伽利略卫星的内部结构模型以及平衡状态参数

木星的4颗大卫星都是同步轨旋卫星，常被称为伽利略卫星，美国发射的伽利略飞船自1995年12月抵达木星系统后，近几年来对木星的4颗伽 利略卫星进行了一系列的探测。利用飞船探测的最新资料（参看表1）作为约束条件，建立了伽利略卫星的一组内部结构模型（参看表3－6）；然后按照同步轨旋卫星的形状理论公式计算了它们的平衡形状参数（参看表7），以木卫一为例，其三轴椭球体的3个轴分别是1830．73，1819．89和1816．27km；最后，将计算结果与已有的研究结果作了比较和讨论。     

伽利略飞船:拥抱木星

“伽利略”飞船拍摄了许多“木卫一”火山爆发的照片，并且找到“木卫二”冰层下面似乎有很多液态水和稀薄氧气层的证据。这些证据使科学家们相信在太阳系中，“木卫二”很可能有生命存在。“伽利略”飞船还曾经探索过“木卫三”，发现这颗卫星有自己的磁场。美国宇航局探索木星的“伽利略”飞船开始最后一次飞行， 9月21日，飞船将俯冲奔向木星，与空气摩擦燃烧，最后化为灰烬，消失在木星周围的大气层里。“伽利略”飞船燃料即将耗尽，在完成最后的飞行之后，不能调整自己的轨道，也不能使天线转向地球，只有消失在木星的大气层里。这样的…     

木星的卫星上发现有机分子

据英国《新科学家》周刊1997年4月5日报道，伽利略号宇宙飞船可能已拍摄到木星的两个卫星（fIOU－tymede和Calisto）表面含有碳分子和氮分子的闪光。碳和氨是创造生命的关键元素，它们在木星的卫星L出现，说明在太阳系的其他天体曾经有活的生命存在。科学家们在上个月休斯顿月球和行星研究学术讨论会上宣布了这一结果。他们根据伽利略宇宙飞船上的近红外线测绘光谱仪收集到的数据，分析了木星这两颗卫星表面的化学成分，发现了有机分子。近红外线科研小组的科学家之一，夏威夷大学的托马斯·麦科德指出，木星的这两个卫星上出现的四种新物…     

木星一号星上的火山活动 与地球的比较

太阳系中能量最大的火山并不是在地球上发现的，而是在木星一号卫星Io（伊俄）上。地球和Io是太阳系中仅有的拥有高温的活火山的星体，但Io上的火山却更大，更热，运动也更剧烈。本书包含了从伽利略飞船上得到的最新结果，以及Io上不同尺度和样式的火山活动，并把这些火山和目前地球上的火山做了一个比较。本书提供了关于火山形成和喷发的背景知识，并且定量地解释了如何分析用从太空飞船和望远镜上得到的遥感数据来揭示火山运动过程。     

木星：行星、卫星和磁层

本书是根据2001年4月在美国Colorad洲Boulder城召开的关于探测木星国际学术会议的产物，当时约有250人参加，是继国际先后6次空间飞船从事木星探测的成果。关于木星的第一本专著由T．Gehres主编，于1976年出版，作者80人；本书主编3人，均为大学教授，并先后参加空间飞船探测计划，作者约168人，篇幅达700多页。本书为英国剑桥大学出版社所组织“剑桥行星科学系列”之一，随后先后又出版《流星》、《火星表面》和《火星地质学》等书。     

（Ⅲ）m=0类二次系统的极限环问题，（Ⅰ）

彗星的空间探测是当代前沿课题．本文首先概述彗星的主要研究结果．彗星的本体是不大的‘脏雪球’彗核；随着接近太阳，其表面冰升华并带出尘埃而形成彗发，发生复杂的物理-化学过程；太阳辐射压和太阳风推斥彗发的尘埃和离子而形成彗尾；彗星尘散失在轨道附近而成为流星群．虽然地面观测到彗发和彗尾的丰富资料，但对彗核却了解甚少，需要发射飞船进行空间探测；接着，从探测彗核的真实性质、采集彗星样品分析成分、探索彗星活动和机制、彗星的有机物与生命起源、彗星-地球关系、太阳系起源和演化线索几方面阐述彗星的空间探测的科学意义；然后，综述彗星空间探测的一些计划进展情况，总结彗星空间探测的重要成果；最后，讨论未来的彗星空间探测的科学目标，包括高轨卫星采集彗星尘、搜寻近地小彗星、搜寻未知彗星、发射更优秀飞船探测不同彗星．     

