The modeling of the dynamics of the solar system needs astrometric observations on a large interval of time: to validate the scenarios of evolution of the system and to be able to provide ephemerides extrapolable in the next future.

The Gaia reference star catalogue will allow us to make astrometric reductions of observations with an increased accuracy thanks to new positions of stars. The challenge consists in increasing the astrometric accuracy of the reduction process. More, Gaia will observe solar system objects and we should define which objects will need ground based or space observations in the near future. The Phemu campaign were a valuable source of astrometric data and should be evaluated in the scope of the Gaia accuracy.

Our meeting will be organized in two parts:

-On October 14-15-16, in Meudon observatory, a workshop where we will discuss in small groups about the following questions and try to answer them. Please propose a talk on one of these topics.

- Which objects are still worth to be observed since Gaia will observe most of solar system objects?
- For which objects, ground based observations will be necessary completing space probes data? Which telescopes and targets for next astrometric observations?
- How to increase the astrometric reduction using the Gaia reference catalogue?
- For which past observations should we make a new reduction with the Gaia catalogue?
- How to increase the accuracy of the mu