astronomical and physical aspects of the chelyabinsk event … · 2014. 1. 30. · solar system...

ISSN 0038�0946, Solar System Research, 2013, Vol. 47, No. 4, pp. 240–254. © Pleiades Publishing, Inc., 2013.Original Russian Text © V.V. Emel’yanenko, O.P. Popova, N.N. Chugai, M.A. Shelyakov, Yu.V. Pakhomov, B.M. Shustov, V.V. Shuvalov, E.E. Biryukov, Yu.S. Rybnov, M.Ya. Marov,L.V. Rykhlova, S.A. Naroenkov, A.P. Kartashova, V.A. Kharlamov, I.A. Trubetskaya, 2013, published in Astronomicheskii Vestnik, 2013, Vol. 47, No. 4, pp. 262–277.

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1. INTRODUCTION

A general picture of the Chelyabinsk event on Feb�ruary 15, 2013, has been established in detail. At about9:20 a.m. local time (03:20 GMT), a space object 16–19 m in size entered the Earth’s atmosphere at anangle of less than 20° relative to the horizon. Theapproach of this quite large object to the Earth was notnoticed by any of the existing means of space� andground�based observations of celestial bodies. Onlyafter its entry into the atmosphere did it became a phe�nomenon attracting the attention of humankind. Theinteraction with the atmosphere led to strong glow(a phenomenon called a fireball or bolide). In severalseconds, the glow intensity exhibited significantgrowth and the maximum flash was observed approxi�mately 11–12 s after appearance of the meteor. Wit�nesses reported that, at the moment of the flash(explosion), the glow intensity was much brighter thansunlight and even heat could be felt. Both prior to andafter the flash, the track of the bolide was clearly seenin the sky. An explosive (shock) wave came within sev�eral minutes (video records are indicative of a 77 s to3 min time interval and above), depending on thelocation. According to the Russian Ministry of Emer�gency Situations, the damage caused by the explosivewave was detected in Chelyabinsk and over ten regionsof the Chelyabinsk oblast. The most significantdestruction was observed in Chelyabinsk, Korkino andKopeisk, and the village of Roza. More than

1500 patients asked for medical aid, of which about100 were hospitalized (two in reanimation), being pre�dominantly injured by broken glass from windows.With respect to the number of wounded people, thismeteorite fall has no analogues.

A large number of small (not exceeding 2 cm)meteoroid fragments (i.e., residue from the celestialbody remaining upon reaching the ground) have beenfound over a wide territory. According to the first com�munication from V.I. Grokhovskii (Committee forMeteorites, Russian Academy of Sciences), particlesfound in the first days after the meteorite fall in thevicinity of Chebarkul Lake by an expedition from theUral Federal University (Yekaterinburg) exhibit ameteorite nature and belong to the class of commonchondrites. Subsequent expeditions from the Vernad�sky Institute of Geochemistry and Analytical Chemis�try, South�Ural State University (Chelyabinsk), UralFederal University (Yekaterinburg), and the Instituteof Astronomy added many samples. A chemical anal�ysis performed at the Meteoritics Laboratory of theVernadsky Institute allowed the meteorite to be classi�fied to the LL chondrite group.

The pattern outlined above is close to the classicaldescription of the entry of a large celestial body intothe Earth’s atmosphere. Generally speaking, the Che�lyabinsk event is not a rare astronomical phenomenon.Figure 1 (reproduced from Ivanov and Hartmann,2007) shows a distribution of the frequency P of colli�

Astronomical and Physical Aspects of the Chelyabinsk Event (February 15, 2013)

V. V. Emel’yanenkoa, O. P. Popovab, N. N. Chugaia, M. A. Shelyakova, Yu. V. Pakhomova, B. M. Shustova, V. V. Shuvalovb, E. E. Biryukovc, Yu. S. Rybnovb, M. Ya. Marovd, L. V. Rykhlovaa,

S. A. Naroenkova, A. P. Kartashovaa, V. A. Kharlamovb, and I. A. Trubetskayaba Institute of Astronomy, Russian Academy of Sciences, Moscow, 119017 Russia

b Institute of Geosphere Dynamics, Russian Academy of Sciences, Moscow, 119334 Russiac South�Ural State University, Chelyabinsk, 454080 Russia

d Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, 119991 RussiaReceived April 1, 2013

Abstract—Various observational data including infrasound, seismic, optical (onboard) monitoring, groundvideo and photo records, and evidence from witnesses of the Chelyabinsk event on February 15, 2013, havebeen analyzed. The extensive material gathered has provided a base for investigations of the physical proper�ties of the object, the results of which are discussed. A bolide light curve is constructed, which shows a mul�tiplicity of flashes. Estimations of the energy of the meteoroid explosion, which took place in the atmosphereat an altitude of about 23 km, show evidence of the formation of a high�power shock wave equivalent to 300–500 kilotons of TNT. The object diameter corresponding to this energy falls within the range 16–19 m. Thetrajectory of the meteor is outlined. It is preliminarily concluded that the Chelyabinsk meteorite was a repre�sentative the Apollo asteroid family.

DOI: 10.1134/S0038094613040114

SOLAR SYSTEM RESEARCH Vol. 47 No. 4 2013

ASTRONOMICAL AND PHYSICAL ASPECTS OF THE CHELYABINSK EVENT 241

sions of the Earth with celestial bodies of dimension D.For bodies within 1–30 m, this distribution obeys thelaw P = 8 × 10–8D–2.95 year–1 (D expressed in kilome�ters). Thus, collisions with bodies of the order of theChelyabinsk meteoroid take place on the average onceper 60–100 years.

Among the data available on similar events, we canmention bolides observed on August 3, 1963 (PrinceEdward Islands, South Africa, estimated energy 260–1000 kilotons TNT, Silber et al., 2009); February 1,1994 (Marshall Islands, South Africa, estimatedenergy ~40 kiloton TNT, Popova and Nemchinov,2005); and October 8, 2009 (Indonesia, estimatedenergy ~50 kilotons TNT, Silber et al., 2011). In Rus�sia, most recent event was observed on September 24,2002 (Vitim River, estimated energy ~2.4 kiloton TNT,Adushkin et al., 2004). Nevertheless, the Chelyabinskevent can be recognized as unique. For the first time inour history, the collision with a large celestial body wasrecorded in great detail, which made a thorough scien�tific analysis of this event possible.

