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1.
《Icarus》1987,69(3):550-556
A meteorite-dropping event was observed by the camera network in western Canada on February 6, 1980, precisely 3 years after the fall of the Innisfree meteorite. The orbits of the two objects are essentially identical, making this the first observational evidence for multiple falls from the same orbit. Minor differences in the argument of perihelion and longitude of the node were presumably caused by Earth perturbations at times of previous close encounters. An impact location near the town of Ridgedale, Saskatchewan, is indicated with a predicted mass of 1.8 kg for the object. The Ridgedale event was much less luminous than Innisfree, with a peak absolute panchromatic magnitude near −7.5 with no evidence for the multiple fragmentation observed for Innisfree. Considerations of the probability of detecting two related objects with the meteorite camera networks suggest that Innisfree (a brecciated LL chondrite) was a near-surface fragment from a recent parent object with a radius of several tens of meters. A campaign to locate the Ridgedale object is planned since its recovery would allow various comparisons of great interest with the Innisfree chondrite.  相似文献   

2.
In the five years from June, 1967, to June, 1972, a total of 99 meteorites were found in Roosevelt County, New Mexico and in adjoining Curry County. Of this number, 74 were found by one man. The finds include two achondrites, one pallasite, one carbonaceous chondrite, and 95 chondrites. They appear to represent more than 50 separate meteorite falls. The finding of a large number of meteorites in a small area provides data for an estimate of the probable quantity and average size of the meteorite specimens reaching the earth. The problems involved in allocating a total of 17 available local place names among more than 50 meteorite falls are discussed.  相似文献   

3.
A 701 kg iron meteorite has recently been discovered near the Mount Manning Range in Western Australia. The meteorite has a fan-shaped or delta wing configuration, one side being smooth and slightly concave with a well-defined fusion crust, whilst the other side is rough, convex and possesses numerous regmaglypts. It is probable that the meteorite pentrated much of the earth's atmosphere in an aerodynamically stable orientation, typical of the stalled attitude of delta wing aircraft. The meteorite is a member of Chemical Group 1C. A comparison of the chemical composition, surface features, microstructure and location of this meteorite with the Mount Dooling meteorite confirms that the find is a larger specimen of Mount Dooling. It is possible that other fragments of the Mount Dooling meteorite may be found in the Mount Manning Range region.  相似文献   

4.
Abstract— A large meteorite fall in southern Germany on April 6, 2002 was captured by camera stations of the European Fireball Network (EN) which routinely monitors the night sky over central Europe. From analysis of the images, a prediction on the geographic location of the meteorite strewn field could be made. Following systematic ground searches in difficult high‐mountain terrain, three fragments of a rare EL6 enstatite chondrite were recovered during search campaigns in the summers of 2002 and 2003. “Neuschwanstein” is the fourth meteorite fall in history that has been photographed by fireball networks and the fragments of which have been found subsequently. It is the first time since the beginning of the EN operation in the early sixties that the photographic observations have made a meteorite recovery possible.  相似文献   

5.
Abstract— Among the three large camera networks carrying out fireball observations through the seventies and eighties, the “European Fireball Network” is the last one still in operation. The network today consists of more than 34 all-sky and fish-eye cameras deployed with ～100 km spacing and covering an area of ～106 km2, in the Czech and Slovak Republics, Germany, as well as parts of Belgium, Switzerland, and Austria. Network operation results in ～10 000 image exposures per year, which represent on average 1200 h of clear sky observations—as imaging periods are restricted due to daylight, moonlight, and clouds. The cameras detect currently large meteors at a rate of ～50 per year; this is in good agreement with the encounter rates determined in previous fireball studies. From sightings of “meteorite candidates” (fireballs that may have deposited meteorites) and meteorite recoveries in the network area, we estimate that 15% of the influx of meteoritic matter is currently observed by the cameras, whereas <1% is recovered on the ground. Issues to be addressed by future fireball observations include the study of very large meteoroids (>1000 kg) for which statistics are currently very poor and an examination of their relationship to NEOs (near-Earth objects) identified by current NEO search programs.  相似文献   

