Motion of a Meteoroid Released from an Asteroid

Evidence of asteroid surface features as regolith grains and larger boulders implies resurfacing possibility due to external forces such as gravitational tidal force during close planet encounters. Motion of a meteoroid released from an asteroid in the gravitational fields of the asteroid and the Earth is modeled. We are interested mainly in a distance between the meteoroid and the asteroid as a function of the time. Applications to Itokawa and some close approaching NEAs are presented.     

On the Possible Hazard on the Major Cities Caused by Asteroid Impact in the Pacific Ocean – II

Earlier, it was pointed out that asteroids with diameters close to 200 m that hit the Pacific Ocean once in 10⁴ y create large tsunami waves which could cause serious hazards to the cities and countries lying along the periphery. Here, a more detailed investigation is carried out in relation to tsunami hazards created by earthquakes. It is shown that the energy involved in the asteroid induced tsunami wave is some 300 times greater than large tsunami waves and 100 times greater than the Chile tsunami of 1960, the largest this century. Second, if the impact should take place in the Pacific south of Japan, so that the tsunami wave enters Tokyo Bay, the damage could cost 800 billion dollars, which is 6 times greater than the damage due to the Hanshin (Kōbe-Osaka) earthquake of 1995. This revised version was published online in July 2006 with corrections to the Cover Date.     

近地天体探测现状

本文简要介绍了国内外近地天体探测工作的现状,还介绍了我国正在建造的近地天体探测望远镜的情况。     

Detection of Collisional Asteroid Orbits Under Observable Nonlinearity in the Problem of Orbit Improvement

Solar System Research - A method has been developed for detecting collisional orbits of asteroids in the initial confidence region with a noticeable nonlinearity in the problem of improving their...     

Approximate Analytical Theory of Satellite Orbit Prediction Presented in Spherical Coordinates Frame

A comparative review of analytic theories for the motion of Earth satellites in quasi-circular orbits written in the spherical coordinate frame is presented. The theory of motion is developed for satellites in quasi-circular and quasi-equatorial orbits subjected to geopotential, luni-solar and solar radiation pressure force perturbations. The intermediate orbit is Keplerian and the equations of motion are solved by the Lyapunov–Poincaré small parameter method. Both resonant and non-resonant cases are considered. The results can be useful for the development of a complete theory of weakly eccentric orbits.     

An Upper Limit of Mass for a Stable Minor Planet in the Main Asteroid Belt

The stability of an imaginary planet located in the present main asteroid belt is studied with a 7-body model (Sun, Mars, Jupiter, Saturn, Uranus, Neptune and the imaginary planet). The fourth-order Hermite algorithm P(EC)³ is used, which has a very small secular energy error for the integration of periodic orbits with a constant time-step. The evolution of orbits is followed up to 10⁸ years. Our numerical results show that the low-order resonances with Jupiter can enhance the stability of the imaginary planet in some cases. The survival probability of the imaginary planet decreases with the planet mass. The upper limit of the imaginary planet's mass that can survive in the main belt is around 10²⁵ kg, i.e., about the Earth's mass.     

基于不同轨道高度iHCO通信卫星的CAPS星座优化研究

基于通信卫星的导航系统可以利用比地球静止轨道（Geostationary Earth Orbit,GEO）高约200 km的倾斜高圆轨道（inclined Highly Circular Orbit,iHCO）通信卫星组成导航星座.结合两种轨道高度的倾斜高圆轨道通信卫星,仿真分析了利用倾斜高圆轨道卫星组成的中国区域定位系统（Chinese Area Positioning System,CAPS）的导航性能,并讨论了利用倾斜高圆轨道卫星组成的中国区域定位系统实现中国区域覆盖的最佳星座布局.     

卫星轨道理论的深入研究及其在定轨、预报和参数测定中的应用

自从1957年第1颗人造地球卫星Sputnik升空以来,人类进入空间时代已过半个世纪,这50多年中卫星技术日趋成熟.这篇论文根据作者在博士研究生阶段参加的3项课题撰写而成.这3项课题涉及了人造地球卫星轨道理论及应用的几个主要方面,具有一定的代表性,也能够展示目前卫星轨道研究的主要内容、手段以及在应用领域中的重要作用.     

