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Background Briefing:
Impact Air Blasts Produced by Near-Earth Asteroids

                     Dr. David A. Kring
                 PI of the LPI-JSC NLSI Team




                                                   Detail from CLSE (Daniel D. Durda) image at
                                          http://www.lpi.usra.edu/nlsi/training/illustrations/bombardment/
BRIEFING ABSTRACT


                    On Friday, 15 February
                    2013, a small asteroid
                    penetrated Earth’s
                    atmosphere and
                    catastrophically disrupted
                    over Russia, injuring people
                    and damaging buildings in
                    the area around Chelyabinsk
                    (55.2N, 61.4E). The injuries
                    and damage were caused by
                    shock waves and associated
                    air blasts. I have received a
                    lot of queries about these
                    types of events and have
                    collated some notes here to
                    address them.

                             Detail from CLSE (Daniel D. Durda) image at
                    http://www.lpi.usra.edu/nlsi/training/illustrations/bombardment/
CURRENT ESTIMATES OF EVENT PROPERTIES

Based on information released by Peter Brown and/or attributed to NASA
  (as of 18 February 2013)

•   Diameter of asteroid = 55 ft (17 m)
•   Mass of asteroid = 10,000 tons
•   Velocity of asteroid = 40,000 mph (17-18 km/s)
•   Blast altitude = 15 to 20 km
•   Equivalent energy of the explosive event = 500 kt of TNT

NOTE: Other sources have generated different estimates for the values above;
these values are preliminary and may change significantly.

The event was roughly an order of magnitude more energetic than the Sikhote-Alin
event of 1947 (~10 kt), but roughly an order of magnitude less energetic than the
Tunguska event of 1908 (~2-20 MT).
Caveats: Estimates of past events (even historical events like Tunguska) come with
lots of uncertainty.
That uncertainty underscores the need for modern, high-quality measurements of
impact-generated air blast events.
CURRENT ESTIMATES OF EVENT PROPERTIES

Based on information reported from Russia
  (as of 18 February 2013)

• A portion of the catastrophically fragmented asteroid survives
• The meteoritic material resembles ordinary chondrites – which are from a class
  of stony asteroids that contain a small amount of metal

                                                            Gold Basin event

Previously, the largest documented explosive
fragmentation of an ordinary chondritic
asteroid occurred over northwestern Arizona in
the Gold Basin area. That event involved an
~8 meter diameter asteroid with the kinetic
energy equivalent to 5 to 50 kt of TNT. Several
thousand relics of the asteroid were found in
the desert. See Kring et al. (2001) for details.
IMPACT VELOCITY

                                                                        Typical asteroid velocity

                                                                        Average impact
                                                                        velocities of asteroids
                                                                        hitting the Earth are
                                                                        about 18 km/s.
                                                                        The object that hit Earth
                                               15 February 2013 event
                                                                        15 February 2013 has an
                                                                        estimated velocity of 17-
                                                                        18 km/s, which is typical
                                                                        of an asteroid and much
                                                                        lower than that of typical
                                                                        comets.
                                                                        Thus, the velocity and
Illustration credit: CLSE (Shaner and Kring)
                                                                        the recovery of ordinary
                                                                        chondrites are
                                                                        consistent.
COMPONENTS OF IMPACT AIR BLASTS




• Ballistic shock wave produced when an asteroid penetrates the atmosphere with
  speed equal to or in excess of 11.2 km/s (≥25,000 mph)
• Explosive shock wave produced when the object catastrophically fragments in the
  atmosphere or hits the surface to produce an impact crater
• The shock waves are accompanied by high-velocity air blasts
• Similar effects were measured around nuclear explosions test sites
CASE STUDY OF AN IMPACT AIR BLAST – BARRINGER (METEOR) CRATER

                                              20-50 m iron asteroid   Small cratering events
                                              ~50,000 yrs ago
                                              Northern Arizona        In small events, the fireball,
                                                                      shock wave, and airblast are
                                                                      the major environmental
                                                                      effects.