6.
Abstract– We describe the geological, morphological, and climatic setting of the San Juan meteorite collection area in the Central Depression of the Atacama Desert (Chile). Our recovery activities yielded 48 meteorites corresponding to a minimum of 36 different falls within a 3.88 km2 area. The recovery density is in the range 9–12 falls km?2 depending on pairing, making it the densest among meteorite collection areas in hot deserts. This high meteorite concentration is linked to the long‐standing hyperaridity of the area, the stability of the surface pebbles (> Ma), and very low erosion rates of surface pebbles (approximately 30 cm Ma?1 maximum). The San Juan meteorite population is characterized by old terrestrial ages that range from zero to beyond 40 ka, and limited weathering compared with other dense collection areas in hot desert. Chemical weathering in San Juan is slow and mainly controlled by the initial porosity of meteorites. As in the Antarctic and other hot deserts, there is an overabundance of H chondrites and a shortage of LL chondrites compared with the modern falls population, suggesting a recent (< few ka) change in the composition of the meteorite flux to Earth.  相似文献   

7.
One of the most important steps in the recovery and study of meteorites is the concise naming of each fall so that confusion of one fall with another is avoided. The presently-used system of naming meteorite falls has been arrived at through an evolutionary process spurred on by necessity. The evolutionary history of the naming of meteorite falls is briefly sketched. Current naming practices are defined and the mounting problems of the present system are discussed. Measures for forestalling growing confusion in the naming of contiguous and overlapping falls, based upon a partial survey of curators of meteorite collections, are presented. A suggestion for the elimination of confusion in the dating of meteorite discoveries is included  相似文献   

8.
Abstract— The discovery of 154 meteorite fragments within an 11 km2 area of wind-excavated basins in Roosevelt County, New Mexico, permits a new calculation of the accumulation rate of meteorite falls at the Earth's surface. Thermoluminescence dating of the coversand unit comprising the prime recovery surface suggests the maximum terrestrial age of the meteorites to be about 16.0 ka. The 68 meteorite fragments subjected to petrological analyses represent a minimum of 49 individual falls. Collection bias has largely excluded carbonaceous chondrites and achondrites, requiring the accumulation rate derived from the recovered samples to be increased by a factor of 1.25. Terrestrial weathering destroying ordinary chondrites can be modelled as a first-order decay process with an estimated half-life of 3.5 ± 1.9 ka on the semiarid American High Plains. Having accounted for the age of the recovery surface, area of field searches, pairing of finds, collection bias and weathering half-life, we calculate an accumulation rate of 9.4 × 102 falls/a per 106 km2 for falls > 10 g total mass. This figure exceeds the best-constrained previous estimate by more than an order of magnitude. One possible reason for this disparity may be the extraordinary length of the fall record preserved in the surficial geology of Roosevelt County. The high accumulation rate determined for the past 16 ka may point to the existence of periods when the meteorite fall rate was significantly greater than at present.  相似文献   

9.
Photographic methods for the location of meteorite falls are restricted to hours of darkness and limited by weather conditions, resulting in a low detection rate. The importance of rapid recovery of newly-fallen meteorites leads to the consideration of seismic methods for the location of impact points. The purpose of this paper is to discuss the degree to which seismic networks can augment the detection of meteorites by conventional means. Factors involved in the generation of seismic waves are considered. The present sophistication of experimental and computational techniques in seismology should enable a microearthquake detection network to locate within 2 km the impacts of larger meteorites. The detection limits are determined by meteorite size and the configuration and instrumentation of the seismograph network.  相似文献   

