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1.
Wing-Huen IP 《Astrophysics and Space Science》1975,38(2):475-481
The possibility of incorporating the resonant effect and jet stream formation process into the problems of the Hilda asteroids and Kirkwood gaps is discussed qualitatively. It appears that formation of the precursor jet streams of the resonant asteroids in the main belt would be suppressed due to the collisional perturbation effect of the ambient matter in this region. Together with the biased distribution of near-resonant asteroids, the depletion across the Kirkwood gaps could be understood. Within the context of jet stream theory the existence of Hilda asteroids outside the main belt requires the original limit of the main belt to be not much more extensive than the present value of 3.5 AU. This is suggestive of a cosmogonic origin of the observed outer limit. 相似文献
2.
Close encounters of asteroids with the Earth can lead to a transition to resonant orbits, close encounters, and collisions in the future. The structure of the sets of possible collisions of asteroids with the Earth is similar to a fractal structure thanks to resonant returns of asteroids. Areas of semi-major axes and positions and sizes of gaps leading to collisions with the Earth for Apophis asteroids 2007 VK184 and 2011 AG5 are given. 相似文献
3.
Michèle Moons 《Celestial Mechanics and Dynamical Astronomy》1996,65(1-2):175-204
The study of mean motion resonance dynamics was motivated by the search for an explanation for the puzzling problem of the Kirkwood gaps. The most important contributions in this field within the last 32 years are reviewed here. At the beginning of that period, which coincides with the first long-term numerical investigations of resonant motion, different hypotheses (collisional, gravitational, statistical and cosmological) to explain the origin of the gaps were still competing with each other. At present, a general theory, based on gravitational mechanisms only, is capable of explaining in a uniform way all the Kirkwood gaps except the 2/1 one. Indeed, in the 4/1, 3/1, 5/2 and 7/3 mean motion commensurabilities, the overlap of secular resonances leads to almost overall chaos where asteroids undergo large and wild variations in their orbital elements. Such asteroids, if not thrown directly into the Sun, are sooner or later subject to strong close encounters with the largest inner planets, the typical time scale of the whole process being of the order of a few million years. Unfortunately, this mechanism is not capable of explaining the 2/1 gap where the strong chaos produced by the overlapping secular resonances does not attain orbits with moderate eccentricity, of low inclination and with low to moderate amplitude of libration. In the light of the most recent studies, it appears that the 2/1 gap is the global consequence of slow diffusive processes. At present, the origin of these processes remains under study. 相似文献
4.
An essential role in the asteroidal dynamics is played by the mean motion resonances. Two-body planet–asteroid resonances are widely known, due to the Kirkwood gaps. Besides, so-called three-body mean motion resonances exist, in which an asteroid and two planets participate. Identification of asteroids in three-body (namely, Jupiter–Saturn–asteroid) resonances was initially accomplished by Nesvorný and Morbidelli (Nesvorný D., Morbidelli, A. [1998]. Astron. J. 116, 3029–3037), who, by means of visual analysis of the time behaviour of resonant arguments, found 255 asteroids to reside in such resonances. We develop specialized algorithms and software for massive automatic identification of asteroids in the three-body, as well as two-body, resonances of arbitrary order, by means of automatic analysis of the time behaviour of resonant arguments. In the computation of orbits, all essential perturbations are taken into account. We integrate the asteroidal orbits on the time interval of 100,000 yr and identify main-belt asteroids in the three-body Jupiter–Saturn–asteroid resonances up to the 6th order inclusive, and in the two-body Jupiter–asteroid resonances up to the 9th order inclusive, in the set of ～250,000 objects from the “Asteroids – Dynamic Site” (AstDyS) database. The percentages of resonant objects, including extrapolations for higher-order resonances, are determined. In particular, the observed fraction of pure-resonant asteroids (those exhibiting resonant libration on the whole interval of integration) in the three-body resonances up to the 6th order inclusive is ≈0.9% of the whole set; and, using a higher-order extrapolation, the actual total fraction of pure-resonant asteroids in the three-body resonances of all orders is estimated as ≈1.1% of the whole set. 相似文献
5.
