**DPS 2001 meeting, November 2001**

*Session 37. Galilean and Other Outer Planet Satellite Posters*

Displayed, 9:00am Tuesday - 3:00pm Saturday, Highlighted, Friday, November 30, 2001, 9:00-10:30am, French Market Exhibit Hall
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## [37.13] Phobos and Triton at Resonances

*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 1^{0} to more than 20^{0}. 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

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