ISSN 00380946, 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.

Astronomical and Physical Aspects of the 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. Trubetskayab a Institute of Astronomy, Russian Academy of Sciences, , 119017 b Institute of Geosphere Dynamics, Russian Academy of Sciences, Moscow, 119334 Russia c South State University, Chelyabinsk, 454080 Russia d Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia Received April 1, 2013

Abstract—Various observational data including infrasound, seismic, optical (onboard) monitoring, ground video and photo records, and evidence from witnesses of the Chelyabinsk event on February 15, 2013, have been 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 explosion, which took place in the atmosphere at an altitude of about 23 km, show evidence of the formation of a highpower shock wave equivalent to 300– 500 kilotons of TNT. The object diameter corresponding to this energy falls within the range 16–19 m. The trajectory of the meteor is outlined. It is preliminarily concluded that the Chelyabinsk was a repre sentative the Apollo family. DOI: 10.1134/S0038094613040114

1. INTRODUCTION 1500 patients asked for medical aid, of which about 100 were hospitalized (two in reanimation), being pre A general picture of the Chelyabinsk event on Feb dominantly injured by broken glass from windows. ruary 15, 2013, has been established in detail. At about With respect to the number of wounded people, this 9:20 a.m. local time (03:20 GMT), a space object 16– has no analogues. 19 m in size entered the Earth’s atmosphere at an angle of less than 20° relative to the horizon. The A large number of small (not exceeding 2 cm) approach of this quite large object to the Earth was not meteoroid fragments (i.e., residue from the celestial noticed by any of the existing means of space and body remaining upon reaching the ground) have been groundbased observations of celestial bodies. Only found over a wide territory. According to the first com after its entry into the atmosphere did it became a phe munication from V.I. Grokhovskii (Committee for nomenon attracting the attention of humankind. The , Russian Academy of Sciences), particles interaction with the atmosphere led to strong glow found in the first days after the meteorite fall in the (a phenomenon called a fireball or bolide). In several vicinity of Lake by an expedition from the seconds, the glow intensity exhibited significant Ural Federal University () exhibit a growth and the maximum flash was observed approxi meteorite nature and belong to the class of common mately 11–12 s after appearance of the meteor. Wit . Subsequent expeditions from the Vernad nesses reported that, at the moment of the flash sky Institute of Geochemistry and Analytical Chemis (explosion), the glow intensity was much brighter than try, SouthUral State University (Chelyabinsk), Ural sunlight and even heat could be felt. Both prior to and Federal University (Yekaterinburg), and the Institute after the flash, the track of the bolide was clearly seen of Astronomy added many samples. A chemical anal in the sky. An explosive (shock) wave came within sev ysis performed at the Laboratory of the eral minutes (video records are indicative of a 77 s to Vernadsky Institute allowed the meteorite to be classi 3 min time interval and above), depending on the fied to the LL group. location. According to the Russian Ministry of Emer The pattern outlined above is close to the classical gency Situations, the damage caused by the explosive description of the entry of a large celestial body into wave was detected in Chelyabinsk and over ten regions the Earth’s atmosphere. Generally speaking, the Che of the . The most significant lyabinsk event is not a rare astronomical phenomenon. destruction was observed in Chelyabinsk, Korkino and Figure 1 (reproduced from Ivanov and Hartmann, Kopeisk, and the village of Roza. More than 2007) shows a distribution of the frequency P of colli

240 ASTRONOMICAL AND PHYSICAL ASPECTS OF THE CHELYABINSK EVENT 241

1E+5 1E+4 Observed NEA LINEAR, Stuart and Binzel, 1994 1000 , Rabinowitz et al., 2000 100 NEAT, Rabinowitz et al., 2000 Terrestrial bolides, Brown et al., 2002 10 1 A 0.1 –1.3 0.01 –1.7 0.001 –8 –2.95 P = 8 × 10 DP 0.0001 B From cratering –3 1E–5 1E–6 Probability of impact per 1 year P = 2.8 × 10–6 D –2.3 1E–7 –6 –1.7 P P = 1.5 × 10 DP 1E–8 1E–9 1E–10 0.0001 0.001 0.01 0.1 1 10 100 1000 D , km P B H ~ 18 16 14 12

Fig. 1. Frequency of collisions of the Earth with celestial bodies of various dimensions. sions of the Earth with celestial bodies of dimension D. useful for many specialists and the more so for For bodies within 1–30 m, this distribution obeys the advanced amateurs. law P = 8 × 10–8D–2.95 year–1 (D expressed in kilome Section 2 presents the observational data based on ters). Thus, collisions with bodies of the order of the optical, infrasound, and seismic detection. Section 3 Chelyabinsk meteoroid take place on the average once describes a large number of video and photo records per 60–100 years. following penetration of the observed body through Among the data available on similar events, we can the Earth’s atmosphere. Section 4 considers various mention bolides observed on August 3, 1963 (Prince evidences from witnesses of the Chelyabinsk event. Edward Islands, South Africa, estimated energy 260– Section 5 describes the construction of the bolide light 1000 kilotons TNT, Silber et al., 2009); February 1, curve. Section 6 presents estimations of the energy of 1994 (Marshall Islands, South Africa, estimated a celestial body, while Section 7 gives preliminary energy ~40 kiloton TNT, Popova and Nemchinov, results of determining the impact trajectory and 2005); and October 8, 2009 (Indonesia, estimated parameters. energy ~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, 2. INFRASOUND, SEISMIC, AND OPTICAL Adushkin et al., 2004). Nevertheless, the Chelyabinsk MONITORING event can be recognized as unique. For the first time in The entrance and destruction of large celestial bod our history, the collision with a large celestial body was ies in the Earth’s atmosphere is a source of light, recorded in great detail, which made a thorough scien acoustic, infrasound, and seismic waves. The main tific analysis of this event possible. source of perturbations in the atmosphere is a shock This article presents the first results of an analysis wave. Acoustic waves (20 Hz–20 kHz) mostly propa carried out by experts from academic institutions. Of gate through relatively short distances (within 2– course, this study is by no means exhaustive in all 2.5 times the altitude of bolide destruction—the zone respects, since a deeper insight in many directions is of direct communication). The infrasound spectral yet to come. However, the data below provide a com interval covers lowfrequency acoustic waves from plex notion about the Chelyabinsk event, which will be 20 Hz to a limit of 3 × 10–3 Hz. Since the infrasonic