                                                                      The blast effect was
                                                                      immediately lethal for human-
                                                                      sized animals within the inner
                                                                      6 km diameter circle.

                                                                      Severe lung damage would
                                                                      occur within the next 10-12
                                                                      km diameter circle due to the
                                                                      pressure pulse alone and
                                                                      animals would be severely
                                                                      injured and unlikely to survive.
 See Kring (1997) and Grieve & Kring (2007) for details
CASE STUDY OF AN IMPACT AIR BLAST – BARRINGER (METEOR) CRATER

                                              20-50 m iron asteroid   Small cratering events
                                              ~50,000 yrs ago
                                              Northern Arizona        Winds would exceed 1500
                                                                      km/hr within the inner circle
                                                                      and still exceed 100 km/hr at
                                                                      radial distances of 25 km (3rd
                                                                      circle).

                                                                      The outermost ~50 km circle
                                                                      represents the outer limit of
                                                                      severe to moderate damage
                                                                      to trees and human-structures
                                                                      of comparable strength.




 See Kring (1997) and Grieve & Kring (2007) for details
CASE STUDY OF AN IMPACT AIR BLAST – BARRINGER (METEOR) CRATER

                                              20-50 m iron asteroid   Small cratering events
                                              ~50,000 yrs ago
                                              Northern Arizona        Such an event today could
                                                                      decimate the population of an
                                                                      urban area equivalent to the
                                                                      size of Kansas City, U.S.A.
                                                                      (population 425,000).




 See Kring (1997) and Grieve & Kring (2007) for details                40 km circle corresponding to severe to
                                                                       moderate damage.
CASE STUDY OF AN IMPACT AIR BLAST – MANICOUAGAN

                                          Manicouagan

                                          Larger impact cratering
                                          events will produce air
                                          blasts that affect a larger
                                          area.

                                          Manicouagan is a crater
                                          with a diameter of ~100
                                          km.

                                          That impact air blast
                                          affected a large fraction
                                          of Canada.
Grieve and Kring (2007)
CASE STUDY OF AN IMPACT AIR BLAST – CHICXULUB CRATER

                                                          Dinosaur-killing event

                                                          At the extremely large
                                                          end of the spectrum is
                                                          the Chicxulub impact
                                                          event that caused a
                                                          mass extinction 65
                                                          million years ago.

                                                          The air blast produced
                                                          by that impact event
                                                          affected a large fraction
                                                          of North America.

                                                          The airblast is only one
See Emiliani et al. (1981) and Kring (2007) for details   of many environmental
                                                          effects produced by this
                                                          size of impact event.
IMPACT AIR BLASTS OF DIFFERENT SIZES

                                                                                               Impact air blasts

                                                                                               The Chelyabinsk event is
                                                                                               at the extreme (small)
                                                                                               end of the types of
                                                                                               events that produce air
                                                                                               blasts.
                                                                                               Less frequent, larger
                                                                                               events can affect larger
                                                                                               areas.

                                                                                               As the world’s population
                                                                                               grows and occupies a
                                                                                               larger fraction of the
                                                                                               Earth’s surface, events
Modified after Figure 1.5 of Grieve and Kring (2007). Please see that paper or PPTx            like Chelyabinsk will
notes (below) for a description of the uncertainties associated with the data plotted in the
diagram                                                                                        become more common.
SOURCES OF NEAR-EARTH ASTEROIDS

                                  NEA source region

                                  Near-Earth asteroids
                                  come from the main
                                  asteroid belt.

                                  Their orbits, once nearly
                                  circular, have been
                                  perturbed by
                                  gravitational processes
                                  into elliptical orbits that
                                  cross the orbit of Earth.

