Steve Chesley, Jet Propulsion Laboratory, Pasadena, CA

On October 6, 2008, the small newly discovered near-Earth asteroid 2008 TC3 was found to be on an Earth-impacting trajectory, with impact less than 20 hours away. This was the first ever predicted impact of a near-Earth object. Fortunately, it was immediately clear that the object was only a few meters in size and would almost certainly break up when it entered the Earth's atmosphere. We review the pre-impact orbit computations and predictions, the post-impact reconstructions of the trajectory, and the trajectory geometry. The first prediction of impact was made by the Minor Planet Center (MPC), which quickly made the discovery and subsequent follow-up observations available to the astronomical community and contacted both the NASA/JPL Near-Earth Object Program Office and NASA headquarters. Within an hour of receiving the initial data set, JPL predicted that the atmospheric entry would occur over northern Sudan around 02:46 UT on October 7. As the day progressed and more data arrived from the MPC, the impact prediction accuracy continued to improve. A press release was issued at 21:30 UT announcing the predicted impact later that night. Detections of the actual atmospheric impact event suggested that it was an airburst explosion at an altitude of 37 km with an energy equivalent to about one kiloton of TNT explosives. The airburst occurred at 02:45:45 UT at about 32.2 East longitude and 20.8 North latitude, matching the final impact predictions to within 0.2 s in time and 1.5 km in position.