This article presents the first results of an analysiscarried out by experts from academic institutions. Ofcourse, this study is by no means exhaustive in allrespects, since a deeper insight in many directions isyet to come. However, the data below provide a com�plex notion about the Chelyabinsk event, which will be

useful for many specialists and the more so foradvanced amateurs.

Section 2 presents the observational data based onoptical, infrasound, and seismic detection. Section 3describes a large number of video and photo recordsfollowing penetration of the observed body throughthe Earth’s atmosphere. Section 4 considers variousevidences from witnesses of the Chelyabinsk event.Section 5 describes the construction of the bolide lightcurve. Section 6 presents estimations of the energy ofa celestial body, while Section 7 gives preliminaryresults of determining the impact trajectory andparameters.

2. INFRASOUND, SEISMIC, AND OPTICAL MONITORING

The entrance and destruction of large celestial bod�ies in the Earth’s atmosphere is a source of light,acoustic, infrasound, and seismic waves. The mainsource of perturbations in the atmosphere is a shockwave. Acoustic waves (20 Hz–20 kHz) mostly propa�gate through relatively short distances (within 2–2.5 times the altitude of bolide destruction—the zoneof direct communication). The infrasound spectralinterval covers low�frequency acoustic waves from20 Hz to a limit of 3 × 10–3 Hz. Since the infrasonic

1E–100.0001 10001001010.10.010.001

1E+5

1E+4

1000

100

10

1

0.1

0.01

0.001

0.0001

1E–5

1E–6

1E–7

1E–8

1E–9

From cratering

–1.3

–1.7

–3

A

B

B

Observed NEALINEAR, Stuart and Binzel, 1994Spacewatch, Rabinowitz et al., 2000

NEAT, Rabinowitz et al., 2000Terrestrial bolides, Brown et al., 2002

P = 8 × 10–8 DP–2.95

P = 1.5 × 10–6 DP–1.7

P = 2.8 × 10–6 DP–2.3

18 16 14 12

DP, km

Pro

babi

lity

of

imp

act

per

1 y

ear

H ~

Fig. 1. Frequency of collisions of the Earth with celestial bodies of various dimensions.

242


EMEL’YANENKO et al.

waves weakly decay in the atmosphere, the infrasoundgenerated by bolides (and other sources) can bedetected over quite large distances. These perturba�tions can propagate in atmospheric waveguidesformed at various altitudes by temperature gradients,wind velocity and direction over distances up to severalthousand kilometers. A downward shock wave reachesthe ground and generates seismic waves, which can bedetected at distances up to several hundred kilometersand above.

The Chelyabinsk event of February 15, 2013 (Che�lyabinsk bolide), is an outstanding phenomenon in theseries of meteoroid penetrations due to (i) large zoneof disturbance (broken windows, ceilings, frames,etc.) and (ii) much varied evidence–including instru�mental data such as video and photo records, satelliteonboard monitoring, infrasound and seismic response,dusty trace observations (both space�based and ground),and an extensive field of meteorite residue.

The radiation from Chelyabinsk bolide was verybright, classified as superbolide (fireball brighter that17th stellar magnitude). These bolides are detected byonboard sensors of geostationary satellites of theUnited States Department of Defense (Tagliaferriet al., 1994). This satellite observation network is pri�marily intended to monitor nuclear tests, while theobservation of bolides is a by�product. On the average,about 30 flashes are typically observed every year at30–45 km altitudes over the Earth, with a duration of1–3 s and an average energy equivalent to 0.01–1 kilo�ton TNT. The complete data of optical observationsfor 1994–1996 (51 events) have been analyzed (Nem�tchinov et al., 1997). Based on these data, the kineticenergy of meteoroids entering in the Earth’s atmo�sphere was estimated at 0.06–40 kilotons TNT.Unfortunately, the complete information on theevents detected by satellites is now unavailable forobjective scientific analysis but, in some cases (Vitimbolide, asteroid 2008 TC3), partial data have beenreported. For the Chelyabinsk event, coordinates ofthe maximum brightness site (54.8° N, 61.1° E), alti�tude (23.3 km), and velocity (18.6 km/s) have beenpublished, and a little later the radiated energy wasestimated (http://neo.jpl.nasa.gov/fireballs/) (seeSection 6). Note that the coordinates of the site ofmaximum brightness on the Chelyabinsk meteoroidtrajectory have been determined using several videorecords (Borovicka et al., 2013).

Among the data of onboard monitoring systemsavailable previously, the maximum kinetic energyamounted to ~40 kilotons TNT (Popova and Nemchi�nov, 2005), which is significantly lower than most ofthe energy estimates for the Chelyabinsk meteoroid.For the period of 1960–1974, infrasound waves havebeen detected for some bolides by microbarometersystems deployed at that time in the United States(ReVelle, 1997). The most intense of these events for14 years (August 3, 1963, Prince Edward Islands,South Africa) had an estimated energy of 300–

1000 kiloton TNT (Silber et al., 2009), which is com�parable with the energy estimates for the Chelyabinskmeteoroid.

Eleven infrasound detection stations of the Com�prehensive Nuclear�Test�Ban Treaty Organization(CTBTO) recorded the fall of the Chelyabinsk aster�oid (CTBTO press release, 18.02.2013: http://www.ctbto.org/press�centre/press�releases/2013/russian�fireball�largest�ever�detected�by�ctbtos�infrasound�sensors/). In addition, the infrasound response hasalso been detected by other stations. In particular, theinfrasound generated by the Chelyabinsk bolide wasdetected by microbarometers with 0.001–10 Hz band�pass at the Institute of Geosphere Dynamics (IGD) inMoscow and at the Geophysical Observatory in Mikh�nevo (Moscow oblast). This infrasound was alsodetected in Tomsk. The location of the major energyrelease (54°35.4′ N, 61°45.5′ E) was determined towithin 40 km using the data of IGD infrasonic stationsand CTBTO station (IS31, Aktyubinsk).

