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Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Observational Data
  5. Fireball Trajectory
  6. Velocity
  7. Light Curve
  8. Seismic Data Analysis
  9. Model of the Fireball and the Meteorite Fall
  10. Description of Meteorite Finds and Their Locations
  11. Radiant and Heliocentric Orbit
  12. Discussion
  13. Acknowledgments
  14. Acknowledgments
  15. References

Abstract– We report an analysis of instrumental observations of a very bright fireball which terminated with a meteorite fall near the town of Jesenice in Slovenia on April 9, 2009, at 0h59m46s UT. The fireball designated EN090409 was recorded photographically and photoelectrically by two southern stations of the Czech part of the European Fireball Network (EN). Simultaneously, a part of the luminous trajectory was also captured by two all-sky CCD systems and one video camera of the Slovenian meteor network. In addition to these optical recordings, the sonic booms produced by the Jesenice fireball were detected at 16 seismic stations located within 150 km of the trajectory. From all these records, we reconstructed the fireball’s atmospheric trajectory, basic geophysical data, the possible impact area, and the original heliocentric orbit of the meteoroid. Using a detailed fireball light curve, we modeled the atmospheric fragmentation of the meteoroid. Both the atmospheric behavior and the heliocentric orbit proved to be quite normal in comparison with other observed meteorite falls. The Jesenice orbit is markedly different from the Příbram and Neuschwanstein orbital meteorite pair, which fell on similar dates (April 7, 1959, and April 6, 2002, respectively). Three meteorites with a total weight of 3.6 kg (until April 2010) were found in a high mountain area near the town of Jesenice. They are classified as L6 ordinary chondrites (Bischoff et al. 2010).


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Observational Data
  5. Fireball Trajectory
  6. Velocity
  7. Light Curve
  8. Seismic Data Analysis
  9. Model of the Fireball and the Meteorite Fall
  10. Description of Meteorite Finds and Their Locations
  11. Radiant and Heliocentric Orbit
  12. Discussion
  13. Acknowledgments
  14. Acknowledgments
  15. References

Precise fireball data, especially associated with recovered meteorites, are very important and provide information about the population and physical characteristics of small interplanetary bodies in near-Earth space and also about their parent bodies—asteroids and comets. Backward numerical integration of the known orbit provides valuable information about the type of evolutionary path of the meteoroid in the solar system, and can even yield the link to a particular parent body. Similarly important is the study of the processes accompanying the atmospheric flight of the meteoroid. The known properties of the meteorite (density, mass, shape, etc.) enable calibration of the fireball data so that other fireballs without recovered meteorites can provide relevant information on the physical properties of their respective meteoroids.

Only in a dozen cases was the fireball preceding a meteorite fall instrumentally recorded from at least two sites so that its atmospheric trajectory and orbit could be determined. Moreover, only about half of them were recorded by dedicated programs, and the meteorites were recovered in the predicted impact locations on the basis of the evaluation of available instrumental records. The situation for the other cases was reversed; meteorites were found prior to evaluation of the casual records. The precision and reliability of trajectories, velocities, and orbits for these cases vary widely, from relatively good, to rather less trustworthy, according to the kind, quality, and number of available records.

Here we report a new instrumentally documented meteorite fall recorded by two automated fireball observatories (AFO) in the Czech part of the European Fireball Network (EN) and also by two all-sky CCD systems and one video camera of the Slovenian meteor network. This is a case which is in the intermediate category of the previously discussed fireball–meteorite classification because the fireball was recorded by regular observing programs, but meteorites were found independently before the evaluation of these records.

Observational Data

  1. Top of page
  2. Abstract
  3. Introduction
  4. Observational Data
  5. Fireball Trajectory
  6. Velocity
  7. Light Curve
  8. Seismic Data Analysis
  9. Model of the Fireball and the Meteorite Fall
  10. Description of Meteorite Finds and Their Locations
  11. Radiant and Heliocentric Orbit
  12. Discussion
  13. Acknowledgments
  14. Acknowledgments
  15. References

Casual Eyewitness Observations and Descriptions of the Event

Although the sky was rather clear over Carinthia and north Slovenia at the time of the fireball (about 3 a.m. local time), only a few eyewitnesses (<10 people in Austria) reported the observations of the fireball. This may well be attributed to the early morning hour at which it appeared. On the other hand, this meteoroid caused very intense sound phenomena and acoustic effects. Many people reported that they were roused from sleep and alarmed by the loud detonations and by a roaring thunder-like sound. Most of the witnesses misinterpreted these phenomena as a light earthquake.

Witnesses who acoustically detected the event and were located directly north of the Karavanke Mountains reported a noise like a collision of two freight trains. People that were quite close to the event felt the shock wave and heard the rattling of open windows. Especially in the region northwest of the Slovenian town of Jesenice (up to a distance of 80 km), an intense thunderclap was heard, which was loud enough to wake many up.

As mentioned above, this fireball event was seen by several eyewitnesses as well. By chance, these people were not sleeping at 3 a.m. local time, and they were rewarded with viewing a spectacular bolide on this clear night (with the full Moon high up in the southwestern sky). A resident of Friesach (near the Steiermark/Carinthia border, about 65 km from point of the maximum light) was standing in front of his house and was able to describe the apparent path of the fireball in the sky until its disappearance behind a nearby ridge. This witness also noticed some kind of electrophonic noise (simultaneously with the visual observation), but he did not hear any thunder afterwards. For this important eyewitness, the fireball head appeared comparable to the size of the full Moon, with a broad tail that was about 10 times longer than its head diameter. Another interesting observation of the bolide’s light and sound came from a man living in the Carinthian town of Obervellach (northwest of Spittal/Drau, about 80 km from point of the maximum light). Through an open window he saw a whitish, bright fireball for a few seconds, until it vanished behind the Karavanke mountain range. He waited anxiously for an impact of the penetrating body, and finally after 3 or 4 min, he heard a loud thunderclap and a dull rumbling sound.

An impressive eyewitness account comes from Velenje in NE Slovenia, some 80 km due east of the fireball’s brightest part. The eyewitness’s attention was caught by the bright light of the fireball entering her bedroom through a window. She had enough time to walk up to the window and observe the fireball. It was described as a brilliant blue-green, comparable to the brightness of the full Moon, trailing a long orange tail. At the end of its flight, it fragmented into a multitude of fragments that she described as “golden” in color. Three or four large fragments were noted, but the entire number of visible fragments was at least 10. No sound was reported.

One of the most stunning and important witness reports came from the northern city limits of the Slovenian town of Jesenice. On April 8, 2009, a forest fire had occurred, and during the following night several men of the local fire brigade kept a fire watch. Four of the fire fighters were on alert at 3 a.m. CEST, and they were able to observe the final stage of this extraordinary fireball and meteorite fall from a very short distance. Actually, these men were only 2.5 km away from the landing site of the meteorites! All of a sudden, the entire sky turned bright white for about 3 s. Immediately following the flash, two bright separate fireballs with tails were visible moving in the direction of the village of Bled, and they faded out above the mountains at the southern horizon. Shortly (about 5 s) after the visual appearance, the four men registered three thunderclaps, the first one was rather weak, the following two were deafening. Apparently, the fire fighters witnessed the glowing of the meteoroid at a quite low altitude.

