[meteorite-list] 'All Clear' Given on Potential 2040 Impact of Asteroid 2011 AG5

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 21 Dec 2012 11:50:34 -0800 (PST)
Message-ID: <201212211950.qBLJoYqB006551_at_zagami.jpl.nasa.gov>

http://neo.jpl.nasa.gov/news/news176.html

"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 8.2-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.

[Graph of 2011 AG5's orbit prior to new position data]
[Graph of 2011 AG5's orbit after new position]
The position data obtained for near-Earth asteroid 2011 AG5 in October
2012 was used to update its orbit and dramatically reduce its future
orbital uncertainties in February 2040. In the first plot, the
asteroid's possible positions in space (region of uncertainty) prior to
the orbit improvement is an extremely lengthy arc that includes the
position of the Earth. Hence an Earth collision could not be ruled out.
However, the observational data in October 2012 allowed a sixty-fold
improvement in the 2040 region of uncertainty and the second plot shows
that this, now much smaller, arc no long includes the Earth. Hence an
Earth impact by 2011 AG5 in February 2040 is no longer possible.

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.
Received on Fri 21 Dec 2012 02:50:34 PM PST