Seismic vibrations caused by the bolide entranceinto the atmosphere have been also detected by a largenumber of seismic stations at distances within hundredsand thousands of kilometers. Approximate coordinatesof the source of seismic oscillations (55.150° N, 61.410° E;USGS web�site: http://comcat.cr.usgs.gov/earthquakes/eventpage/us2013lra1#summary) are rather far fromthe approximate trajectory of bolide motion. The cor�responding earthquake magnitude was rated 2.7–4according to various estimates.

3. ANALYSIS OF VIDEO RECORDS

A unique feature of the Chelyabinsk event is that,for the first time in the history of observations, thereare many video and photo records of the entrance andflight of this celestial body in the Earth’s atmosphere.At present, more than 150 records are available,mostly from dashboard cameras (event data recorders)and outdoor surveillance cameras. For most videorecords, the observation point coordinates have beendetermined. Among the available data, about60 records are of scientific significance, from whichthe trajectory of the body, the bolide light curve, thealtitude and consequences of its destruction can bedetermined.

Among the most interesting records, there aresome showing both the bolide flash and the moment ofshock wave arrival. These records have been mademostly in Chelyabinsk and sites situated to the south ofthis city. In Fig. 2, white marks indicate the sites ofmost important video recordings. Video recordingsites cover an area of about 8000 square kilometers,which extends 135 km north to south (from northernregions of Chelyabinsk to Troitsk) and 85 km west toeast (from the village of Mirnyi to Troitsk). Themoment of shock wave arrival was most pronouncedon records made in Chelyabinsk and surroundings,where it was manifested by sounds of the explosion,



window breakage, etc. At more considerable distancesfrom the epicenter, the shock wave arrival is mani�fested by camera vibrations (in Troitsk) or perturba�tions (Mirnyi).

Calculations of the time passed from the instant ofthe flash to shock wave arrival show that the minimumperiod occurs in Pervomaiskii village (77 s), while themaximum delay is observed in Mirnyi village (4 min49 s) and Troitsk village (4 min 55 s). In Chelyabinsk, theshock wave delay varied from 2 min 15 s to 2 min 52 s.

Another important group includes video recordscontaining the partial or complete flight of the body inthe atmosphere and the corresponding trace. Amongthese, 38 records clearly display the flight and allowthe coordinates of the observation point to be deter�mined with good precision. Figure 3 presents selectedshots from some of these records.

Figure 4 shows sites from which partial (whitemarks) and complete (black marks) video records ofthe body’s flight have been made. These record sitescover an area of about 215000 square kilometers,which extends 540 km north to south (from NizhniiTagil to Kartala) and 440 km west to east (fromBeloretsk to Tyumen). The most distant site from theepicenter of the bolide explosion, where a video recordof the event was made, is Tyumen (about 340 km). Inaddition to the sites shown in Fig. 4, there are recordsfrom some other sites, including even more distantones (e.g., Orenburg, 570 km from the epicenter).However, these data are less informative than thosepresented in Fig. 4 for various reasons such as poorquality, motion of the recorder, uncertainty of its coor�dinates, etc.).

A separate group of video records shows conse�quences of the catastrophic fragmentation of the bodyin the atmosphere. There are eleven videos of this kindmade in Chelyabinsk, Korkino, Kopeisk, Kras�nogorsk, and Emanzhelinsk. From these data, onemay conclude that both residential houses and indus�trial buildings in Chelyabinsk and towns situated to thesouth of this city have been damaged. For example,most windows were broken in a brick plant in Eman�zhelinsk and in the YuzhUralKarton plant of Korkino.In Chelyabinsk, windows were broken together withframes in the State Railway Institute and in a fast�foodrestaurant. Analogous damage was observed inKopeisk and Krasnogorsk.

In addition to videos, there are photographs withevidence of the Chelyabinsk event, which were taken3–5 min after the entry into the atmosphere. Mostphotos were made with mobile phones in Chelyabinskand close�lying towns and villages (Miass, Kashino,Varlamovo, etc.). In most cases, these are partial or com�plete images of the trace left by the bolide. Figure 5 showssome illustrative shots.

Noteworthy photographs have been made by MaratAkhmetvaleev using a camera fixed on a support nearthe Miass river (one kilometer away from the Kommunarpond) in Chelyabinsk. These excellent images show boththe flash and trace left by the meteor (Fig. 6).

Another interesting photograph has been providedby Denis Siv’yuk, which shows the image of the mete�orite trajectory as seen on a radar display of theChelyabinsk airport (Fig. 7). A thorough analysis ofthis image will be made subsequently with allowancefor the radar characteristics.

M51

M36

P360

M5

Zlatoust

Miass

Chebarkul’

Uchaly

Chelyabinsk oblast

Chelyabinsk

Kopeisk

Korkino

Troitsk

Fig. 2. A map showing sites from which video records were made showing both the bolide flash and the moment of shock wavearrival.

244



Considerable scientific potential is offered by on�line video records of the Intercommunication Co.,which have been provided by its general directorE.O. Kalinin. These records have been made by syn�chronized cameras in Chelyabinsk, Miass, Zlatoust,and Chebarkul.

4. EVIDENCE OF WITNESSES

The available photo and video records are supple�mented by a large volume of evidence and observa�tions made by witnesses. This evidence was collectedfrom the mass media and from a questioning of wit�nesses and official services during the expedition orga�nized in March 9–26, 2013, by the IGD and the Insti�tute of Astronomy.

According to witnesses in Chelyabinsk, the bodyappearing in the sky looked like a dark point, whichexhibited rapid growth and left a smoky trace behind.The moving body was followed by two equal bands.

The flash lasted for several seconds with increasingintensity. At maximum intensity, the surroundingobjects were difficult to recognize. Some witnessestold that the body flight was accompanied by crack�ling, which probably indicated that the Chelyabinskbolide was electrophonic. Many witnesses, especiallythose in towns close to the anticipated trajectory (e.g.,Korkino), told that it was possible to feel heat afterflash and, after some time, an odor (fresh or burnt).After the flash and disintegration of the body, a ratherlarge fragment continued to move along the same tra�jectory, but at a lower apparent velocity.

In several minutes after the flash, came the soundof a loud explosion. The first powerful sound was fol�lowed by several less intense explosions. In addition toChelyabinsk, these could be heard in Korkino, Eman�zhelinsk, Kopeisk, Shelomentsevo, Pervomaiskii, andsome other towns and villages. However, it should benoted that several witnesses in Miass pointed out thatno explosion sounds had been heard in their town.

