infrasonic technology workshop november 3-7, 2008, bermuda, u.k

Infrasonic Technology Workshop November 3-7, 2008, Bermuda, U.K.

Session 6: Infrasound from Geophysical SourcesPresentation:

INFRASOUND FROM 2008TC3 ON 7 OCTOBER 2008

D.O. ReVelle EES-17, Geophysics Group, Los Alamos National Laboratory Los Alamos, New Mexico 87545 USA

P.G. Brown, W.N. Edwards and E. A. SilberPhysics and Astronomy Department, University of Western Ontario London, Ontario, Canada N6A 3K7

Summary of Presentation• Introduction and Overview

Some recent bolides The Meteor-Bolide Interaction Spectrum

• Astronomically Predicted Impact Location of 2008TC3: N. Sudan

• U.S. Government Public Release: Satellite Detection of 2008TC3 Geographic location and breakup height details Amount of light radiated in the optical, etc.

• Entry Dynamics Modeling Summary Direct and Inverse Entry Modeling Approaches

• Direct TPFM Entry Modeling Summary and Results• Inverse Entry Modeling Results Summary and Results

• Summary and Conclusions

Bolide Diversity: Recent Polish fireball, Moravka and Tagish Lake

Moravka – Janov Video

Tagish Lake smoke trailwith solar illumination

Polish fireball: 13 June 2006; 17:15 UTC- Persistent Smoke Trail

Telescopic Image from Elginfield Observatory

Meteor-Atmosphere Interaction Spectrum

MassLoss(%)

100.0

0.0

Micro-meteoroids

Shootingstars

Ordinary bolides

Super-bolidesImpact and explosivecratering

DinosaurExtinction(Tertiary-CretaceousBoundary)

No light from ablationand no sound

Light,but nosound at the ground

Intenselight andweakinfrasound

Intense light and strong infrasound and internal atmospheric gravity and Lamb waves

Tektitestrewnfields

Tsunami formation following oceanic impact

Climatechange

Shockwaves

Freemoleculeflow

Continuum fluid flow

Size1 m 1 m 10 km

BrightnessFull moonVenus SunFaintest

stars

and meteoroids

Velocitydependent

???

Electro-phonicsounds

Projected Impact Spot

Courtesy of Euromet: Meteosat Image of Impactof 2008TC3: Near-IR channel at 3.90 m

US Government Public Announcement of Satellite Detection of 2008TC3

• US Government Official Announcement: Public Release of satellite information for Asteroid 2008TC3 and Bolide Detection

• 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 deg N. latitude, 31.4 deg E. longitude.

• The object detonated at an altitude of approximately 37 km at: 20.8 deg N. latitude, 32.2 deg E. longitude.

• The total radiated energy was approximately 4.01011 joules.  This is equivalent to approximately 0.10 kT of radiated optical energy (assuming a 6000 K black body). 

• This event origin time is completely confirmed by infrasonic array detections made at I32 in Kenya and at I31 in Kazakhstan. 

Entry Information and KeyModeling Assumptions Made for 2008TC3

• Entry into the sensible atmosphere from a westerly direction and terminated over eastern Africa: September 7, 2008 Predicted Impact: Latitude 20.855 N; Longitude 31.697 E

• Entry angle of radiant: 70.9 from the zenith (Observed)• Entry velocity: 12.82 km/s (Observed)• Initial radius 2.0 meters (from astronomical/astrometric data)• Hypersonic Aerodynamic Entry Modeling:

DIRECT (Top-down) solutions INVERSE (Bottom-up) solutions Modeling: Homogeneous or Porous Meteoroid Structure Spherical unchanging shape ( 2/3) assumed throughout In TPFM DIRECT Entry Model runs, 64 fragments allowed In INVERSE Entry Model runs- No fragmentation allowed

Entry Modeling Approaches-I

• DIRECT TPFM (Triggered Progressive Fragmentation Model)-Entry modeling (ReVelle, 2005, 2007) Top-down Approach Initial size, velocity, entry angle, shape, shape change, bulk

density (Bolide group designation for homogeneous bodies- Discrete designation or porous meteoroids within a continuum of possible bulk density values), etc. assumed and:

Detailed stagnation point heat transfer calculations performed using:

• Radiation, convection/conduction Mechanical, stagnation point progressive fragmentation model

utilized for either homogeneous or porous meteoroids with differing “breaking” strengths assigned for each type.

