排序方式： 共有40条查询结果，搜索用时 15 毫秒
1.
The trans-Neptunian belt has been subject to a strong depletion that has reduced its primordial population by a factor of one hundred over the solar system's age. One by-product of such a depletion process is the existence of a scattered disk population in transit from the belt to other places, such as the Jupiter zone, the Oort cloud or interstellar space. We have integrated the orbits of the scattered disk objects (SDOs) so far discovered by 2500 Myr to study their dynamical time scales and the probability of falling in each of the end states mentioned above, paying special attention to their contribution to the Oort cloud. We found that their dynamical half-time is close to 2.5 Gyr and that about one third of the SDOs end up in the Oort cloud. 相似文献
2.
3.
Adrián Brunini 《Monthly notices of the Royal Astronomical Society》1998,293(4):405-410
In this paper we consider the dynamical evolution and orbital stability of objects in the asteroid belt. A simple physical model, including full gravitational perturbations from both giant planets, is used to compute the dynamical evolution of 1000 test particles simulating the primitive asteroids. The criterion of planet crossing (or close approach in the case of resonant objects) is used to reject particles from the simulation. 44 per cent of the particles survived for the whole time-span covered by the numerical integration (∼109 yr).
The 4:1, 3:1 and to a lesser extent the 2:1 Kirkwood gaps are formed in ∼107 yr of evolution, representing direct numerical evidence about their gravitational origin.
We found that the rms eccentricity and inclination of the sample experience a fast increase during the first 106 yr. The final rms eccentricity is 0.11, ∼60 per cent smaller than the present rms eccentricity (0.17). Nevertheless, the gravitational action of the giant planets suffices to prevent the formation of large objects, allowing catastrophic collisions and the subsequent depletion of material from this zone of the Solar system. The excited eccentricity by Jupiter and Saturn may favour mutual encounters and the further increase of the relative velocities up to their present values. 相似文献
The 4:1, 3:1 and to a lesser extent the 2:1 Kirkwood gaps are formed in ∼10
We found that the rms eccentricity and inclination of the sample experience a fast increase during the first 10
4.
The SIRGAS permanent GPS network which is in fact the IGS network densification for the American continent, consists today of more than 200 stations covering the continent and islands. It is currently processed by the IGS RNAAC SIR centre at Deutsches Geodätisches Forschungsinstitut producing weekly free solutions relying on IGS final orbits and EOP that contribute to the ITRF through IGS. By August 2006, the SIRGAS Working Group I had accepted five proposals for experimental processing centers within the region that would collaborate with IGS RNAAC SIR. One of them, Centro de Procesamiento La Plata (CPLat) in Argentina, began processing 60 stations on October 2006. By January 2007 CPLat reached operational capability, delivering weekly free solution SINEX files, with an internal consistency of 1.5 mm average for the horizontal components, and 3 mm in the vertical. Comparisons with IGS global and IGS RNAAC SIR weekly solutions were taken as external consistency indications, showing average RMS residuals of 1.8, 2.4 and 5 mm for the north, east, and vertical component, respectively. Analysis and comparison of adjusted solution time series from CPLat and other processing centers has proved to be highly valuable for solution QC, namely detection and identification of station anomalous behavior or modelling problems. These procedures will ensure the maintenance of the performance specifications for CPLat solutions. Action is being taken in order to guarantee the continuity of this effort beyond the experimental phase. 相似文献
5.
Hilda asteroids and comets are similar from the compositional point of view. The D-taxonomic class prevailing among Hildas has all the characteristics found in cometary spectra. Jupiter Family Comets (JFCs) coming from the trans-neptunian region are under the gravitational control of Jupiter, making them a dynamically unstable population with a mean dynamical lifetime of 104 to 105 years. In contrast, Hilda asteroids residing in the 3:2 mean motion resonance with Jupiter are a very stable population. But once they escape from the resonance, they are dynamically controlled by Jupiter, and in this sense their behavior resembles that of JFC. We performed a numerical simulation to analyze the dynamical evolution that Hildas follow after escaping from the resonance, and their contribution to the JFC population. We found that 8% of the particles leaving the resonance end up impacting Jupiter. 98.7% of the escaped Hildas live at least 1000 years as a JFC, with a mean lifetime of 1.4×106 years. In particular, escaped Hildas stay mainly in the region of perihelion distances greater than 2.5 AU. On the other hand, the number of escaped Hildas reaching the inner Solar System (q<2.5 AU) is negligible. So, there are almost no Hilda asteroids among the NEO population. We also analyzed the possibility that the Shoemaker-Levy 9 were an escaped Hilda asteroid. In this case, it would be possible to give stronger constraints to its pre-capture orbital elements. 相似文献
6.