Consequences of the shock wave were numerousbroken windows in Chelyabinsk and close�lying townsand villages. In some buildings, frames and ceilingswere also broken, and an old warehouse wall of theChelyabinsk Zinc Plant was destroyed. In Pervo�maiskii (one of the closest villages to the center ofmaximum energy release, see Section 7), there weremany broken windows, especially in schools and kin�dergartens, but stronger glass packets frequentlyremained intact. It was also pointed out that largeschool windows facing eastward were hardly affected.

The total area of broken windows was rather large:more than 7300 buildings were damaged in 11 munic�ipal regions of the Chelyabinsk oblast. Most windowswere blown out in old houses. For example, in594 buildings damaged in Korkino region, there were7938 windows with wooden frames and only 1077 glassunits. In industrial buildings, big windows with thickglass were blown. In some cases (e.g., Pribor Plant,South�Ural State University, Chelyabinsk State Agri�cultural Engineering University), windows on thesouthern side were broken inward, while those on thenorthern side were blown outward; the same wasnoticed in Korkino. In some cases (Pervomaiskii,South�Ural State University) inner windows or eveninner sides of glass units were broken. As a rule, win�dows were more frequently blown in panel buildingsand less frequently in brick ones. In private (small)houses, windows were less frequently broken, exceptthose with destroyed frames. The glazing of enclosedbalconies was damaged almost everywhere irrespectiveof the building type (concrete panel or brick).

The character of destruction and structure of theChelyabinsk meteoroid can be judged from the frag�ments recovered and their distribution. Many frag�ments covered by a fused crust have been found nearthe village of Deputatskii, where even the roof of asmall building was damaged. Relatively small (centi�meter�sized) fragments included meteorites incom�

000 km/h2013/02/15 09:20:34

2013/02/1509:20:46 Mio 238

02/15/2013 09:23:38

Fig. 3. Selected shots from video records of the Chelya�binsk meteoroid flight.



pletely covered by fused crust, which showed that frag�mentation continued as the velocity decreased. Somemeteorite seekers pointed out that, westward fromDeputatskii along the meteorite trajectory, not a singlefragment was found over several kilometers, which wasevidence of the complicated character of the fragmen�tation process. The search for meteorite fragments wasfavored by weather: quite clear and sunny, free ofsnowfalls, it facilitated detecting meteorite material(fragments left entry holes in the snow, which con�tained ice columns with a fragment at the end). Itshould be also noted that the shock wave cleared upvirtually all chimneys in houses under the trajectoryand removed small coked stones, which were some�times confused with meteorite fragments. The sites offallen fragments attracted animals (including crowsand foxes), which was probably evidence of some odor.

It would be of considerable interest to look forhypothetical large fragments of the meteorite. There isstill some hope that a rather large fragment about 1 min diameter could have fallen into Chebarkul Lake.However, even the circular edge of the hole in the ice,the lack of splashed water around it, and the absenceof cracks in the ice cast doubts. Photographs made byE.O. Kalinin from an airplane showed holes in lakesand quarries under the trajectory (Etkul region). Thesetraces resembled a snowflake pattern with a hole at themiddle and expanding cracks in the ice, but no frag�ments have been found in this region.

5. PHOTOMETRY OF BOLIDE FLASH

Numerous video records obtained from outdoorsurveillance cameras and dashboard cameras can be

used for constructing a bolide light curve. This proce�dure implies the collection and analysis of video filessuitable for photometry, selecting zones for brightnessmeasurement, calibration of brightness, calculation ofbolide brightness, and normalization of measurementsto a common scale of brightness and time. Unfortu�nately, both outdoor surveillance and dashboard cam�eras are not particularly applicable to precise photo�metry and have limitations. The main one of these issmall dynamical range. As a rule, the cameras havelarge fields of vision and measure the exposure withrespect to the average illuminance over the shot. At thesunrise, the illuminance is yet relatively low, while thebolide has a much greater brightness both at the begin�ning of its flight in the atmosphere and at the moment

M51

M30

Yekaterinburg

Bashkortostan

Chelyabinsk

Chelyabinsk oblast

Qostanay

Kurgan oblast

Tyumen oblast

North�Kazakhstan

Fig. 4. A map showing sites from which partial (white marks) and complete (black marks) video records of the flight of the bodywere made.

Fig. 5. Photographs of the inversion trace.

246



of flash. For this reason, the image of the bolide isalmost always overexposed. However, during the flash,the light is scattered by the Earth’s surface and variousobjects, so that the brightness of scattered lightbecomes comparable with that of objects in the frame.This circumstance allows the relative flux of radiationfrom the bolide at this moment and the temporal vari�ation of this flux to be evaluated.

At the first stage, video files have been selected inwhich clearly visible, but not overexposed, scatteredlight from bolide flash is present. Since it is highlyprobable that light scattering is anisotropic, the varia�tion of the brightness of scattered light for any regionis not proportional to a change in the bolide bright�ness. The more isotropic is light scattering, the higherthe accuracy of measurement of relative bolide bright�ness. Another important condition for high�qualitymeasurement of the bolide light curve is the absence ofshadowing on the measured areas. Video files forwhich these conditions were not satisfied wereexcluded from photometric analysis.

The second important problem with cameras istheir automatic control of the diaphragm. During theflash, the illuminance reaches a sunny day level andthe diaphragm is significantly reduced. Therefore, it isnecessary to have a zone in the frame where the bright�ness is independent and remains constant. This can bea non�overexposed sky region or a lamp. In the case ofa dashboard camera, it is important to analyze thebolide light scattering on front windshield of the car. Ifthe sky in the direction of vision was absent or the glasswas dirty, the video files had to be rejected.

In the case of frames imaging the bolide, anotherproblem is encountered because all other objects are inthe dark and it is impossible to measure the scatteredlight intensity. This difficulty is especially manifestedupon the flash, when the bolide brightness rapidlydecays but the diaphragm is closed for about a seconddue to the inertia of automatics. These frames are darkand unacceptable for photometric measurements.This problem was especially serious for most videosfrom Chelyabinsk and environs. The available videofiles have been checked for the possibility of photom�etry at a minimum diaphragm. Records from neigh�boring regions were more acceptable for the photo�metric measurements.

