TITLE:
Assesment of different formation scenarios and dynamics of
the ring system of (10199) Chariklo
AUTHOR:
Mario Daniel Melita
Instituto de Astronomia y Fisica del Espacio (CONICET-UBA). CABA. Argentina
melita@iafe.uba.ar
ABSTRACT:
The discovery of ring systems around objects of the outer Solar System
provide a strong motivation to apply theoretical models in order to
estimate better their physical and orbital properties, and to
investigate the scenarios about their origin.
We first consider the possibility that the material of the ring is
originated by the disgregation of a satellite that reaches a distance
in which the tidal field of the asteroid is capable of disrupting a
satellite object. We discuss the conditions such that the putative
satellite approaches the asteroid as a consequence of the tidal
interaction. A 3-body encounter is also considered as a transport
mechanism. Then, we study the case in which the ring is formed by the
ejecta of a craterizing collision on the asteroid and we constraint
the parameters of plausible collisions for the event. Finally, we
consider that the ring material originates form a catastrophic
collision between a background object and a satellite of the asteroid,
located at a mean distance corresponding to the present-day location
of the ring. We compute the typical timescales for these scenarios.
We estimate that to be tidally disgregated, a satellite must be larger
than 6.5 km approximatelly at the location of the rings. The mechanism
by which the satellite approaches the asteroid was most probably not
tidal. Collisonal scenarios are both physically plausible, but
semi-analitical estimations indicate that the probability of the
corresponding collisions is vey low.
In order to evaluate if the ring can be eccentric, we review the
condition of apse-alinement across the ring and the balance between
the energy rate provided by the satellite and the internal
dissipation, as derived from the variational equations of motion of
the Lagrangian-displacements of the ring-particle orbits. We use the
case of the epsilon-ring of Uranus, to validate our derivations and
illustrate the basic dynamical principles of these type of rings.
When the balance conditions that we predict are applied to the ring
system of (10199) Chariklo, we are able to calculate the necessary
mass of the shepherd satellites to prevent the eccentricity decay, as
a function of its orbital location, for two different models of
dissipation. We conclude that the satellite mass necessary to maintain
the m=1 eccentric mode in the ring, would be similar or smaller than
the one needed to contain the rings radially.
Our estimation of the most plausible combinations of eccentricity,
eccentricity gradient and surface density are based in a a standard
model for the surface radial density distribution, which roughly
agrees with the optical depth profile derived by the stellar
occultations. The results are critically dependent on the value of the
form factor of the second degree harmonic of the gravitational
potential of the Centaur, J_2. We conclude that for some of its
remarkably large presently estimated values, the rings would have to
be un-realistically dense to compensate the differential precession
induced by the oblateness of the (10199) Chariklo.