Soon after receiving media reports about a bright fireball over southern Austria (Carinthia) and the Karavanke Mountains (Slovenia), Thomas Grau made a field trip to this area and interviewed many casual witnesses of this extraordinary event. He localized the possible area where meteorites might be found and spread this information among local people. It significantly helped in finding the first meteorite.

Instrumental Optical Data

For the scientific description of this extraordinary fireball, it is important that the fireball was recorded also by several dedicated optical instruments. It was registered photographically and photoelectrically by two southern stations of the Czech part of the EN. Simultaneously, the beginning part of the luminous trajectory was also captured by two all-sky CCD systems and one video camera of the Slovenian meteor network. The records from the Czech cameras were most crucial for determination of the fireball atmospheric trajectory, basic geophysical data, the possible impact area, and the original heliocentric orbit.

Photographic and Photoelectric Records From the Czech Cameras of the EN

The most important records were taken by two AFO of the Czech part of the EN (Spurný et al. 2006), which directly recorded the luminous trajectory of the fireball. Despite less-than-ideal weather conditions over the Czech Republic (see Fig. 1), the two Czech southern stations Churáňov (EN04) and Kunžak (EN02) had partly clear sky and were in full operation during the fireball passage. Other stations of the EN in the Czech Republic, Germany, Austria, and Slovakia were either too far from the fireball trajectory or had bad weather. The images taken at the Churáňov and Kunžak stations are presented in Figs. 2 and 3. Only parts of the all-sky images with the fireball and its enlargement are shown for each station. As can be seen from Figs. 2 and 3, the fireball was just above the instrument sensitivity limit, although in reality it was very bright (as described later it reached −15 absolute magnitude). This significant attenuation was caused partly by high extinction and partly by the fact that the exposure was taken during an almost full Moon night. The extinction was not caused only by the fireball’s very low altitude above the horizon at both stations (the end of the recorded fireball path is <5° above the ideal horizon at both stations), but it was also amplified by the high altitude clouds in the direction of the fireball. Despite the faintness of the fireball record at both stations, we were not only able to measure points on the recorded path, which was important for determination of the atmospheric trajectory, but also to distinguish several shutter breaks on both images. This was crucial for determination of the initial velocity and the heliocentric orbit. All this was possible thanks to the superb quality of the fish-eye lenses (Zeiss-Distagon 3.5/30 mm) in combination with the large format panchromatic films Ilford FP4 (9×12 cm, 8 cm diameter of the sky), which are used in all AFOs.

image

Figure 1.  The meteorological situation over Central Europe at the time of the Jesenice fireball as imaged by the Meteosat satellite. The ground projection of the fireball is marked by the arrow, full squares show positions of individual stations where the fireball was recorded (04 denotes Churáňov, 02 Kunžak, CV Črni Vrh, and RZ Rezman).

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image

Figure 2.  Part of the all-sky image (large) and detail (upper right corner) of the Jesenice fireball from the Czech station 04 Churáňov. The fireball is very close to the southern horizon and 278–285 km from the station. Because of the large distance and the presence of cirrus clouds, the fireball looks quite dim. The terminal part is hidden behind a tree.

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image

Figure 3.  Part of the all-sky image (large) and detail (upper right corner) of the Jesenice fireball from the Czech station 02 Kunžak. The fireball is very close to the southern horizon and 302–304 km from the station. Because of the large distance and the presence of cirrus clouds, the fireball looks quite dim. The bright trail over the SW horizon is the Moon.

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All AFOs are also equipped with photoelectric sensors, which continuously record the total brightness of the sky in relative units with a temporal resolution of 0.002 s. The sensors work even under a cloudy sky. Sensors at six Czech stations recorded the Jesenice fireball. These records were used for precise timing of the fireball and for constructing the light curve.

Photographic and Video Records From Slovenia

The fireball was recorded by two digital all-sky cameras and two TV meteor cameras located at Črni Vrh Observatory and Rezman Observatory.

The Črni Vrh image (Fig. 4) was acquired by the optical system based on a convex mirror with an SBIG ST-7XMEI CCD equipped with a wide-field 16 mm f/2.8 lens. Its primary function is weather monitoring in support of the NEO search program at the observatory, typically taking 60 s exposures. It is also one of three currently operating all-sky cameras of the Slovenian meteor network. The all-sky image is cropped in the northern and southern parts of the sky. Unfortunately, this significantly affected the record of the fireball, with about the last third of its path outside of the field of view. Another complication is that at the time of the fireball passage the sky at Črni Vrh Observatory was covered by thin high clouds. Only a few stars are visible in the image.

image

Figure 4.  The picture taken by the digital all-sky mirror camera at the Slovenian station Črni Vrh. In this 61 s exposure, the fireball is seen near top center (the terminal part is unfortunately out of the field of view), and an almost full Moon at the right bottom (it causes the vertical strip of saturated pixels). Unfortunately, the sky was very cloudy (high clouds) and only a few bright stars could be used for reduction. This camera is not equipped with a rotating shutter for velocity measurements.

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Three instrumental records were made at Rezman Observatory. Here, the sky was also partly cloudy at the time of the fireball. The all-sky camera is a Watec Wat-120 camera equipped with a Fujinon 1.4–3.1 mm f/1.4 zoom lens. The camera integrates two hundred and fifty-six 0.04 s long frames into one JPEG image of 10.24 s total exposure. The fireball was captured on two successive images. The first image shows the beginning of the fireball up to the brightness of about −8 magnitudes. However, the second image, where a larger part of the fireball trajectory should be recorded, is completely saturated in the direction of the fireball and no part of the fireball is seen.

The beginning part of the fireball was also recorded by the wide-field video camera STEFKA. This is a Mintron 12V6-EX camera with Computar 3.8 mm f/0.8 lens. STEFKA is pointed NW and has a field of view 89° × 69°. The fireball was unfortunately captured only on the first 12 frames (0.52 s) and after that time the automated software stopped recording. Moreover, this beginning part of the trajectory was near the radiant so it is only about 2° long and as the fireball significantly increased brightness, it was very difficult to use this record for precise positional purposes and velocity determination as well.

The third Rezman record was taken by a similar system used for meteor spectroscopy. This system consists of a Mintron 12V1 camera equipped with a Computar 8 mm f/0.8 lens and a diffraction grating (1000 grooves mm−1). It was used in combination with the UFOCapture software to obtain an uncompressed AVI movie of the event. The camera covers a field of 45° × 34° and was pointed to the ESE (azimuth about 105°) at about 45° elevation. The grating was oriented vertically so that spectra were horizontal. Neither the fireball nor the Moon spectrum protruded into the field of view of the camera. However, indirect observation of the fireball through its illumination of the sky could be used, as discussed later, for construction of the light curve.