Rodney S. Gomes Tabaré Gallardo Julio A. Fernández Adrián Brunini 《Celestial Mechanics and Dynamical Astronomy》2005,91(1-2):109-129
We study the transfer process from the scattered disk (SD) to the high-perihelion scattered disk (HPSD) (defined as the population
with perihelion distances q > 40 AU and semimajor axes a>50 AU) by means of two different models. One model (Model 1) assumes
that SD objects (SDOs) were formed closer to the Sun and driven outwards by resonant coupling with the accreting Neptune during
the stage of outward migration (Gomes 2003b, Earth, Moon, Planets 92, 29–42.). The other model (Model 2) considers the observed population of SDOs plus clones that try to compensate for observational
discovery bias (Fernández et al. 2004, Icarus , in press). We find that the Kozai mechanism (coupling between the argument of perihelion, eccentricity, and inclination),
associated with a mean motion resonance (MMR), is the main responsible for raising both the perihelion distance and the inclination
of SDOs. The highest perihelion distance for a body of our samples was found to be q = 69.2 AU. This shows that bodies can
be temporarily detached from the planetary region by dynamical interactions with the planets. This phenomenon is temporary
since the same coupling of Kozai with a MMR will at some point bring the bodies back to states of lower-q values. However,
the dynamical time scale in high-q states may be very long, up to several Gyr. For Model 1, about 10% of the bodies driven
away by Neptune get trapped into the HPSD when the resonant coupling Kozai-MMR is disrupted by Neptune’s migration. Therefore,
Model 1 also supplies a fossil HPSD, whose bodies remain in non-resonant orbits and thus stable for the age of the solar system,
in addition to the HPSD formed by temporary captures of SDOs after the giant planets reached their current orbits. We find
that about 12 – 15% of the surviving bodies of our samples are incorporated into the HPSD after about 4 – 5 Gyr, and that
a large fraction of the captures occur for up to the 1:8 MMR (a ⋍ 120 AU), although we record captures up to the 1:24 MMR
(a ≃ 260 AU). Because of the Kozai mechanism, HPSD objects have on average inclinations about 25°–50°, which are higher than
those of the classical Edgeworth–Kuiper (EK) belt or the SD. Our results suggest that Sedna belongs to a dynamically distinct
population from the HPSD, possibly being a member of the inner core of the Oort cloud. As regards to 2000 CR105 , it is marginally within the region occupied by HPSD objects in the parametric planes (q,a) and (a,i), so it is not ruled
out that it might be a member of the HPSD, though it might as well belong to the inner core. 相似文献
7.
We investigate the possibility of gravitational capture of planetesimals as temporary or permanent satellites of Uranus and Neptune during the process of planetary growth. The capture mechanism is based in the enhancement of the Hill's sphere of action not only due to the mass acquired by the planet, but also by the variation of the planet-Sun distance as a consequence of the scattering of planetesimals by the planets of the outer solar system. Our calculations indicate that satellite capture was very important, specially during the first stages of the accretion process, contributing in a significant way to the planetary growth. 相似文献
8.
9.
O. G. Benvenuto † A. Brunini ‡ 《Monthly notices of the Royal Astronomical Society》2005,356(4):1383-1395
We present a numerical code for computing all stages of the formation and evolution of giant planets in the framework of the core instability mechanism. This code is a non-trivial adaption of the stellar binary evolution code and is based on a standard Henyey technique. To investigate the performance of this code we applied it to the computation of the formation and evolution of a Jupiter mass object from a half Earth core mass to ages in excess of the age of the Universe.
We also present a new smoothed linear interpolation algorithm devised especially for the purpose of circumventing some problems found when some physical data (e.g. opacities, equation of state, etc.) are introduced into an implicit algorithm like the one employed in this work. 相似文献
We also present a new smoothed linear interpolation algorithm devised especially for the purpose of circumventing some problems found when some physical data (e.g. opacities, equation of state, etc.) are introduced into an implicit algorithm like the one employed in this work. 相似文献
10.
We analyze the Centaur population as a group of objects with perihelion distances (q) of less than 30 AU and heliocentric distances outside the orbit of Jupiter, formed by objects entering this region from the Scattered Disk (SD). We perform a numerical integration of 95 real Scattered Disk Objects (SDOs) extracted from the Minor Planet Center database and of 905 synthetic SDOs compensating for observational biases. SDOs have in the Centaur zone a mean lifetime of 72 Myr, though this number falls with a decrease of q. After this incursion, 30% of them enter the zone interior to Jupiter's orbit. We find that the contribution to the Centaur population from the SD gives a total of ∼2.8×108 Centaurs with a radius R>1 km. We also propose a model for the intrinsic distribution of orbital elements of Centaurs and their distance and apparent magnitude distribution. 相似文献