共查询到20条相似文献，搜索用时 15 毫秒
1.
Modeling of migrating grains on asteroid’s surface 总被引：1，自引：0，他引：1
2.
Binary systems are quite common within the populations of near-Earth asteroids, main-belt asteroids, and Kuiper belt asteroids. The dynamics of binary systems, which can be modeled as the full two-body problem, is a fundamental problem for their evolution and the design of relevant space missions. This paper proposes a new shape-based model for the mutual gravitational potential of binary asteroids, differing from prior approaches such as inertia integrals, spherical harmonics, or symmetric trace-free tensors. One asteroid is modeled as a homogeneous polyhedron, while the other is modeled as an extended rigid body with arbitrary mass distribution. Since the potential of the polyhedron is precisely described in a closed form, the mutual gravitational potential can be formulated as a volume integral over the extended body. By using Taylor expansion, the mutual potential is then derived in terms of inertia integrals of the extended body, derivatives of the polyhedron’s potential, and the relative location and orientation between the two bodies. The gravitational forces and torques acting on the two bodies described in the body-fixed frame of the polyhedron are derived in the form of a second-order expansion. The gravitational model is then used to simulate the evolution of the binary asteroid (66391) 1999 KW4, and compared with previous results in the literature. 相似文献
3.
《New Astronomy》2019
In the current study, we use the polyhedral model to compute the potential of the asteroid. There are five equilibrium points in the gravitational field of the asteroid 283 Emma. We concluded that the zero-velocity surfaces and the equilibrium points change with the suppositive variation of the rotational speed of the asteroid. It is found that if the rotational speed equals a half as it is in present, the number of equilibrium points is also five. However, if the rotational speed equals twice as it is in present, there are only three equilibrium points left. Four different periodic orbits are calculated using the hierarchical grid searching method. We calculated characteristic multipliers of periodic orbits to investigate the stability of these periodic orbits. The orbit near the primary's equatorial plane is more likely to be stable when the separation/ primary-radius is a large number. 相似文献
4.
《天文和天体物理学研究(英文版)》2017,(12)
In asteroid rendezvous missions, the dynamical environment near an asteroid's surface should be made clear prior to launch of the mission. However, most asteroids have irregular shapes,which lower the efficiency of calculating their gravitational field by adopting the traditional polyhedral method. In this work, we propose a method to partition the space near an asteroid adaptively along three spherical coordinates and use Chebyshev polynomial interpolation to represent the gravitational acceleration in each cell. Moreover, we compare four different interpolation schemes to obtain the best precision with identical initial parameters. An error-adaptive octree division is combined to improve the interpolation precision near the surface. As an example, we take the typical irregularly-shaped nearEarth asteroid 4179 Toutatis to demonstrate the advantage of this method; as a result, we show that the efficiency can be increased by hundreds to thousands of times with our method. Our results indicate that this method can be applicable to other irregularly-shaped asteroids and can greatly improve the evaluation efficiency. 相似文献
5.
We used binary octahedrons to investigate the dynamical behaviors of binary asteroid systems. The mutual potential of the binary polyhedron method is derived from the fourth order to the sixth order. The irregular shapes, relative orbits, attitude angles, as well as the angular velocities of the binary asteroid system are included in the model. We investigated the relative trajectory of the secondary relative to the primary, the total angular momentum and total energy of the system, the three-axis attitude angular velocity of the binary system, as well as the angular momentum of the two components. The relative errors of the total angular momentum and the total energy indicate that the calculation has a high precision. It is found that the influence of the orbital and attitude motion of the primary from the gravitational force of the secondary is obvious. This study is useful in understanding the complicated dynamical behaviors of the binary asteroid systems discovered in our Solar system. 相似文献
6.
Walter Petry 《Astrophysics and Space Science》1991,175(1):1-14
The study of a previously proposed theory of gravitation in flat space-time (Petry, 1981a) is continued. A conservation law for the angular momentum is derived. Additional to the usual form, there must be added a term coming from the spin of the gravitational field. The equations of motion and of spin angular momentum for a spinning test particle in a gravitational field are given. An approximation of the equations of the spin angular momentum in the rest frame of the test particle is studied. For a gyroscope in an orbit of a rotating massive body (e.g., the Earth) the precession of the spin axis agrees with the result of Einstein's general theory of relativity. 相似文献
7.