                                  The pre-impact orbits of
                                  previously fallen
                                  meteorites illustrate this
                                  point.
THE STRUCTURAL INTEGRITY OF NEAR-EARTH ASTEROIDS


 The measured compressive strengths of ordinary chondrites may not be the best
 measure of the structural integrity of near-Earth asteroids (see Kring et al. 1996
 for evidence and discussion).

 Instead, the strength of material may be limited to structural flaws (like fractures
 or material contrasts) rather than the strength of individual clasts within them.

 The fall phenomena associated with meteorites support the idea that structural
 flaws limit the strength of near-Earth asteroid material. For example, fragmental
 breccias preferentially fall apart in Earth’s atmosphere and produce meteorite
 showers (Kring et al. 1999).

 IMPORTANT : The Chelyabinsk event, if documented well, can be used to
 determine the strength of the near-Earth asteroid, which is a fundamental
 parameter needed for impact mitigation strategies.
REFERENCES

Emiliani, C., E. B. Kraus, and E. M. Shoemaker (1981) Sudden death at the end of
the Mesozoic. Earth and Planetary Science Letters 55, 317-334.

Grieve, R. A. F. and D. A. Kring (2007) The geologic record of destructive impact
events on Earth. In Comet/Asteriod Impacts and Human Society, P. Bobrowsky
and H. Rickman (eds.), Springer, Berlin, pp. 3-24.

Kring, D. A. (1997) Air blast produced by the Meteor Crater impact event and a
reconstruction of the affected environment. Meteoritics and Planetary Science 32,
517-530.

Kring, D. A. (2007) The Chicxulub impact event and its environmental
consequences at the Cretaceous-Tertiary boundary. Palaeogeography,
Palaeoclimatology, Palaeoecology 255, 4-21.

Kring, D. A., T. D. Swindle, D. T. Britt, and J. A. Grier (1996) Cat Mountain: A
meteoritic sample of an impact-melted asteroid regolith. Journal of Geophysical
Research 101, 29353-29371.
REFERENCES

Kring, D. A., D. H. Hill, J. D. Gleason, D. T. Britt, G. J. Consolmagno, M. Farmer, S.
Wilson, and R. Haag (1999) Portales Valley: A meteoritic sample of the brecciated
and metal-veined floor of an impact crater on an H-chondrite asteriod. Meteoritics
and Planetary Science 34, 663-669.

Kring, D. A., A. J. T. Jull, L. R. McHargue, P. A. Bland, D. H. Hill, and F. J. Berry
(2001) Gold Basin meteorite strewn field, Mojave Desert, northwestern Arizona:
Relic of a small late Pleistocene impact event. Meteoritics and Planetary Science
36, 1057-1066.
Additional Slides
SIKHOTE-ALIN EVENT 1947


 12 February 1947
 Iron asteroid (type IIAB coarsest octahedrite)

 46°9’36” N, 134°39’12” E
 Sikhote-Alin Mountains, 25 miles from Novopoltavka, Maritime Province, Russia

 A shower of fireballs produced 106 impact holes, the largest 28 meters in
 diameter, over an area of 100 by 660 meters.

 Over 27,000 kg of metal was found, the largest fragment weighing 300 kg.

 Some of the metal have a characteristic shrapnel appearance.
TUNGUSKA EVENT 1908


 30 June 1908
 Believed to be a stony asteroid

 60°54’ N, 101°57’ E
 Krasnoyarskiy Kray, Evenki, Russia

 An immense fireball and a catastrophic air blast flattened a large section of forest
 and may have initiated short-lived fires.

 Estimated mass of object is one thousand to one million tons.

