Editing Planetary core (section)

==== Outer gas and ice giants ====
Current understanding of the outer planets in the solar system, the ice and gas giants, theorizes small cores of rock surrounded by a layer of ice, and in Jupiter and Saturn models suggest a large region of liquid metallic hydrogen and helium.<ref name="de pater 2015" /> The properties of these metallic hydrogen layers is a major area of contention because it is difficult to produce in laboratory settings, due to the high pressures needed.<ref>{{Cite journal|last=Castelvecchi|first=Davide|date=2017-01-26|title=Physicists doubt bold report of metallic hydrogen|journal=Nature|volume=542|issue=7639|pages=17|doi=10.1038/nature.2017.21379|pmid=28150796|issn=0028-0836|bibcode=2017Natur.542...17C|doi-access=free}}</ref> Jupiter and Saturn appear to release a lot more energy than they should be radiating just from the sun, which is attributed to heat released by the hydrogen and helium layer. Uranus does not appear to have a significant heat source, but Neptune has a heat source that is attributed to a “hot” formation.<ref name="de pater 2015" />