NEO News (10/07/08) First reports on Sudan bolide

From Dave Morrison...

NEO News (10/07/08) First reports on Sudan bolide

While I have not yet seen any eyewitness accounts from ground observers in Africa, here are two early reports that the bolide (now designated as asteroid 2008 TC3, surely the shortest-lived asteroid name, since it was destroyed a few hours after the name was given) did explode in the atmosphere above Sudan early this morning.

David Morrison

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From Peter Brown (pbrown@uwo.ca): A very preliminary examination of several infrasound stations proximal to the predicted impact point for the NEO 2008 TC3 has yielded one definite airwave detection from the impact. The airwave was detected at the Kenyian Infrasonic Array, (IMS station IS32), beginning near 05:10 UT on Oct 7, 2008 and lasting for several minutes. The signal correlation was highest at very low frequencies - the dominant period of the waveform was 5-6 seconds. The backazimuth of the signal over the entire 7 element array is shown in the attached map - it clearly points to within a few degrees of the expected arrival direction. Moreover, assuming a stratospheric mean signal speed of 0.28 km/s, the arrival time corresponds to an origin time near 02:43 UT, which is consistent with the expected impact time near 02:45:40 UT given expected variations in stratospheric arrival speeds. The dominant period of 5-6 seconds corresponds to an estimated energy (using the AFTAC period at maximum amplitude relationship from ReVelle, 1997) of 1.1 - 2.1 kilotons of TNT. The five other closest infrasound stations were briefly examined for obvious signals and showed none - more detailed signal processing of these additional data are ongoing in the search for additional signals.

Peter Brown
Canada Research Chair in Meteor Science
University of Western Ontario, London, ON

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From Spaceweather.com: ASTEROID IMPACT--UPDATE: Asteroid 2008 TC3 hit Earth this morning, Oct. 7th, and exploded in the atmosphere over northern Sudan. An infrasound array in Kenya recorded the impact. Dr. Peter Brown of the University of Western Ontario has inspected the data and he estimates that the asteroid hit at 0243 UTC with an energy between 1.1 and 2.1 kilotons of TNT. Most of the 3-meter-wide space rock should have been vaporized in the atmosphere with only small pieces reaching the ground as meteorites.

No pictures of the fireball have been submitted; the impact occurred in a remote area with few and possibly no onlookers capable of recording the event. So far, the only report of a visual sighting comes from Jacob Kuiper, General Aviation meteorologist at the National Weather Service in the Netherlands:

"Half an hour before the predicted impact of asteroid 2008 TC3, I informed an official of Air-France-KLM at Amsterdam airport about the possibility that crews of their airliners in the vicinity of impact would have a chance to see a fireball. And it was a success! I have received confirmation that a KLM airliner, roughly 750 nautical miles southwest of the predicted atmospheric impact position, has observed a short flash just before the expected impact time 0246 UTC. Because of the distance it was not a very large phenomenon, but still a confirmation that some bright meteor has been seen in the predicted direction.

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Erik Asphaug of University of California, Santa Cruz, asks rhetorically: How would the US respond if the identical impact was forecast over, say, Bozeman? On the one hand we expect that the public would behave themselves, but some in the discussion felt that the public would freak out entirely out of proportion.

David Morrison comments: This issue of public response to a very small impact has been discussed previously, including mention in three of my papers (see below), but in fact no one knows the answer. The issue is important because impacts this small are relatively common:

Morrison, D., R. Binzel, C.R. Chapman, and D. Steel, "Impacts and the Public: Communicating the Nature of the Impact Hazard." In Mitigation of Hazardous Comets and Asteroids (M. Belton, T. Morgan, N. Samarasinha & D. Yeomans, eds.). Cambridge University Press, Cambridge (2004).

Morrison, D. "Defending the Earth against Asteroids: The Case for a Global Response," Science and Global Security 13:105-116 (2005).

Morrison, D. "The Impact Hazard: Advanced NEO Surveys and Societal responses," In Comet/Asteroid Impacts and Human Society (P. Bobrowsky & H. Rickman, eds.) Springer, New York (2007)

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