  We present large scale electronic structure based molecular dynamics
simulations of liquid methane at planetary conditions. In particular, we
address the controversy of whether or not the interior of Uranus and Neptune
consists of diamond. In our simulations we find no evidence for the formation
of diamond, but rather sp2-bonded polymeric carbon. Furthermore, we predict
that at high tem- perature hydrogen may exist in its monoatomic and metallic
state. The implications of our finding for the planetary models of Uranus and
Neptune are in detail discussed.
