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1.
A great volume of data has been accumulated thus far related to the photoregistration of the paths of meteor bodies in the terrestrial atmosphere. Most images have been obtained by four bolide networks, which operate in the USA, Canada, Europe, and Spain in different time periods. The approximation of the actual data using theoretical models makes it possible to achieve additional estimates, which do not directly follow from the observations. In the present study, we suggest an algorithm to find such parameters of the theoretical relationship between the height and the velocity of the bolide motion that help to fit observations along the luminous part of the trajectories in the best way. The main difference from previous studies is that the given observations are approximated using the analytical solution of the equations of meteor physics. The model presented in this study was applied to a number of bright meteors observed by the Canadian camera network and by the US Prairie network and to the Benésov bolide, which is one of the largest fireballs registered by the European network. The correct mathematical modeling of meteor events in the atmosphere is necessary for further estimates of the key parameters, including the extra-atmospheric mass, the ablation coefficient, and the effective enthalpy of evaporation of entering bodies. In turn, this information is needed by some applications, namely, those aimed at studying the problems of asteroid and comet security, to develop measures of planetary defense, and to determine the bodies that can reach Earth’s surface.  相似文献   

2.
The extra-atmospheric masses of meteoric bodies have previously been determined using the so-called photometric formula, by integrating the luminosity along the visible portion of the trajectory. On the other hand, the mass of a meteoroid characterizes the braking height and intensity of the meteoroid in the atmosphere. Some studies note a substantial disagreement between the masses obtained in these two ways, using bolides of the European Bolide Network and of the US Prairie Network as examples. In nearly all cases, the photometric mass exceeds the mass determined from the braking intensity by an order of magnitude or more. Two explanations were suggested for this fact. According to one of them, a swarm of fragments, similar in size, rather than a single body is moving. This swarm brakes as an individual fragment, while it glows as a collection of fragments; i.e., it is much brighter than an individual fragment. The extra-atmospheric mass is determined here by properly fitting the parameters describing the braking of the meteor along the entire visible section of the trajectory. The results obtained for the bolides of the Canadian Network confirm again that the photometric approach is not tenable.  相似文献   

3.
Abstract— We present data for 259 meteoric fireballs observed with the Canadian camera network, including velocities, heights, orbits, luminosities along each trail, estimates of preatmospheric masses and surviving meteorites (if any) as well as membership in meteor showers. Some 213 of the events comprise an unbiased sample of the 754 fireballs observed in a total of 1.51 × 1010 km2 h of clear-sky observations. The number of fireballs and the amount of clear sky in which they were recorded are given for each day of the year. We find at least 37% of the unbiased sample are members of some 15 recognized meteor showers. Preatmospheric masses, based on an assumed luminous efficiency of 0.04 for velocities >10 km s?1, range from 1 g for some very fast fireballs up to hundreds of kilograms for the largest events. We present plots and equations for the flux, as a function of initial mass, for the entire group of fireballs and for some subgroups: meteorite-dropping objects; meteor shower members; groups that appear to be mainly of asteroidal or cometary origin; and for very fast objects. For masses of a few kilograms, asteroidal objects outnumber cometary ones. Cometary objects attain greater peak brightness than asteroidal ones of equal mass largely due to higher velocity, but also because they fragment more severely. For 66 fireballs, we estimate the meteoroid density using photometric and dynamic masses. Presumed cometary objects have typical densities near 1.0, while asteroidal values show two groups that suggest meteoroids similar to carbonaceous and ordinary chondrites. Our basic data may be used by others for further studies or to reexamine our results using assumptions different from those employed in this paper.  相似文献   

4.
We propose a new approach for studying the radiation of a fireball, one of the main processes which occur when the meteor body enters the planetary atmosphere. The only quantities which directly follow from the available observations are the fireball brightness, its height above sea level, the length along the trajectory, and as a consequence its velocity as a function of time. Other important parameters like meteoroid’s mass, its shape, bulk and grain density, temperature remain unknown. The present study takes recent results in fireball aerodynamics and considers them together with the classical postulate that a fraction of the meteoroid kinetic energy is transformed into radiation during its flight. This gives us a new analytical dependence, which in particular shows that the fireball luminosity in general is proportional to the body pre-entry mass value, its initial velocity to the power of 3, and the sine of the slope between horizon and trajectory. Research helps in finding an answer to the general important question: Which fraction of the fireball kinetic energy is transformed into light during meteoroid drag and ablation in the atmosphere?  相似文献   

