Sounds like a gas giant that got its atmosphere ripped off from some nearby catastrophe. Like a massive gamma ray burst from a supermassive, or maybe a hungry neutron star just strolling thru the neighborhood. Or it could be the end results of a 2nd generation vampiric double star system that formed after a supernova, hence all the heavy metals. Perhaps coalescing back into a smaller star and a hot Jupiter/brown dwarf.