基于嫦娥一号卫星激光测高观测的月球地形模型CLTM-s01

利用中国第一颗探月卫星嫦娥一号第一次正飞阶段获取的约300多万个有效激光测高数据点, 得到了改进的360阶次球谐函数展开月球全球地形模型CLTM-s01(Chang’E-1 Lunar Topography Model s01). 该模型以月球质心为参考球心, 以月球平均半径1738 km正球面为参考基准, 径向高程测量精度约为31 m, 沿赤道区域空间分辨率约为0.25°(7~8 km). 该模型首次利用激光测高数据得到月球极区高精度高分辨率月球地形图, 在空间覆盖、模型精度和空间分辨率上较早期模型均有较大改进. 利用该模型得到的月球平均半径为(1737013±2) m, 月球的赤道半径为(1737646±4) m, 月球的极半径为(1735843±4) m, 月球的形状扁率为1/963.7526, 月球的形状中心和质量中心在月固坐标系下的偏差为(-1.777, -0.730, 0.237) km. CLTM-s01所得到的月球形状基本参数与历史值相当, 但由于有更强的两极观测数据约束, 由该模型计算出的这些参数可信度更高.     

月球八大秘闻

月球从地球偷能量地球上的潮汐现象多数是由月亮引起的(太阳的作用稍小一点),潮汐的秘密是这样的:由于月亮绕着地球旋转,地球上的海洋受到月球的引力牵引作用,面对月亮的那一面就出现高潮,这恐怕     

再探月球背面

何谓"月球背面"?受地球和月球之间的潮汐力影响,月球的自转变慢,以至于它总是以同一个半球面(所谓"月球正面")朝向地球,而月球的另一面,我们从地球上是看不全的(在某些条件下能看到18%),这就是所谓的"月球背面",也被称为"月球另一面"。需要特别说明的是,月球背面不能与"月球暗面"混淆。所谓月球暗面,是指在特定时间不能被太阳照亮的月球     

用流场分析法确定Chézy系数C

根据笔者关于脉动切应力的假设,建立了明槽均匀流基本方程;对二维和矩形断面等简单情形,给出了流速分布和Chézy系数C的公式;对梯形和其它断面形状,建议了一个数值方法和估算Chézy系数C的方法.给出了糙率n和糙度k_1的对应表,据此对矩形断面明槽的C值作了计算比较,以说明表格的适用性.     

切向极化薄壁压电陶瓷圆管电声换能器理论

本文在简化假设下,导出切向极化压电陶瓷薄壁国管换能器无负载电导纳方程,它可用以计算k_(31),k_(33),d_(31)和d_(33)等机电参量,进而建立薄壁管在水介质中振动方程,给出直至超过径向共振频率的宽频域内发射声功率和接收灵敏度关系式。顺便就辐射阻抗对发射声功率与接收灵敏度的影响作了讨论。本文所建议的方法,在计算切向极化(还有径向极化)陶瓷圆管换能器的发射与接收特性上,具有明显的优点。     

月球表面核反应堆电源方案

 月球基地的建立首先需要解决能源供给问题, 核反应堆电源具有功率大、寿命长、环境适应性强等优点, 是月球基地及其他深空探测任务的理想能源。分析了目前可用于月球基地的能源情况, 针对性地提出40 kW_e月球表面核反应堆电源的设计理念, 经初步优化设计, 给出该电源的方案和总体设计参数, 并从物理、屏蔽、热工、结构方面对电源方案进行分析和论证。结果表明:该电源方案合理可行, 能够满足安全和寿期要求。     

月球探测器精确相对动力学模型及其应用

在地月会合坐标系下建立了月球探测器的相对动力学模型, 模型中考虑了太阳、地球和月球的真实天体力学环境. 给出了太阳引力摄动下地月会合坐标系绝对角速度的简单但精确的表达式. 所提供的相对动力学模型与J2000坐标系下的绝对动力学模型完全等价. 如果将太阳引力常数置为零, 模型则退化为椭圆型限制性三体问题模型; 如果再将月球轨道偏心率置为零, 模型则进一步退化为圆型限制性三体问题模型. 基于本文模型导出了计算地月系统的共线和三角拉格朗日平动点更精确位置的迭代格式, 它与儒略时刻以及所考虑的时间范围有关. 所提供的相对动力学模型对经由拉格朗日点的探月轨道设计有重要参考价值.     