The Slovenian cameras have higher sensitivity, but lower resolution, than the Czech cameras. The higher sensitivity was useful for capturing the beginning of the fireball. However, the middle part of the fireball was severely saturated and, unfortunately, none of the cameras recorded the end of the fireball. The positional reduction was further complicated by the low number of stars visible in the images. We used images from other nights to overcome this problem, but this procedure was only partially successful. The spectral video, where only illumination of the sky was recorded, proved to be useful for independent determination of the fireball light curve.

Seismic Data

The detection of sonic waves generated by large fireballs by seismic stations is relatively common (e.g., Brown et al. 2003; ReVelle et al. 2004). The acoustic energy is generated in the form of a near-cylindrical blast wave propagating perpendicularly to the trajectory and, in case of severe meteoroid fragmentation, also at a number of point sources corresponding to individual fragmentation events (Borovička and Kalenda 2003). The Jesenice fireball was detected at 16 seismic stations located within 150 km of the trajectory. Complicating interpretation was the fact that the fireball appeared during one of the aftershocks of the L’Aquila earthquake (L’Aquila, Italy, 00:53:00 UT, 42.51°N, 13.33°E, M = 5.3). The absolute amplitude of the unfiltered signal was about 100 times larger than the amplitude of the fireball sonic waves, obtained after filtering.

Fireball Trajectory

  1. Top of page
  2. Abstract
  3. Introduction
  4. Observational Data
  5. Fireball Trajectory
  6. Velocity
  7. Light Curve
  8. Seismic Data Analysis
  9. Model of the Fireball and the Meteorite Fall
  10. Description of Meteorite Finds and Their Locations
  11. Radiant and Heliocentric Orbit
  12. Discussion
  13. Acknowledgments
  14. Acknowledgments
  15. References

From the description of all available optical records, it is evident that it was a very difficult task to determine the atmospheric trajectory of the Jesenice fireball. In addition to the analysis of all available instrumental records, the knowledge of the position of the first recovered meteorite was very helpful in finding the final unambiguous trajectory solution.

The final trajectory solution is based mainly on the reduction of all-sky images from the Czech stations Kunžak and Churáňov, tuned to fit the meteorite positions. Data from Črni Vrh and Rezman Observatories are in general agreement with the solution, but show some small systematic trends. This situation is shown in Fig. 5 where lateral deviations of lines of sight for each measured point on each station are plotted as a function of the length along the trajectory. The scatter of measured points is relatively small and defines well the average trajectory. The standard deviation of the mathematical fit is 58 m. However, we estimate the real uncertainty of the trajectory to be about 200 m. Still, this is a very good result when one takes into account the quality of the original records and the large distance of both Czech stations. Even for the low resolution video data, the deviations are no larger than several hundred meters. Additionally, the seismic data are in good agreement with the trajectory (see below). Despite the relatively unfavorable conditions, all trajectory data are consistent and provide a good picture of this extraordinary event. The positions of the stations with respect to the fireball trajectory are schematically plotted in Fig. 1, where the meteorological situation is also shown. The basic atmospheric trajectory data for each station are collected in Table 1.

image

Figure 5.  Lateral deviations of lines of sight in relation to the average trajectory represented by a zero line (Y-axis is highly enlarged). The average trajectory is computed only from Czech all-sky cameras (St. 02 Kunžak and 04 Churáňov). The intersection angle between the planes from these two stations is 20.7°. Note that only well-defined points measured along the fireball image at each station are used for the average trajectory computation and are shown in this figure. These points may not include the very beginnings and very ends of the fireball records (given in Table 1).

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Table 1.   The basic atmospheric trajectory data from optical records taken at four different stations. Data from Rezman (RZ1—video, RZ2—all-sky) cameras are taken from projection of the measured values and best reduction fit on the average trajectory resulting from analysis of records from both Czech stations (#02 and #04). RB,E, HB,E, ϕB,E, λB,E,, and ElB,E are range, height, latitude, longitude, and elevation of beginning and end points for the given station, respectively, L is the length of the recorded luminous trajectory.
St.RB (km)RE (km)HB (km)HE (km)L (km)ϕB (°)λB (°)ϕE (°)λE (°)ElB (°)ElE (°)
02304.8307.161.631.535.146.615213.762346.502713.930810.24.4
04280.6288.263.432.635.946.621913.752346.506913.924511.65.0
CV112.671.874.233.447.646.66213.69246.51013.92040.426.8
RZ1111.0100.673.564.011.046.65913.69646.62413.74941.539.5
RZ21278788514246.7113.6246.5813.8243.836.2

The fireball’s luminous trajectory began (as first detected by Rezman all-sky camera) at an altitude of almost 88 km, close to the village of Paternion in Carinthia, Austria (see Fig. 6). The photographic cameras registered the fireball somewhat later (see Table 1). Most of the luminous atmospheric flight of the Jesenice fireball was over the Carinthia region in Austria. The fireball flew almost directly above the large town of Villach. The atmospheric trajectory was relatively steep with the angle to the Earth’s surface of 58.8°. Unfortunately, no record contains the real end of the fireball. The deepest parts of the luminous trajectory were too attenuated by high extinction for both Czech cameras to record, so the real end was far below their sensitivity limit. Moreover, at the Churáňov station, the fireball terminated behind trees. The Slovenian cameras missed the end point for various instrumental reasons, as described earlier. The deepest optically recorded point on the luminous trajectory is at a height of 31.4 km from the Kunžak station. From the analysis of the photometric and seismic data given below, we know that the maximum brightness of −15 magnitudes was reached in a very sharp flare at an altitude of 26 km over Slovenia near the village of Dovje. The modeled end of ablation was at a height of 18 km near the village of Hrušica and the most probable meteorite impact area is about 4 km long and lies south of town Jesenice on the Mežakla plateau in the northeastern part of the Julian Alps.

image

Figure 6.  Ground projection of the atmospheric trajectory of the Jesenice fireball. The solid line is the part of the trajectory recorded by optical instruments (BRZ is beginning from Rezman video record, B04 and E02 is the beginning and the end of the trajectory from Churáňov and Kunžak stations, ECV is the end from Črni Vrh image, the dashed line is the prolongation of the atmospheric flight with points of maximum light (h = 26 km) and the real end of the luminous trajectory (Eabl, h = 18 km). M1, M2, and M3 are the positions of the recovered meteorites.

