CCO Tracks Asteroid’s Death Plunge

Image sequence showing changing brightness of asteroid 2008 TC3.

October 7, 2008 — Something happened yesterday that got professional and amateur astronomers whipped into a rare frenzy. A telescope in Arizona discovered a small asteroid that, for the first time ever, was certain to hit Earth — and it gave us only 19 hours’ advance warning. Fortunately, the object (designated 2008 TC3) was far too small to reach the ground intact. Instead, it exploded this morning at a height of about 23 miles (37 km) over Sudan in northeast Africa, lighting up the predawn darkness and frightening thousands of Sudanese making their way home after morning prayers.

In the hours before the asteroid’s demise, the world’s astronomers amassed nearly 600 observations. Yet few were more important than a long sequence of images taken by Marek Kozubal and Ron Dantowitz. In a perfect example of being in the right place at the right time, the Clay Center Observatory was in a position to track the asteroid in the hours just preceding its fateful collision, and the skies were clear over Boston that evening.

However, this unusual target proved a real challenge to observe, because it was both moving quickly and accelerating as it drifted across the sky. Fortunately, Kozubal’s experience writing closed-loop tracking software paid off, and he soon had created the specialized code that the telescope’s tracking system would need to keep up with the speeding interloper.

With everything ready, the two astronomers started snapping away with an electronic camera attached to the observatory’s 25-inch telescope. Every 4.1 seconds, another image streamed into computer memory. By the time the asteroid slipped into Earth’s shadow some 2 hours later, they’d amassed 1,770 perfectly exposed images. Other observatories captured the asteroid’s spectrum and its position, but no one else photographed it so extensively.

Even without the aid of computer analysis, Kozubal and Dantowitz could see that the asteroid was changing brightness dramatically, an indication that it was irregularly shaped and spinning or tumbling. Three Czech researchers led by Peter Scheirich have deduced both the shape of 2008 TC3 (like a loaf of bread with a flat side) and how it was tumbling just before striking Earth.

Although seemingly chaotic, the asteroid’s motion resulted from twirling around two different spin axes every 99 and 97 seconds. This conclusion relied heavily on the long sequence of images taken by the Clay Center Observatory. According to Czech asteroid specialist Petr Pravec, Kozubal and Dantowitz’s observations of the asteroid were unique. “Without them,” he noted, “we wouldn’t know much about its rotation.”