 Traces of surviving material from the impactor have been reported, but the object
 was effectively obliterated in the explosion.
OTHER EVENTS FOR COMPARISON

Barringer Meteorite Crater (aka Meteor Crater), Arizona, ~50,000 years ago
     • Estimated equivalent energy of cratering event ranges from ~2 to ~20 MT
     • Iron asteroid
     • Estimated diameter ranges from ~10 to ~50 m

Gold Basin, Arizona, 15-20 thousand years ago (Kring et al. 2001)
    • Estimate equivalent energy of 5 to 50 kt of TNT
    • ~8 meter diameter object
    • Asteroid was composed of a breccia from the L-chondrite parent body

Asteroid 2008 TC3, Sudan, 2008 (Shaddad et al. 2010)
    • Estimated equivalent energy of 1.2 kt of TNT
    • Breccia

Indonesia 8 October 2009 (Silber et al. 2011)
    • Estimated equivalent energy of atmospheric blast = 8 to 67 kt of TNT
    • Favored best estimate of ~50 kt
    • Type of asteroid unknown
OTHER EVENTS FOR COMPARISON

Sutter’s Mill, California, 22 April 2012 (Jenniskens et al. 2012)
    • Estimated equivalent energy of 4.0 (-2.2/+3.4) kt of TNT
    • High-speed entry velocity of 28.6 km/s
    • ~2.5 m object
    • Composed of regolith breccia from a carbonaceous chondrite parent body
ORDINARY CHONDRITE ASTEROID SAMPLES

We have over 50,000 samples of near-Earth asteroids in our collections

That includes a large number of samples from ordinary chondrite parent bodies.

There are at least three types of ordinary chondrite parent bodies:
    • Type H – 17,747 meteorite samples
    • Type L – 15,734 meteorite samples
    • Type LL – 5,839 meteorite samples
    • Totaling nearly 40,000 samples from ordinary chondrite parent bodies
    • Per the Meteoritical Bulletin Database
CURRENT ESTIMATES OF EVENT PROPERTIES

Current estimates are based on infrasound data from the International Monitory
System (IMS) operated by the Comprehensive Nuclear-Test-Ban Treaty
Organization (CTBTO).

Estimates are also possible from satellite energy spectra, ground-based radar data,
and from the range of damage on the surface if the blast height is known.

The energy of the event and blast height are first-order products of the data
analysis. If a velocity is known, then the mass of the object can be inferred from the
kinetic energy (1/2 mv2). If a density is assumed, then the average size of the
object can be estimated. Passage through the atmosphere can decelerate the
object (hence affect velocity) and shed mass.

Any meteoritic material found can be used to refine the assumed density.
SMALL METEOR SEEN FROM THE INTERNATIONAL SPACE STATION (ISS)

                                          Meteors

                                          Most debris hitting the
                                          Earth’s atmosphere is
                                          too small to penetrate
                                          and burns up without
                                          causing any damage.
                                          Astronaut ISS
                                          photograph of meteor as
                                          it passes through the
                                          atmosphere.
                                          The image was taken on
                                          August 13, 2011, during
ISS028-E-024847                           the Perseid Meteor
                                          Shower of particles that
                                          originate from Comet
                                          Swift-Tuttle.
PENETRATING EARTH’S ATMOSPHERE

                                 Meteoroids in Earth’s atmosphere
     Krinov
                                 The atmosphere is an effective filter
                                 of impacting debris
                                 Intermediate-size objects that are
                                 not destroyed in the upper
                                 atmosphere can fragment, producing
                                 a shower of debris, or survive nearly
                                 intact, producing a single meteorite.

                                 Multiple fragmentation events are
                                 possible.

                                 Larger objects that are not
                                 significantly decelerated and reach
                                 the ground can produce
                                 hypervelocity impact craters.
NOT ALL METEORITE SHOWERS PRODUCE DAMAGING AIRBLASTS

                               Portales Valley event

                               At~7:30 am on 13 June 1998, a
                               meteoroid entered Earth’s
                               atmosphere and fell near Portales,
                               New Mexico.

                               Witnesses reported hearing
                               detonations and seeing smoke trails
                               in the sky.

                               Before hitting the ground, the
                               meteoroid fragmented at least once,
                               producing a strewn field with a
                               length over 10 km.

