Cooling of Dense Gas by H2O Line Emission and an Assessment of its Effects in Chondrule-Forming Shocks

We consider gas at densities appropriate to protoplanetary disks and calculate its ability to cool due to line radiation emitted by H2O molecules within the gas. Our work follows that of Neufeld & Kaufman (1993; ApJ, 418, 263), expanding on their work in several key aspects, including use of a much expanded line database, an improved escape probability formulism, and the inclusion of dust grains, which can absorb line photons. Although the escape probabilities formally depend on a complicated combination of optical depth in the lines and in the dust grains, we show that the cooling rate including dust is well approximated by the dust-free cooling rate multiplied by a simple function of the dust optical depth. We apply the resultant cooling rate of a dust-gas mixture to the case of a solar nebula shock pertinent to the formation of chondrules, millimeter-sized melt droplets found in meteorites. Our aim is to assess whether line cooling can be neglected in chondrule-forming shocks or if it must be included. We find that for typical parameters, H2O line cooling shuts off a few minutes past the shock front; line photons that might otherwise escape the shocked region and cool the gas will be absorbed by dust grains. During the first minute or so past the shock, however, line photons will cool the gas at rates ~ 10,000 K/hr, dropping the temperature of the gas (and most likely the chondrules within the gas) by several hundred K. Inclusion of H2O line cooling therefore must be included in models of chondrule formation by nebular shocks.Comment: Accepted for publication in The Astrophysical Journa

The Alpha Particle X-Ray Spectrometer (APXS): Results from Gusev Crater and Calibration Report

The chemical composition of rocks and soils on Mars analyzed during the Mars Exploration Rover Spirit Mission was determined by X-ray analyses with the Alpha Particle X-Ray Spectrometer (APXS). Details of the data analysis method and the instrument calibration are presented. Measurements performed on Mars to address geometry effects and background contributions are shown. Cross calibration measurements among several instrument sensors and sources are discussed. An unintentional swap of the two flight instruments is evaluated. New concentration data acquired during the first 470 sols of rover Spirit in Gusev Crater are presented. There are two geological regions, the Gusev plains and the Columbia Hills. The plains contain soils that are very similar to previous landing sites on Mars. A meteoritic component in the soil is identified. Rocks in the plains revealed thin weathering rinds. The underlying abraded rock was classified as primitive basalt. One of these rocks contained significant Br that is probably associated with vein-filling material of different composition. One of the trenches showed large subsurface enrichments of Mg, S, and Br. Disturbed soils and rocks in the Columbia Hills revealed different elemental compositions. These rocks are significantly weathered and enriched in mobile elements, such as P, S, Cl, or Br. Even abraded rock surfaces have high Br concentrations. Thus, in contrast to the rocks and soils in the Gusev Plains, the Columbia Hills material shows more significant evidence of ancient aqueous alteration

Short-lived Nuclei in the Early Solar System: Possible AGB Sources

(Abridged) We review abundances of short-lived nuclides in the early solar system (ESS) and the methods used to determine them. We compare them to the inventory for a uniform galactic production model. Within a factor of two, observed abundances of several isotopes are compatible with this model. I-129 is an exception, with an ESS inventory much lower than expected. The isotopes Pd-107, Fe-60, Ca-41, Cl-36, Al-26, and Be-10 require late addition to the solar nebula. Be-10 is the product of particle irradiation of the solar system as probably is Cl-36. Late injection by a supernova (SN) cannot be responsible for most short-lived nuclei without excessively producing Mn-53; it can be the source of Mn-53 and maybe Fe-60. If a late SN is responsible for these two nuclei, it still cannot make Pd-107 and other isotopes. We emphasize an AGB star as a source of nuclei, including Fe-60 and explore this possibility with new stellar models. A dilution factor of about 4e-3 gives reasonable amounts of many nuclei. We discuss the role of irradiation for Al-26, Cl-36 and Ca-41. Conflict between scenarios is emphasized as well as the absence of a global interpretation for the existing data. Abundances of actinides indicate a quiescent interval of about 1e8 years for actinide group production in order to explain the data on Pu-244 and new bounds on Cm-247. This interval is not compatible with Hf-182 data, so a separate type of r-process is needed for at least the actinides, distinct from the two types previously identified. The apparent coincidence of the I-129 and trans-actinide time scales suggests that the last actinide contribution was from an r-process that produced actinides without fission recycling so that the yields at Ba and below were governed by fission.Comment: 92 pages, 14 figure files, in press at Nuclear Physics

