Past exam of the short options paper shared by Prelims and Parts A and B of the physics course of the University of Oxford / 2016 / S29 / 3 / 5 / Solution

Helium becoming partially immiscible in dense hydrogen can form helium-rich droplets that settle inward. Gravitational energy release and associated thermal evolution can supply extra luminosity, while the upper hydrogen envelope becomes helium depleted. Different interior temperature-pressure histories can make separation stronger in Saturn than in Jupiter.

The source's ratio is reversed for this intended explanation. Depleting helium lowers He/H and raises H/He. For a concrete example, keeping ten hydrogen units while reducing one helium unit to one half changes H/He from ten to twenty, not to a lower value. Thus the literal statement that Saturn has lower H/He cannot simultaneously be used as evidence for the stated upper-envelope helium-depletion mechanism. If the intended comparison is lower He/H, the observations and extra heat are mutually consistent with helium rain. Composition measurements and interior modeling are still needed; excess heat alone does not uniquely prove that process.^[ref]