DOI: 10.1126/science.1242642
, 1069 (2013);342 Science
et al.Olga P. Popova
Characterization
Chelyabinsk Airburst, Damage Assessment, Meteorite Recovery, and
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Chelyabinsk Airburst, Damage
Assessment, Meteorite Recovery,
and Characterization
Olga P. Popova,
1
Peter Jenniskens,
2,3
* Vacheslav Emel’yanenko,
4
Anna Kartashova,
4
Eugeny Biryukov,
5
Sergey Khaibrakhmanov,
6
Valery Shuvalov,
1
Yurij Rybnov,
1
Alexandr Dudorov,
6
Victor I. Grokhovsky,
7
Dmitry D. Badyukov,
8
Qing-Zhu Yin,
9
Peter S. Gural,
2
Jim Albers,
2
Mikael Granvik,
10
Läslo G. Evers,
11,12
Jacob Kuiper,
11
Vladimir Kharlamov,
1
Andrey Solovyov,
13
Yuri S. Rusakov,
14
Stanislav Korotkiy,
15
Ilya Serdyuk,
16
Alexander V. Korochantsev,
8
Michail Yu. Larionov,
7
Dmitry Glazachev,
1
Alexander E. Mayer,
6
Galen Gisler,
17
Sergei V. Gladkovsky,
18
Josh Wimpenny,
9
Matthew E. Sanborn,
9
Akane Yamakawa,
9
Kenneth L. Verosub,
9
Douglas J. Rowland,
19
Sarah Roeske,
9
Nicholas W. Botto,
9
Jon M. Friedrich,
20,21
Michael E. Zolensky,
22
Loan Le,
23,22
Daniel Ross,
23,22
Karen Ziegler,
24
Tomoki Nakamura,
25
Insu Ahn,
25
Jong Ik Lee,
26
Qin Zhou,
27,28
Xian-Hua Li,
28
Qiu-Li Li,
28
Yu Liu,
28
Guo-Qiang Tang,
28
Takahiro Hiroi,
29
Derek Sears,
3
Ilya A. Weinstein,
7
Alexander S. Vokhmintsev,
7
Alexei V. Ishchenko,
7
Phillipe Schmitt-Kopplin,
30,31
Norbert Hertkorn,
30
Keisuke Nagao,
32
Makiko K. Haba,
32
Mutsumi Komatsu,
33
Takashi Mikouchi,
34
(the Chelyabinsk Airburst Consortium)
The asteroid impact near the Russian city of Chelyabinsk on 15 February 2013 was the largest airburst
on Earth since the 1908 Tunguska event, causing a naturaldisasterinanareawithapopulation
exceeding one million. Because it occurred in an era with modern consumer electronics, field sensors,
and laboratory techniques, unprecedented measurements were made of the impact event and the
meteoroidthatcausedit.Here,wedocumenttheaccount of what happened, as understood now, using
comprehensive data obtained from astronomy, planetary science, geophysics, meteorology, meteoritics,
and cosmochemistry and from social science surveys. A good understanding of the Chelyabinsk
incident provides an opportunity to calibrate the event, with implications for the study of near-Earth
objects and developing hazard mitigation strategies for planetary protection.
C
helyabinsk Oblast experienced an impact
that was 100 times more energetic than the
recent 4 kT of TNT–equivalent Sutter’s Mill
meteorite fall (1). This was the biggest impact ov er
land since the poorly observed Tungus ka impact in
1908, for which kinetic energy estimates range from
3to5(2)to10to50MT(3). From the measured
period of infrasound waves circum-traveling the
globe (4), an early estimate of ~ 470 kT was derived
for Chelyabinsk (5). Infrasound data from Russia
and Kazakhstan provide 570 T 150 kT ; see supple-
mentary materials (SM) section 1.4 (6). Spaceborne
visible and near-infrared observations (7) recorded a
total irradiated energy of 90 kT (5, 8), corresponding
to a kinetic ener gy of 590 T 50 kT using the
calibration by Nemtchinov et al.(9). All values are
uncertain by a factor of two because of a lack of
calibration data at those high energies and altitudes.
