  The Saturn System has been studied in detail by the Cassini-Huygens Mission.
A major thrust of those investigations has been to understand how Saturn formed
and evolved and to place Saturn in the context of other gas giants and
planetary systems in general. Two models have been proposed for the formation
of the giant planets,the core accretion model and the disk instability model.
The heavy element enrichment, core size, and internal structure of Saturn,
compared to Jupiter strongly favor the core accretion model as for Jupiter. Two
features of the core accretion model that are distinct from the disk
instability model are the growth of a core with a mass several times that of
the Earth, followed by runaway collapse of gas onto the core once a mass
threshold is reached. The heavy element core grows slowly over millions of
years through accretion of cm-m sized pebbles, even larger bodies, and moon
sized embryos in the gaseous disk. The abundance pattern of heavy elements is
thus a key constraint on formation models. C, N, S, and P at Saturn are
presently known to varying degree of uncertainty. The He to H ratio in the
atmosphere is crucial for understanding heat balance, interior processes, and
planetary evolution, but present values at Saturn range from low to high,
allowing for a wide range of possibilities. While the very low values are
favored to explain excess luminosity, high values might indicate presence of
layered convection in the interior, resulting in slow cooling. Additional
insight into Saturn's formation comes from the unique data on the rings from
Cassini's Grand Finale orbits. While the solar system is the only analog for
the extra solar systems, detection of the alkali metals and water in giant
exoplanets is useful for understanding the formation and evolution of Saturn,
where such data are presently lacking.