5.
Minor bodies that, at the present stage, have orbital characteristics similar to those of the Pribram meteorite and that differ from it in the date of activity of the radiants by no more than a 1.2-month period in either direction were detected on the basis of catalog data on the orbits of asteroids, individual fireballs, and fireball and meteor streams obtained from photographic observations. The following objects comprising the Prbram family are among such minor bodies: three asteroids (1863, 4486, and J98S70J) of the Apollo group, three fireball streams, five meteor streams, and ten fireballs. This extensive system of bodies consists of three branches: a Northern (N), an Ecliptical (Q), and a Southern (S) Branch. The family of meteor streams associated with the periodic comet Pons–Winnecke appears to be related to this family. Thus, there emerges an intricate complex of small bodies that is similar to the well-known Taurid complex. In the distribution of various populations of minor bodies according to the quantity c of the Tisserand criterion, both of these complexes of minor bodies, like the group of cometoids (or cometlike asteroids), are situated in the region of unstable motion or, to be more exact, near the gap that arises in the L 2 and L 3 collinear points of libration.  相似文献   

6.
We explored how justifiable the use of a model with a constant mass loss parameter as applied is to real meteor events. The model with variable mass loss parameter used in this work is based on the calculation of the luminosity parameter and of the radiative heat exchange coefficient at separate points of trajectory. Agreement between models with constant and variable mass loss parameters is demonstrated by the example of observations of two big meteor bodies (MORP 219 and MORP 872).  相似文献   

7.
Abstract Anomalous sounds from large meteor fireballs, anomalous because they are audible simultaneously with the sighting, have been a matter for debate for over two centuries. Only a minority of observers perceive them. Ten years ago a viable physical explanation was developed (Keay, 1980a) which accounts for the phenomenon in terms of ELF/VLF radiation from the fireball plasma being transduced into acoustic waves whenever appropriate objects happen to be in the vicinity of an observer. This explanation has now been verified observationally and supported by other evidence including the study of meteor fireball light curves reported here.  相似文献   

8.
Jack D. Drummond 《Icarus》1982,49(1):143-153
A compilation of theoretical meteor radiants is presented for all numbered (through 2525) asteroids which approach the Earth's orbit to within 0.20 AU. On the basis of orbital similarity, asteroids associated with current meteor streams and Prairie Network fireballs are listed; plausible associations with medieval fireball radiants are also given. The best defunct comet candidates in terms of meteoric evidence appear to be 2101 Adonis and 2201 1947XC. Asteroids which may be either extinct comets or perturbed main belt asteroids accompanied by collisional debris (represented by fireballs) are 1917 Cuyo, 2202 Pele, 2061 Anza, and 2340 Hathor. 1566 Icarus and 1981 Midas are the only asteroids whose orbits approach to less than 0.07 AU of the Earth's orbit, have a northern radiant, and still show no certain meteoric activity. The majority of Atens, Apollos, and Amors do not pass sufficiently close (<0.07 AU) to the Earth's orbit for a reasonable expectation of meteoric activity, or have radiants south of ?20° declination, requiring southern hemisphere observations.  相似文献   

9.
The existing methods for determining the extra-atmospheric mass of meteor bodies from observations of their movement in the atmosphere allow a certain arbitrariness. Active attempts to overcome the discrepancy between the results of calculations based on different approaches often lead to physically incorrect conclusions. A way out is to laboriously accumulate the estimates and computation results and to consistently remove ambiguities. To correctly interpret the observed brightness of a meteor, one should use contemporary methods and the results of physical studies of the emitting gas. In the present work, the extra-atmospheric masses of small meteoroids of the Prairie and Canada bolide camera networks were calculated from the observed braking. It turned out that, in many cases, the conditions of movement of meteor bodies in the atmosphere corresponded to a free molecular airflow about a body. The so-called dynamic mass of the bodies was estimated from the real densities of the meteoroid material, which corresponded to monolithic water ice and stone, and for the proper values of the product of the drag coefficient and shape factor. When producing the trial function for the body trajectories in the “velocity-altitude” variables, we did not allow for fragmentation explicitly, since it is less probable for small meteoroids than for large ones. As before, our estimates differ substantially from the photometric masses published in the corresponding tables.  相似文献   

10.
The state of the art in the theory of processing of visual observations of meteor streams is considered. Of the three widely used methods of visual-observation processing, the method developed at the Engel'gardt Astronomical Observatory provides the highest accuracy of conversion to the hourly rate of meteors. For the first time, the dependence of the fine structures of the Geminid, Perseid, and Leonid streams on the minimum detected mass of meteor bodies is obtained from visual observations. A shift in the position of an activity maximum for smaller masses in the direction of lower solar longitudes is confirmed for the Geminids. For the Perseids, an activity maximum for meteor bodies with mass exceeding 0.01 g, sets in earlier than for smaller particles. In the Leonid swarm, no correlation was found between the node longitude of the mean swarm orbit and mass of meteor bodies.  相似文献   

