NASA announced today that Asteroid 2011 AG5 is unlikely to hit Earth in 2040. However, if the asteroid passes through a “keyhole in space” in 2023, the chances that it could collide will rise astronomically. Further observations next year through 2016 will reassess the likelihood of a future catastrophe.
"While there is general consensus there is only a very small chance that we could be dealing with a real impact scenario for this object, we will still be watchful and ready to take further action if additional observations indicate it is warranted," said Lindley Johnson, program executive for the Near-Earth Object (NEO) Observation Program at NASA Headquarters in Washington.
Several years ago another asteroid, named Apophis, was thought to pose a similar impact threat in 2036. Additional observations taken from 2005 through 2008 enabled NASA scientists to refine their understanding of the asteroid's path, which showed a significantly reduced likelihood of a hazardous encounter.
"Any time we're able to observe an asteroid and obtain new location data, we're able to refine our calculations of the asteroid's future path," said Don Yeomans, manager of NASA's NEO Program Office at the Jet Propulsion Laboratory in Pasadena, Calif. "When few observations exist, our initial orbit calculation will include a wider swath to account for uncertainties. With more data points, the knowledge of the potential positions of the asteroid improves and the swath becomes smaller — typically eliminating the risk of an impact."
Observations of 2011 AG5 have been limited to date because of its present location beyond the orbit of Mars and in the daytime sky on the other side of the sun. In fall 2013, conditions will improve to allow space- and ground-based telescopes to better track the asteroid's path. At that time, 2011 AG5 will be 147 million kilometers from Earth but favorably located for observations in the late evening sky.
The level of hazard will gain even more clarity in 2023, when the asteroid is approximately 1.8 million kilometers from Earth. If 2011 AG5 passes through a 365-kilometer region in space called a keyhole in early February 2023, Earth's gravitational pull could influence the object's orbital path just enough to bring it back for an impact on February 5, 2040. If the asteroid misses the keyhole, an impact in 2040 will not occur.
"Given our current understanding of this asteroid's orbit, there is only a very remote chance of this keyhole passage even occurring," said Johnson.
Although scientists widely expect it to be a safe flyby, they acknowledge the slight chance that computed odds could rise as a result of observations to be taken from 2013 to 2016. According to experts, even if the odds do increase, there is still ample time to plan and carry out at least one of several viable missions to change the asteroid's course.