I have a question for those who like to think scientifically. What do you think would happen to a world that has double in mass. How deep do you think the mechanic should go in development of a fictional story?
Not sure what your question is, but a world with double mass would have a diameter of 1.25992 [2^(1/3)] times the radius or diameter of the original.
I assume that you mention double the mass because you want higher gravity? I don't know, but my thoughts are as follows: - There would be a thicker, soupier atmosphere with fiercer weather. A moon like ours would be further away and have less impact upon tidal patterns. It would also have less of a stabilising factor meaning wilder fluctuations in long term climate (as the planet would essentially rock on its axis). The planets surface would be flatter, because higher land would erode more quickly. The transition from the buoyancy provided by water to a higher level of land gravity would make this evolutionary leap less likely. Any plant and animal life would be more squat and sturdier. Birds or other flying creatures would be less likely. Air travel would be unlikely. Escaping the planet's atmosphere would be a vastly harder task, and probably would not happen until life has developed beyond our current technology. They are my initial thoughts.
It's important to distinguish between gravity, and surface gravity. A planet with twice as much mass would have twice as much gravitational pull. But if it also doubled in diameter (ie its density remains constant), its surface gravity would be the same. So if you're standing on the surface you might not feel any different, but that moon orbiting around it might suddenly get pulled into a collision.
If the planet doubled in diameter it would have eight times the mass. Consider the mass of the planet to be a point in the center of the sphere. Neglecting the gravitational constant, the ratio of gravitational force in the two systems would be ((8m1 m2)/((2r)^2))/((m1 m2)/r^2) = 2 So the surface force would be twice as great at twice the diameter and same density. (Unless I'm missing something.)
It would all depend on whether the planet's diameter "swelled" in size as the mass increased or remained constant. And the Earth and moon orbit their common center of gravity/mass, so that would be affected too and screw the tides up in some fashion, though I have no idea how much.
I quote the post I responded to: "twice the diameter and same density". Of course this planet would probably collapse down to a smaller diameter in reality.
You're right. My bad. My point was just that we can't know how it would affect surface gravity without also knowing the diameter and/or density. Neither of which were provided in the OP, so it's hard to answer the question without speculating.
Seems to me this is where the OP was going: Short answer, any life on the planet would likely be fucked since there's no way for a planet to gain mass (let alone double) without some form of accretion. Unless there's some "magic" at work, in which case the physics are irrelevant.
The diameter would remain the same. Basically, what I'm looking at is what would happen if our planet was merged with another planet from another dimension; hense a sudden doubling of mass. While I am aware that everything would go all funky monkey, not making it so drastic that the planet would explode but would not be able to maintain in the long term. Would be kinda a short story if the planet blew up immediately.
If you suddenly packed twice the mass into the same volume as the earth? Well the earth is at an energy equilibrium. The downward pull of gravity is balanced by the electromagnetic forces and heat between atoms. If you suddenly double the density, the temperature would go through the roof. The planet would essentially explode. Of course, gravity would prevent an outward explosion. It's probably swell and bounce a few times before setting into a ball of liquid. Gravity does not appear to have much affect on atmosphere thickness. There are other factors that are orders of magnitudes more impactful. Also, to be clear, in a denser atmosphere, flight would be easier, not harder. The atmosphere is an ocean of air. In an ocean of water, most creatures "fly." The atmosphere of Venus is so thick that the soviet unions lander didn't even need a parachute. The 2500 pound mostly spherical object basically sunk to the surface, even a small amount of lift would have made it neutrally boyant.
The above answers strike me as correct, and I especially like newjerseyrunner's.Have you considered dark matter as a way around the problems? Dark matter does not interact with normal matter, and has never been directly detected or studied except via the effects of it's gravity. So it could be almost anything, with whatever properties you need, and a dark matter 'planet' could occupy the same space as ours without interacting with it in any way except gravitationally. The various huge holes, physics wise, can be papered over because you can attribute any properties you wish to dark matter in your fictional universe, as long as they are self consistent - not a scientifically perfect solution, but you are writing a story not a physics paper after all...
Yeah I agree with it as well and a dark planet wouldn't work because (Without giving too much plot away) Basically, our world is merged with another from a different dimension. aka: everyone on earth are now face to face with the person they would have been if they had made a different choice somewhere in there life. I've been thinking about how to get around the planet blowing up within the hour, (would make for a very short story if that happened.) So what I'm thinking is just having the event pull the people from that dimension to ours first and then their existence here would create kinda of a magnet effect in which unless they are all returned their planet will start to merge with ours.
I basically agree with what newjerseyrunner said. As an additional thought: I would have to check the maths , but if the earth gained enough mass it would-among other things- fuck up its orbit. In fact, it is currently believed that the moon was created when a protoplanet gained so much mass through accretion it wasn't able to mantain a stable orbit anymore and crashed with baby earth.