SOLAR SYSTEM RESEARCH Vol. 47 No. 4 2013 242 EMEL’YANENKO et al. waves weakly decay in the atmosphere, the infrasound 1000 kiloton TNT (Silber et al., 2009), which is com generated by bolides (and other sources) can be parable with the energy estimates for the Chelyabinsk detected over quite large distances. These perturba meteoroid. tions can propagate in atmospheric waveguides Eleven infrasound detection stations of the Com formed at various altitudes by temperature gradients, prehensive NuclearTestBan Treaty Organization wind velocity and direction over distances up to several (CTBTO) recorded the fall of the Chelyabinsk aster thousand kilometers. A downward shock wave reaches oid (CTBTO press release, 18.02.2013: http://www. the ground and generates seismic waves, which can be ctbto.org/presscentre/pressreleases/2013/russian detected at distances up to several hundred kilometers fireballlargesteverdetectedbyctbtosinfrasound and above. sensors/). In addition, the infrasound response has The Chelyabinsk event of February 15, 2013 (Che also been detected by other stations. In particular, the lyabinsk bolide), is an outstanding phenomenon in the infrasound generated by the Chelyabinsk bolide was series of meteoroid penetrations due to (i) large zone detected by microbarometers with 0.001–10 Hz band of disturbance (broken windows, ceilings, frames, pass at the Institute of Geosphere Dynamics (IGD) in etc.) and (ii) much varied evidence–including instru Moscow and at the Geophysical Observatory in Mikh mental data such as video and photo records, satellite nevo (). This infrasound was also onboard monitoring, infrasound and seismic response, detected in Tomsk. The location of the major energy dusty trace observations (both spacebased and ground), release (54°35.4′ N, 61°45.5′ E) was determined to and an extensive field of meteorite residue. within 40 km using the data of IGD infrasonic stations The radiation from Chelyabinsk bolide was very and CTBTO station (IS31, Aktyubinsk). bright, classified as superbolide (fireball brighter that Seismic vibrations caused by the bolide entrance 17th stellar ). These bolides are detected by into the atmosphere have been also detected by a large onboard sensors of geostationary satellites of the number of seismic stations at distances within hundreds United States Department of Defense (Tagliaferri and thousands of kilometers. Approximate coordinates et al., 1994). This satellite observation network is pri of the source of seismic oscillations (55.150° N, 61.410° E; marily intended to monitor nuclear tests, while the USGS website: http://comcat.cr.usgs.gov/earthquakes/ observation of bolides is a byproduct. On the average, eventpage/us2013lra1#summary) are rather far from about 30 flashes are typically observed every year at the approximate trajectory of bolide motion. The cor 30–45 km altitudes over the Earth, with a duration of responding earthquake magnitude was rated 2.7–4 1–3 s and an average energy equivalent to 0.01–1 kilo according to various estimates. ton TNT. The complete data of optical observations for 1994–1996 (51 events) have been analyzed (Nem tchinov et al., 1997). Based on these data, the kinetic 3. ANALYSIS OF VIDEO RECORDS energy of entering in the Earth’s atmo A unique feature of the Chelyabinsk event is that, sphere was estimated at 0.06–40 kilotons TNT. for the first time in the history of observations, there Unfortunately, the complete information on the are many video and photo records of the entrance and events detected by satellites is now unavailable for flight of this celestial body in the Earth’s atmosphere. objective scientific analysis but, in some cases (Vitim At present, more than 150 records are available, bolide, asteroid 2008 TC3), partial data have been mostly from dashboard cameras (event data recorders) reported. For the Chelyabinsk event, coordinates of and outdoor surveillance cameras. For most video the maximum brightness site (54.8° N, 61.1° E), alti records, the observation point coordinates have been tude (23.3 km), and velocity (18.6 km/s) have been determined. Among the available data, about published, and a little later the radiated energy was 60 records are of scientific significance, from which estimated (http://neo.jpl.nasa.gov/fireballs/) (see the trajectory of the body, the bolide light curve, the Section 6). Note that the coordinates of the site of altitude and consequences of its destruction can be maximum brightness on the Chelyabinsk meteoroid determined. trajectory have been determined using several video Among the most interesting records, there are records (Borovicka et al., 2013). some showing both the bolide flash and the moment of Among the data of onboard monitoring systems shock wave arrival. These records have been made available previously, the maximum kinetic energy mostly in Chelyabinsk and sites situated to the south of amounted to ~40 kilotons TNT (Popova and Nemchi this city. In Fig. 2, white marks indicate the sites of nov, 2005), which is significantly lower than most of most important video recordings. Video recording the energy estimates for the Chelyabinsk meteoroid. sites cover an area of about 8000 square kilometers, For the period of 1960–1974, infrasound waves have which extends 135 km north to south (from northern been detected for some bolides by microbarometer regions of Chelyabinsk to Troitsk) and 85 km west to systems deployed at that time in the United States east (from the village of Mirnyi to Troitsk). The (ReVelle, 1997). The most intense of these events for moment of shock wave arrival was most pronounced 14 years (August 3, 1963, Prince Edward Islands, on records made in Chelyabinsk and surroundings, South Africa) had an estimated energy of 300– where it was manifested by sounds of the explosion,