The manner in which this kinetic energy was
deposited in the atmosphere determined what
shock wave reached the ground. Dash-camera
and security camera videos of the fireball (Fig. 1)
provide a light curve with peak brightness of
–27.3 T 0.5 magnitude (Fig. 2) (SM section 1.2).
The integrated light curve is consistent with other
energy estimates if the panchromatic luminous
efficiency was 7 T 3%. Theoretical estimates un-
der these conditions range from 5.6 to 13.2% (10).
Calibrated video observations provided a tra-
jectory and pre-atmospheric orbit (T able 1) (SM
section 1.1). The fireball was first recorded at
97-km altitude, moving at 19.16 T 0.15 km/s with
entry angle 18.3 T 0.2° with respect to the horizon,
which is slightly faster than reported earlier (11).
Combined with the best kinetic energy estimate,
an entry mass of 1.3 × 10
7
kg (with a factor of two
uncertainty) and a diameter of 19.8 T 4.6 m is de-
rived, assuming a spherical shape and the meteorite-
derived density of 3.3 g/cm
3
basedonx-raycomputed
tomography (SM section 4.2, table S16).
Size and speed suggest that a shock wave first
developed at 90 km. Observations show that dust
formation and fragmentation started around 83 km
and accelerated at 54 km (figs. S16 and S22).
Peak radiation occurred at an altitude of 29.7 T
0.7 km at 03:20:32.2 T 0.1s UTC (SM section
1.1-2), at which time spaceborne sensors mea-
sured a meteoroid speed of 18.6 km/s (5). Frag-
mentation left a thermally emitting debris cloud
in this period, the final burst of which occurred at
27.0-km altitude (Fig. 1), with dust and gas set-
tling at 26.2 km and with distinctly higher billow-
ing above that location (fig. S22). The dust cloud
split in two due to the buoyancy of the hot gas,
leading to two cylindrical vortices (12).
Compared with the much larger T unguska event
(2, 3), Chelyabinsk was only on the threshold of
forming a common shock wave around the frag-
ments when it broke at peak brightness (SM section
1.2). Fragments were spatially isolated enough to be
efficiently decelerated, avoiding the transfer of mo-
mentum to lower altitudes and resul t i n g in les s
da m ag e whe n the bla st wav e rea c he d the ground.
Damage Assessment
In the weeks after the event, 50 villages were vis-
ited to verify the extent of glass damage. The
resulting map (Fig. 3) demonstrates that the shock
wave had a cylindrical component, extending fur-
thest perpendicular to the trajectory. There was
little coherence of the shock wave in the forward
direction, where the disturbance was of long du-
ration, shaking buildings and making people run
outside, but causing no damage.
RESEARCH ARTICLE
1
Institute for Dynamics of Geospheres of the Russian Academy
of Sciences, Leninsky Prospect 38, Building 1, Moscow, 119334,
Russia.
2
SETI Institute, 189 Bernardo Avenue, Mountain View,
CA 94043, USA.
3
NASA Ames Research Center, Moffett Field,
Mail Stop 245-1, CA 94035, USA.
4
Institute of Astronomy of
the Russian Academy of Sciences, Pyatnitskaya 48, Moscow,
119017, Russia.
5
Department of Theoretical Mechanics, South
Ural State University, Lenin Avenue 76, Chelyabinsk, 454080,
Russia.
6
Chelyabinsk State University, Brat yev K ashirinyh Street
129, Chelyabinsk, 454001, Russia.
7
Institute of Physics and Tech-
nology, Ural Federal University, Mira Street 19, Yekaterinburg,
620002, Russia.
8
Vernadsky Institute of Geochemis try and
Analytical Chemistry of the RAS, Kosygina Street 19, Moscow,
119991, Russia.