Extreme 54Cr-rich nano-oxides in the CI chondrite Orgueil -Implication for a late supernova injection into the Solar System

Systematic variations in 54Cr/52Cr ratios between meteorite classes (Qin et al., 2010a; Trinquier et al., 2007) point to large scale spatial and/or temporal isotopic heterogeneity in the solar protoplanetary disk. Two explanations for these variations have been proposed, with important implications for the formation of the Solar System: heterogeneous seeding of the disk with dust from a supernova, or energetic-particle irradiation of dust in the disk. The key to differentiating between them is identification of the carrier(s) of the 54Cr anomalies. Here we report the results of our recent NanoSIMS imaging search for the 54Cr-rich carrier in the acid-resistant residue of the CI chondrite Orgueil. A total of 10 regions with extreme 54Cr-excesses ({\delta}54Cr values up to 1500 %) were found. Comparison between SEM, Auger and NanoSIMS analyses showed that these 54Cr-rich regions are associated with one or more sub-micron (typically less than 200 nm) Cr oxide grains, most likely spinels. Because the size of the NanoSIMS primary O- ion beam is larger than the typical grain size on the sample mount, the measured anomalies are lower limits, and we estimate that the actual 54Cr enrichments in three grains are at least 11 times Solar and in one of these may be as high as 50 times Solar. Such compositions strongly favor a Type II supernova origin. The variability in bulk 54Cr/52Cr between meteorite classes argues for a heterogeneous distribution of the 54Cr carrier in the solar protoplanetary disk following a late supernova injection event. Such a scenario is also supported by the O-isotopic distribution and variable abundances in different planetary materials of other presolar oxide and silicate grains from supernovae

APXS ANALYSES OF BOUNCE ROCK: THE FIRST SHERGOTTITE ON MARS

During the MER Mission, an isolated rock at Meridiani Planum was analyzed by the Athena instrument suite [1]. Remote sensing instruments noticed its distinct appearance. Two areas on the untreated rock surface and one area that was abraded with the Rock Abrasion Tool were analyzed by Microscopic Imager, Mossbauer Mimos II [2], and Alpha Particle X-ray Spectrometer (APXS). Results of all analyses revealed a close relationship of this rock with known basaltic shergottites

Two Years of Chemical Sampling on Meridiani Planum by the Alpha Particle X-Ray Spectrometer Onboard the Mars Exploration Rover Opportunity

For over two terrestrial years, the Mars Exploration Rover Opportunity has been exploring the martian surface at Meridiani Planum using the Athena instrument payload [1], including the Alpha Particle X-Ray Spectrometer (APXS). The APXS has a small sensor head that is mounted on the robotic arm of the rover. The chemistry, mineralogy and morphology of selected samples were investigated by the APXS along with the Moessbauer Spectrometer (MB) and the Microscopic Imager (MI). The Rock Abrasion Tool (RAT) provided the possibility to dust and/or abrade rock surfaces down to several millimeters to expose fresh material for analysis. We report here on APXS data gathered along the nearly 6-kilometers long traverse in craters and plains of Meridiani

Chemical Diversity along the Traverse of the Rover Spirit at Gusev Crater

The Alpha-Particle-X-ray Spectrometer (APXS) is part of the in situ payload of the Mars Exploration Rovers. It has determined the chemical composition of soils and rocks along the nearly 6 km long traverse of the rover Spirit. The measuring method a combination of PIXE and XRF using Cm244 sources - allowed the unambiguous identification of elemental compositions with high precision. Besides sample triage and quantification of saltforming elements as indicators for aqueous alteration, the APXS also delivered important constraints to mineralogy intruments (i.e., Mossbauer (MB), MiniTES, Pancam) on minerals and rock types. The mineralogy instruments on the other hand provided constraints on minerals used for APXS normative calculations and, e.g. allowed the attribution of S to sulfate, instead of sulfide or elemental sulfur. This abstract gives an updated overview of the data obtained up to our current rover position on sol 720 at the eastern base of the Columbia Hills. We will emphasize elemental correlations that imply the presence of certain minerals that can not be identified by the MER mineralogy instruments

