Letters of Intent received in 2016

LoI 2018-1940
New challenges in our Solar System ephemerides

Topics

Ephemerides, solar system dynamics, relativity, chaos, exotic perturbations. Extreme accuracy measurements: asteroid and planetary radar, space-borne astrometry, pulsar timing. Improvements in ephmerides for planets, satellites, asteroids, trans-neptunians, extrasolar planets.

Rationale

The progress in understanding the dynamics of the orbits of celestial
bodies in our solar system and in the accuracy in the predictions of
the future state, that is of the ephemerides, has been huge. This is
due to both improved theoretical understanding and progress in
measurement accuracy. The distinction between high accuracy
ephemerides, required for some bodies (including Earth and other
planets visited by space probes) and lower accuracy ephemerides for
minor bodies, such as asteroids and natural satellited, has become
less significant, since all bodies perturb each other and relative
positions are important in some circumstances, such as close
approaches.

Part of the recent advances have been obtained through technological
developments for dedicated observation programs, data center and data
dissemination, statistical, data analysis. Other through high quality
spaces missions data, and new catalogues for astrometric references or
data reduction. This progress shall continue, but we cannot be limited
by a "normal science" mode, as if there were no conceptual
difficulties and it is only the matter of accumulating more and better
data.

The progress in accuracy has lead the state of the art to a frontier
where fundamental limitations are reached; there are many of
these. First, the dynamical problem being non-integrable, chaos is
everywhere in the phase space of our solar system, although it may be
more apparent in some regions than in others; chaos is by itself a
fundamental limitation to accuracy of any prediction, and one big
subject is how to cope with this and still maintain the capability of
some prediction, possibly in a probabilistic framework.

Second, in the past the relativistic corrections were needed for the
top quality ephemerides of the few main bodies, while asteroids,
comets, satellites were hadled with either Newtonian or partially
relativistic models. Now, with the advent, e.g., of asteroid radar
astrometry and space-borne optical astrometry, a full relativistic
framework is compulsory for every category of orbits: the question is not anymore whether relativity is relevant for the ephemerides, but whether the ephemerides are relevant for relativity, that is whether the best determined orbits (of both natural and artificial bodies) are confirming, or rather challenging, the theory of Einstein.

Third, exotic physical effects are now to be considered as part of the dynamical model: e.g., non-gravitational perturbations become relevant for accurate predictions (in the future and in the past) of the orbits of bodies of several km diameter, not just for artificial satellites.

We need a single forum in which to discuss all of these problems and fundamental limitations, not just to marginally further improve the accuracies, but to transform the limitations into opportunities. Can chaos, relativity, exotic perturbations, reference systems difficult\ to be defined, and many other technical issues become the focus of innovative research in Celestial Mechanics, Astrometry, Radioscience, Physiscs of small bodies, and in the long term dynamics of the Solar System? On which key problems should we concentrate our efforts?

This Symposium will focus on the astrometry, dynamics, celestial
mechanics, and ephemerides of solar system bodies under development, based on various observations facilities, ancient as well future one. A particular point will be made with the advent of GAIA catalogues, ICRF, and new ground-and-space surveys.