The impact trajectory of asteroid 2008 TC3.

The impact of asteroid 2008 TC 3 was an unprecedented event—the first ever predicted impact of a near-Earth object. When it was first detected about 20 h before impact, 2008 TC 3 was still farther away than the Moon. Once it was recognized as an impactor and announced as such, 2008 TC 3 began to receive considerable attention from astronomical observers. Using the unprecedented dataset of nearly 900 astrometric observations and the latest observation debiasing and weighting techniques, we estimate the precise trajectory of 2008 TC 3 and its impact ground track. At the entry point into the atmosphere, the 3- σ formal uncertainty in predicted position is an ellipse only 1.4 km × 0.15 km in size. The locations of the many meteorites recovered from the desert floor mark the asteroid’s actual ground track and provide a unique opportunity to validate trajectory models. We find that the second-order zonal harmonics of the Earth gravity field moves the ground track by more than 1 km and the location along the ground track by more than 2 km, while non-zonal and higher order harmonics change the impact prediction by less than 20 m. The contribution of atmospheric drag to the trajectory of 2008 TC 3 is similar to the numerical integration error level, a few meters, down to an altitude of 50 km. Integrating forward to lower altitudes and ignoring the break-up of 2008 TC 3 , atmospheric drag causes an along-track deviation that can be as large as a few kilometers at sea level. [ABSTRACT FROM AUTHOR]