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Zlatoust M51 Chelyabinsk Kopeisk Chebarkul’

M5 Korkino

Chelyabinsk oblast P360

Uchaly

M36 Troitsk

Fig. 2. A map showing sites from which video records were made showing both the bolide flash and the moment of shock wave arrival. window breakage, etc. At more considerable distances A separate group of video records shows conse from the epicenter, the shock wave arrival is mani quences of the catastrophic fragmentation of the body fested by camera vibrations (in Troitsk) or perturba in the atmosphere. There are eleven videos of this kind tions (Mirnyi). made in Chelyabinsk, Korkino, Kopeisk, Kras Calculations of the time passed from the instant of nogorsk, and Emanzhelinsk. From these data, one the flash to shock wave arrival show that the minimum may conclude that both residential houses and indus period occurs in Pervomaiskii village (77 s), while the trial buildings in Chelyabinsk and towns situated to the maximum delay is observed in Mirnyi village (4 min south of this city have been damaged. For example, 49 s) and Troitsk village (4 min 55 s). In Chelyabinsk, the most windows were broken in a brick plant in Eman shock wave delay varied from 2 min 15 s to 2 min 52 s. zhelinsk and in the YuzhUralKarton plant of Korkino. In Chelyabinsk, windows were broken together with Another important group includes video records frames in the State Railway Institute and in a fastfood containing the partial or complete flight of the body in restaurant. Analogous damage was observed in the atmosphere and the corresponding trace. Among Kopeisk and Krasnogorsk. these, 38 records clearly display the flight and allow the coordinates of the observation point to be deter In addition to videos, there are photographs with mined with good precision. Figure 3 presents selected evidence of the Chelyabinsk event, which were taken shots from some of these records. 3–5 min after the entry into the atmosphere. Most photos were made with mobile phones in Chelyabinsk Figure 4 shows sites from which partial (white and closelying towns and villages (Miass, Kashino, marks) and complete (black marks) video records of Varlamovo, etc.). In most cases, these are partial or com the body’s flight have been made. These record sites plete images of the trace left by the bolide. Figure 5 shows cover an area of about 215000 square kilometers, some illustrative shots. which extends 540 km north to south (from Nizhnii Tagil to Kartala) and 440 km west to east (from Noteworthy photographs have been made by Marat Beloretsk to Tyumen). The most distant site from the Akhmetvaleev using a camera fixed on a support near epicenter of the bolide explosion, where a video record the Miass river (one kilometer away from the Kommunar of the event was made, is Tyumen (about 340 km). In pond) in Chelyabinsk. These excellent images show both addition to the sites shown in Fig. 4, there are records the flash and trace left by the meteor (Fig. 6). from some other sites, including even more distant Another interesting photograph has been provided ones (e.g., Orenburg, 570 km from the epicenter). by Denis Siv’yuk, which shows the image of the mete However, these data are less informative than those orite trajectory as seen on a radar display of the presented in Fig. 4 for various reasons such as poor Chelyabinsk airport (Fig. 7). A thorough analysis of quality, motion of the recorder, uncertainty of its coor this image will be made subsequently with allowance dinates, etc.). for the radar characteristics.

SOLAR SYSTEM RESEARCH Vol. 47 No. 4 2013 244 EMEL’YANENKO et al. The flash lasted for several seconds with increasing intensity. At maximum intensity, the surrounding objects were difficult to recognize. Some witnesses told that the body flight was accompanied by crack ling, which probably indicated that the Chelyabinsk bolide was electrophonic. Many witnesses, especially those in towns close to the anticipated trajectory (e.g., Korkino), told that it was possible to feel heat after flash and, after some time, an odor (fresh or burnt). 000 km/h After the flash and disintegration of the body, a rather 2013/02/15 09:20:34 large fragment continued to move along the same tra jectory, but at a lower apparent velocity. In several minutes after the flash, came the sound of a loud explosion. The first powerful sound was fol lowed by several less intense explosions. In addition to Chelyabinsk, these could be heard in Korkino, Eman zhelinsk, Kopeisk, Shelomentsevo, Pervomaiskii, and some other towns and villages. However, it should be noted that several witnesses in Miass pointed out that no explosion sounds had been heard in their town. Consequences of the shock wave were numerous 2013/02/15 broken windows in Chelyabinsk and closelying towns 09:20:46 Mio 238 and villages. In some buildings, frames and ceilings 02/15/2013 09:23:38 were also broken, and an old warehouse wall of the Chelyabinsk Zinc Plant was destroyed. In Pervo maiskii (one of the closest villages to the center of maximum energy release, see Section 7), there were many broken windows, especially in schools and kin dergartens, but stronger glass packets frequently remained intact. It was also pointed out that large school 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 windows were blown out in old houses. For example, in Fig. 3. Selected shots from video records of the Chelya 594 buildings damaged in Korkino region, there were binsk meteoroid flight. 7938 windows with wooden frames and only 1077 glass units. In industrial buildings, big windows with thick glass were blown. In some cases (e.g., Pribor Plant, Considerable scientific potential is offered by on SouthUral State University, Chelyabinsk State Agri line video records of the Intercommunication Co., cultural Engineering University), windows on the which have been provided by its general director southern side were broken inward, while those on the E.O. Kalinin. These records have been made by syn northern side were blown outward; the same was chronized cameras in Chelyabinsk, Miass, , noticed in Korkino. In some cases (Pervomaiskii, and Chebarkul. SouthUral State University) inner windows or even inner sides of glass units were broken. As a rule, win dows were more frequently blown in panel buildings 4. EVIDENCE OF WITNESSES and less frequently in brick ones. In private (small) The available photo and video records are supple houses, windows were less frequently broken, except mented by a large volume of evidence and observa those with destroyed frames. The glazing of enclosed tions made by witnesses. This evidence was collected balconies was damaged almost everywhere irrespective from the mass media and from a questioning of wit of the building type (concrete panel or brick). nesses and official services during the expedition orga The character of destruction and structure of the nized in March 9–26, 2013, by the IGD and the Insti Chelyabinsk meteoroid can be judged from the frag tute of Astronomy. ments recovered and their distribution. Many frag According to witnesses in Chelyabinsk, the body ments covered by a fused crust have been found near appearing in the sky looked like a dark point, which the village of Deputatskii, where even the roof of a exhibited rapid growth and left a smoky trace behind. small building was damaged. Relatively small (centi The moving body was followed by two equal bands. metersized) fragments included meteorites incom