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Velocity

  1. Top of page
  2. Abstract
  3. Introduction
  4. Observational Data
  5. Fireball Trajectory
  6. Velocity
  7. Light Curve
  8. Seismic Data Analysis
  9. Model of the Fireball and the Meteorite Fall
  10. Description of Meteorite Finds and Their Locations
  11. Radiant and Heliocentric Orbit
  12. Discussion
  13. Acknowledgments
  14. Acknowledgments
  15. References

The information about the fireball’s velocity is quite limited. The video from Rezman Observatory could not be used for a reliable velocity determination for several reasons. As noted above, the positional reduction was very difficult. Moreover, the fireball was captured near the radiant point and therefore exhibited a very low angular velocity. The combination of the low angular velocity with the low resolution of this wide-field video, along with the fact that the fireball brightness was increasing enormously during the recorded part of the trajectory (making the fireball image progressively larger), resulted in big uncertainties in the measurement. We were able to restrict the velocity only to 15 ± 3 km s−1.

The camera at Črni Vrh has no shutter for velocity measurements. The images for the regular EN cameras in Kunžak and Churáňov contain almost no recognizable shutter breaks because of the large distance to the fireball and poor observing conditions. Nevertheless as discussed above, we were able to measure a few shutter breaks in the middle of the trajectory at both stations. Both stations proved to be in good agreement. When the length was plotted along the trajectory as a function of time (Fig. 7), a velocity of 13.73 ± 0.25 km s−1 was obtained, valid for the middle height of the measured points, which was 54 km. This single velocity value was used in the modeling of the fireball (see the Model of the Fireball and the Meteorite Fall section).

image

Figure 7.  The length along the trajectory as a function of relative time for EN02 and EN04 stations. Both stations used a shutter producing 15 breaks per second. The time is counted from the first shutter break at EN04. For EN02, time was shifted so that the lengths corresponded. The velocity computed only from EN02 would be 13.5 km s−1; EN04 (which covers only small interval) would give 14.5 km s−1.

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Light Curve

  1. Top of page
  2. Abstract
  3. Introduction
  4. Observational Data
  5. Fireball Trajectory
  6. Velocity
  7. Light Curve
  8. Seismic Data Analysis
  9. Model of the Fireball and the Meteorite Fall
  10. Description of Meteorite Finds and Their Locations
  11. Radiant and Heliocentric Orbit
  12. Discussion
  13. Acknowledgments
  14. Acknowledgments
  15. References

Three instruments recorded the light curve useful for photometry of the fireball: the all-sky photoelectric radiometers at EN stations 02 and 04 and the spectral video camera at Rezman Observatory. In fact, four other EN stations recorded the light curve as well, but the signal was low because of the even larger distance to the fireball compared with stations 02 and 04. These records were useful for independent confirmation of the light curve profile and absolute timing of the event. The raw data from EN02 and EN04 are compared in Fig. 8. The radiometers produce high-resolution light curves with 500 measurements per second. Despite the relatively low signal, both curves are virtually identical, which demonstrates the quality of the instrument and fidelity of the recorded data. The fireball was first detected at about 0:59:42.8 UT. After an initial increase in brightness, the fireball exhibited quasi-periodic fluctuations with the frequency increasing with time until a big flare at 0:59:45.75 UT. Within the next 0.5 s, five smaller flares followed. The final flare was detected at 0:59:46.75 UT, but with very low signal because the fireball was very low in the sky at both stations (2° above the horizon). Nevertheless, it is present in both records and is certainly real.

image

Figure 8.  Radiometric light curves from stations EN02 and EN04. The EN02 curve was shifted vertically for clarity. Intensity is given in linear scale in the internal units of the instruments.

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The absolute calibration of radiometric curves poses some problems. The sensitivity depends on current conditions (sky brightness and cloudiness) and is a sharp function of zenith distance of the object, especially for objects close to the horizon. The response of the radiometer as a function of zenith distance was measured in the laboratory. For absolute calibration, we used another fireball, EN300807 Martin. That fireball was observed by the same camera at EN02 Kunžak as Jesenice under similar conditions—during full Moon and close to the horizon (although not as close as Jesenice). The absolute brightness of the Martin fireball was determined by photographic photometry at a station much closer to the fireball. We believe that our calibration of the Kunžak radiometer is precise within 0.3 magnitudes.

As described in the Photographic and Video Records From Slovenia section, the spectral video camera at Rezman Observatory recorded the fireball indirectly. Although neither the fireball nor its spectrum appeared in the field of view, the software saved the video from 0:59:42.2 to 0:59:47.1 UT showing fluctuations of the sky brightness caused by the fireball (we later shifted the time by 0.1 s to conform to the radiometric records). The sky was partly covered by cirrus clouds. We computed the fireball light curve by comparing the sky illumination caused by the fireball with the illumination caused by the Moon. The Moon was located above the SW horizon (azimuth 222°, elevation 25°), 89° from the center of the field of view. Both the Moon and its spectrum were outside the field of view. The magnitude of the Moon was Mm = −12.5. The fireball was in the NW part of the sky, around azimuth 300°, moving from elevation 33° to 17°. The angular distance from the center of the field changed from 101° to 117°, i.e., it was only slightly larger than for the Moon. The apparent brightness of the fireball was computed from the equation:

  • image(1)

where B is the average pixel signal in the field of view during the fireball, Bm is the average pixel signal after the fireball (only moonlight), and Bd is the average pixel signal on April 14, when the sky was clear and the Moon was below the horizon (a dark frame). As the documentation of the Mintron 12V1 camera indicates that the camera operates with gamma factor γ = 0.45, we performed the following pixel correction to all pixels of all images before applying Equation 1:

  • image(2)

The conversion to absolute magnitude was done by correcting for the fireball distance (78–52 km) and for differential extinction for the fireball and the Moon, assuming an extinction coefficient of 0.4 magnitudes. The latter correction did not exceed 0.35 magnitudes.

The resulting light curves are given in Fig. 9. Both Kunžak and Rezman curves show the same features (flares), but the slope of the brightness increase is different. Interestingly, if we omit the gamma correction for the Rezman camera, the slopes become very similar, but the whole Rezman curve is then shifted by about 1 magnitude downwards. In any case, the calibration of the Kunžak radiometer is more certain and we will use the Kunžak curve for fireball modeling. Only the late flare at 0:59:46.75 UT is better seen in the Rezman light curve because of low signal-to-noise ratio at Kunžak toward the end of the fireball.

image

Figure 9.  Observed and modeled fireball light curve as a function of time. Black dots are values from Rezman video. The crosses connected by dashed line are the same data but without the gamma correction (see text). The thin line is the calibrated radiometric curve from EN02 Kunžak. The Kunžak curve was smoothed by averaging 12 consecutive measurements. The latter part shows big scatter because of very low signal (see Fig. 8). The thick gray curve is the output of the fragmentation model.

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The fireball reached a peak absolute magnitude of −15. The late flare was of magnitude of about −12. Note that we obtained the light curve as a function of time. The assignment of time to fireball heights was not possible from optical data, as no fireball image contains the position of the flares. All optical records terminate higher. In this respect, we had to rely on seismic data.