9
Department of Earth and Planetary Sciences,
University of California at Davis, Davis, CA 95616, USA.
10
Depart-
ment of Physics, University of Helsinki, P.O. Box 64, 00014
Helsinki, Finland.
11
Koninklijk Nederlands Meteorologisch In-
stituut, P.O. Box 201, 3730 AE De Bilt, Netherlands.
12
Depart-
ment of Geoscience and Engineering, Faculty of Civil Engineering
and Geosciences, Delft University of Technology, P.O. Box
5048, 2600 GA Delft, Netherlands.
13
Tomsk State University,
Lenina Prospect 36, Tomsk, 634050, Russia.
14
Research and
Production Association “Typhoon,” Floor 2, 7 Engels Street,
Obninsk, 249032, Russia.
15
Support Foundation for Astronomy
“Ka-Dar,” P.O. Box 82, Razvilka, 142717, Russia.
16
Science and
Technology Center of the Social and Youth Initiatives Organi-
zation, 3-12-63 Udal’tsova Street, Moscow, 119415, Russia.
17
University of Oslo, Physics Building, Sem Saelands Vel 24,
0316 Oslo, Norway.
18
Institute of Engineering Sciences Urals
Branch of the Russian Academy of Sciences, Komsomolskaya
Street 34, Yekaterinburg, 620049, Russia.
19
Center for Mo-
lecular and Genomic Imaging, University of California, Davis,
Davis, CA 95616, USA.
20
Department of Earth and Planetary
Sciences, American Museum of Natural History, New York, NY
10024, USA.
21
Department of Chemistry, Fordham University,
Bronx, NY 10458, USA.
22
Astromaterials Research and Ex-
ploration Science, NASA Johnson Space Center, Houston, TX
77058, USA.
23
Jacobs Technology, 2224 Bay Area Boulevard,
Houston, TX 77058, USA.
24
Institute of Meteoritics, University of
New Mexico, Albuquerque, NM 87131–0001, USA.
25
De-
partment of Earth and Planetary Materials Science, Tohoku
University, Aramaki, Aoba, Sendai, Miyagi 980-8578, Japan.
26
Division of Polar Earth-System Sciences, Korea Polar Research
Institute, 26 Songdomi Rae, Yeonsu-gu, Incheon 406-840,
Korea.
27
National Astronomical Observatories, Beijing, Chinese
Academy of Sciences, Beijing 100012, China.
28
State Key
Laboratory of Lithospheric Evolution, Institute of Geology and
Geophysics, Chinese Academy of Sciences, Beijing 100029,
China.
29
Department of Geological Sciences, Brown Univer-
sity, Providence, RI 02912, USA.
30
Analytical BioGeoChemistry,
Helmoltz Zentrum Muenchen, Ingoldstäter Landstrasse 1,
D-85764 Obeschleissheim, Germany.
31
Technical University
Muenchen, Analytical Food Chemistry, Alte Akademie 10, D-85354
Freising, Germany.
32
Geochemical Research Center, The Uni-
versity of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033,
Japan.
33
Waseda Institute for Advanced Study, Waseda Uni-
versity, 1-6-1 Nishiwaseda, Shinjuku, Tokyo 169-8050, Japan.
34
Department of Earth and Planetary Science, The University of
Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
*Corresponding author. E-mail: petrus.m.jenniskens@nasa.gov
www.sciencemag.org SCIENCE VOL 342 29 NOVEMBER 2013 1069
The strength of this shock wave on the ground
was modeled (SM section 2.4), assuming that an
overpressure of Dp > 500 Pa was required (13).
A 520-kT event, with detonations spread over al-
titudes ranging from 34 to 27 km and 24 to 19 km,
would cause damage out to a distance of 120 km
with the observed shape (Fig. 3). The fragments
that penetrated below 27 km must have contrib-
uted to the damage in order to match the shock-
wave arrival times (SM section 2.4).
