[fc417fc802]

Is it Jupiter that's unusually dense or this planet that's unusually light? Related, any idea what the feasible range of densities is for a planet of a given size? I always assumed something as large as Jupiter would be impossible for a human to set foot on due to being crushed.

A ball of foamed rock the size of a planet is an amusing thought but I have to assume that's physically impossible.

[Tuna-Fish]

Jupiter is a gas giant. It's near the threshold where adding more mass to it makes it smaller, not larger, as the added gravitational pull would make it denser.

But what would make it larger is if it was warmer. The radius of a planet like jupiter scales to the 1.6th power of it's temperature. Jupiter is actually slowly shrinking in size as the primordial heat of its formation is radiated away.

[exe34]

Jupiter has no surface to set foot on, unless you count the hypothetical earth size rock inside all the gas. What would happen is that you would sink and get crushed long before you got to the rock.

[fc417fc802]

Pedantry. (Well I suppose it's at least a valid point that without a solid surface there probably isn't anything for a human to want to bother visiting in the first place.)

This one presumably doesn't have a surface either, yet an earlier commenter spoke of surface gravity. Doesn't it surprise you in the slightest that two planets of the same size could have gravity that differs by such a wide margin?

[exe34]

I worked in the area a long time ago, so as it happens, no, but I can see how it's unintuitive!

Surface gravity in this case would be the visible radius - the same way we talk about the surface gravity of the sun, and mean the photosphere.