Seismic Data Analysis

  1. Top of page
  2. Abstract
  3. Introduction
  4. Observational Data
  5. Fireball Trajectory
  6. Velocity
  7. Light Curve
  8. Seismic Data Analysis
  9. Model of the Fireball and the Meteorite Fall
  10. Description of Meteorite Finds and Their Locations
  11. Radiant and Heliocentric Orbit
  12. Discussion
  13. Acknowledgments
  14. Acknowledgments
  15. References

The atmospheric flight of a meteoroid generates various types of sonic waves. The first kind of such waves is near-cylindrical waves, which propagate perpendicular to the fireball trajectory. Such waves are observable only in the belt between the beginning point (usually corresponds to the beginning of meteoroid ablation) and the terminal point of supersonic part of fireball trajectory (Borovička and Kalenda 2003). The energy concentration of near-cylindrical wave is mostly perpendicular to the fireball trajectory with its maximum around the main fragmentation point.

The second kind of sonic waves is spherical waves, which are generated along the entire trajectory with the maxima around fragmentation points (Borovička and Kalenda 2003). The energy concentration is maximal in the direction of fireball flight, but they are detectable in all directions.

The most difficult task in seismic data analysis is the evaluation of which kind of sonic waves are detected on different seismic stations and their cross-correlation between seismic stations or channels. We started our analysis by detection of all possible sonic waves in the available seismic records (Table 2; Fig. 10). Because the sonic waves came at the same time period as the aftershock of the Aquila earthquake, the amplitudes of the sonic waves were up to 100 times smaller than the raw recorded seismic signal (see Fig. 12). We used the most simple three-point filter to find sonic waves signatures in the seismic record which had very high frequency content.

Table 2.   List of seismic stations that detected the fireball. In the individual columns are listed codes and names of individual stations, country where they are located, their geographic coordinates and altitude, time of the maximum signal (Tfrag), time of the last supersonic point (Tterm), time of the very early sonic waves (Tfirst), and distance of the station to the point of maximum signal (R).
CodeNameCountryLatitude (°)Longitude (°)Altitude (km)TfragTtermTfirstR (km)
ACOMAcomizzaITA46.547913.51491.7261:02:111:02:11 42.7
ARSAArzbergAUT47.250515.52320.5771:07:511:07:51 148.6
BOJSBojanciSLO45.504415.25180.2521:07:581:07:55 150.4
CADSČadrgSLO46.228113.73680.7511:02:04  42.1
CEYCerknicaSLO45.738114.42210.5791:04:49 1:05:2394.1
CRESČrešnjevec pod O.SLO45.826015.45780.4331:07:221:07:171:08:15139.4
GORSGorjušeSLO46.317413.99991.0481:01:361:00:52 31.7
GROSGrobnikSLO46.461015.50180.9301:06:301:06:24 121.2
KBAKoelnbreinsperreAUT47.078413.34471.7211:04:23 1:04:2384.6
LJULjubljanaSLO46.043814.52780.3961:03:46  90.0
MYKATerra Mystica, N.AUT46.629913.64160.9091:01:551:01:55 38.7
OBKAHochobirAUT46.509214.54891.0751:02:351:02:02 51.9
PERSPerniceSLO46.636515.11390.7951:05:01  93.6
ROBSRobičSLO46.244513.50940.2451:02:351:02:33 51.0
SABOSabotinoITA45.987513.63360.6211:03:301:03:11 70.3
SOKASobothAUT46.678015.03271.0081:04:451:04:04 88.7
image

Figure 10.  Locations of seismic stations that detected the fireball acoustic signal. Ground projection of the fireball trajectory is shown as arrow.

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image

Figure 12.  Seismic signal at station CRES. The arrow indicates a secondary maximum generated by an early fragmentation of the meteoroid.

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Examples of sonic waves from the fireball are shown in Fig. 11. Our procedure was to first determine the time of maximum of sonic wave arrival at each station (Table 2). Then, the events were cross-correlated to reveal the location of the maximal signal at each station. The largest signal was received at station MYKA. This station lies close to the fireball trajectory and the signal was produced by the near-cylindrical blast wave. On the other hand, the maximum at station KBA, which lies further uprange the trajectory, came from an early fragmentation of the meteoroid. At station CRES, lying far beyond the end of the fireball, the largest concentration of energy comes from the final part of the fireball. Nevertheless, another signal came about a minute later (Fig. 12). That signal originated in the early fragmentation of the meteoroid. The final parts of supersonic flight of individual fragments were probably also responsible for the thunderclaps heard by the witnesses located close to the fireball terminal point (see the Casual Eyewitness Observations and Descriptions of the Event section).

image

Figure 11.  Seismic signature of the fireball at selected stations. Filtered signal of the vertical components is shown. Ellipses mark the sonic waves, which are verified in seismic signal.

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At most stations, several phases of sonic waves are present. Three fragmentations of the meteoroid and also the end of the supersonic trajectory were localized using the arrival times of sonic waves at individual stations and taking into account the drift caused by atmospheric winds. The method is described in more detail in Borovička and Kalenda (2003). The vertical wind profile was taken from the radiosonde measurements in Udine, Italy at 0 UT and is shown in Fig. 13. The prevailing wind was from west to northwest. The horizontal drift of acoustic waves caused by the winds amounted to 500 m for propagation between the height 30 km and the ground.

image

Figure 13.  Vertical profile of atmospheric wind azimuth and speed measured in Udine, Italy on April 9, 0 UT (source: University of Wyoming).

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The resulting locations are given in Table 3. The probable uncertainty is 500 m in the horizontal direction and 800 m in the vertical direction. Except for the early fragmentation point, which was identified at two stations only, these locations were obtained independently of any optical data (only the time of the fireball was taken into account). The agreement of both methods (optical and seismic) is excellent. The two independently located fragmentation points given in Table 3 lie only 200 and 280 m, respectively, from the (extrapolated) trajectory computed above. The last supersonic point was located 1 km off the optically determined trajectory to the southwest.

Table 3.   Locations of three meteoroid fragmentation events and the end of supersonic trajectory from seismic data.
EventLatitude (°)Longitude (°)Height
Early fragmentation46.558413.842245.9
Main fragmentation46.484813.957126.4
Third fragmentation46.480113.962425.2
Last supersonic point46.432714.016715.3

Model of the Fireball and the Meteorite Fall

  1. Top of page
  2. Abstract
  3. Introduction
  4. Observational Data
  5. Fireball Trajectory
  6. Velocity
  7. Light Curve
  8. Seismic Data Analysis
  9. Model of the Fireball and the Meteorite Fall
  10. Description of Meteorite Finds and Their Locations
  11. Radiant and Heliocentric Orbit
  12. Discussion
  13. Acknowledgments
  14. Acknowledgments
  15. References

To synthesize all available data and obtain a general picture of the event, the fireball was modeled using the classical equations for motion, ablation, and radiation of the meteoroid in the atmosphere (Ceplecha et al. 1998). We started the modeling at a height of 80 km. The fireball trajectory was known from optical records as previously described. The initial (model input) velocity was adjusted so that the modeled velocity at 54 km matched the measured velocity of 13.73 km s−1 (see above). The initial mass of the meteoroid and the fragmentation points along the trajectory were found by the trial-and-error method so that the observed light curve was reasonably fit. It was assumed that the main flare on the light curve corresponded to the main fragmentation point located from the seismic data, i.e., that it occurred at the height of 26.4 km. This correspondence is confirmed by the location of another fragmentation at the height of 25.2 km and, at the same time, the presence of other flares just after the main flare.