The number of houses damaged per 1000 in-
habitants (table S11) (SM section 2.3) falls off with
distance from the airburst source (r)asr
–2.6 T 1.2
,
with overpressure calculated to fall off as r
−2.4
(fig. S39). In Chelyabinsk itself, 3613 apartment
buildings (about 44%) had shattered and broken
glass, but these were not evenly distributed in the
city (fig. S37). Sharp sounds heard after the shock
wave also point to the fragmentation’s causing a
complicated distribution of pressure. Structural dam-
age included the collapse of a zinc factory roof.
Directly below the fireball’s path, the shock
wave was strong enough to blow people off their
feet. In Yemanzhelinsk, window frames facing the
trajectory were pushed inwards, and suspended
ceilings were sucked down above broken win-
dows (fig. S36G). There was no structural dam-
age to buildings, other than a statue of Pushkin
inside the local library, cracked by a blown-out
window frame. Cracks in walls were documented
in nearby Baturinsky and Kalachevo.
Electrophonic sounds were heard (SM section
1.6), but there was no evidence of an electro-
magnetic pulse (EMP) under the track in neigh-
boring Emanzhelinka. Due to shock-wave–induced
vibrations, electricity and cell phone connectivity
was briefly halted in the Kunashaksky district at
the far northern end of the damage area. The gas
supply was briefly interrupted in some districts
because of valves reacting to the vibrations.
People found it painful to look at the bright
fireball, but glancing away prevented lasting eye
damage. Of 1 113 respondents to an Internet sur-
vey who were outside at the time, 25 were sun-
burned (2.2%), 315 felt hot (28%), and 415
(37%) felt warm (SM section 2.2). Mild sunburns
were reported throughout the survey area (table
S7), reflecting the fact that ultraviolet (UV) flux
density falls off as ~r
−2
. In Korkino, 30 km from
the point of peak brightness, one resident reported
getting a mild sunburn on the face, followed by
peeling of skin. Such effects occur at a minimum
erythema dose of ~1000 J/m
2
(14)of290-to320-nm
radiation (mostly UV-B). Assuming 6000-K radia-
tion (9), the calculated dose would have been
~200 J/m
2
at Korkino. Ground reflectance of UV
light by snow may have further increased the dose.
Out of the total 1674 collected Internet re-
sponses, 374 mention 452 body injuries or incon-
veniences (SM section 2.2). Of those, 5.3% reported
sunburn, 48% eyes hurt, and 2.9% retinal burns. Be-
cause of the shock wave, 6.4% reported a con-
cussion or mental confusion, upset, or exhaustion as
a result of excessive stress. Flying glass and falling
building debris affected a relatively small fraction of
respondents: 4.8% reported cuts and 2.9% reported
bruises, but no broken bones were reported.
The percentage of people asking for medical
assistance (table S10) dropped with distance ac-
cording to r
–3.2 T 0.5
(SM section 2.1). The ma-
jority of injuries (1210) took place in the densely
populated Chelyabinsk city, but the highest frac-
tion of people asking for assistance was near the
trajectory track in the Korkinsky district (0.16%).
Meteorite Recovery
Shock radiation contributed to surface heating and
ablation but did not completely evaporate all
fragments of Chelyabinsk, unlike in the case of
Tunguska (3). Meteorites of ~0.1 g fell near
Aleksandrovka close to the point of peak bright-
ness, masses of ~100 g fell further along the tra-
jectory near Deputatskiy, a nd at least one of
3.4 kg fell near Timiryazevskiy. One hit the roof
of a house in Deputatskiy (fig. S46). Falling-
sphere models suggest that they originated at 32-
to 26-km altitude (fig. S52), where the meteor
mod el shows rapid fragmentation (fig. S18C).
The location of the meteorites is consistent with
prevailing northwest winds of 5 to 15 m/s (fig. S24).
An estimated 3000 to 5000 kg fell in this area
(SM section 3.1).
Two main fragments survived the disruption
at 29.7 km. They flared around 24 km, with one
falling apart at 18.5 km and the other remaining
luminous down to 13.6 km (Fig. 1 and fig. S15).
