近地小行星轨道演化的数值研究与辛算法有效性的探讨

本文采用改进的显式辛算法（symplecticalgorithm）和嵌套的RKF7（8）积分器对43颗已命名（或编号）的近地小行星的轨道演化进行数值研究．在力学模型上,除考虑各大行星的引力振动外,还增加了后牛顿效应,而在算法上则着重探索辛算法在近地小行星轨道演化研究中的应用前景,特别是当小行星与某一大行星靠近时辛算法的有效性．本文的结果可为了解近地小行星的轨道演化状况和对它们进行监测提供可靠的信息．     

宇宙信息

WISE首次发现近地小行星 美国宇航局的大视场红外巡天探测器（WISE）新发现了它的首颗近地小行星,而预计在整个工作寿命中它总共会发现大约数百颗。：这颗直径1千米的小行星编号为2010 AB78,发现于2010年1月12日。发现时它距离地球大约1．58亿千米,不会对地球构成威胁,在未来的几个世纪中它也不会接近地球。这颗小行星在一条椭圆轨道上绕太阳运动,而它的轨道面也并不和地球公转轨道面重合。     

太阳之秘

太阳是宇宙无数恒星中唯一对地球生命和演化至关重要的天体。天体演化理论揭示：这颗地球生命赖以生存的天体已经漫长地演化了40亿年地球上的主要能源,除了地热和人造核能之外,包括石油（远古太阳能）、煤炭（远古太阳能）、天然气（远古太阳能）、风电（准实时太阳能）.     

近地小行星轨道演化的研究现状

近地小行星由于与地球的特殊关系为世人所瞩目, 对其研究始于５０ 年代, 近年来已成为太阳系动力学中的一个热门课题。全面地介绍了近年来关于近地小行星（ 小天体） 的研究状况, 包括对近地小行星轨道演化的研究方法和主要结果。阐明了在轨道演化过程中相应力学模型的选取、有关数值方法的引用以及积分步长变化的处理等具体问题, 并介绍了轨道长期共振的作用以及对这种共振的处理方法, 最后给出了根据目前研究所知的与地球轨道距离最近的一些小行星的轨道特征等。     

高雄星发现记

北京时间2009年8月7日上午,国际小行星中心式批准命名一颗编号为215080的小行星为“高雄星”。这颗直径在1千米至3千米范围内的小行星,由中国台湾蔡元生天体搜寻团队测量员袁凤芳于今年3月20日发现,5月9日得到永久编号后马上提出命名申请。“高雄星”有自己的椭圆形移动轨道,平均4．66年接近地球一次,距离地球最近距离为2亿千米,最远为6亿千米。目前,“高雄星”离地球的距离为4亿千米。     

小行星钟山1号、钟山2号

1974年冬,我们在使用400/3000双筒镜进行的观测工作当中,发现了一些小行星.其中有两颗小行星,轨道近日距较小,轨道倾角较大.发现的时候,正当它们大冲之后,比较靠近地球,显现出颇为快速的视运动.对这两颗星,我们分别追踪得到14次与7次观测,均各有五十多天的弧长.现将观测数据和据此计算出的轨道根数列表于后.     

土星的季节

地球的自转轴与其绕日轨道面垂直方向的偏离,即黄赤交角（以下称“倾角”）为23°．5。地球白转与公转运动的结合产生了地球上的昼夜交替、四季变化和五带（热带、南北温带和南北寒带）的区分。虽然土星的赤道面与其绕日轨道面的交角与地球的相近,为26°．7,但各个季节的天数要比地球上相应的季节长得多,这是因为土星的公转周期为地球的29．5倍。     

卫星星座的结构演化

主要研究星座几何结构的演化问题，分析了在地球扁率摄动和卫星的入轨偏差影响下轨道的演化过程，以卫星的相位和升交点赤经为参数描述了星座结构演化的一般规律，又以星下点轨迹变化和星下点的相互位置关系的变化为参数描述了区域星座结构演化的地域特性．分析表明，地球扁率摄动将导致星座结构的整体漂移，而卫星的入轨偏差则会导致星座几何结构的紊乱，特别是轨道半长轴的偏差，将是影响星座几何结构稳定性的决定因素．     

