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1.
Up to now, 17 Neptune Trojan asteroids have been detected with their orbits being well determined by continuous observations. This paper analyzes systematically their orbital dynamics. Our results show that except for two temporary members with relatively short lifespans on Trojan orbits, the vast majority of Neptune Trojans located within their orbital uncertainties may survive in the solar system age. The escaping probability of Neptune Trojans, through slow diffusion in the orbital element space in 4.5 billion years, is estimated to be ～50%. The asteroid 2012 UW177 classified as a Centaur asteroid by the IAU Minor Planet Center currently is in fact a Neptune Trojan. Numerical simulations indicate that it is librating on the tadpole-shaped orbit around the Neptune's L4 point. It was captured into the current orbit approximately 0.23 million years ago, and will stay there for at least another 1.3 million years in the future. Its high inclination of i ≈ 54° not only makes it the most inclined Neptune Trojan, but also makes it exhibit the complicated and interesting co-orbital transitions between the leading and trailing Trojans via the quasi-satellite orbit phase. 相似文献
2.
3.
Asteroid families are believed to originate by catastrophic disruptions of large asteroids. They are nowadays identified as clusters in the proper orbital elements space. The proper elements are analytically defined as constants of motion of a suitably simplified dynamical system. Indeed, they are generally nearly constant on a 107-108-year time scale. Over longer time intervals, however, they may significantly change, reflecting the accumulation of the tiny nonperiodic evolutions provided by chaos and nonconservative forces. The most important effects leading to a change of the proper orbital elements are (i) the chaotic diffusion in narrow mean motion resonances, (ii) the Yarkovsky nongravitational force, and (iii) the gravitational impulses received at close approaches with large asteroids. A natural question then arises: How are the size and shape of an asteroid family modified due to evolution of the proper orbital elements of its members over the family age? In this paper, we concentrate on the dynamical dispersion of the proper eccentricity and inclination, which occurs due to (i), but with the help of (ii) and (iii). We choose the Flora family as a model case because it is unusually dispersed in eccentricity and inclination and, being located in the inner main belt, is intersected by a large number of effective mean motion resonances with Mars and Jupiter. Our results suggest that the Flora family dynamically disperses on a few 108-year time scale and that its age may be significantly less than 109 years. We discuss the possibility that the parent bodies of the Flora family and of the ordinary L chondrite meteorites are the same object. In a broader sense, this work suggests that the common belief that the present asteroid families are simple images of their primordial dynamical structure should be revised. 相似文献
4.
Many asteroids with a semimajor axis close to that of Mars have been discovered in the last several years. Potentially some of these could be in 1:1 resonance with Mars, much as are the classic Trojan asteroids with Jupiter, and its lesser-known horseshoe companions with Earth. In the 1990s, two Trojan companions of Mars, 5261 Eureka and 1998 VF31, were discovered, librating about the L5 Lagrange point, 60° behind Mars in its orbit. Although several other potential Mars Trojans have been identified, our orbital calculations show only one other known asteroid, 1999 UJ7, to be a Trojan, associated with the L4 Lagrange point, 60° ahead of Mars in its orbit. We further find that asteroid 36017 (1999 ND43) is a horseshoe librator, alternating with periods of Trojan motion. This asteroid makes repeated close approaches to Earth and has a chaotic orbit whose behavior can be confidently predicted for less than 3000 years. We identify two objects, 2001 HW15 and 2000 TG2, within the resonant region capable of undergoing what we designate “circulation transition”, in which objects can pass between circulation outside the orbit of Mars and circulation inside it, or vice versa. The eccentricity of the orbit of Mars appears to play an important role in circulation transition and in horseshoe motion. Based on the orbits and on spectroscopic data, the Trojan asteroids of Mars may be primordial bodies, while some co-orbital bodies may be in a temporary state of motion. 相似文献
5.
