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1.
E.F. Helin  E.M. Shoemaker 《Icarus》1979,40(3):321-328
Photographic coverage of about 80,000 deg2 of sky with the Palomar 46-cm Schmidt camera has yielded 12 new planet-crossing asteroids as well as many objects in the main asteroid belt. The estimated population of planet-crossing asteroids includes ～100 Atens, 700 ± 300 Apollos, 1000–2000 Amors, 10,000 ± 5000 Mars crossers, and ～5000 Mars grazers.  相似文献   

2.
The orbits of 13 Trojan asteroids have been calculated numerically in the model of the outer solar system for a time interval of 100 million years. For these asteroids Milani et al. (1997) determined Lyapunov times less than 100 000 years and introduced the notion "asteroids in stable chaotic motion". We studied the dynamical behavior of these Trojan asteroids (except the asteroid Thersites which escaped after 26 million years) within 11 time intervals - i.e. subintervals of the whole time - by means of: (1) a numerical frequency analysis (2) the root mean square (r.m.s.) of the orbital elements and (3) the proper elements. For each time interval we compared the root mean squares of the orbital elements (a, e and i) with the corresponding proper element. It turned out that the variations of the proper elements ep in the different time intervals are correlated with the corresponding r.m.s.(e); this is not the case for sin Ip with r.m.s.(i). This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

3.
More than 7 000 positions of moving objects were detected on 33 films obtained with the Schmidt telescope at the European Southern Observatory in Chile during August and September 1995. The majority of these asteroids are previously unobserved. This paper presents the results for 62 unnumbered asteroids with provisional designations found in the fields. References to the derived positions for these asteroids are given and improved orbital elements have been calculated using all available positions.  相似文献   

4.
Two-colour photoelectric light curves of the RS CVn-type eclipsing system UV Psc, obtained in 1985 and 1986, are presented. Present work also deals with the Fourier analysis of the outside-eclipse light variations for five years' light curves (1981, 1982, 1984, 1985, 1986). Based on this analysis, the amplitude variations of the so-called wave-like distortion and its migration period have been investigated. The amplitude of the wave-like distortion seems to vary with a very rough period of 4–5 years, and the migration period of the wave minimum appears to be one of the three different (2.3, 0.7, 0.4 years) but most possible values among some others.  相似文献   

5.
In order to clarify the early warning and response requirements of near-Earth asteroids impact, the concept of “short-term hazardous asteroids” is proposed, that is, near-Earth asteroids with an equivalent diameter greater than 10 meters that may pose a threat to the Earth in the next 100 years. Based on the 756 short-term hazardous asteroids that have been discovered so far, the orbital distribution characteristics of short-term hazardous asteroids are analyzed, and the study shows that their orbital distribution differs from that of general near-Earth asteroids: the semi-major axis of the short-term hazardous asteroids is more concentrated in 1 au, and the orbital plane is more concentrated in the ecliptic plane. On the basis of the quantity model of near-Earth asteroids, a preliminary estimation model for the quantity of short-term hazardous asteroids is established, and the population of short-term hazardous asteroids with potential threat in the next 100 years is predicted. Some specific research on short-term hazardous asteroids is of great significance to the development of near-Earth asteroid search and monitoring strategies.  相似文献   

6.
为更明确近地小行星撞击地球威胁的监测预警需求, 提出了"短期威胁小行星"的概念, 即未来100yr内可能对地球造成撞击威胁且等效直径大于10m的近地小行星. 以目前已发现的756颗短期威胁小行星为基础, 分析短期威胁小行星的轨道分布特点, 研究显示其与一般近地小行星的轨道分布存在差异, 短期威胁小行星的轨道半长轴更集中于1au, 轨道面更集中于黄道面. 基于近地小行星的数量模型, 初步建立了短期威胁小行星的数量估计模型, 并预估了未来100yr内存在撞击可能的短期威胁小行星的总体数量. 短期威胁小行星的特定研究对制定近地小行星搜巡监测策略有重要意义.  相似文献   