Light-curve modeling (SM section 1.2) suggests
that from this material another ~1 ton in larger
fragments up to 100 to 400 kg in mass reached
the ground. A 7-m-sized hole was discovered in
70-cm-thick ice on Lake Chebarkul (fig. S53A),
in line with the trajectory (SM section 1.1). A
lakeshore video security camera, pointed to the
site, recorded the impact (fig. S53B). Small me-
teorite fragments were recovered over an area up
to 50 m from the impact location (Fig. 4C). Im-
pact models (figs. S18 and S54) suggest a 200- to
1000-kg meteorite would be required to create
such a hole. A mass of ≥570 kg was recovered
from the lake bed (fig. S53C).
The combined 4 to 6 tons of surviving me-
teorites is only 0.03 to 0.05% of the initial mass.
Seventy-six percent of the meteoroid evaporated,
with most of the remaining mass converted into
Fig. 1. Meteoroid fragmentation stages in vid-
eotakenbyA.IvanovinKamensk-Uralskiy.(A)
Fireball just before peak brightness, at the moment
when camera gain was first adjusted. (B)Endof
main disruption. (C) Onset of secondary disruption.
(D) End of secondary disruption; main debris cloud
continues to move down. (E) Two main fragments
remain. (F)Singlefragmentremains.(G)Thermal-
ly emitting debris cloud at rest with atmosphere.
(H) Final fragment continues to penetrate. Meteor
moved behind distant lamp posts. (I and J)Detail
of the thermal emission from a photograph by
Mr. Dudarev (I) and M. Ahmetvaleev ( J), after sky
subtractionwithhigh-passfilterandcontrasten-
hancement. Altitude scale is uncertain by T0.7 km.
Fig. 2. Fireball visual mag-
nitude irradiance light curve,
normalized to 100-km dis-
tance. The bold dashed line
shows the model fit to the light
curve (SM section 1.2), with thin
lines showing total mass of all
fragments passing a given altitude
(kg) and the altitude-dependent
rate of energy deposition as a
fraction of the original kinetic
energy (km
−1
).
29 NOVEMBER 2013 VOL 342 SCIENCE www.sciencemag.org1070
RESEARCH ARTICLE
dust (SM section 1.3). W itnesses reported smell-
ing “sul fur” and burning odors over a wide region
concentrated near the fireball trajectory , starting
about an hour after the fireball and lasting through
much of the day (SM section 1.5) (fig. S34).
Characterization of Recovered Meteorites
The unusually effective fragmentation and small
surviving mass may have been caused by struc-
tural and material weakness. The asteroid had a
lower compressive strength than the ~330 MPa
measured for recovered, surviving meteorites (SM
section S4.1). The light curve (Fig. 2) is modeled
with fragmentation starting at a low 0.2 MPa dy-
namic pressure but tolerating higher pressure with
decreasing fragment size. This is similar to other
meteorite falls, where initial weakness was attributed
to macroscopic cracks or microscopic porosity (15).
For Chelyabinsk, however , the physical weakness
is not microporosity related. X-ray computed to-
mography (SM section 4.2) revealed a degree of
compaction consistent with the lack of intragranular
porosity typical of LL chondrites (16).
Some laboratory-broken meteorites fragmented
along shock veins (fig. S55), a possible weakness
in the material that could have contributed to the
abundant dust formation. The meteorite is com-
posed of a breccia (17) of mildly shocked lighter
clasts and moderately shocked darker clasts with
abundant thin to cm-wide shock melt veins (Fig.
4A) (SM section 4.4). A peculiar feature is that
some shock veins exhibit a metal layer located
~20 micrometers inside the vein, which follows
the outer contours of the vein (Fig. 4B), indicat-
ing that metal initially segregated from the most
rapidly solidifying rims of the vein. This could
contribute to weakness. Metal-rich tendrils also
project outward from the vein.