The luminosity of each fragment was computed from the equation:

  • image(3)

where τ(v) is the luminous efficiency, which depends on the velocity v, m is mass, and t is time. For the luminous efficiency, we assumed a simple function:

  • image(4)

i.e., that τ is 5.5% at a velocity of 15 km s−1 and decreases linearly with decreasing velocity. This value lies within the range published for τ in the literature and should be good within a factor of two.

In the case of a fragmentation event, it was assumed that a part of the mass is lost in the form of dust, i.e., that the sum of masses of daughter fragments is lower than the mass of the parent fragment. It is the quickly evaporating dust that produces the flares. The total luminosity produced by the flare was computed from

  • image(5)

where v is the fireball velocity at the moment of fragmentation and Δm is the total mass of the dust. This luminosity was then spread artificially into the interval of 0.14 s, with 25% of it produced during the first 0.02 s after the fragmentation and then gradually decreasing. The duration of the flares was set to conform to the smoothed light curve. The high-resolution radiometric curves showed that the flares were in fact shorter. Nevertheless, modeling the details of high temporal resolution light curves was not attempted. We were more interested in the general energy balance and focused on fitting the low-resolution light curves.

At each step, the luminosities of all fragments and the evaporating dust produced during the fragmentations were summed and the absolute magnitude of the fireball was computed from

  • image(6)

where the fact that the radiative output of a meteor of zero absolute magnitude is 1500 W (Ceplecha et al. 1998) was used.

The dynamics of the fragments were computed from the integral solution of drag and ablation equations (Ceplecha et al. 1998). According to experience with other fireballs (Borovička and Kalenda 2003; Ceplecha and ReVelle 2005), a low value of the intrinsic ablation coefficient (describing the mass loss between fragmentations) was used, namely 0.0035 s2 km−2. The product of the drag coefficient and the shape coefficient, ΓA, was set to 1.0 before the first fragmentation and to 0.8 afterwards. The lower Γ toward the end of the trajectory also follows our experience with the Morávka fireball (Borovička and Kalenda 2003). The bulk density of the meteoroid was set to 3400 kg m−3.

We obtained the following probable scenario. The initial mass of the meteoroid was 170 kg and the initial velocity 13.78 km s−1. At the height of 46 km, the meteoroid (still 168.5 kg of mass) disrupted into six nearly equal fragments (25–40 kg). This fragmentation was accompanied by only a small release of dust. Such early fragmentations without significant flares were already (indirectly) revealed for the Benešov and Morávka fireballs (Borovička et al. 1998; Borovička and Kalenda 2003). In the present case, there is direct evidence for early disruption from the seismic data. Moreover, we were not able to fit the final part of the light curve without the early disruption. The remaining mass toward the end of the trajectory would have remained high.

The fit of the beginning and middle part of the light curve was only approximate. The fireball exhibited many fluctuations of brightness in this phase (see Fig. 8). We attribute the fluctuations to instabilities in the ablation rate or minor dust releases, but a detailed modeling of these variations was beyond the scope of this study. We only note that such variations were observed in other bright fireballs as well (e.g., Spurný and Borovička 2001).

More important were the significant flares starting with the main flare at the height of 26.4 km. It is not possible to reveal the detailed fragmentation sequence. We simply assumed that each of the six fragments formed at 46 km disrupted once at lower heights. These fragmentations were accompanied by a significant release of dust, which caused the flares. To map the possible extent of the meteorite strewn field, we assumed that each fragmentation produced three bodies of different masses. In this way, 18 modeled meteorites were produced. The actual number of meteorites is, of course, totally unknown. It is quite possible that the meteoroids fragmented repeatedly as was the case of the Morávka fireball (Borovička and Kalenda 2003) and the number of meteorites will be therefore larger. The total mass of the meteorites is better restricted by the brightness of the fireball in the final phase. As our modeled light curve is somewhat brighter at the end than the observations suggest (see Fig. 9), the calculated meteorite mass (∼34 kg) should be considered an upper limit.

In our scenario, five of the six primary fragments broke up between the heights 26.4 and 23.0 km. At that time, their masses were 20–35 kg and velocities 9–11 km s−1. The masses of daughter fragments were between 0.1 and 8 kg in our model. The total amount of dust released during these five fragmentation events was about 100 kg. The dust release during break-ups was therefore the main process of mass loss, as was the case in Morávka (Borovička and Kalenda 2003). The last primary fragment continued to the height of 19.3 km, where it finally broke up, causing the final flare of the fireball. The mass and velocity before the break-up were 20 kg and 6 km s−1, respectively. The amplitude of the flare was high (see Fig. 9) and most of the mass (18.5 kg) must have been lost as dust. The surviving meteoroid masses were 0.2–1 kg in our model.

The modeled masses of all fragments are plotted in Fig. 14. All fragments were followed by the ablation model until their velocity dropped below 3 km s−1. After that, their dark flight was computed by the method of Ceplecha (1987) using the wind profile from Fig. 13. We assumed that all fragments followed initially the same trajectory (i.e., we neglected any impulses gained during breakups) and were spherical. As the wind azimuth was similar to the azimuth of the fireball flight, there was only small lateral displacement of the meteorites. The resulting locations of meteorites are plotted in Fig. 15. As the fireball trajectory was tuned according to the known meteorite locations, the predicted meteorite positions overlap well with the actual meteorite locations. Nevertheless, we can compare the modeled mass distribution of meteorites with the actual meteorites.

image

Figure 14.  Modeled masses of individual fragments as a function of time (thin lines). The masses are plotted until the fragment breakup or until the end of ablation at a velocity of 3 km s−1. The thick line shows overall mass of all existing macroscopic fragments. The dashed line shows the hypothetical mass in the absence of fragmentation.

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image

Figure 15.  Map of the strewn field. Possible meteorite locations from the fireball model with their masses in kg are plotted together with the locations and masses of the recovered meteorites. The terminal part of the luminous trajectory of the fireball is plotted with a thick line. The dashed ellipse shows the approximate uncertainty in the trajectory position. The dashed lines show the uncertainty in predicted meteorite positions due to the uncertainty of the fireball only. Additional lateral spread of meteorites can be expected as a consequence of lateral velocities gained during atmospheric fragmentations and nonspherical shapes of the meteorites. The location of the eyewitnesses of the terminal part of the fireball is marked with an inverted triangle.

