Ceres,a wet planet: The view after Dawn

Ceres, a nearly 1000-km diameter body located in the Solar System’s main asteroid belt, has been classified under many categories: planet, comet, asteroid, minor planet and, presently, dwarf planet. No matter what the designation, Ceres has experienced major planetary processes. Its evolution has been controlled by water, making it a most unusual, interesting and accessible inner Solar System object that can inform the evolution of outer Solar System moons and other dwarf planets. Early telescopic observations suggested a hydroxylated mineralogy similar to carbonaceous chondrite meteorites and a size and mass indicating a bulk density that implied a water content of 17?27 wt%. Thermodynamic modeling of Ceres’ evolution indicated that thermal aqueous evolution likely occurred. The Dawn Mission produced a huge increase in our understanding of Ceres, confirming but vastly extending the early knowledge. Dawn, carrying multispectral cameras, a visible-infrared imaging spectrometer and a nuclear spectrometer, orbited Ceres between 2015–2018 (after orbiting Vesta) at a number of different altitudes, ultimately reaching 35 km from the surface at periapsis. Observations of almost the entire surface and gravity field mapping revealed multiple geological and internal features attributed to the effects of water. The surface displays cryovolcanic-like and flow structures, exposed phyllosilicates, carbonates, evaporites and water ice. The subsurface shows partial differentiation, decreasing viscosity with depth, and lateral density heterogeneity. Ceres appears to be geologically active today and possesses liquid water/brine pockets or even an extended liquid layer in the interior, confirming an “Ocean World” designation in today’s vernacular.     

Atmospheric pressure and CO2 concentration of potential habitable planet HD40307g

HD40307g is the closest potentially habitable planet discovered today orbiting a K2V star and will be a prime target for future TPF-like missions if its existence is confirmed.Although the atmosphere of HD40307g should be denser and contain more CO2 judging from the amount of radiation it receives from its star,it is unknown how dense and how much CO2 the planetary atmosphere should have.Thus more knowledge on its atmosphere is useful.For HD40307g to have Earth-like climate(288 K global mean surface temperature),we obtain the following combination of atmospheric pressure and CO2 mixing ratio:(1)10-bar+3%CO2;(2)5-bar+10%CO2;(3)3-bar+30%CO2.     

寻找地外生命的进展与前景

介绍并探讨了人类运用天文学、深空探测及计算机模拟与统计等多种方法和手段在太阳系内的地外天体及太阳系外的类地行星上寻找地外生命的进展,如:美国航空航天局及欧空局的一系列探测器都发现火星土壤略呈碱性可能适宜生命的存在,火星大气正在不断释放可能由火星地质或生物作用产生的甲烷;表面为巨厚的水冰覆盖的木卫二如果内部炽热,则极有可能存在生命;而土卫六则非常类似现代生命起源理论中生命起源时的原始地球。对彗星的撞击探测结果表明,其内部存在着有机物和黏土矿物,可能给早期原始地球带来了有机物甚至生命;对太阳系外的射电天文观测则发现了仅银河系中就有无数的类地行星。不仅如此,"寻找地外智慧生命"计划还试图通过倾听地外智慧生命的通讯信号和主动发射地球人类的通讯信号以和地外智慧生命取得联系。美国航空航天局发射了带有地球位置及生命信息的太阳系外探测器,也做出了类似的努力。从取得的探测结果和重要发现来看,地外可能存在着适宜生命产生及演化的条件,这使我们看到了寻找地外生命的新曙光。但囿于对地外生命形式认识的缺乏和深空探测技术的限制,目前想要找到它们还是个极其艰巨的任务。     

煤中微量元素分布特征初步研究

 采自我国不同聚煤区的不同时代的89件煤样品,用中子活化分析法(INAA)分别测定了29种微量元素。据统计分析结果表明:(1)绝大多数微量元素的平均值高于世界的平均值,含量范围也较美国宽。我国各聚煤区不同时代间相比较,煤中大多数元素的平均含量和富集因数,从华南二叠纪至华北石炭—二叠纪到全国中-新生代逐渐降低。(2)中-新生代的煤中,元素间的相关性较好,华南二叠纪次之,而华北石炭—二叠纪的煤最差。(3)REE分布模式类型以中-新生代的煤最复杂;而华北石炭—二叠纪的煤较简单。     

Sub-brown dwarfs as seats of life based on non-polar solvents: Thermodynamic restrictions

Sub-brown dwarfs (SBD) might originate either around a star or in solitary fashion. These bodies can retain atmospheres composed of molecular gases, which, upon cooling, have basal pressures of tens of bars or more. Pressure-induced opacity of these gases prevents such a body from eliminating its internal radioactive heat and its surface temperature can exceed the melting point of the life-supporting solvent for an extended period of time. Earth life uses water as a solvent but synthesis of observational data makes it possible to conceive chemical reactions that might support life involving non-carbon compounds, occurring in solvents other than water. In this paper a non-polar solvent is considered: ethane. Thermodynamic requirements to be fulfilled by a hypothetic gas constituent of a life-supporting SBD atmosphere are studied. Three gases are analyzed: nitrogen, carbon dioxide and methane. For thermodynamic reasons carbon dioxide is excluded from the list of candidate gases. We show that bodies with ethane oceans are possible in interstellar space. This may happen on SBD of (significantly) smaller or larger mass than the Earth. Generally, in case of SBD smaller in size than the Earth, the atmosphere exhibits a convective layer near the surface and a radiative layer at higher altitudes while the atmosphere of SBDs larger in size than Earth does not exhibit a convective layer. The prescribed thermodynamic state of ethane on the surface has some influence on the features of the atmosphere. The atmospheric mass of a life-hosting SBD of Earth size is two or three orders of magnitude larger than the mass of Earth atmosphere.     

