Wow, there's nothing like an asteroid slamming into Earth to get professional and amateur astronomers whipped into a frenzy.
That's what happened on Monday morning when Maine skywatcher Bill Gray noticed something unique about a small asteroid discovered the previous night by Richard Kowalski and others at an observatory in Arizona. Gray's electronic posting to other asteroid aficionados began, "It looks as if Mt. Lemmon has found the first object . . . with a near certainty of hitting the earth."
Never mind that the object (designated 2008 TC3), was no bigger than a car, so in all likelihood it would explode harmlessly in the atmosphere with the kinetic-energy equivalent of 1,000 or 2,000 tons of TNT. That's no big deal as impacts go — objects of that size and energy hit somewhere on Earth every month or so.
Even so, the world's astronomers kicked into high gear, amassing 570 observations between the space rock's discovery until it slipped into Earth's shadow about an hour before impact. All that in just 19 hours! My email in box was lit up like a Christmas tree! As the observations piled up, dynamicists at JPL boldly announced that the mini-asteroid would slam into Earth at 2:46 Universal Time on October 7th. Ground zero was somewhere over northern Sudan — and at night! For anyone in that part of northeast Africa, it was going to be quite a show.
So what happened? The impact did occur as predicted, but so far there's no confirmation that anyone on the ground saw it. S&T contributing editor Johnny Horne, who's a photographer for the Fayetteville Observer, received a negative report from Khartoum, Sudan's capital. Khartoum and Mecca are the closest significant cities to the impact site, but each is still roughly 300 miles away. This part of the world is exceedingly arid and sparsely populated — people living there have far bigger issues on their minds.
Nor have we received any confirmed sightings from countless observers in Europe who went out in the hopes of seeing the flash.
However, Peter Brown, a meteor researcher at the University of West Ontario, reports that the airburst was recorded by at least one infrasound sensor operated by the International Monitoring System, whose primary purpose is detecting surreptitious nuclear tests. Brown confirms that the impact energy ranged from 1,100 to 2,100 tons of TNT.
Visually, the most compelling evidence comes from nighttime visual and infrared images acquired by the European Space Agency's Meteosat 8 weather satellite. Zdenek Charvat (Czech Hydrometeorological Institute), who first noticed the flash in the Meteosat images, reports that the spot is apparent in all 12 spectral channels, which span wavelengths from 0.5 to 14 microns).
But the satellite's scanning imager takes about 5 minutes to record each frame, so there's no way to extract the exact time of the spot's appearance. But the flare seems to be in the right spot, corresponding to longitude 32.37° east and latitude +20.89° and an altitude of 14 to 20 miles (22 to 30 km). One frame hints at an apparent trail about 2 miles long.
Meanwhile, telescopic observations show that 2008 TC3 was gyrating wildly before it hit. According to Czech asteroid specialist Petr Pravec, it was "definitely a tumbler." His analysis reveals two distinct periods of 49 and 98 seconds long. One is probably due to rotation and the other to spin-axis precession, but he can't tell yet which is which. But he notes that this ranks (or ranked!) as one of the three fastest-spinning asteroids known.
"It would be good to mention the role of Marek Kozubal and Ron Dantowitz at the Clay Center Observatory" Pravec told me. "Their photometric observations of the asteroid have been unique, and without them we wouldn't know much about its rotation."
I don't think we've heard the last word on this little party-crasher. After all, the U.S. Department of Defense has "assets" well suited to recording explosions in that part of the world. And from time to time the DoD's scientists have shared what they know with their civilian counterparts. So stay tuned for further developments!
You can read our original announcement about this asteroid here.