New observations of asteroid Apophis, reported at the Division for Planetary Sciences meeting in Puerto Rico, indicate that the chances of its striking the Earth in 2036 must be recalculated, diminishing from roughly 1 in 45,000 to 1 in 250,000. There goes one disaster scenario, but enter another: An impact possibility exists for the year 2068. Says David Tholen (University of Hawaii):

“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. That’s slightly closer to Earth than most of our communications and weather satellites.”

Too close for comfort, but a miss is a miss. Apophis reappears from behind the Sun in 2010 and is sure to be the object of even more intense scrutiny in years to come. But bear in mind that, just as we were able to refine our figures for the 2029 and 2036 encounters, we will probably be able to reduce the 1 in 333,000 chance now calculated for Apophis to actually strike in 2068.

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Image: Asteroid Apophis will keep us occupied for some time in figuring out the chances it will strike the Earth at some future date. Perhaps more important, it serves as a reminder of the number of near-Earth objects we have yet to identify. Most of the data for the latest Apophis updates come from the University of Hawaii’s Institute for Astronomy in Manoa. Credit: UH/IA.

Remember that we’ve only known about this object since its 2004 discovery, and the subsequent finding that an impact probability (for April 13, 2029) existed caused a bit of a sensation before it was discounted. Now we’ve shoved Apophis back to 2068, but it continues to remind us that our catalog of Earth-crossing objects is anything but complete. Don Yeomans (JPL) notes that the Near-Earth Object Program Office at JPL offers a Twitter feed (@AsteroidWatch), or you can check the AsteroidWatch Web site.

Related: Also from the Division of Planetary Sciences meeting comes further word about the small asteroid 2008 TC3 that fell to Earth last year. This was the first asteroid to have been studied before it hit the Earth. Astronomers Marek Kozubal and Ron Dantowitz of the Clay Center Observatory (Brookline, MA) tracked the object for two hours just before impact. Peter Scheirich (Ondrejov Observatory, Czech Republic) and colleagues deduced that it was shaped like ‘a loaf of walnut raisin-bread.’

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Image: Artist’s conception of 2008 TC3 approaching the Earth. Credit: SETI Institute.

I do a lot of baking and my walnut-raisin bread isn’t shaped much different from my standard sandwich loaf, so I’m uncertain about the detail here. But it’s fascinating to learn from forensic evidence presented at the DPS session that fragments of 2008 TC3 are of a type called ‘polymict ureilite.’ The meteorites show traces of being heated to 1150-1300 degrees Celsius before cooling rapidly, a process in which carbon in the asteroid turned part of its olivine mineral iron into metallic iron. A SETI Institute news release explains the significance of this:

… asteroid 2008 TC3 is the remains of a minor planet that endured massive collisions billions of years ago, melting some of the minerals, but not all, before a final collision shattered the planet into asteroids.

The news release, by the way, is written by Peter Jenniskens, who traveled to the impact site in the Sudan to study the asteroid and retrieved numerous fragments. And this is interesting: Despite the torturous impacts — the carbon in these meteorites is the most ‘cooked’ of all known meteorites, and carbon crystals of graphite and nano-diamonds have been detected — some of the original organic material survived. Polycyclic aromatic hydrocarbons have turned up in abundance, and Michael Callahan and colleagues (NASA GSFC) reported that they even found traces of surviving amino acids.

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