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Yekaterinburg Tyumen oblast

Chelyabinsk Kurgan oblast

Bashkortostan M51 Chelyabinsk oblast

M30 NorthKazakhstan

Qostanay

Fig. 4. A map showing sites from which partial (white marks) and complete (black marks) video records of the flight of the body were made. pletely covered by fused crust, which showed that frag used for constructing a bolide light curve. This proce mentation continued as the velocity decreased. Some dure implies the collection and analysis of video files meteorite seekers pointed out that, westward from suitable for photometry, selecting zones for brightness Deputatskii along the meteorite trajectory, not a single measurement, calibration of brightness, calculation of fragment was found over several kilometers, which was bolide brightness, and normalization of measurements evidence of the complicated character of the fragmen to a common scale of brightness and time. Unfortu tation process. The search for meteorite fragments was nately, both outdoor surveillance and dashboard cam favored by weather: quite clear and sunny, free of eras are not particularly applicable to precise photo snowfalls, it facilitated detecting meteorite material metry and have limitations. The main one of these is (fragments left entry holes in the snow, which con small dynamical range. As a rule, the cameras have tained ice columns with a fragment at the end). It large fields of vision and measure the exposure with should be also noted that the shock wave cleared up respect to the average illuminance over the shot. At the virtually all chimneys in houses under the trajectory sunrise, the illuminance is yet relatively low, while the and removed small coked stones, which were some bolide has a much greater brightness both at the begin times confused with meteorite fragments. The sites of ning of its flight in the atmosphere and at the moment fallen fragments attracted animals (including crows and foxes), which was probably evidence of some odor. It would be of considerable interest to look for hypothetical large fragments of the meteorite. There is still some hope that a rather large fragment about 1 m in 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 absence of cracks in the ice cast doubts. Photographs made by E.O. Kalinin from an airplane showed holes in lakes and quarries under the trajectory (Etkul region). These traces resembled a snowflake pattern with a hole at the middle 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 outdoor surveillance cameras and dashboard cameras can be Fig. 5. Photographs of the inversion trace.

SOLAR SYSTEM RESEARCH Vol. 47 No. 4 2013 246 EMEL’YANENKO et al.

Fig. 6. Photographs made by Marat Akhmetvaleev. of flash. For this reason, the image of the bolide is The second important problem with cameras is almost always overexposed. However, during the flash, their automatic control of the diaphragm. During the the light is scattered by the Earth’s surface and various flash, the illuminance reaches a sunny day level and objects, so that the brightness of scattered light the diaphragm is significantly reduced. Therefore, it is becomes comparable with that of objects in the frame. necessary to have a zone in the frame where the bright This circumstance allows the relative flux of radiation ness is independent and remains constant. This can be from the bolide at this moment and the temporal vari a nonoverexposed sky region or a lamp. In the case of ation of this flux to be evaluated. a dashboard camera, it is important to analyze the At the first stage, video files have been selected in bolide light scattering on front windshield of the car. If which clearly visible, but not overexposed, scattered the sky in the direction of vision was absent or the glass light from bolide flash is present. Since it is highly was dirty, the video files had to be rejected. probable that light scattering is anisotropic, the varia In the case of frames imaging the bolide, another tion of the brightness of scattered light for any region problem is encountered because all other objects are in is not proportional to a change in the bolide bright the dark and it is impossible to measure the scattered ness. The more isotropic is light scattering, the higher light intensity. This difficulty is especially manifested the accuracy of measurement of relative bolide bright upon the flash, when the bolide brightness rapidly ness. Another important condition for highquality decays but the diaphragm is closed for about a second measurement of the bolide light curve is the absence of due to the inertia of automatics. These frames are dark shadowing on the measured areas. Video files for and unacceptable for photometric measurements. which these conditions were not satisfied were This problem was especially serious for most videos excluded from photometric analysis. from Chelyabinsk and environs. The available video files 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 video files have been selected that are listed in Table 1. In this table, the first column is the file number, the second column 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 on a computer with OS Linux. Each video file was divided by mplayer program into PNG frames, in which rect angular zones were defined for the measurement of scattered light intensity from bolide (Im) and a stan std Fig. 7. Image of a meteorite trajectory as seen on a radar dard region (I ). Separate frames have been pro display of the Chelyabinsk airport. cessed using a program written in Perl using an

