Meteorite Shower Research Articles

The Leedey, Oklahoma, chondrite: Fall, petrology, chemistry and an unusual Fe, Ni‐FeS inclusion

Abstract— The Leedey, Oklahoma, meteorite shower fell on 1943 November 25, following a fireball which was visible across much of southwestern Oklahoma and northcentral Texas. The shower produced 24 stones with a total mass of ∼51.5 kg. The stones formed a strewnfield ∼18 km in length in the same direction as the observed path of the meteor (N50°W). Leedey is classified as an L6(S3) ordinary chondrite. We report bulk major element chemical analyses from four separate laboratories. Leedey contains an unusual 6 by 8 mm composite Fe,Ni‐FeS grain, which is composed of a 3 mm kamacite grain adjacent to a 5 mm troilite grain. A 50–100 μm rim of high‐Ni (45–55 wt%) taenite (tetrataenite) occurs at the boundary between kamacite and troilite. A single, zoned pyrophanite grain is observed at the boundary between the inclusion troilite and host silicates. An origin as a foreign particle incorporated after metamorphism or during impact melting appears unlikely. This particle likely formed by a complex set of processes, including melting in the nebula, parent body metamorphism and reheating by later shock, mirroring the history of the host chondrite.

The fall of the St‐Robert meteorite

Abstract The St‐Robert (Québec, Canada) meteorite shower occurred on 1994 June 15 at 0h02m UT accompanied by detonations audible for >200 km from the fireball endpoint. The fireball was recorded by visual observers in Vermont, New York State, New Hampshire, Québec and Ontario as well as by optical and infrared sensors in Earth‐orbit. Penetration to an altitude of 36 km occurred ∼60 km to the northeast of Montreal, where the bolide experienced several episodes of fragmentation. A total of 20 fragments of this H5 chondrite, comprising a total mass of 25.4 kg, were recovered in an ellipse measuring 8 × 3.5 km. One fragment of the shower partially penetrated the aluminum roof of a shed.Interpretation of the visual and satellite data suggests that the fireball traveled from south‐southwest to north‐northeast, with a slope from the horizontal of 55°–61°. A statistical evaluation of the likely heliocentric orbits for the body prior to collision with the Earth, coupled with theoretical modeling of the entry, suggests an entry velocity in the range of 12.7–13.3 km/s; the meteoroid had moved in a low‐inclination orbit, with orbital perihelion located extremely close to the Earth's orbit.From satellite optical data, it is found that the photometric mass consumed during the largest detonation is ∼1200 kg. Estimation of the amplitude of the acoustic signal detected by the most distant observer yields a source energy near 0.5 kt TNT equivalent energy, which corresponds to a mass of order 10 metric tonnes. This measure is uncertain to approximately one order of magnitude. Theoretical modeling of the entry of the object suggests a mass near 1600 kg. Cosmogenic radionuclide activities constrain the lower initial mass to be ∼700 kg with an upper limit near 4000 kg. Seismic data possibly associated with the fireball suggest extremely poor coupling between the airwave and the ground.The total mass estimated to have reached the ground is ∼100 kg (in material comprising >55 g fragments), while the preatmospheric mass is found to be most probably in the range of 1200–2000 kg.

The luminescence flaw detection as a method for revealing iron meteorites microstructure features

Abstract The method of luminescence flaw detection has been applied to the detection of microstructure features of meteorites, minerals and samples of cosmic matter. The present paper considers the basic procedures of the method. We discuss main experimental results of the application of the method to meteorites from the Sikhote Alin meteorite shower, alongside with practical recommendations for its implementation. Besides, some other related questions are discussed.

The Mbale meteorite shower

Abstract— On 1992 August 14 at 12:40 UTC, an ordinary chondrite of type L5/6 entered the atmosphere over Mbale, Uganda, broke up, and caused a strewn field of size 3 × 7 km. Shortly after the fall, an expedition gathered eye witness accounts and located the position of 48 impacts of masses between 0.1 g and 27.4 kg. Short‐lived radionuclide data were measured for two specimens, one of which was only 12 days after the fall. Subsequent recoveries of fragements has resulted in a total of 863 mass estimates by 1993 October. The surfaces of all fragments contain fusion crust. The meteorite shower caused some minor inconveniences. Most remarkably, a young boy was hit on the head by a small specimen.The data are interpreted as to indicate that the meteorite had an initial mass between 400–1000 kg (most likely ∼1000 kg) and approached Mbale from Az = 185 ± 15, H = 55 ± 15, and V∞ = 13.5 ± 1.5/s. Orbital elements are given. Fragmentation of the initial mass started probably above 25 km altitude, but the final catastrophic breakup occurred at an altitude of 10–14 km. An estimated 190 ± 40 kg reached the Earth's surface minutes after the final breakup of which 150 kg of material has been recovered.

