3 ms·

A larger planet doesn't necessarily equal higher gravity at the surface.

taskforcegemini 4y ago
maybe not necessarily, but anything else is probably not very likely
dreamcompiler 4y ago
Sure. An extremely advanced civilization could hollow it out and make a "Dyson planet" -- or just build a shell from scratch -- but it ain't gonna form through natural processes. I suppose somewhere in the universe there could be a dust cloud of pure lithium that eventually coalesces into a planet, but that seems extremely unlikely. (Interesting premise for a SF story though.)
- midoridensha 4y ago
  >An extremely advanced civilization could hollow it out and make a "Dyson planet" -- or just build a shell from scratch Wouldn't this be impossible because of the planet's molten core? Or am I just biased because our planet has a molten core and I'm assuming it's necessary for a life-bearing planet, or at least unavoidable for any planet where its host star hasn't burned out from old age? Finally, even if you could remove the molten (or solid) core of a planet, wouldn't the shell collapse due to gravity and other forces? It seems to me that all these planetary engineering ideas really don't make that much sense. If you have such advanced technology that you can do these things, wouldn't it be faster and easier to build an O'neill cylinder and get exactly the environmental conditions you desire?
  - dreamcompiler 4y ago
    I can't really imagine how hollowing out a planet could work, but I suppose if you figured out a way to do it you could replace the iron core with superheated water or something similarly less dense than iron. That's why I also suggested just building a shell from scratch. It would effectively be a very tiny Dyson sphere.
bee_rider 4y ago
The gravitational acceleration at the surface is proportional to M/r^2 (where M is the mass and r is radius), and the mass should be proportional to r^3 assuming (big assumption here, but still) the density is constant. IMO, it is pretty notable that the acceleration at the surface is only linearly proportional the the radius for a constant density, I'd expect something much worse. Of course we can play with the density but chemistry is, like, way harder than physics.

maybe not necessarily, but anything else is probably not very likely

Sure. An extremely advanced civilization could hollow it out and make a "Dyson planet" -- or just build a shell from scratch -- but it ain't gonna form through natural processes. I suppose somewhere in the universe there could be a dust cloud of pure lithium that eventually coalesces into a planet, but that seems extremely unlikely. (Interesting premise for a SF story though.)

midoridensha 4y ago
>An extremely advanced civilization could hollow it out and make a "Dyson planet" -- or just build a shell from scratch Wouldn't this be impossible because of the planet's molten core? Or am I just biased because our planet has a molten core and I'm assuming it's necessary for a life-bearing planet, or at least unavoidable for any planet where its host star hasn't burned out from old age? Finally, even if you could remove the molten (or solid) core of a planet, wouldn't the shell collapse due to gravity and other forces? It seems to me that all these planetary engineering ideas really don't make that much sense. If you have such advanced technology that you can do these things, wouldn't it be faster and easier to build an O'neill cylinder and get exactly the environmental conditions you desire?
- dreamcompiler 4y ago
  I can't really imagine how hollowing out a planet could work, but I suppose if you figured out a way to do it you could replace the iron core with superheated water or something similarly less dense than iron. That's why I also suggested just building a shell from scratch. It would effectively be a very tiny Dyson sphere.

bee_rider 4y ago

The gravitational acceleration at the surface is proportional to M/r^2 (where M is the mass and r is radius), and the mass should be proportional to r^3 assuming (big assumption here, but still) the density is constant. IMO, it is pretty notable that the acceleration at the surface is only linearly proportional the the radius for a constant density, I'd expect something much worse. Of course we can play with the density but chemistry is, like, way harder than physics.