Makoto Yoshikawa 《Celestial Mechanics and Dynamical Astronomy》1992,54(1-3):287-290
Motions of asteroids in mean motion resonances with Jupiter are studied in three-dimensional space. Orbital changes of fictitious asteroids in the Kirkwood gaps are calculated by numerical integrations for 105 – 106 years. The main results are as follows: (1) There are various motions of resonant asteroids, and some of them are very complicated and chaotic and others are regular. (2) The eccentricity of some asteroids becomes very large, and the variation of the inclination is large while the eccentricity is large. (3) In the 3:1 resonance, there is a long periodic change in the variation of the inclination, when (7 : ) is a simple ratio (7: longitude of perihelion, : longitude of node). (4) In the 7:3 resonance, the variation of the inclination of some resonant asteroids is so large that prograde motion becomes retrograde. Some asteroids in the 7:3 resonance can collide with the Sun as well as with the inner planets. 相似文献
6.
W. -H. Ip 《Astrophysics and Space Science》1976,44(2):373-383
Schubart's model of a planar, elliptic restricted three-body problem is used to study the orbital motion of the Hilda asteroids from thePalomar-Leiden Survey. The 3:2 resonant coupling to Jupiter of some of these small asteroids are found to be stable. However, some of the small asteroids with absolute magnitudeg>15 have large amplitude of variation in their orbital elements in one libration period. Since the lifetime scales against catastrophic collision of the Hilda asteroids are estimated to be several times larger than those of the main belt objects, a significant portion of these resonant asteroids could be the original members of the Hilda group. From this point of view, it is suggested that such size-dependence of resonant orbital motions might be the result of the cosmogonic effects ofjet stream accretion. 相似文献
7.
A. Lemaitre 《Celestial Mechanics and Dynamical Astronomy》1984,34(1-4):329-341
A possible mechanism to explain the depletion of the Kirkwood gaps in the asteroid belt would be the slow dissipation of the solar nebula at the origin of the Solar System. The effects of this dissipation on a uniform distribution of asteroids are explored by means of the adiabatic invariant theory for the 2/1, 3/1 and 5/2 resonance cases. The framework is the restricted, circular and planar three body problem. 相似文献
8.
The size distribution of main belt of asteroids is determined primarily by collisional processes. Large asteroids break up and form smaller asteroids in a collisional cascade, with the outcome controlled by the strength-size relationship for asteroids. In addition to collisional processes, the non-collisional removal of asteroids from the main belt (and their insertion into the near-Earth asteroid (NEA) population) is critical, and involves several effects: strong resonances increase the orbital eccentricity of asteroids and cause them to enter the inner planet region; chaotic diffusion by numerous weak resonances causes a slow leak of asteroids into the Mars- and Earth-crossing populations; and the Yarkovsky effect, a radiation force on asteroids, is the primary process that drives asteroids into these resonant escape routes. Yarkovsky drift is size-dependent and can modify the main-belt size distribution. The NEA size distribution is primarily determined by its source, the main-belt population, and by the size-dependent processes that deliver bodies from the main belt. All of these effects are simulated in a numerical collisional evolution model that incorporates removal by non-collisional processes. We test our model against a wide range of observational constraints, such as the observed main-belt and NEA size distributions, the number of asteroid families, the preserved basaltic crust of Vesta and its large south-pole impact basin, the cosmic ray exposure ages of meteorites, and the cratering records on asteroids. We find a strength-size relationship for main-belt asteroids and non-collisional removal rates from the main belt such that our model fits these constraints as best as possible within the parameter space we explore. Our results are consistent with other independent estimates of strength and removal rates. 相似文献
9.
An analysis of ordered and chaotic regions of motion in the outer asteroid belt has shown that once the eccentricity of Jupiter is introduced the chaotic regions of the circular model are quite easily depleted. This suggests that also objects in neighbouring regions must be strongly perturbed. Therefore it is not surprising that many outer belt asteroids have been reported in the literature as resonant or anyway dynamically protected. By using the planar elliptic restricted 3-body model we have investigated the motion of outer belt asteroids which had not been suspected to librate. We find 3 cases of libration and 11 cases of e, coupling that can be explained within the theory of secular resonances. It is thus established that in the outer belt only resonant and dynamically protected asteroids can have lifetimes of the same order as the age of the Solar System. 相似文献
10.