                               See Kring et al. (1999) for details.
REFERENCES FOR ADDITIONAL SLIDES


Kring, D. A., D. H. Hill, J. D. Gleason, D. T. Britt, G. J. Consolmagno, M. Farmer, S.
Wilson, and R. Haag (1999) Portales Valley: A meteoritic sample of the brecciated
and metal-veined floor of an impact crater on an H-chondrite asteroid. Meteoritics
and Planetary Science 34, 663-669.

Krinov, E. L. (1966) Giant Meteorites. (Translated from Russian by J. S.
Romankiewicz.) Pergamon Press, New York, 397p.

Jenniskens, P. et al. (2012) Radar-enabled recovery of the Sutter’s Mill meteorite, a
carbonaceous chondrite regolith breccia. Science 338, 1583-1587.

Shaddad, M. H. et al. (2010) The recovery of asteroid 2008 TC3. Meteoritics and
Planetary Science 45, 1557-1589.

Silber, E. A., A. Le Pichon, and P. G. Brown (2011) Infrasonic detection of a near-
Earth asteroid object impact over Indonesia on 8 October 2009. Geophysical
Research Letters 38, L12201, doi:10.1029/2011GL047633.

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Kring background briefing about impact air blasts 18_feb2013

  • 1. Background Briefing: Impact Air Blasts Produced by Near-Earth Asteroids Dr. David A. Kring PI of the LPI-JSC NLSI Team Detail from CLSE (Daniel D. Durda) image at http://www.lpi.usra.edu/nlsi/training/illustrations/bombardment/
  • 2. BRIEFING ABSTRACT On Friday, 15 February 2013, a small asteroid penetrated Earth’s atmosphere and catastrophically disrupted over Russia, injuring people and damaging buildings in the area around Chelyabinsk (55.2N, 61.4E). The injuries and damage were caused by shock waves and associated air blasts. I have received a lot of queries about these types of events and have collated some notes here to address them. Detail from CLSE (Daniel D. Durda) image at http://www.lpi.usra.edu/nlsi/training/illustrations/bombardment/
  • 3. CURRENT ESTIMATES OF EVENT PROPERTIES Based on information released by Peter Brown and/or attributed to NASA (as of 18 February 2013) • Diameter of asteroid = 55 ft (17 m) • Mass of asteroid = 10,000 tons • Velocity of asteroid = 40,000 mph (17-18 km/s) • Blast altitude = 15 to 20 km • Equivalent energy of the explosive event = 500 kt of TNT NOTE: Other sources have generated different estimates for the values above; these values are preliminary and may change significantly. The event was roughly an order of magnitude more energetic than the Sikhote-Alin event of 1947 (~10 kt), but roughly an order of magnitude less energetic than the Tunguska event of 1908 (~2-20 MT). Caveats: Estimates of past events (even historical events like Tunguska) come with lots of uncertainty. That uncertainty underscores the need for modern, high-quality measurements of impact-generated air blast events.
  • 4. CURRENT ESTIMATES OF EVENT PROPERTIES Based on information reported from Russia (as of 18 February 2013) • A portion of the catastrophically fragmented asteroid survives • The meteoritic material resembles ordinary chondrites – which are from a class of stony asteroids that contain a small amount of metal Gold Basin event Previously, the largest documented explosive fragmentation of an ordinary chondritic asteroid occurred over northwestern Arizona in the Gold Basin area. That event involved an ~8 meter diameter asteroid with the kinetic energy equivalent to 5 to 50 kt of TNT. Several thousand relics of the asteroid were found in the desert. See Kring et al. (2001) for details.
  • 5. IMPACT VELOCITY Typical asteroid velocity Average impact velocities of asteroids hitting the Earth are about 18 km/s. The object that hit Earth 15 February 2013 event 15 February 2013 has an estimated velocity of 17- 18 km/s, which is typical of an asteroid and much lower than that of typical comets. Thus, the velocity and Illustration credit: CLSE (Shaner and Kring) the recovery of ordinary chondrites are consistent.