Martin Connors Christian Veillet Ramon Brasser Paul Wiegert Paul Chodas Seppo Mikkola Kimmo Innanen 《Meteoritics & planetary science》2004,39(8):1251-1255
Abstract— The newly discovered asteroid 2003 YN107 is currently a quasi‐satellite of the Earth, making a satellite‐like orbit of high inclination with apparent period of one year. The term quasi‐satellite is used since these large orbits are not completely closed, but rather perturbed portions of the asteroid's orbit around the Sun. Due to its extremely Earth‐like orbit, this asteroid is influenced by Earth's gravity to remain within 0.1 AU of the Earth for approximately 10 years (1997 to 2006). Prior to this, it had been on a horseshoe orbit closely following Earth's orbit for several hundred years. It will re‐enter such an orbit, and make one final libration of 123 years, after which it will have a close interaction with the Earth and transition to a circulating orbit. Chaotic effects limit our ability to determine the origin or fate of this object. 相似文献
8.
L. C. Garcia de Andrade 《Astrophysics and Space Science》1992,198(1):79-83
The equivalence of Lagrangian containing gravitational, electromagnetic, scalar, and torsion fields is discussed. It is shown that the equation for the variation of the scalar field leads to a torsion wave equation generated by electromagnetic field leads to a torsion wave equation generated by electromagnetic fields. The system is proved to be equivalent to a Proca field coupling torsion non-minimally to a massive photon and having the scalar Higgs field as a strength of this photon-torsion coupling. The generalized Maxwell equations containing the scalar fields are obtained. The torsion potential around the Sun or a more massive collapsing star in the weak field limit is estimated. 相似文献
9.
M. G. D’Urso 《Celestial Mechanics and Dynamical Astronomy》2014,120(4):349-372
We extend a recent approach for computing the gravity effects of polyhedral bodies with uniform density by the case of bodies with linearly varying density and by consistently taking into account the relevant singularities. We show in particular that the potential and the gravity vector can be given an expression in which singularities are ruled out, thus avoiding the introduction of small positive numbers advocated by some authors in order to circumvent undefined operations. We also prove that the entries of the second derivative exhibit a singularity if and only if the observation point is aligned with an edge of a face of the polyhedron. The formulas presented in the paper have been numerically checked with alternative ones derived on the basis of different approaches, already established in the literature, and intensively tested by computing the gravity effects induced by real asteroids with arbitrarily assigned density variations. 相似文献
10.
Leszek Czechowski 《Earth, Moon, and Planets》1991,52(2):113-130
The tidal effects on a fractured asteroid are considered. The asteroid is assumed to consist of two parts. In gravitational field of another body the motion of one part of the asteroid in relation to second part may be initiated. The necessary conditions for this motion are determined and amount of heat that can be generated is calculated for some cases. It is suggested that metamorphic episodes found in some meteorites are the results of such heating. 相似文献
11.
A. A. Saaryan 《Astrophysics》1995,38(1):55-67
The low-energy string gravitation is investigated for the case of reduction with a variable (in string units) inner space. A flat cosmological model of the corresponding four-dimensional theory is constructed. The model equations are analyzed qualitatively for a potential-dominated scalar field as the source. It is demonstrated that an extended inflation stage with one purely scalar dilaton field is possible here, in contrast with the case of a constant inner space. The pattern of cosmological evolution in various conformal representations is discussed.Translated from Astrofizika, Vol. 38, No. 1, pp. 99–119, January–March, 1995. 相似文献
12.
C. C. Leiby Jr. 《Astrophysics and Space Science》1972,17(2):368-377
The Maxwell equations for gravitational fields previously assumed by Sciama are derived from elementary considerations. The
Lagrangian for a gravitating mass in a non-inertial coordinate system yields equations of motion leading to force definitions
for a gravitational field intensity and a gravitational induction field. The non-inertial velocity of the coordinate system
plays the role of a vector potential contributing to the generalized momenta of bodies moving in the system. A Lagrangian
density constructed from the force-defined fields then lead to the source definitions of gravitational fields. It is found
that positive field energy densities require repulsive gravitational forces, whereas attractive forces imply the violation
of the conservation of energy. This paradox is resolved by representing gravitational quantities as pure-imaginary entities.