11.
Since 2006, systematic double-station photographic observations of fireballs using all-sky cameras equipped with Zeiss Distagon “fisheye” objectives (f/3.5, f = 30 mm) with a 180° field of view have been carried out at two observatories, Gissar (GisAO) and Sanglokh (IAOS), of the Institute of Astrophysics of the Tajik Academy of Sciences. In the method of astrometric reduction of fireball photographs, the empirical formulae for converting the measured coordinates to horizontal celestial coordinates are used. These formulae contain 12 unknown constants to be determined by the least-squares method and the iteration method. Such an approach enables the determination of the coordinates of an object at any point of the celestial hemisphere with a precision close to the theoretical limit whose value is quite comparable with the measurement errors. In the photometric reduction, the dependence of the measured width of the diurnal star trails on their magnitudes was used. As a result of astrometric and photometric reduction of the double-station photographs of five fireballs, the data on atmospheric trajectories, the coordinates of radiants, orbits in interplanetary space, light curves, and photometric masses of meteoroids which produced fireballs were obtained, and the belonging of fireballs to the known meteor showers was determined as well.  相似文献   

12.
Abstract– A new approach has been formulated to solve for the straight line trajectory of a meteor through the atmosphere when given multiple camera views of the meteor’s luminous track. Using a motion propagation model in 3‐D space plus time, and iteratively solving for all free model parameters simultaneously, one can obtain a fully coupled solution to the apparent radiant direction, 3‐D begin position, atmospheric entry speed, deceleration terms, and timing offsets when using data from unsynchronized video cameras. A Monte Carlo component adds empirical error estimation for each of the key model parameters computed. This multiparameter fitting method extends the allowable collection geometries for meteor trajectory estimation to lower convergence angles between camera‐meteor‐camera lines of sight and smaller site separation distances.  相似文献   

13.
Problems of hypervelocity interaction of large bodies with the Earth's atmosphere has attracted more attention during last few years. Several new concepts of dynamical explosive fragmentation of strong interplanetary bodies at extremely low heights under dynamic pressures of hundreds of Mdyn/cm2 were published. Comparison of these theoretical models with precise observations has not yet been done, because data on atmospheric penetration of large bodies are not available.Single body theory with sudden gross-fragmentation was successfully applied to photographic observations of fireballs. The largest bodies observed have sizes up to several meters. The highest dynamic pressure acting on these observed bodies reached slightly over 100 Mdyn/cm2. All these photographed fireballs follow theoretical concepts of motion of either the single-body or the single-body with gross-fragmentation under dynamic pressures in the range from 1 to 12 Mdyn/cm2. When this theory has been applied to photographic observations, typical standard deviation of the distance flown in the trajectory has been found in a range of 10 to 30 m for one observed distance corresponding also to the geometrical precision of the observations. This model can explain all good observations of atmospheric trajectories of meteoroids up to initial sizes of several meters with high precision. Also the three photographed and one videorecorded meteorite falls fit to this concept completely.The most important phenomenon of atmospheric motion of meteoroids up to several meters in size is the ablation with final stage of hot vapor from ablated material. Spectral records of meteoroids up to several meters in size, down to a height of 16 km and for various velocities show overwhelming radiation of rather low excited metalic atoms (several eV; temperatures 3000 to 5000 K) in the pass-band of visible light. Radiation from high excited atoms of either atmospheric or ablational origin forms only an insignificant part of visible radiation.Contrary to this regime, theories of very large bodies contain ablation mostly in the form of explosive fragmentation. Ablation at higher heights is negligible. This absence of classical ablation and fragmentation at low dynamic pressures for large bodies (contrary to observations of smaller bodies) brings the body to lower heights without too much change of size and makes thus the dynamic pressure much higher than in reality. In any case the change of body dynamics and radiation going from sizes of several meters (observed regime) to sizes of several tens of meters (hypothetical regime) may be crucial for our understanding of dynamics and radiation of large body penetration through the low atmosphere to the Earth's surface. Observations of atmospheric trajectory of these bodies with sufficiently high precision are extremely needed.  相似文献   