  • 6. COMPONENTS OF IMPACT AIR BLASTS • Ballistic shock wave produced when an asteroid penetrates the atmosphere with speed equal to or in excess of 11.2 km/s (≥25,000 mph) • Explosive shock wave produced when the object catastrophically fragments in the atmosphere or hits the surface to produce an impact crater • The shock waves are accompanied by high-velocity air blasts • Similar effects were measured around nuclear explosions test sites
  • 7. CASE STUDY OF AN IMPACT AIR BLAST – BARRINGER (METEOR) CRATER 20-50 m iron asteroid Small cratering events ~50,000 yrs ago Northern Arizona In small events, the fireball, shock wave, and airblast are the major environmental effects. The blast effect was immediately lethal for human- sized animals within the inner 6 km diameter circle. Severe lung damage would occur within the next 10-12 km diameter circle due to the pressure pulse alone and animals would be severely injured and unlikely to survive. See Kring (1997) and Grieve & Kring (2007) for details
  • 8. CASE STUDY OF AN IMPACT AIR BLAST – BARRINGER (METEOR) CRATER 20-50 m iron asteroid Small cratering events ~50,000 yrs ago Northern Arizona Winds would exceed 1500 km/hr within the inner circle and still exceed 100 km/hr at radial distances of 25 km (3rd circle). The outermost ~50 km circle represents the outer limit of severe to moderate damage to trees and human-structures of comparable strength. See Kring (1997) and Grieve & Kring (2007) for details
  • 9. CASE STUDY OF AN IMPACT AIR BLAST – BARRINGER (METEOR) CRATER 20-50 m iron asteroid Small cratering events ~50,000 yrs ago Northern Arizona Such an event today could decimate the population of an urban area equivalent to the size of Kansas City, U.S.A. (population 425,000). See Kring (1997) and Grieve & Kring (2007) for details 40 km circle corresponding to severe to moderate damage.
  • 10. CASE STUDY OF AN IMPACT AIR BLAST – MANICOUAGAN Manicouagan Larger impact cratering events will produce air blasts that affect a larger area. Manicouagan is a crater with a diameter of ~100 km. That impact air blast affected a large fraction of Canada. Grieve and Kring (2007)
  • 11. CASE STUDY OF AN IMPACT AIR BLAST – CHICXULUB CRATER Dinosaur-killing event At the extremely large end of the spectrum is the Chicxulub impact event that caused a mass extinction 65 million years ago. The air blast produced by that impact event affected a large fraction of North America. The airblast is only one See Emiliani et al. (1981) and Kring (2007) for details of many environmental effects produced by this size of impact event.
  • 12. IMPACT AIR BLASTS OF DIFFERENT SIZES Impact air blasts The Chelyabinsk event is at the extreme (small) end of the types of events that produce air blasts. Less frequent, larger events can affect larger areas. As the world’s population grows and occupies a larger fraction of the Earth’s surface, events Modified after Figure 1.5 of Grieve and Kring (2007). Please see that paper or PPTx like Chelyabinsk will notes (below) for a description of the uncertainties associated with the data plotted in the diagram become more common.
  • 13. SOURCES OF NEAR-EARTH ASTEROIDS NEA source region Near-Earth asteroids come from the main asteroid belt. Their orbits, once nearly circular, have been perturbed by gravitational processes into elliptical orbits that cross the orbit of Earth. The pre-impact orbits of previously fallen meteorites illustrate this point.