小行星主带上单个行星的质量上限

介绍了N体模拟的Hermite算法,并利用该算法研究了不同质量行星在小行星主带上轨道的演化情况．采用的演化模型是太阳系N体模型(N=7),即把水星、金星、地球的质量加到太阳上,忽略冥王星,同时在小行星主带附近增加一个假想行星,系统演化时间为1亿年．数值模拟显示能够稳定存在于小行星主带上的单个天体的质量上限其量级为10~(25)kg．模拟同时还显示在某些情况下,假想行星与木星之间的低阶共振可以增强系统的稳定性．     

Determination of the Proper Motions and Membership of the Globular Cluster M3 and of its Orbit in the Galaxy

We examine 14 plates of the globular cluster M3 (NGC 5272) taken with the 40 cm refractor at the Sheshan station of Shanghai Astronomical Observatory. The plates span over a period of about 77 years. The positions and absolute proper motions of eight stars in the Hipparcos Catalogue and of 49 stars in the Tycho-2 Catalogue are used as the reference frame. The astrometric reduction is made with the central overlapping principle. The absolute proper motions of 534 stars in a region of about 100' × 100' around the cluster are measured. With the new proper motion data the membership probabilities of the stars are determined. The average absolute proper motion obtained for the cluster is -0.06@0.30 mas yr-1 in R.A. and -2.6@0.30 mas yr-1 in Decl. By combining this result with the known distance and radial velocity of the cluster, we also obtained the Galactic orbit of M3 for a chosen three-component Galactic potential.     

液核地球自转速率变化的带谐潮效应Ⅱ--数值计算与比较

地球自转速率的潮汐变化可由无量纲参数k/cm)(k和cm分别为壳幔的有效Love数和有效极转动惯量)来表征。对于一个具有弹性地幔、平衡海潮和核幔不耦合的地球k/cm=0.944,且与潮波频率无关。海潮的非平衡扰动使k/cm为复数,且与频率有关。大气对自转速率有效勒夫数的贡献约为Δkat=0.0075。同时地幔滞弹性对勒夫数也产生扰动。利用本文得到的理论公式和最新的潮汐数据计算了地球自转速率的潮汐变化,及其有关地球物理机制的影响。     

液核地球自转速率变化的带谐潮效应Ⅰ--理论公式

根据液核地球动力学原理,重新推导了在日月子引潮力作用下的地球自转速率变化的理论公式,由此明确地引入了液核影响因子,它与地球和液核的极转动惯量的变化有关。不同于Yoder.C.F(1981)的理论,本文给出了基于引潮力位Doodson展开的地球自转速率变化、日长变化和世界时变化的理论公式,指出尺度因子的转动惯量应取为地幔的有效极转动惯量,Love数应取地幔的有效Love数的理由。     

一个边缘耀斑(后)环系速度场的近似计算

利用“多云模型”方法,从云南天文台二维多波段太阳光谱仪观测到的Ｈβ光谱资料中导出１９８９年８月１７日太阳西边缘的一个大的耀斑环系不同时间的视向速度场．为了解释观测速度场的主要特征,本文采用如下假设和近似：环内物质在太阳重力、磁场应力和环内气压梯度力联合作用下由环足沿螺旋磁力线上升运动．应用ＭＨＤ理论计算了它的理论速度场．通过两者的比较发现,计算出的速度场与第一时段的观测速度场基本相似,这似乎对耀斑物质蒸发模型提供了支持．     

Response of a Disk Galaxy to a Satellite Galaxy in Elliptical Orbit

We use a 2-dimensional self consistent N-body simulation code in order to investigate the evolution of spiral structure in a disk galaxy caused by one small companion galaxy orbiting in elliptical orbit around the main disk galaxy. In all cases one can see spiral arms forming in the disk of the main galaxy. Our numerical results suggest that there is a connection between the shape of the spiral arms and the eccentricity of the companion's orbit. We also examine the maximum density distribution on the spiral arms and the influence of the companion on the velocity RMS of the stars that form the disk of the main galaxy. This revised version was published online in July 2006 with corrections to the Cover Date.     

