The Pecora Escarpment (PCA) 91020 EL3 chondrite and deformation on theEL3 asteroid
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BOLEAGA, Y.↗
Engineering topics
Friedrich, J. M.
Publications and source records attributed to Friedrich, J. M..
The proton charge radius extracted from the initial-state radiation experiment at MAMI
Abstract We report on a comprehensive reinterpretation of the existing cross-section data for elastic electron-proton scattering obtained by the initial-state radiation technique, resulting in a significantly improved accuracy of the extracted proton charge radius. By refining the external energy corrections we have achieved an outstanding description of the radiative tail, essential for a detailed investigation of the proton finite-size effects on the measured cross sections. This development, together with a novel framework for determining the radius, based on a regression analysis of the cross sections employing a polynomial model for the form factor, led us to a new value for the charge radius, which is $$(0.878 \pm 0.011_\mathrm {stat.}\pm 0.031_\mathrm {sys.}\pm 0.002_\mathrm {mod.})\,\mathrm {fm}$$ ( 0.878 ± 0 . 011 stat . ± 0 . 031 sys . ± 0 . 002 mod . ) fm
Physics↗
Effect of Tube-Based X-Ray Microtomography Imaging on the Amino Acid and Amine Content of the Murchison CM2 Chondrite
X-ray and synchrotron X-ray micro-computed tomography (micro-CT) are increasingly being used for three dimensional reconnaissance imaging of chondrites and returned extraterrestrial material prior to detailed chemical and mineralogical analyses. Although micro-CT imaging is generally considered to be a non-destructive technique since silicate and metallic minerals in chondrites are not affected by X-ray exposures at the intensities and wavelengths typically used, there are concerns that the use of micro-CT could be detrimental to the organics in carbonaceous chondrites. We recently conducted a synchrotron micro-CT experiment on a powdered sample of the Murchison CM2 carbonaceous chondrite exposed to a monochromatic high energy (approximately 48 kiloelectronvolts) total X-ray radiation dose of approximately 1 kilogray (kGy) using the Advanced Photon Source beamline 13-BMD (13-Bending Magnet-D Beamline) at Argonne National Laboratory and found that there were no detectable changes in the amino acid abundances or enantiomeric compositions in the chondrite after exposure relative to a Murchison control sample that was not exposed. However, lower energy bremsstrahlung X-rays could interact more with amino acids and other lower molecular weight amines in meteorites. To test for this possibility, three separate micro-CT imaging experiments of the Murchison meteorite using the GE Phoenix v/tome/x s 240 kilovolt microfocus high resolution tungsten target X-ray tube instrument at the American Museum of Natural History (AMNH) were conducted and the amino acid abundances and enantiomeric compositions were determined. We also investigated the abundances of the C1-C5 amines in Murchison which were not analyzed in the first study.
Microtomography Imaging↗
Bunburra Rockhole: Exploring the Geology of a New Differentiated Basaltic Asteroid
Bunburra Rockhole (BR) is the first recovered meteorite of the Desert Fireball Network. It was initially classified as a basaltic eucrite, based on texture, mineralogy, and mineral chemistry but subsequent O isotopic analyses showed that BR's composition lies significantly far away from the HED group of meteorites. This suggested that BR was not a piece of the HED parent body (4 Vesta), but other explanations could also account for the observed oxygen signatures. Possible scenarios include contamination by components from other bodies (chondrites or other achondrites) or that 4 Vesta may not be as equilibrated as hypothesized. After examining multiple pieces with different instruments (CT scans and x-ray maps), no obvious evidence of contamination was found. If BR is not from Vesta, a conundrum exists as no unusual features were found in mineral and bulk trace element chemistry as exist for other anomalous basaltic achondrites such as Ibitira or Asuka 881394. These meteorites have distinct petrological and geochemical characteristics, in addition to their anomalous O isotope compositions, that set them apart from eucrites. Thus, early results provided a somewhat ambiguous picture of BR's petrogenesis and parentage. To clarify the nature of the relationship, if any, between BR and eucrites, we have performed a correlated stable isotope and bulk chemical study of several lithologic fragments.
Benedix, G.K.↗
Particle Size Distributions Obtained Through Unfolding 2D Sections: Towards Accurate Distributions of Nebular Solids in the Allende Meteorite
Size distributions of nebular solids in chondrites suggest an efficient sorting of these early forming objects within the protoplanetary disk. The effect of this sorting has been documented by investigations of modal abundances of CAIs (e.g., [1-4]) and chondrules (e.g., [5-8]). Evidence for aerodynamic sorting in the disk is largely qualitative, and needs to be carefully assessed. It may be a way of concentrating these materials into planetesimal-mass clumps, perhaps 100 fs of ka after they formed. A key parameter is size/density distributions of particles (i.e., chondrules, CAIs, and metal grains), and in particular, whether the radius-density product (rxp) is a better metric for defining the distribution than r alone [9]. There is no consensus between r versus rxp based models. Here we report our initial tests and preliminary results, which when expanded will be used to test the accuracy of current dynamical disk models.
Christoffersen, P. A.↗
Olivine in Almahata Sitta - Curiouser and Curiouser
Almahata Sitta (hereafter Alma) is an anomalous, polymict ureilite. Anomalous features include low abundance of olivine, large compositional range of silicates, high abundance and large size of pores, crystalline pore wall linings, and overall finegrained texture. Tomography suggests the presence of foliation, which is known from other ureilites. Alma pyroxenes and their interpretation are discussed in two companion abstracts. In this abstract we discuss the composition of olivine in Alma, which is indicative of the complexity of this meteorite.
Zolensky, M. E.↗
Oxygen Isotope Composition of Almahata Sitta
The name Almahata Sitta is applied collectively to some hundreds of stones that were found in a linear strewn field in the Nubian Desert coincident with the projected Earth-impacting orbit of the Asteroid 2008 TC3. Fragments of the meteorite were collected in December 2008 and March 2009, 2 to 5 months after the asteroid exploded in Earths atmosphere on 7 October 2008.
Rumble, D.↗
Mineralogy of the Almahata Sitta Ureilite
Mineralogy & Petrography: Almahata Sitta, deriving from the asteroid 2008 TC3, is a coarse-grained- to porous, fine-grained, fragmental breccia with subrounded mineral fragments and olivine aggregates embedded in a cataclastic matrix of ureilitic material. Mineral fragments include polycrystalline olivine, low-calcium, pigeonite, and augite. Abundant carbonaceous aggregates containing graphite, microdiamonds and aliphatics. Kamacite, Cr-rich troilite, silica and schreibersite are abundant. The compositional range of the silicates is characteristic of the ureilites as a group, but unusually broad for an individual ureilite. The dense lithology is typical for ureilites, but the porous lithology is anomalous. In the porous lithology pore walls are largely coated by crystals of olivine. Classification: Almahata Sitta is an anomalous, polymict eucrite. Anomalous features include large compositional range of silicates, high abundance and large size of pores, crystalline pore wall linings, and fine-grained texture. Tomography reveals that the pores define thin, discontinuous "sheets" connected in three dimensions, suggesting that they outline grains that have been incompletely welded together. The crystals lining the pore walls are probably vapor phase deposits. Therefore Almahata Sitta may represent an agglomeration of coarse- to fine-grained, incompletely reduced pellets formed during impact, and subsequently welded together at high temperature.
Zolensky, Michael E.↗