Mineralogy and chemistry of Rumuruti: The first meteorite fall of the new R chondrite group

Abstract— The Rumuruti meteorite shower fell in Rumuruti, Kenya, on 1934 January 28 at 10:43 p.m. Rumuruti is an olivine‐rich chondritic breccia with light‐dark structure. Based on the coexistence of highly recrystallized fragments and unequilibrated components, Rumuruti is classified as a type 3–6 chondrite breccia. The most abundant phase of Rumuruti is olivine (mostly Fa∼39) with about 70 vol%. Feldspar (∼14 vol%; mainly plagioclase), Ca‐pyroxene (5 vol%), pyrrhotite (4.4 vol%), and pentlandite (3.6 vol%) are major constituents. All other phases have abundances below 1 vol%, including low‐Ca pyroxene, chrome spinels, phosphates (chlorapatite and whitlockite), chalcopyrite, ilmenite, tridymite, Ni‐rich and Ge‐containing metals, kamacite, and various particles enriched in noble metals like Pt, Ir, arid Au. The chemical composition of Rumuruti is chondritic. The depletion in refractory elements (Sc, REE, etc.) and the comparatively high Mn, Na, and K contents are characteristic of ordinary chondrites and distinguish Rumuruti from carbonaceous chondrites. However, S, Se, and Zn contents in Rumuruti are significantly above the level expected for ordinary chondrites. The oxygen isotope composition of Rumuruti is high in δ17O (5.52 ‰) and δ18O (5.07 ‰).Previously, a small number of chondritic meteorites with strong similarities to Rumuruti were described. They were called Carlisle Lakes‐type chondrites and they comprise: Carlisle Lakes, ALH85151, Y‐75302, Y‐793575, Y‐82002, Acfer 217, PCA91002, and PCA91241, as well as clasts in the Weatherford chondrite. All these meteorites are finds from hot and cold deserts having experienced various degrees of weathering. With Rumuruti, the first meteorite fall has been recognized that preserves the primary mineralogical and chemical characteristics of a new group of meteorites. Comparing all chondrites, the characteristic features can be summarized as follows: (a) basically chondritic chemistry with ordinary chondrite element patterns of refractory and moderately volatile lithophiles but higher abundances of S, Se, and Zn; (b) high degree of oxidation (37–41 mol% Fa in olivine, only traces of Fe, Ni‐metals, occurrence of chalcopyrite); (c) exceptionally high Δ17O values of about 2.7 for bulk samples; (d) high modal abundance of olivine (∼70 vol%); (e) Ti‐Fe3+−rich chromite (∼5.5 wt% TiO2); (f) occurrence of various noble metal‐rich particles; (g) abundant chondritic breccias consisting of equilibrated clasts and unequilibrated lithologies.With Rumuruti, nine meteorite samples exist that are chemically and mineralogically very similar. These meteorites are attributed to at least eight different fall events. It is proposed in this paper to call this group R chondrites (rumurutiites) after the first and only fall among these meteorites. These meteorites have a close relationship to ordinary chondrites. However, they are more oxidized than any of the existing groups of ordinary chondrites. Small, but significant differences in chemical composition and in oxygen isotopes between R chondrites and ordinary chondrites exclude formation of R chondrites from ordinary chondrites by oxidation. This implies a separate, independent R chondrite parent body.

A recent meteorite shower in Antarctica with an unusual orbital history

The Antarctic meteorite collection has proved to be a source of many important discoveries, including a number of previously unknown or very rare meteorite types. A thermoluminescence (TL) survey of meteorite samples recovered by the 1988/89 European expedition and pre-1988 American expeditions to the Allan Hills Main blue ice field resulted in the discovery of 15 meteorites with very high TL levels ( > 100 krad at 250°C in the glow curvc). It is likely that these samples are fragments of a single meteoroid body which: (1) fell very recently and (2) experienced a decrease in orbital perihelia from ⩾ 1.1 AU to 1 AU within the last 10 5 yr. Carbon-14 data for two of the samples confirm their young terrestrial age compared to most Antarctic meteorites. Studies of the cosmogenic isotopes in at least one non-Antarctic meteorite which also has very high natural TL, Jilin, indicate that the meteorite experienced a multi-stage irradiation history, the most recent stage being 0.4 Ma in duration following a major break-up of the object. These meteorites, and the few equivalent modern falls, are the only documented samples from bodies which were recently in Earth-approaching (Amor) orbits (i.e., with perihelion > 1.0 AU), as opposed to the Earth-crossing (Apollo) orbits which are the source of most other meteorites. Their rarity indicates that such rapid orbit changes are unusual for meteoroid bodies and may be the result of isolated, large break-up events.