Constraints on the Variations of the Fundamental Couplings

We reconsider several current bounds on the variation of the fine-structure constant in models where all gauge and Yukawa couplings vary in an interdependent manner, as would be expected in unified theories. In particular, we re-examine the bounds established by the Oklo reactor from the resonant neutron capture cross-section of 149Sm. By imposing variations in \Lambda_{QCD} and the quark masses, as dictated by unified theories, the corresponding bound on the variation of the fine-structure constant can be improved by about 2 orders of magnitude in such theories. In addition, we consider possible bounds on variations due to their effect on long lived \alpha- and \beta-decay isotopes, particularly 147Sm and 187Re. We obtain a strong constraint on \Delta \alpha / \alpha, comparable to that of Oklo but extending to a higher redshift corresponding to the age of the solar system, from the radioactive life-time of 187Re derived from meteoritic studies. We also analyze the astrophysical consequences of perturbing the decay Q values on bound state \beta-decays operating in the s-process.Comment: 25 pages, latex, 5 eps figure

The origin of the Moon within a terrestrial synestia

The giant impact hypothesis remains the leading theory for lunar origin. However, current models struggle to explain the Moon's composition and isotopic similarity with Earth. Here we present a new lunar origin model. High-energy, high-angular momentum giant impacts can create a post-impact structure that exceeds the corotation limit (CoRoL), which defines the hottest thermal state and angular momentum possible for a corotating body. In a typical super-CoRoL body, traditional definitions of mantle, atmosphere and disk are not appropriate, and the body forms a new type of planetary structure, named a synestia. Using simulations of cooling synestias combined with dynamic, thermodynamic and geochemical calculations, we show that satellite formation from a synestia can produce the main features of our Moon. We find that cooling drives mixing of the structure, and condensation generates moonlets that orbit within the synestia, surrounded by tens of bars of bulk silicate Earth (BSE) vapor. The moonlets and growing moon are heated by the vapor until the first major element (Si) begins to vaporize and buffer the temperature. Moonlets equilibrate with BSE vapor at the temperature of silicate vaporization and the pressure of the structure, establishing the lunar isotopic composition and pattern of moderately volatile elements. Eventually, the cooling synestia recedes within the lunar orbit, terminating the main stage of lunar accretion. Our model shifts the paradigm for lunar origin from specifying a certain impact scenario to achieving a Moon-forming synestia. Giant impacts that produce potential Moon-forming synestias were common at the end of terrestrial planet formation.Comment: Accepted for publication in Journal of Geophysical Research: Planets. Main text: 44 pages, 24 figures. Supplement: 16 pages, 5 figures, 3 table

Die Rolle der neutralen Sphingomyelinase bei der Kontrolle emotionalen Verhaltens im Tiermodell an der weiblichen Maus

