pass in order for there to be a real chance of an Earth impact in 2040 – is roughly 62 miles (100 kilometers) wide.

"Although this keyhole is considerably larger than the Apophis keyhole in 2029, it would still be a straightforward task to alter the asteroid’s trajectory enough to miss the keyhole – and hence the impact in 2040," Yeomans noted, referring to the asteroid Apophis, which could threaten Earth in 2036 if it zips through a keyhole in 2029.

"The prudent course of action is then to wait at least until the 2013 observations are processed before making any preliminary plans for a potential deflection mission," Yeomans said.

Processing additional observations in the 2013-2016 time period, he added, "will almost certainly see the impact probability for 2011 AG5 significantly decrease."

Further observations
"Yes, the object 2011 AG5 was much discussed at the AT 14 meetings last week, but perhaps prematurely," said Lindley Johnson, NASA’s NEO Observations Program Executive in Washington.

Johnson said NEO watchers have flagged the asteroid "as one we should keep an eye on." At present, he said, while researchers have better preliminary orbit data for 2011 AG5 than for many other asteroids in the NEO catalog, "we have only medium confidence in the derived orbital parameters."

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"Fortunately, we are confident our uncertainties in the current orbit model will be reduced when we will have good observation opportunities in September 2013 with the larger follow-up assets," Johnson told Space.com. Observing opportunities are even better, he added, starting in November 2015 and for several months thereafter.

"This, in turn, will enable us to better assess the likelihood of any 'keyhole' passage in 2023 and therefore a much higher fidelity assessment of any impact probability for the 2040 time frame," Johnson said. [5 Reasons to Care About Asteroids]

"So, rather than a need to immediately jump to space mission solutions, the situation with 2011 AG5 shows the value of finding potentially hazardous objects early enough so that there is time for a methodical approach of observation and assessment as input to any need for an expensive spacecraft mission," Johnson said. "A more robust survey capability would improve the data available to make such assessments."

Decision challenge
Longtime NEO specialist and former Apollo astronaut Russell Schweickart played an active role in the dialogue about 2011 AG5. He represented the Association of Space Explorers Committee on Near Earth Objects and presented to the Action Team an analysis of the situation with 2011 AG5.

The space rock presents a "decision challenge" to the international community, Schweickart suggested, "in the unlikely chance that its current low, but significant probability of impacting Earth in 2040 continues to increase after additional tracking becomes available."

Schweickart spotlighted a rough Association of Space Explorers analysis of the options to deflect the asteroid in the future, in the unlikely scenario that the Earth impact probability continues to increase.

He also provided to the Action Team several new appraisals of options for deflection of asteroid 2011 AG5 to avoid a potentially dangerous Earth encounter in 2040.

Delayed deflection campaign
A strategy for keyhole deflection should be drawn up very soon, if not now, Schweickart suggested. Asteroid 2011 AG5 represents an actual threat that underscores the need for a NEO hazard decision-making structure within the UN COPUOS, he said.

Based on the latest analysis, Schweickart reported, a deflection campaign delayed until after the 2023 close approach appears marginally possible, as long as a decision to commit is made immediately thereafter.

In the low-probability case in which the impact threat of the asteroid persists beyond its 2013 apparition, "should a keyhole deflection campaign be forgone — for whatever reason — the international community may be faced with the difficult decision of choosing between an expensive multikinetic impactor or a nuclear explosive to prevent an impact should the NEO indeed pass through the keyhole," Schweickart said.

The timelines that would be required to mount a successful deflection of the asteroid, Schweickart told Space.com, might be challenging. 

But first things first: Researchers stress that more study of the asteroid’s trajectory is called for. The next tracking opportunities of 2011 AG5 will occur in September 2013, and then again in November 2015.

NASA chief: We still have time
In response to a letter from Schweickart regarding 2011 AG5, NASA Administrator Charles Bolden said that 2011 AG5 is "high on NASA’s list of NEOs to monitor for impact hazard potential." Bolden added that "we take these duties very seriously.".

Bolden also noted the opportunities for highly accurate ground-based observations in the near future.

"Based on these observations, a more informed assessment can then be made on the need for any type of mitigation," he said.

Bolden also remarked that the asteroid makes an apparition in 2015, more than seven years before the close keyhole passage in 2023 that could set in motion an Earth impact in the 2040 time frame.

"As a point of comparison, NASA’s Deep Impact mission [which smashed a probe into Comet Tempel 1 in 2005] was conducted in six years from selection to impact under much less urgency, demonstrating the adequacy of a seven-year period for any necessary response," Bolden said.

Leonard David has been reporting on the space industry for more than five decades. He is a winner of last year's National Space Club Press Award and a past editor-in-chief of the National Space Society's Ad Astra and Space World magazines. He has written for Space.com since 1999.

© 2013 Space.com. All rights reserved. More from Space.com.