HD 12661行星系统构形的形成与稳定性

最近的多普勒观测表明恒星HD 12661周围存在两颗中等偏心率轨道上运行的行星,内行星的最小质量为2．3木星质量,轨道周期为263．6天;外行星的最小质量为1．57木星质量,轨道周期为1444．5天．该系统的稳定性要求两颗行星处在平运动轨道共振．用数值方法研究了该系统形成初期在恒星气体盘作用下的轨道迁移与稳定性,计算了行星在迁移中被平运动共振俘获的概率．发现这两颗行星目前很可能正处在11:2平运动共振边缘,且运动是混沌的,从而澄清了关于系统目前构形的不同说法,并且很可能在系统形成后行星迁移到目前构形时,气体盘几乎消失了．     

校园天文实践活动(五)——观测大行星的视运动

实验原理:太阳系中有各种各样的天体,九大行星是其中的佼佼者。除地球外的八大行星根据其轨道在地球轨道的内外不同,分为内行星和外行星。内行星轨道靠近太阳,因此总在太阳附近出现,只有傍晚和凌晨才能见到,分别称为“昏星”和“晨星”。外行星轨道位于地球轨道之外,可与太阳分处地球的两边,这种现象称为“冲”。在每年的冲日前后较长的一段时间内都能观测到外行星。这些不同决定了内行星和外形星的观测是有差别的。当天空中同时出现几颗行星时,它们总是几乎在一条直线上,这条线称为“黄道”。这是因为可见的     

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.     

共振在近地小行星轨道演化中的作用

本文采用了合理的力学模型和可靠的计算方法,研究了近地小行星轨道运动,揭示了共振（轨道共振和长期共振）在其轨道演化中的作用,并初步探讨了近地小行星的起源问题。     

The use of radar observations of Near-Earth Asteroids in the determination of the dynamical equinox

Near-Earth Asteroids (NEAs) are Solar system special class objects attracting the attention of astronomical community especially during several of the last decades. To some extent the NEAs have an advantage over the minor planets of the main belt: due to close and regular approaches to the Earth the radar observations of NEAs can be obtained for the greater number of objects than for those of the main belt of the minor planets. In this paper the use of all available radar observations together with optical ones resulting in the combined data analysis solution is discussed for different problems such as the asteroid orbits and catalog orientation parameters determination. In particular the problem of the motion of the dynamical equinox in the Hipparcos reference system is considered. About 13000 radar and optical observations of 24 NEAs and main belt minor planets have been used to obtain the precise asteroid orbits, FK5 catalogue orientation parameters and the motion of the dynamical equinox from 1750 till 2000 in the Hipparcos system.     

The orbital evolution of NEAs and the resonances with Jupiter

two near-earth-asteroids associated with resonances with Jupiter are studied over a time span of 10⁵ yrs. We found that asteroid (887) is temporary trapped in the 3:1 resonance; thus indicating that this resonance could be a source of short-lived NEAs. We also found that asteroid (3552) with a large eccentricity and a high inclination is wandering about the 1:1 resonant region.     

Influence of the YORP effect on rotation rates of near‐Earth asteroids

The distribution of near‐Earth asteroid (NEA) rotation rates differs considerably from the similar distribution of Main Belt asteroids (MBAs) by the presence of excesses of fast and slow rotators, which are not observed or not so prominent in the distribution for MBAs. Among possible reasons for the difference, there can be influence of solar radiation on spin rate of small NEAs, the so‐called “YORP effect,” which appears due to reflection, absorption, and IR re‐emission of the sunlight by an irregularly shaped rotating asteroid. It is known that the YORP‐effect action strongly depends on the amount of solar energy obtained by the body (insolation), its size, and albedo. The analysis of observation data has shown that: (1) the mean diameter of NEAs decreases from the middle of the distribution to its ends, that is, the excesses of slow rotators (ω ≤ 2 rev day^?1) and fast rotators (ω ≥ 8 rev day^?1) are composed of smaller NEAs than in the middle of the distribution; (2) NEAs of both excesses are in the orbits where their insolation is about 8–10% larger than that of NEAs in the middle of the distribution; and (3) the objects in both excesses have a little lower albedo on average than that of objects in the middle of the distribution. All these results qualitatively agree well with the YORP‐effect action and may be considered as independent arguments in favor of it.     