The mineral compositional ranges (SM sec-
tion 4.4) are slightly larger than those reported
before (18), but still compatible with a classifi-
cation as LL5, shock stage S4 (19). The classi-
fication as LL chondrite is substantiated by oxygen
and chromium isotope studies (SM section 4.5 to
4.7), which put the meteorite near the L end of
the LL field (20, 21) (Fig. 4D and fig. S68). Iron
content and oxidation state also support the LL
chondrite classification (Fig. 4E and fig. S58).
Rare earth element abundances are more similar
to L chondrites (Fig. 4F and table S18), whereas
one measuring reflectance spectrum better matches
that of H chondrites (fig. S72).
The Chelyabinsk (LL) parent body experienced
a substantial thermal and/or collision resetting event
115 T 21 million years after the formation of the
solar system (25), not experienced by most other
LL chondrites, possibly due to a major impact
event near its site of origin on the parent body . The
phosphate U-Pb age is 4452 T 21 million years
(SM section 4.8) (fig. S70), much younger than the
majority of other ordinary chondrite phosphate ages
dated by conventional thermal ionization mass
spectrometry methods (22, 23). Perhaps one other
piece of evidence for this is the 4.48 T 0.12 billion
years Pb-Pb isochron age of phosphates in a granite-
like fragment found in the LL3 to LL6 chondrite
regolith breccia Adzhi-Bogdo (24), an observed
fall in Mongolia in 1949.
Chelyabinsk shows a common orientation of
metal grains indicating an impact-related petro-
fabric (fig. S59), stronger than that seen in any other
ordinary chondrite of any shock stage (26) (fig. S60).
This petrofabric probably reflects the most recent
extraterrestrial shock event experienced by the
Table 1. Atmospheric trajectory and pre-atmospheric orbit for the Chelyabinsk meteoroid, with 2 standard deviation uncertainties. Angular
elements are for equinox J2000.0.
Atmospheric trajectory Chelyabinsk Pre-atmospheric orbit Chelyabinsk Itokawa
H
b
(beginning height, km) 97.1 T 1.6 T
J
(Tisserand’s parameter) 3.87 T 0.24 4.90
H
m
(peak brightness, km) 29.7 T 1.4 a (semimajor axis, AU) 1.76 T 0.16 1.324
H
f
(disruption, km) 27.0 T 1.4 e (eccentricity) 0.581 T 0.018 0.280
H
e
(end height, km) 13.6 T 1.4 q (perihelion distance, AU) 0.739 T 0.020 0.953
V
∞
(entry speed, km/s) 19.16 T 0.30 w (argument of perihelion, °) 108.3 T 3.8 162.8
h (entry elevation angle, °) 18.3 T 0.4 W (longitude of ascending node, °) 326.4422 T 0.0028 69.1
a
z
(entry azimuth angle from south, °) 283.2 T 0.4 i (inclination, °) 4.93 T 0.48 1.6
V
g
(geocentric entry speed, km/s) 15.3 T 0.4 Q (aphelion distance, AU) 2.78 T 0.20 1.70
Ra
g
(geocentric right ascension of radiant, °) 333.2 T 1.6 T
p
(perihelion time) 2012-12-31.9 T 2.0 2013-07-10.8
Dec
g
(geocentric declination of radiant, °) +0.3 T 1.8 Epoch (ET) 2013-02-15.139 2013-04-18.0
Fig. 3. Map of glass damage on the ground with models of overpressure. Field survey data are shown
in solid orange circles for reported damage and open black circles for no damage; solid red circles show the
most damaged villages in each district, as reported by the government. Each point, irrespective of population
density, represents one of many villages or city districts scattered throughout the area. Model contours (with
progressive gray scale) represent kinetic energies and overpressures from inside out: 300 kT D p > 1000 Pa,
520 kT D p > 1000 Pa, 300 kT D p > 500 Pa, and 52 0 kT D p > 500 Pa, respectively. Also shown are the locations
of meteorite finds (yellow points) and the ground-projected fireball trajectory (black line), moving from 97-km
altitude on the right to 14-km altitude on the left. Whiteshowsthefireballbrightnessonalinearscale.
