In situ identification,pairing, and classification of meteorites from Antarctica through magnetic susceptibility measurements

Abstract— We report on the effectiveness of using magnetic measurements in the search for meteorites on the Antarctic ice sheet, which is thus far the Earth's most productive terrain. Magnetic susceptibility measurements carried out with a pocket meter (SM30) during the 2003/04 PNRA meteorite collection expedition to northern Victoria Land (Antarctica) proved to be a rapid, sensitive, non‐destructive means for the in situ identification, pairing, and classification of meteorites. In blue ice fields characterized by the presence of moraines and glacial drifts (e.g., Miller Butte, Roberts Butte, and Frontier Mountain), magnetic susceptibility measurements allowed discrimination of meteorites from abundant terrestrial stones that look like meteorites thanks to the relatively high magnetic susceptibility of the former with respect to terrestrial rocks. Comparative measurements helped identify 16 paired fragments found at Johannessen Nunataks, thereby reducing unnecessary duplication of laboratory analyses and statistical bias. Following classifications schemes developed by us in this and previous works, magnetic susceptibility measurements also helped classify stony meteorites directly in the field, thereby providing a means for selecting samples with higher research priority. A magnetic gradiometer capable of detecting perturbations in the Earth's magnetic field induced by the presence of meteorites was an efficient tool for locating meteorites buried in snow along the downwind margin of the Frontier Mountain blue ice field. Based on these results, we believe that magnetic sensors should constitute an additional payload for robotic search for meteorites on the Antarctic ice sheet and, by extension, on the surface of Mars where meteorite accumulations are predicted by theoretical works. Lastly, magnetic susceptibility data was successfully used to crosscheck the later petrographic classification of the 123 recovered meteorites, allowing the detection of misclassified or peculiar specimens.     

The Meteoritical Bulletin,No. 102

Meteoritical Bulletin 102 contains 3141 meteorites including 12 falls (Boumdeid (2003), Boumdeid (2011), Braunschweig, Chelyabinsk, Dongyang, Draveil, Heyetang, Indian Butte, Katol, Ladkee, Ouadangou, Xining), with 2611 ordinary chondrites, 264 HED achondrites, 124 carbonaceous chondrites, 30 ureilites, 20 Martian meteorites, 16 primitive achondrites, 16 Rumuruti chondrites, 15 mesosiderites, 12 iron meteorites, 10 lunar meteorites, 9 enstatite chondrites, 4 enstatite achondrites, 4 Pallasites, 4 ungrouped achondrites, and 2 angrites, and with 1708 from Antarctica, 956 from Africa, 294 from South America, 126 from Asia, 47 from North America, 6 from Europe (including Russia), and 4 from Oceania. Information about approved meteorites can be obtained from the Meteoritical Bulletin Database (MBD) available on line at http://www.lpi.usra.edu/meteor/ .     

Late accretion and lithification of chondritic parent bodies: Mg isotope studies on fragments from primitive chondrites and chondritic breccias

Abstract— Recent results of isotopic dating studies (¹⁸²Hf‐¹⁸²W, ²⁶Al‐²⁶Mg) and the increasing number of observed igneous and metamorphosed fragments in (primitive) chondrites provide strong evidence that accretion of differentiated planetesimals predates that of primitive chondrite parent bodies. The primitive chondrites Adrar 003 and Acfer 094 contain some unusual fragments that seem to have undergone recrystallization. Magnesium isotope analyses reveal no detectable radiogenic ²⁶Mg in any of the studied fragments. The possibility that evidence for ²⁶Al was destroyed by parent body metamorphism after formation is not likely because several other constituents of these chondrites do not show any metamorphic features. Since final accretion of a planetesimal must have occurred after formation of its youngest components, formation of these parent bodies must thus have been relatively late (i.e., after most ²⁶Al had decayed). Al‐Mg isotope data for some igneous‐textured clasts (granitoids and andesitic fragments) within the two chondrite regolith breccias Adzhi‐Bogdo and Study Butte reveal also no evidence for radiogenic ²⁶Mg. As calculated from the upper limits, the formation of these igneous clasts, the incorporation into the parent body regolith, and the lithification must have occurred at least 3.8 Myr (andesite in Study Butte) and 4.7 Myr (granitoids in Adzhi‐Bogdo) after calcium‐aluminum‐rich inclusions (CAI) formation. The absence of ²⁶Mg excess in the igneous inclusions does not exclude ²⁶Al from being a heat source for planetary melting. In large, early formed planetesimals, cooling below the closure temperature of the Al‐Mg system may be too late for any evidence for live ²⁶Al (in the form of ²⁶Mg excess) to be preserved. Thus, growing evidence exists that chondritic meteorites represent the products of a complex, multi‐stage history of accretion, parent body modification, disruption and re‐accretion.     

