[Source: NASA, Near Earth Object Program, full page: (LINK). Edited.]
"All Clear" Given on Potential 2040 Impact of Asteroid 2011 AG5
NASA/JPL Near-Earth Object Program Office / December 21, 2012
NASA scientists have announced that new observations of 2011 AG5 show that this asteroid, once thought to have a worrisome potential to threaten Earth, no longer poses a significant risk of impact. The orbital uncertainties of the 140m diameter near-Earth asteroid had previously allowed a 0.2% chance of collision in Feb. 2040, leading to a call for more observations to better constrain the asteroid's future course.
Answering the call, University of Hawaii astronomers Dave Tholen, Richard Wainscoat and Marco Micheli used the Gemini 8-meter telescope at Mauna Kea, Hawaii to successfully recover and observe the small and very faint asteroid on October 20, 21 and 27, 2012. In addition to improving our knowledge of the orbit, the Gemini observations also suggest the asteroid varies in brightness as it rotates and therefore may be elongated. Gemini is managed by the Association of Universities for Research in Astronomy (AURA). In addition to the Gemini measurements, Tholen, Micheli and Garrett Elliott obtained less conclusive observations on October 9 & 10 with the University of Hawaii 2.2-meter telescope, also situated on the summit of Mauna Kea. After extensive astrometric analysis by the team in Hawaii, all observations were then sent to the International Astronomical Union's Minor Planet Center in Cambridge, Massachusetts.
An analysis of the new data conducted by NASA's Near-Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena, California, shows that the risk of collision in 2040 has been eliminated. The updated trajectory of 2011 AG5 is not significantly different, but the new observations have reduced the orbit uncertainties by more than a factor of 60, meaning that the Earth's position in February 2040 no longer falls within the range of possible future paths for the asteroid. With the updated orbit, the asteroid will pass no closer than 890,000 km (over twice the distance to the moon) in Feb. 2040, the epoch of the prior potential collision.
Earlier in 2012, NASA's NEO Program Office conducted a contingency deflection analysis for the 2040 potential impact of 2011 AG5. Among the findings was that any new observations either in 2012, or in 2013 when the object will be much easier to observe, had a 95% likelihood of eliminating the hazard posed by 2011 AG5. If the potential for impact had been confirmed, the impact odds could have risen as high as 1 in 10, but the study released in May 2012 found that scenario to be unlikely. While the interest in 2011 AG5 has been reduced by the new results, the experience gained by studying this potential real-world deflection problem has demonstrated that NASA is well situated to predict the trajectories of Earth threatening asteroids.