The Košice meteorite fall: Atmospheric trajectory,fragmentation, and orbit

The Ko?ice meteorite fall occurred in eastern Slovakia on February 28, 2010, 22:25 UT. The very bright bolide was imaged by three security video cameras from Hungary. Detailed bolide light curves were obtained through clouds by radiometers on seven cameras of the European Fireball Network. Records of sonic waves were found on six seismic and four infrasonic stations. An atmospheric dust cloud was observed the next morning before sunrise. After careful calibration, the video records were used to compute the bolide trajectory and velocity. The meteoroid, of estimated mass of 3500 kg, entered the atmosphere with a velocity of 15 km s^?1 on a trajectory with a slope of 60° to the horizontal. The largest fragment ceased to be visible at a height of 17 km, where it was decelerated to 4.5 km s^?1. A maximum brightness of absolute stellar magnitude about ?18 was reached at a height of 36 km. We developed a detailed model of meteoroid atmospheric fragmentation to fit the observed light curve and deceleration. We found that Ko?ice was a weak meteoroid, which started to fragment under the dynamic pressure of only 0.1 MPa and fragmented heavily under 1 MPa. In total, 78 meteorites were recovered in the predicted fall area during official searches. Other meteorites were found by private collectors. Known meteorite masses ranged from 0.56 g to 2.37 kg. The meteorites were classified as ordinary chondrites of type H5 and shock stage S3. The heliocentric orbit had a relatively large semimajor axis of 2.7 AU and aphelion distance of 4.5 ± 0.5 AU. Backward numerical integration of the preimpact orbit indicates possible large variations of the orbital elements in the past due to resonances with Jupiter.     

The Žďár nad Sázavou meteorite fall: Fireball trajectory,photometry, dynamics,fragmentation, orbit,and meteorite recovery

We report a comprehensive analysis of the instrumentally observed meteorite fall ??ár nad Sázavou, which occurred in the Czech Republic on December 9, 2014, at 16:16:45–54 UT. The original meteoroid with an estimated initial mass of 150 kg entered the atmosphere with a speed of 21.89 km s^?1 and began a luminous trajectory at an altitude of 98.06 km. At the maximum, it reached ?15.26 absolute magnitude and terminated after a 9.16 s and 170.5 km long flight at an altitude of 24.71 km with a speed of 4.8 km/s. The average slope of the atmospheric trajectory to the Earth's surface was only 25.66°. Before its collision with Earth, the initial meteoroid orbited the Sun on a moderately eccentric orbit with perihelion near Venus orbit, aphelion in the outer main belt, and low inclination. During the atmospheric entry, the meteoroid severely fragmented at a very low dynamic pressure 0.016 MPa and further multiple fragmentations occurred at 1.4–2.5 MPa. Based on our analysis, so far three small meteorites classified as L3.9 ordinary chondrites totaling 87 g have been found almost exactly in the locations predicted for a given mass. Because of very high quality of photographic and radiometric records, taken by the dedicated instruments of the Czech part of the European Fireball Network, ??ár nad Sázavou belongs to the most reliably, accurately, and thoroughly described meteorite falls in history.     

Video observations, atmospheric path, orbit and fragmentation record of the fall of the Peekskill meteorite

Large Near-Earth-Asteroids have played a role in modifying the character of the surface geology of the Earth over long time scales through impacts. Recent modeling of the disruption of large meteoroids during atmospheric flight has emphasized the dramatic effects that smaller objects may also have on the Earth's surface. However, comparison of these models with observations has not been possible until now. Peekskill is only the fourth meteorite to have been recovered for which detailed and precise data exist on the meteoroid atmospheric trajectory and orbit. Consequently, there are few constraints on the position of meteorites in the solar system before impact on Earth. In this paper, the preliminary analysis based on 4 from all 15 video recordings of the fireball of October 9, 1992 which resulted in the fall of a 12.4 kg ordinary chondrite (H6 monomict breccia) in Peekskill, New York, will be given. Preliminary computations revealed that the Peekskill fireball was an Earth-grazing event, the third such case with precise data available. The body with an initial mass of the order of 10(4) kg was in a pre-collision orbit with a = 1.5 AU, an aphelion of slightly over 2 AU and an inclination of 5 degrees. The no-atmosphere geocentric trajectory would have lead to a perigee of 22 km above the Earth's surface, but the body never reached this point due to tremendous fragmentation and other forms of ablation. The dark flight of the recovered meteorite started from a height of 30 km, when the velocity dropped below 3 km/s, and the body continued 50 km more without ablation, until it hit a parked car in Peekskill, New York with a velocity of about 80 m/s. Our observations are the first video records of a bright fireball and the first motion pictures of a fireball with an associated meteorite fall.     