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Naturally, the more massive meteorites are expected further downrange the trajectory, i.e., to the southeast. There is some mixing of masses caused by the fact that different meteorites originated from fragmentations at different heights. This mixing, however, cannot explain the position of the meteorite 2, weighing only 0.36 kg and lying quite far to the southeast (see the next section). As the meteorite has a complete fusion crust, it could not have separated from a larger fragment in the final part of the flight. The meteorite is, however, quite flat. It is likely that aerodynamic effects caused it to land in a different place than expected for a spherical body of the same mass. The other two meteorites lay more or less where expected. It is possible that the computed masses are little bit overestimated.

Description of Meteorite Finds and Their Locations

  1. Top of page
  2. Abstract
  3. Introduction
  4. Observational Data
  5. Fireball Trajectory
  6. Velocity
  7. Light Curve
  8. Seismic Data Analysis
  9. Model of the Fireball and the Meteorite Fall
  10. Description of Meteorite Finds and Their Locations
  11. Radiant and Heliocentric Orbit
  12. Discussion
  13. Acknowledgments
  14. Acknowledgments
  15. References

The simple triangulation of the few qualitatively good visual observations from Carinthia and especially the close-up view of the Jesenice fire brigade led Thomas Grau to the well-founded suspicion that during this fireball event some meteorites had dropped in the area around the Slovenian town of Jesenice. He started an individual systematic search in this area in early May 2009. Most promising were the southern slopes of the Karavanke Mountains, north of Jesenice, as the mountain meadows were already snow-free. Unfortunately, his search was not successful. But he issued some articles in local newspapers about a possible meteorite fall in the region.

Stimulated by one of the newspaper articles, two local mountain hikers happened to find coincidentally the first piece of the Jesenice fall. On May 17, 2009, Jožef Pretnar and Bojana Krajnc spotted a peculiar rock in an impact hole in the almost 1300 m high mountain forest region Mežakla, south of Jesenice, while climbing up to the summit of Planski vrh. The next day, Thomas Grau was able to identify the rock as a genuine meteorite and to secure the impact site. Obviously, the meteorite reached the ground with a relatively high velocity and it hit strong limestone bedrock. The meteorite was found fractured into many pieces, the largest weighing about 997 g. In total, about 2293 g of fragments was recovered from the impact site at 46°25′16.9″N, 14°03′07.8″E.

A second piece of this meteorite fall, a complete individual of 361 g was found on July 21, 2009 by Ralph Sporn and Martin Neuhofer, about 400 m south of the first find location at 46°25′4.7″N, 14°03′11.6″E. Finally, a third piece (also a complete meteorite specimen) of 956 g was recovered by Danijel Repe on August 27, 2009, 740 m northwest of the Jesenice I impact site, at 46°25′28.4″N, 14°02′37.3″E. Additional coordinated group search efforts that covered over 80 ha of the strewn field failed to produce additional finds. The known total weight of the Jesenice meteorites is 3.61 kg (valid at the time of writing of this article in April 2010). Further search efforts are planned.

The Jesenice meteorite is classified as a weakly shocked (S3) L6 ordinary chondrite (Bischoff et al. 2010). Data about the recovered meteorites are collected in Table 4.

Table 4.   Details of recovered meteorites.
MeteoriteMass (kg)CoordinatesDate of recoveryFinder
Longitude (E)Latitude (N)Altitude (m)
M12.29314.05217°46.42136°1280May 17, 2009Jožef Pretnar, Bojana Krajnc
M20.36114.05322°46.41797°1148July 21, 2009Ralph Sporn, Martin Neuhofer
M30.95614.04369°46.42456°1188August 27, 2009Danijel Repe

Radiant and Heliocentric Orbit

  1. Top of page
  2. Abstract
  3. Introduction
  4. Observational Data
  5. Fireball Trajectory
  6. Velocity
  7. Light Curve
  8. Seismic Data Analysis
  9. Model of the Fireball and the Meteorite Fall
  10. Description of Meteorite Finds and Their Locations
  11. Radiant and Heliocentric Orbit
  12. Discussion
  13. Acknowledgments
  14. Acknowledgments
  15. References

From the exact time of the fireball passage, its initial velocity, and position of the apparent radiant, we computed the heliocentric orbit using the procedure described in Ceplecha (1987). These input parameters are, however, determined with different precision and reliability. The time of the fireball passage is known very precisely from the fast photometer placed in each AFO because the time of the AFO computer is continuously corrected through direct internet connection with a time server. We recorded the light curve of the Jesenice fireball from six independent AFOs. The time resolution of the light curve record is 2 ms and because we were able to identify a very sharp maximum flare on each record, we determined its absolute time as 0:59:45.75 ± 0.02 s UT. For determination of the heliocentric orbit, we took the time of the meteoroid where it started its luminous trajectory, i.e., the extrapolated time of the first optical recording at the altitude of 88 km. This brings a small additional uncertainty in time determination which is caused mainly by the modeled deceleration profile deeper in the atmosphere. Nevertheless, the resulting time (see Table 5) is much more precise than the other parameters determined from photographic records.

Table 5.   Radiant and orbital elements (J2000.0) of the Jesenice meteorite fall.
Time0h59m40.5s ± 0.1s
αR (°)177.6 ± 0.6
δR (°)60.4 ± 0.4
v (km s−1)13.78 ± 0.25
αG (°)159.9 ± 1.2
δG (°)58.7 ± 0.5
vG (km s−1)8.3 ± 0.4
vH (km s−1)35.6 ± 0.3
a (AU)1.75 ± 0.07
e0.431 ± 0.022
q (AU)0.9965 ± 0.0006
Q (AU)2.51 ± 0.14
ω (°)190.5 ± 0.5
Ω (°)19.196
i (°)9.6 ± 0.5
P (years)2.32 ± 0.13

The second important parameter is the initial velocity. As discussed in the Velocity and Model of the Fireball and the Meteorite Fall sections, we were able to determine only an average velocity, given the short part of the trajectory where we could distinguish breaks at both Czech stations. A very important check of the reliability of this value is the good agreement of the independent measurements of the several breaks visible from both stations (shown in Fig. 7). In fact, the precision of this mathematical fit is about two times better than the resulting standard deviation of the initial velocity which we took for orbital computations. We were more conservative (as was also the case for radiant determination as discussed below) because the value of the initial velocity (again in Table 5) is an extrapolation of this single value and this extrapolation can cause some additional uncertainty due to use of estimated modeled atmospheric drag above the altitude where the average velocity was measured.