Source and mobility of minor and trace elements in a volcanic aquifer system: Mt. Vulture (southern Italy)

In this paper we provide a geochemical investigation on 34 groundwater samples in the Mt. Vulture volcanic aquifer representing one of the most important groundwater resources of the southern Italy pumped for drinking and irrigation supply. The present study includes the first data on the abundance and mobility of minor and trace elements and the thermodynamic considerations on water–rock interaction processes in order to evaluate the conditions of alkali basalt weathering by waters enriched in magma-derived CO₂. The results highlight the occurrence of two hydrofacies: bicarbonate alkaline-earth and alkaline waters deriving from low-temperature leaching of volcanic rocks of Mt. Vulture, and bicarbonate-sulfate-alkaline waters (high-salinity waters) related to prolonged water circulation in alkali and feldspathoids-rich pyroclastic layers interbedded with clay deposits. The Al-normalized relative mobility (RM) of metals in Vulture's aquifer varies over a wide range (10^− 1 < RM < 10⁴), confirming that the basalt weathering is not a congruent and isochemical process. Chemical equilibrium studies show that the bicarbonate alkaline-earth and alkaline waters, having a short interaction with silicate minerals, plot very close to the kaolinite–smectite stability boundary, whereas the high-salinity waters fall in the stability field of smectite and muscovite because of prolonged interaction with alkali and feldspathoids-rich pyroclastic layers. Overall, for the bicarbonate alkaline-earth and alkaline waters, the release of toxic metals in solutions is related to the spatial variation of host-rock geochemistry, the high-salinity waters, collected near urban areas, show values higher than legal limits for Ni and As, likely as a consequence of anthropogenic contribution.     

碰撞作用与类地行星起源探讨

类地行星挥发性元素普遍亏损很可能是由于太阳星云早期剧烈的太阳活动引起的。当气体、尘粒、挥发性元素和水被驱赶出内太阳系时，只有米级到公里级的物质保存下来并堆积成星子，最终吸积星子形成类地行星。我们认为类地行星的初始物质主要是已分异的星子和一些未分异的球粒陨石质星子或不同类型的陨石母体，最靠近太阳形成的星子具有最低的ＦｅＯ／（ＦｅＯ＋ＭｇＯ）值，水星是在靠近太阳的高度还原条件下吸积成分类似ＥＨ球粒陨石的星子形成的。地球的初始物质为分异的铁陨石及Ｈ群球粒陨石。随着距太阳距离增大及温度降低，陨石形成的部位大致为：ＥＨ、ＥＬ－ＩＡＢ－ＳＮＣ（辉玻无球粒陨石、辉橄无球粒陨石、纯橄无球粒陨石）－Ｅｕｃ（钙长辉长无球粒陨石）－Ｈ、Ｌ、ＬＬ－ＣＶ、ＣＭ、ＣＯ－Ｃｌ－彗星。物体之间、星子之间及行星与星子之间的碰撞对太阳系的形成和演化起着重要的作用。     

深空探测器精密定轨与重力场解算系统(WUDOGS)及其应用分析

WUDOGS是武汉大学自主研发的深空探测器精密定轨与重力场解算软件系统。该软件目前已经具备月球、火星探测器的高精度定轨能力。本文首先简要介绍了WUDOGS设计思路及其主要功能,然后重点介绍了WUDOGS与国际上领先水平的行星探测器精密定轨软件系统GEODYN-Ⅱ的交叉验证测试过程。结果表明:对于探测器的轨道预报,WUDOGS与GEODYN-Ⅱ的1个月位置差异小于0.3mm,2d位置差值小于5×10-3 mm;双程测距、双程测速的理论计算值和GEODYN-Ⅱ的差值分别在0.06 mm、0.002 mm/s的水平;对月球探测器"嫦娥一号"的精密定轨显示WUDOGS和GEODYN-Ⅱ符合在2cm水平,对火星探测器MEX的精密定轨显示WUDOGS和欧空局精密轨道符合在25m水平。该软件目前的研发情况及其与国外研究水平的对比表明WUDOGS具有良好的应用前景,对满足我国后续深空探测发展的需求以及深空探测器精密定轨软件的研发具有重要意义。     

太阳系外恒星行星系统的探测与研究进展

随着对外太空探索脚步的加快，人类开始对与太阳系具有相似结构的恒星行星系统越来越感兴趣，因为它们有可能也拥有智慧生命。简单介绍了目前地外恒星行星系统的探测情况，分析了现在比较常用的几种探测方法的可行性和适用范围，重点讨论了利用视向速度法得到的结果及其意义。近年来，各种探索地外行星的小卫星的升空以及探测技术的进步使得大批高质量数据获得成为可能。可以预见，在未来几年内，地外恒星行星系统的探索将会进入一个蓬勃发展阶段。     

The Eddington Mission

The Eddington mission was given full approval by the European Space Agency on the 23rd May 2002, with launch scheduled for 2007/8. Its science objectives are stellar evolution and asteroseismology, and planet finding. In its current design it consists of 4 × 60 cm folded Schmidt telescopes, each with 6^o × 6^o field of view and its own CCD array camera. Eddington will spend 2 years primarily devoted to asteroseismology with 1–3 months on different target fields monitoring up to 50,000 stars per field, and 3 years continuously on a single field monitoring upwards of 100,000 stars for planet searching. The asteroseismic goal is to be able to detect oscillations frequencies of stars with a precision 0.1–0.3 μHz, to probe their interior structure and the study the physical processes that govern their evolution. This revised version was published online in August 2006 with corrections to the Cover Date.