Monte Carlo modeling of sodium in Mercury’s exosphere during the first two MESSENGER flybys

We present a Monte Carlo model of the distribution of neutral sodium in Mercury’s exosphere and tail using data from the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft during the first two flybys of the planet in January and September 2008. We show that the dominant source mechanism for ejecting sodium from the surface is photon-stimulated desorption (PSD) and that the desorption rate is limited by the diffusion rate of sodium from the interior of grains in the regolith to the topmost few monolayers where PSD is effective. In the absence of ion precipitation, we find that the sodium source rate is limited to ∼10⁶-10⁷ cm⁻² s⁻¹, depending on the sticking efficiency of exospheric sodium that returns to the surface. The diffusion rate must be at least a factor of 5 higher in regions of ion precipitation to explain the MASCS observations during the second MESSENGER flyby. We estimate that impact vaporization of micrometeoroids may provide up to 15% of the total sodium source rate in the regions observed. Although sputtering by precipitating ions was found not to be a significant source of sodium during the MESSENGER flybys, ion precipitation is responsible for increasing the source rate at high latitudes through ion-enhanced diffusion.     

The Hg geochemistry of a geothermal stream, Steamboat Creek, Nevada: natural vs. anthropogenic influences

 A series of water samples from Steamboat Creek, Nevada, was analyzed for total mercury concentrations. Concentrations from these waters were 40 to 60 times higher than the pristine mountain streams entering the creek. The major source of the mercury entering Steamboat Creek is probably from gold/silver processing that took place in the 1860s. Received: 10 March 1997 · Accepted: 2 September 1997     

河北怀来地震台4号观测井水汞的有震异常分析

利用河北怀来4井1990年至2002年的水汞观测资料，对怀来4井汞量异常进行了分析，分析结果显示，怀来4井水汞异常与地震的对应率较好，1990年以来，其异常对于测点监测范围的有感地震及中小地震和距离测点较远的范围内发生的5．0级以上地震有很高的对应率。     

贵州万山汞矿尾矿堆及地表水的环境地球化学特征

对贵州万山汞矿区尾渣堆(主要为炉渣组成)、地表水及河流沉淀物的汞迁移进行了研究。由于赋矿岩石为白云岩，高温煅烧的炉渣中含CaO等碱性物质，炉渣的风化作用释放出汞以及碱性水．流经尾渣堆的地表水碱性强(pH10．6-11．8)、电导率高，且具有明显不同的主要离子组成．万山汞矿矿石单一，主要为辰砂，其他矿石极少，因此炉渣及其渗滤水中除汞外的重金属含量很低．尾渣堆中的汞及碱性物质是对周围环境的主要威胁．在尾渣堆下游汞含量很快降低，约300n，范围内水中的溶解汞从300—1900，ng/L降至72ng／L，而且水的碱性也被中和．但是，由于尾渣堆中的汞及碱性物质含量高，尾渣堆的长时间风化及水流的溶解会将大量汞搬运到周围的土壤及水体并对生物产生不利影响．     

A comparison of anthropogenic mercury pollution in Kastela Bay (Croatia) with pristine estuaries in Ore (Sweden) and Krka (Croatia)

Anthropogenic mercury pollution was studied in Kastela Bay (Croatia), 10 years after chloralkaline plant (PVC) stopped production. The concentration of total mercury determined in sediments which are composed mainly of calcite and quartz, are in the range 14,280-30,400 ng/g. The values are higher than reported in the literature for Elbe and Seine estuaries and also above 25,000 ng/g used for criterion in remediation project in Minamata Bay. The concentration of methylmercury 6.05-36.74 ng/g are typical for slightly to highly contaminated estuarine sediments. The low ratio of methylmercury to total mercury found in sediments of Kastela Bay is in the range 0.04-0.18%. It can be explained that in this region predominate conditions which do not promote in-situ methylation. Sediments were found to be highly anoxic. Concentrations of total mercury in unfiltered surface waters are in the range 69-145 ng/l and in unfiltered bottom waters in the range 230-1,418 ngl(-1). High concentrations found in bottom waters suggest that either resuspension or partial dissolution of sediments takes place. An experiment performed on filtered and unfiltered waters showed that about 85% of total mercury in surface water and almost 100% in bottom water was retained on 45 microm filters. To demonstrate contrasts, two pristine estuaries from norths and south Europe were studied. Silicious sediments of Ore estuary (Sweden) and calcareous sediments of Krka estuary (Croatia) have total mercury concentrations close to accepted background level. The ratio of methylmercury to total mercury is < or = 1% in all samples with one exception. The highest observed ratio (2.70%) was in the surface sediment from E2 station in Krka estuary measured in March 2000. This location is suitable for studying methylmercury formation in pristine environment.     