As a result of the preliminary analysis, eight videofiles have been selected that are listed in Table 1. In thistable, the first column is the file number, the secondcolumn refers to the Internet source, and the next col�umns indicate the site of observation, the type of cam�era, and the speed of recording (fps).

The selected video material has been processed ona computer with OS Linux. Each video file was dividedby mplayer program into PNG frames, in which rect�angular zones were defined for the measurement ofscattered light intensity from bolide (Im) and a stan�dard region (Istd). Separate frames have been pro�cessed using a program written in Perl using an

Fig. 6. Photographs made by Marat Akhmetvaleev.

Fig. 7. Image of a meteorite trajectory as seen on a radardisplay of the Chelyabinsk airport.



Image::Magic library for image processing. For everyrectangular zone, average values were determined inthree color channels—red (IR), green (IG), and blue(IB)—and the relative brightness of the bolide was

defined as Im = + + /3. Theresults of analysis for all video files were comparedupon normalization of the bolide brightness as Im =(Im – Ibg)/(Imax – Ibg), where Ibg is the initial brightness(prior to bolide flight) and Imax is the maximum bright�ness during the flash.

The temporal scale was determined by the ratio ofthe frame number (n (to the speed of recording (fps):t = n/fps. The time was measured relative to a momentclose to the maximum brightness. Figure 8 shows oneof the highest quality bolide light curves, which wasconstructed using video file no. 8 (Table 1).

According to video file no. 7, the bolide was visiblebeginning at t = –11.5 s (relative to zero point inFig. 8) and exhibited significant growth in brightnessat t > –5 s. The bolide light curve shows three charac�teristic regions: preliminary flash (t ≈ –2.0 s); mainflash (t ≈ 0 s), and last flash (t ≈ 1.4 s). The character�istic duration of the preliminary flash (on a 0.5 relativebrightness level according to various files) is about 1 sand the main flash is about 1.5–2 s long. Then, mete�oroid fragments continue their flight in the atmo�sphere and exhibit one more flash in about ~0.8 s thatis accompanied by additional glow in the trace. Theduration of this flash does not exceed 0.4 s. Finally, thebrightness exhibits a sharp drop and the scattered lightof the bolide is no longer detected.

The bolide light curve reflects a nonuniform glowintensity along the trajectory and the main maxima ofbrightness must correspond to those in the spatial dis�tribution of glow sources. Figure 9 shows an imagetaken from video no. 4, where the bolide tail revealstwo bright flashes. Using relative distances betweenobjects on the frame (church and roads) and compar�ing azimuthal angles on the Yandex.map and Goo�gle.map, the angular scale was evaluated at 0.058 ±0.004 deg/pixel. Once the distance from the observa�

( R RI Im std

G GI Im std )B BI I

m std

tion site to the bolide trace is known (180 km), thelengths of bright regions can be estimated at 23.2 ±1.5 km and 7.8 ± 0.9 km. An analysis of the bolidemotion in these frames yields a velocity estimate of18.8 ± 0.1 km/s, at which speed the transit time of thebolide required for the formation of these two tracks is1.2 ± 0.1 and 0.4 ± 0.1 s, respectively, and the intervalbetween the centers of the tracks is 1.2 ± 0.3 s. Thesevalues are consistent with the main and last flashes onthe bolide light curve.

6. ENERGY ESTIMATIONS

As was shown in the preceding section, the mainstage of meteoroid deceleration in the atmospheretook place over a pathlength of about 23 km. There�fore, the shock wave in the first seconds possessed acylindrical geometry. For a total explosion energy ofE = 300 kilotons TNT at an altitude of 23 km (see Sec�tion 7), the radius of a cylindrical shock wave in twoseconds is about 1.3 km. For a point explosion of thesame energy, the radius would be about 2.5 km. Animportant parameter that characterizes the effects ofasymmetry at the stage of a strong explosion in expo�nential atmosphere is the dynamic scale R = (E/P)1/3.At an altitude of 23 km, this value is R = 6.3 km (i.e.,somewhat below the altitude scale H = 7.6 km of theexponential atmosphere). This result implies that thetop–bottom asymmetry (typical of a strong explosionin the exponential atmosphere) is not as pronounced(Korobeinikov, 1971). Moreover, at large distances(r 10 km) from the site of explosion, a cylindricalshock wave transforms into a spherical wave. Duringthe analysis of shock wave effects at r ~ 40 km, weignored deviations from the spherical symmetry andconsidered the explosion to be instantaneous.

The fact of windows blowing out and the amount ofthis damage in Chelyabinsk, allowing for the shockwave delay, can be used to estimate the explosionenergy. According to video records, the shock wavereached a region of Lesoparkovaya street (center ofChelyabinsk) in 141.5 s. The estimated energy

�

Table 1. List of video files used for photometric measurements

No. Video URL Observation site Camera type Recording speed (fps)

1 http://www.youtube.com/watch?v=IcRCVOapPyA Chelyabinsk oblast, private ware�house

Outdoor 6

2 http://www.youtube.com/watch?v=xanoIUJ9kKU Chelyabinsk, pl. Revolutsii Outdoor 103 http://www.youtube.com/watch?v=VjtM5GUjmSY M5 Road to Chelyabinsk Dashboard 254 http://www.youtube.com/watch?v=iCawTYPtehk Kamensk�Uralskii, crossing of

ul. Lenina and pl. PobedyDashboard 29.97

5 http://www.youtube.com/watch?v=XqZhMClRHpM Chelyabinsk, ul. Pervoi Pyatiletki Dashboard 256 http://www.youtube.com/watch?v=gQ6Pa5Pv_io Chelyabinsk, ul. Lesoparkovaya Dashboard 207 http://www.youtube.com/watch?v=hD2iySyG090 Bashkortostan, Beloretsk Dashboard 308 http://www.youtube.com/watch?v=L3rMDmv08FQ Chelyabinsk oblast, Miass Dashboard 15

248



depends on the adopted value of overpressure in theshock wave, at which windows are blown. Accordingto published data (Mannan and Lees, 2005), an over�pressure of Δp = 0.1 psi (1 psi = 0.69 kPa) correspondsto the fracture of 5% of windows, while Δp = 0.21 psiincreases the amount of damage to 50%. At the centerof Chelyabinsk, the proportion of broken windows wasmuch less than 50% and closer to 5%. Since the mini�mum overpressure for blowing windows is sometimesestimated at 0.15 psi (Brown and Loewe, 2003), weassume the 0.1–0.15 psi (0.7–1 kPa) range for thepressure of the shock wave at the center of Chelya�binsk.

