A critical evaluation of oxidation versus reduction during metamorphism of L and LL group chondrites,and implications for asteroid spectroscopy

Abstract— Modal mineralogies of individual, equilibrated (petrologic type 4–6 L and LL chondrites have been measured using an electron microprobe mapping technique, and the chemical compositions of coexisting silicate minerals have been analyzed. Progressive changes in the relative abundances and in the molar Fe/Mn and Fe/Mg ratios of olivine, low‐Ca pyroxene, and diopside occur with increasing metamorphic grade. Variations in olivine/low‐Ca pyroxene ratios (Ol/Px) and in metal abundances and compositions with petrologic type support the hypothesis that oxidation of metallic iron accompanied thermal metamorphism in ordinary chondrites. Modal Ol/Px ratios are systematically lower than normative Ol/Px ratios for the same meteorites, suggesting that the commonly used C.I.P.W. norm calculation procedure may not adequately estimate silicate mineral abundances in reduced chondrites. Ol/Px ratios calculated from visible and near‐infrared (VISNIR) reflectance spectra of the same meteorites are not in agreement with other Ol/Px determinations, possibly because of spectral complexities arising from other minerals in chondrites. Characteristic features in VISNIR spectra are sensitive to the proportions and compositions of olivine and pyroxenes, the minerals most affected by oxidative metamorphism. This work may allow spectral calibration for the determination of mineralogy and petrologic type, and thus may be useful for spectroscopic studies of asteroids.     

Aquifer Storage Recovery (ASR) of chlorinated municipal drinking water in a confined aquifer

About 1.02 × 10⁶ m³ of chlorinated municipal drinking water was injected into a confined aquifer, 94–137 m below Roseville, California, between December 2005 and April 2006. The water was stored in the aquifer for 438 days, and 2.64 × 10⁶ m³ of water were extracted between July 2007 and February 2008. On the basis of Cl⁻ data, 35% of the injected water was recovered and 65% of the injected water and associated disinfection by-products (DBPs) remained in the aquifer at the end of extraction. About 46.3 kg of total trihalomethanes (TTHM) entered the aquifer with the injected water and 37.6 kg of TTHM were extracted. As much as 44 kg of TTHMs remained in the aquifer at the end of extraction because of incomplete recovery of injected water and formation of THMs within the aquifer by reactions with free-chlorine in the injected water. Well-bore velocity log data collected from the Aquifer Storage Recovery (ASR) well show as much as 60% of the injected water entered the aquifer through a 9 m thick, high-permeability layer within the confined aquifer near the top of the screened interval. Model simulations of ground-water flow near the ASR well indicate that (1) aquifer heterogeneity allowed injected water to move rapidly through the aquifer to nearby monitoring wells, (2) aquifer heterogeneity caused injected water to move further than expected assuming uniform aquifer properties, and (3) physical clogging of high-permeability layers is the probable cause for the observed change in the distribution of borehole flow. Aquifer heterogeneity also enhanced mixing of native anoxic ground water with oxic injected water, promoting removal of THMs primarily through sorption. A 3 to 4-fold reduction in TTHM concentrations was observed in the furthest monitoring well 427 m downgradient from the ASR well, and similar magnitude reductions were observed in depth-dependent water samples collected from the upper part of the screened interval in the ASR well near the end of the extraction phase. Haloacetic acids (HAAs) were completely sorbed or degraded within 10 months of injection.     

The Millennium Galaxy Catalogue: bulge–disc decomposition of 10 095 nearby galaxies

We present near-infrared (NIR) adaptive optics-assisted spectroscopic observations of the  CO (Δμ= 2)  absorption bands towards the centre of the giant elliptical galaxy NGC 1399. The observations were made with NAOS-CONICA (on the European Southern Observatory's Very Large Telescope) and have a full width at half-maximum resolution of 0.15 arcsec (14 pc). Kinematic analysis of the observations reveals a decoupled core and strongly non-Gaussian line-of-sight velocity profiles in the central 0.2 arcsec (19 pc). NIR imaging also indicates an asymmetric elongation of the central isophotes in the same region.
We use spherical orbit-superposition models to interpret the kinematics, using a set of orthogonal 'eigen-velocity profiles' that allow us to fit models directly to spectra. The models require a central black hole of mass  1.2^+0.5_−0.6× 10⁹ M_⊙  , with a strongly tangentially biased orbit distribution in the inner 40 pc.     

Results from the Wide Angle Search for Planets Prototype (WASP0) – II. Stellar variability in the Pegasus field

Recent wide field photometric surveys, which target a specific field for long durations, are ideal for studying both long- and short-period stellar variability. Here, we report on 75 variable stars detected during the observations of a field in Pegasus using the Wide Angle Search for Planets Prototype (WASP0) instrument, 73 of which are new discoveries. The variables detected include 16 δ Scuti stars, 34 eclipsing binaries, 3 BY Draconis stars and 4 RR Lyraes. We estimate that the fraction of stars in the field brighter than   V ∼ 13.5  exhibiting variable behaviour with an amplitude greater than 0.6 per cent rms is ∼0.4 per cent. These results are compared with other wide field stellar variability surveys, and implications for detecting transits due to extra-solar planets are discussed.     

Formation of the prelunar accretion disk

According to the single-impact hypothesis for forming the Moon, the angular momentum needed for the present Earth-Moon system can be imparted to the proto-Earth by a collision with a body having one-tenth of the mass or more. The collision must vaporize a large amount of rock which must stay in the form of vapor after expanding in density by a factor of several, so that pressure gradients can accelerate significant amounts of the matter into orbital motion about the proto-Earth. A successful theory must put considerably more than a lunar mass into orbit, having considerably more angular momentum than is needed to assemble a lunar mass in orbit at 3 Earth radii. Such a collision has been simulated by a particular form of a particle-in-cell representation of hydrodynamics and 78 cases have been run representing variations in a variety of parameters. A significant fraction of the cases were successful in creating a satisfactory prelunar accretion disk. A fairly common characteristic of these cases was the presence of an excess velocity in the collision (above that of a parabolic orbit), implying that the projectile involved in the collision existed in an Earth-crossing orbit of significant ellipticity. A majority of the mass of the prelunar accretion disk is contributed by the projectile.     

Possible influence of comets on the chemical evolution of the galaxy

It has been suggested by Cameron that a cloud of comets containing a mass of condensable elements, comparable to the mass of such elements in the sun, formed on the outskirts of the solar system. If the formation of such comet clouds is a general feature of star formation, they constitute a significant sink of elements heavier than helium. It is shown here that this process provides a possible explanation for the very slow rate at which the mean metal abundance of disk stars has increased during the lifetime of the Galaxy.