Infrasonic Measurements of the Carancas, Peru Meteorite Fall P. Brown 1, W.N. Edwards 1, A. Le Pichon 2, K. Antier 2, D.O. ReVelle 3, G. Tancredi 4, S. Arrowsmith 3 1 Dept. of Physics and Astronomy, U. of Western Ontario, London, ON, Canada N6A 3K7 2 Commissariat à l’Energie Atomique, Centre DAM - Ile de France, Département Analyse Surveillance Environnement, Bruyères-le-Châtel, Arpajon Cedex, France 3 EES-17, Geophysics Group – Earth and Environmental Science Division, Los Alamos National Laboratory, P.O. Box 1663, MS D401, Los Alamos, NM USA 4 Dpto. Astronomía, Fac. Ciencias, Iguá 4225, Montevideo, Uruguay. Infrasound Technology Workshop

What happened? 15/9/2007 – ~ 11:45 LT (16:45 UT) a bright fireball was observed in the sky near the Peru/Bolivia border, leaving behind a smoke trail. Strong explosions lasting several seconds were heard in an area of several tens of km. A ground-level explosion was observed as well as the formation of a thick cloud of dust like a mushroom cloud. The shock wave of the ground level explosion produced vibration in several houses and some animals were knocked down due to the shock wave. The roof of a shed was impacted by ejecta. At the site where the explosion and the dust cloud was observed, the local people found a ~14m crater. The crater was half-fill by underground water. The water was bubbling and noxious fumes were coming out the water. Several pieces of atypical material was collected from inside and outside the crater. Several persons got sick.

Photo of the smoke trail

Crater: diameter 14m

Carancas crater

Carancas meteorites Photo José Ishitsuka Photo Hernando Nuñez

Puzzles presented by this event What happened to the original meteorite? Was it fragmented and totally dispersed during the impact? How was it possible that a chondritic meteorite of just a few meters in size could get through the atmosphere without being completely disrupted? Under what conditions could this event happen again?

From Bland and Artemieva (2003) This figure portrays the ratio of final mass to initial mass for stoney meteorites (top) and irons (bottom) From Hills and Goda (1998)

Constraints on the explosion energy The explosion produced by the impact of the meteorite with the ground was witnessed by several people. The explosion created an expanding cloud of dust and debris and a shock wave. Local blast constraints: A man standing ~400m from the crater site saw the expanding dust cloud, heard the explosion but did not suffer any injury, nor did he fall down. A man riding a bicycle ~100m from the crater fell down and he felt a bit dizzy due to the explosion, but his eardrums were not ruptured. He was riding in a direction orthogonal to the line connecting to the crater. A bull similar to the Lidia bull-fighting breed was at ~200m from the crater. It fell down and broke one of its horns. The bull weighed ~500 kg. A mud shed with metal roof at ~120m was not seriously damaged. The shed has no glass windows. It was hit by ejecta from the crater that bent a metal sheet of the roof.

Pressures for 1 & 3 ton TNT

Cratering Energetics from Holsapple and Housen (2007)

Available Instrumental Data Infrasound: –IS08 (Bolivia): Two strong airwave arrivals associated with the event (80.3 km range) –IS41PY (Paraguay): Very weak signal (1663 km range) Seismic: –Bolivian Short-period seismic stations (BBOD, BBOE, BBOK, BBOB) Detect impact directly (Pg waves) and airwave arrivals –LPAZ (Bolivia): Pg arrival (106 km)

Time from UT Amplitude (nm) Amplitude (Pa) 12

Arrival Angle ~ 14° Arrival Azimuth ~ 228 ° Arrival Angle ~ 19° Arrival Azimuth ~ 215 ° Bp 0.3 – 8 Hz

Atmosphere

Pg waves from Crater Formation UT + Displacement (nm) Crater formation time = ± 0.4 UT P g wave velocity = 5.1 ± 0.1 km/s

