How many earth-sized worlds can fit in the habitable zone?

Question

I am imagining a scenario where the planets, not just Mars and Venus, but Uranus Saturn and Neptune, have been terraformed, the latter three by stripping away their atmospheres to leave the terrestrial earth-sized cores. (Jupiter was not terraformed for reasons I will not bore you with here). Could these three additional planets be moved into sol’s habitable zone without drastically influencing the orbits of the other terrestrial planets?

Answer 1

The problem you're trying to solve by moving planets was already solved in the process of getting to this point.

Gravitational binding energy of Saturn would be roughly: $\frac{6GM^2}{7R}$ for mass M, radius R, gravitational constant G.

Inputting the appropriate values for Saturn, you just did order of $10^{35} J$ of work to eject most of Saturn's mass to a very distant orbit. Earth receives order of $10^{24} J$ of work from the sun annually. If it took you much less than a hundred billion years per planet to eject the unwanted mass, you already have a mechanism for delivering far more energy to the planet annually than Earth receives from the sun.

You also probably have no particular use for planets if you can do such things. Just live on a proper ringworld or Dyson swarm like a civilized human being, not a primitive planet like some tree-swinging ape.

Answer 2

Perpendicular Orbits

The planets naturally orbit in the same plane (left) Any arrangement will settle into a plane given enough time. But those timescales are too long for us puny humans to worry about.

So we should make the planets so they orbit perpendicular to each other. Or at least as perpendicular as we can manage while having five or six of them. Then offset the orbits an hour so the planets have different length days.

The advantage here is that on average some of the influence of the planets on each other will cancel. For example the pink planet will sometimes pull the red planet upwards (relative to the red circle) and sometimes downwards. On average these effects cancel.

This is a chaotic system. So you still need to nudge the planets every few millennia if something goes awry. But that is nothing next to the effort required to realign them in the first place.

Answer 3

If you can terraform Saturn, Uranus, and Neptune by removing most of tteir mass and and using up a tremenous about of energy doing, so, why move them to the inner solar system to keep them warm?

Why not build artifical satellites which circle those worlds and use giant fusion generatiors to generate energy to power giant lamps, pointed at the planet, to light it? And why not have giant fusion power generators on the planet to power giant heaters which warm up the planet?

That should take a tiny fraction of the energy needed to move planets.

Or why not cover the entire surfaces of those planets with giant multistory buildings so that they are essentially planet-wide indoor cities, with artifically powered light and heat?

I note that the surface gravity of Saturn is 1.065 g, of Uranus is 0.886 g, and of Neptune is 1.137 g. Those should be bearable for human colnists.

But those planets don't have solid surfaces. The surface gavities are calculated for the opaque cloud layers at the tops of their massive atmospheres. If you take away the atmospheres the rocky cores of these planets should still be several times as massive as Earth, and they should have much higher surface gravities.

So have you calculated the surface gravities of the cores of the planets once their atmosphers are removed? Will the surface graavity be survivable for humans? Or will there be massive suse of anti gravity technology?