Sikhote-Alin Meteorite Research Articles

Neutron activation analysis of meteorites at the VR-1 training reactor

Samples of space objects were characterized using instrumental neutron activation analysis (NAA) combined with conversion electron Mössbauer spectrometry. Fragments of Moldavites, Muonionalusta meteorite and Sikhote-Alin meteorite were irradiated in the thermal neutron field of the low-power VR-1 training reactor operated by the Czech Technical University in Prague. Activated samples were investigated by means of nuclear gamma-spectrometry technique (semiconductor HPGe detector). Qualitative analysis revealed the occurrence of Na, Al, Mg, Cl, K, Ti, V, Mn, Fe, Sr, and Ba in Moldavites, Na, Cl, Mn, Fe, Co, Cu, Ni, As, and Au in Muonionalusta iron meteorite, and Ni, Co, Fe, and Mn in Sikhote-Alin iron meteorite. Employing the comparative NAA, the concentration of Na, Al, K, Ti, V, Fe, and Sr in Moldavite, concentration of Na, Fe, Ni, and Au in Muonionalusta meteorite, and concentration of Ni in Sikhote-Alin meteorite was determined. Moreover, Muonionalusta meteorite structure was investigated using the conversion electron Mössbauer spectrometry at room temperature, and α-(Fe, Ni) phase and γ-(Fe, Ni) phase were identified. The obtained results clearly show that the low-power VR-1 research reactor (80 W) is an excellent tool for NAA experiments, and that nuclear-analytical techniques can provide useful data for other scientific branches.

Hydrothermal modification of the Sikhote-Alin iron meteorite under low pH geothermal environments. A plausibly prebiotic route to activated phosphorus on the early Earth

The Sikhote-Alin (SA) meteorite is an example of a type IIAB octahedrite iron meteorite with ca. 0.5wt% phosphorus (P) content principally in the form of the siderophilic mineral schreibersite (Fe,Ni)3P. Meteoritic in-fall to the early Earth would have added significantly to the inventory of such siderophilic P. Subsequent anaerobic corrosion in the presence of a suitable electrolyte would produce P in a form different to that normally found within endogenous geochemistry which could then be released into the environment. One environment of specific interest includes the low pH conditions found in fumaroles or volcanically heated geothermal waters in which anodic oxidation of Fe metal to ferrous (Fe2+) and ferric (Fe3+) would be coupled with cathodic reduction of a suitable electron acceptor. In the absence of aerobic dioxygen (Eo=+1.229V), the proton would provide an effective final electron acceptor, being converted to dihydrogen gas (Eo=0V). Here we explore the hydrothermal modification of sectioned samples of the Sikhote-Alin meteorite in which siderophilic P-phases are exposed. We report on both, (i) simulated volcanic conditions using low pH distilled water and (ii) geothermally heated sub-glacial fluids from the northern Kverkfjöll volcanic region of the Icelandic Vatnajoküll glacier. A combination of X-ray photoelectron spectroscopy (XPS) and electrochemical measurements using the scanning Kelvin probe (SKP) method reveals that schreibersite inclusions are significantly less susceptible to anodic oxidation than their surrounding Fe–Ni matrix, being some 550mV nobler than matrix material. This results in preferential corrosion of the matrix at the matrix-inclusion boundary as confirmed using topological mapping via infinite focus microscopy and chemical mapping through Raman spectroscopy. The significance of these observations from a chemical perspective is that electrochemically noble inclusions such as schreibersite are likely to have been released into the geological environment through an undermining corrosion of the surrounding matrix, thus affording localised sources of available water-soluble, chemically reactive P in the form of H-phosphite [H2PO3-, Pi(III) as determined by 31P NMR spectroscopy]. This compound has been shown to have considerable prebiotic chemical potential as a source of condensed P-oxyacids. Here we demonstrate that Pi(III) resulting from the hydrothermal modification of Sikhote-Alin by sub-glacial geothermal fluids can be readily dehydrated into the condensed P-oxyacid pyrophosphite [H2P2O52-, PPi(III)] by dry-heating under mild (85°C) conditions. The potential significance of this latter condensed P-compound for prebiotic chemistry is discussed in the light of its modified chemical properties compared to pyrophosphate [H2P2O72-, PPi(V)].