太阳10cm波爆发与共生的硬X射线耀斑中精细结构的分析

利用日本“Ｙｏｈｋｏｈ”卫星的资料及北京天文台２８４０ＭＨｚ的射电观测资料,对１９９２年６月７日的太阳爆发事件进行了分析,结果表明,在这次爆发的脉冲相期间存在着大小两种时间尺度的脉动分量,大尺度的脉动周期约为３０ｓ,小尺度脉动周期为１－４ｓ。利用硬Ｘ射线成像观测结果,发现大尺度的脉动与硬Ｘ射线源区的一系列变化相对应。文中给出了一个环－环相互作用的ＭＨＤ振荡调制物理图像。     

An Electron Density Model above the Sunspot from a Mapping of NOAA 7260 at 17 GHz

The brightness temperature distribution of microwave emission in a solar active region generally shows a ring structure, with a dip at the centre. However, no dip was found in the Nobeyama Radioheliograph left handed circular polarization (LCP) image on 1992 August 18; instead, there was a peak. This is a completely LCP source with zero right-handed circular polarization (RCP). We examine this structure in terms of the joint effect of gyroresonance and bremsstrahlung mechanism with a raised electron density above the central part of the sunspot, and the commonly assumed temperature and vertical dipole magnetic field models. The raised electron density is found to be 1.4 × 1011 cm-3 at the chromosphere base.     

Orbit classification in the meridional plane of a disk galaxy model with a spherical nucleus

We investigate the regular or chaotic nature of star orbits moving in the meridional plane of an axially symmetric galactic model with a disk and a spherical nucleus. We study the influence of some important parameters of the dynamical system, such as the mass and the scale length of the nucleus, the angular momentum or the energy, by computing in each case the percentage of chaotic orbits, as well as the percentages of orbits of the main regular resonant families. Some heuristic arguments to explain and justify the numerically derived outcomes are also given. Furthermore, we present a new method to find the threshold between chaos and regularity for both Lyapunov Characteristic Numbers and SALI, by using them simultaneously.     

Origin of the ocean on the Earth: Early evolution of water D/H in a hydrogen-rich atmosphere

The origin of the Earth's ocean has been discussed on the basis of deuterium/hydrogen ratios (D/H) of several sources of water in the Solar System. The average D/H of carbonaceous chondrites (CC's) is known to be close to the current D/H of the Earth's ocean, while those of comets and the solar nebula are larger by about a factor of two and smaller by about a factor of seven, respectively, than that of the Earth's ocean. Thus, the main source of the Earth's ocean has been thought to be CC's or adequate mixing of comets and the solar nebula. However, those conclusions are correct only if D/H of water on the Earth has remained unchanged for the past 4.5 Gyr. In this paper, we investigate evolution of D/H in the ocean in the case that the early Earth had a hydrogen-rich atmosphere, the existence of which is predicted by recent theories of planet formation no matter whether the nebula remains or not. Then we show that D/H in the ocean increases by a factor of 2-9, which is caused by the mass fractionation during atmospheric hydrogen loss, followed by deuterium exchange between hydrogen gas and water vapor during ocean formation. This result suggests that the apparent similarity in D/H of water between CC's and the current Earth's ocean does not necessarily support the CC's origin of water and that the apparent discrepancy in D/H is not a good reason for excluding the nebular origin of water.     

On the Stability of Planar Oscillations and Rotations of a Satellite in a Circular Orbit

We deal with the stability problem of planar periodic motions of a satellite about its center of mass. The satellite is regarded a dynamically symmetric rigid body whose center of mass moves in a circular orbit.By using the method of normal forms and KAM theory we study the orbital stability of planar oscillations and rotations of the satellite in detail. In two special cases we investigate the orbital stability analytically by introducing a small parameter. In the general case, numerical calculations of Hamiltonian normal form are necessary.