Infrasound from the 2008 TC3 impact on Oct 7, 2008 Part I D.O. ReVelle1 and P. Brown2 1EES-17, Geophysics Group – Earth and Environmental Science Division, Los Alamos National Laboratory, P.O. Box 1663, MS D401, Los Alamos, NM 87545 USA 2Dept. of Physics and Astronomy, U. of Western Ontario, London, ON, Canada N6A 3K7

Chronology of Events At 0630 UT on Oct 6, 2008 Catalina Sky Survey discovers an NEA (designated 8TA9D69) Follow up observations over the next few hours produce a preliminary orbit which intersects the Earth. At 15 UT on Oct 6, the Minor Planet Center announces that orbit will intersect the Earth; confirmed by JPL and NeoDYS Between 16 – 20 UT Oct 6, NASA HQ alerted officials at the National Security Council, the Office of Science and Technology Policy, the Department of State, the Department of Defense Northern Command and Joint Space Operations Center From 15 UT Oct 6 – 0150 UT Oct 7 more than two dozen observatories contribute hundreds of additional measurements At 0245:40 UT object enters atmosphere over Sudan – Egypt border

Importance of Event First time an impactor has been detected in space BEFORE impact Allows detailed cross calibration between space characteristics of NEAs (brightness, albedo, size, composition, rotation) and fireball properties Opens the prospect of recovery of meteorites – providing end to end sample return mission equivalent science

Observations – Pre-impact Spectrum is flat suggesting C or M type asteroid Rotation period ~49 sec (or 97 sec) M. Kozubal & Ron Dantowitz / Clay Center Observatory

Impact Asteroid tracked until it enters Earth shadow at 01:50 UT Most accurately known orbit for any object to have impacted the Earth La Sagra Sky Survey, Spain

Orbit and Entry Details Most accurately known orbit for any object to have impacted the Earth Quantity Value Impact Time (50 km) 02:45:42.3 UT Impact Latitude 20.855 N Impact Longitude 31.814 E Entry Velocity 12.82 km/s Entry Angle 19.2 degrees Hmag 30.67 ± 0.37 Est. Diameter (m) 2-5 m

Observations - Impact Sensors aboard US satellites detected the impact of a bolide over Africa on 7 October 2008 at 02:45:40 UT. The initial observation put the object at 65.4 km altitude at 20.9 degrees North Latitude, 31.4 degrees East Longitude. The object detonated at an altitude of approximately 37 km at 20.8 degrees North Latitude, 32.2 degrees East Longitude. The total radiated energy was approximately 4.0X1011 J. This is equivalent to approximately 0.1 KT of radiated energy (assumes a 6000 Kelvin black body). Meteosat 8 Images (Euromet)

Satellite vs. JPL Data

Meteorites on the Ground? Based on the satellite measured end height, known velocity and estimated energy, fireball PE ~ -6 This implies the object was an extremely weak cometary-type object Flight characteristics suggest object is even weaker than Tagish Lake meteorites Any meteorites on the ground would be particularly interesting!

Part II

Part III

I32KE Observations

I32KE Observations - II Quantity Value Start of Signal 05:09:25 UT Duration 155 sec Peak-to-Peak Amplitude 14 ± 13 mPa Period at Maximum Amplitude 4.7 ± 0.1 sec Range 2451 km Celerity 0.282 km/s

I31KZ Observations

I31KZ Observations Quantity Value Start of Signal 06:23:20 UT Duration 484 sec Peak-to-Peak Amplitude 7.4 ± 7.7 mPa Period at Maximum Amplitude 2.8± 0.1 sec Range 3979 km Celerity 0.304 km/s

Atmosphere Stratospheric winds are directed mainly to the ENE

Infrasonic Energy Yields For comparison – satellite yield is 1.0 kTon Yield Relation I32KE I31KZ Edwards et al (2007) – Small Bolides (Amplitude + Winds+Range) 0.01 kTon ReVelle (1997) – AFTAC – (Period only) 0.92 kTon 0.06 kTon Davidson and Whitaker (1992) – (Amplitude + Winds+Range) 0.08 kTon 0.43 kTon

Backup

I50GB – Possible Detection?????