Pyroxene mineralogies of near‐Earth vestoids

Abstract— We have calculated pyroxene mineralogies of seven near‐Earth asteroids (NEAs) with reflectance spectra similar to HEDs (howardites, eucrites, and diogenites). Two different sets of formulas (Gaffey et al. 2002; Burbine et al. 2007) are used to calculate the pyroxene mineralogies of the NEAs from their Band I and II centers. The band centers have been adjusted to compensate for the low temperatures on the asteroid surfaces. All of the derived mineralogies from the Gaffey et al. (2002) formulas and the Burbine et al. (2007) formulas overlap. The derived wollastonite (Wo) contents are very similar with differences being only approximately 1 mol%. The derived ferrosilite (Fs) contents differ by only 3 to 8 mol%. The determined pyroxene mineralogies for all seven near‐Earth vestoids are consistent with eucrites or howardites. None of the objects have pyroxene mineralogies consistent with diogenites. The absence of near‐Earth vestoids with pyroxene mineralogies similar to diogenites may indicate that it is difficult to produce sizeable (km‐sized or larger) bodies that are predominantly composed of diogenitic material, suggesting these objects are rubble piles of mixed ejecta.     

Singularly weighted symplectic forms and applications to asteroid motion

New techniques to study Hamiltonian systems with Hamiltonian forcing are proposed. They are based on singularly weighted symplectic forms and transformations which preserve these forms. Applications pertaining to asteroid motion are outlined. These involve the presence of both Jupiter and Saturn.     

Mineralogies and source regions of near-Earth asteroids

Near-Earth Asteroids (NEAs) offer insight into a size range of objects that are not easily observed in the main asteroid belt. Previous studies on the diversity of the NEA population have relied primarily on modeling and statistical analysis to determine asteroid compositions. Olivine and pyroxene, the dominant minerals in most asteroids, have characteristic absorption features in the visible and near-infrared (VISNIR) wavelengths that can be used to determine their compositions and abundances. However, formulas previously used for deriving compositions do not work very well for ordinary chondrite assemblages. Because two-thirds of NEAs have ordinary chondrite-like spectral parameters, it is essential to determine accurate mineralogies. Here we determine the band area ratios and Band I centers of 72 NEAs with visible and near-infrared spectra and use new calibrations to derive the mineralogies 47 of these NEAs with ordinary chondrite-like spectral parameters. Our results indicate that the majority of NEAs have LL-chondrite mineralogies. This is consistent with results from previous studies but continues to be in conflict with the population of recovered ordinary chondrites, of which H chondrites are the most abundant. To look for potential correlations between asteroid size, composition, and source region, we use a dynamical model to determine the most probable source region of each NEA. Model results indicate that NEAs with LL chondrite mineralogies appear to be preferentially derived from the ν₆ secular resonance. This supports the hypothesis that the Flora family, which lies near the ν₆ resonance, is the source of the LL chondrites. With the exception of basaltic achondrites, NEAs with non-chondrite spectral parameters are slightly less likely to be derived from the ν₆ resonance than NEAs with chondrite-like mineralogies. The population of NEAs with H, L, and LL chondrite mineralogies does not appear to be influenced by size, which would suggest that ordinary chondrites are not preferentially sourced from meter-sized objects due to Yarkovsky effect.     

近地小行星发现数目与发现场景的统计分析

近地小行星是一类可能对地球安全造成潜在威胁的太阳系小天体, 目前绝大部分的近地小行星是由地基望远镜发现的, 且数目仍在不断增加. 为了对我国未来开展近地小行星发现监测提供参考和借鉴, 利用国际小行星中心公开的数据库对所有近地小行星首次发现时刻的观测资料开展了多维度统计分析. 发现望远镜探测能力的限制会对近地小行星的发现造成选择效应, 导致不同轨道类型近地小行星发现的相对比例逐年变化且与直径有关. 另外, 结合数值模拟获得的轨道数据, 对近地小行星首次发现时的观测场景进行了还原, 获得了发现时刻近地小行星位置在不同天球坐标系的分布, 分析了其分布特征与季节、测站纬度和小行星直径的依赖关系. 最后, 通过分析数据定量考察了太阳、月球和银道面对近地小行星发现的影响, 发现地基望远镜一般难以发现来自太阳方向90$^\circ$范围内直径140m以下的近地小行星, 并且随着小行星直径的减小该限制范围也将变大; 月光污染对近地小行星发现的影响也非常显著, 望月前后几天的观测限制可导致约29%的目标无法被发现, 而且分析表明农历上半月发现的目标一般比下半月发现的更难以被跟踪观测; 银道面特别是银心方向会对近地小行星发现产生影响, 使得黄道面附近存在与季节相关的观测``盲区''.