Thus characterized, the equations which define gravitational fields become identical to Maxwell's equations but are pure-imaginary.
This suggests a combined representation for gravitational and electromagnetic fields which, in covariant form, indicates both
the well known equivalence of mass and energy and a possible equivalence of charge and energy. From orthogonality considerations,
it is conjectured that this latter energy is gravitational, and that, whereas gravitational fields interact with electromagnetic
energy, electromagnetic fields interact with gravitational energy.
Parts of this work were completed at Air Force Cambridge Research Laboratories, Bedford, Mass., U.S.A. 相似文献
13.
Thomas J. ZEGA Laurence A. J. GARVIE Istvn D
DONY Heiner FRIEDRICH Rhonda M. STROUD Peter R. BUSECK 《Meteoritics & planetary science》2006,41(5):681-688
Abstract— We used high‐resolution transmission electron microscopy (HRTEM), electron tomography, electron energy‐loss spectroscopy (EELS), and energy‐dispersive spectroscopy (EDS) to investigate the structure and composition of polyhedral serpentine grains that occur in the matrices and fine‐grained rims of the Murchison, Mighei, and Cold Bokkeveld CM chondrites. The structure of these grains is similar to terrestrial polygonal serpentine, but the data show that some have spherical or subspherical, rather than cylindrical morphologies. We therefore propose that the term polyhedral rather than polygonal be used to describe this material. EDS shows that the polyhedral grains are rich in Mg with up to 8 atom% Fe. EELS indicates that 70% of the Fe occurs as Fe3+. Alteration of cronstedtite on the meteorite parent body under relatively oxidizing conditions is one probable pathway by which the polyhedral material formed. The polyhedral grains are the end‐member serpentine in a mineralogic alteration sequence for the CM chondrites. 相似文献
14.
We investigate the flux of main-belt asteroid fragments into resonant orbits converting them into near-Earth asteroids (NEAs), and the variability of this flux due to chance interasteroidal collisions. A numerical model is used, based on collisional physics consistent with the results of laboratory impact experiments. The assumed main-belt asteroid size distribution is derived from that of known asteroids extrapolated down to sizes of ≈ 40 cm, modified in such a way to yield a quasi-stationary fragment production rate over times ≈ 100 Myr. The results show that the asteroid belt can supply a few hundred km-sized NEAs per year, well enough to sustain the current population of such bodies. On the other hand, if our collisional physics is correct, the number of existing 10-km objects implies that these objects either have very long-lived orbits, or must come from a different source (i.e., comets). Our model predicts that the fragments supplied from the asteroid belt have initially a power-law size distribution somewhat steeper than the observed one, suggesting preferential removal of small objects. The component of the NEA population with dynamical lifetimes shorter than or of the order of 1 Myr can vary by a factor reaching up to a few tens, due to single large-scale collisions in the main belt; these fluctuations are enhanced for smaller bodies and faster evolutionary time scales. As a consequence, the Earth's cratering rate can also change by about an order of magnitude over the 0.1 to 1 Myr time scales. Despite these sporadic spikes, when averaged over times of 10 Myr or longer the fluctuations are unlikely to exceed a factor two. 相似文献
15.
Stability of Surface Motion on a Rotating Ellipsoid 总被引：2，自引：0，他引：2
The dynamical environment on the surface of a rotating, massive ellipsoid is studied, with applications to surface motion on an asteroid. The analysis is performed using a combination of classical dynamics and geometrical analysis. Due to the small sizes of most asteroids, their shapes tend to differ from the classical spheroids found for the planets. The tri-axial ellipsoid model provides a non-trivial approximation of the gravitational potential of an asteroid and is amenable to analytical computation. Using this model, we study some properties of motion on the surface of an asteroid. We find all the equilibrium points on the surface of a rotating ellipsoid and we show that the stability of these points is intimately tied to the conditions for a Jacobi or MacLaurin ellipsoid of equilibria. Using geometrical analysis we can define global constraints on motion as a function of shape, rotation rate, and density, we find that some asteroids should have accumulation of material at their ends, while others should have accumulation of surface material at their poles. This study has implications for motion of a rover on an asteroid, and for the distribution of natural material on asteroids, and for a spacecraft hovering over an asteroid. 相似文献
16.