14.
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15.
We investigate the possibility of detectable meteor shower activity in the atmosphere of Venus. We compare the Venus-approaching population of known periodic comets, suspected cometary asteroids and meteor streams with that of the Earth. We find that a similar number of Halley-type comets but a substantially lesser population of Jupiter family comets approach Venus. Parent bodies of prominent meteor showers that might occur at Venus have been determined based on minimum orbital distance. These are: Comets 1P/Halley, parent of the η Aquarid and Orionid streams at the Earth; 45P/Honda-Mrkos-Pajdusakova which currently approaches the venusian orbit to 0.0016 AU; three Halley-type comets (12P/Pons-Brooks, 27P/Crommelin and 122P/de Vico), all intercepting the planet's orbit within a 5-day arc in solar longitude; and Asteroid (3200) Phaethon, parent of the December Geminids at the Earth. In addition, several minor streams and a number of cometary asteroid orbits are found to approach the orbit of Venus sufficiently close to raise the possibility of some activity at that planet. Using an analytical approach described in Adolfsson et al. (Icarus 119 (1996) 144) we show that venusian meteors would be as bright or up to 2 magnitudes brighter than their Earth counterparts and reach maximum luminosity at an altitude range of 100-120, 20-30 km higher than at the Earth, in a predominantly clear region of the atmosphere. We discuss the feasibility of observing venusian showers based on current capabilities and conclude that a downward-looking Venus-orbiting meteor detector would be more suitable for these purposes than Earth-based monitoring. The former would detect a shower of an equivalent Zenithal Hourly Rate of at least several tens of meteors.  相似文献   

16.
The comparison of the Tunguska body explosion with the effect of terminal flares of meteors and fireballs leads us to the conclusion that these events are of a similar nature but differ only by their scale. We consider that the dynamics of progressive breaking and evaporation of meteoric bodies during their entry into the terrestrial atmosphere could explain the terminal burst. An extremely porous body model for the Tunguska meteorite was analysed and rejected as unsatisfactory. The realistic values of the initial velocity (～30 km/sec) and of the inclination angle for the Tunguska's trajectory (5–15°) give orbital elements not in contradiction with the cometary origin of the Tunguska body.  相似文献   

17.
Abstract— Precise atmospheric trajectories including dynamic and photometric data on thirteen of the brightest Leonid fireballs have been determined from the double‐station photographic observations of Leonid meteors during the ground‐based expedition to China in 1998 November. the expedition was organized as a collaboration between the dutch and chinese academy of sciences and was supported by the leonid multi‐instrument aircraft campaign (mac) program (jenniskens and butow, 1999). All data presented here were taken at Xinglong Observatory and at a remote station, Lin Ting Kou near Beijing, on the night of 1998 November 16/17. At the Xinglong station, photographic cameras were accompanied by an all‐sky television camera equipped with an image intensifier and 15 mm fish‐eye objective in order to obtain precise timings for all observed meteors up to magnitude +2. Whereas beginning heights of photographed meteors are all lower than 130 km, those observed by the all‐sky television system are at ～160 km, and for three brightest events, even > 180 km. Such high beginnings for meteors have never before been observed. We also obtained a precise dynamic single‐body solution for the Leonid meteor 98003, including the ablation coefficient, which is an important material and structural quantity (0.16 s2 km?2). From this and from known photometry, we derived a density of this meteoroid of 0.7 g/cm3. Also, all PE coefficients indicate that these Leonid meteors belonged to the fireball group IIIB, which is typical for the most fragile and weak interplanetary bodies. From a photometric study of the meteor lightcurves, we found two typical shapes of light curves for these Leonid meteors.  相似文献   

18.
中国古代火流星记录的统计分析   总被引：1，自引：0，他引：1  
本文对中国古代火流星记录,按年统计,用功率谱这一数学方法对它们进行分析。结果发现声音是衡量火流星起源的一个重要参数。有声音的火流星具有170.6±0.0,102.4±0.0,66.1±2.2,27.3±0.4,23.3±0.0,17.9±0.4,14.8±0.1,12.4±0.1,10.5±0.3年的可能周期。有声火流星与陨石坠落周期基本相同,是与陨石同源的,来自小行星带。我们认为影响有声火流星和陨石下落的因素是太阳辐射引起的Yarkovsky效应和木星摄动。有声火流星的10.5±0.3,23.2±0.0,66.1±2.2年周期与Yarkovsky效应有关。12.4±0.1,17.9±0.4,102.4±0.0,170.6±0.0周期与木星摄动有关。至于14.8±0.1,27.3±0.4的周期,可能是木星摄动与Yarkovsky效应联合作用或其他原因所致。  相似文献   

19.
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.  相似文献   

20.
The ballistic coefficients and ablation parameters of Prairie Network (United States) fireballs are determined by the best fitting in velocity–height variables. The braking trajectories based on the model of successive destruction with ablation are used as the test functions. The fitting accuracy of the observed trajectory was found to be approximately the same for the model of successive destruction and for the model of motion of a single body. At least, the fitting accuracy allows us neither to confirm nor to reject the fragmentation of meteoroids within the luminous segment of the trajectory. The previously noted excess of the observed luminosity of the fireballs studied here (Popova, 1997) over the value calculated for the dynamical mass, which was estimated from the model of a single body (Kulakov and Stulov, 1992), can be explained by deviations of the meteoroid shapes from a sphere.  相似文献   

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