Summary

2008 TC3 was the first object detected in space prior to impacting the Earth. Discovery occurred at 06:39 UTC on 7 October 2008 by the Catalina Sky Survey and the meteoroid entered the atmosphere over Sudan 20 hours after the first detection. The object exploded at an altitude of approximately 37 kilometres and deposited numerous meteorites over the Nubian desert. 

Discovery circumstances and follow-up

The asteroid was first observed by Richard Kowalski with the Catalina Sky Survey 1.5 m telescope at Mt. Lemmon, Arizona, USA. It was immediately followed up by the discoverers and by other stations in the US, Australia, Asia and Europe, ensuring the collection of more than 800 astrometric observations and an extremely accurate trajectory determination. Physical observations, including a spectrum and a lightcurve, could be obtained just before impact, allowing for a taxonomic classification and a determination of the asteroid's shape and tumbling rotational state. 

Trajectory in Space

In the video below, the vernal equinox is to the right, while the view is tilted 45 degrees to the ecliptic.

2D Impact Corridor

The plot below shows the entry point at an altitude of 100 km above the sea level.

3D Impact Corridor

The highlighted area in the animation below represents the 1-σ (in red) and the 3-σ (in orange) fall area of the propagated object without including the atmospheric effects.

Atmospheric Phase Details

At least one infrasound sensor operated by the International Monitoring System detected the event. The estimates of the impact energy ranged from 1100 to 2100 tonnes of TNT. The explosion was recorded directly by METEOSAT-8. No visual sightings reported from the ground, except one webcam from a beach in Egypt and report from a KLM airliner pilot flying over Chad. 

Search for Meteorites

Roughly two months after impact a dedicated campaign successfully recovered meteorite fragments associated with the fall. The meteorite fall is now known as Almahata Sitta, and it belongs to a rare class known as ureilites.