Video observations, atmospheric path, orbit and fragmentation record of the fall of the Peekskill meteorite

Large Near-Earth-Asteroids have played a role in modifying the character of the surface geology of the Earth over long time scales through impacts. Recent modeling of the disruption of large meteoroids during atmospheric flight has emphasized the dramatic effects that smaller objects may also have on the Earth's surface. However, comparison of these models with observations has not been possible until now. Peekskill is only the fourth meteorite to have been recovered for which detailed and precise data exist on the meteoroid atmospheric trajectory and orbit. Consequently, there are few constraints on the position of meteorites in the solar system before impact on Earth. In this paper, the preliminary analysis based on 4 from all 15 video recordings of the fireball of October 9, 1992 which resulted in the fall of a 12.4 kg ordinary chondrite (H6 monomict breccia) in Peekskill, New York, will be given. Preliminary computations revealed that the Peekskill fireball was an Earth-grazing event, the third such case with precise data available. The body with an initial mass of the order of 10⁴ kg was in a pre-collision orbit with a = 1.5 AU, an aphelion of slightly over 2 AU and an inclination of 5. The no-atmosphere geocentric trajectory would have lead to a perigee of 22 km above the Earth's surface, but the body never reached this point due to tremendous fragmentation and other forms of ablation. The dark flight of the recovered meteorite started from a height of 30 km, when the velocity dropped below 3 km/s, and the body continued 50 km more without ablation, until it hit a parked car in Peekskill, New York with a velocity of about 80 m/s. Our observations are the first video records of a bright fireball and the first motion pictures of a fireball with an associated meteorite fall.     

The Winchcombe fireball—That lucky survivor

On February 28, 2021, a fireball dropped ∼0.6 kg of recovered CM2 carbonaceous chondrite meteorites in South-West England near the town of Winchcombe. We reconstruct the fireball's atmospheric trajectory, light curve, fragmentation behavior, and pre-atmospheric orbit from optical records contributed by five networks. The progenitor meteoroid was three orders of magnitude less massive (∼13 kg) than any previously observed carbonaceous fall. The Winchcombe meteorite survived entry because it was exposed to a very low peak atmospheric dynamic pressure (∼0.6 MPa) due to a fortuitous combination of entry parameters, notably low velocity (13.9 km s⁻¹). A near-catastrophic fragmentation at ∼0.07 MPa points to the body's fragility. Low entry speeds which cause low peak dynamic pressures are likely necessary conditions for a small carbonaceous meteoroid to survive atmospheric entry, strongly constraining the radiant direction to the general antapex direction. Orbital integrations show that the meteoroid was injected into the near-Earth region ∼0.08 Myr ago and it never had a perihelion distance smaller than ∼0.7 AU, while other CM2 meteorites with known orbits approached the Sun closer (∼0.5 AU) and were heated to at least 100 K higher temperatures.     

