The 7th and 8th planets have iron cores.

The biggest assumption made today about the outer most planets is that they are frozen hydrogen/helium/ methane planets without a core.

I dispute that assumption simply because there are a great number of small iron/nickel core planets further out in a belt. It would be a terrible assumption that none of these asteroid sized planets did not get pulled down to the gravity center of Uranus and Neptune in the past.

Uranus apparently has a cold core. Neptune has a hot core of about 7-8K F. degrees. Neptune also has huge winds in the mantle atmosphere of the planet. That is a lot of energy.

I think Uranus may also have such a hot core but it is hidden by the thick atmosphere. Neptune possibly has a much larger iron core at a distance that one would assume would create a very cold planet. Unless a series of asteroids collided with said planet in the past creating a heavier core than assumed. Such a core is quite likely to be about the size of Earth and the gravity is approximately 1.19 that of Earth. Give or take.

The reason Uranus should be hotter than it is would be that it sits on its side. That directly conflicts with the magnetic field of the Sun creating and generating a lot of electricity in huge electrical storms above the surface. But what if Uranus is a shell? What if it is heated internally inside an icy shell with an internal ocean beneath the shell kept hot by a hot core? Probably not.

But Neptune does have a hot core. There has to be a zone that is warm enough for life.