Entry Modeling Approaches- II• INVERSE entry modeling (McIntosh, 1970; ReVelle, 1979, 2005)

Bottom-Up Approach Mean shape, entry angle, ablation parameters specified with

each group- NO fragmentation parameters utilized Bolide groups- Homogeneous with only discrete bulk density

values with heating parameters specified for each group Using either (all parameters observed at or near the end of the

luminous flight):• Crater field size at a specified height above the surface used

and/or:• End height (as in this case):

• Initial parameters iterated in order to determine if solutions exist: Initial velocity and initial radius (spherical unchanging shape) Wave drag coefficient shape factor product, including errors

2008TC3 Direct Entry Inputs• 1.00 RINF Initial bolide/meteor radius (m) [= 0.000001 - 1000.0]

• 12.82 VINF Initial velocity (km/s) [=11.2 - 73.0]

• 70.90 ZR Entry angle to vertical at top of atmosphere: deg [=0.0 - 80.0]

• 32.0 NBMX Maximum number of pieces of fragmentation [=1 - 1000]

• 1.209 SFINF Shape factor (area/ volume**2/3) 1.209= sphere [1.209 - 2.0]

• 0.6667 MU Shape change factor 2/3= no change [-3 to 2/3]

• 4.605 D Kinetic energy left at end height [2.303 - 4.605] i.e. [10 - 1%]

• 1.0 BRKTST Allow breakup 0= no; 1= yes [0 or 1]

• 1.0 FRGTST Fragments in wake 0= remain; 1= stay with body [0 or 1]

• 1.0 PORTST Allow porous materials 0= no-porosity; 1= porous [0 or 1]

• 1.0 SIGTEST Ablation parameter 0= no change; 1= full change [0 or 1]

• 0.0 MUTEST Shape change factor 0= constant; 1= variable [0 or 1]

• 1.0 ISTHRM Vertical structure 0= isothermal; 1= non-isothermal [0 or 1]

• 0.0 RHOTST Atmospheric density profile 0= winter; 1= summer [0 or 1]

• 0.70 POR [0 to 1]

TPFM Entry Modeling Results- Summary• Modeled as either porous (P) or homogeneous (H) body

• Modeled as either a collective wake (CW) behavior or as non-collective wake behavior (NCW)

• BEST FIT so far (End height fit and not a light curve fit):

• CW P = 70 %; 2 m diameter spherical; = 2/3 Bolide

Group IIIA (Strong cometary material), but the implied luminous efficiency compared to released satellite data is ~100 % (However, our very well calibrated differential luminous efficiency prediction for this case is ~1 %).

Entry modeling: Sphere; = 2/32 m diameter 70 % porous chondritic asteroid

Entry modeling: Sphere; = 2/32 m diameter 70 % porous chondritic asteroid

Entry modeling: Sphere; = 2/32 m diameter 70 % porous chondritic asteroid

Entry modeling: Sphere; = 2/32 m diameter 70 % porous chondritic asteroid

Entry modeling: Sphere; = 2/32 m diameter 70 % porous chondritic asteroid

Entry modeling: Sphere; = 2/32 m diameter 70 % porous chondritic asteroid

Entry modeling: Sphere; = 2/32 m diameter 70 % porous chondritic asteroid

Entry modeling: Sphere; = 2/32 m diameter 70 % porous chondritic asteroid

Entry modeling: Sphere; = 2/32 m diameter 70 % porous chondritic asteroid

Inverse Entry Modeling Iterations• Solution Search Parameters:

1 km/s < V < 20 km/s (Higher velocities not applicable) 0.01 m < R < 100 m (Larger and smaller sizes not applicable) Bolide groups searched: I (Ordinary chondrite), II

(Carbonaceous chondrite), IIIA (Strong cometary material), IIIB (Weak cometary material)

Nominal ablation parameters, , and bulk densities, m, for each group (Ceplecha et al, 1997): Homogeneous meteor model, Porosity limit = 0 %

Number of fragments = 1 (Only the original body without fragments).

Wave drag coefficient, CD = 0.92, Spherical unchanging shape Isothermal, hydrostatic model atmosphere utilized Observed end height with a specified error bar

Inverse Entry Modeling Summary

ObservedEntryvelocity

Summary and Conclusions• For the first time an astronomical object (in this case a small

asteroid or a large meteor-fireball) was observed with telescopes prior to its entry into the atmosphere. The primary purpose of such telescopic systems is to search for the potential “killer” bolides that could end life on Earth as we now know it.

• Official U.S. Government satellite detection data announced

• Modeling using LANL entry modeling codes DIRECT: Consistent with a Group IIIA bolide (Strong

cometary material) INVERSE: Consistent with a Group IIIA or Group IIIB bolide

• Detected by the CTBT IMS (International Monitoring System) infrasonic pressure wave arrays in Kenya and in Kazakhstan. Great circle bearing intersection confirms astronomical impact

location predictions. Great circle bearing intersection confirms event origin time.