7.
The orbital evolutions of the asteroid 3040 Kozai and model asteroids with similar orbits have been investigated. Their osculating orbits for an epoch 1991 December 10 were numerically integrated forward within the interval of 20,000 years, using a dynamical model of the solar system consisting of all inner planets, Jupiter, and Saturn.The orbit of the asteroid Kozai is stable. Its motion is affected only by long-period perturbations of planets. With change of the argument of perihelion of the asteroid Kozai, the evolution of the model asteroid orbits changes essentially, too. The model orbits with the argument of perihelion changed by the order of 10% show that asteroids with such orbital parameters may approach the Earth orbit, while asteroids with larger changes may even cross it, at least after 10,000 years. Long-term orbital evolution of asteroids with these orbital parameters is very sensitive on their angular elements.  相似文献   

8.
The dynamics of near-Earth asteroids near mean motion resonances with the Earth or other planets is considered. The probability domains of the motion of some near-Earth asteroids close to low-order resonances are presented. The investigations have been carried out by means of a numerical integration of differential equations, taking into account the perturbations from the major planets and the Moon. For each investigated object an ensemble of 100 test particles with orbital elements nearby those of the nominal orbit has been constructed and its evolution has been retraced over the time interval (–3000, +3000 years). The initial set of orbits has been generated on the basis of probable variations of the initial orbital elements obtained from the least square analysis of observations.This revised version was published online in October 2005 with corrections to the Cover Date.  相似文献   

9.
A summary is given about the Minor Planet survey performed in 1986 on Tautenburg Schmidt plates. There were discovered 129 asteroids and calculated 312 positions for them. These are 29 numbered objects and 100 asteroids with provisional designations, six of them have no new designations. Tautenburg observations could give a tribute to five planets numbered in the period of this report, including the asteroid 1981 VW1 discovered in Tautenburg which received the number (3499) and the name Hoppe.  相似文献   

10.
Jack D. Drummond 《Icarus》1982,49(1):143-153
A compilation of theoretical meteor radiants is presented for all numbered (through 2525) asteroids which approach the Earth's orbit to within 0.20 AU. On the basis of orbital similarity, asteroids associated with current meteor streams and Prairie Network fireballs are listed; plausible associations with medieval fireball radiants are also given. The best defunct comet candidates in terms of meteoric evidence appear to be 2101 Adonis and 2201 1947XC. Asteroids which may be either extinct comets or perturbed main belt asteroids accompanied by collisional debris (represented by fireballs) are 1917 Cuyo, 2202 Pele, 2061 Anza, and 2340 Hathor. 1566 Icarus and 1981 Midas are the only asteroids whose orbits approach to less than 0.07 AU of the Earth's orbit, have a northern radiant, and still show no certain meteoric activity. The majority of Atens, Apollos, and Amors do not pass sufficiently close (<0.07 AU) to the Earth's orbit for a reasonable expectation of meteoric activity, or have radiants south of ?20° declination, requiring southern hemisphere observations.  相似文献   

11.
This article describes a citizen‐science project conducted by the Spanish Virtual Observatory (SVO) to improve the orbits of near‐Earth asteroids (NEAs) using data from astronomical archives. The list of NEAs maintained at the Minor Planet Center (MPC) is checked daily to identify new objects or changes in the orbital parameters of already catalogued objects. Using NEODyS we compute the position and magnitude of these objects at the observing epochs of the 938 046 images comprising the Eigth Data Release of the Sloan Digitised Sky Survey (SDSS). If the object lies within the image bound‐aries and the magnitude is brighter than the limiting magnitude, then the associated image is visually inspected by the project's collaborators (the citizens) to confirm or discard the presence of the NEA. If confirmed, accurate coordinates and, sometimes, magnitudes are submitted to the MPC. Using this methodology, 3226 registered users have made during the first fifteen months of the project more than 167 000 measurements which have improved the orbital elements of 551 NEAs (6% of the total number of this type of asteroids). Even more remarkable is the fact that these results have been obtained at zero cost to telescope time as NEAs were serendipitously observed while the survey was being carried out. This demonstrates the enormous scientific potential hidden in astronomical archives. The great reception of the project as well as the results obtained makes it a valuable and reliable tool for improving the orbital parameters of near‐Earth asteroids. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

