Assessing spectral evidence of aqueous activity in two putative martian paleolakes

We evaluate the evidence for the presence of mineral spectral signatures indicative of the past presence of water at two putative paleolakes on Mars using observations by the Mars Reconnaissance Orbiter (MRO) Compact Reconnaissance Image Spectrometer for Mars (CRISM). CRISM spectra of both sites are consistent with laboratory spectra of Mg-rich phyllosilicates. Our analysis represents the first detailed evaluation of these locations. The spatial occurrence and association with topographic features within the craters is distinctly different for the two sites. The occurrence of these minerals supports the conclusion that water was once active in the areas sampled by these craters. The distribution of the phyllosilicates in Luqa does not provide distinctive evidence for the presence of a previous standing body of water and is consistent with either impact emplacement or post-impact alteration. For Cankuzo, the phyllosilicate distribution provides evidence of a layer in the crater wall indicative of aqueous activity, but does not require a paleolake.     

Radar and photometric observations and shape modeling of contact binary near-Earth Asteroid (8567) 1996 HW1

We observed near-Earth Asteroid (8567) 1996 HW1 at the Arecibo Observatory on six dates in September 2008, obtaining radar images and spectra. By combining these data with an extensive set of new lightcurves taken during 2008-2009 and with previously published lightcurves from 2005, we were able to reconstruct the object’s shape and spin state. 1996 HW1 is an elongated, bifurcated object with maximum diameters of 3.8 × 1.6 × 1.5 km and a contact-binary shape. It is the most bifurcated near-Earth asteroid yet studied and one of the most elongated as well. The sidereal rotation period is 8.76243 ± 0.00004 h and the pole direction is within 5° of ecliptic longitude and latitude (281°, −31°). Radar astrometry has reduced the orbital element uncertainties by 27% relative to the a priori orbit solution that was based on a half-century of optical data. Simple dynamical arguments are used to demonstrate that this asteroid could have originated as a binary system that tidally decayed and merged.     

A new systematic approach using the Modified Gaussian Model: Insight for the characterization of chemical composition of olivines, pyroxenes and olivine-pyroxene mixtures

An automatic procedure has been implemented on the original MGM approach (Sunshine et al., 1990) in order to deal with an a priori unknown mafic mineralogy observed in the visible-near infrared by reflectance spectroscopy in the case of laboratory or natural rock spectra. We consider all the mixture possibilities involving orthopyroxene, clinopyroxene and olivine, and use accordingly for each configuration different numbers of Gaussians, depending on the potential complexity of the mixture. A key issue is to initialize the MGM procedure with a proper setting for the Gaussians parameters. An automatic analysis of the shape of the spectrum is first performed. The continuum is handled with a second order polynomial adjusted on the local maxima along the spectrum and Gaussians parameters initial settings are made on the basis of laboratory results available in the literature in the case of simple mixtures of mafic minerals. The returned MGM solutions are then assessed on spectroscopic grounds and either validated or discarded, on the basis of a mineralogical sorting.The results presented in this paper are a first quantitative step to characterize both modal and chemical compositions of pyroxenes and olivines. A demonstration of the methodology on specific examples of binary and ternary olivine-pyroxenes mixtures has been made, which shows that the different non-linear effects which affect the Gaussian parameters (center and strength) can be successfully handled. Of note is the fact that the band center positions associated with the different mafic minerals are not set here in the inverse problem, and thus the MGM outputs are truly informative of the chemical composition of pyroxenes and olivines. With the consideration of some limits on the detection thresholds, these results are quite promising for increasing the operational use of the Modified Gaussian Model with large hyperspectral data sets in view of establishing detailed mineralogical mappings of magmatic units.     

The influence of Mercury’s inner core on its physical libration

As Mercury orbits the Sun, gravitational torques on its equatorial elliptical shape give rise to a planetary libration. The amplitude of Mercury’s libration, as determined from Earth-based radar speckle pattern observations, suggests that only the mantle participates in the motion. This indicates a decoupling between the core and the mantle, and therefore that the outermost part of the core must be fluid. If a solid inner core is present at the center of Mercury, the equatorial elliptical shape of the latter may become misaligned with that of Mercury’s mantle, leading to an internal gravitational torque between the two. If this torque is large, it may participate in the dynamics of Mercury’s libration. The goal of this work is to determine whether Mercury’s observed librations can be used to place constraints on the properties of its inner core. We present a comparison between predicted and observed librations for a range of interior models of Mercury, with various inner core sizes and fluid core densities. We show that a marginally better fit to observations can be achieved for interior models that have an inner core radius larger than 400 km. However, the improvement in fit is small, and it is not possible to draw robust conclusions on the size of Mercury’s inner core on the basis of existing libration data. Nevertheless, our study demonstrates that the influence of the inner core on the libration of Mercury could be detected with a decade worth of accurate observations.     