CsCrCl_3晶体的光谱研究

本文基于弱场图象，利用Ｒａｃａｈ不可约张量算符法，建立了ｄ４（Ｃ＇３ｖ）离子含旋轨耦合作用的完全能量矩阵。借助此矩阵，利用完全能量矩阵的对角化方法，对ＣｓＣｒＣｌ３晶体的光谱进行了理论计算，其结果同实验结果很吻合。同时，本文从理论上证明了２３２２８ｃｍ（－１）、２３３１０ｃｍ（－１）这两条强谱线产生于双中心跃迁。     

8Kb／sLD－CELP编码器的研究

描述了一种８Ｋｂ／ｓ的低延迟ＣＥＬＰ编码器．这种编码器采用后向自适应技术，所使用的激励矢量长度很短，使得单向编译码延迟小于５ｍｓ，计算复杂度也由于使用了“形状－增益”码本而得到降低．这种编码算法包括：（１）用于ＬＰＣ分析的汉明窗（Ｈａｍｍｉｎｇｗｉｎｄｏｗｓ）；（２）三抽头基音预测器和１０阶ＬＰＣ预测器的级联；（３）对数增益预测器；（４）闭环搜索．     

伽利略号:揭开木星的面纱

"伽利略"探测器在经过大约36亿公里和长达6年多的空间旅行后,于1995年7月到达木星轨道,并将其携带的木星大气探测器以预定的角度送入木星大气层,顺利地完成了飞向木星的艰难任务,同时开始了对木星进行的为期两年的探测活动。 "伽利略"探测器向木星发射的木星大气探测器,重339公斤,于12月7日飞进环境恶劣、飞速旋转的木星大气层,执行一项有去无回的探测任务,首     

粗糙集的RBF表示与非监督模式分类

提出了一种粗糙集的ＲＢＦ网络表示形式，在集值测度意义下，将粗糙集的语义表达进行了有效的描述，并构造了其自适应自组织的遗传学习机制．其创新性主要表现在：（１）通过ＲＢＦ网络有效地构造了粗糙集在模式分类中的自适应表示形式；（２）在遗传算法中引入了元进化自调整机制；（３）以粗糙集意义下的非线性映射方式提高了模式分类的计算效率．图３，表１，参４．     

Thickness constraints on the icy shells of the galilean satellites from a comparison of crater shapes

A thin outer ice shell on Jupiter's large moon Europa would imply easy exchange between the surface and any organic or biotic material in its putative subsurface ocean. The thickness of the outer ice shell is poorly constrained, however, with model-dependent estimates ranging from a few kilometres to ten or more kilometres. Here I present measurements of depths of impact craters on Europa, Ganymede and Callisto that reveal two anomalous transitions in crater shape with diameter. The first transition is probably related to temperature-dependent ductility of the crust at shallow depths (7 8 km on Europa). The second transition is attributed to the influence of subsurface oceans on all three satellites, which constrains Europa's icy shell to be at least 19 km thick. The icy lithospheres of Ganymede and Callisto are equally ice-rich, but Europa's icy shell has a thermal structure about 0.25 0.5 times the thicknesses of Ganymede's or Callisto's shells, depending on epoch. The appearances of the craters on Europa are inconsistent with thin-ice-shell models and indicate that exchange of oceanic and surface material could be difficult.     

Ultraviolet emissions from the magnetic footprints of Io, Ganymede and Europa on Jupiter

Io leaves a magnetic footprint on Jupiter's upper atmosphere that appears as a spot of ultraviolet emission that remains fixed underneath Io as Jupiter rotates. The specific physical mechanisms responsible for generating those emissions are not well understood, but in general the spot seems to arise because of an electromagnetic interaction between Jupiter's magnetic field and the plasma surrounding Io, driving currents of around 1 million amperes down through Jupiter's ionosphere. The other galilean satellites may also leave footprints, and the presence or absence of such footprints should illuminate the underlying physical mechanism by revealing the strengths of the currents linking the satellites to Jupiter. Here we report persistent, faint, far-ultraviolet emission from the jovian footprints of Ganymede and Europa. We also show that Io's magnetic footprint extends well beyond the immediate vicinity of Io's flux-tube interaction with Jupiter, and much farther than predicted theoretically; the emission persists for several hours downstream. We infer from these data that Ganymede and Europa have persistent interactions with Jupiter's magnetic field despite their thin atmospheres.     

