2008 TC₃

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The blue line represents the trajectory of the meteoroid approaching the Earth

Ground path of the meteoroid over Sudan. The red line is the object's path, terminating where it would have hit the ground. The green line is the infrasound detection of the object's explosion. METEOSAT IR fireball location indicated by orange crosshairs. Predicted altitude as the object crossed the Nile River and several other points are listed. Exact path and fireball altitude have not been confirmed.

2008 TC₃ (Catalina Sky Survey temporary designation 8TA9D69) was a meteoroid 2 to 5 meters (7 to 16 ft) in diameter that entered Earth's atmosphere on October 7, 2008, at 02:46 UTC (5:46 a.m. local time).^[1] It exploded an estimated 37 kilometers (23 mi) above the Nubian Desert in Sudan. A search of the impact zone that began on December 2008 turned up 8.7 pounds (3.9 kg) of meteorites in 280 fragments, which are surviving pieces of the meteoroid. The meteorites are of a rare type known as ureilites, which contain, among other minerals, nanodiamonds.^[2][3][4]

[edit] Discovery

The meteoroid was discovered by Richard A. Kowalski at the Catalina Sky Survey (CSS) 1.5-meter telescope at Mount Lemmon, north of Tucson, Arizona, USA, on October 6, 06:39 UTC, about 20 hours before the impact.^[5][6][7]

The meteoroid was notable as the first such body to be observed and tracked prior to reaching Earth.^[8] The process of detecting and tracking a near-Earth object, an effort sometimes referred to as Spaceguard, was put to a test. In total, 586 astrometric and almost as many photometric observations were performed by 27 amateur and professional observers in less than 19.0 hours and reported to the Minor Planet Center, which issued 25 Minor Planet Electronic Circulars with new orbit solutions in eleven hours as observations poured in. On October 7, 01:49 UTC,^[7] the meteoroid entered the shadow of the Earth which made further observations impossible. Impact predictions were performed by University of Pisa's CLOMON 2 semi-automatic monitoring system^[9][10] as well as Jet Propulsion Laboratory's Sentry system. Spectral observations that were performed by astronomers at the 4.2-meter William Herschel Telescope at La Palma, Canary Islands are consistent with either a C-type or M-type asteroid.

[edit] Explosion

The object is confirmed to have entered Earth's atmosphere as a meteor above northern Sudan at a velocity of 12.8 kilometres per second (29,000 mph). Estimated trajectory has the object coming out of the western sky at an azimuth of 281 degrees, and an altitude angle of 19 degrees to the local horizon.

Meteosat 8 / EUMETSAT IR image of the 2008 TC3 explosion. Copyright 2008 EUMETSAT

It exploded tens of kilometers above the ground with the energy of 0.9 to 2.1 kilotons of TNT, causing a large fireball or bolide^[11] in the early morning sky.^[12] Very few people inhabit the remote area of the Nubian Desert where the explosion took place; The Times, however, reported that the meteoroid's "light was so intense that it lit up the sky like a full moon and an airliner 1,400 km (870 miles) away reported seeing the bright flash."^[13] A webcam captured the flash lighting up El-Gouna beach 725 kilometres north (see this webcam frame).^[14] A low-resolution image of the explosion was captured by the weather satellite Meteosat 8.^[15] The Meteosat images place the fireball at 21°00′N 32°09′E / 21.00°N 32.15°E / 21.00; 32.15 (2008 TC3 fireball).^[16] Infrasound detector arrays in Kenya also detected a sound wave from the direction of the expected impact corresponding to energy of 1.1 to 2.1 kilotons of TNT.^[17] Meteoroids of this size hit Earth about two or three times a year.^[18]

The trajectory showed intersection with Earth's surface at roughly 20°18′N 33°30′E / 20.3°N 33.5°E / 20.3; 33.5 (2008 TC3 projected impact)^[19] though the object was expected to break up perhaps 100–200 kilometers (62–120 mi) west as it descended, somewhat east of the Nile River, and about 100 kilometers (62 mi) south of the Egypt–Sudan border.

According to U.S. government sources^[20][21] U.S. satellites detected the impact at 02:45:40 UT, with the initial detection at 20°54′N 31°24′E / 20.9°N 31.4°E / 20.9; 31.4 (2008 TC3 initial detection) at 65.4 kilometers (40.6 mi; 35.3 nmi) altitude and final explosion at 20°48′N 32°12′E / 20.8°N 32.2°E / 20.8; 32.2 (2008 TC3 final explosion) at 37 kilometers (23 mi; 20 nmi) altitude. These images have not been publicly released.

