Minor element (Ca, Cr, and Mn) concentrations in amoeboid olivine aggregates (AOAs) from primitive chondrites were measured and compared with those predicted by equilibrium condensation in the solar nebula. CaO concentrations in forsterite are low, particularly in porous aggregates. A plausible explanation appears that an equilibrium Ca activity was not maintained during the olivine condensation. CaO and MnO in forsterite are negatively correlated, with CaO being higher in compact aggregates. This suggests that the compact aggregates formed either by a prolonged reheating of the porous aggregates or by condensation and aggregation of forsterite during a very slow cooling in the nebula.

Patches of clastic matrix (15 to 730 m in size) constitute 4.9 vol% of EH3 Yamato (Y-) 691 and 11.7 vol% of EH3 Allan Hills (ALH) 81189. Individual patches in Y-691 consist of 1) ~25 vol% relatively coarse opaque grain fragments and polycrystalline assemblages of kamacite, schreibersite, perryite, troilite (some grains with daubrelite exsolution lamellae), niningerite, oldhamite, and caswellsilverite; 2) ~30 vol% relatively coarse silicate grains including enstatite, albitic plagioclase, silica and diopside; and 3) an inferred fine nebular component (~45 vol%) comprised of submicrometer-size grains. Clastic matrix patches in ALH 81189 contain relatively coarse grains of opaques (~20 vol%; kamacite, schreibersite, perryite and troilite) and silicates (~30 vol%; enstatite, silica and forsterite) as well as an inferred fine nebular component (~50 vol%). The O-isotopic composition of clastic matrix in Y-691 is indistinguishable from that of olivine and pyroxene grains in adjacent chondrules; both sets of objects lie on the terrestrial mass-fractionation line on the standard three-isotope graph. Some patches of fine-grained matrix in Y-691 have distinguishable bulk concentrations of Na and K, inferred to be inherited from the solar nebula. Some patches in ALH 81189 differ in their bulk concentrations of Ca, Cr, Mn, and Ni. The average compositions of matrix material in Y-691 and ALH 81189 are similar but not identical—matrix in ALH 81189 is much richer in Mn (0.23 +/- 0.05 versus 0.07 +/- 0.02 wt%) and appreciably richer in Ni (0.36 +/- 0.10 versus 0.18 +/- 0.05 wt%) than matrix in Y-691. Each of the two whole-rocks exhibits a petrofabric, probably produced by shock processes on their parent asteroid.

We describe the results of a variety of model calculations for predictions of observable results of the LCROSS mission to be launched in 2009. Several models covering different aspects of the event are described along with their results. Our aim is to bracket the range of expected results and produce a useful guide for mission planning. In this paper, we focus on several different questions, which are modeled by different methods. The questions include the size of impact crater, the mass, velocity, and visibility of impact ejecta, and the mass and temperature of the initial vapor plume. The mass and velocity profiles of the ejecta are of primary interest, as the ejecta will be the main target of the S-S/C observations. In particular, we focus on such quantities as the amount of mass that reaches various heights. A height of 2 km above the target is of special interest, as we expect that the EDUS impact will take place on the floor of a moderate-sized crater ~30 km in diameter, with a rim height of 12 km. The impact ejecta must rise above the crater rim at the target site in order to scatter sunlight and become visible to the detectors aboard the S-S/C. We start with a brief discussion of crater scaling relationships as applied to the impact of the EDUS second stage and resulting estimated crater diameter and ejecta mass. Next we describe results from the RAGE hydrocode as applied to modeling the short time scale (t 0.1 s) thermal plume that is expected to occur immediately after the impact. We present results from several large-scale smooth-particle hydrodynamics (SPH) calculations, along with results from a ZEUS-MP hydrocode model of the crater formation and ejecta mass-velocity distribution. We finish with two semi-analytic models, the first being a Monte Carlo model of the distribution of expected ejecta, based on scaling models using a plausible range of crater and ejecta parameters, and the second being a simple model of observational predictions for the shepherding spacecraft (S-S/C) that will follow the impact for several minutes until its own impact into the lunar surface. For the initial thermal plume, we predict an initial expansion velocity of ~7 km s^(-1), and a maximum temperature of ~1200 K. Scaling relations for crater formation and the SPH calculation predict a crater with a diameter of ~15 m, a total ejecta mass of ~106 kg, with ~10^4 kg reaching an altitude of 2 km above the target. Both the SPH and ZEUS-MP calculations predict a maximum ejecta velocity of ~1 km s^(-1). The semi-analytic Monte Carlo calculations produce more conservative estimates (by a factor of ~5) for ejecta at 2 km, but with a large dispersion in possible results.

It is proposed that the chondrules in enstatite chondrites formed near the Sun from rain-like supercooled liquid silicate droplets and condensed Fe-Ni alloys in thermodynamic equilibrium with a slowly cooling nebula. FeO formed and dissolved in the droplets in an initial stage when the nucleation of iron was blocked, and was later mostly reduced to unalloyed Fe. At high temperatures, the silicate droplets contained high concentrations of the less volatile components CaO and Al2O3. At somewhat lower temperatures the equilibrium MgO content of the droplets was relatively high. As cooling progressed, some droplets gravitated toward the Sun, and moved in other directions, depleting the region in CaO, Al2O3, and MgO and accounting for the relatively low observed CaO/SiO2, Al2O3/ SiO2, and MgO/SiO2 ratios in enstatite chondrites. At approximately 1400 K, the remaining supercooled silicate droplets crystallized to form MgSiO3 (enstatite) with small amounts of olivine and a high-SiO2 liquid phase which became the mesostases. The high enstatite content is the result of the supercooled chondrules crystallizing at a relatively low temperature and relatively high total pressure. Finally, FeS formed at temperatures below 680 K by reaction of the condensed Fe with H2S. All calculations were performed with the evaluated optimized thermodynamic databases of the FactSage thermodynamic computer system. The thermodynamic properties of compounds and solutions in these databases were optimized completely independently of any meteoritic data. Agreement of the model with observed bulk and phase compositions of enstatite chondrules is very good and is generally within experimental error limits for all components and phases.

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.

The measured Cu and Cr contents in magmatic iron meteorites appear to contradict the behavior predicted by experimental fractional crystallization studies currently available. To investigate the origin of Cu and Cr concentrations observed in these meteorites, a thorough set of solid metal/liquid metal experiments were conducted in the Fe-Ni-S system. In addition to Cu and Cr, partitioning values were also determined for As, Au, Bi, Co, Mo, Ni, Pb, Rh, Ru, Sb, Sn, V, and Zn from the experiments. Experimental results for Cu and Cr showed similar chalcophile partitioning behavior, whereas these elements have differently sloped trends within magmatic iron meteorite groups. Thus, fractional crystallization alone cannot control both the Cu and Cr concentrations in these iron meteorite groups. A simple fractional crystallization model based on our experimental Cu partitioning results was able to match the Cu versus Au trend observed in the S-poor IVB iron meteorite group but not the decreasing Cu versus Au trends in the IIAB and IIIAB groups or the unique S-shaped Cu versus Au trend in the IVA group. However, the crystallization model calculations were found to be very sensitive to the specific choice for the mathematical expression of D(Cu), suggesting that any future refinement of the parameterization of D(Cu) should include a reassessment of the Cu fractional crystallization trends. The Cr versus Au trends in magmatic iron meteorite groups are steeper than those of Cu and not explained by fractional crystallization. Other influences, such as the removal of chromite from the crystallizing system or sampling biases during iron meteorite compositional analyses, are likely responsible for the Cr trends in magmatic iron meteorite groups.