10.
The Sutter's Mill C‐type meteorite fall occurred on 22 April 2012 in and around the town of Coloma, California. The exact location of the meteorite fall was determined within hours of the event using a combination of eyewitness reports, weather radar imagery, and seismometry data. Recovery of the first meteorites occurred within 2 days and continued for months afterward. The recovery effort included local citizens, scientists, and meteorite hunters, and featured coordination efforts by local scientific institutions. Scientific analysis of the collected meteorites revealed characteristics that were available for study only because the rapid collection of samples had minimized terrestrial contamination/alteration. This combination of factors—rapid and accurate location of the event, participation in the meteorite search by the public, and coordinated scientific investigation of recovered samples—is a model that was widely beneficial and should be emulated in future meteorite falls. The tools necessary to recreate the Sutter's Mill recovery are available, but are currently underutilized in much of the world. Weather radar networks, scientific institutions with interest in meteoritics, and the interested public are available globally. Therefore, it is possible to repeat the Sutter's Mill recovery model for future meteorite falls around the world, each for relatively little cost with a dedicated researcher. Doing so will significantly increase the number of fresh meteorite falls available for study, provide meteorite material that can serve as the nuclei of new meteorite collections, and will improve the public visibility of meteoritics research.  相似文献   

11.
A brilliant smoking meteor appeared in a clear sky in bright sunlight at 11 a.m., July 24, 1922 near Wynyard, Saskatchewan, Canada. The sight and thunderous sounds were witnessed by many hundreds of people in the rural district but no craters or meteorites were found at that time. Investigation and interviews with surviving witnesses in 1981 indicated a defined area near Big Quill Lake in which a meteorite may have fallen. Field investigation led to the Wynyard meteorite which had been found by a farmer sometime in the late 1960's at 104° 11'W 51°33'N. The Wynyard meteorite is a chondrite weighing 3.5 kg. It is moderately weathered and it may or may not have been part of the 1922 fall.  相似文献   

12.
The size distribution of 15,000 fragments from the Norton County meteorite was examined with size-frequency histogram. The size is measured in phi units. The estimates of the moments β1 and β2 of the empirical distribution were used for approximating the latter with a theoretical frequency curve in terms of the Pearson system It was suggested that the beta distribution obtained from the Pearson system can be regarded as a superposition of two simpler distributions: a near to normal one, corresponding to a slower process of fragmentation, and a power-law one, assumed to result from fast fragmentation process. … All meteorite falls are important but some are more important than others … … This fall was of outstanding importance because with its arrival the entire picture of the word meteorite as portrayed in the total of collections throughout the world was notably altered … H. H. Nininger, 1949. Significance of the Norton, Kansas, meteorite in Transactions of the Kansas Academy of Sciences 52 , 113.  相似文献   

13.
The recovery of several thousand meteorite fragments from Antarctica has led to speculation that accumulations may occur on the Earth's other major ice caps. Meteorites falling over the past 80,000 years on the Devon Island ice cap in the Canadian Arctic may be exposed at the surface near the ice cap margin. From the terrestrial meteorite flux, ice movement rates, and fragmentation factors it is calculated that 12,560 samples of 150 g mass are potentially concentrated in a 65 km2 zone along the northwest margin. A search of this region on foot and by helicopter in July, 1981, failed to recover any specimens. Although metre-sized gneissic boulders, plucked from the underlying Precambrian basement, were concentrated in this zone it is postulated that the unseasonal 30 cm snow cover on the ice prohibited the recognition of possible meteorite specimens, which may average only 5 cm in diameter.  相似文献   

14.
The statistics of meteorite falls and finds are presented. Histograms give the distribution of falls as a function of year, month and time of day. The distributions of the retrieved masses of fallen and found meteorites are given, as is also their distribution over the Earth's surface. The data for this analysis have been taken from the British Museum's Catalogue of Meteorites (1966) and Appendix (1977).  相似文献   