Review of the Barringer crater studies and views on the crater’s origin

The first scientific studies of Barringer crater, Arizona, USA (also known as the Coon Butte crater), began more than a century ago; however, views on the crater’s origin have been contradictory. At the beginning of the 20th century, D.M. Barringer, a mining engineer, became interested in the possibility of finding large useable iron masses in this crater and searched for these masses for more than 25 years, standing up for the idea of the crater’s meteoric origin, contrary to the objections of opponents who tried to indicate that the crater was caused by terrestrial geological processes. Mining, accompanied by different scientific works, made it possible to obtain reliable data on the structure and impact origin of the crater; however, attempts to find meteorite iron deposits in this crater were unsuccessful. Barringer crater was the first object on the Earth where purposeful studies were performed for many decades and made it possible to develop many criteria of the impact origin of circular geological structures and mechanisms of formation of these structures, as well as to compare this crater with similar morphostructures on the surfaces of other planets. These studies have played an important role in the formation and development of the theory of impact cratering, which has been generally acknowledged in present-day science.     

NEW SPECIMENS FROM THE FAUCETT,MISSOURI, METEORITE LOCALITY

In December, 1966, Brookins and Twiss reported the finding of two specimens of an olivine-bronzite chondrite near Faucett, Missouri. Since that date, six additional specimens have been found. Another probable specimen was found but later lost. This paper describes the circumstances of all nine finds and presents a map of the discovery sites.     

Carbon,nitrogen, and oxygen abundances in Procyon,Sun, and Arcturus

Ci, Ni, andOi permitted and forbidden lines in the near-infrared spectra of Procyon (F5 IV–V), Sun (G2 V), and Arcturus (K2 IIIp) have been analyzed to determine their carbon, nitrogen, and oxygen abundances. Procyon is found to have normal abundances while Arcturus is found to have an enhanced nitrogen abundance by a factor of 1.03 dex relative to the Sun. The dependence of the derived abundances on the effective temperature and luminosity is investigated.Much of the work reported here was contained in the Ph.D. thesis of the author submitted to the Istanbul University, Turkey, in 1986.     

THE GALATIA,KANSAS, CHONDRITE

The Galatia meteorite was found in August, 1971, approximately 7 km ENE of Galatia, Barton County, Kansas (98° 53′W., 38° 39.5′N). The single stone weighed 23.9 kg and is partially weathered. Olivine (Fa_24.9) and pyroxene (Fs_20.9) compositions indicate L-group classification, and textural observations indicate that the stone is of petrologic type 6. Galatia is similar in many respects to the Otis L6 chondrite (found 20 km to the west), but it does not have the brecciated structure of Otis and, thus, it is not part of the same fall.     

Absorption gradient in galaxies,V

The same procedure mentioned in Papers I, II, III for studying the surface distribution of dark clouds is used to study the same phenomenon in the galaxies NGC 253, NGC 2841, NGC 5321, NGC 5194, and NGC 5195 radially and angularly. The general form (sinusoidal distribution function) found earlier is still representative for the present results. Internal absorption was found to vary along these two variables (radially and angularly) in the same way as was found earlier for M31 (the papers cited at the end) which may lead to the assumption of universality of this phenomenon.     