Trajectory Possible Trajectory hypotheses to explain double signal: 1.Airshock from ballistic arrival and airwave from crater production 2.Airshock from ballistic arrival and fragmentation event 3.Double fragmentation events Additional constraining data for fireball direction: 1.South of IS08 2.Consistent with eyewitnesses near crater describing E->W path 3.Crater ejecta concentrated to SW and SSW Trajectory azimuth confined to ~easterly radiant azimuths

Quasi - Ballistic Wave Model Use timing for crater formation as constraint and minimize residuals from line source –Free parameters are azimuth and altitude of radiant and velocity Allow ray deviations up to ~20° from perpendicular NON-BALLISTIC NON-BALLISTIC QUASI-BALLISTIC QUASI-BALLISTIC BALLISTIC V

Quasi - Ballistic Wave - Solutions Assuming first arrival from IS08 is associated with crater formation AND is associated with major arrival at other stations get celerities from 0.31 – 0.33 km/s clustered around 0.33 km/s (plausible) Second arrival at IS08 and secondary arrivals at seismic stations are taken to be ballistic arrival Solutions have possible azimuths from 75 – 125 and steep elevations (>60 degs)

Point Source Solutions Several arrival combinations possible – associations uncertain Main Result – Point source solutions for all combinations cluster from ° az and entry angles from 32° – 60° with heights clustering at 20 ± 3 km and 30 ± 2 km for all solutions Best fit presuming both main arrivals are fragmentation related and forced to fit IS08 backazimuths is az ~ 90° and 35° elevation

Radiant Azimuth Entry Angle IS08 2 nd arrival azimuth fit with 1 st arrival crater airwave Line Source Model – differing signal picks From Le Pichon et al (2008)

Crater Energetics – IS08 From airwave at IS08 can apply empirical yield relations to estimate source energy (presuming first airwave arrival at IS08 is from crater or very late stage fragmentation event) –Davidson and Whitaker (1992): E s = 4.5 tons TNT Signal PropertyWavetrain #1Wavetrain #2 Zero – Peak Amplitude (Pa)0.76 ± ± 0.14 Peak-Peak Amplitude (Pa)1.91 ± ± 0.25 Period at Max Amplitude (sec)0.52 ± ± 0.20 Summary of IS08 airwave arrival data:

Airwave data from I41PY: Energy Estimations: Crater Energetics – I41PY Signal PropertyValue Zero – Peak Amplitude (Pa)0.03 ± 0.01 Peak-Peak Amplitude (Pa)0.04 ± 0.02 Period at Max Amplitude (sec)1.2 ± 0.2 SourceRelationEnergy (tons of TNT) ReVelle (1997) ; US Nuclear Tests AFTAC (period at max amplitude) Blanc et al (1997) ; French Nuclear Tests (amplitude + range) Edwards et al (2006) ; Comparison of bolide infrasound and satellite data (amplitude, winds and range) 10 ± 5 4 ± 3 5 ± 2

Seismic Energies/Efficiencies From seismic arrivals, the crater explosion produced an equivalent local seismic magnitude ~ M L = 1.3 ± 0.1 Corresponds to seismic energy of ~10 6 J Event energy ~3 tons TNT ~10 10 J Seismic efficiency ~10 -4 Shishkin (2007) theory predicts ~10 -5 to 10 -6

Modelling Entry modelling (two separate models) Orbital solutions limit initial v < 17 km/s to have aphelia inside Jupiters orbit Assumption is no major fragmentation

Summary : Conclusions Initial mass of meteoroid – kg –Initial radius is 0.6 – 1 m –Most probable near lower end of range Initial velocity 12 – 17 km/s –Initial energy ~0.1 – 0.4 kT TNT Impacting ground ~1.5 – 4 km/s (model dependent); PDFs suggest 3-6 km/s Impactor mass at ground – kg (model dependent) Impact energy ~a few tons TNT Seismic Impact Efficiency ~10 -4

Working Hypothesis The Carancas meteoroid was unusually strong, with few stress cracks (Y ~ 15 MPa) It did not fragment significantly and therefore did not loose all of its pre-encounter cosmic velocity (having a ~few percent of its pre- encounter KE upon impact). Models based on average properties miss important details “The enemy of the conventional wisdom is not ideas but the march of events” –J. K. Galbraith