15.
Abstract— We explore the orbital dynamics of Earth‐crossing objects with the intent to understand the time scales under which an “orbital stream” of material could produce time‐correlated meteorite falls. These “meteoroid streams” have been suggested to be associated with three well‐known meteorite‐dropping fireballs (Innisfree, Peekskill, and P?íbram). We have performed two different analyses of the statistical significance of the “orbital similarity,” in particular calculating how often orbits of the same level of similarity would come from a random sample. Secondly, we have performed extremely detailed numerical integrations related to these three cases, and we find that if they were streams of objects in similar orbits, then they would become “decoherent” (in the sense that the day‐of‐fall of meteorites of these streams become almost random) on time scales of 104–105 yr. Thus, an extremely recent breakup would be required, much more recent that the cosmic ray exposure ages of the recovered falls in each case. We conclude that orbital destruction is too efficient to allow the existence of long‐lived meteoroid streams and that the statistical evidence for such streams is insufficient; random fall patterns show comparable levels of clustering.  相似文献   

16.
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.  相似文献   

17.
Data of sunspot groups at high latitude (35°), from the year 1874 to the present (2000 January), are collected to show their evolutional behaviour and to investigate features of the yearly number of sunspot groups at high latitude. Subsequently, an evolutional pattern of sunspot group number at high latitude is given in this paper. Results obtained show that the number of sunspot groups of a solar cycle at high latitude rises to a maximum value about 1 yr earlier than the time of the maximum of sunspot relative numbers of the solar cycle, and then falls to zero more rapidly. The results also show that, at the moment, solar activity described by the sunspot relative numbers has not yet reached its minimum. In general, sunspot groups at high latitude have not appeared on the solar disc during the last 3 yr of a Wolf solar cycle. The asymmetry of the high latitude sunspot group number of a Wolf solar cycle can reflect the asymmetry of solar activity in the Wolf solar cycle, and it is suggested that one could further use the high latitude sunspot group number during the rising time of a Wolf solar cycle, maximum year included, to judge the asymmetry of solar activity over the whole solar cycle.  相似文献   

18.
Abstract— Thirteen new meteorites and three meteorite inclusions have been analyzed. Their results have been incorporated into earlier published data for a comprehensive reference to all analyzed meteorites at the Smithsonian Institution. The six tables facilitate a convenient overlook of meteorite data. Table 1 presents an alphabetical list of analyzed meteorites, Table 2 chemical analyses of stony meteorites, Table 3 chemical analyses of iron meteorites, Table 4 elemental composition of stony meteorites, Table 5 average composition of carbonaceous chondrites and achondrites (falls and finds), and Table 6 presents average composition of H, L, LL, and Antarctic chondrites (falls and finds). The tables are available online at the journal's Web site http:meteoritics.org .  相似文献   

19.
流星监测网是小尺寸近地小天体撞击监测、判断陨石落点的主要工具. 提出了一种基于多站布局的全天视频相机组网监测系统, 并在江苏及周边构建了一个区域级原型系统, 实现了火流星监测组网控制、视频数据采集、数据处理及流星体定轨的完整流程. 通过1yr的实测运行表明, 该系统可观测流星极限视星等为-1.0等, 可以实现绝对星等-2.5等流星的完备检测; 根据监测数据得到火流星通量为2.68×10-7km-2 ·h-1;群流星和偶发流星占比分别为46%和54%,偶发流星中类小行星轨道和类彗星轨道比例分别为27.1%和72.9,统计结果与国际主要流星监测网相接近,验证了监测网系统在实际组网使用中的监测能力.  相似文献   

20.
Abstract— Statistics of witnessed and recovered meteorite falls found in Chinese historical texts for the period from 700 B.C. to A.D. 1920 are presented. Several notable features can be seen in the binned distribution as a function of time. An apparent decrease in the number of meteorite reports in the 18th century is observed. An excess of observed meteorite falls in the period from 1840 to 1880 seems to correspond to a similar excess in European data. A x2 probability test suggests that the association between the two data sets are real. Records of human casualties and structural damage resulting from meteorite falls are also given. A calculation based on the number of casualty events in the Chinese meteorite records suggests that the probability of a meteorite striking a human is far greater than previous estimates. However, it is difficult to verify the accuracy of the reported casualty events.  相似文献   

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