www.sciencemag.org SCIENCE VOL 342 29 NOVEMBER 2013
1071
RESEARCH ARTICLE
Chelyabinsk meteoroid. The magnetic suscep-
tibility value is at the upper end of the range for LL
ty p e (fig. S61) (27), closer to L-type chondrites,
suggestive of higher metal content in Chelyabinsk
than a typical LL chondrite. However, detailed anal-
ysis of the remanent magnetization suggests that
a shock event or the conditions of atmospheric
entry led to substantial resetting of the remanence
(SM section 4.3).
Recent meteoroid heating events are normally
recorded by thermoluminescence (TL) (SM sec-
tion 4.10). In this case, the induced TL level of
Chelyabinsk is lower than other petrographic type
5 or 6 chondrites, possibly because shock meta-
morphism to the level of S4 (30 to 35 GPa) (fig.
S79) destroyed feldspar , the mineral phase re-
sponsible for the TL signal (28). Atmospheric
heating did not cause loss of natural TL signal,
the steep thermal gradient being consistent with a
very thin fusion crust on the measured samples
(29). The natural TL value is consistent with the
meteoroid’s having been heated at a perihelion
distance of 0.6 to 0.8 astronomical units (AU)
(Table 1).
The shock did not remove all organic matter
from the meteorite. Methanol-soluble polar org anic
compounds (SM section 4.11) were detected in
impact melt vein and chondrite fractions using
electrospray ionization ion cyclotron resonance
Fourier-Transform mass spectrometry (30). Out
of more than 18,000 resolved mass peaks, 2536
could be assigned to compounds containing C,
H, N, O, or S. The organic signature is typical of
other shocked LL chondrites, showing a higher
abundance of oxygen and nitrogen atoms in the
impact melt (fig. S83). The presence of oxygen-
ated sulfur is indicated by CHOS compounds
containing on average three more oxygen atoms
than CHO and CHNO compounds. The high
abundance of CHOS compounds in a homolo-
gous series across the entire mass range testifies
that most of these did not result from terrestrial
contamination.
Impact shock–induced fracturing on the
Chelyabinsk parent body was followed by melt-
ing of metal and sulfides, which are pressure-
driven through the cracks. There are cases in
which this increased a meteorite’s mechanical
strength, the residual heat facilitating the process.
However , in the case of Chelyabinsk, the produc-
tion of cracks weakened the meteorite material
more than shock melting increased its strength.
Source and Evolution of the
Chelyabinsk Meteoroid
Chelyabinsk adds an LL5 type meteorite to a
short list (SM section 1.1) of 18 different types of
meteorites with known pre-atmospheric orbits (1).
Only 8.2% of falls are LL chondrites (31). The
Chelyabinsk meteorite is of particular interest be-
cause it is of the same type as asteroid Itokawa,
from which samples were collected by the
Hayabusa Mission (32). Indeed, both Itokawa
and Chelyabinsk have similar low-inclined low-
semimajor axis orbits (Table 1), which, according
to one model (33), imply a 62%, 11%, and 25%
probability for Chelyabinsk (and 71%, 0%, and
29% probability for Itokawa) of originating from
the secular n
6
resonance, the 3:1 mean-motion
resonance, and the Intermediate Mars Crosser re-
gion, respectively. Multiplying these probabilities,
assuming all LL chondrites enter the near-Earth
object region through the same escape route, there
is now an 86% probability that they originated
from n
6
. This supports the hypothesis (34)that
they originated from the inner part of the LL-type
(35) Flora asteroid family , which straddles the n
6
resonance in 1.6° to 7.7° inclined orbits (36).
As a group, LL chondrites have a cosmic ray
exposure age peaking at ~17 million years (34).
