[en] The research of Smith et al. (1978) and Oliver et al. (1981) on the Abee meteorite's possible negative tellurium anomaly is extended. Two sets of measurements of the tellurium isotopic composition of Abee are reported, and the meteoritic data are compared with a terrestrial tellurium standard. No isotopic anomalies can be distinguished within the error limits. However, further work on the isotopic composition of Te in residues from the Allende meteorite need to be pursued by accurate mass spectrometric analysis. 23 references

[en] Different sets of initial conditions for impacts of stray objects on solid surfaces of planetary bodies or asteroids have been computed for cooling times of chondrules. The results of the calculations indicate cooling times shorter than 60 seconds for condensed matter from 10 to the 4th to 10 to the 15th g generated by impact and initial temperatures of the gas phase formed up to presumed degeneracy limit of 150,000 K. To retain solid impact products originated that way on meteorite parent bodies by gravitational forces, a target diameter of at least 800 km is required. It is shown that chondrule formation by impact seems to be an unlikely event. 29 references

[en] Various types of meteorites have experienced processes of condensation, accretion, metamorphism, differentiation, brecciation, irradiation and fragmentation. A typical view of meteorite formation has been that the processes following accretion take place in a few asteroidal-sized (approximately 100 km) objects. Discovery of decay products of now extinct Al-26 and Pd-107 in meteorites, discovery of isotopic heterogeneity among meteorite types, re-analysis of meteorite cooling rates, and continuing study of meteoritic compositions have led some meteoriticists to conclude that meteorites obtained their chemical, isotopic, and some textural characteristics in objects initially less than 10 km in diameter. Such a scenario, which is described in this paper, raises the possibility that some of these small planetesimals may have been 'condensation nuclei' for the formation of comets as well as the precursors of asteroids

[en] Pb-Pb and Rb-Sr internal isochrons have been determined in the Saint Severin amphoterite. The Sr age and initial ratio are, respectively, 4.61 +- 0.15 b.y. (lambda =1.39 X 10^-11yr^-1) and 0.69903 +- 0.00020 (2sigma errors). Evidence is presented for acceptance of radiogenic Sr from whitlockite, possibly from troilite, during events younger than 3.1 b.y., thus giving too high initial ratios. The Pb-Pb age, determined from plagioclase, whole rock and very radiogenic whitlockite is 4.543 +- 0.019 b.y. (2sigma errors), using the new U decay constants. Both U-Pb and Th-Pb ages of whitlockite are concordant at 4.54 b.y. The range of the Th/U ratio of whitlockite is 9-11, in agreement with the value of Crozaz [Earth Planet. Sci. Lett. 23(1974) 164-169]. The results are compared with the other Rb-Sr and U-Pb data on chondrites and achondrites. (Auth.)

[en] Two hypotheses are proposed for the aqueous alteration of carbonaceous chondrites within their parent bodies, in which respectively the alteration occurs (1) throughout the parent body interior, or (2) in a postaccretional surface regolith; both models assume an initially homogeneous mixture of ice and rock that is heated through the decay of Al-26. Water is seen to exert a powerful influence on chondrite evolution through its role of thermal buffer, permitting substitution of a low temperature aqueous alteration for high temperature recrystallization. It is quantitatively demonstrated that liquid water may be introduced by either hydrothermal circulation, vapor diffusion from below, or venting due to fracture. 104 refs

[en] A neutron-irradiated bulk sample of the Murray (C-2) carbonaceous chondrite was etched with H₂O₂ and then divided into colloidal and non-colloidal fractions. The H₂O₂ treatment removed approx. 80% of the trapped Xe and greatly increased variations in the ¹²⁹Xe/¹³²Xe ratio measured in stepwise heating. The colloid showed very little excess ¹²⁹Xe, but the anti-colloid gave a fairly good I-Xe correlation corresponding to formation 3.7 +- 2.1 m.y. after Bjurboele. (orig./ME)

[en] The ferromagnesian chondrules in Allende follow a trend in the oxygen three-isotope plot that diverges significantly from the 16-O mixing line defined by light and dark inclusions and the matrix of the meteorite. The trend probably results from isotopic exchange with an external gaseous reservoir during the process of chondrule formation sometime after the establishment of the isotopic compositions of the inclusions and matrix. The Allende chondrules approach, but do not reach, the isotopic compositions of chondrules in unequilibrated ordinary chondrites, implying exchange with a similar ambient gas, but isotopically different solid precursors for the two types of meteorite. 8 references

No abstract available

[en] The majority of basaltic asteroids are found in the inner main belt, although a few have also been observed in the outer main belt and near-Earth space. These asteroids-referred to as V-types-have surface compositions that resemble that of the 530 km sized asteroid Vesta. Besides the compositional similarity, dynamical evidence also links many V-type asteroids to Vesta. Moreover, Vesta is one of the few asteroids to have been identified as source of specific classes of meteorites, the howardite, eucrite, and diogenite achondrites (HEDs). Despite the general consensus on the outlined scenario, several questions remain unresolved. In particular, it is not clear if the observed spectral diversity among Vesta, V-types, and HEDs is due to space weathering, as is thought to be the case for S-type asteroids. In this Letter, SDSS photometry is used to address the question of whether the spectral diversity among candidate V-types and HEDs can be explained by space weathering. We show that visible spectral slopes of V-types are systematically redder with respect to HEDs, in a similar way to what is found for ordinary chondrite meteorites and S-types. On the assumption that space weathering is responsible for the slope mismatch, we estimated an upper limit for the reddening timescale of about 0.5 Ga. Nevertheless, the observed slope mismatch between HEDs and V-types poses several puzzles to understanding its origin. The implication of our findings is also discussed in light of the Dawn mission to Vesta.

[en] Cosmogenic Ne-21 is used widely to calculate exposure ages of stone meteorites. In order to do so, the production rate P(21) must be known. This rate, however, is dependent on the chemical composition of the meteorite as well as the mass of, and position within, the meteoroid during its exposure to the cosmic radiation. Even for a mean shielding the production rates determined from measurments of different radionuclides vary by a factor of two. A method that can be used to determine exposure ages of meteorites that avoids shielding and chemical composition corrections is the -81-Kr-Kr-method. However, for chondrites, in many cases, the direct determination of production rates for the Kr isotopes is prevented by the trapped gases and the neutron effects on bromine. Therefore, this method was applied to four eucrite falls and then their 81-Kr-83-Kr-ages were compared to their cosmogenic Ne-21 and Ar-38 concentrations. The eucrites Bouvante-le-Haut, Juvinas, Sioux County, and Stannern were chosen for these measurements because of their similar chemical composition regarding the major elements