Spectral reflectance properties of carbonates from terrestrial analogue environments: Implications for Mars

Spectroscopic analysis of carbonate-bearing samples from a variety of terrestrial environments provides important insights into spectroscopy-based investigations of Mars designed to detect the presence of carbonate minerals. In order to better address the spectral detectability of carbonates on Mars, we examined the spectral reflectance properties of carbonates and carbonate-bearing lithologies from a variety of terrestrial environments, including impact structures (Haughton, St. Martin, Eagle Butte), landslides (Frank), quarrying operations (Hecla), carbonates affected by weathering (Haughton, East German Creek), and sulfide-sulfate-carbonate assemblages (Central Manitoba). The goal is to identify processes and environments that can affect spectroscopy-based carbonate detection, for more detailed follow-on studies. Common carbonates appear to be stable, from a spectroscopic perspective, to various tectonic processes. Iron oxides/hydroxides do not appear to significantly affect spectral detectability of carbonates, as the spectrum-altering effects of these phases are largely restricted to the region below ∼1 μm, while useful carbonate absorption bands occur longward of ∼1.8 μm. Carbonate detection and characterization in the 0.35-2.5-μm region is largely restricted to a single absorption feature in the 2.3-μm region, which can be problematic for robust carbonate identification. While tectonic processes and iron oxide/hydroxide staining do not appear to significantly impair carbonate detection based on the 2.3-μm region absorption band, a number of other factors can affect carbonate detection. These include the fact that this absorption band is weak compared to many other minerals, a number of other minerals also exhibit absorption bands in this wavelength region (leading to possible misidentifications), and that even small abundances of minerals that absorb strongly in this region will reduce the strength of the carbonate absorption band. Identifying the nature of accessory minerals associated with carbonates can be used to constrain possible formation environments. Ongoing research at carbonate-bearing terrestrial analogue sites will continue to provide new insights into the occurrence and detection of carbonates on Mars.     

X-ray,Hα, and radio observations of the two-ribbon flare of 16 May, 1981

The paper is a contribution to the study of two-ribbon flares. A variety of observational material, i.e. Hα pictures, radio spectrum in the frequency band of 150–1000 MHz, radio map at 6 cm, fluxes at other frequencies, magnetograms and X-ray flux in a broad energy interval, enabled us to study the development of the 16 May, 1981 flare. The onset of the flare could be described by the model of Van Tend and Kuperus. A diminishing of the magnetic shear during the activation of the filament was observed. From radio and X-ray data it was found that pulsed acceleration took place in the region under the rising filament, the electrons propagating in a limited region both upwards to greater heights and downwards into the footpoints. Internal oscillations of the filament were observed. A manifestation of the primary process of interplanetary shock-wave generation was found. The 6 cm radio sources could be localized in the footpoints of magnetic loops.     

The Anoka,Minnesota, Iron Meteorite*

Abstract The Anoka, Minnesota, meteorite was found on the Joe Fields Farm at location coordinates 45° 12′ N, 93° 26′ W. It is a fine octahedrite distinguished by large fields of dense plessite. The chemical analysis of the meteorite is 84.9 percent iron, 11.75 nickel and 0.51 cobalt.     

THE SEMINOLE,GAINES CO., TEXAS,METEORITE

The Seminole Meteorite was found near Seminole, Texas in 1961 and recognized as a meteorite in 1963. Two fragments weighing a total of 41.1 kg were recovered. Analyses showed these to be fragments of a single black olivine-bronzite, or H4-group chondrite, showing brecciation and a moderate number of individual chondrules     

Target rocks,impact glasses,and melt rocks from the Lonar impact crater,India: Petrography and geochemistry

Abstract— The Lonar crater, India, is the only well‐preserved simple crater on Earth in continental flood basalts; it is excavated in the Deccan trap basalts of Cretaceous‐Tertiary age. A representative set of target basalts, including the basalt flows excavated by the crater, and a variety of impact breccias and impact glasses, were analyzed for their major and trace element compositions. Impact glasses and breccias were found inside and outside the crater rim in a variety of morphological forms and shapes. Comparable geochemical patterns of immobile elements (e.g., REEs) for glass, melt rock and basalt indicates minimal fractionation between the target rocks and the impactites. We found only little indication of post‐impact hydrothermal alteration in terms of volatile trace element changes. No clear indication of an extraterrestrial component was found in any of our breccias and impact glasses, indicating either a low level of contamination, or a non‐chondritic or otherwise iridium‐poor impactor.     