月球探测的进展与我国月球探测的科学目标

在简述月球探测的历程与趋势的基础上,强调当代月球探测的总体目标为：(1)研究月球与地月系的起源和演化,特别是月球大气层与磁场的消失,矿物与岩石的分布和形成环境、月壤和内部层圈结构的形成以及月球演化的历程;(2)探测月球的资源、能源和特殊环境的开发利用及对人类社会长期可持续发展的支撑。我国不载人月球探测划分为绕、落及回三个阶段。为了全球性、整体性重新认识月球,绕月卫星探测的科学目标为获取全月面三维影像,探测14种有用元素的全球分布与丰度,探测月壤厚度并估算^3He资源量以及太阳活动对空间环境的影响。“落”为月球探测器软着陆就位探测和月球车巡视探测,建立月基光学、低频射电和极紫外天文观测平台。“回”为月球探测器软着陆就位探测和取样返回地面。     

求Ramsey数最优下界值的递归算法

要确定每个具体的Ramsey数的数值是相当困难的,至今人们只求出了为数很少的几个Ramsey数的数值.人们在研究Ramsey数性质的同时,也在估计Ramsey数的数值,得出了某些Ramsey数的下界值,但工作进展缓慢.本文提出了一种计算Ramsey数最优下界值的递归算法,该算法利用当今关于Ramsey数的最新结果,能得出Ramsey数的目前最优下界值.1 算法描述不妨将本算法定名为G,参数个数为1个以上(可变化),算法允许递归调用,其输出值为Ramsey数的目前最优下界值.C(k_1,k_2…,k_n)表示以k_1,k_2…,k_n作为输入,通过算法G所得到的输出结果,即C(k_1,k_2…,k_n)表示的是G算出的Ramsey数N(k_1,k_2,…,k_n;2)的目前最优下界值,其中N(k_1,k_2…,k_n;2)的含意与文献[2]中有关含意相同.算法G:     

参数p（x）为分段常数时斯图谟——刘维尔问题的格林函数及其定性性质

本文导出了参数p(x)为分段常数时斯图谟—刘维尔方程的格林函数,证明了所导出的格林函数的若干定性性质,给出了参数p(x)为分段常数时非线性斯图谟—刘维尔方程边值问题解的积分公式。     

Seismic tomography of the Moon

We attempted to determine the first three-dimensional P and S wave velocity and Poisson＇s ratio structures of the lunar crust and mantle down to 1000 km depth under the near-side of the Moon by applying seismic tomography to the moonquake arrival-time data recorded by the Apollo seismic network operated during 1969 to 1977. Our results show that significant lateral heterogeneities may exist in the lunar interior. Because there is no plate tectonics in the Moon, the lateral heterogeneities may be produced at the early stage of the Moon formation and evolution, and they have been preserved till today. There seems to be a correlation between the distribution of deep moonquakes and lateral velocity variations in the lunar lower mantle, suggesting that the occurrence of deep moonquakes may be affected by the lunar structural heterogeneity in addition to the tidal stresses. Although this is an experimental work and the result is still preliminary, it indicates that tomographic imaging of the lunar interior is feasible.     

Late formation and prolonged differentiation of the Moon inferred from W isotopes in lunar metals

The Moon is thought to have formed from debris ejected by a giant impact with the early 'proto'-Earth and, as a result of the high energies involved, the Moon would have melted to form a magma ocean. The timescales for formation and solidification of the Moon can be quantified by using 182Hf-182W and 146Sm-142Nd chronometry, but these methods have yielded contradicting results. In earlier studies, 182W anomalies in lunar rocks were attributed to decay of 182Hf within the lunar mantle and were used to infer that the Moon solidified within the first approximately 60 million years of the Solar System. However, the dominant 182W component in most lunar rocks reflects cosmogenic production mainly by neutron capture of 181Ta during cosmic-ray exposure of the lunar surface, compromising a reliable interpretation in terms of 182Hf-182W chronometry. Here we present tungsten isotope data for lunar metals that do not contain any measurable Ta-derived 182W. All metals have identical 182W/184W ratios, indicating that the lunar magma ocean did not crystallize within the first approximately 60 Myr of the Solar System, which is no longer inconsistent with Sm-Nd chronometry. Our new data reveal that the lunar and terrestrial mantles have identical 182W/184W. This, in conjunction with 147Sm-143Nd ages for the oldest lunar rocks, constrains the age of the Moon and Earth to Myr after formation of the Solar System. The identical 182W/184W ratios of the lunar and terrestrial mantles require either that the Moon is derived mainly from terrestrial material or that tungsten isotopes in the Moon and Earth's mantle equilibrated in the aftermath of the giant impact, as has been proposed to account for identical oxygen isotope compositions of the Earth and Moon.     