Conditions are presented for maintenance of asteroid magnetospheres by dipole moments and for propagation of whistler mode noise in the solar wind at asteroid distances. Surface field intensities less than one thousandth that of the Earth are found adequate for supporting magnetospheres in the quiet solar wind surrounding the larger asteroids. Magnetospheric diameters are likely to be small, however, and difficult to identify without targeted, close-approach flybys. Under most ordinary conditions, whistler noise generated in an asteroidal shock or by other interaction with the solar wind will not propagate back upstream toward the sun, but may form a detectable wake downstream. Pure standing whistler wavefronts could be a unique asteroidal phenomenon. 相似文献
17.
Paul R. WEISSMAN Michael D. HICKS Paul A. ABELL Young‐Jun CHOI Stephen C. LOWRY 《Meteoritics & planetary science》2008,43(5):905-914
Abstract— ESA's Rosetta spacecraft will fly by main‐belt asteroid 2867 Steins on September 5, 2008. We obtained new visible wavelength spectra of 2867 Steins on December 19, 2006 (UT), using the Palomar 5 m telescope and the facility Double Spectrograph. Two sets of spectra, taken ～3 h apart, one half of the rotation period for 2867 Steins, show it to be an E‐type asteroid. The asteroid displays a 0.50 μm feature that is considered diagnostic of the E(II) sub‐class, but is deeper than any previously observed E‐type. This feature is most likely due to the presence of oldhamite (CaS) on the asteroid's surface. Also, the observed Steins spectra are far redder than any other known E‐types. There is potential evidence for heterogeneity on hemispheric scales, one side of the asteroid appearing to be significantly redder than the other. No known recovered meteorite sample matches the unusual spectra of 2867 Steins, but the closest analog would be similar to an enstatite achondrite (aubrite). 相似文献
18.
Faith Vilas David J. Tholen Larry A. Lebofsky Humberto Campins Glenn J. Veeder Richard P. Binzel Alan T. Tokunaga 《Icarus》1985,63(2):201-205
Visual and infrared observations were made of Amor asteroid 1982 DV during its discovery apparition. Broadband visual and near-infrared photometry shows that it is an S-class asteroid. Narrowband spectrophotometry shows an absorption feature due to olivine or pyroxene or both centered at 0.93 μm. Applying a nonrotating thermal model to 10-μm photometry, the geometric albedo is calculated to be approximately 0.27. The geometric albedo for a slowly rotating, rocky surface was calculated for 1 night to be 0.15, consistent with S-class asteroid albedos. Thus, 1982 DV is either one of the most reflective S-class asteroids known, or a significant amount of bare rock is exposed on the asteroid's surface. For the nonrotating model, ellipsoidal dimensions for 1982 DV are 3.5 × 1.4 × 1.4 km. 相似文献
19.
A great number of probable encounters of asteroid 2015 RN35 with the Earth have been found; many of them were unknown earlier. The main characteristics and properties of the corresponding trajectories have been obtained. Probable impacts of the asteroid Apophis with the Earth are also discussed. The results suggest that the multitudes of potential impacts of hazardous asteroids with the Earth can be and must be analyzed in more detail. Such an analysis is required to plan and implement the measures on preventing the asteroid impact hazard. 相似文献
20.
This paper gives a full nonlinear version of Newtonian gravity in which the gravitational energy acts as a source of the gravitational
field. The generalized field equation for the scalar gravitational potential is solved for a spherically symmetric localized
distribution of matter. It is shown that the perihelia of orbits of test particles in such a field precess steadily. The effect
is, however, too small to account for the observed shift in the perihelion of planet Mercury. Further, the bending of light
in this theory is zero. It is suggested that these inadequacies of the quasi-Newtonian framework call for more sophisticated
approaches to gravity. 相似文献