The Orgueil meteorite: 150 years of history

The goal of this paper is to summarize 150 yr of history of a very special meteorite. The Orgueil meteorite fell near Montauban in southwestern France on May 14, 1864. The bolide, which was the size of the full Moon, was seen across Western France, and almost immediately made the news in local and Parisian newspapers. Within a few weeks of the fall, a great diversity of analyses were performed under the authority of Gabriel Auguste Daubrée, geology professor at the Paris Museum, and published in the Comptes Rendus de l'Académie des Sciences. The skilled scientists reported the presence of iron sulfides, hydrated silicates, and carbonates in Orgueil. They also characterized ammonium salts which are now gone, and observed sulfates being remobilized at the surface of the stone. They identified the high water and carbon contents, and noted similarities with the Alais meteorite, which had fallen in 1806, 300 km away. While Daubrée and his colleagues noted the similarity of the Orgueil organic matter with some terrestrial humus, they were cautious not to make a direct link with living organisms. One century later, Nagy and Claus were less prudent and announced the discovery of “organized” elements in some samples of Orgueil. Their observations were quickly discredited by Edward Anders and others who also discovered that some pollen grains were intentionally placed into the rock back in the 1860s. Orgueil is now one of the most studied meteorites, indeed one of the most studied rocks of any kind. Not only does it contain a large diversity of carbon‐rich compounds, which help address the question of organo‐synthesis in the early solar system but its chemical composition is also close to that of the Sun's photosphere and serves as a cosmic reference. Secondary minerals, which make up 99% of the volume of Orgueil, were probably formed during hydrothermal alteration on the parent‐body within the first few million years of the solar system; their study is essential to our understanding of fluid–rock interaction in asteroids and comets. Finally, the Orgueil meteorite probably originated from a volatile‐rich “cometary” outer solar system body as indicated by its orbit. Because it bears strong similarities to other carbonaceous chondrites that originated on dark asteroids, this cometary connection supports the idea of a continuum between dark asteroids and comets.     

The August θ‐Aquillid fireballs and possible relationship with the asteroid 2004MB6

Three bright fireballs belonging to the August θ‐Aquillid (ATA) meteor shower were photographed by the Tajikistan fireball network in 2009. Two of them are classified as the meteorite‐dropping fireballs according to the determined parameters of the atmospheric trajectories, velocities, masses, and densities. Detection of the more dense bodies among cometary meteoroids points to a heterogeneous composition of the parent comet, and supports the suggestion that some meteorites might originate in the outer solar system, in the given case from the Jupiter‐family comet reservoir. A search for the stream's parent was undertaken among the near‐Earth asteroids (NEAs); as a result, the asteroid 2004MB6 was identified as a possible progenitor of the ATA meteoroid stream. Investigation of the orbital evolution of the 2004MB6 and the fireball‐producing meteoroid TN170809A showed that both objects have similar secular variations in the orbital elements during 7 kyr. The comet‐like orbit of the 2004MB6 and its association with the ATA shower suppose a cometary origin of the asteroid.     

Analysis of instrumental observations of the Jesenice meteorite fall on April 9, 2009

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 P?íbram 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 ).     

The Tajikistan superbolide of July 23, 2008. I. Trajectory,orbit, and preliminary fall data

The results of the atmospheric trajectory, radiant, heliocentric orbit, and preliminary strewn field calculations for an extremely bright slow‐moving fireball are presented. In the evening hours of July 23, 2008, a bright object entered Earth's atmosphere over Tajikistan. The fireball had a ?20.3 maximum absolute magnitude and a spectacularly long persistent dust trail remained visible over a widespread region of Tajikistan for about 28 minutes after sunset. The fireball was also recorded by a visible‐light satellite system at 14 h 45 min 25 s UT, and the dust trail was imaged by video and photocameras. A unique aspect of this event is that it was detected by two infrasound and five seismic stations too. The bolide was first recorded at a height of 38.2 km, reached its maximum brightness at a height of 35.0 km, and finished at a height of 19.6 km. The first breakup occurred under an aerodynamic pressure of approximately 1.6 MPa, similar to the values derived for breakups of the scarcely reported meteorite‐dropping bolides. The fireball's trajectory and dynamic results suggest that meteorite survival is likely. The meteoroid followed an Apollo‐like asteroid orbit comparable to those derived for previously recovered meteorites with accurately known orbits.     

