不同测站近地小行星地基观测效能评估研究

目标的完备性搜索是开展近地小行星预警和防御的前提. 为量化评价近地小行星观测效能, 提高监测设备使用效率, 提出一种综合望远镜参数和测站天文条件的观测效能评估方法. 以观测目标信噪比作为检测指标, 设定检测条件形成目标检测方法, 定义评价指标用于评估近地小行星观测效能. 再基于近地小行星轨道数据和尺度分布模型, 建立近地小行星轨道数据模拟样本库. 最后选取中国科学院紫金山天文台盱眙观测站和中国科学院国家天文台冷湖观测台址, 仿真分析近地天体望远镜对直径0.01--30km近地小行星的观测效能, 结果表明: 不考虑两观测站年有效观测时间差异, 近地天体望远镜在冷湖观测全尺寸模拟样本的效能比在盱眙提高了5.21倍, 其中对1km以上直径目标的观测效能相当, 对1km以下直径目标的观测效能差异开始显现, 对0.1km以下直径目标冷湖优势更显著.     

Mining the CFHT Legacy Survey for known Near Earth Asteroids

The Canada‐France‐Hawaii Legacy Survey (CFHTLS) comprising about 25 000 MegaCam images was data mined to search for serendipitous encounters of known Near Earth Asteroids (NEAs) and Potentially Hazardous Asteroids (PHAs). A total of 143 asteroids (109 NEAs and 34 PHAs) were found on 508 candidate images which were field corrected and measured carefully, and their astrometry was reported to Minor Planet Centre. Both recoveries and precoveries (apparitions before discovery) were reported, including data for 27 precovered asteroids (20 NEAs and 7 PHAs) and 116 recovered asteroids (89 NEAs and 27 PHAs). Our data prolonged arcs for 41 orbits at first or last opposition, refined 35 orbits by fitting data taken at one new opposition, recovered 6 NEAs at their second opposition and allowed us to ameliorate most orbits and their Minimal Orbital Intersection Distance (MOID), an important parameter to monitor for potential Earth impact hazard in the future (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Refinement of Near Earth Asteroids’ orbital elements via simultaneous measurements by two observers

The aspects of triangulation of Near Earth Asteroids by two arbitrarily positioned observers (one spaceborne and the other Earth-bound, as well as both spaceborne) are being investigated, and the resulting orbital elements are compared to those gained through common orbital determination and refinement techniques. The main advantages of the method proposed in this work are, that given the approximate position of an asteroid, high quality orbital elements can be acquired very rapidly using two observations only.     

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 F-type asteroids with small inversion angles of polarization

UBVRI polarimetric observations carried out in 1997-2004 for the F-type Asteroids 302 Clarissa, 419 Aurelia, 704 Interamnia, and 762 Pulcova (V band only) are presented. Asteroid 419 Aurelia is characterized by a negative polarization branch which is unusual for low-albedo asteroids. Its depth is about 1%, while the inversion angle, close to 14°, reaches the smallest value ever observed for asteroids. This is the first definite example of a minor body exhibiting a considerable decrease of both the depth and width of the negative polarization branch in comparison with polarization properties of other low-albedo bodies, mimicking a behavior previously found in laboratory measurements of extremely dark surfaces. The F-type Asteroids 302 Clarissa and 704 Interamnia are also characterized by unusually small inversion angles compared to other asteroid types, while Asteroid 762 Pulcova seems to have an ordinary negative polarization branch. Laboratory measurements of low-albedo samples and computer simulations of light scattering by particles of irregular shapes were made to interpret observational data. We find that an optical homogeneity of regolith microstructure at scales of the order of visible light wavelengths may be responsible for relatively small values of the depth of the negative polarization branch and of the inversion angle. Peculiar features of the F-type asteroids compared to other taxonomic classes are discussed.     

