Gaseous core
It has long been hypothesised that the composition of the atmosphere has been modified by processes in the interior of the planets. Now, some researchers have done simulations for the atmosphere of Neptune and reported that some of the gases in its atmosphere are originating from deep within the planet. Jupiter, Saturn, Uranus and Neptune have atmospheres which are somewhat like the Sun in composition, that is, the atmospheres have a preponderance of hydrogen and helium. The only difference is that the atmospheres in these planets have molecules of these gases and not atoms like the Sun.