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Asteroid Apophis: Good News and Bad News


Apophis is 270 meters wide, approximately the size of three football fields. Observations by David Tholen on the UH 2.2-meter telescope are used to update orbit calculations.

IfA asteroid hunter David Tholen has some good news and some bad news for us. The good news is that the estimated probability of asteroid Apophis colliding with Earth in 2036 has been reduced from 1 chance in about 45,000 to 1 chance in about 250,000. The bad news is that the improved orbit determination for Apophis has revealed a new impact possibility in 2068.

The new estimates are based on an extensive set of observations obtained at Mauna Kea Observatories and analyzed by Tholen, former IfA postdoctoral researcher Fabrizio Bernardi (now at the University of Pisa, Italy), and current IfA graduate students Marco Micheli and Garrett Elliott.

 "Our new orbit solution shows that Apophis will miss Earth's surface in 2036 by a scant 20,270 miles, give or take 125 miles," Tholen said. "That's slightly closer to Earth than most of our communications and weather satellites." He credits the large telescopes and superb atmospheric conditions on Mauna Kea for being able to make these determinations.

With the possibility of an impact in 2068, Apophis will become the target of even more observations as soon as it reappears from behind the Sun in 2010 and beyond.

Apophis was discovered in 2004 by Tholen, Bernardi, and Roy Tucker of the University of Arizona. The asteroid became famous about six months later when additional observations indicated an impact probability as high as 1 chance in 37 on April 13, 2029 (coincidentally, a Friday). But prediscovery observations identified in data taken earlier in that year soon showed that the asteroid would miss Earth in 2029.

The improved orbit determination was presented at the annual meeting of the Division for Planetary Sciences of the American Astronomical Society held in Puerto Rico in early October.