12.
International programs of observations of selected minor planets have lasted about 50 years and the last one comes to the end in 2000. The main aim of these observational programs consists in obtaining the orientation of the stellar reference frame with respect to the dynamical one using observations of the bright minor planets. The observations are also useful for the orbital improvements of the asteroids themselves. They are available from the author via e-mail at the address .During the above mentioned period more than 23 000 observations of minor planets, referred to different reference star catalogues, have been obtained. The reduction procedure of observations to the PPM star catalogue is described. The orientation parameters are given and discussed.  相似文献   

13.
The orbits of the asteroids crossing the orbit of the Earth and other planets are chaotic and cannot be computed in a deterministic way for a time span long enough to study the probability of collisions. It is possible to study the statistical behaviour of a large number of such orbits over a long span of time, provided enough computing resources and intelligent post processing software are available. The former, problem can be handled by exploiting the enormous power of parallel computing systems. The orbit of the asteroids can be studied as a restricted (N+M)-body problem which is suitable for the use of parallel processing, by using one processor to compute the orbits of the planets and the others to compute the orbits the asteroids. This scheme has been implemented on LCAP-2, an array of IBM and FPS processors with shared memory designed by E. Clementi (IBM). The parallelisation efficiency has been over 80%, and the overall speed over 90 MegaFLOPS; the orbits of all the asteroids with perihelia lower than the aphelion of Mars (410 objects) have been computed for 200,000, years (Project SPACEGUARD). The most difficult step of the project is the post processing of the very large amount of output data and to gather qualitative information on the behaviour of so many orbits without resorting to the traditional technique, i.e. human examination of output in graphical form. Within Project SPACEGUARD we have developed a qualitative classification of the orbits of the planet crossers. To develop an entirely automated classification of the qualitative orbital behaviour-including crossing behaviour, resonances (mean motion and secular), and protection mechanisms avoiding collisions-is a challenge to be met.  相似文献   

14.
The Sun-to-Mercury mass ratio adopted by the International Astronomical Union (6023600 ± 250) was obtained in 1987 by analyzing Mariner 10 observations (Anderson et al. 1987) and since then has not been improved. The large number of asteroids in Mercury-approaching orbits and the ever-increasing accuracy of their observations allow the mass of Mercury to be estimated by a different method. We have improved the orbital parameters of 43 asteroids and obtained 6023440 ± 530 for the Sun-to-Mercury mass ratio through a simultaneous solution based on their optical and radar observations. A further improvement in this estimate is possible in the immediate future owing to the rapid increase in the number of known asteroids whose observations can be used to solve this problem.  相似文献   

15.
The pumping up of orbital inclinations of asteroids caused by sweeping secular resonances associated with depletion of a protoplanetary disk is discussed, focusing on the dependence on the disk inclinations and surface density distribution. The asteroids have large mean inclinations that cannot be explained by present planetary perturbations alone. It has been suggested that the sweeping secular resonances caused by disk depletion are responsible for these high inclinations. Nagasawa et al. (2000, Astron. J.119, 1480-1497) showed that the inclinations of asteroids are pumped up if the disk is depleted in an inside-out manner on a time scale longer than 3×105 years. Their assumed disk midplane is not on the invariant plane. However, it should be affected by the inclination of the disk plane. Here we investigate the dependence on the disk inclinations. We assume a disk depletion model in which the disk inside the jovian orbit has been removed and the residual outer disk is uniformly depleted. We calculate the locations of the secular resonances and the excitation magnitude of the inclinations with analytical methods. We found that the inclinations are pumped up to the observational level for a depletion time scale longer than 106 years in the case of the disk plane that coincides with the invariant plane. The required time scale is longest (3×106 years) if the disk plane coincides with the jovian orbital plane. However, it is still within the observationally inferred depletion time scale. We also studied dependence on a disk surface density gradient and found that the results do not change significantly as long as the inner disk depletion is faster than the outer disk one.  相似文献   