THE ELLA ISLAND,GREENLAND, CHONDRITE

The Ella Island, Greenland, meteorite was found in August of 1971. Electron microprobe study of the meteorite revealed it to contain olivine, low-calcium pyroxene, high-calcium pyroxene, plagioclase, kamacite, taenite, chromian-hercynite and troilite. On the basis of fayalite and ferrosilite content, poorly-defined chondrules, absence of glass in chondrules, presence of well-developed feldspar in the matrix and chondrules, and degree of recrystallization of the matrix, the Ella Island meteorite is classified as an L-6 chondrite.     

The Caltech solar site survey, 1965–1967

We describe the Caltech solar site survey in 1965–1967 directed by R. B. Leighton. The solar seeing at 102 locations in 34 sites in Southern California was evaluated by 6009 visual estimates with portable telescopes. Cloud cover and other meteorological factors were also measured, and sunlight recorders were operated at several sites. We have reanalyzed much of the data to determine its consistency and learn what else we could about the sites. The visual estimates show good internal consistency and correlation with photographic data.The seeing was found to be best at various sites associated with water, and we point out the importance of the Bowen ratio in determining the influence of water vapor on seeing. It was found that seeing at the different sites was not well correlated in time.The seeing was found to be best at Lake Elsinore, an inland sink. Good seeing was also found on the Caltech campus and at Big Bear Lake in the San Bernardino Mountains. Taking into account the better sky transparency and the feasibility of constructing an observatory in the lake, we chose Big Bear Lake for the site of a new observatory. The lack of correlation of seeing with transparency suggests the benefits of several smaller telescopes, targeted at specific goals, located at sites chosen for those goals.     

The UBV orbital phase curves of Rhea,Dione, and Tethys

Orbital phase curves are reported for Rhea (SV), Dione (SIV), and Tethys (SIII). Variations of 0.2 mag. and 0.8 mag. were found for Rhea and Dione respectively, while no variation of Tethys was detected. Some color variations are also reported.     

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 MILLS,NEW MEXICO,CHONDRITE — A NEW FIND

A mineralogical and chemical analysis has been performed on a slice of the Mills, New Mexico, chondrite, which was found in August 1970. The mineralogical composition is olivine Fa_19.5, bronzite, Fs_17.4, plagioclase, nickel-iron, troilite and ilmenite. The chemical analysis confirms that Mills is a typical bronzite, H5 chondrite, with considerable degree of weathering, as indicated by the presence of large amounts of Fe₂O₃. A comparison with other stones found in the same New Mexico region by Nininger may show a possible relation between Mills and previous finds.     

HAMMOND DOWNS,A NEW CHONDRITE FROM THE TENHAM AREA,QUEENSLAND, AUSTRALIA

Among a collection of meteorites from the area of the Tenham shower (Queensland, Australia) was a 27 kg stone which proved to be different from the other Tenham stones. It is a bronzite, H4, chondrite, the principal minerals being olivine (average composition Fa _18.8), clinobronzite and bronzite (average composition Fs_16.4), nickel-iron, and troilite; it is considerably weathered, much of the nickel-iron being converted to limonite. It has a highly chondritic structure, with devitrified glass within the chondrules, and without visible plagioclase. This meteorite was found about 1950 near the Hammond Downs station, hence the name; its coordinates are lat 25° 28′ S., long 142° 48′ E.     

GOMEZ,TERRY COUNTY,TEXAS: A NEW METEORITE FIND

The Gomez meteorite, weighing slightly over 47 kg, was found near the town of Gomez, Terry County, Texas (33° 10′53 “N, 102° 24′5” W) prior to 1974. It is a highly weathered, equilibrated L-6 chondrite of composition Fa 26, Fs 23. A large number of chromite grains and possibly partially weathered lawrencite grains were noted.