The Villalbeto de la Peña meteorite fall: II. Determination of atmospheric trajectory and orbit

Abstract— The L6 ordinary chondrite Villalbeto de la Peña fall occurred on January 4, 2004, at 16: 46: 45 ± 2 s UTC. The related daylight fireball was witnessed by thousands of people from Spain, Portugal, and southern France, and was also photographed and videotaped from different locations of León and Palencia provinces in Spain. From accurate astrometric calibrations of these records, we have determined the atmospheric trajectory of the meteoroid. The initial fireball velocity, calculated from measurements of 86 video frames, was 16.9 ± 0.4 km/s. The slope of the trajectory was 29.0 ± 0.6° to the horizontal, the recorded velocity during the main fragmentation at a height of 27.9 ± 0.4 km was 14.2 ± 0.2 km/s, and the fireball terminal height was 22.2 ± 0.2 km. The heliocentric orbit of the meteoroid resided in the ecliptic plane (i = 0.0 ± 0.2°), having a perihelion distance of 0.860 ± 0.007 AU and a semimajor axis of 2.3 ± 0.2 AU. Therefore, the meteorite progenitor body came from the Main Belt, like all previous determined meteorite orbits. The Villalbeto de la Peña fireball analysis has provided the ninth known orbit of a meteorite in the solar system.     

The Bunburra Rockhole meteorite fall in SW Australia: fireball trajectory,luminosity, dynamics,orbit, and impact position from photographic and photoelectric records

Abstract– We report an analysis of the first instrumentally observed meteorite fall in Australia, which was recorded photographically and photoelectrically by two eastern stations of the Desert Fireball Network (DFN) on July 20, 2007. The meteoroid with an initial mass of 22 kg entered the atmosphere with a low speed of 13.36 km s^?1 and began a luminous trajectory at an altitude of 62.83 km. In maximum, it reached ?9.6 absolute magnitude and terminated after a 5.7 s and 64.7 km long flight at an altitude of 29.59 km with a speed of 5.8 km s^?1. The angle of the atmospheric trajectory to the Earth’s surface was 30.9°. The first organized search took place in October 2008 and the first meteorite (150 g) was found 97 m southward from the predicted central line at the end of the first day of searching (October 3, 2008). The second stone (174 g) was recovered 39 m northward from the central line, both exactly in the predicted mass limits. During the second expedition in February 2009, a third fragment of 14.9 g was found again very close (～100 m) from the predicted position. Total recovered mass is 339 g. The meteorite was designated Bunburra Rockhole (BR) after a nearby landscape structure. This first DFN sample is an igneous achondrite. Initial petrography indicated that BR was a brecciated eucrite but detailed analyses proved that BR is not a typical eucrite, but an anomalous basaltic meteorite ( Bland et al. 2009 ). BR was delivered from an unusual, Aten type orbit (a < 1 AU) where virtually the entire orbit was contained within Earth’s orbit. BR is the first achondrite fall with a known orbit and it is one of the most precise orbits ever calculated for a meteorite dropping fireball.     

The Morávka meteorite fall: 3. Meteoroid initial size,history, structure,and composition

Abstract— The properties and history of the parent meteoroid of the Morávka H5–6 ordinary chondrites have been studied by a combination of various methods. The pre‐atmospheric mass of the meteoroid was computed from fireball radiation, infrasound, seismic signal, and the content of noble gases in the meteorites. All methods gave consistent results. The best estimate of the pre‐atmospheric mass is 1500 ± 500 kg. The fireball integral bolometric luminous efficiency was 9%, and the acoustic efficiency was 0.14%. The meteoroid cosmic ray exposure age was determined to be (6.7 ± 1.0) × 10⁶ yr. The meteorite shows a clear deficit of helium, both ³He and ⁴He. This deficit can be explained by solar heating. Numerical backward integration of the meteoroid orbit (determined in a previous paper from video records of the fireball) shows that the perihelion distance was probably lower than 0.5 AU and possibly as low as 0.1 AU 5 Ma ago. The collision which excavated Morávka probably occurred while the parent body was on a near‐Earth orbit, as opposed to being confined entirely to the main asteroid belt. An overview of meteorite macroscopic properties, petrology, mineralogy, and chemical composition is given. The meteorites show all mineralogical features of H chondrites. The shock level is S2. Minor deviations from other H chondrites in abundances of trace elements La, Ce, Cs, and Rb were found. The ablation crust is enriched with siderophile elements.     