The auroral footprint of Enceladus on Saturn

Although there are substantial differences between the magnetospheres of Jupiter and Saturn, it has been suggested that cryovolcanic activity at Enceladus could lead to electrodynamic coupling between Enceladus and Saturn like that which links Jupiter with Io, Europa and Ganymede. Powerful field-aligned electron beams associated with the Io-Jupiter coupling, for example, create an auroral footprint in Jupiter's ionosphere. Auroral ultraviolet emission associated with Enceladus-Saturn coupling is anticipated to be just a few tenths of a kilorayleigh (ref. 12), about an order of magnitude dimmer than Io's footprint and below the observable threshold, consistent with its non-detection. Here we report the detection of magnetic-field-aligned ion and electron beams (offset several moon radii downstream from Enceladus) with sufficient power to stimulate detectable aurora, and the subsequent discovery of Enceladus-associated aurora in a few per cent of the scans of the moon's footprint. The footprint varies in emission magnitude more than can plausibly be explained by changes in magnetospheric parameters--and as such is probably indicative of variable plume activity.     

Io as a source of the jovian dust streams

Streams of dust emerging from the direction of Jupiter were discovered in 1992 during the flyby of the Ulysses spacecraft, but their precise origin within the jovian system remained unclear. Further data collected by the Galileo spacecraft, which has been orbiting Jupiter since December 1995, identified the possible sources of dust as Jupiter's main ring, its gossamer ring, comet Shoemaker-Levy 9 (ref. 8) and Io. All but Jupiter's gossamer ring and Io have since been ruled out. Here we find that the dominant source of the jovian dust streams is Io, on the basis of periodicities in the dust impact signal. Io's volcanoes, rather than impact ejecta, are the dust sources.     

Discovery of two new satellites of Pluto

Pluto's first known satellite, Charon, was discovered in 1978. It has a diameter (approximately 1,200 km) about half that of Pluto, which makes it larger, relative to its primary, than any other moon in the Solar System. Previous searches for other satellites around Pluto have been unsuccessful, but they were not sensitive to objects less, similar150 km in diameter and there are no fundamental reasons why Pluto should not have more satellites. Here we report the discovery of two additional moons around Pluto, provisionally designated S/2005 P 1 (hereafter P1) and S/2005 P 2 (hereafter P2), which makes Pluto the first Kuiper belt object known to have multiple satellites. These new satellites are much smaller than Charon, with estimates of P1's diameter ranging from 60 km to 165 km, depending on the surface reflectivity; P2 is about 20 per cent smaller than P1. Although definitive orbits cannot be derived, both new satellites appear to be moving in circular orbits in the same orbital plane as Charon, with orbital periods of approximately 38 days (P1) and approximately 25 days (P2).     

Origin of the obliquities of the giant planets in mutual interactions in the early Solar System

The origin of the spin-axis orientations (obliquities) of the giant planets is a fundamental issue because if the obliquities resulted from tangential collisions with primordial Earth-sized protoplanets, then they are related to the masses of the largest planetesimals out of which the planets form. A problem with this mechanism, however, is that the orbital planes of regular satellites would probably be uncorrelated with the obliquities, contrary to observations. Alternatively, they could have come from an external twist that affected the orientation of the Solar System plane; but in this model, the outer planets must have formed too rapidly, before the event that produced the twist. Moreover, the model cannot be quantitatively tested. Here I show that the present obliquities of the giant planets were probably achieved when Jupiter and Saturn crossed the 1:2 orbital resonance during a specific migration process: different migration scenarios cannot account for the large observed obliquities. The existence of the regular satellites of the giant planets does not represent a problem in this model because, although they formed soon after the planetary formation, they can follow the slow evolution of the equatorial plane it produces.     