The last important input entry is the position of the apparent radiant (see Table 5). This is the result of the average trajectory computation from all measured points on all used stations. As was mentioned above in the Fireball Trajectory section, we used for this purpose mainly data from both Czech stations. We also used the known position of the meteorites. Similarly, as was the case for the velocity determination, we again took an error value two times bigger than was determined from the mathematical fit. It is in good agreement with the estimated uncertainty of the atmospheric trajectory which we got from the spread of several possible solutions resulting from reduction uncertainties of both Czech stations.

The resulting values of the heliocentric orbit of the Jesenice meteoroid and its plot projected onto the ecliptic plane are shown in Fig. 17 and Table 5. The Jesenice orbit is a typical Apollo-type orbit with the aphelion lying in the middle parts of the Main Belt. In this respect, the Jesenice meteorite is quite common as compared to other known meteorite orbits.

image

Figure 17.  Orbit of the Jesenice meteorite along with the Příbram and Neuschwanstein pair in the inner solar system. All orbits are projected onto the ecliptic plane. inline image indicates the vernal equinox.

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Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Observational Data
  5. Fireball Trajectory
  6. Velocity
  7. Light Curve
  8. Seismic Data Analysis
  9. Model of the Fireball and the Meteorite Fall
  10. Description of Meteorite Finds and Their Locations
  11. Radiant and Heliocentric Orbit
  12. Discussion
  13. Acknowledgments
  14. Acknowledgments
  15. References

The Jesenice fireball data are limited in the sense that there are no data on deceleration. Direct imaging of the fragments is also not available. On the other hand, we have a detailed light curve, although the calibration to absolute magnitudes is somewhat uncertain. Seismic data also provided important constraints. The trajectory was determined well and the initial velocity and orbit are known with reasonable precision, better than for some other documented meteorite falls. The available data enabled us to construct a general model of the fireball. As with most other meteorite falls, atmospheric fragmentation of the meteoroid was very important. A detailed fragmentation sequence could not be determined, but the heights of fragmentations and the masses involved could be restricted.

The general data on the Jesenice meteorite fall are summarized in Table 6. The derived initial mass of about 170 kg resulted from modeling of the known light curve. The mass is rather uncertain because of uncertainties in absolute photometry and in the assumed luminous efficiency. The corresponding radius of 23 cm falls well between the two disagreeing estimates made from meteorite isotopes by Bischoff et al. (2010) and Ott et al. (2010), namely <20 and >30 cm, respectively. The terminal mass, i.e., the total mass of fallen meteorites, is also uncertain because there are no images of the terminal parts of the fireball which means no direct information about dynamics is available. Our modeled mass of 34 kg is probably at least slightly overestimated. The probable range is 10–30 kg. Of this, 3.6 kg has been recovered at the time of writing. As the strewn field is covered by mountain forest, it is no surprise that the majority of meteorites have not been found.

Table 6.   Geophysical data on the Jesenice meteorite fall.
Initial velocity13.78 ± 0.25 km s−1Extrapolation from average velocity at 54 km
Initial mass170 ± 80 kgPhotometric mass
Trajectory slope59°From the horizontal
Beginning height88 kmAt Rezman all-sky image
Terminal height∼18 kmModeled height at the end of Rezman light curve
Duration6.6 s 
Peak absolute magnitude−15 ± 0.5 
Dynamic pressure at the first fragmentation0.3 MPaAt the height of 46 km
Maximum dynamic pressure3.9 MPaAt the height of 23 km
Estimated total fallen mass10–30 kg 
Recovered mass3.61 kgAs of spring 2010
Number of recovered meteorites3As of spring 2010

The meteorites are L6 ordinary chondrites (Bischoff et al. 2010), a common type of meteorite. The behavior of the meteoroid in the atmosphere was also typical. Recently, the strength of meteorite-dropping meteoroids was compared with regard to the dynamic pressure which caused their atmospheric fragmentation (Popova et al., unpublished data). The early disruption of the Jesenice meteoroid occurred at the dynamic pressure of only 0.3 MPa. The main fragmentation at the heights 23–26.5 km occurred under dynamic pressures of up to 3.9 MPa (see Fig. 16). These values are comparable to Morávka and intermediate among the documented falls of ordinary chondrites (Popova et al., unpublished data). The relatively high surviving mass fraction (we estimate that ∼10% of the original mass landed as meteorites) was caused by the favorably low entry velocity.

image

Figure 16.  Modeled dynamic pressures experienced by individual fragments as a function of time.

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The heliocentric orbit of the Jesenice meteoroid is a typical Apollo-type orbit with the aphelion lying in the middle part of the Main Belt. In this regard, the Jesenice orbit is the most common type among known orbits of meteorites. Until the time of the Jesenice fall, 12 similar cases were known (Popova et al., unpublished data) and only one, Bunburra Rockhole (Bland et al. 2009), has a different type of orbit (Aten). An exceptional feature of the Jesenice fall was, however, the date on which it occurred. It was almost exactly 50 yr after the first instrumentally recorded meteorite fall, Příbram (Ceplecha 1961), and 7 yr after the Neuschwanstein meteorite fall (Spurný et al. 2002). These two very well-documented meteorite falls had almost identical orbits (Spurný et al. 2003). This evoked the possibility of membership of the Jesenice meteorite in this potential meteorite stream. However, we showed that the heliocentric orbit of the Jesenice meteorite significantly differs from the Příbram–Neuschwanstein orbital pair (see Fig. 17).

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Observational Data
  5. Fireball Trajectory
  6. Velocity
  7. Light Curve
  8. Seismic Data Analysis
  9. Model of the Fireball and the Meteorite Fall
  10. Description of Meteorite Finds and Their Locations
  11. Radiant and Heliocentric Orbit
  12. Discussion
  13. Acknowledgments
  14. Acknowledgments
  15. References

Acknowledgments— This work was supported by GA ČR grant 205/08/0411 and the EU grant MRTN-CT-2006-035519. The institutional research plan number is AV0Z10030501.

We are grateful to Herman Mikuž of the Črni Vrh Observatory for providing the fireball images. Rezman Observatory is acknowledged for hosting the cameras used to record the fireball. We thank Dr. Mladen Zivcic, Dr. Rita Maurers, and Dr. Jan Zedník for help with seismic data preparation.

We also gratefully acknowledge helpful comments by the referees Dr. P. Brown and Dr. O. Popova.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Observational Data
  5. Fireball Trajectory
  6. Velocity
  7. Light Curve
  8. Seismic Data Analysis
  9. Model of the Fireball and the Meteorite Fall
  10. Description of Meteorite Finds and Their Locations
  11. Radiant and Heliocentric Orbit
  12. Discussion
  13. Acknowledgments
  14. Acknowledgments
  15. References
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  • Borovička J., Popova O. P., Nemtchinov I. V., Spurný P., and Ceplecha Z. 1998. Bolides produced by impacts of large meteoroids into the Earth’s atmosphere: Comparison of theory with observations. I. Benešov bolide dynamics and fragmentation. Astronomy & Astrophysics 334:713728.
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