This document provides background information on air blasts produced by near-Earth asteroids. It summarizes current estimates of the properties of the February 2013 Chelyabinsk event based on preliminary data. The event is estimated to have involved a 17 meter asteroid with a velocity of 40,000 mph that exploded 15-20 km above the Earth's surface with an energy equivalent to 500 kilotons of TNT. The briefing also discusses past asteroid air blast events like Tunguska and Barringer Crater for comparison. It examines the components of impact air blasts and how blast areas scale with the size of the impacting object.
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.