The character of orbital evolution for bodies moving near the if 1 : 3 commensurability with Jupiter was studied by model calculations for the time interval of ～500 years. A comparison of oscillations of the orbital elements a, e, q and q′ is made for ensembles of bodies along three starting orbits in the vicinity of the sharp commensurability with Jupiter. These orbits are eccentric ones of low inclinations having perihelia near the Earth's orbit. Examples of a deceleration of the rate of orbital evolution near the sharp commensurability are revealed. The existence of a group of asteroids connected with the Kirkwood gap, i.e., being in a resonant motion with Jupiter, is suggested. A connection of asteroids 887 Alinda and 1915 Quetzalcoatl with this gap is confirmed. 相似文献
6.
O. Karlsson 《Astronomische Nachrichten》2011,332(6):562-579
An investigation is carried out looking at correlations between the orbital elements of collisional targets and projectiles, estimating the number of interlopers in Trojan collisional families, and at the possibility of determining the ages of the Jupiter Trojan families by orbital integration. Real Trojans are integrated and close encounters are recorded in order to evaluate collisional circumstances between Trojans. Fictitious collisional families are created and integrated for 10 MJyr (million Julian years) forward in time and back again to the time of the collision in order to check the performance of the integrator, and the behaviour of the fictitious collisional fragments. Proper elements are calculated for the detection of family clustering using the hierarchically clustering method. This method presents little difficulty finding fictitious families in the Trojan swarms even in areas with densely populated backgrounds. However, even when the background is relatively sparse in objects, several interlopers can be connected to the family at velocity differences below 100 m s–1. On the other hand, in densely populated backgrounds the contamination of interlopers should be less than 30%. Providing gravity is the only significant force acting on the Trojans and resonance effects are weak, the shape the collision fragments create in the proper element space are preserved on the GJyr scale, and collisions can be tracked with orbital integrations for ages of at least 100 MJyr. However, the shape of artificial families does not correspond to suggested real families. This points to the need of including non‐gravitational forces such as the Yarkovsky effect in order to simulate the family evolution. As a consequence age determination by orbital integration might be severely restricted and previous investigations involving long term orbital integrations might have tobe recalculated (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
7.
Asteroid orbits using phase-space volumes of variation 总被引：2，自引：0，他引：2
K. Muinonen J. Virtanen M. Granvik T. Laakso 《Monthly notices of the Royal Astronomical Society》2006,368(2):809-818
We present a statistical orbit computation technique for asteroids with transitional observational data, that is, a moderate number of data points spanning a moderate observational time interval. With the help of local least-squares solutions in the phase space of the orbital elements, we map the volume of variation as a function of one or more of the elements. We sample the resulting volume using a Monte Carlo technique and, with proper weights for the sample orbital elements, characterize the six-dimensional orbital-element probability density function. The volume-of-variation (VOV) technique complements the statistical ranging technique for asteroids with exiguous observational data (short time intervals and/or small numbers of observations) and the least-squares technique for extensive observational data. We show that, asymptotically, results using the new technique agree closely with those from ranging and least squares. We apply the technique to the near-Earth object 2004 HA39 , the main-belt object 2004 QR and the transneptunian object 2002 CX224 recently observed at the Nordic Optical Telescope on La Palma, illustrating the potential of the technique in ephemeris prediction. The VOV technique helps us assess the phase transition in orbital-element probability densities, that is, the non-linear collapse of wide orbital-element distributions to narrow localized ones. For the three objects above, the transition takes place for observational time intervals of the order of 10 h, 5 d and 10 months, respectively, emphasizing the significance of the orbital-arc fraction covered by the observations. 相似文献
8.