Chelyabinsk, on the other hand, was exposed only
since ~1.2 million years ago (SM section 4.12).
The responsible breakup that first exposed the
Chelyabinsk meteoroid surface to cosmic rays was
not likely part of the ongoing collision cascade in
the asteroid main belt that followed the forma-
tion of the Flora family. Although fast path-
ways exist that can bring meteoroids from all
three resonances into a Chelyabinsk-like orbit in
about 0.2 million years, such cases are rare (table
S6). More likely , Chelyabinsk was exposed only
since being ejected from the resonance, due to
breakup from either thermal stresses, rotational
spin-up, or tidal forces in terrestrial planet en-
counters. The required structural weakness may
have come from macroscopic cracks or from a
weakly consolidated rubble-pile morphology.
If tidal forces disrupted the Chelyabinsk me-
teoroid (37), events were set in motion 1.2 million
years ago during what was likely an earlier close
encounter with Earth, when a 20-m sized chunk
of subsurface Flora-family parent body rubble,
rich in shock veins, separated from a larger ob-
ject. The rest of that rubble could still be part of
the near-Earth object population.
Fig. 4. Meteorite material properties, chemical and isotopic compositions. (A) Chelyabinsk
meteorite (diameter ~4 cm) showing shock veins. (B)Feelementmapofashockvein.Notethemetallayer
(shown in green) located ~20 micrometers inside the vein. (C) Meteorite fragments recovered from the ice-
covered lake Chebarkul. (D) D
17
O versus Fa molar percent of olivine in Chelyabinsk, compared with other
ordinary chondrites of type H, L, and LL (38). Fa is defined as molar ratio of Fe/(Fe+Mg) in olivine. Average
D
17
O values from the University of New Mexico (UNM) [1.15 T 0.06 per mil (‰)] and from the Korea Polar
Research Institute (KOPRI) (1.31 T 0.04‰) for Chelyabinsk likely reflect indigenous heterogeneity in oxygen
isotopes. Solid symbols are Fa number measured in this study (SM section S4.3), whereas open symbols are
from (18). (E) Ratio plots of the three major elements (Mg, Si, Fe; together with oxygen >90% of mass) for
Chelyabinsk and the main chondrite groups. The bulk Earth and bulk silicate Earth compositions were taken
from (39), chondrite compositions from (40). (F) CI chondrite normalized rare earth elemental pattern of
Chelyabinsk compared with the average chondrite group compositions of (38, 41).
29 NOVEMBER 2013 VOL 342 SCIENCE www.sciencemag.org
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RESEARCH ARTICLE
![Fig. 4. Meteorite material properties, chemical and isotopic compositions. (A) Chelyabinsk meteorite (diameter ~4 cm) showing shock veins. (B) Fe element map of a shock vein. Note the metal layer (shown in green) located ~20 micrometers inside the vein. (C) Meteorite fragments recovered from the icecovered lake Chebarkul. (D) D17O versus Fa molar percent of olivine in Chelyabinsk, compared with other ordinary chondrites of type H, L, and LL (38). Fa is defined as molar ratio of Fe/(Fe+Mg) in olivine. Average D17O values from the University of New Mexico (UNM) [1.15 T 0.06 per mil (‰)] and from the Korea Polar Research Institute (KOPRI) (1.31 T 0.04‰) for Chelyabinsk likely reflect indigenous heterogeneity in oxygen isotopes. Solid symbols are Fa number measured in this study (SM section S4.3), whereas open symbols are from (18). (E) Ratio plots of the three major elements (Mg, Si, Fe; together with oxygen >90% of mass) for Chelyabinsk and the main chondrite groups. The bulk Earth and bulk silicate Earth compositions were taken from (39), chondrite compositions from (40). (F) CI chondrite normalized rare earth elemental pattern of Chelyabinsk compared with the average chondrite group compositions of (38, 41).](/figures/fig-4-meteorite-material-properties-chemical-and-isotopic-35s15x93.webp)