A viscous liquid, yes. That flows slowly, yes. But on a timescale of tens of millennia all planets are liquid drops.
That's what I'm effectively wondering about.
In a setting, I imagine there's a solar system where there's a world that gets smashed (as planets sometimes do) by some enormous collision. It's probably a glancing collision rather than a cosmic "bullseye."
The reason why this is interesting to 'ordinary spacefarers' as opposed to astrophysicists is that it happened "just yesterday" as far as time is concerned - within the last few thousand years instead of millions of years ago.
My intention is to create a system that is dangerous to simply navigate around in, but is also insanely lucrative. While the intruder body that passed through the system probably has some long-term effects on orbits, that's not going to concern people too much.
What is going to be more interesting is that this collision has exposed and fragmented the core of the planet. Due to the way that heavier materials sink in during planetary formation, this stuff is usually not accessible to humans. However, in this case, the event is recent enough that there's still large chunks (at least in human terms) of elements which are scarce normally that you can exploit of a purity and quantity sufficient to make it worth hauling between solar systems (this setting has FTL travel).
The danger is that where the choicest items are, there's also a lot of debris, some of it quite fast moving. Much of it is eccentric or unstable orbits since the event was soon enough that various natural forces (such as gravity) that clean things up and make them more sane for starships have only begun to work on thinning out the debris.
So I'm mostly curious how a system like this would look.
My (mostly uneducated) guess is that there might be a mostly molten (?) remainder of the world, possibly in a new, skewed (and unstable) orbit, surrounded by a cloud of debris ranging from dust to large pieces, with the cloud gradually thinning out the further from the collision site you go. However, a lot of debris is in weird, eccentric orbits where they won't be a few thousand years.