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[en] Although it is by no means clear that the Titius--Bode law of planetary distances is indeed a ''law'' (even though there are enticing indications), it is proposed that if one assumes that the law is a ''law'' and that the planets obey it, then this argues against recent large-scale evolution in the solar system. Put another way: one can believe in the Titius--Bode law or in recent large-scale evolution or in neither of them. But it appears difficult to believe in both of them
[en] The frequency distribution of the asteroidal mean motions shows the well known Kirkwood gaps which are found near the commensurabilities 3/1, 5/2, 7/3, and 2/1. The number of asteroids in the gaps is significantly smaller than those in the corresponding regions around these commensurabilities. In the outer part of the asteroidal belt, the frequency distribution is reversed: The number of asteroids at the commensurabilities 3/2, 4/3, and 1/1 is much larger than in the region around these commensurabilities. This reversal of the frequency distribution is one of the main problems of any hypothesis that tries to explain the Kirkwood gaps, since it is not at all obvious how asteroids can stay close to the commensurabilities 3/2 and 4/3 but avoid the commensurabilities 3/1, 5/2, 7/3 and 2/1. Different attempts have been made to explain the Kirkwood gaps based on statistical, gravitational, collisional or cosmogonic mechanisms. The author reviews each of these mechanisms. (Auth.)
[en] The major concern of this section will be to outline the ways in which measurements of isotope abundances have been used to determine the chronology of the origin and evolution of the solar system. In passing it should be remembered that the use of isotopic information is by no means restricted simply to the measurement of time scales and, particularly in recent years, isotope abundances have been used to investigate problems as diverse as the heat sources in the early solar nebula and the chemical evolution of the Earth's mantle. The fundamental property of isotopes which makes them especially useful for dating and other applications is the fact that, apart from a limited amount of mass fractionation, the composition of an isotopic mixture is unaffected by chemical processes. In those cases where mass fractionation does occur this effect may itself be useful, particularly as a source of information on temperatures. Since our main theme is time the events discussed in this section will be most conveniently presented as a chronological sequence, progressing from some time before the solar system existed down to the present day. (orig./WL)
[en] The cold classical population of the Kuiper Belt exhibits a wide variety of unique physical characteristics, which collectively suggest that its dynamical coherence has been maintained throughout the solar system's lifetime. Simultaneously, the retention of the cold population's relatively unexcited orbital state has remained a mystery, especially in the context of a solar system formation model, that is driven by a transient period of instability, where Neptune is temporarily eccentric. Here, we show that the cold belt can survive the instability, and its dynamical structure can be reproduced. We develop a simple analytical model for secular excitation of cold Kuiper Belt objects and show that comparatively fast apsidal precession and nodal recession of Neptune, during the eccentric phase, are essential for preservation of an unexcited state in the cold classical region. Subsequently, we confirm our results with self-consistent N-body simulations. We further show that contamination of the hot classical and scattered populations by objects of similar nature to that of cold classicals has been instrumental in shaping the vast physical diversity inherent to the Kuiper Belt.
[en] We have analyzed the first 3.75 years of data from the Taiwanese American Occultation Survey (TAOS). TAOS monitors bright stars to search for occultations by Kuiper Belt objects (KBOs). This data set comprises 5 x 105 star hours of multi-telescope photometric data taken at 4 or 5 Hz. No events consistent with KBO occultations were found in this data set. We compute the number of events expected for the Kuiper Belt formation and evolution models of Pan and Sari, Kenyon and Bromley, Benavidez and Campo Bagatin, and Fraser. A comparison with the upper limits we derive from our data constrains the parameter space of these models. This is the first detailed comparison of models of the KBO size distribution with data from an occultation survey. Our results suggest that the KBO population is composed of objects with low internal strength and that planetary migration played a role in the shaping of the size distribution.
[en] The question about possible structure of outer (beyond Neptune) regions of the Solar system is studied within the scope of the new cosmogonical model of formation of planetary systems. It is shown that under certain conditions the evolutionary process in zones of the protoplane ary cloud beyond Neptune may lead to formation of an asteroid belt but not to formation of a planet. The hypothesis is stated that at present unknown asteroid belts exist in this region. Pluto is assumed to be an asteroid of one of these belts. This hypothesis is a development of Cameron's idea (1962) about the possibility of existence of considerable amount of matter immediately beyond the Neptune orbit
[en] Most descriptions of the solar system quite properly emphasize the larger bodies: the Sun, planets and to some extent the satellite systems. However, from some points of view, including that of this course, the smaller bodies which traverse the regions between the planets are of comparable importance. The comets, asteroids and Earth-approaching Apollo-Amor objects are our only surviving relics of the planetesimals which accreted to form the planets. The record of the impacts of these smaller bodies with the planets is provided by the cratered planetary surfaces, and is a principal tool in correlating the geological evolution of these planets. Most of our detailed knowledge concerning conditions in the formative solar system is obtained from petrographic, chemical and isotopic studies of meteorites, which are fragments of some, and possibly all, classes of these smaller bodies. (orig./WL)
[en] In the recent years, the 'Nice' model of solar system formation has attained an unprecedented level of success in reproducing much of the observed orbital architecture of the solar system by evolving the planets to their current locations from a more compact configuration. Within the context of this model, the formation of the classical Kuiper Belt requires a phase during which the ice giants have a high eccentricity. An outstanding question of this model is the initial configuration from which the solar system started out. Recent work has shown that multi-resonant initial conditions can serve as good candidates, as they naturally prevent vigorous type-II migration. In this paper, we use analytical arguments, as well as self-consistent numerical N-body simulations to identify fully resonant initial conditions, whose dynamical evolution is characterized by an eccentric phase of the ice giants, as well as planetary scattering. We find a total of eight such initial conditions. Four of these primordial states are compatible with the canonical 'Nice' model, while the others imply slightly different evolutions. The results presented here should prove useful in further development of a comprehensive model for solar system formation.
[en] We have obtained a full suite of Spitzer observations to characterize the debris disk around HR 8799 and to explore how its properties are related to the recently discovered set of three massive planets orbiting the star. We distinguish three components to the debris system: (1) warm dust (T ∼ 150 K) orbiting within the innermost planet; (2) a broad zone of cold dust (T ∼ 45 K) with a sharp inner edge orbiting just outside the outermost planet and presumably sculpted by it; and (3) a dramatic halo of small grains originating in the cold dust component. The high level of dynamical activity implied by this halo may arise due to enhanced gravitational stirring by the massive planets. The relatively young age of HR 8799 places it in an important early stage of development and may provide some help in understanding the interaction of planets and planetary debris, an important process in the evolution of our own solar system.