Meteosat observation of the atmospheric entry of 2008 TC3 over Sudan and the associated dust cloud

We analyzed serendipitous observations by the Meteosat 8 weather satellite of the fireball caused by the entry of the small asteroid (or large meteoroid) 2008 TC3 over northern Sudan on October 7, 2008. Meteosat 8 scans the Earth in 5 min cycles. The fireball was captured in the 2: 45 UT images in four visible-near infrared channels (0.6-1.6 mu m) at a height of 45 km, and in eight mid infrared channels (3.9-13.4 mu m) at a height of 33 km. The latter channels also detected at least two dust clouds deposited in the atmosphere at the heights of about 44 and 36 km. The dust deposition was a result of severe atmospheric fragmentation of the asteroid, accompanied by fireball flares, which could be detected in the light scattered by the Earth's surface. The fireball brightness was measured at two random heights, 45 and 37.5 km, where it reached -18.8 and -19.7 mag, respectively. The peak brightness was probably higher than -20 mag. The color temperature of the fireball at 45 km was 3650 +/- 100 K. Infrared spectra of the fresh dust clouds were dominated by the 10 mu m Si-O band caused by recondensed amorphous silicates. Five minutes later, the dust clouds were detected in absorption of thermal radiation of the Earth. At that time, the silicates were largely crystalline, suggesting silicate smoke temperatures exceeding 1000 K. The total mass of the silicate smoke was estimated to be 3100 +/- 600 kg. More mass was probably contained in larger, micron sized, and colder dust particles resulting from incomplete sublimation of the asteroidal material and detected later by Meteosat 8 and 9 in scattered sunlight. Based on the heights of asteroid fragmentations, we guess that the bulk porosity of 2008 TC3 was of the order of 50%, i.e. higher than the porosity of the recovered meteorite Almahata Sitta.