Discovery of 12 satellites of Saturn exhibiting orbital clustering.

The giant planets in the Solar System each have two groups of satellites. The regular satellites move along nearly circular orbits in the planet's orbital plane, revolving about it in the same sense as the planet spins. In contrast, the so-called irregular satellites are generally smaller in size and are characterized by large orbits with significant eccentricity, inclination or both. The differences in their characteristics suggest that the regular and irregular satellites formed by different mechanisms: the regular satellites are believed to have formed in an accretion disk around the planet, like a miniature Solar System, whereas the irregulars are generally thought to be captured planetesimals. Here we report the discovery of 12 irregular satellites of Saturn, along with the determinations of their orbits. These orbits, along with the orbits of irregular satellites of Jupiter and Uranus, fall into groups on the basis of their orbital inclinations. We interpret this result as indicating that most of the irregular moons are collisional remnants of larger satellites that were fragmented after capture, rather than being captured independently.     

Energetic neutral atoms from a trans-Europa gas torus at Jupiter

The space environments--or magnetospheres--of magnetized planets emit copious quantities of energetic neutral atoms (ENAs) at energies between tens of electron volts to hundreds of kiloelectron volts (keV). These energetic atoms result from charge exchange between magnetically trapped energetic ions and cold neutral atoms, and they carry significant amounts of energy and mass from the magnetospheres. Imaging their distribution allows us to investigate the structure of planetary magnetospheres. Here we report the analysis of 50-80 keV ENA images of Jupiter's magnetosphere, where two distinct emission regions dominate: the upper atmosphere of Jupiter itself, and a torus of emission residing just outside the orbit of Jupiter's satellite Europa. The trans-Europa component shows that, unexpectedly, Europa generates a gas cloud comparable in gas content to that associated with the volcanic moon Io. The quantity of gas found indicates that Europa has a much greater impact than hitherto believed on the structure of, and the energy flow within, Jupiter's magnetosphere.     

The sources of sodium escaping from Io revealed by spectral high definition imaging

On Jupiter's moon Io, volcanic plumes and evaporating lava flows provide hot gases to form an atmosphere that is subsequently ionized. Some of Io's plasma is captured by the planet's strong magnetic field to form a co-rotating torus at Io's distance; the remaining ions and electrons form Io's ionosphere. The torus and ionosphere are also depleted by three time-variable processes that produce a banana-shaped cloud orbiting with Io, a giant nebula extending out to about 500 Jupiter radii, and a jet close to Io. No spatial constraints exist for the sources of the first two; they have been inferred only from modelling the patterns seen in the trace gas sodium observed far from Io. Here we report observations that reveal a spatially confined stream that ejects sodium only from the wake of the Io-torus interaction, together with a visually distinct, spherically symmetrical outflow region arising from atmospheric sputtering. The spatial extent of the ionospheric wake that feeds the stream is more than twice that observed by the Galileo spacecraft and modelled successfully. This implies considerable variability, and therefore the need for additional modelling of volcanically-driven, episodic states of the great jovian nebula.     

A giant planet orbiting the 'extreme horizontal branch' star V 391 Pegasi

After the initial discoveries fifteen years ago, over 200 extrasolar planets have now been detected. Most of them orbit main-sequence stars similar to our Sun, although a few planets orbiting red giant stars have been recently found. When the hydrogen in their cores runs out, main-sequence stars undergo an expansion into red-giant stars. This expansion can modify the orbits of planets and can easily reach and engulf the inner planets. The same will happen to the planets of our Solar System in about five billion years and the fate of the Earth is matter of debate. Here we report the discovery of a planetary-mass body (Msini = 3.2M(Jupiter)) orbiting the star V 391 Pegasi at a distance of about 1.7 astronomical units (au), with a period of 3.2 years. This star is on the extreme horizontal branch of the Hertzsprung-Russell diagram, burning helium in its core and pulsating. The maximum radius of the red-giant precursor of V 391 Pegasi may have reached 0.7 au, while the orbital distance of the planet during the stellar main-sequence phase is estimated to be about 1 au. This detection of a planet orbiting a post-red-giant star demonstrates that planets with orbital distances of less than 2 au can survive the red-giant expansion of their parent stars.