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T. Yokoyama, C. Nascimento, M.R. Mana (UNESP)
The current routes of Phobos and Triton which are spiralling in towards their host planets can give rise to interesting discussions. In the case of Phobos, some important resonances between the elements of the satellite and the mean motion of the Sun can occur. In this work, considering the precession of Mars' equator and also the variation of the obliquity we show a possible and interesting case of capture in a 2:1 resonance (longitude of Phobos' node and mean motion of the Sun). In this scenario, Phobos' inclination suffers a large variation, increasing rapidly, from 10 to more than 200. This capture, however, is temporary and our calculations show that escape occurs before any other critical inclination is attained.
For Triton, under certain hypothesis on the tidal model, we obtained a simplified equation that gives the evolution of its inclination in terms of the semi-major axis (Chyba, Jankowski, Nicholson, 1989). Then it is possible to predict the values of Triton's inclination when some mean motion resonances between Triton and Proteus will occur. An analytical expansion of the classical disturbing function for the retrograde case is obtained in order to better understand the problem. The effects of these retrograde resonances are studied and mainly, for first order resonances they become very important since Proteus' eccentricity undergoes large variations. In many cases the final result is an escaping trajectory. Therefore the onset of this instability can become important for the whole Neptunian inner satellites.
This research was funded by FAPESP (98-15867-8, 00-14405-2).
The author(s) of this abstract have provided an email address for comments about the abstract: tadashi@ms.rc.unesp.br