On the use of iron by the Eskimos in Greenland

Seventy-four iron objects were randomly selected from the archaeological items found in Greenland and have been stored in Copenhagen since about 1850. The objects consist of knives, ulos (knife used by Eskimo women for skinning), and harpoon blades, but also several nonworked fragments and some “hammerstones” were included. The objects were subjected to microscopical examination and x-ray microanalysis to determine their nature and mode of fabrication. The objects may be sorted into three groups. The majority of tools found north of Melville Bay were produced from small fragments of the Cape York iron meteorite shower that fell near Savigsivik over 2000 years ago. Half of the objects found in the Disko Bay area may be traced to occurrences of iron-bearing basalt, while the other half were produced from wrought iron. Some of these wrought-iron tools originated at Norse settlements and were apparently carried as far north as 77° by Norse ships as early as the 12th Century. Other wrought-iron tools were introduced by whalers, mainly of Dutch, Spanish and British origin, after about a.d. 1575. Some tools may derive from iron nails and hoops from wrecked ships. No signs of indigenous iron production have been detected.

Further finds of the Derrick Peak meteorite, Transantarctic Mountains, and implications for terrestrial age

Abstract— Nine additional iron meteorite fragments weighing a total of 72 kg were recovered from the Derrick Peak area by a Canterbury Museum geological party in late 1988. One iron was located in the Onnum Valley, 6 km south of the previous finds. Geochemical analysis indicates that all irons belong to a single meteorite shower, greatly increasing the known extent of the fall zone. Kamp and Lowe (1982) have previously estimated the terrestrial age of the meteorite from glacial geological evidence. The location of the 1988 finds supports Kamp and Lowe's interpretation that the meteorites lie in situ, but recent revisions of the chronology of Cenozoic glacial history of the region reduce the interpreted terrestrial age. An age of between Oxygen Isotope stages 6 and 2 is probable (190–125 to 35–12 ka BP). This conflicts with a terrestrial age estimate of 1.0 ± 0.1 Ma BP from cosmogenic radionuclides.

Ca+emission in the sunlit ionosphere

In the course of a program of twilight airglow observations from the McDonald Observatory in southwest Texas, the resonance fluorescence emissions from calcium ions were measured. In particular, twilight sequences were obtained during the period of December 19–22, 1987, which coincided with the Ursids meteorite shower. During this meteorite event the intensities of the Ca+ emission lines at 3934 Å increased to the point that the surface brightness profiles could be inverted to volume emission rate profiles. These profiles show evidence for strong spatial redistribution of the Ca+ over the course of three days. Prior to the onset of the meteorite activity, emissions from the Ca+ originate from below 100 km, on the occasions when the emissions are visible. By the evening of December 19 a peak is measurable at 108 km. On the morning of December 22, a high‐altitude peak was observed above 250 km, with a larger peak down at approximately 85 km. By the evening of December 22, the emission had substantially intensified, with the peak of the layer being at 80 km or below, but with emission being produced all the way up to at least 160 km. Observations of these emissions during meteor shower periods could provide a valuable tracer for the processes responsible for the transport of ions in the D, E, and F region, allowing the full altitude and latitude extent of the distribution to be determined.

The Torino, H6, meteorite shower

Abstract— A meteorite shower fell at Torino, Italy on 18 May 1988. Petrographic studies indicate that the stone is an H6 chondrite having features of moderate to severe shock. Chemical analyses of the meteorite are reported. Cosmic ray produced 3He, 21Ne and 126Xe yield an exposure age of about 48 Ma. The cosmic ray track densities in three fragments range between 1.8 to 5 × 105/cm2 suggesting about 99% mass ablation in the atmosphere.Twelve radioisotopes with half lives ranging between 5.6 days to 7.3 × 105 years have been measured with high precision (2 to 10%). Marginal signals were observed for several short‐lived nuclides and upper limits were obtained for the activity levels of eight radionuclides (24Na, 48Cr, 57Ni, 47Sc, 47Ca, 59Fe, 42Ar and 44Ti) some of which have not been hitherto detected in fresh falls. The data are generally consistent with the nuclide production by galactic cosmic rays when modulation due to the solar cycle is taken into consideration.The preatmospheric radius of the chondrite is estimated to be 20 cm, consistent with track densities and activity levels of 60Co, 26Al and other radionuclides.

