1. 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 USA
2Dept. of Physics and Astronomy, U. of Western Ontario, London, ON, Canada N6A 3K7

2. 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

3. 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

4. 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

5. 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

6. 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 N
Impact Longitude E
Entry Velocity
12.82 km/s
Entry Angle
19.2 degrees
Hmag
30.67 ± 0.37
Est. Diameter (m)
2-5 m

8. 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)

9. Satellite vs. JPL Data

10. 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!

11. Part II

12. Part III

13. I32KE Observations

14. 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

15. I31KZ Observations

16. 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

17. Atmosphere
Stratospheric winds are directed mainly to the ENE

18. 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

19. Backup

20. I50GB – Possible Detection?????