We present a physical model to explain the existence of a class of large-lightcurve-amplitude, rapidly rotating asteroids found most commonly among objects in the size range 100–300 km diameter. A significant correlation between rotation period and lightcurve amplitude exists for asteroids in this size range in the sense that those with larger amplitudes spin more rapidly and hence these objects have high rotational angular momenta. Since this is a property of Jacobi ellipsoids, we have investigated whether these asteriods might be examples of triaxial equilibrium ellipsoids. We find that objects rotating with periods of 6 hr must have densities between 1.1 and 1.4 g cm?3, while those rotating in 4 hr would have densities between 2.4 and 3.2 g cm?3. If this model is valid then at least some of these asteroids have rather low mean densities. The reality of this result and its interpretation in terms of collisional evolution of the asteroids is discussed. 相似文献
11.
At present, approximately 1500 asteroids are known to evolve inside or sticked to the exterior 1:2 resonance with Mars at a ? 2.418 AU, being (142) Polana the largest member of this group. The effect of the forced secular modes superposed to the resonance gives rise to a complex dynamical evolution. Chaotic diffusion, collisions, close encounters with massive asteroids and mainly orbital migration due to the Yarkovsky effect generate continuous captures to and losses from the resonance, with a fraction of asteroids remaining captured over long time scales and generating a concentration in the semimajor axis distribution that exceeds by 20% the population of background asteroids. The Yarkovsky effect induces different dynamics according to the asteroid size, producing an excess of small asteroids inside the resonance. The evolution in the resonance generates a signature on the orbits, mainly in eccentricity, that depends on the time the asteroid remains captured inside the resonance and on the magnitude of the Yarkovsky effect. The greater the asteroids, the larger the time they remain captured in the resonance, allowing greater diffusion in eccentricity and inclination. The resonance generates a discontinuity and mixing in the space of proper elements producing misidentification of dynamical family members, mainly for Vesta and Nysa-Polana families. The half-life of resonant asteroids large enough for not being affected by the Yarkovsky effect is about 1 Gyr. From the point of view of taxonomic classes, the resonant population does not differ from the background population and the excess of small asteroids is confirmed. 相似文献
12.
The strength of regolith and rubble pile asteroids 总被引：1，自引：0，他引：1
We explore the hypothesis that, due to small van der Waals forces between constituent grains, small rubble pile asteroids have a small but nonzero cohesive strength. The nature of this model predicts that the cohesive strength should be constant independent of asteroid size, which creates a scale dependence with relative strength increasing as size decreases. This model counters classical theory that rubble pile asteroids should behave as scale‐independent cohesionless collections of rocks. We explore a simple model for asteroid strength that is based on these weak forces, validate it through granular mechanics simulations and comparisons with properties of lunar regolith, and then explore its implications and ability to explain and predict observed properties of small asteroids in the NEA and Main Belt populations, and in particular of asteroid 2008 TC3. One conclusion is that the population of rapidly rotating asteroids could consist of both distributions of smaller grains (i.e., rubble piles) and of monolithic boulders. 相似文献
13.
Tabaré Gallardo 《Icarus》2006,184(1):29-38
The aim of this work is to present a systematic survey of the strength of the mean motion resonances (MMRs) in the Solar System. We know by applying simple formulas where the resonances with the planets are located but there is no indication of the strength that these resonances have. We propose a numerical method for the calculation of this strength and we present an atlas of the MMRs constructed with this method. We found there exist several resonances unexpectedly strong and we look and find in the small bodies population several bodies captured in these resonances. In particular in the inner Solar System we find one asteroid in the resonance 6:5 with Venus, five asteroids in resonance 1:2 with Venus, three asteroids in resonance 1:2 with Earth and six asteroids in resonance 2:5 with Earth. We find some new possible co-orbitals of Earth, Mars, Saturn, Uranus and Neptune. We also present a discussion about the behavior of the resonant disturbing function and where the stable equilibrium points can be found at low and high inclination resonant orbits. 相似文献
14.
Tabaré Gallardo 《Icarus》2007,190(1):280-282
An excess of around 400 asteroids in the distribution of the semimajor axes of the asteroids is identified by means of numerical integrations as generated by a population of approximately 1000 asteroids evolving inside the exterior resonance 1:2 with Mars. Approximately 200 asteroids are librating around the asymmetric libration centers and their evolution in a time-scale of 1 million years appears stable but with a strong influence of Mars' eccentricity. The biggest Mars 1:2 resonant asteroid is (142) Polana. 相似文献
15.