Farmington Meteorite: A fragment of an Apollo asteriod?

We have attempted to reconstruct the orbit of the Farmington L5 chondrite which fell in Kansas in 1890. Because its radiation age is uniquely short (25 000 years), its orbit should still closely resemble that of its parent body. A search of 280 contemporary newspapers and other sources turned up more than 60 useable eyewitness reports from 32 localities, which led to the following estimate of the apparent radiant: height 60°, azimuth 20°, with an uncertainty of about 10°. Orbital elements were determined for this radiant for four plausible preatmospheric velocities: 13, 16, 19, and 22 km/sec. The results show quite definitely that Farmington had a small orbit of low inclination: semimajor axis 1–1.9 AU, perihelion ? 0.4 AU, aphelion ? 3.0 AU, inclination ? 16°. Because of the short radiation age, the parent body of Farmington must already have been in an Earth-crossing orbit when the meteorite was ejected from it by an impact. Of the 11 known Earth-crossing asteroids with encounter velocities below 22 km/sec, 1862 Apollo, Hermes, and 1865 Cerberus are passable matches, while 1620 Geographos and 1685 Toro are more marginal possibilities. Apparently Earth-crossing asteroids are the immediate parent bodies of at least some meteorites. Their ultimate source must be the ultimate source of most stony meteorites.     

The orbit,atmospheric dynamics,and initial mass of the Park Forest meteorite

Abstract— The fireball accompanying the Park Forest meteorite fall (L5) was recorded by ground‐based videographers, satellite systems, infrasound, seismic, and acoustic instruments. This meteorite shower produced at least 18 kg of recovered fragments on the ground (Simon et al. 2004). By combining the satellite trajectory solution with precise ground‐based video recording from a single site, we have measured the original entry velocity for the meteoroid to be 19.5 ± 0.3 km/s. The earliest video recording of the fireball was made near the altitude of 82 km. The slope of the trajectory was 29° from the vertical, with a radiant azimuth (astronomical) of 21° and a terminal height measured by infrared satellite systems of 18 km. The meteoroid's orbit has a relatively large semi‐major axis of 2.53 ± 0.19 AU, large aphelion of 4.26 ± 0.38 AU, and low inclination. The fireball reached a peak absolute visual magnitude of ?22, with three major framentation episodes at the altitudes of 37, 29, and 22 km. Acoustic recordings of the fireball airwave suggest that fragmentation was a dominant process in production of sound and that some major fragments from the fireball remained supersonic to heights as low as ?10 km. Seismic and acoustic recordings show evidence of fragmentation at 42, 36, 29, and 17 km. Examination of implied energies/initial masses from all techniques (satellite optical, infrasound, seismic, modeling) leads us to conclude that the most probable initial mass was (11 ± 3) × 10³ kg, corresponding to an original energy of ?0.5 kt TNT (2.1 times 10¹² J) and a diameter of 1.8 m. These values correspond to an integral bolometric efficiency of 7 ± 2%. Early fragmentation ram pressures of <1 MPa and major fragmentations occurring with ram pressures of 2–5 MPa suggest that meter‐class stony near‐Earth asteroids (NEAs) have tensile strengths more than an order of magnitude lower than have been measured for ordinary chondrites. One implication of this observation is that the rotation period for small, fast‐rotating NEAs is likely to be >30 seconds.     