  • 14. THE STRUCTURAL INTEGRITY OF NEAR-EARTH ASTEROIDS The measured compressive strengths of ordinary chondrites may not be the best measure of the structural integrity of near-Earth asteroids (see Kring et al. 1996 for evidence and discussion). Instead, the strength of material may be limited to structural flaws (like fractures or material contrasts) rather than the strength of individual clasts within them. The fall phenomena associated with meteorites support the idea that structural flaws limit the strength of near-Earth asteroid material. For example, fragmental breccias preferentially fall apart in Earth’s atmosphere and produce meteorite showers (Kring et al. 1999). IMPORTANT : The Chelyabinsk event, if documented well, can be used to determine the strength of the near-Earth asteroid, which is a fundamental parameter needed for impact mitigation strategies.
  • 15. REFERENCES Emiliani, C., E. B. Kraus, and E. M. Shoemaker (1981) Sudden death at the end of the Mesozoic. Earth and Planetary Science Letters 55, 317-334. Grieve, R. A. F. and D. A. Kring (2007) The geologic record of destructive impact events on Earth. In Comet/Asteriod Impacts and Human Society, P. Bobrowsky and H. Rickman (eds.), Springer, Berlin, pp. 3-24. Kring, D. A. (1997) Air blast produced by the Meteor Crater impact event and a reconstruction of the affected environment. Meteoritics and Planetary Science 32, 517-530. Kring, D. A. (2007) The Chicxulub impact event and its environmental consequences at the Cretaceous-Tertiary boundary. Palaeogeography, Palaeoclimatology, Palaeoecology 255, 4-21. Kring, D. A., T. D. Swindle, D. T. Britt, and J. A. Grier (1996) Cat Mountain: A meteoritic sample of an impact-melted asteroid regolith. Journal of Geophysical Research 101, 29353-29371.
  • 16. REFERENCES Kring, D. A., D. H. Hill, J. D. Gleason, D. T. Britt, G. J. Consolmagno, M. Farmer, S. Wilson, and R. Haag (1999) Portales Valley: A meteoritic sample of the brecciated and metal-veined floor of an impact crater on an H-chondrite asteriod. Meteoritics and Planetary Science 34, 663-669. Kring, D. A., A. J. T. Jull, L. R. McHargue, P. A. Bland, D. H. Hill, and F. J. Berry (2001) Gold Basin meteorite strewn field, Mojave Desert, northwestern Arizona: Relic of a small late Pleistocene impact event. Meteoritics and Planetary Science 36, 1057-1066.
  • 18. SIKHOTE-ALIN EVENT 1947 12 February 1947 Iron asteroid (type IIAB coarsest octahedrite) 46°9’36” N, 134°39’12” E Sikhote-Alin Mountains, 25 miles from Novopoltavka, Maritime Province, Russia A shower of fireballs produced 106 impact holes, the largest 28 meters in diameter, over an area of 100 by 660 meters. Over 27,000 kg of metal was found, the largest fragment weighing 300 kg. Some of the metal have a characteristic shrapnel appearance.
  • 19. TUNGUSKA EVENT 1908 30 June 1908 Believed to be a stony asteroid 60°54’ N, 101°57’ E Krasnoyarskiy Kray, Evenki, Russia An immense fireball and a catastrophic air blast flattened a large section of forest and may have initiated short-lived fires. Estimated mass of object is one thousand to one million tons. Traces of surviving material from the impactor have been reported, but the object was effectively obliterated in the explosion.
  • 20. OTHER EVENTS FOR COMPARISON Barringer Meteorite Crater (aka Meteor Crater), Arizona, ~50,000 years ago • Estimated equivalent energy of cratering event ranges from ~2 to ~20 MT • Iron asteroid • Estimated diameter ranges from ~10 to ~50 m Gold Basin, Arizona, 15-20 thousand years ago (Kring et al. 2001) • Estimate equivalent energy of 5 to 50 kt of TNT • ~8 meter diameter object • Asteroid was composed of a breccia from the L-chondrite parent body Asteroid 2008 TC3, Sudan, 2008 (Shaddad et al. 2010) • Estimated equivalent energy of 1.2 kt of TNT • Breccia Indonesia 8 October 2009 (Silber et al. 2011) • Estimated equivalent energy of atmospheric blast = 8 to 67 kt of TNT • Favored best estimate of ~50 kt • Type of asteroid unknown
