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IAA Transactions, No. 8, ``Celestial Mechanics'', 2002
Two problems in solar systems dynamics, possible
solutions and future
A. Fienga
IMCCE­Observatoire de Paris, Paris, France
In this contribution, two major aspects of the new challenges of the solar
system dynamics are presented. These two aspects are related to the precision of
observations and the lacks of modelizations in orbit computations.
The first part of this contribution presents the impact on the solar system
dynamics of the zonal and regional errors of astrometric and stellar catalogues
currently used as reference frames by observers and theoreticians. An example of
such impact is given by presenting the new results obtained with the monotoring
of 40 ICRF optical counterparts (Fienga et Andrei [3]). These results show how
the ties between reference frames could be a critical question for accurate celestial
mechanics. This is illustrated with the new orbit of the Saturn satellite, Phoebe
(Fienga et al., [5]). Some perspectives and possible consequences of such surveys
are presented as well.
The second part deals with the analyse of the present limitations of the plane­
tary ephemerides. Some possible solutions and perspectives for the future French
ephemerides are discussed. As it was demonstrated by (Standish and Fienga [4]),
the perturbations of the Mars orbit by the asteroids are difficult to modelize and
they present now the main limitation of the present theory of Mars motion. Dif­
ferent aspects of the results are reminded. However, a more important part of this
presentation is dedicated to the introduction of possible solutions and perspec­
tives. Two ways of solving this problem can be chosen. The first one deals with the
lack of modelization of the asteroid perturbations. As it was firstly introduced by
Plakhov in 1968, computed by Mayo [7], Bange [1] and Krasinsky [6], a possible
model of the mass distribution of the main belt asteroids as a torque can be set
up. This solution gives a more elegant description than the present modelization
but it will not solve completely the major difficulty of this question, i.e. the accu­
rate estimation of the masses of the main asteroids. The second complementary
path for solving the problem of the asteroid perturbations is the accurate mass
determinations. To do so, as it was demonstrated for example by Michalak [8],
Viateau and Rapaport [10] and Bange [2], the close--encounters over a small arc
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of orbit could give a good estimation of asteroid masses. On the other hand, the
present improvements of stellar and astrometric catalogues combined with the use
of very accurate and powerful algorithms of astrometric reduction (Fienga and
Andrei [3]) could garantie a very accurate determination of an arc of asteroid or­
bits. These very accurate orbit determinations would allow to estimate detectable
mutual perturbations. We define a detectable mutual perturbation when the per­
turbation of an asteroid orbit induced by some other asteroid produce variations
in right ascension and declination bigger than 0.1 arcsecond.
In conclusion, a program of asteroid observations prepared by simulations of
mutual perturbations is introduced. This program will gather all the phenomena
which could be observed from the ground before, during and after the GAIA
mission.
References
1. Bange J. PhD Thesis, Observatoire de Paris, 1998a.
2. Bange J. A&A, 340, L1, 1998b.
3. Fienga A., Andrei H. A. A&A., 2002 (in press).
4. Standish E. M., Fienga A. A&A, 2001, 384, 322.
5. Fienga A., Arlot J­E., Baron N., Bec­Borsenberger A., Crochot A.,
Emelyanov N. V., Thuillot W. A&A, 2002 (in press).
6. Krasinsky G. et al. IAA Communications, 2001, No. 139.
7. Mayo A. Cel. Mech. & Dyn. Astron., 1979, 19, 317.
8. Michalak G. A&A, 2001, 374, 703.
9. Plakhov Y. V. Geodesy and Aerophotography. 1968, 1, 38.
10. Viateau B., Rapaport M. A&A, 2001, 370, 602.
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