A realistic dependence of Δp on r for a meteoroiddecelerated in the exponential atmosphere can, inprinciple, be calculated in the framework of a three�

dimensional hydrodynamic model. However, for ourrough estimates it is expedient to use scaling rela�tions—in particular, a modified Sachs rule—thevalidity of which is confirmed by hydrodynamic simu�lations (Lutzky and Lehto, 1968; Korobeinikov et al.,1977). Using these scaling relations, it is possible tocalculate the overpressure in a shock wave propagatingtoward the ground, provided that the dependence ofΔp on r for a standard energy E1 (e.g., 1 kiloton TNT)in a homogeneous medium at a sea level pressure isknown (Glasstone and Dolan, 1977). In the caseunder consideration, this standard dependence hasbeen used to calculate a distance to the epicenter forwhich the shock wave delay would be 141.5 s. Theshock wave velocity at the given altitude was calculatedallowing for a finite pressure in the blast wave and thetemperature dependence of the velocity of sound. Fig�ure 10 shows results for a bolide explosion at altitudes23 and 27 km and six energies within 100–600 kilotonsTNT. The overpressure in a shock wave at the center ofChelyabinsk falls in the interval of critical pressures forwindow breakage (0.7–1 kPa) at the explosion ener�gies within the 200–500 kilotons TNT range (Fig. 10).However, taking into account that the shock wavecould be doubly amplified upon reflection from theEarth’s surface (Glasstone and Dolan, 1977), thelower energy limit should be reduced to 100 kilotonsTNT. Thus, the total shock wave energy falls within100–500 kilotons TNT. Approximately 15–18% of theliberated meteorite energy is radiated (Popova and

0

–5 –4 –3 –2 –1 0 1 2 3 4–6

0.2

0.4

0.6

0.8

1.0R

elat

ive

brig

htn

ess

Time (relative to main flash), s

Fig. 8. Bolide light curve constructed using video file no. 8 (Table 1). Negative brightness at t = 2 s is related to instrumental effectsat a minimum value of the diaphragm.

1

2

Fig. 9. Trace of bolide as imaged in video no. 4, whereregions 1 and 2 correspond to the main and last flashes,respectively.



Nemchinov, 2005) and less than 5% is expended onevaporation. It is not quite clear what is the mass andkinetic energy of deposited coarse fragments. If thisfraction is also negligibly small, then the relativelysmall energy consumption for radiation and evapora�tion gives us grounds to estimate the initial kineticenergy of the Chelyabinsk meteorite at 100–500 kilo�tons TNT.

Additional factors capable of influencing theenergy estimation are a nonspherical shape of theshock wave and the refraction of a shock wave in theatmosphere. The effect of nonsphericity for a shockwave propagating almost perpendicularly to the trajec�tory is relatively small. The role of refraction can besignificant at large distances from the epicenter. Thiscan be illustrated by calculations of the propagation ofa weak shock wave in terms of the geometric acoustics(Fig. 11). An acoustic beam propagating from 23 kmaltitude at 55° relative to the vertical, reaches the sur�face at a distance of d = 32.8 km from the epicenter fort = 133.7 s at a constant velocity of sound of 300 m/s.Taking into account the temperature dependence ofthe velocity of sound and the refraction of a shockwave in the atmosphere, we obtain somewhat greatervalues of d = 35.7 km for t = 140.7 s. With allowancefor the wind with a “standard” altitude velocity profile andan amplitude of 40 m/s at 12 km, we have d = 41.1 km att = 147 s for downwind propagation and d = 32.4 km at t =139.6 s for upwind propagation. These estimates implythat the features of a weak shock wave propagation inthe real atmosphere can modify the arrival time of thedisturbance and the estimated distance to the epicen�ter in a range above 40 km. At the same time, the cur�vature of acoustic rays for distances under consider�ation (~38 km/s) is rather small and can be ignored forrough estimations. On the whole, all the aforemen�tioned factors can somewhat change the estimation ofthe energy, but hardly by more than factor of 1.5.

Using the known dependencies of overpressure onthe distance (Tsikulin, 1969) for spherical and cylin�drical shock wave sources in the exponential isother�mal atmosphere (Fig. 12) and adopting the same range

0.4

35

0.6

0.8

1.0

1.2

36 37 38 39 40

h = 23 km

h = 27 km600

100

d, km

Δp, kPа

Fig. 10. Plot of the overpressure Δp versus distance r fromthe epicenter to dashboard camera at the center of Che�lyabinsk. Squares correspond to models, for which thetime of sound wave propagation is 141 s at an altitude of 23and 27 km and the explosion energy varies from 100 to600 kilotons TNT (left to right) at a step of 100 kilotonsTNT. Dashed lines show the accepted range of excess pres�sures capable of blowing out about 5% of windows.

0 20

10

20

40 60 80 0 20 40 60 80d, kmd, km

z, km

c + u

c c

c – u

65°65°55°55°

Fig. 11. Trajectories of acoustic rays emitted from 23 km altitude at 55° and 65° angle relative to vertical with allowance for (solidcurves) taking into account only the temperature dependence of the sound velocity and (dotted curves) the temperature depen�dence of the sound velocity and the wind with a “standard” altitude velocity profile for (left panel) downwind and (right panel)upwind propagation. At distances below 40 km from the epicenter, the influence of ray curvature is relatively weak.

250



of window�blowing pressures (700–1000 Pa), we mayconclude that (for maximum distances of 40–50 kmfrom the epicenter to regions of significant damage)the meteoroid energy must be within 100–340 kilo�tons TNT at an altitude of 22 km. The presence of anear�ground temperature inversion (i.e., temperatureincrease with altitude) in Chelyabinsk on February 15,2013, could decrease the shock wave amplitude on theaverage by 15% (accordingly, allowance for this effectwould increase the estimated energy).

