Somewhere along the line we stopped calling Uranus and Neptune “gas giants” and started calling them “ice giants”.
Their surfaces are incredibly cold frozen places with even gasses like Nitrogen wanting to condense.
BUT, they have a hot planetary core. This implies some kind of vulcanism and a layer where the water ice melts to be just water. We know now that life evolved in volcanic mud pots (the mineral ratios in life match that environment) and that chemo-synthetic life exists. So nothing prevents life from evolving inside the wet warm interior of those planets. While it might only be microbial (hard to be a large animal inside rock or mud or ice…) it ought to exist, IMHO.
Because of its great distance from the Sun, Neptune’s outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching 55 K (−218 °C; −361 °F). Temperatures at the planet’s centre are approximately 5,400 K (5,100 °C; 9,300 °F.
Somewhere between 9,300 F molten rock and -361 F frozen air ought to be liquid warm water. Just sayin’…
Uranus has less internal heat, but ought to still have enough at some depth as it does radiate some excess heat:
Uranus’s atmosphere is similar to Jupiter’s and Saturn’s in its primary composition of hydrogen and helium, but it contains more “ices” such as water, ammonia, and methane, along with traces of other hydrocarbons. It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K (−224 °C; −371 °F), and has a complex, layered cloud structure with water thought to make up the lowest clouds and methane the uppermost layer of clouds. The interior of Uranus is mainly composed of ices and rock.
The total power radiated by Uranus in the far infrared (i.e. heat) part of the spectrum is 1.06±0.08 times the solar energy absorbed in its atmosphere. Uranus’s heat flux is only 0.042±0.047 W/m2, which is lower than the internal heat flux of Earth of about 0.075 W/m2.
So not as good a candidate, but still a possible.
I’ve not seen anyone else put forward this idea; OTOH, I’ve not looked very hard ;-)
It’s a fairly obvious set of connections to make, so I’d expect it to be made often.
So crazy talk, or a reasonable thing to expect?