Mining the ESO WFI and INT WFC archives for known Near Earth Asteroids. Mega‐Precovery software

The ESO/MPG WFI and the INT WFC wide field archives comprising 330 000 images were mined to search for serendip‐itous encounters of known Near Earth Asteroids (NEAs) and Potentially Hazardous Asteroids (PHAs). A total of 152 as‐teroids (44 PHAs and 108 other NEAs) were identified using the PRECOVERY software, their astrometry being measured on 761 images and sent to the Minor Planet Centre. Both recoveries and precoveries were reported, including prolonged orbital arcs for 18 precovered objects and 10 recoveries. We analyze all new opposition data by comparing the orbits fitted before and after including our contributions. We conclude the paper presenting “Mega‐Precovery”, a new online service focused on data mining of many instrument archives simultaneously for one or a few given asteroids. A total of 28 instrument archives have been made available for mining using this tool, adding together about 2.5 million images forming the “Mega‐Archive”     

Book and Multimedia Reviews

Book reviewed in this article: Hazards Due to Comets & Asteroids edited by T. Gehrels. Collecting Meteorites: Starting in Your Own Back Yard by H. Carman and T. Kapitany.     

Eliminating Virtual Impactors with the Very Large Telescope: An ESO Program with the FORS2 Camera

We have used the ESO Very Large Telescope (VLT) to perform as trometric observations of Near Earth Asteroids (NEAs) having remote collision possibilities with the Earth. The observations were made for those objects which became too faint to be observed elsewhere. Using the 4 hours allocated in the semester April–September 2003, 5 faint NEAs were observed. As a result, no NEA that could impact the Earth was lost.     

Book Reviews

Book reviewed in this article: The Meteorite and Tektite Collector's Handbook by Philip M. Bagnall Comets, Asteroids, and Meteorites by the editors of Time-Life Books     

A closer look at main belt asteroids 1: WF/PC images

We present new reconstructions of images of main belt Asteroids 9 Metis, 18 Melpomene, 19 Fortuna, 216 Kleopatra, and 624 Hektor, made with the uncorrected Wide-Field/Planetary Camera (WF/PC) on the Hubble Space Telescope (HST). Deconvolution with the MISTRAL algorithm demonstrates that these asteroids are clearly resolved. We determine diameters, albedos, and lower limits to axial ratios for these bodies. We also review the process used to restore the aberrated images. No surface features or companions are found, but the rotation of 216 Kleopatra is clearly seen. The asteroidal albedos are similar to those determined by other procedures.     

Book and Multimedia Reviews

Books Reviewed in this article: Rogue Asteroids and Doomsday Comets by Duncan Steel. Annual Review of Astronomy and Astrophysics, Volume 33 edited by G. Burbidge and A. Sandage. Life in the Universe (A Scientific American Special Issue). W. H. Freeman and Company     

A New Protocol for the Astrometric Follow-up of Near Earth Asteroids

A new protocol was devised to improve the efficiency of astrometric follow-up observations of Near Earth Asteroids for the accurate determination of their orbits. It was implemented in the activities of the Spaceguard Central Node (SCN, a facility of the Spaceguard Foundation, established with the support of the European Space Agency) in the form of a Priority List. Here we describe this protocol and results obtained during five years of activity (2000–2004).     

近地小行星轨道演化的研究

本文主要阐述了近年来我们在近地小行星轨道演化研究所获得的一些基本结果,即合理的力学模型和相应的有效算法,并以实际预报算例与有关权威性的结果作了比较,证实这些研究结果确实是可信的。     

Time to Perform the Physical Observations of Asteroids

The astrometric observations of asteroids are often performednear their opposition, where they have faster apparent motions andbrighter visual magnitudes. However, the physical observations ofasteroids (photometric and spectral) often require longer exposuretimes as well as brighter magnitudes for better signal-to-noiseratio, which are combined effects of both apparent moving speedsand visual magnitudes. We derive the equations of the apparentmotion of asteroid in geocentric ecliptic coordinates. Comparisonof the apparent magnitudes of asteroid at opposition and atstationary shows that the magnitude differences in the two casesare around 1 magnitude in average for most main belt asteroids,but are much larger for Near Earth Asteroids. Combining withcomparison of asteroid apparent motion, the proper time forasteroid physical observation in different cases are discussed.     