The energy of meteoroids is usually estimated withallowance for the period (or frequency) of the maxi�mum amplitude (or pressure amplitude) of measuredinfrasound oscillations with the aid of approximationsnormalized for various kinds of explosions. The spreadof these estimations is rather large. A comparison ofvarious estimations of the pressure amplitude at a dis�tance of 1000 km for an equivalent energy of 1 kilotonTNT (Ens et al., 2012) showed that these values candiffer by almost two orders of magnitude. The knownenergies of 70 satellite bolides (ranging within 0.02–20 kilotons TNT), for which an infrasound signal wassimultaneously recorded, allowed the most reliableapproximation to be selected in the indicated energyrange (Ens et al., 2012). The application of thisapproach to infrasound data of the Chelyabinsk eventyields an estimated energy of 1000 kilotons TNT,although this value is far beyond the range of eventsconsidered by Ens et al. (2012). Characteristic fre�quencies in the spectra of infrasound signals measuredat IDG and CTBTO (Aktyubinsk) infrasonic stationsare within 0.012–0.025 Hz, which allow the Chelyab�

insk meteoroid energy to be estimated at 300–1400 kilotons TNT.

A series of model calculations has been performedfor explosions of various energies at different altitudes.The computations used a SOVA code (Shuvalov,1999) on a 1000 × 500 cell difference grid. The simu�lations took into account variations of the air densityand temperature with altitude in the framework of astandard atmosphere model CIRA; the wind velocitywas set to be zero, since a real wind distribution at themoment of “explosion” was unknown; and the tabu�lated equation of state for air was employed (Kuz�netsov, 1965). The calculations yielded maximumpressure at various points on the Earth’s surface withallowance for the shock wave reflection from ground.The results (Fig. 13) show that a 300�kiloton TNTexplosion at a 25�km altitude produces destructionclose to that observed upon the fall of the Chelyabinskasteroid.

As noted above, seismic vibrations caused by theChelyabinsk bolide’s entry into the atmosphere havebeen detected by a large number of seismic stations.Estimation of the bolide energy from these data is atask for future investigations.

According to data from the satellite monitoringnetwork, the energy radiated by the Chelyabinskbolide amounted to 3.75 × 1014 J, which is approxi�mately equivalent to 90 kilotons TNT (http://neo.jpl.nasa.gov/fireballs/). Nemtchinov et al., 1997,obtained the following expression for the integral radi�ation efficiency defined as the ratio of the total radia�tion energy to the initial kinetic energy:

η = Er/Ek,

5001

1000

1500

2000

100010010

0 km

20 km

30 km

40 km

50 km

Ove

rpre

ssur

e, P

a

Equivalent energy, kilotons TNT

Fig. 12. Plots of the overpressure on the Earth’s surface at various distances from the source projection versus equivalent energyof a 20�km�long cylindrical source at a 22 km altitude.



where Er is the radiated energy (measured by a detec�tor) and Ek is the kinetic energy of the meteoroid. Fora radiated energy of ~90 kilotons TNT and an integralefficiency of 14–16.5%, the kinetic energy amounts to540–640 kilotons TNT. Brown et al., 2002, estimatedthe integral radiation efficiency using several eventsdetected by the satellite monitoring network, forwhich independent estimations of the initial energy(mostly from infrasound data) were available. For theChelyabinsk bolide, the efficiency amounts to 20%,which corresponds to an initial kinetic energy of450 kilotons TNT. It should be noted that the energyof events used to obtain the approximated relation wassignificantly lower than the energy of the Chelyabinskmeteoroid (0.1–25 kilotons TNT). The accuracy ofestimations of the total radiation efficiency (and,hence, of the energy) is no better than 1.5–2 times;nevertheless, these data allow the kinetic energy of theChelyabinsk meteoroid to be estimated from radiatedenergy as 450–640 kilotons TNT.

In concluding this section, it can be ascertainedthat the energy estimated from the overpressure

needed for window breakage in Chelyabinsk amountsto 100–500 kilotons TNT, while the infrasound datayield 300–1400 kilotons TNT. Thus, the two methodsare consistent within 300–500 kilotons TNT. Themethod based on the radiated energy, supported by thehydrodynamic estimates, leads to a conclusion that300–500 kilotons TNT is most probable estimate firthe meteoroid energy.

7. ESTIMATED TRAJECTORY OF MOTION, PARAMETERS, AND TYPE

OF CELESTIAL BODY

From the astronomic standpoint, the most inter�esting question is what was the orbit of the body onapproaching the Earth and its genesis in terms ofknown groups of space objects representing small bod�ies of the Solar System.

The trajectory of motion has been establishedbased on the processing of numerous video records.Figure 14 shows a projection of the trajectory onto theEarth’s surface. A comparison of the moment of max�

1.001000 80604020

1.01

1.02

1.03

1.04

R, km

P/P0

E300H25

E50H20

E300H40

E50H25

E3H5

E10H15

Fig. 13. Plots of the pressure P/P0 (normalized to normal) on the Earth’s surface versus distance R from the projection of energyrelease point for explosions of various energy (E, kilotons TNT) at different altitudes (H, km) (indicated on the curves). The hor�izontal line corresponds to an overpressure of 500 Pa.

252



imum glow intensity and the onset of damage allowedthe altitude h to be determined at which the mostintense destruction of the body took place. The resultsof processing of four video files with minimum delaytimes of the shock wave (Pervomaiskii, Emanzhelinsk,and Korkino) in terms of the approximation a spheri�cal shock wave propagating at a velocity of 300 m/sgive h = 22.9 ± 0.2 km. The epicenter of explosion wasnear Pervomaiskii. Allowing for more distant videorecords (Chelyabinsk), h = 23.9 ± 1.4 km. Estimations inthe cylindrical wave approximation yield h = 23.0 kmabove Pervomaiskii and h = 24.9 ± 0.4 km for the energyrelease from a body occurring about 8 km to the east.Evidently, these are preliminary estimates. More accu�rate data will be obtained upon determining the orbitof this celestial body.