A New Look at the Galim (a) and Galim (b) Meteorites

AbstractSmall stones were recovered from a meteorite shower observed in Cameroon on November 13, 1952. The majority are LL6 specimens, Galim (a), but one is a chondrule-rich enstatite chondrite, Galim (b). Petrology and mineral chemistry were determined on polished sections of both types. Galim (a) has undergone multiple brecciation. During the first, chromite apparently recrystallized in healed fractures under more reducing conditions than those which prevailed when the silicates recrystallized. Galim (b) shows some features of petrologic type 3 but differs considerably from the other unequilibrated E chondrites. It is suggested that Galim (a) and Galim (b) belong to the same meteorite shower.

On meteorite orbits

The new method of calculation of meteorite orbits based on the analysis of meteorite showers scattering patterns is suggested. Elements of orbits of 14 meteorites are listed. Correlations between oribt type and petrological type of meteorite are absent.

Meteoritic iron, telluric iron and wrought iron in Greenland

Seventyfour iron objects have been randomly selected from the Greenland archaeological material accumulated in Copenhagen since about 1850. The objects comprise knives, ulos and harpoon blades from most of West Greenland but also include several unworked fragments and some "hammerstones". The objects have been subjected to microscopic and X-ray microanalytic studies to determine their origin and mode of fabrication. The objects fall into three distinct groups. North of the Melville Bugt a majority of the tools have been produced from small fragments of the Cape York iron meteorite shower, that fell near Savigsivik more than 2000 years ago. Some of the meteoritic iron was carried across Smith Sund and as far as Hudson Bay, while transport south along the Greenland coast apparently was more sporadic. In the Disko Bugt area half of the objects may be traced to the occurrences of basalt with pea-sized iron inclusions, while the other half has been made of wrought iron. In the south all ten objects were produced from wrought iron. Some of the wrought iron tools originate from Norse settlements and have apparently been carried as far north as 76°-77° by Norse ships as early as the 12th century. Other wrought iron tools have been introduced by whalers, probably mainly of Dutch, Spanish and British origin, after about 1575 A.D. Some tools may have been manufactured from iron nails, and fittings from wrecked ships. No signs of indigenous iron production have been detected.

Relation between bright nights and meteoritic showers

From examination of published data, we find a strong correlation between the "bright-night" phenomenon and meteoritic showers. We show how the N atoms and nitric oxide molecules produced along meteor trails give a continuous emission due to NO2, the enhancement of which is at the origin of bright nights. At the same time the hydroxyl emission is enhanced.

FURTHER FINDS FROM THE MUNDRABILLA METEORITE SHOWER

Two new large iron meteorites, weighing 840 kg and 800 kg respectively, have been recovered from the Nullarbor Plain in the vicinity of the original Mundrabilla meteorite site, and are now at the Western Australian Museum in Perth. Numerous small knucklebone‐shaped irons were also found at Tookana Rock Hole in the vicinity of Eucla. X‐ray fluorescence spectrometry of these meteorites confirms that the additional finds are members of the Mundrabilla meteorite shower.

Planet(oid) core crystallisation and fractionation—evidence from the Agpalilik mass of the Cape York iron meteorite shower

Metallographic and chemical study of the Agpalilik mass (20 t) of the Cape York iron meteorite shower (totalling > 58 t), which belongs to the most populous group IIIAB, reveals evidence of the mode of crystallisation and fractionation of key elements consistent with a dentritic solidification of at least part of the once fully molten meteorite parent body metallic core. We assess systematic chemical gradients displayed by Ir and Au across an 85 cm section that is inferred to be perpendicular to the parent body gravitational field; these gradients are too large to be part of the fractionation resulting from the general fractional crystallisation radially outward of the IIIAB core. They are interpreted as representing a dendritic growth mode also explaining the characteristic elongated and orientated sulphide nodules found in Agpalilik and which signify trapped liquid of the late(st) stage(s) of crystallisation. Detailed mineralogic and chemical characterisation of the Agpalilik liquid-solid transformation products allow modelling of the entire crystallisation history commencing with dendritic metal precipitation through an ultimate troilite-taenite-Cu eutectic, representing a crystallisation range spanning approx. 1350-700°C. This constitutes a model system of the maximum potential fractionation of the parent body core, being a ‘telescoped’ forecasting of possible later events in the solidifying supernascent core pool. Adequate description of the salient phase relations requires the quaternary FeNiSP system; the essentials of the major element fractionation can be encompassed by the residual system FeNiS. Viewed as a study in analogo of possible ways of crystallisation-fractionation of the cores of other inner solar system bodies, a broader scope can be attached to these findings. Provided the case can be made for comparable chemistry with the modelled system, which is the case for most iron meteorite groups, for the Earth at least some evidence for a match is at hand, taking into consideration the inherent large ambient pressure differences. Some aspects of the present inner/outer core solidification/fractionation of the Earth's core would appear to be susceptible to interpretation within the confines of the principles of the present planet(oid) core crystallisation-fractionation model.