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Table 1. List of video files used for photometric measurements Recording No. Video URL Observation site Camera type speed (fps) 1 http://www.youtube.com/watch?v=IcRCVOapPyA Chelyabinsk oblast, private ware Outdoor 6 house 2 http://www.youtube.com/watch?v=xanoIUJ9kKU Chelyabinsk, pl. Revolutsii Outdoor 10 3 http://www.youtube.com/watch?v=VjtM5GUjmSY M5 Road to Chelyabinsk Dashboard 25 4 http://www.youtube.com/watch?v=iCawTYPtehk KamenskUralskii, crossing of Dashboard 29.97 ul. Lenina and pl. Pobedy 5 http://www.youtube.com/watch?v=XqZhMClRHpM Chelyabinsk, ul. Pervoi Pyatiletki Dashboard 25 6 http://www.youtube.com/watch?v=gQ6Pa5Pv_io Chelyabinsk, ul. Lesoparkovaya Dashboard 20 7 http://www.youtube.com/watch?v=hD2iySyG090 Bashkortostan, Beloretsk Dashboard 30 8 http://www.youtube.com/watch?v=L3rMDmv08FQ Chelyabinsk oblast, Miass Dashboard 15

Image::Magic library for image processing. For every tion site to the bolide trace is known (180 km), the rectangular zone, average values were determined in lengths of bright regions can be estimated at 23.2 ± three color channels—red (IR), green (IG), and blue 1.5 km and 7.8 ± 0.9 km. An analysis of the bolide (IB)—and the relative brightness of the bolide was motion in these frames yields a velocity estimate of mstd mstd mstd 18.8 ± 0.1 km/s, at which speed the transit time of the defined as m /3. The I = (IIRR + IIGG + IIBB) bolide required for the formation of these two tracks is results of analysis for all video files were compared ± ± m 1.2 0.1 and 0.4 0.1 s, respectively, and the interval upon normalization of the bolide brightness as I = between the centers of the tracks is 1.2 ± 0.3 s. These (Im – Ibg)/(Imax – Ibg), where Ibg is the initial brightness values are consistent with the main and last flashes on (prior to bolide flight) and Imax is the maximum bright the bolide light curve. ness during the flash. The temporal scale was determined by the ratio of the frame number (n (to the speed of recording (fps): 6. ENERGY ESTIMATIONS t = n/fps. The time was measured relative to a moment As was shown in the preceding section, the main close to the maximum brightness. Figure 8 shows one stage of meteoroid deceleration in the atmosphere of the highest quality bolide light curves, which was took place over a pathlength of about 23 km. There constructed using video file no. 8 (Table 1). fore, the shock wave in the first seconds possessed a According to video file no. 7, the bolide was visible cylindrical geometry. For a total explosion energy of beginning at t = –11.5 s (relative to zero point in E = 300 kilotons TNT at an altitude of 23 km (see Sec Fig. 8) and exhibited significant growth in brightness tion 7), the radius of a cylindrical shock wave in two at t > –5 s. The bolide light curve shows three charac seconds is about 1.3 km. For a point explosion of the teristic regions: preliminary flash (t ≈ –2.0 s); main same energy, the radius would be about 2.5 km. An flash (t ≈ 0 s), and last flash (t ≈ 1.4 s). The character important parameter that characterizes the effects of istic duration of the preliminary flash (on a 0.5 relative asymmetry at the stage of a strong explosion in expo brightness level according to various files) is about 1 s nential atmosphere is the dynamic scale R = (E/P)1/3. and the main flash is about 1.5–2 s long. Then, mete At an altitude of 23 km, this value is R = 6.3 km (i.e., oroid fragments continue their flight in the atmo somewhat below the altitude scale H = 7.6 km of the sphere and exhibit one more flash in about ~0.8 s that exponential atmosphere). This result implies that the is accompanied by additional glow in the trace. The top–bottom asymmetry (typical of a strong explosion duration of this flash does not exceed 0.4 s. Finally, the in the exponential atmosphere) is not as pronounced brightness exhibits a sharp drop and the scattered light (Korobeinikov, 1971). Moreover, at large distances of the bolide is no longer detected. (r ӷ 10 km) from the site of explosion, a cylindrical The bolide light curve reflects a nonuniform glow shock wave transforms into a spherical wave. During intensity along the trajectory and the main maxima of the analysis of shock wave effects at r ~ 40 km, we brightness must correspond to those in the spatial dis ignored deviations from the spherical symmetry and tribution of glow sources. Figure 9 shows an image considered the explosion to be instantaneous. taken from video no. 4, where the bolide tail reveals The fact of windows blowing out and the amount of two bright flashes. Using relative distances between this damage in Chelyabinsk, allowing for the shock objects on the frame (church and roads) and compar wave delay, can be used to estimate the explosion ing azimuthal angles on the Yandex.map and Goo energy. According to video records, the shock wave gle.map, the angular scale was evaluated at 0.058 ± reached a region of Lesoparkovaya street (center of 0.004 deg/pixel. Once the distance from the observa Chelyabinsk) in 141.5 s. The estimated energy