Philippe Lamy Pierre Vernazza Joel Poncy Vincent Martinot Emmanuel Hinglais Elisabet Canalias Jim Bell Dale Cruikshank Olivier Groussin Joern Helbert Francesco Marzari Alessandro Morbidelli Pascal Rosenblatt Holger Sierks 《Experimental Astronomy》2012,33(2-3):685-721
In our present understanding of the Solar System, small bodies (asteroids, Jupiter Trojans, comets and TNOs) are the most direct remnants of the original building blocks that formed the planets. Jupiter Trojan and Hilda asteroids are small primitive bodies located beyond the ‘snow line’, around respectively the L4 and L5 Lagrange points of Jupiter at ～5.2?AU (Trojans) and in the 2:3 mean-motion resonance with Jupiter near 3.9?AU (Hildas). They are at the crux of several outstanding and still conflicting issues regarding the formation and evolution of the Solar System. They hold the potential to unlock the answers to fundamental questions about planetary migration, the late heavy bombardment, the formation of the Jovian system, the origin and evolution of trans-neptunian objects, and the delivery of water and organics to the inner planets. The proposed Trojans’ Odyssey mission is envisioned as a reconnaissance, multiple flyby mission aimed at visiting several objects, typically five Trojans and one Hilda. It will attempt exploring both large and small objects and sampling those with any known differences in photometric properties. The orbital strategy consists in a direct trajectory to one of the Trojan swarms. By carefully choosing the aphelion of the orbit (typically 5.3?AU), the trajectory will offer a long arc in the swarm thus maximizing the number of flybys. Initial gravity assists from Venus and Earth will help reducing the cruise time as well as the ΔV needed for injection thus offering enough capacity to navigate among Trojans. This solution further opens the unique possibility to flyby a Hilda asteroid when leaving the Trojan swarm. During the cruise phase, a Main Belt Asteroid could be targeted if requiring a modest ΔV. The specific science objectives of the mission will be best achieved with a payload that will perform high-resolution panchromatic and multispectral imaging, thermal-infrared imaging/ radiometry, near- and mid-infrared spectroscopy, and radio science/mass determination. The total mass of the payload amounts to 50?kg (including margins). The spacecraft is in the class of Mars-Express or a down-scaled version of Jupiter Ganymede Orbiter. It will have a dry mass of 1200?kg, a total mass at launch of 3070?kg and a ΔV capability of 700?m/s (after having reached the first Trojan) and can be launched by a Soyuz rocket. The mission operations concept (ground segment) and science operations are typical of a planetary mission as successfully implemented by ESA during, for instance, the recent flybys of Main Belt asteroids Steins and Lutetia. 相似文献
9.
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
10.
B. Érdi 《Celestial Mechanics and Dynamical Astronomy》1987,43(1-4):303-308
The motion of the Trojan asteroids is studied in the elliptic restricted three-body problem of the Sun-Jupiter-asteroid system. Long periodic perturbations of the orbital elements are discussed. Relations between dynamical parameters are considered and comparisons are made with Bien's and Schubart's results. 相似文献
11.
Bálint Érdi 《Celestial Mechanics and Dynamical Astronomy》1984,34(1-4):435-441
The author's earlier solution for Trojan asteroids is developed further. It is shown that depending on the amplitude of libration around the Lagrangian point L4, there is a critical inclination which determines the sign of the variation of the ascending node. If the orbital inclination of a Trojan is smaller than the critical one, then the ascending node decreases and otherwise it increases. The variation of the eccentricity and of the longitude of the perihelion has also a dependence on the critical inclination. 相似文献
12.