Meteorites in Antarctica — Statistics on falls, concentration, recovery and alteration on ice-sheet

The Antarctic meteorites are distributed on the blue-ice area surfaces in the ablation zone of the Antarctic ice-sheet, to where meteorites have been transported by the ice-flow within the ice-sheet from the wider accumulation zone. Among the Antarctic meteorite collection H- and L-chondrites are most abundant; this is also true in the non-Antarctic meteorite collection. Meteorite showers also are involved in the collection. Several new types of stony meteorites have been discovered from the Antarctic meteorite collection. The mass and shape of Antarctic meteorites are in agreement with those of resultant fragments of high-speed impact basaltic rocks. In Antarctica, small fragments of meteorite smaller than 1 kg in weight can easily be found and collected. The solidification and the gas retention ages of Antarctic meteorites also are concentrated around 4.5×10 9 years, but some of them are considerably younger. Their cosmic-ray exposure ages are extended up to 9×10 6 years and their terrestrial ages are 9×10 4-7×10 5 years.

Introductory remarks

For almost two centuries the study of meteorites has been associated with both technical and philosophical developments in various scientific disciplines, examples being the work of H. C. Sorby on optical mineralogy ( .1860-1880) and of V. M. Goldschmidt on the distribution of the chemical elements ( ca . 1920-1950). The most important of these developments probably took place during the decade from 1965 to 1974. Although it is no coincidence that this period includes the time of the Apollo landings on the Moon, chance also played a part by sending to Earth the Allende and Murchison meteorite showers, without which several important discoveries would have been delayed. The years from 1975 until the present have largely seen the expansion and consolidation of data and theories, with only a few real innovations. The time was thus ripe for a discussion on meteoritic research as an encouragement to further advances in knowledge.

The Dhajala meteorite

SummaryThe Dhajala meteorite shower, the latest recorded fall in India, comprises pieces fragmented near the lower limit of the break-up zone. The meteorite is a chondrite consisting of silica-rich chondrules making up to 34 vol.%, and fine-grained, Fe-Ni metal-rich groundmass admixed with a few irregular lithic fragments. Dhajala contains olivine of variable compositions, ortho- and clinopyroxenes, troilite, kamacite, taenite, chromite, and clear to opaque glass; magnetite occurs only in the fusion crust. The chondrules, which are of variable shape, mineral composition, and texture, represent different stages of quenching, leading to incomplete crystallization of minerals and some degree of disparity between norm and mode. Lithophile elements are less in Dhajala than in average chondrites. Two chemical analyses of Dhajala are presented and it has 27·10% total iron and 2·38 % sulphur (maximum). Chemical and petrological data indicate that it is an H3 olivine-bronzite chondrite. Evidence for the crystallization of chondrules from melt is overwhelming. Some chondrules have been permeated by later troilite and NiFe from the groundmass, which might have crystallized directly from a gaseous environment.

Laser sounding of atmospheric sodium interpretation in terms of global atmospheric parameters

Measurements of the night-time atmospheric sodium layer have been performed over a period of 3 years, using a Lidar facility set up at the Haute Provence Observatory. A photochemical and dynamical model of the upper atmosphere between 25 and 150 km has been used to simulate the behaviour of the atmospheric sodium and to compare it with the experimental results as derived from a statistical study of the spatial parameters of the layer. Evidence is given for a sodium source at the upper levels together with the determination of minimum values of the integrated eddy diffusion coefficient between 82 and 95 km. Stratifications occurring in the layer are related to the propagation of gravity waves at the corresponding heights. Sporadic enhancements of the total column abundance of sodium during meteoritic showers are reported giving evidence for a meteoritic origin of a part of the sodium.