The reality is we dont really know. The "surface" in this article is where the pressure is largely 1 atm. And at that pressure its mostly liquid (albeit hot)

[–] shadowspirit@lemmy.world 3 points 1 year ago* (last edited 1 year ago) (1 children)

That's a good question that hopefully someone more learned will be able to respond to but you know most of the Earth's surface is water so I suppose Neptune has a surface. I don't know what the technical definition is but I'm assuming it's where particulate / molecules in the atmosphere change states due to temperature and pressure. A bit like how we have H2O in the form of gas as water vapor in the atmosphere and at the surface a liquid as water. The closer you are to the center of the planet the higher the pressure and the temperature.

[–] octoperson@sh.itjust.works 3 points 1 year ago

If the pressure is high enough, you can get a smooth transition between gas and liquid without any sort of boundary that you could identify as a surface. That's thought to be what happens on Jupiter, don't know about Neptune