Generalized Averaging Principle and the Secular Evolution of Planet Crossing Orbits

Planet crossing orbits give rise to mathematical singularities that make it not possible to apply the classical averaging principle to study the qualitative evolution of Near Earth Asteroids (NEAs). Recently this principle has been generalized to deal with crossings in a mathematical model with the planets on circular coplanar orbits. More accuracy is needed to compute the averaged evolution of planet crossing orbits for different purposes: computing reliable crossing times for the averaged motion, writing more precise proper elements and frequencies for NEAs, etc. In this paper we present the generalization of the averaging principle using a model where the eccentricity and the inclination of the planets are taken into account.     

BOOK REVIEWS

Book reviewed in this article: Moon Trip by Bert King. University of Houston Press Proceedings of the Twentieth Lunar and Planetary Science Conference edited by Virgil L. Sharpton and Graham Ryder. Asteroids II edited by R. P. Binzel, T. Gehrels and M. S. Matthews.     

About Hypothesis of the Superconducting Origin of the Saturn’s Rings

Hypothesis of possible superconductivity of the iced matter of the rings of Saturn (based on the data of Voyager and Pioneer space missions) allow us to explain many phenomena which have not been adequately understood earlier. Introducing into planetary physics force of magnetic levitation of the superconducting iced particle of the rings, which interact with magnetosphere of the planet, becomes to be possible to explain origin, evolution, and dynamics of the rings; to show how the consequent precipitation of the rings’ matter upon the planet was concluded; how the rings began their rotation; how they were compressed by the magnetic field into the thin disc, and how this disc was fractured into hundreds of thousands of separated rings; why in the ring B do exist “spokes”; why magnetic field lines have distortion near by ring F; why there is a variable azimuth brightness of the ring A; why the rings reflected radio waves so efficiently; why exists strong electromagnetic radiation of the rings in the 20.4 kHz–40.2 MHz range and Saturnian kilometric radiation; why there is anomalous reflection of circularly polarized microwaves; why there are spectral anomalies of the thermal radiation of the rings; why the matter of the various rings does not mix but preserves its small-scale color differences; why there is an atmosphere of unknown origin nearby the rings of Saturn; why there are waves of density and bending waves within Saturn’s rings; why planetary rings in the solar system appear only after the Belt of Asteroids (and may be the Belt of Asteroids itself is a ring for the Sun); why our planet Earth has no rings of its own.     

Books and Multimedia Review

Book reviewed in this article: Asteroids: A History by Curtis Peebles. Physics Meets Mineralogy: Condensed‐Matter Physics in Geosciences edited by Hideo Aoki, Yasuhiko Syono and Russell J. Hemley. Building Planet Earth: Five Billion Years of Earth History by Peter Cattermole.     

Utilization of an H-reversal trajectory of a solar sail for asteroid deflection

Near Earth Asteroids have a possibility of impacting the Earth and always represent a threat. This paper proposes a way of changing the orbit of the asteroid to avoid an impact. A solar sail evolving in an H-reversal trajectory is utilized for asteroid deflection. Firstly, the dynamics of the solar sail and the characteristics of the H-reversal trajectory are analyzed. Then, the attitude of the solar sail is optimized to guide the sail to impact the target asteroid along an H-reversal trajectory. The impact...     

UESAC — The Uppsala-ESO Survey of Asteroids and Comets

The Uppsala-ESO Survey of Asteroids and Comets was undertaken to find previously undetected comets in the vicinity of Jupiter. Over 15000 positions of moving objects have been detected on 74 plates obtained from the European Southern Observatory in Chile and from the Anglo-Australian Observatory in Australia in 1992 and 1993. Two or more positions were secured for about 3300 asteroids and orbits have so far been calculated for 1944 asteroids. The main bulk of these asteroids are previously undetected. We present absolute magnitudes and diameters for asteroids which have an accurate orbit. The magnitude and diameter distributions are compared to the results of the Palomar-Leiden Survey of Faint Minor Planets.