The first estimated orbit of the Chelyabinsk mete�oroid was reported on February 21, 2013 (Zuluaga andFerrin, 2013). This orbit was determined using a singlevideo record made in Chelyabinsk. Then, a telegramno. 3423 of the International Astronomic Union wasreported on February 23, 2013, in which Czechastronomers (Borovicka et al., 2013) presented theirvariant. Note that the first report (Zuluaga and Ferrin,

2013) described the method of obtaining data, whilethe second (Borovicka et al., 2013) did not. In the nextwork, Zuluaga et al. (2013) presented a new variant ofthe orbit, which was based on four video records. Table 2summarizes the results of the preliminary determina�tion of the orbit of the Chelyabinsk meteorite.

As can be seen from Table 2, the results of variousdeterminations significantly differ with respect tosome parameters, e.g., the spread of probable values ofthe semimajor axis and ascending node�perihelionangle. Even two works of the same group gave substan�tially different results. Nevertheless, the data of Table 2allow us to unambiguously conclude that the Chelya�binsk meteorite belongs to the Apollo asteroid family.

To more exactly determine the orbit, specialists ofthe IGD and Institute of Astronomy observed thenight sky for linking the video records to the trajectoryof the Chelyabinsk meteorite. When these records areprocessed, the orbit parameters will be determinedmore reliably. Preliminary determination of the orbitof the Chelyabinsk meteorite prior to its approachingthe Earth, which has been performed at the Depart�ment of Space Astrometry of the Institute of Astron�omy, gave the following orbit parameters: semimajoraxis, a = 1.77 AU; perihelion distance, q = 0.75 AU;orbit inclination, i = 4.3°.

In addition, specialists of the Institute of Astron�omy (Terentjeva and Bakanas, 2013) analyzed theavailable catalogues of meteorite orbits. According tothe database of the IAU Meteor Data Center in Lund(Sweden), a meteor swarm has been found that can berelated to the Chelyabinsk bolide and called diurnalPegasus Aquarids, which consists of three branches:northern, ecliptical, and southern. This study wasbased on the elements of the orbit reported by Borov�icka et al. (2013).

Specialists of the Vernadsky Institute of Geochem�istry and Analytical Chemistry carried out a prelimi�nary investigation of the geochemical characteristicsof the meteorite and obtained the first data on the typeof this body. A petrographic�mineralogical analysis(Nazarov and Badyukov, 2013) showed that most ofthe fragments collected have a chondrite structure,containing up to 60% of irregular chondrules with anaverage size of about 1 mm in a matrix of broken chon�drules and mineral grains; the main mineral phases areolivine and orthopyroxene. Quantitative analysis ofthe chemical composition showed that the samplesrepresent a typical chondrite of the LL group with a

Fig. 14. Projection of the trajectory of the body onto theEarth’s surface (straight segment) from Etkul to Pervo�maiskii.

Table 2. Preliminary parameters of the orbit of the Chelyabinsk meteorite

Semimajor axis, AU Eccentricity

Inclination, deg

Argument of perihe�lion, deg

Longitude of ascending node, deg Reference

1.73 ± 0.23 0.51 ± 0.08 3.45 ± 2.02 120.62 ± 2.77 326.7 ± 0.79 Zuluaga and Ferrini, 2013

1.55 0.5 3.6 109.7 326.41 Borovicka et al., 20131.26 ± 0.05 0.52 2.984 95.5 ± 2 326.5 ± 0.3 Zuluaga et al., 2013



relatively small content of iron and the presence ofkamacite and taenite in the metal phase. Theincreased content of cobalt in kamacite and the entirechemistry of mineral phases confirm the assignment ofchondrite to the LL group. Some additional charac�teristics allow the chondrite to be classified into5th petrological type. The structure of fragments,most of which is an impact�fused breccia, revealedthin dark streaks filled with a fine�grained impact�fused material. The presence of glide planes at thecontacts of cracks and the matrix suggested a frictionorigin of this phase. Apparently, fractionation of themeteorite body took place at the boundaries of darkimpact�fused inclusions and bright fine�grainedmatrix, since fragments consisting entirely of the darkand bright material are rare.

8. CONCLUSION

There has been a single case in the history when ameteoroid was observed for a relatively long time(about 20 h) before its entry into the Earth’s atmo�sphere (Jenniskens et al., 2009). That meteoroid haddimensions within 3–5 m. Another meteoroid (aster�oid name 2008 TC3) has been noticed accidentally,albeit in the framework of a systematic survey. At largedistances, bodies with dimensions below 20 m cannotbe detected because of limitations with respect to theresolving power of modern survey telescopes. At shortdistances, the main difficulty is the short time fordetecting an object.

Astronomically, the Chelyabinsk event is a typicalcase of an asteroid entering the Earth’s atmosphere.However, this event is rather unusual for modern his�tory with respect to the size of a celestial body, densityof population in the region of the fall, the scale ofdamage and number of injured people, and theamount of observational data that provide a basis fordetailed investigation of the physical properties of theobject.

It should be emphasized that the Chelyabinskmeteoroid could not be detected by all technicalmeans available at present. The optical spectral rangeis excluded, since the celestial body approached theEarth from the the Sunward side: the incidence anglerelative to the Sun direction was as small as 15°. Radiofrequency monitoring of a short�range space region isalso not effective. First, the range of these systems is5–10 thousand kilometers, which, for a celestial bodywith a velocity of 20–30 km/s, implies an approachtime of several minutes (too short to respond). Sec�ond, these systems cannot observe bodies in this broadrange of velocities (frequency limitations of the chan�nels).

ACKNOWLEDGMENTS

The authors are grateful to all witnesses of the phe�nomenon, who kindly reported and presented photo

and video records of the event over Chelyabinsk onFebruary 15, 2013. Special thanks to Eduard Kalinin,Evgenii Tvorogov, Marat Akhmetvaleev, DenisSiv’yuk, Nikolai Ivanov, Dmitrii Volkov, AleksandrIvanov, Aleksandr Yashen’kin, Ermek Aisin, AndreiMostovoi, S. Kaigorodtsev, and Nikita Vasil’ev.

This work was supported in part by Federal Tar�geted Program “Scientific and Educational HumanResources of Innovation�Driven Russia” for 2009–2013 and the Presidium of the Russian Academy ofSciences (program no. 22 “Fundamental Processes ofResearch and Exploration of Solar System”).

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Translated by P. Pozdeev

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