滇西水汞观测的地震短临预报指标

通过对滇西下关,弥渡,洱源江干,洱源滇２０＃,保山等水汞在１２次地震前异常特征分析的结果表明,汞异常形态清楚,异常变化率大,单项以多点突跳为主,整体以群体突跳为主,短临异常持续时间数十天,地震多数发生在首次异常后２３－１１１天的８８天之内;大震存在中短期异常和时空演变规律,对应地震范围受震中距和地震构造的双重制约,似乎与孕震能大小和传播途径有关,大体存在的异常持续时间越长,异常数量越多,震级越大的     

氡,汞测量用于断裂活动性和分段的研究

作者首先给出海原活动断裂带从边沟至硝口的３条较长次级剪切断层，干盐池拉分盆地和边沟推挤构造区内的断层，以及尾端挤压构造区内的六盘山东麓逆断层的气氡，气汞浓度测量结果，然后分析了断层气浓度与断层活动性之间的关系，研究结果表明，测试条件大体一致的基础上，气氡，气汞浓度与断层活动性之间有着明显的对应关系，从而证明了断层气测量方法对于活断层分段和活动性研究是一种有效的手段。     

汞在460、534地区的分布特征及其找铀矿的意义

本文在介绍一种新的土壤汞量测量找矿方法的同时,着重用大量的实测数据阐明汞在460铀矿床上的分布特征。汞在该矿床上部“黑矿”中的平均含量高达11430ppb,最高达193800ppb,而一般岩石中的汞含量只有数十至数百个ppb。通过对铀矿石及其主岩中的汞的热释谱分析,发现释汞主峰温度在350℃以上的中温、高温相态汞与铀矿化关系密切。铀矿床上部土壤汞晕规模大(550×350m~2),平均含量可达563ppb,最高达6080ppb,平均衬度16,最高达174。汞含量随着采样深度的加深而升高。在矿床外围测出了相似的汞晕,并进行了成矿预测。上述成果已用于生产。     

Mercury: the enigmatic innermost planet

The planet Mercury, a difficult object for study by astronomical observation and spacecraft exploration alike, poses multiple challenges to our general understanding of the inner planets. Mercury’s anomalously high uncompressed density implies a metal fraction of 60% or more by mass, an extreme outcome of planetary formational processes common to the inner solar system. Whether that outcome was the result of chemical gradients in the early solar nebula or removal by impact or vaporization of most of the silicate shell from a differentiated protoplanet can potentially be distinguished on the basis of the chemical composition of the present crust. Our understanding of the geological evolution of Mercury and how it fits within the known histories of the other terrestrial planets is restricted by the limited coverage and resolution of imaging by the only spacecraft to have visited the planet. The role of volcanism in Mercury’s geological history remains uncertain, and the dominant tectonic structures are lobate scarps interpreted as recording an extended episode of planetary contraction, issues that require global imaging to be fully examined. That Mercury has retained a global magnetic field when larger terrestrial planets have not stretches the limits of standard hydromagnetic dynamo theory and has led to proposals for a fossil field or for exotic dynamo scenarios. Hypotheses for field generation can be distinguished on the basis of the geometry of Mercury’s internal field, and the existence and size of a fluid outer core on Mercury can be ascertained from measurements of the planet’s spin axis orientation and gravity field and the amplitude of Mercury’s forced librations. The nature of Mercury’s polar deposits, suggested to consist of volatile material cold-trapped on the permanently shadowed floors of high-latitude impact craters, can be tested by remote sensing of the composition of Mercury’s surface and polar atmosphere. The extremely dynamic exosphere, which includes a number of species derived from Mercury’s surface, offers a novel laboratory for exploring the nature of the complex and changing interactions among the solar wind, a small magnetosphere, and a solid planet. Recent ground-based astronomical measurements and several new theoretical developments set the stage for the in-depth exploration of Mercury by two spacecraft missions within the coming decade.     

Clausthalite in coal

A lead selenide mineral, tentatively identified as clausthalite (PbSe) based on optical microscopy, scanning electron microscopy with energy-dispersive X-ray (EDAX), electron microprobe, and scanning proton microprobe (SPM), has been described in a number of coals. While clausthalite has been mentioned as a possible source of Se in coal, it is present in such small quantities and sizes, that the mineral identification has not been absolutely confirmed. The mineral specimens examined in this study would contribute, not only to the Pb and Se concentrations in the coal, but also, in at least one case, to Hg concentrations.