Near-infrared spectroscopy of primitive asteroid families

We compare 13 near-infrared (0.8-2.4 μm) spectra of two low albedo C complex outer-belt asteroid families: Themis and Veritas. The disruption ages of these two families lie at opposite extremes: 2.5 ± 1.0 Gyr and 8.7 ± 1.7 Myr, respectively. We found striking differences between the two families, which show a range of spectral shapes and slopes. The seven Themis family members (older surfaces) have “red” (positive) slopes in the 1.6-2.4 μm region; in contrast, the six Veritas members (younger surfaces) have significantly “flatter” slopes at these same wavelengths. Moreover, the two families are characterized by different concavity at shorter (1.0-1.5 μm) wavelengths with the Themis group being consistently flat or concave up (smile) and the Veritas group being consistently concave down (frown). Each family contains a broad range of diameters, suggesting our results are not due to comparisons of asteroids of different sizes. The statistically significant clustering of the two spectral groups could be explained by one of the following three possibilities or a combination of them: (1) space weathering effects, (2) differences in original composition, or (3) differences in thermal history perhaps as a result of the difference in parent body sizes. As a result of our analyses, we propose a new method to quantify broad and shallow structures in the spectra of primitive asteroids. We found reasonable matches between the observed asteroids and individual carbonaceous chondrite meteorites. Because these meteoritic fits represent fresh surfaces, space weathering is neither necessary nor ruled out as an explanation of spectral differences between families. The six Veritas family near-infrared (NIR) spectra represent the first NIR analysis of this family, thus significantly increasing our understanding of this family over these wavelengths.     

Star‐forming galaxies observed with X‐shooter

In the last couple of decades hundreds of studies have explored the nature of star‐forming galaxies at different redshifts. This contribution focuses on X‐shooter observations of star‐burst galaxies at 0 < z < 6 from commissioning runs, science verification, and regular observations, and demonstrates the capability of the new instrument in this competitive field. Observations of gravitationally lensed galaxies show that X‐shooter has no limitation in the redshift desert (1.4 < z < 2) where the strong optical emission lines are shifted to the near‐IR region. Physical properties of galaxies, such as masses, metallicities, abundance ratios, and star formation rates can be derived from observations with relatively short integration times for faint galaxies. The simultaneous UV to near‐IR spectral coverage makes derivation of physical quantities more reliable because there are no differential slit losses as may occur when observations from different optical and near‐IR instruments are used. Over the entire redshift range, spectra of faint galaxies will allow us to better measure stellar ages and dominating ionisation sources compared to broad band spectral energy distribution measurements (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

北斗与GPS组合伪距单点定位精度分析

主要介绍了北斗与G PS组合单点定位时的原理和模型,根据自编程序,利用同济大学TJA站的数据进行计算及分析比较GPS伪距、北斗伪距、北斗/GPS组合伪距单点定位的精度。结果表明：北斗伪距单点定位的精度平面方向上达到3m以内,高程方向优于8 m ,满足普通导航定位的需求。北斗/G PS组合伪距单点定位精度明显优于单系统。在单系统观测条件差时,组合系统可以减少对单一系统的依赖性,而且还可以增强卫星定位的稳定性和可靠性。     

上海深井地震综合观测地磁资料分析

运用崇明长江农场台和浦东张江台新建地震综合深井地磁三分量资料,宋用小波变化方法,研究地磁场井下观测方式、数据质量和噪声特性.结果表明:①深井地磁观测资料日变形态明显,与地面观测资料一致性较好;②深井地磁观测能滤除大部分空间变化磁场产生的扰动;③深井观测的背景噪声幅度小,扰动频段集中.     

黄土高原陆面过程观测试验的仪器精度和观测误差分析

利用"黄土高原陆面过程观测试验"2009年定西站的平行对比观测资料,分析了微气象观测仪器的精度和观测误差.结果显示:在大多数情况下,A301P型风杯风速计和HMP45D型温湿传感器对风温湿的观测偏差分别不超过±0.10m.s-1、±0.16℃和±1.00%;107型和109型温度传感器对土壤温度的观测偏差分别不超过±0.1℃和±0.03℃;HFP01型热通量板对土壤热通量的观测偏差不超过±11W.m-2;涡动协方差系统(CAST3+Li7500)观测计算得到的感热、潜热和动量通量的偏差分别不超过±8W.m-2、±8W.m-2、±0.02kg.m-1.s-2.此试验对于大气风速、温度、相对湿度、土壤湿度和温度、地表辐射以及地表通量这些要素的观测,相同型号仪器之间的数据都很一致.并且不同型号仪器进行对比观测风速、土壤温度、净辐射、向下长短波辐射和土壤热通量得到的结果也较一致.结果表明,该试验大多数仪器有比较高的精度,仪器之间也比较一致,观测误差较小,基本能够满足陆面过程观测的要求.     

全国铀矿资源潜力评价航放数据处理与研究

全国铀矿资源潜力评价航放数据处理与研究通过对各铀成矿区带航空放射性特征分析研究,提取了与铀矿化密切相关的航放铀含量异常及高场和航放多元信息异常,总结了花岗岩型、火山岩型、碳硅泥岩型和砂岩型等4大类型铀矿的航空放射性特征及预测要素组合模式。该组合模式在铀资源潜力评价中应用效果十分显著。航放异常信息的合理组合,能有效地加强和突出与铀矿化相关的放射性异常信息及成矿环境信息,对全国铀矿资源潜力评价和铀矿普查找矿具有重要意义。