An early lunar core dynamo driven by thermochemical mantle convection

Although the Moon currently has no internally generated magnetic field, palaeomagnetic data, combined with radiometric ages of Apollo samples, provide evidence for such a magnetic field from approximately 3.9 to 3.6 billion years (Gyr) ago, possibly owing to an ancient lunar dynamo. But the presence of a lunar dynamo during this time period is difficult to explain, because thermal evolution models for the Moon yield insufficient core heat flux to power a dynamo after approximately 4.2 Gyr ago. Here we show that a transient increase in core heat flux after an overturn of an initially stratified lunar mantle might explain the existence and timing of an early lunar dynamo. Using a three-dimensional spherical convection model, we show that a dense layer, enriched in radioactive elements (a 'thermal blanket'), at the base of the lunar mantle can initially prevent core cooling, thereby inhibiting core convection and magnetic field generation. Subsequent radioactive heating progressively increases the buoyancy of the thermal blanket, ultimately causing it to rise back into the mantle. The removal of the thermal blanket, proposed to explain the eruption of thorium- and titanium-rich lunar mare basalts, plausibly results in a core heat flux sufficient to power a short-lived lunar dynamo.     

嫦娥1号绕月探测——中国航天迈向深空

随着1994年的“克莱门汀”号和1998年的“月球勘探者”号月球探测器的发射成功和取得的新的科学发现,在21世纪初,世界各国相继宣布以月球和火星探测为中心的深空探测计划,掀起自阿波罗计划之后的第二次月球探测高潮。中国在卫星应用和载人航天取得突破性进展之后,适时开展月球探测,填补了中国在深空探测领域的空白。绕月探测工程的实施经历了长达10年的政治、经济、科技等方面的综合论证,于2004年初开始正式启动。2007年初,第一颗月球探测卫星——嫦娥1号的各项设施已经全部准备就绪,待命出厂,择机发射,以确保首发必成。嫦娥1号绕月探测卫星的科学目标包括绘制月球立体地图、探测月表物质成分、探测月壤厚度和探测地月空间环境等4项科学任务。     

An impact-driven dynamo for the early Moon

The origin of lunar magnetic anomalies remains unresolved after their discovery more than four decades ago. A commonly invoked hypothesis is that the Moon might once have possessed a thermally driven core dynamo, but this theory is problematical given the small size of the core and the required surface magnetic field strengths. An alternative hypothesis is that impact events might have amplified ambient fields near the antipodes of the largest basins, but many magnetic anomalies exist that are not associated with basin antipodes. Here we propose a new model for magnetic field generation, in which dynamo action comes from impact-induced changes in the Moon's rotation rate. Basin-forming impact events are energetic enough to have unlocked the Moon from synchronous rotation, and we demonstrate that the subsequent large-scale fluid flows in the core, excited by the tidal distortion of the core-mantle boundary, could have powered a lunar dynamo. Predicted surface magnetic field strengths are on the order of several microteslas, consistent with palaeomagnetic measurements, and the duration of these fields is sufficient to explain the central magnetic anomalies associated with several large impact basins.     