16.
More than 7000 positions of moving objects have been detected on 33 films obtained with the Schmidt telescope at the European Southern Observatory in Chile during August and September 1995. The majority of these asteroids are previously unobserved. This paper presents the astrometric methods as well as the magnitude determinations. The derived positions for the numbered asteroids are presented and for these improved orbital elements have been calculated using all available positions.  相似文献   

17.
本文给出了对行星状星云NGC2346核星AGK3—0°695从1981年到1987年这段期间内所做的照相观测结果。从中我们看到该天体自1981年底开始出现的大变幅食光变现象持续数年之后,从1986年开始其光变幅度迅速减小,由85年的Δm～4~m减小到86年的Δm～1~m.1。而且到1987年其光变曲线仅存Δm～0~m.4的不规则亮度起伏,已无明显的周期性光变现象,文中对此现象做了初步分析讨论。  相似文献   

18.
Recent theoretical and observational work has shown that the asteroids belonging to the Taurid meteoroid complex have a cometary nature. If so, then they might possess related meteoroid streams producing meteor showers in the Earth atmosphere. We studied the orbital evolution of ten numbered Taurid complex asteroids by the Halphen-Goryachev method. It turned out that all of these asteroids are quadruple crossers relative to the Earth's orbit. Therefore their proposed meteoroid streams may in theory each produce four meteor showers. The theoretical orbital elements and geocentric radiants of these showers are determined and compared with the available observational data. The existence of the predicted forty meteor showers of the ten Taurid complex asteroids is confirmed by a search of the published catalogues of observed meteor shower radiants and orbits, and of the archives of the IAU Meteor Data Center (Lund). The existence of meteor showers associated with the Taurid Complex Asteroids confirms that, most likely, these asteroids are extinct comets. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

19.
Six different calibrations of the polarimetric albedo scale of asteroids have been published so far. Each of them contains its particular random and systematic errors and yields its values of geometric albedo. On the one hand, this complicates their analysis and comparison; on the other hand, it becomes more and more difficult to decide which of the proposed calibrations should be used. Moreover, in recent years, new databases on the albedo of asteroids obtained from the radiometric surveys of the sky with the orbital space facilities (the InfraRed Astronomical Satellite (IRAS), the Japanese astronomical satellite AKARI (which means “light”), the Wide-field Infrared Survey Explorer (WISE), and the Near-Earth Object Wide-field Survey Explorer (NEOWISE)) have appeared; and the database on the diameters and albedos of asteroids obtained from their occultations of stars has substantially increased. Here, we critically review the currently available calibrations and propose a new generalized calibration derived from the interrelations between the slope h and the albedo and between Pmin and the albedo. This calibration is based on all of the available series of the asteroid albedos and the most complete data on the polarization parameters of asteroids. The generalized calibration yields the values of the polarimetric albedo of asteroids in the system unified with the radiometric albedos and the albedos obtained from occultations of stars by asteroids. This, in turn, removes the difficulties in their comparison, joint analysis, etc.  相似文献   

20.
Among the very few tabulated asteroids with perihelion inside or closely outside the Earth's orbit some have periods nearly commensurable with the Earth's. The perturbed orbit of one of these, 1685 Toro, has been integrated over 1200 years. The results show that Toro is at present captured in resonance with the Earth and also that Venus has a drastic influence on the orbital elements. Toro's orbit is librating with a main period of 800 years and peak-to-peak amplitude of about 65°. The mechanism of libration is discussed.Paper dedicated to Professor Hannes Alfvén on the occasion of his 70th birthday, 30 May 1978.  相似文献   

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