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T. Guillot (Observatoire de la C\^ote d'Azur)
New constraints on the composition and structure of Jupiter and Saturn will be derived using all available observations and including uncertainties on required physical data (equation of state, opacities...). A first result is that interior models of Jupiter and Saturn do not necessarily require the presence of a dense central core to fit their gravitational potential. The maximum mass of this core appears to be 12 M\oplus for Jupiter and 15 M\oplus for Saturn. The total amount of elements other than hydrogen and helium is between 11 and 45 M\oplus in Jupiter, and between 20 and 30 M\oplus in Saturn.
It is essential that these uncertainties be reduced in order to properly understand the formation of giant planets in general. In order to do so, a more accurate equation of state of hydrogen at high density needs to be calculated. I will show that some solutions can be eliminated (therefore providing better constraints) using {\it evolution} models. However, this heavily depends on physical assumptions on the mecanisms that lead to helium depletion in the external regions of these planets.