Hypervelocity capture of meteoritic particles in nonsilica aerogels     

Steven M. JONES  George FLYNN 《Meteoritics & planetary science》2011,46(9):1253-1264

Abstract– The Stardust mission captured particles from the comet 81P/Wild 2 in gradient density silica aerogel and returned the collected samples to earth in 2006. The analyses of these particles have revealed several new insights into the formation of our solar system. However, since the aerogel used as the capture material was silica, the elemental analyses of the silica‐rich particles were made more complicated in certain ways due to the mixing of the silicon of the particles and that of the aerogel. By using a nonsilica aerogel, future elemental analyses of silica–rich particles captured in aerogel could be made more straightforward. Resorcinol/formaldehyde (RF), alumina, and zirconia aerogels were impact tested with meteoritic fragments and the captured fragments were mapped with synchrotron‐based X‐ray microprobe (XRM) and the particles were analyzed with X‐ray fluorescence (XRF). The resorcinol/formaldehyde aerogel proved to be the best capture material, in that it could be keystoned and XRF could be used to locate and analyze particles that were less than 10 μm.  相似文献   

Petrogenesis of the Eastern Bushveld Complex: Crystallization of the Middle Critical Zone     

FLYNN  R. T.; ULMER  G. C.; SUTPHEN  C. F. 《Journal of Petrology》1978,19(1):136-152

The bronzite—chromite-anorthite assemblage of the F—unit(Cameron & Emerson, 1959) from the Critical Zone of theBushveld Igneous Complex, was examined with the aid of an electrolyticcell designed after Sato (1971). The resultant fO₂-T data reveala last equilibration at an fO₂ value of 10^{11·82 ±·40} atm and at a temperature of 1091 ± 35 °C.These fO₂-T data when compared with: (1) a one atmosphere quenching—technique solidus determinationof 1110 ± 5 °C, (2) the Bushveld plagioclase compositional trends (Cameron,1970), (3) Bushveld petrofabric examinations (Cameron, 1969) (4) phase equilibria in the system CaO–MgO–FeO–CaAl₂Si₂O₈–SiO₂(Roeder & Osborn, 1966), (5) phase equilibria in the system CaAl₂Si₂O₈–NaAlSi₃O₈–SiO₂–MgO–Fe–O₂–H₂O–CO₂(Eggler, 1974), all support the idea that the Eastern Bushveld magma was notappreciably differentiating in the middle Critical Zone betweenF and the L Horizons, an accumulation of nearly 220 meters.  相似文献   

Experimental investigation of the impact fragmentation of blocks embedded in regolith     

Daniel D. DURDA  Clark R. CHAPMAN  Mark J. CINTALA  George J. FLYNN  Melissa M. STRAIT  Anderson MINNICK 《Meteoritics & planetary science》2011,46(1):149-155

Abstract– We present results of a set of impact experiments designed to examine the effects of impacts onto rocky blocks resting on and embedded within regoliths. The targets were approximately 500 g granodiorite blocks, struck with one‐eighth inch aluminum spheres at nominal speeds of approximately 5 km s^?1. The granodiorite blocks were emplaced in 20–30 grade silica sand to simulate an asteroidal or lunar regolith; block burial depths ranged from resting flush on the surface to submerged completely below the surface. We observe a trend for largest remnant mass to increase with block burial depth. Documentary still image and high‐speed video of the resulting block fragments and surrounding regolith reveal new insights into the morphologies of blocks and secondary craters observed on asteroids like 433 Eros.  相似文献   

Assessment and control of organic and other contaminants associated with the Stardust sample return from comet 81P/Wild 2     

Scott A. SANDFORD  Saša BAJT  Simon J. CLEMETT  George D. CODY  George COOPER  Bradley T. DEGREGORIO  Vanessa De VERA  Jason P. DWORKIN  Jamie E. ELSILA  George J. FLYNN  Daniel P. GLAVIN  Antonio LANZIROTTI  Thomas LIMERO  Mildred P. MARTIN  Christopher J. SNEAD  Maegan K. SPENCER  Thomas STEPHAN  Andrew WESTPHAL  Sue WIRICK  Richard N. ZARE  Michael E. ZOLENSKY 《Meteoritics & planetary science》2010,45(3):406-433