Hintergrund und Ziele: Depressionen und Angststörungen zählen zu den häufigsten und schwerwiegendsten psychiatrischen Erkrankungen weltweit, deren Pathogenese bis heute nicht vollumfassend beschrieben ist. Ein Überschuss an Ceramid im Gehirn konnte bereits mit der Pathogenese der Depression assoziiert werden. Die Inhibition der Sauren Sphingomyelinase wurde darüber hinaus als Zielstruktur antidepressiver Pharmakotherapie identifiziert. Die Rolle der Neutralen Sphingomyelinase 2 (NSM), eines weiteren Schlüsselenzyms des Ceramid- Metabolismus, bei der Regulation von emotionalem Verhalten ist bis dato noch nicht abschließend geklärt. In der vorliegenden Arbeit wurde daher erstmals die Auswirkung einer partiellen Inaktivierung der NSM auf das emotionale Verhalten an der weiblichen Maus untersucht. Methoden: Als Versuchstiere dienten 11 weibliche C75BL/6 Wildtyp-Mäuse (NSM WT) und 12 weibliche heterozygote fro/wt-Mutanten (NSM fro). Die heterozygote fragilitas ossium- Mutation (fro) führt zum partiellen Knockout des für die NSM kodierenden Smpd3-Gens. In den Verhaltenstests Open Field Test (OFT), Elevated Plus Maze (EPM), Light-Dark-Box (LDB), Novelty Suppressed Feeding (NSF), Forced Swim Test (FST) und Sucrose Preference Test (SPT) wurden die Versuchstiere auf ängstliche und depressionsähnliche Verhaltensänderungen hin untersucht. Ergebnisse und Beobachtungen: NSM fro-Mäuse zeigten im NSF und im FST ein signifikant verringertes depressionsähnliches Verhalten. Im SPT konnte hingegen kein signifikanter Unterschied hinsichtlich des anhedonen Verhaltens bei NSM fro-Mäusen gegenüber NSM WT- Mäusen festgestellt werden. Im EPM und in der LDB zeigten NSM fro-Mäuse ein signifikant verringertes Angstverhalten, während im OFT kein signifikanter Unterschied hinsichtlich des Angst- und Explorationsverhaltens beobachtet wurde. Die NSM fro-Mutation hatte in den Verhaltenstests keinen signifikanten Einfluss auf die allgemeine Bewegungsaktivität. Schlussfolgerungen und Diskussion: Erstmalig konnte gezeigt werden, dass die NSM fro- Mutation bei der weiblichen Maus antidepressive und anxiolytische Effekte zu vermitteln scheint. Die NSM als Schlüsselenzym der Ceramid-Synthese könnte demnach eine wichtige Rolle bei der Regulation von emotionalem Verhalten einnehmen. Die Inhibition der NSM stellt einen vielversprechenden pharmakologischen Angriffspunkt innerhalb des Ceramid- Stoffwechsels dar. Die weitere Erforschung der NSM im Rahmen der Pathogenese von Depression und Angst erscheint als ein lohnender Gegenstand zukünftiger präklinischer und klinischer Forschung.Objectives: Depressive disorders and anxiety disorders are among the most common and severe psychiatric illnesses worldwide, the pathogenesis of which is not yet fully understood. An abundance of ceramide in the brain has already been associated with the pathogenesis of depression. Furthermore, the inhibition of acid sphingomyelinase was identified as a target structure of antidepressant pharmacotherapy. The role of neutral sphingomyelinase 2 (NSM), another key enzyme in ceramide metabolism, in the regulation of emotional behavior has not yet been fully clarified. Therefore, the effect of the partial inactivation of the NSM on emotional behavior of the female mouse was examined for the first time. Design and methods: 11 female C75BL/6 wildtype mice (NSM WT) and 12 female heterozygous fro/wt mutants (NSM fro) served as experimental animals. The heterozygous fragilitas ossium (fro) mutation leads to a partial knockout of the NSM encoding Smpd3 gene. In the behavioral tests Open Field Test (OFT), Elevated Plus Maze (EPM), Light Dark Box (LDB), Novelty Suppressed Feeding (NSF), Forced Swim Test (FST) and Sucrose Preference Test (SPT), the animals were examined for anxiety-like and depressive-like behavioral changes. Observations and results: NSM fro mice showed significantly reduced depressive-like behavior in the NSF and in the FST. No significant change in the anhedonic tone of NSM fro mice could be observed in the SPT. In the EPM and in the LDB, NSM fro mice showed a significantly reduced anxiety-like behavior, while no significant difference of anxiety-like behavior and exploratory behavior was observed in the OFT. The NSM fro mutation had no significant impact on general locomotion in the behavioral tests. Conclusions: The NSM fro mutation appears to mediate antidepressant and anxiolytic effects in female mice. The NSM as a key enzyme of ceramide synthesis therefore seems to play an important role in the regulation of emotional behavior. The inhibition of NSM presents a promising target for the regulation of ceramide metabolism. Further investigation of NSM in the context of the pathogenesis of anxiety and depression is a worthwhile focus of future experimental and clinical research