  The determination of Saturn's atmospheric noble gas abundances are critical
to understanding the formation and evolution of Saturn, and giant planets in
general. These measurements can only be performed with an entry probe. A Saturn
probe will address whether enhancement in heavy noble gases, as was found in
Jupiter, are a general feature of giant planets, and their ratios will be a
powerful constraint on how they form. The helium abundance will show the extent
to which helium has phase separated from hydrogen in the planet's deep
interior. Jupiter's striking neon depletion may also be tied to its helium
depletion, and must be confirmed or refuted in Saturn. Together with Jupiter's
measured atmospheric helium abundance, a consistent evolutionary theory for
both planets, including "helium rain" will be possible. We will then be able to
calibrate the theory of the evolution of all giant planets, including
exoplanets. In addition, high pressure H/He mixtures under giant planet
conditions are an important area of condensed matter physics that are beyond
the realm of experiment.
