Monday, December 31, 2007

Mars Impact Probability Increases to 4 Percent

Don Yeomans, Paul Chodas and Steve Chesley
NASA/JPL Near-Earth Object Program Office
December 28, 2007

The impact probability for a collision of asteroid 2007 WD5 with Mars on January 30 has increased from 1.3% to 3.9%.

Pre-discovery observations of asteroid 2007 WD5, taken on November 8, 2007 have allowed its orbit to be refined and the uncertainties for the late January Mars encounter have been improved. The impact probability resulting from the recent orbit refinement has increased to a surprising 3.9% (about 1 in 25 odds). The uncertainty region during the Mars encounter now extends over 400,000 km along a very narrow ellipsoid that is only 600 km wide. Since the uncertainty region intersects Mars itself, a Mars impact is still possible. However, the most likely scenario is that additional observations of the asteroid will allow the uncertainty region to shrink so that a Mars impact is ruled out. In the unlikely event of an impact, the time would be 2008 January 30 at 10:56 UT (2:56 a.m. PST) with an uncertainty of a few minutes.

The current position of asteroid 2007 WD5, with its orbit shown in blue

The current position of asteroid 2007 WD5, with its orbit shown in blue.
The asteroid's orbit stretches from just outside the Earth's orbit at its
closest point to the Sun, to the outer reaches of the asteroid belt at its

Updated Uncertainty region at closest approach to Mars

Updated Uncertainty Region for 2007 WD5 at encounter with Mars, shown as white dots.
The thin white line is the orbit of Mars. The blue line traces the motion of
the center of the uncertainty region, which is the most likely position of
the asteroid.

The pre-discovery observations were located by Andy Puckett, a recent Ph.D. from the University of Chicago who has since moved to the University of Alaska Anchorage. Dr. Puckett located the observations in the archive of the Sloan Digital Sky Survey II, which contains extensive repeat coverage of 300 square degrees along the sky's celestial equator. The observations were taken using a 2.5 meter aperture telescope at the Apache Point Observatory near Cloudcroft, New Mexico. For the recent orbit refinement, these pre-discovery observations on November 8 were added to the existing observations provided by the Catalina Sky Survey and Spacewatch observatories (both near Tucson AZ) as well as New Mexico Tech's Magdalena Ridge Observatory.
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