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1.0

0.8

0.6

0.4 Relative brightness Relative

0.2

0

–6 –5 –4 –3 –2 –1 0 1 2 3 4 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 effects at a minimum value of the diaphragm. depends on the adopted value of overpressure in the dimensional hydrodynamic model. However, for our shock wave, at which windows are blown. According rough estimates it is expedient to use scaling rela to published data (Mannan and Lees, 2005), an over tions—in particular, a modified Sachs rule—the pressure of Δp = 0.1 psi (1 psi = 0.69 kPa) corresponds validity of which is confirmed by hydrodynamic simu to the fracture of 5% of windows, while Δp = 0.21 psi lations (Lutzky and Lehto, 1968; Korobeinikov et al., increases the amount of damage to 50%. At the center 1977). Using these scaling relations, it is possible to of Chelyabinsk, the proportion of broken windows was calculate the overpressure in a shock wave propagating much less than 50% and closer to 5%. Since the mini toward the ground, provided that the dependence of mum overpressure for blowing windows is sometimes Δp on r for a standard energy E1 (e.g., 1 kiloton TNT) estimated at 0.15 psi (Brown and Loewe, 2003), we in a homogeneous medium at a sea level pressure is assume the 0.1–0.15 psi (0.7–1 kPa) range for the known (Glasstone and Dolan, 1977). In the case pressure of the shock wave at the center of Chelya under consideration, this standard dependence has binsk. been used to calculate a distance to the epicenter for Δ which the shock wave delay would be 141.5 s. The A realistic dependence of p on r for a meteoroid shock wave velocity at the given altitude was calculated decelerated in the exponential atmosphere can, in allowing for a finite pressure in the blast wave and the principle, be calculated in the framework of a three temperature dependence of the velocity of sound. Fig ure 10 shows results for a bolide explosion at altitudes 23 and 27 km and six energies within 100–600 kilotons TNT. The overpressure in a shock wave at the center of 1 Chelyabinsk falls in the interval of critical pressures for window breakage (0.7–1 kPa) at the explosion ener gies within the 200–500 kilotons TNT range (Fig. 10). 2 However, taking into account that the shock wave could be doubly amplified upon reflection from the Earth’s surface (Glasstone and Dolan, 1977), the lower energy limit should be reduced to 100 kilotons Fig. 9. Trace of bolide as imaged in video no. 4, where TNT. Thus, the total shock wave energy falls within regions 1 and 2 correspond to the main and last flashes, 100–500 kilotons TNT. Approximately 15–18% of the respectively. liberated meteorite energy is radiated (Popova and

SOLAR SYSTEM RESEARCH Vol. 47 No. 4 2013 ASTRONOMICAL AND PHYSICAL ASPECTS OF THE CHELYABINSK EVENT 249

Δp, kPа Additional factors capable of influencing the energy estimation are a nonspherical shape of the h = 23 km shock wave and the refraction of a shock wave in the 1.2 atmosphere. The effect of nonsphericity for a shock h = 27 km 600 wave propagating almost perpendicularly to the trajec 1.0 tory is relatively small. The role of refraction can be significant at large distances from the epicenter. This 0.8 can be illustrated by calculations of the propagation of a weak shock wave in terms of the geometric acoustics (Fig. 11). An acoustic beam propagating from 23 km 0.6 altitude at 55° relative to the vertical, reaches the sur 100 face at a distance of d = 32.8 km from the epicenter for 0.4 t = 133.7 s at a constant velocity of sound of 300 m/s. Taking into account the temperature dependence of 35 36 37 38 39 40 the velocity of sound and the refraction of a shock d, km wave in the atmosphere, we obtain somewhat greater values of d = 35.7 km for t = 140.7 s. With allowance Fig. 10. Plot of the overpressure Δp versus distance r from for the wind with a “standard” altitude velocity profile and the epicenter to dashboard camera at the center of Che an amplitude of 40 m/s at 12 km, we have d = 41.1 km at lyabinsk. Squares correspond to models, for which the t = 147 s for downwind propagation and d = 32.4 km at t = time of sound wave propagation is 141 s at an altitude of 23 and 27 km and the explosion energy varies from 100 to 139.6 s for upwind propagation. These estimates imply 600 kilotons TNT (left to right) at a step of 100 kilotons that the features of a weak shock wave propagation in TNT. Dashed lines show the accepted range of excess pres the real atmosphere can modify the arrival time of the sures capable of blowing out about 5% of windows. disturbance 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 Nemchinov, 2005) and less than 5% is expended on ation (~38 km/s) is rather small and can be ignored for evaporation. It is not quite clear what is the mass and rough estimations. On the whole, all the aforemen kinetic energy of deposited coarse fragments. If this tioned factors can somewhat change the estimation of fraction is also negligibly small, then the relatively the energy, but hardly by more than factor of 1.5. small energy consumption for radiation and evapora Using the known dependencies of overpressure on tion gives us grounds to estimate the initial kinetic the distance (Tsikulin, 1969) for spherical and cylin energy of the at 100–500 kilo drical shock wave sources in the exponential isother tons TNT. mal atmosphere (Fig. 12) and adopting the same range

z, km

cc 20 c + u c – u

10

° ° 55° 65 65 55°

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

Fig. 11. Trajectories of acoustic rays emitted from 23 km altitude at 55° and 65° angle relative to vertical with allowance for (solid curves) 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.

SOLAR SYSTEM RESEARCH Vol. 47 No. 4 2013 250 EMEL’YANENKO et al.