Asteroid families are groupings of minor planets identified by clustering in their proper orbital elements; these objects have spectral signatures consistent with an origin in the break-up of a common parent body. From the current values of proper semimajor axes a of family members one might hope to estimate the ejection velocities with which the fragments left the putative break-up event (assuming that the pieces were ejected isotropically). However, the ejection velocities so inferred are consistently higher than N-body and hydro-code simulations, as well as laboratory experiments, suggest. To explain this discrepancy between today’s orbital distribution of asteroid family members and their supposed launch velocities, we study whether asteroid family members might have been ejected from the collision at low speeds and then slowly drifted to their current positions, via one or more dynamical processes. Studies show that the proper a of asteroid family members can be altered by two mechanisms: (i) close encounters with massive asteroids, and (ii) the Yarkovsky non-gravitational effect. Because the Yarkovsky effect for kilometer-sized bodies decreases with asteroid diameter D, it is unlikely to have appreciably moved large asteroids (say those with D > 15 km) over the typical family age (1-2 Gyr).For this reason, we numerically studied the mobility of family members produced by close encounters with main-belt, non-family asteroids that were thought massive enough to significantly change their orbits over long timescales. Our goal was to learn the degree to which perturbations might modify the proper a values of all family members, including those too large to be influenced by the Yarkovsky effect. Our initial simulations demonstrated immediately that very few asteroids were massive enough to significantly alter relative orbits among family members. Thus, to maximize gravitational perturbations in our 500-Myr integrations, we investigated the effect of close encounters on two families, Gefion and Adeona, that have high encounter probabilities with 1 Ceres, by far the largest asteroid in the main belt. Our results show that members of these families spreads in a of less than 5% since their formation. Thus gravitational interactions cannot account for the large inferred escape velocities.The effect of close encounters with massive asteroids is, however, not entirely negligible. For about 10% of the simulated bodies, close encounters increased the “inferred” ejection velocities from sub-100 m/s to values greater than 100 m/s, beyond what hydro-code and N-body simulations suggest are the maximum possible initial ejection velocity for members of Adeona and Gefion with D > 15 km. Thus this mechanism of mobility may be responsible for the unusually high inferred ejection speeds of a few of the largest members of these two families.To understand the orbital evolution of the entire family, including smaller members, we also performed simulations to account for the drift of smaller asteroids caused by the Yarkovsky effect. Our two sets of simulations suggest that the two families we investigated are relatively young compared to larger families like Koronis and Themis, which have estimated ages of about 2 Byr. The Adeona and Gefion families seems to be no more than 600 and 850 Myr old, respectively. 相似文献
13.
Bálint Érdi 《Celestial Mechanics and Dynamical Astronomy》1981,24(4):377-390
An asymptotic solution for the cylindrical coordinates of Trojan asteroids is derived by using a three-variable expansion method in the elliptic restricted three-body problem. The perturbations of the orbital elements are obtained from this solution by applying the formulas of the two-body problem. The main perturbations of the mean motion are studied in detail. 相似文献
14.
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
15.
We present new near-infrared spectra of 20 Trojan asteroids. The spectra were recorded at the NASA Infrared Telescope Facility (IRTF) using the recently commissioned medium-resolution spectrograph SpeX and at the Multiple Mirror Telescope (MMT) using the instrument FSPEC. Spectra of all of these objects were measured in K-band (1.95-2.5 μm), 8 of these in L-band (2.8-4.0 μm), and 14 in the range 0.8-2.5 μm. These observations nearly double the number of published 0.8-2.5 μm spectra of Trojan asteroids and provide the first systematic study of the L-band region for these distant asteroids. The data show that the red spectral slope measured in the near-IR extends through the L-band, though it is not as steep here as at shorter wavelengths. A significant diversity is apparent in the near-IR spectral slopes of this sampling of objects. Most of the spectra do not contain any definitive absorption features characteristic of surface composition (e.g., H2O, organics, silicates) as seen on main-belt asteroids and several Centaur and Kuiper Belt objects. A few objects may display spectral activity, and the reliability of these possible features is discussed. While these spectra are generally compatible with silicate surfaces to explain the spectral slope mixed with some fraction of low albedo material, there is no absolute indication of silicates. The spectral slope could also be explained by the presence of hydrocarbons, but the lack of absorption features, especially in L-band where very strong fundamental absorptions from these molecules appear, constrains the character and abundance of these materials at the surface. 相似文献
16.
Balint Érdi 《Celestial Mechanics and Dynamical Astronomy》1996,65(1-2):149-164
There has been a renewed interest in the Trojan problem in recent years. Significant progress has been made in discovering and understanding dynamical features of motion of Jupiter's Trojan asteroids. The dynamics of hypothetical Trojan-type asteroids of other major planets has also been the subject of several recent investigations. This paper offers an overview on the current status of researches on real and hypothetical Trojan asteroids of the major planets. Results of analytical and numerical works are surveyed. Questions of dynamical properties, long-term evolution of orbits, stability regions around the triangular Lagrangian points are discussed among other problems of the Trojans. 相似文献
17.
