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First Earth-Colliding Asteroid Detected Before Impact

A space rock the size of a car collided with the Earth early on the morning of 7 October, twenty hours after its discovery by the Mount Lemmon Survey in Arizona. Although previous impacting objects have been seen by virtue of the bright fireballs they produce when they hit the atmosphere and vaporize, the asteroid designated 2008 TC3 was the first to be picked up telescopically on its final approach before reaching Earth.

The asteroid was discovered as a small dot of light, shining by reflected sunlight, a little farther away than the Moon. Observations from Arizona and Australia, spanning the first nine hours, showed that the asteroid would be pulled in by Earth's gravity and end its life as a spectacular fireball over Sudan, about an hour before dawn local time. European telescopes took over to track 2008 TC3 during its final hours.

Airbursts of this size during the atmospheric entry of small asteroids are not uncommon, and occur somewhere over the globe every few months on average. Indeed many have been imaged in recent years by US Department of Defense satellites. The energy yield is equivalent to about one kiloton of TNT explosive. The two nuclear bombs that ended the Second World War in Asia were twenty kilotons or so, but the important difference is the shielding effect of the Earth's atmosphere, preventing the incoming extra-terrestrial bodies from reaching ground level, instead dumping the energy at a safe height. By comparison the Tunguska bolide, the object that devastated two thousand square kilometres of Siberian forest exactly a century ago this year, was large enough to penetrate the atmosphere to within a few miles of the ground - too close for comfort - before undergoing its final explosion.

Among the astronomers observing this object were Henry Hsieh and Sam Duddy from Queen's University Belfast and Gavin Ramsay from Armagh Observatory, having been alerted to the event by Queen's colleague Alan Fitzsimmons during their night's observing at the William Herschel Telescope on the Spanish island of La Palma.

FOR FURTHER INFORMATION PLEASE CONTACT: Dr David Asher at the Armagh Observatory, College Hill, Armagh, BT61 9DG; Tel.: +44-(0)28-3752-2928; djaat signarm.ac.uk; and Professor Alan Fitzsimmons at the Astrophysics Research Centre, Queen's University Belfast, Belfast, BT7 1NN; Tel.: +44-(0)28-9097-3124; a.fitzsimmonsat signqub.ac.uk.

See also:
Why Asteroid 2008 TC3 Represents a Landmark
Announcement from Minor Planet Center
Fireball seen from METEOSAT-8 spacecraft
NASA JPL - pre-impact
NASA JPL - post-impact
Spaceweather
Mount Lemmon Survey
Tunguska Images
NEO Impact Hazard

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Last Revised: 2008 October 13th
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