Joachim Schubart 《Celestial Mechanics and Dynamical Astronomy》1973,8(2):219-220
This is a brief report on three theoretical projects about asteroids. The results presented here were recently obtained at the Astronomisches Rechen-Institut in Heidelberg, and it is planned to publish them in astronomy and Astrophysics in detail. The first project is a continuation of former work on asteroids with a mean motion commensurable to that of Jupiter (compare Schubart, 1968). In the two other cases the problem consists in the best possible determination of the value of a planetary mass in units of solar mass.Presented at the Conference on Celestial Mechanics, Oberwolfach, Germany, August 27–September 2, 1972. 相似文献
16.
The simplest model of a resonant problem of second order is the planar and circular case. Simplification like this is very old and for 3/1 resonance, several authors have studied this problem with different purposes. In this work, we test this model for the available asteroids, by applying Hori's perturbation method. Explicit solutions of the intermediate orbit are obtained. In the plane of two constants of the problem, all types of motion are described. By testing the model, it is shown that, in general, one can confirm results of numerical integrations indicating libration for a few number of asteroids and circulation for most of them. However, agreement in numerical values for amplitude and period of librations seems to be not possible mainly if Jupiter's eccentricity is neglected. On the other hand, even though there might be some physical reasons determining that only asteroids with high eccentricity may librate, it is shown that, from mathematical point of view, libration may occur even in the case of small eccentricities provided that some relations are satisfied. 相似文献
17.
We identify the asteroids in three-body mean-motion resonances with Jupiter and Mars on the set of all known on April 2016 numbered asteroids (467308 objects). The resonant objects are identified by the direct analysis of the behavior (libration/circulation) of the resonant arguments on 100000 yrs. All essential perturbations during the integration of the equations of the motion are taken into account. The number of the asteroids in different resonances has been calculated for all possible resonances with the order less or equal 6. 相似文献
18.
Lars Danielsson 《Earth, Moon, and Planets》1978,18(3):265-272
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
19.
D.J. Scheeres 《Icarus》2007,189(2):370-385
The energetics and dynamics of contact binary asteroids as they approach and pass the rotational fission limit is studied. We presume that the asteroids are subject to an external torque, such as from the YORP effect, that increases their angular momentum. Furthermore, we assume the asteroids can be described by a fairly minimal model comprised of a sphere and ellipsoid resting on each other. The minimum energy configurations for contact binary asteroids at different levels of angular momentum are computed and discussed. We find distinct transitions between different configurations as the angular momentum of the system is increased. These indicate that rapidly rotating contact binary asteroids may seek out clearly different relative configurations than slowly rotating systems. We find a single end state of the systems prior to rotational fission, and distinct dynamical outcomes as a function of mass distribution and shape when the rotational fission limit is exceeded. Our theoretical results agree qualitatively with observed properties of near-Earth asteroids, and can be used to help explain the spin-rate barrier, contact binaries, and the observed morphology of most NEO binaries. 相似文献
20.
M. Bro&#; D. Vokrouhlický F. Roig D. Nesvorný W. F. Bottke A. Morbidelli 《Monthly notices of the Royal Astronomical Society》2005,359(4):1437-1455
The 2/1 mean motion resonance with Jupiter, intersecting the main asteroid belt at ≈3.27 au, contains a small population of objects. Numerical investigations have classified three groups within this population: asteroids residing on stable orbits (i.e. Zhongguos), those on marginally stable orbits with dynamical lifetimes of the order of 100 Myr (i.e. Griquas), and those on unstable orbits. In this paper, we reexamine the origin, evolution and survivability of objects in the 2/1 population. Using recent asteroid survey data, we have identified 100 new members since the last search, which increases the resonant population to 153. The most interesting new asteroids are those located in the theoretically predicted stable island A, which until now had been thought to be empty. We also investigate whether the population of objects residing on the unstable orbits could be resupplied by material from the edges of the 2/1 resonance by the thermal drag force known as the Yarkovsky effect (and by the YORP effect, which is related to the rotational dynamics). Using N -body simulations, we show that test particles pushed into the 2/1 resonance by the Yarkovsky effect visit the regions occupied by the unstable asteroids. We also find that our test bodies have dynamical lifetimes consistent with the integrated orbits of the unstable population. Using a semi-analytical Monte Carlo model, we compute the steady-state size distribution of magnitude H < 14 asteroids on unstable orbits within the resonance. Our results provide a good match with the available observational data. Finally, we discuss whether some 2/1 objects may be temporarily captured Jupiter-family comets or near-Earth asteroids. 相似文献