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

Infrasound from the 2008 TC3 impact on Oct 7, 2008

Part I

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

La Sagra Sky Survey, Spain

Asteroid tracked until it enters Earth shadow at 01:50 UT

Most accurately known orbit for any object to have impacted the Earth

Orbit and Entry Details

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 ValueStart 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 ValueStart 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

Wind Speed (m/s)-30 -20 -10 0 10 20 30

Hei

ght (

km)

0

10000

20000

30000

40000

50000

60000 ZonalMeridional

Sound Speed (m/s)

260 280 300 320 340 360 380

Hei

ght (

km)

0

10000

20000

30000

40000

50000

60000

CsCeff (East)

Ceff (South)

Infrasonic Energy Yields

Yield Relation I32KE I31KZ

Edwards et al (2007) – Small Bolides (Amplitude + Winds+Range)

0.01 kTon 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

For comparison – satellite yield is 1.0 kTon

Backup

I50GB – Possible Detection?????