An analysis of Fe and Ni distribution in M1, M2 and M3 sites of iron–nickel phosphides extracted from Sikhote-Alin meteorite using Mössbauer spectroscopy with a high velocity resolution

Study of two iron–nickel phosphides crystals (rhabdite and schreibersite) extracted from Sikhote-Alin (IIAB) iron meteorite was performed using Mössbauer spectroscopy with a high velocity resolution at various temperatures. On the basis of Mössbauer data the temperature dependences of magnetic hyperfine fields for Fe atoms in the crystallographically non-equivalent M1, M2 and M3 sites of rhabdite were shown as well as Fe and Ni occupancies of these sites were evaluated for both phosphides.

A novel sample decomposition technique at atmospheric pressure for the determination of Os abundances in iron meteorites using isotope dilution inductively coupled plasma-mass spectrometry.

A safe and reliable analytical technique for the determination of Os abundances in ten iron meteorites of various chemical groups was developed using isotope dilution inductively coupled plasma-mass spectrometry coupled with a sample decomposition technique. A major advantage of the sample decomposition technique developed here is that the pressure inside the reaction flask is not increased through the decomposition reaction because the flask is a fully opened system, obviating the risk of explosion of the glass apparatus. Another advantage is that there is no restriction in the sample size being decomposed. In this study, about 2 g of metallic sample were decomposed safely, and this sample size, > 10 times larger than that typically used for the Carius tube technique, allows one to obtain more reliable Os data for heterogeneous samples. The metallic samples were decomposed in a glass flask purged with Ar. Since the O2 was purged from the reaction flask, Os was not oxidised to volatile OsO4, thereby preventing significant evaporation loss of Os. The typical recovery of Os throughout the sample decomposition and separation processes was > 80%, and the total Os blank through the decomposition of a 1 g amount of sample was less than 20 pg. Os abundances were determined by means of stable isotope dilution mass spectrometry using a 190Os-enriched isotopic tracer. Except for Sikhote-Alin, the measured Os abundances in almost all the iron meteorites exhibited a good agreement with the previously published Os abundance data, within the analytical uncertainty achieved in this study (2-5%). For the Sikhote-Alin meteorite, on the basis of a better correlation between Os and Ir abundances, we believe that our Os abundance data should be more reliable. The Os abundance data obtained in this work clearly demonstrated the suitability of the newly developed sample decomposition procedure for low level Os determinations.

Radiation ages of different fragments of the Sikhote-Alin meteorite fall

Seven specimens from five different fragments of the Sikhote-Alin iron meteorite have been analyzed for their content of 39Ar, 38Ar, 21Ne, and 3He. The 39Ar- 38Ar-cosmic ray exposure ages calculated from these data are (450 ± 20) × 10 6 yr for four of the fragments, that of one fragment is only (145 ± 11) × 10 6 yr. The discrepancy is explained as due to a collisional break-up of the meteorite less than approximately 150 × 10 6 yr ago.

Three Years of New Investigations of Sikhote-Alin Meteorite Shower

Three Years of New Investigations of Sikhote-Alin Meteorite Shower

Studies of particles for extraterrestrial origin: 1. Chemical analyses of 118 particles

Dust particles of probable or known extraterrestrial origin were gathered, for the purpose of comparison, from a number of sources, including the stratosphere, 750-year-old Greenland ice, 55-year-old antarctic ice, the antarctic atmosphere, a New Mexico mountaintop, glacial ice caves, and the place of fall of the Siberian Sikhote-Alin meteorite shower. Out of the wide variety of types of particles in these samples, 118 representative particles were subjected to detailed chemical analysis by the electron-beam microanalyzer technique. The Fe/Ni ratios of 5 particles point undoubtedly to their meteoritic origin. From their high Fe/Si ratio some 35 others are thought to be extraterrestrial A few objects are identified from their compositions as being of obvious terrestrial origin. The cosmic influx of dust on the earth's surface is computed to be more than 105 tons per year.

Uranium in the Sikhote-Alin Meteorite and its Relation to the Lead Method of Age Determination

THE ages of lead of Earth and of meteorites are commonly based on the assumption that when these bodies were formed they contained lead of the same isotopic composition1,2. The present differences in the isotopic compositions of the lead in meteorites and also between common terrestrial lead and meteorite lead are due to radiogenic contributions from uranium and thorium since that time.