Interactive: Below the belt

Photos: Month in Space: January 2014

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  1. Southern stargazing

    Stars, galaxies and nebulas dot the skies over the European Southern Observatory's La Silla Paranal Observatory in Chile, in a picture released on Jan. 7. This image also shows three of the four movable units that feed light into the Very Large Telescope Interferometer, the world's most advanced optical instrument. Combining to form one larger telescope, they are greater than the sum of their parts: They reveal details that would otherwise be visible only through a telescope as large as the distance between them. (Y. Beletsky / ESO) Back to slideshow navigation
  2. A balloon's view

    Cameras captured the Grandville High School RoboDawgs' balloon floating through Earth's upper atmosphere during its ascent on Dec. 28, 2013. The Grandville RoboDawgs’ first winter balloon launch reached an estimated altitude of 130,000 feet, or about 25 miles, according to coaches Mike Evele and Doug Hepfer. It skyrocketed past the team’s previous 100,000-feet record set in June. The RoboDawgs started with just one robotics team in 1998, but they've grown to support more than 30 teams at public schools in Grandville, Mich. (Kyle Moroney / AP) Back to slideshow navigation
  3. Spacemen at work

    Russian cosmonauts Oleg Kotov, right, and Sergey Ryazanskiy perform maintenance on the International Space Station on Jan. 27. During the six-hour, eight-minute spacewalk, Kotov and Ryazanskiy completed the installation of a pair of high-fidelity cameras that experienced connectivity issues during a Dec. 27 spacewalk. The cosmonauts also retrieved scientific gear outside the station's Russian segment. (NASA) Back to slideshow navigation
  4. Special delivery

    The International Space Station's Canadian-built robotic arm moves toward Orbital Sciences Corp.'s Cygnus autonomous cargo craft as it approaches the station for a Jan. 12 delivery. The mountains below are the southwestern Alps. (NASA) Back to slideshow navigation
  5. Accidental art

    A piece of art? A time-lapse photo? A flickering light show? At first glance, this image looks nothing like the images we're used to seeing from the Hubble Space Telescope. But it's a genuine Hubble frame that was released on Jan. 27. Hubble's team suspects that the telescope's Fine Guidance System locked onto a bad guide star, potentially a double star or binary. This caused an error in the tracking system, resulting in a remarkable picture of brightly colored stellar streaks. The prominent red streaks are from stars in the globular cluster NGC 288. (NASA / ESA) Back to slideshow navigation
  6. Supersonic test flight

    A camera looking back over Virgin Galactic's SpaceShipTwo's fuselage shows the rocket burn with a Mojave Desert vista in the background during a test flight of the rocket plane on Jan. 10. Cameras were mounted on the exterior of SpaceShipTwo as well as its carrier airplane, WhiteKnightTwo, to monitor the rocket engine's performance. The test was aimed at setting the stage for honest-to-goodness flights into outer space later this year, and eventual commercial space tours.

    More about SpaceShipTwo on PhotoBlog (Virgin Galactic) Back to slideshow navigation
  7. Red lagoon

    The VLT Survey Telescope at the European Southern Observatory's Paranal Observatory in Chile captured this richly detailed new image of the Lagoon Nebula, released on Jan. 22. This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. This image is a tiny part of just one of 11 public surveys of the sky now in progress using ESO telescopes. (ESO/VPHAS team) Back to slideshow navigation
  8. Fire on the mountain

    This image provided by NASA shows a satellite view of smoke from the Colby Fire, taken by the Multi-angle Imaging SpectroRadiometer aboard NASA's Terra spacecraft as it passed over Southern California on Jan. 16. The fire burned more than 1,863 acres and forced the evacuation of 3,700 people. (NASA via AP) Back to slideshow navigation
  9. Where stars are born

    An image captured by NASA's Spitzer Space Telescope shows the Orion Nebula, an immense stellar nursery some 1,500 light-years away. This false-color infrared view, released on Jan. 15, spans about 40 light-years across the region. The brightest portion of the nebula is centered on Orion's young, massive, hot stars, known as the Trapezium Cluster. But Spitzer also can detect stars still in the process of formation, seen here in red hues. (NASA / JPL-Caltech) Back to slideshow navigation
  10. Cygnus takes flight

    Orbital Sciences Corp.'s Antares rocket rises from NASA's Wallops Flight Facility on Wallops Island, Va, on Jan. 9. The rocket sent Orbital's Cygnus cargo capsule on its first official resupply mission to the International Space Station. (Chris Perry / NASA) Back to slideshow navigation
  11. A long, long time ago...

    This long-exposure picture from the Hubble Space Telescope, released Jan. 8, is the deepest image ever made of any cluster of galaxies. The cluster known as Abell 2744 appears in the foreground. It contains several hundred galaxies as they looked 3.5 billion years ago. Abell 2744 acts as a gravitational lens to warp space, brightening and magnifying images of nearly 3,000 distant background galaxies. The more distant galaxies appear as they did more than 12 billion years ago, not long after the Big Bang. (NASA / NASA via AFP - Getty Images) Back to slideshow navigation
  12. Frosty halo

    Sun dogs are bright spots that appear in the sky around the sun when light is refracted through ice crystals in the atmosphere. These sun dogs appeared on Jan. 5 amid brutally cold temperatures along Highway 83, north of Bismarck, N.D. The temperature was about 22 degrees below zero Fahrenheit, with a 50-below-zero wind chill.

    Slideshow: The Year in Space (Brian Peterson / The Bismarck Tribune via AP) Back to slideshow navigation
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