Asteroid 2008 TC3 is surely a sign of progress. The eighty ton asteroid, which made a spectacle of itself upon entry into Earth’s atmosphere on the morning of October 7, 2008, was the first space rock to have been observed before it collided with our planet. What we’re hoping, of course, is that any future objects headed our way will be spotted early enough that, if their size warrants, they can be diverted or destroyed.
It was thought that 2008 TC3 did a good job of destroying itself when it exploded some 37 kilometers above the Nubian desert, but two researchers recently traveled to the Sudan and, with help from students at the University of Khartoum, collected 280 pieces of asteroid over a 29-kilometer field. Peter Jenniskens (SETI Institute) calls the event “…an extraordinary opportunity, for the first time, to bring into the lab actual pieces of an asteroid we had seen in space.” Jenniskens is lead author on the paper that now appears as the cover on the latest Nature.
I mention the significance of detecting objects early, but this one is a reminder of how tough the challenge is, being detected by the Catalina Sky Survey a mere twenty hours before its explosive arrival. We’re going to need longer lead times than that in the event of future emergency, but of course 2008 TC3 was also a tiny object, roughly the size of a truck. It’s also interesting in its own right, as an analysis of its debris shows. So-called F-class asteroids like this one have never before yielded a sample that could be studied in the laboratory. Now it’s giving out potentially useful secrets.
The meteorites it produced — called polymict ureilites — are porous, dark and rich in carbon. Nature is running a gripping account of the fall of 2008 TC3 by Roberta Kwok in the same issue as the Jenniskens paper, from which this snip about the composition of the meteorite:
Jenniskens couriered a sample to Mike Zolensky, a cosmic mineralogist at the NASA Johnson Space Center in Houston, Texas. Examining the rock, Zolensky discovered that it contained large chunks of carbon and glassy mineral grains resembling sugar crystals. Tests at other labs confirmed that the sample was a ureilite, a type of meteorite thought to come from asteroids that have melted during their time in space. Only 0.5% of objects that hit Earth yield fragments in this category. But 2008 TC3’s pieces are strange even for ureilites: they are riddled with an unusually large number of holes, says Zolensky. “It boggles the mind that something that porous could survive as a solid object,” he says.
Mind boggling indeed. And the behavior of 2008 TC3 is also a potent indicator that these meteorites are the fragments of a fragile parent. 2008 TC3’s high-altitude explosion shows that any future F-class asteroid on an Earth-crossing trajectory may be likewise fragile, and thus likely to disintegrate into a lethal rain of debris if simply blown up. Alternative strategies for dealing with such asteroids are under consideration, but knowing which to use on what target is key. That also makes sharpening our asteroid identification skills from afar a continuing priority.
The paper is Jenniskens et al., “The impact and recovery of asteroid 2008 TC3,” Nature 458 (26 March 2009), pp. 485-488 (abstract).