2000 0 km 20 km 30 km 1500 40 km 50 km , Pa

1000 Overpressure

500 1 10 100 1000 Equivalent energy, kilotons TNT

Fig. 12. Plots of the overpressure on the Earth’s surface at various distances from the source projection versus equivalent energy of a 20kmlong cylindrical source at a 22 km altitude. of windowblowing pressures (700–1000 Pa), we may insk meteoroid energy to be estimated at 300– conclude that (for maximum distances of 40–50 km 1400 kilotons TNT. from the epicenter to regions of significant damage) A series of model calculations has been performed the meteoroid energy must be within 100–340 kilo for explosions of various energies at different altitudes. tons TNT at an altitude of 22 km. The presence of a The computations used a SOVA code (Shuvalov, nearground temperature inversion (i.e., temperature 1999) on a 1000 × 500 cell difference grid. The simu increase with altitude) in Chelyabinsk on February 15, lations took into account variations of the air density 2013, could decrease the shock wave amplitude on the and temperature with altitude in the framework of a average by 15% (accordingly, allowance for this effect standard atmosphere model CIRA; the wind velocity would increase the estimated energy). was set to be zero, since a real wind distribution at the moment of “explosion” was unknown; and the tabu The energy of meteoroids is usually estimated with lated equation of state for air was employed (Kuz allowance for the period (or frequency) of the maxi netsov, 1965). The calculations yielded maximum mum amplitude (or pressure amplitude) of measured pressure at various points on the Earth’s surface with infrasound oscillations with the aid of approximations allowance for the shock wave reflection from ground. normalized for various kinds of explosions. The spread The results (Fig. 13) show that a 300kiloton TNT of these estimations is rather large. A comparison of explosion at a 25km altitude produces destruction various estimations of the pressure amplitude at a dis close to that observed upon the fall of the Chelyabinsk tance of 1000 km for an equivalent energy of 1 kiloton asteroid. TNT (Ens et al., 2012) showed that these values can As noted above, seismic vibrations caused by the differ by almost two orders of magnitude. The known Chelyabinsk bolide’s entry into the atmosphere have energies of 70 satellite bolides (ranging within 0.02– been detected by a large number of seismic stations. 20 kilotons TNT), for which an infrasound signal was Estimation of the bolide energy from these data is a simultaneously recorded, allowed the most reliable task for future investigations. approximation to be selected in the indicated energy According to data from the satellite monitoring range (Ens et al., 2012). The application of this network, the energy radiated by the Chelyabinsk approach to infrasound data of the Chelyabinsk event bolide amounted to 3.75 × 1014 J, which is approxi yields an estimated energy of 1000 kilotons TNT, mately equivalent to 90 kilotons TNT (http://neo. although this value is far beyond the range of events jpl.nasa.gov/fireballs/). Nemtchinov et al., 1997, considered by Ens et al. (2012). Characteristic fre obtained the following expression for the integral radi quencies in the spectra of infrasound signals measured ation efficiency defined as the ratio of the total radia at IDG and CTBTO (Aktyubinsk) infrasonic stations tion energy to the initial kinetic energy: η are within 0.012–0.025 Hz, which allow the Chelyab = Er/Ek,

SOLAR SYSTEM RESEARCH Vol. 47 No. 4 2013 ASTRONOMICAL AND PHYSICAL ASPECTS OF THE CHELYABINSK EVENT 251

P/P0 1.04

1.03 E300H25

E50H20 1.02 E300H40

E50H25

1.01

E10H15 E3H5 1.00 0 20 40 60 80 100 R, km

Fig. 13. Plots of the pressure P/P0 (normalized to normal) on the Earth’s surface versus distance R from the projection of energy release 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.

where Er is the radiated energy (measured by a detec needed for window breakage in Chelyabinsk amounts tor) and Ek is the kinetic energy of the meteoroid. For to 100–500 kilotons TNT, while the infrasound data a radiated energy of ~90 kilotons TNT and an integral yield 300–1400 kilotons TNT. Thus, the two methods efficiency of 14–16.5%, the kinetic energy amounts to are consistent within 300–500 kilotons TNT. The 540–640 kilotons TNT. Brown et al., 2002, estimated method based on the radiated energy, supported by the the integral radiation efficiency using several events hydrodynamic estimates, leads to a conclusion that detected by the satellite monitoring network, for 300–500 kilotons TNT is most probable estimate fir which independent estimations of the initial energy the meteoroid energy. (mostly from infrasound data) were available. For the Chelyabinsk bolide, the efficiency amounts to 20%, which corresponds to an initial kinetic energy of 7. ESTIMATED TRAJECTORY OF MOTION, 450 kilotons TNT. It should be noted that the energy PARAMETERS, AND TYPE of events used to obtain the approximated relation was OF CELESTIAL BODY significantly lower than the energy of the Chelyabinsk From the astronomic standpoint, the most inter meteoroid (0.1–25 kilotons TNT). The accuracy of esting question is what was the orbit of the body on estimations of the total radiation efficiency (and, approaching the Earth and its genesis in terms of hence, of the energy) is no better than 1.5–2 times; known groups of space objects representing small bod nevertheless, these data allow the kinetic energy of the ies of the Solar System. Chelyabinsk meteoroid to be estimated from radiated energy as 450–640 kilotons TNT. The trajectory of motion has been established based on the processing of numerous video records. In concluding this section, it can be ascertained Figure 14 shows a projection of the trajectory onto the that the energy estimated from the overpressure Earth’s surface. A comparison of the moment of max