EUMETSAT fireball images

Meteosat 8 / EUMETSAT visual image of first light flare from 2008 TC3 with lat/long reference. Copyright 2008 EUMETSAT

Meteosat 8 / EUMETSAT IR image of main fireball from 2008 TC3. Copyright 2008 EUMETSAT.

Meteosat images combined, showing offset from first light flare to main IR flare. Copyright 2008 EUMETSAT

[edit] Recovered fragments

2008 TC3 fragment found on Feb. 28, 2009 by Peter Jenniskens, with help from students and staff of the University of Khartoum. Nubian Desert, Sudan.

[edit] Search

A search of the impact zone that began on December 6, 2008, turned up 8.7 pounds (3.9 kg) of rock in 280 fragments. These meteorites are collectively named Almahata Sitta, which means "Station Six^[22] " in Arabic and is a train station between Wadi Halfa and Khartoum, Sudan. This search was lead by Peter Jenniskens from the SETI Institute, California and Muawia Shaddad of the University of Khartoum in Sudan, and carried out with collaboration of students and staff of the University of Khartoum. The first 15 meteorites were found in the first three days of the search. Numerous witness were interviewed and the search was guided with search grid and specific target area produced by NASA's Jet Propulsion Laboratory, in Pasadena, California.^{[23][24][25][26][27]} While fragments have been found before from fireballs seen in the sky, this was the first time fragments had been found from an object that was previously tracked in outer space before hitting Earth.^[23]

[edit] Analysis

Samples of the Almahata Sitta meteorite were sent for analysis to Ames in California, the Johnson Space Center in Houston, the Carnegie Institution of Washington, and Fordham University in New York City.^[23] One fragment was analyzed.^[28] The total recovered mass was 3.95 kg or 8 lb 11 oz. The results indicate that it is an anomalous ultra-fine-grained porous polymict ureilite achondrite, with large carbonaceous grains.^[28] Reflectance spectra indicate the meteoroid as an F-type asteroid class.^[28] The fragile material of this class firmly links it to anomalous dark carbon-rich ureilites.^[28]

[edit] Coming Full Circle

Richard Kowalski received a tiny fragment of Almahatta Sitta, a gift from friends and well-wishers on the Minor Planet Mailing List, which Kowalski founded in order to help connect professional and amateur astronomers. ^[29]

[edit] See also

• Carbonaceous chondrites
• List of notable asteroids
• The Great Daylight 1972 Fireball
• Impact event

[edit] Notes

[edit] References

• Jenniskens, P.; et al. (2009), "The impact and recovery of asteroid 2008 TC₃", Nature, Letters, Vol. 458, pp. 485-488, 2009 March 26, with supplemental online material; and front cover photo of magazine issue of one of the fragments.
• Kwok, Roberta (2009), "The Rock That Fell to Earth", Nature, News Feature, Vol. 458, pp. 401-403, 2009 March 26.

[edit] External links

External images
	An image of 2008 TC3
	Animation of 2008 TC3
	Smoky trail (spaceweather.com November 8, 2008)

Wikimedia Commons has media related to: 2008 TC3

• Remanzacco Observatory photographs of the incoming space rock
• Telescopio Nazionale Galileo photograph of 2008 TC3
• Animation of impact from the asteroid's point of view (Pasquale Tricarico of the Planetary Science Institute)
• News bulletin from NASA Near Earth Object Program
• Impact Trajectory on October 7, 2008
• Circled, the object caught on camera as it sped towards Earth
• The full story of Earth-impacting asteroid 2008 TC₃ by Emily Lakdawalla (The Planetary Society Blog)
• 2008 TC3: A Serendipitous Event^{[dead link]} by Tavi Greiner (The Slooh SkyLog)
• NASA, Near Earth Object Program, November 4, 2008
• Announcement with animation
• Atkinson, Nancy. "Where Are the Images from Asteroid 2008 TC3?". Universe Today. Archived from the original on 2009-06-10. http://www.webcitation.org/5hQnWJm4F. Retrieved 2009-06-08. 
• "webcam record of flash effect from Red Sea beach at El Gouna, Egypt, 725 km away" (GIF). Archived from the original on 2009-06-10. http://www.webcitation.org/5hQ21i9j3. Retrieved 2009-06-08.  (linked from #PGJ2008TC3)
• Javaux, Gilbert. "P.G.J.- 2008 TC3... Première détection d'un astéroïde avant son impact sur Terre" (in French). Archived from the original on 2009-06-10. http://www.webcitation.org/5hQqCC1J0. Retrieved 2009-06-08.  (orbits, charts, observation records, fragment analysis)
• Online science newsletter article published March 12, 2009
• BBC article about the asteroid, March 25, 2009
• APOD Astronomy Picture of the Day