【死在火星上】小说免费阅读，请收藏 全本免费小说【qbmfxs.com】
tudies and aims of this research
In addition to the vagueness of the concept of stability， the planets in our Solar system show a character typical of dynamical chaos (Sussman & Wisdom 1988， 1992). The cause of this chaotic behaviour is now partly understood as being a result of resonance overlapping (Murray & Holman 1999; Lecar， Franklin & Holman 2001). However， it would require integrating over an ensemble of planetary systems including all nine planets for a period covering several 10 Gyr to thoroughly understand the long-term evolution of planetary orbits， since chaotic dynamical systems are characterized by their strong dependence on initial conditions.
From that point of view， many of the previous long-term numerical integrations included only the outer five planets (Sussman & Wisdom 1988; Kinoshita & Nakai 1996). This is because the orbital periods of the outer planets are so much longer than those of the inner four planets that it is much easier to follow the system for a given integration period. At present， the longest numerical integrations published in journals are those of Duncan & Lissauer (1998). Although their main target was the effect of post-main-sequence solar mass loss on the stability of planetary orbits， they performed many integrations covering up to ∼1011 yr of the orbital motions of the four jovian planets. The initial orbital elements and masses of planets are the same as those of our Solar system in Duncan & Lissauer's paper， but they decrease the mass of the Sun gradually in their numerical experiments. This is because they consider the effect of post-main-sequence solar mass loss in the paper. Consequently， they found that the crossing time-scale of planetary orbits， which can be a typical indicator of the instability time-scale， is quite sensitive to the rate of mass decrease of the Sun. When the mass of the Sun is close to its present value， the jovian planets remain stable over 1010 yr， or perhaps longer. Duncan & Lissauer also performed four similar experiments on the orbital motion of seven planets (Venus to Neptune)， which cover a span of ∼109 yr. Their experiments on the seven planets are not yet comprehensive， but it seems that the terrestrial planets also remain stable during the integration period， maintaining almost regular oscillations.
本章未完，点击[下一页]继续阅读-->