Cratering rates on the Galilean satellites 总被引：1，自引：0，他引：1
We exploit recent theoretical advances toward the origin and orbital evolution of comets and asteroids to obtain revised estimates for cratering rates in the jovian system. We find that most, probably more than 90%, of the craters on the Galilean satellites are caused by the impact of Jupiter-family comets (JFCs). These are comets with short periods, in generally low-inclination orbits, whose dynamics are dominated by Jupiter. Nearly isotropic comets (long period and Halley-type) contribute at the 1-10% level. Trojan asteroids might also be important at the 1-10% level; if they are important, they would be especially important for smaller craters. Main belt asteroids are currently unimportant, as each 20-km crater made on Ganymede implies the disruption of a 200-km diameter parental asteroid, a destruction rate far beyond the resources of today's asteroid belt. Twenty-kilometer diameter craters are made by kilometer-size impactors; such events occur on a Galilean satellite about once in a million years. The paucity of 20-km craters on Europa indicates that its surface is of order 10 Ma. Lightly cratered surfaces on Ganymede are nominally of order 0.5-1.0 Ga. The uncertainty in these estimates is about a factor of five. Callisto is old, probably more than 4 Ga. It is too heavily cratered to be accounted for by the current flux of JFCs. The lack of pronounced apex-antapex asymmetries on Ganymede may be compatible with crater equilibrium, but it is more easily understood as evidence for nonsynchronous rotation of an icy carapace. 相似文献
18.
采用接近真实太阳系的动力学模型,对主带小行星的动力学演化进行了数值模拟。计算的起始时间是儒略日JD=2.4540005×10~6,计算的时间长度为100万年。力学模型采用n+m体模型,计算程序基于小行星轨道演化的软件Orbit9。对演化结果进行分析可以发现测试粒子与木星的平运动共振对测试粒子稳定性的不同作用,以及在2:3、3:4共振处不同初始ω值对测试粒子演化结果的影响。 相似文献
19.
The evolution of orbits of asteroids found in the IRAS and WISE albedo databases was calculated numerically from 2005 to 2016. It follows from the analysis of the obtained results that a certain nongravitational effect (NGE) currently affects the motion of a considerable fraction of main-belt asteroids with diameters up to 40 km. This conclusion agrees with the available data regarding the axial rotation of asteroids. The NGE manifests itself in an increase in the semimajor axes of orbits of low-albedo asteroids relative to the semimajor axes of orbits of high-albedo bodies. The NGE-induced rate of elongation of semimajor axes of asteroids with albedos рv < 0.1 may be as high as (2–8) × 10–8 AU/year. Errors in orbital elements of asteroids (unrelated to the accuracy of observational data used to determine these orbital elements) were found in one of the MPC catalogues for 2003 in the process of estimation of the accuracy of calculations. 相似文献
20.
Richard Greenberg 《Icarus》1978,33(1):62-73
Orbital resonances tend to force bodies into noncircular orbits. If a body is also under the influence of an eccentricity-reducing medium, it will experience a secular change in semimajor axis which may be positive or negative depending on whether its orbit is exterior or interior to that of the perturbing body. Thus a dissipative medium can promote either a loss or a gain in orbital energy. This process may explain the resonant structure of the asteroid belt and of Saturn's rings. For reasonable early solar system parameters, it would clear a gap near the 2:1 resonance with Jupiter on a time scale of a few thousand years; the gap width would be comparable to the Kirkwood gap presently at the location in the asteroid belt. Similarly, a gap comparable in width to Cassini's division would be cleared in Saturn's rings at the 2:1 resonance with Mimas in ～106 yr. Most of the material from the gap would be deposited at the outer edge of ring B. The process would also affect the radial distribution of preplanetary material. Moreover, it provides an explanation for the large amplitude of the Titan-Hyperion libration. Consideration of the effects of dissipation on orbits near the stable L4 and L5 points of the restricted three-body problem indicates that energy loss causes particles to move away from these points. This results explains the large amplitude of Trojan asteroids about these points and the possible capture of Trojan into orbit about Jupiter. 相似文献