May 8-9, 2011 response
ALL planets, yes, I do mean ALL, the planets in our Solar System have iron/nickel/sulfur cores. Before you scream at me, that I am insane and not a scientist, please take these FACTS into consideration:
1) Balls of gas CANNOT physically "hang around' for billions of years without being dissipated by the solar wind if there is no solid/liquid core to provide enough mass to create a gravity well that can retain the gas.
2) ALL the Jovian planets have planetary magnetic fields with dipole moments stronger than Earth's and high rotation rates, which confirms that they have iron/nickel/sulfur cores. Sulfur decreases the the temperature at which the iron/nickel alloy melts, but at high pressures, even iron and nickel will become solid.
3) It is physically and chemically impossible for hydrogen to sink to form a metallic and liquid core of Jovian planet. Hydrogen has the lowest specific gravity (NOT DENSITY) of any element on the periodic table. Hydrogen cannot be at the center of a planet because iron and nickel, which becomes iron pretty rapidly (short half life for the unstable isotopes of nickel), settle to form the core first followed by Fe/Mg and Si/Al along with heavier elements to form the mantles of all planets with enough mass to be spherical.
4) A reasonably high rotation rate and a liquid iron/nickel outer core is required to create and maintain the electric fields and magnetic dynamo of a planetary magnetic field.
5)Liquid and metallic hydrogen LAYERS probably DO form around the iron/nickel cores of Jupiter and MAYBE Saturn, but liquid and metallic hydrogen have electron degeneracy, creating only small scale brief electric currents which do not contribute much to the planetary magnetic field.
6) If a planet has a small mass, there may be insufficient mass in the mantle and crust to keep the outer and inner cores hot enough to NOT crystallize fractionally over long periods of time. If it turns out that Pluto has a global magnetic field, it probably will be a remnant magnetic field for the whole planet, or it may be like Mars, which has regional magnetic fields that very likely come from large iron/nickel asteroids that impacted Mars and went deep into the mantle before their interiors reached the Curie point temperature, melting and causing a loss of magnetism.