SOLAR SYSTEM RESEARCH Vol. 47 No. 4 2013 252 EMEL’YANENKO et al. 2013) described the method of obtaining data, while the second (Borovicka et al., 2013) did not. In the next work, Zuluaga et al. (2013) presented a new variant of the orbit, which was based on four video records. Table 2 summarizes the results of the preliminary determina tion of the orbit of the Chelyabinsk meteorite. As can be seen from Table 2, the results of various determinations significantly differ with respect to some parameters, e.g., the spread of probable values of the semimajor axis and ascending nodeperihelion angle. Even two works of the same group gave substan tially different results. Nevertheless, the data of Table 2 allow us to unambiguously conclude that the Chelya binsk meteorite belongs to the Apollo asteroid family. To more exactly determine the orbit, specialists of the IGD and Institute of Astronomy observed the night sky for linking the video records to the trajectory of the Chelyabinsk meteorite. When these records are processed, the orbit parameters will be determined more reliably. Preliminary determination of the orbit of the Chelyabinsk meteorite prior to its approaching Fig. 14. Projection of the trajectory of the body onto the Earth’s surface (straight segment) from Etkul to Pervo the Earth, which has been performed at the Depart maiskii. ment of Space Astrometry of the Institute of Astron omy, gave the following orbit parameters: semimajor axis, a = 1.77 AU; perihelion distance, q = 0.75 AU; imum glow intensity and the onset of damage allowed orbit inclination, i = 4.3°. the altitude h to be determined at which the most In addition, specialists of the Institute of Astron intense destruction of the body took place. The results omy (Terentjeva and Bakanas, 2013) analyzed the of processing of four video files with minimum delay available catalogues of meteorite orbits. According to times of the shock wave (Pervomaiskii, Emanzhelinsk, the database of the IAU Meteor Data Center in Lund and Korkino) in terms of the approximation a spheri (Sweden), a meteor swarm has been found that can be cal shock wave propagating at a velocity of 300 m/s related to the Chelyabinsk bolide and called diurnal give h = 22.9 ± 0.2 km. The epicenter of explosion was Pegasus Aquarids, which consists of three branches: near Pervomaiskii. Allowing for more distant video northern, ecliptical, and southern. This study was records (Chelyabinsk), h = 23.9 ± 1.4 km. Estimations in based on the elements of the orbit reported by Borov the cylindrical wave approximation yield h = 23.0 km icka et al. (2013). ± above Pervomaiskii and h = 24.9 0.4 km for the energy Specialists of the Vernadsky Institute of Geochem release from a body occurring about 8 km to the east. istry and Analytical Chemistry carried out a prelimi Evidently, these are preliminary estimates. More accu nary investigation of the geochemical characteristics rate data will be obtained upon determining the orbit of the meteorite and obtained the first data on the type of this celestial body. of this body. A petrographicmineralogical analysis The first estimated orbit of the Chelyabinsk mete (Nazarov and Badyukov, 2013) showed that most of oroid was reported on February 21, 2013 (Zuluaga and the fragments collected have a chondrite structure, Ferrin, 2013). This orbit was determined using a single containing up to 60% of irregular with an video record made in Chelyabinsk. Then, a telegram average size of about 1 mm in a matrix of broken chon no. 3423 of the International Astronomic Union was drules and mineral grains; the main mineral phases are reported on February 23, 2013, in which Czech olivine and orthopyroxene. Quantitative analysis of astronomers (Borovicka et al., 2013) presented their the chemical composition showed that the samples variant. Note that the first report (Zuluaga and Ferrin, represent a typical chondrite of the LL group with a

Table 2. Preliminary parameters of the orbit of the Chelyabinsk meteorite Semimajor axis, Inclination, Argument of perihe Longitude Eccentricity Reference AU deg lion, deg of ascending node, deg 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., 2013 1.26 ± 0.05 0.52 2.984 95.5 ± 2 326.5 ± 0.3 Zuluaga et al., 2013

SOLAR SYSTEM RESEARCH Vol. 47 No. 4 2013 ASTRONOMICAL AND PHYSICAL ASPECTS OF THE CHELYABINSK EVENT 253 relatively small content of iron and the presence of and video records of the event over Chelyabinsk on and in the metal phase. The February 15, 2013. Special thanks to Eduard Kalinin, increased content of cobalt in kamacite and the entire Evgenii Tvorogov, Marat Akhmetvaleev, Denis chemistry of mineral phases confirm the assignment of Siv’yuk, Nikolai Ivanov, Dmitrii Volkov, Aleksandr chondrite to the LL group. Some additional charac Ivanov, Aleksandr Yashen’kin, Ermek Aisin, Andrei teristics allow the chondrite to be classified into Mostovoi, S. Kaigorodtsev, and Nikita Vasil’ev. 5th petrological type. The structure of fragments, This work was supported in part by Federal Tar most of which is an impactfused , revealed geted Program “Scientific and Educational Human thin dark streaks filled with a finegrained impact Resources of InnovationDriven Russia” for 2009– fused material. The presence of glide planes at the 2013 and the Presidium of the Russian Academy of contacts of cracks and the matrix suggested a friction Sciences (program no. 22 “Fundamental Processes of origin of this phase. Apparently, fractionation of the Research and Exploration of Solar System”). meteorite body took place at the boundaries of dark impactfused inclusions and bright finegrained matrix, since fragments consisting entirely of the dark REFERENCES and bright material are rare. Adushkin, V.V., Popova, O.P., Rybnov, Yu.S., et al., Geo physical effects of Vitim bolide 24.09.2002, Dokl. Akad. Nauk, 2004, vol. 397, no. 5, pp. 1–4. 8. CONCLUSION Borovicka, J., Spurny, P., and Shrbeny, L., Trajectory and There has been a single case in the history when a orbit of the Chelyabinsk superbolide, in Electronic meteoroid was observed for a relatively long time Telegram, Cambridge, MA: Central Bureau Electronic (about 20 h) before its entry into the Earth’s atmo Telegrams, Int. Astron. Union, 2013, no. 3423. sphere (Jenniskens et al., 2009). That meteoroid had Brown, M.D. and Loewe, A.S., Reference Manual to Miti dimensions within 3–5 m. Another meteoroid (aster gate Potential Terrorist Attacks against Buildings, oid name 2008 TC3) has been noticed accidentally, FEMA, 2003, pp. 4–19. albeit in the framework of a systematic survey. At large Ens, T.A., Brown, P.G., Edwards, W.N., and Silber, E.A., distances, bodies with dimensions below 20 m cannot Infrasound production by bolides: a global statistical be detected because of limitations with respect to the study, J. Atmosph. Sol.Terr. Phys., 2012, vol. 80, resolving power of modern survey telescopes. At short pp. 208–229. distances, the main difficulty is the short time for Glasstone, S. and Dolan, P.J., The Effects of Nuclear Weap detecting an object. ons, US Dep. of Defense, US Dep. of Energy, 1977. 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