The instrumentally recorded fall of the Križevci meteorite,Croatia, February 4, 2011

The Kri?evci H6 meteorite was recovered on the basis of fireball data obtained by the cameras of the Croatian Meteor Network. The fireball, which occurred on February 4, 2011, 23:20:40 UT, was also observed by meteor cameras in Slovenia and by the Autonomous Fireball Observatory in Martinsberg, Austria, which belongs to the European Fireball Network. Here, we present detailed data on fireball trajectory, velocity, deceleration, light curve, and orbit. We also modeled the atmospheric fragmentation of the meteoroid on the basis of the light curve and deceleration. The initial mass of the meteoroid was between 25–100 kg, most probably about 50 kg. Severe fragmentation occurred at heights of approximately 60 and 31 km, under dynamic pressures of 0.1 and 3 MPa, respectively. The peak absolute magnitude of ?13.7 was reached during the second severe fragmentation event. The recovered 291 g meteorite was probably the only fragment with a terminal mass exceeding 100 g. The orbit had a low inclination of 0.6 degrees, perihelion distance 0.74 AU, and semimajor axis 1.54 AU. Kri?evci can be ranked among the 10 best documented meteorite falls.     

Are There Many Inactive Jupiter-Family Comets among the Near-Earth Asteroid Population?

We analyze the dynamical evolution of Jupiter-family (JF) comets and near-Earth asteroids (NEAs) with aphelion distances Q>3.5 AU, paying special attention to the problem of mixing of both populations, such that inactive comets may be disguised as NEAs. From numerical integrations for 2×10⁶ years we find that the half lifetime (where the lifetime is defined against hyperbolic ejection or collision with the Sun or the planets) of near-Earth JF comets (perihelion distances q<1.3 AU) is about 1.5×10⁵ years but that they spend only a small fraction of this time (∼ a few 10³ years) with q<1.3 AU. From numerical integrations for 5×10⁶ years we find that the half lifetime of NEAs in “cometary” orbits (defined as those with aphelion distances Q>4.5 AU, i.e., that approach or cross Jupiter's orbit) is 4.2×10⁵ years, i.e., about three times longer than that for near-Earth JF comets. We also analyze the problem of decoupling JF comets from Jupiter to produce Encke-type comets. To this end we simulate the dynamical evolution of the sample of observed JF comets with the inclusion of nongravitational forces. While decoupling occurs very seldom when a purely gravitational motion is considered, the action of nongravitational forces (as strong as or greater than those acting on Encke) can produce a few Enckes. Furthermore, a few JF comets are transferred to low-eccentricity orbits entirely within the main asteroid belt (Q<4 AU and q>2 AU). The population of NEAs in cometary orbits is found to be adequately replenished with NEAs of smaller Q's diffusing outward, from which we can set an upper limit of ∼20% for the putative component of deactivated JF comets needed to maintain such a population in steady state. From this analysis, the upper limit for the average time that a JF comet in near-Earth orbit can spend as a dormant, asteroid-looking body can be estimated to be about 40% of the time spent as an active comet. More likely, JF comets in near-Earth orbits will disintegrate once (or shortly after) they end their active phases.     

The Morávka meteorite fall: 1. Description of the events and determination of the fireball trajectory and orbit from video records

Abstract— The Morávka (Czech Republic) meteorite fall occurred on May 6, 2000, 11:52 UT, during the daytime. Six H5–6 ordinary chondrites with a total mass of 1.4 kg were recovered. The corresponding fireball was witnessed by thousands of people and also videotaped by 3 casual witnesses. Sonic booms were recorded by 16 seismic stations in the Czech Republic and Poland and by one infrasonic station in Germany. A total of 2.5% of the fireball eyewitnesses reported electrophonic sounds. Satellites in Earth orbit detected part of the fireball light curve. In this first paper from a series of 4 papers devoted to the Morávka meteorite fall, we describe the circumstances of the fall and determine the fireball trajectory and orbit from calibrated video records. Morávka becomes one of only 6 meteorites with a known orbit. The slope of the trajectory was 20.4° to the horizontal, the initial velocity was 22.5 km/s, and the terminal height of the fireball was 21 km. The semimajor axis of the orbit was 1.85 AU, the perihelion distance was 0.982 AU, and the inclination was 32.2°. The fireball reached an absolute visual magnitude of ?20 at a height of 33 km.     

