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: http://star.arm.ac.uk/annrep/annrep2003/node34.html
Дата изменения: Tue May 18 17:48:07 2004 Дата индексирования: Tue Oct 2 05:01:23 2012 Кодировка: Поисковые слова: comet tail |
Mark Bailey has continued to work with Vacheslav Emel'yanenko (South Ural University) and David Asher, and also with Jonathan Horner (University of Oxford) and Wyn Evans (University of Cambridge), to investigate the dynamics of objects with moderate to high-eccentricity orbits in the outer planetary system. The work involves theoretical research on the dynamics of these objects, either Centaurs or Trans-Neptunian Objects (TNOs) over time-scales comparable to the age of the solar system or until they evolve into the Jupiter-family comet system.
The first study (Emel'yanenko et al. 2003) showed that there exist bodies which represent a new population of TNO in the outer solar system, denoted Class O for `outer' TNO. They cannot originate from Centaurs or so-called scattered-disc objects perturbed by close encounters with Neptune because their dynamical lifetime in non-Neptune approaching orbits exceeds the age of the Solar system. Such `outer' orbits are also well separated from those representing the `classical' Edgeworth-Kuiper Belt (EKB), with a gap (considering the objects with perihelion distances q greater than q>38AU) of about 5AU centred at approximately 50AU, i.e. between the semi-major axes of classical Edgeworth-Kuiper belt objects (EKOs) and those of O-types. This work, which shows that the outer objects are predominantly characterized by extremely long dynamical lifetimes under the influence of known planetary perturbations rather than close approaches to Neptune, highlights the importance of understanding the origin of these outer objects. Unless they are affected by hitherto unidentified perturbations their present distribution provides important `fossil' evidence concerning the conditions in the protoplanetary disc since the initial period of planet formation. How the objects in this population were initially formed and placed on their present orbits is thus a key issue for understanding the early history and evolution of the Solar system.
The second study (Horner et al. 2003) introduced a new classification scheme for comet-like bodies in the outer solar system which encompasses the traditional comets as well as the Centaurs and EKOs. The new scheme is based on the observation that, at low inclinations, close encounters with planets often result in near-constant perihelion or aphelion distances, or in perihelion-aphelion interchanges, the minor bodies can be labelled according to the planets predominantly controlling them at perihelion and aphelion. This provides 20 dynamically distinct categories of outer solar system object in the Jovian and trans-Jovian regions, each of which can be further subdivided according to the Tisserand parameter of the orbit with respect to the `controlling' planet. The Tisserand-parameter subdivisions are based on the corresponding values for comets with perihelion distances close to or within the orbit of Jupiter, so the new scheme provides a description for any comet-like body in the solar system. Given the aphelion and perihelion distances, together with the Tisserand parameter with respect to the planet controlling the perihelion, it is straightforward to find the instantaneous dynamical classification of any solar system object according to the new scheme. The usefulness of the system, which extends the existing taxonomy for comets to cover all comet-like bodies in the solar system, was illustrated with examples from numerical simulations and from the present-day solar system.