I found this super interesting as the reason they think it lost its atmosphere is that "left over heat from the planets formation seeps out from its interior and into its thick gaseous layer, heating it so that it escape more easily" and this is called core-powered mass loss.

If it had been solar radiation loss there would have been no water or atmosphere yet it still has some. Kinda wild to think about especially since Neptune is so hot and that isnt even hot enough to cause loss.