Le séminaire a lieu le lundi
13 mai 2002 de 14h30 à 15h30
dans la salle de réunion
du PHC (Observatoire de Nice).
The outer Uranian moons:
New insights in the scenario
of the formation
of the giant planets.
The stochastic processes at the end of the formation of the
planets have been long known (Safronov 1969, Lissauer and Safronov
1991, Harris and Ward 1982). The large spin obliquity of Uranus
(98) is usually attributed to a great tangential collision
with another protoplanet at the end of the accretion process
(Korycansky et al. 1990, Parisi and Brunini 1996, Parisi and
Brunini 1997). If Uranus had had satellites before this event, the
impulse imparted at collision would have produced a shift in the
orbital velocity of the satellites. Outer satellites of Uranus had
been probably unbound (Parisi and Brunini 1996, Parisi and Brunini
1997). The discovery of the outer Uranian satellites (Gladman et al. 1998,2000) sets important constraints in this scenario.
Physical conditions and dynamical constraints in the great collision
scenario and restrictions in the possible mechanisms for the origin of
the outer Uranian satellites are obtained from the knowledge of their
actual orbital properties (Brunini et al. 2002). We conclude that
the existence of these moons implies that their origin must be
connected to a break-up process. Other scenarios for the origin of
them, cast doubts about the occurence of a giant collision at the end
of Uranus' formation process to account for its large spin axis
obliquity. Other mechanisms to account for the large spin axis
inclination of this planet should be investigated.
Brunini A., Parisi M. G. and Tancredi G. 2002.
Constraints to Uranus'
great collision III: The origin of the outer
satellites. Icarus accepted.
Gladman B. J., Nicholson P.D., Burns J.A. , Kavelaars
J.J.,
Marsen B.J., Williams G.V. and Offutt W.B. 1998.
Discovery of two distant irregular moons of Uranus.
Nature 392, p:897-899.
Gladman B.J., Kavelaars J.J., Holman M., Petit
J-M,
Scholl H., Nicholson P.D. and Burns J.A. 2000.
The discovery of
Uranus XIX, XX and XXI. Icarus 147, p: 320-324;
erratum 148, p:320 (2000).
Harris A. W. and Ward W.R. 1982. Dynamical constraints
on the formation
and evolution of planetary bodies. Annu. Rev.
Earth Planet. Sci. 10,
p: 61-108.
Lissauer J. J. and Safronov V. S. 1991. The random
component of planetary
rotation. Icarus 93, p:288-297.
Korycansky D. G., Bodenheimer P., Cassen P. and
Pollak J. B. 1990.
One-dimensional calculations of a large impact
on Uranus,
Icarus 84, p:52-541.
Parisi M. G. and Brunini A. 1996. Dynamical consequences
of Uranus'
great collision. In Chaos in Gravitational N-body
systems
(J.C. Muzzio, S. Ferraz-Mello and J. Henrard,
Eds.), p:291-296
Kluwer Academic Publishers.
Parisi M. G. and Brunini A. 1997. Constraints
to Uranus' great Collision II.
Planetary and Space Science 45, p:181-187.
Safronov V. S. 1969. Evolution of the Protoplanetary
Cloud and Formation
of The Earth and the Planets. NASA TTF-677.