Argon-39 and tritium in meteorites

The radioactive isotopes argon-39 and tritium are measured in a number of iron and stone meteorites. The stable isotope helium-3 is also measured and the argon-38 content is estimated from the helium-3 content. The cosmic ray exposure ages obtained from the argon-39 and argon-38 are: 4·2 × 10 8 years for the Sikhote-Alin iron meteorite, 4·5 × 10 8 years for the Treysa iron meteorite, 0·3 × 10 8 years for the Pitts iron meteorite, 5 × 10 8 years for the Norton County achondrite, and 0·8 × 10 8 years for the St. Michel chondrite. The ratio of tritium to argon-39 radioactivities at the time of fall is 140 ± 20 for the Norton County meteorite, 56 ± 15 for the St. Michel meteorite, 6 ± 1 for the Treysa meteorite, and less than 1 2 for the Sikhote-Alin meteorite. For the stone meteorites this ratio is consistent with the production probabilities and the hypothesis of the constancy of cosmic rays. For the iron meteorites this is lower than expected from the production probabilities. Either the cosmic ray bombardment is not constant or tritium loss from diffusion occurs for the iron meteorites. Also reported is the lack of argon-39 and tritium in a number of undated iron meteorite falls, which indicates that they fell more than 1500 years ago. Only one undated iron meteorite fall, Washington County, gave a small trace of argon-39, indicating that it fell about 1000 years ago. Possible interpretations of the cosmic ray exposure ages are discussed.

Argon-39 and tritium in meteorites.

The radioactive isotopes A39 (26o-year half- life) and tritium (I 2.4-year half-life) were measured in seven iron and in two stony meteorites. A39 was detected and measured in the iron meteorites Sikhote-Alin (1947), Treysa (1916), Pitts (1921), and in the stony meteorites Norton County (1948) and St. Michel (1910). The detection and measurement of A39 in these meteorites makes it possible to determine their argon exposure ages (Fireman, E. L. Nature, i8i, 1613, 1958). On the basis of the same assumptions used in that article, the ages are 4.9 X I0~ years for the Sikhote-Alin meteorite, 5.7 X 108 years for the Treysa meteorite, 6.~ X I0~ years for the Norton County meteorite, 1.7 X 108 years for the St. Michel meteorite, and, for the Pitts meteorite, an unusually low figure in the range of I0~ years. The short argon exposure ages may be interpreted in two ways: they may result from the loss of shielding material, worn off the meteorite in space by interplanetary dust and gas (suggested in private discussion with Professor Fred L. Whipple); or they may represent the times since the breakup of planets. From the lack of A39 in the Carbo and Grant meteorites and the small amount of A39 in the Washington County meteorite whose dates of fall are unknown, one can conclude that Carbo and Grant fell more than 1500 years ago and that the Washington County meteorite fell about 1000 years ago. In the case of the Caflon Diablo meteorite the He3 content is so low that the measured absence of A39 and tritium does not necessarily mean that it fell long ago. The ratio of tritium to A39 radioactivities (decays g~i min-i) in the Norton County meteorite is 230 to I at the time of fall. This ratio in the Sikhote-Alin meteorite is anomalously low being less than I to I at the time of fall. The work was supported in part by a grant from the Atomic Energy Commission. Smithsonian Astrophysical Observatory, Cambridge, Mass.

Argon-39 in the Sikhote-Alin Meteorite Fall

THE radioactive isotope argon-39 (260-year half-life) has been determined in a specimen of the Sikhote-Alin meteorite fall which occurred on February 12, 1947. This fall1 was very large, consisting of more than a hundred fragments weighing up to 300 kgm. The measurements were made on samples taken from a 150-gm. bar of the meteorite obtained from Truman P. Kohman, who in turn received the bar from E. L. Krinov. The bar was piece No. 5, which was sawn from specimen No. 2052, according to E. L. Krinov's designation. Argon-39 was not detected in the Carbo meteorite which was found in Mexico in 1923. The detection and measurement of argon-39 in the Sikhote-Alin meteorite makes it possible to determine a new type of age (argon-38/argon-39), which can be called an argon exposure age. The amount of argon-39 also gives an estimate of the cosmic-ray intensity that irradiated the Sikhote-Alin sample in space. From the lack of argon-39 in the Carbo meteorite, the date of fall of which is unknown, one can conclude that it fell more than 1,500 years ago.