Cryptomare magmatism 4.35 Gyr ago recorded in lunar meteorite Kalahari 009

The origin and evolution of the Moon remain controversial, with one of the most important questions for lunar evolution being the timing and duration of basaltic (mare) magmatism. Here we report the result of ion microprobe U-Pb dating of phosphates in a lunar meteorite, Kalahari 009, which is classified as a very-low-Ti mare-basalt breccia. In situ analyses of five phosphate grains, associated with basaltic clasts, give an age of 4.35 +/- 0.15 billion years. These ancient phosphate ages are thought to represent the crystallization ages of parental basalt magma, making Kalahari 009 one of the oldest known mare basalts. We suggest that mare basalt volcanism on the Moon started as early as 4.35 Gyr ago, relatively soon after its formation and differentiation, and preceding the bulk of lunar volcanism which ensued after the late heavy bombardment around 3.8-3.9 Gyr (refs 7 and 8). Considering the extremely low abundances of incompatible elements such as thorium and the rare earth elements in Kalahari 009 (ref. 9) and recent remote-sensing observations illustrating that the cryptomaria tend to be of very-low-Ti basalt type, we conclude that Kalahari 009 is our first sample of a very-low-Ti cryptomare from the Moon.     

Forming the lunar farside highlands by accretion of a companion moon

The most striking geological feature of the Moon is the terrain and elevation dichotomy between the hemispheres: the nearside is low and flat, dominated by volcanic maria, whereas the farside is mountainous and deeply cratered. Associated with this geological dichotomy is a compositional and thermal variation, with the nearside Procellarum KREEP (potassium/rare-earth element/phosphorus) Terrane and environs interpreted as having thin, compositionally evolved crust in comparison with the massive feldspathic highlands. The lunar dichotomy may have been caused by internal effects (for example spatial variations in tidal heating, asymmetric convective processes or asymmetric crystallization of the magma ocean) or external effects (such as the event that formed the South Pole/Aitken basin or asymmetric cratering). Here we consider its origin as a late carapace added by the accretion of a companion moon. Companion moons are a common outcome of simulations of Moon formation from a protolunar disk resulting from a giant impact, and although most coplanar configurations are unstable, a ～1,200-km-diameter moon located at one of the Trojan points could be dynamically stable for tens of millions of years after the giant impact. Most of the Moon's magma ocean would solidify on this timescale, whereas the companion moon would evolve more quickly into a crust and a solid mantle derived from similar disk material, and would presumably have little or no core. Its likely fate would be to collide with the Moon at ～2-3?km?s(-1), well below the speed of sound in silicates. According to our simulations, a large moon/Moon size ratio (～0.3) and a subsonic impact velocity lead to an accretionary pile rather than a crater, contributing a hemispheric layer of extent and thickness consistent with the dimensions of the farside highlands and in agreement with the degree-two crustal thickness profile. The collision furthermore displaces the KREEP-rich layer to the opposite hemisphere, explaining the observed concentration.     

长江河口北支潮位与潮差的时空变化和机理

考虑长江河口径流、潮汐和风场共同作用,数值模拟和定量分析北支潮位和潮差时空变化和动力机制.北支月平均潮位呈现出从1月到7月逐渐增大,从8月到12月逐渐减小的变化趋势,主要决定于径流量产生的余水位.潮差具有季节变化,一年中出现两次极大值和两次极小值.两次极大值出现在3月(农历二月)和9月(农历八月),两次极小值出现在6月...     

Prolonged KREEP magmatism on the Moon indicated by the youngest dated lunar igneous rock

Primordial solidification of the Moon (or its uppermost layer) resulted in the formation of a variety of rock types that subsequently melted and mixed to produce the compositional diversity observed in the lunar sample suite. The initial rocks to crystallize from this Moon-wide molten layer (the magma ocean) contained olivine and pyroxene and were compositionally less evolved than the plagioclase-rich rocks that followed. The last stage of crystallization, representing the last few per cent of the magma ocean, produced materials that are strongly enriched in incompatible elements including potassium (K), the rare earth elements (REE) and phosphorus (P)--termed KREEP. The decay of radioactive elements in KREEP, such as uranium and thorium, is generally thought to provide the thermal energy necessary for more recent lunar magmatism. The ages of KREEP-rich samples are, however, confined to the earliest periods of lunar magmatism between 3.8 and 4.6 billion years (Gyr) ago, providing no physical evidence that KREEP is directly involved in more recent lunar magmatism. But here we present evidence that KREEP magmatism extended for an additional 1 Gyr, based on analyses of the youngest dated lunar sample.