On the origin of the unusual orbit of Comet 2P/Encke

The orbit of Comet 2P/Encke is difficult to understand because it is decoupled from Jupiter—its aphelion distance is only 4.1 AU. We present a series of orbital integrations designed to determine whether the orbit of Comet 2P/Encke can simply be the result of gravitational interactions between Jupiter-family comets and the terrestrial planets. To accomplish this, we integrated the orbits of a large number of objects from the trans-neptunian region, through the realm of the giant planets, and into the inner Solar System. We find that at any one time, our model predicts that there should be roughly 12 objects in Encke-like orbits. However, it takes roughly 200 times longer to evolve onto an orbit like this than the typical cometary physical lifetime. Thus, we suggest that (i) 2P/Encke became dormant soon after it was kicked inward by Jupiter, (ii) it spent a significant amount of time inactive while rattling around the inner Solar System, and (iii) it only became active again as the ν₆ secular resonance drove down its perihelion distance.     

The orbit of the Dhajala meteorite

Observations of the trail caused by the meteorite which fell around Dhajala, Gujarat (India), on 28 January 1976 have been used to compute the probable orbit of the meteoroid in space. The cosmic ray effects in the meteorite fragments indicate high mass ablation (?90%), suggesting a high velocity (?20 km/sec) of entry into the Earth's atmosphere. The atmospheric trajectory is reasonably well documented and its deviation from the projected ground fallout can be understood in terms of the ambient wind pattern. The apparent radiant of the trail was at a point in the sky with right ascension 165°, declination +60°. Considering the errors in estimating the radiant, we get a range of orbits with a = 2.3 ± 0.8 AU, e = 0.6 ± 0.1, and i = 28 ± 4° with the constraints of a ? 1.5 AU and V_∞ < 25 km/sec (which causes nearly complete evaporation of the meteoroid). Taking V_∞ = 21.5 lm/sec as indicated by the measured mass ablation of the meteorite, the orbital elements are deduced to be $\text{a = 1.8}\text{AU}\text{, e = 0.59, i = 27°.6, ω = 109°.1, Ω = 307°.8,}\text{and}\text{q = 0.74}$.     

The Morávka meteorite fall: 4. Meteoroid dynamics and fragmentation in the atmosphere

Abstract— Detailed analysis of the fragmentation of the Morávka meteoroid during the atmospheric entry is presented. The analysis is based on the measurement of trajectories and decelerations of fragments seen in a video and at the locations of energetic fragmentation events from seismic data obtained at several stations in the vicinity of the fireball trajectory. About 100 individual fragments are seen on video frames. Significant deceleration of the fireball at heights of ?45 km revealed that the meteoroid had already fragmented into ?10 pieces with masses of 100–200 kg, though the fireball still appeared as a single object. At heights of 37–29 km, all primary fragments broke‐up again under dynamic pressures up to 5 MPa. The cascade fragmentation then continued, even though smaller pieces breaking off from the larger masses were increasingly decelerated and the dynamic pressure acting upon them decreased. At each fragmentation, a significant part of the mass was lost in the form of dust or tiny particles. This was the dominant process of mass loss. The continuous ablation due to melting and evaporation of the meteoroid surface was less efficient with a corresponding ablation coefficient of only 0.003 s² km‐². During fragmentation, some pieces achieved lateral velocities up to 300 m/s, about an order of magnitude more than can be explained by aerodynamic loading. The fragmentation continued even after ablation ceased, as demonstrated by the incomplete fusion crust covering all recovered fragments. We estimate that several hundreds of meteorites of a total mass of ?100 kg landed, mostly in a mountainous area not suitable for systematic meteorite searches. Six meteorites with a total mass of 1.4 kg were recovered up to the end of May 2003. Their positions are consistent with the calculated strewn field.