If there’s one true fact about every single gas giant planet ever observed, around the Sun or other stars in the Galaxy, it’s that they all are mainly composed of Hydrogen.  Even though the giants of our solar system such as Neptune and Jupiter seem very different, it is Hydrogen that primarily composes them.  The difference is in the details though.  The blue colour of Neptune is due to the presence of Methane, and even then it only makes up 1.7% of Neptune’s mass. But Hydrogen is light.  Wouldn’t giant planets like hot Jupiters lose their Hydrogen from being blasted...