  • 21. OTHER EVENTS FOR COMPARISON Sutter’s Mill, California, 22 April 2012 (Jenniskens et al. 2012) • Estimated equivalent energy of 4.0 (-2.2/+3.4) kt of TNT • High-speed entry velocity of 28.6 km/s • ~2.5 m object • Composed of regolith breccia from a carbonaceous chondrite parent body
  • 22. ORDINARY CHONDRITE ASTEROID SAMPLES We have over 50,000 samples of near-Earth asteroids in our collections That includes a large number of samples from ordinary chondrite parent bodies. There are at least three types of ordinary chondrite parent bodies: • Type H – 17,747 meteorite samples • Type L – 15,734 meteorite samples • Type LL – 5,839 meteorite samples • Totaling nearly 40,000 samples from ordinary chondrite parent bodies • Per the Meteoritical Bulletin Database
  • 23. CURRENT ESTIMATES OF EVENT PROPERTIES Current estimates are based on infrasound data from the International Monitory System (IMS) operated by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). Estimates are also possible from satellite energy spectra, ground-based radar data, and from the range of damage on the surface if the blast height is known. The energy of the event and blast height are first-order products of the data analysis. If a velocity is known, then the mass of the object can be inferred from the kinetic energy (1/2 mv2). If a density is assumed, then the average size of the object can be estimated. Passage through the atmosphere can decelerate the object (hence affect velocity) and shed mass. Any meteoritic material found can be used to refine the assumed density.
  • 24. SMALL METEOR SEEN FROM THE INTERNATIONAL SPACE STATION (ISS) Meteors Most debris hitting the Earth’s atmosphere is too small to penetrate and burns up without causing any damage. Astronaut ISS photograph of meteor as it passes through the atmosphere. The image was taken on August 13, 2011, during ISS028-E-024847 the Perseid Meteor Shower of particles that originate from Comet Swift-Tuttle.
  • 25. PENETRATING EARTH’S ATMOSPHERE Meteoroids in Earth’s atmosphere Krinov The atmosphere is an effective filter of impacting debris Intermediate-size objects that are not destroyed in the upper atmosphere can fragment, producing a shower of debris, or survive nearly intact, producing a single meteorite. Multiple fragmentation events are possible. Larger objects that are not significantly decelerated and reach the ground can produce hypervelocity impact craters.
  • 26. NOT ALL METEORITE SHOWERS PRODUCE DAMAGING AIRBLASTS Portales Valley event At~7:30 am on 13 June 1998, a meteoroid entered Earth’s atmosphere and fell near Portales, New Mexico. Witnesses reported hearing detonations and seeing smoke trails in the sky. Before hitting the ground, the meteoroid fragmented at least once, producing a strewn field with a length over 10 km. See Kring et al. (1999) for details.
  • 27. REFERENCES FOR ADDITIONAL SLIDES Kring, D. A., D. H. Hill, J. D. Gleason, D. T. Britt, G. J. Consolmagno, M. Farmer, S. Wilson, and R. Haag (1999) Portales Valley: A meteoritic sample of the brecciated and metal-veined floor of an impact crater on an H-chondrite asteroid. Meteoritics and Planetary Science 34, 663-669. Krinov, E. L. (1966) Giant Meteorites. (Translated from Russian by J. S. Romankiewicz.) Pergamon Press, New York, 397p. Jenniskens, P. et al. (2012) Radar-enabled recovery of the Sutter’s Mill meteorite, a carbonaceous chondrite regolith breccia. Science 338, 1583-1587. Shaddad, M. H. et al. (2010) The recovery of asteroid 2008 TC3. Meteoritics and Planetary Science 45, 1557-1589. Silber, E. A., A. Le Pichon, and P. G. Brown (2011) Infrasonic detection of a near- Earth asteroid object impact over Indonesia on 8 October 2009. Geophysical Research Letters 38, L12201, doi:10.1029/2011GL047633.