Abstract– Numerous potential sources of organic contaminants could have greatly complicated the interpretation of the organic portions of the samples returned from comet 81P/Wild 2 by the Stardust spacecraft. Measures were taken to control and assess potential organic (and other) contaminants during the design, construction, and flight of the spacecraft, and during and after recovery of the sample return capsule. Studies of controls and the returned samples suggest that many of these potential sources did not contribute any significant material to the collectors. In particular, contamination from soils at the recovery site and materials associated with the ablation of the heatshield do not appear to be significant problems. The largest source of concern is associated with the C present in the original aerogel. The relative abundance of this carbon can vary between aerogel tiles and even within individual tiles. This C was fortunately not distributed among a complex mixture of organics, but was instead largely present in a few simple forms (mostly as Si‐CH₃ groups). In most cases, the signature of returned cometary organics can be readily distinguished from contaminants through their different compositions, nonterrestrial isotopic ratios, and/or association with other cometary materials. However, some conversion of the carbon indigenous to the flight aerogel appears to have happened during particle impact, and some open issues remain regarding how this C may be processed into new forms during the hypervelocity impact collection of the comet dust.  相似文献   

Infrared spectroscopy of Wild 2 particle hypervelocity tracks in Stardust aerogel: Evidence for the presence of volatile organics in cometary dust     

S. BAJT  S. A. SANDFORD  G. J. FLYNN  G. MATRAJT  C. J. SNEAD  A. J. WESTPHAL  J. P. BRADLEY 《Meteoritics & planetary science》2009,44(4):471-484

Abstract— Infrared spectroscopy maps of some tracks made by cometary dust from 81P/Wild 2 impacting Stardust aerogel reveal an interesting distribution of organic material. Out of six examined tracks, three show presence of volatile organic components possibly injected into the aerogel during particle impacts. When particle tracks contained volatile organic material, they were found to be ‐CH₂‐rich, while the aerogel is dominated by the ‐CH₃‐rich contaminant. It is clear that the population of cometary particles impacting the Stardust aerogel collectors also includes grains that contained little or none of this organic component. This observation is consistent with the highly heterogeneous nature of collected grains, as seen by a multitude of other analytical techniques.  相似文献   

Heating experiments simulating atmospheric entry heating of micrometeorites: Clues to their parent body sources     

ANSGAR GRESHAKE  WOLFGANG KL CK  PETER ARNDT  MISCHA MAETZ  GEORGE J. FLYNN  SASA BAJT  ADDI BISCHOFF 《Meteoritics & planetary science》1998,33(2):267-290

Abstract— Depending on their velocity, entry angle and mass, extraterrestrial dust particles suffer certain degrees of heating during entry into Earth's atmosphere, and the mineralogy and chemical composition of these dust particles are significantly changed. In the present study, pulse-heating experiments simulating the atmospheric entry heating of micrometeoroids were carried out in order to understand the mineralogical and chemical changes quantitatively as well as to estimate the peak temperature experienced by the particles during entry heating. Fragments of the CI chondrites Orgueil and Alais as well as pyrrhotites from Orgueil were used as analogue material. The experiments show that the volatile elements S, Zn, Ga, Ge, and Se can be lost from 50 to 100 μm sized CI meteorite fragments at temperatures and heating times applicable to the entry heating of similar sized cosmic dust particles. It is concluded that depletions of these elements relative to CI as observed in micrometeorites are mainly caused by atmospheric entry heating. Besides explaining the element abundances in micrometeorites, the experimentally obtained release patterns can also be used as indicators to estimate the peak heating of dust particles during entry. Using the abundances of Zn and Ge and assuming their original concentrations close to CI, a maximum heating of 1100–1200 °C is obtained for previously analyzed Antarctic micrometeroites. Thermal alteration also strongly influenced the mineralogy of the meteorite fragments. While the unheated samples mainly consisted of phyllosilicates, these phases almost completely transformed into olivine and pyroxene in the fragments heated to ≥800 °C. Therefore, dust particles that still contain hydrous minerals were probably never heated to temperatures ≥800 °C in the atmosphere. During continued heating, the grain size of the newly formed silicates increased and the composition of the olivines equilibrated. Applying these results quantitatively to Antarctic micrometeorites, typical peak temperatures in the range of 1100–1200 °C during atmospheric entry heating are deduced. This temperature range corresponds to the one obtained from the volatile element concentrations measured in these micrometeorites and points to an asteroidal origin of the particles.  相似文献