I just want to know, hypothetically, what if Jupiter was solid and condensed to the size of Earth. What would it look like? Would it's characteristics (gravity, orbit, rotation, etc) stay the same, or would it adopt new ones? could we maybe even go there?
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2$\begingroup$ Can you edit your question to show some relevance to real-world space exploration? $\endgroup$– Organic MarbleCommented May 7, 2020 at 23:43
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$\begingroup$ The problem with hypotheticals like this is that we typically have to know exactly how you made this change to understand the makeup of the planet and any changes to things like angular momentum. However, you may have decent luck with the (WorldBuilding)[worldbuilding.stackexchange.com] community. They often deal with questions like this. $\endgroup$– Cort AmmonCommented May 8, 2020 at 0:11
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$\begingroup$ @CortAmmon until it breaks up we can assume that angular momentum won't change, but it looks like it would break up. $\endgroup$– uhohCommented May 8, 2020 at 0:46
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1$\begingroup$ Jupiter in fact has a liquid metallic core detected by the Juno probe. It has about the size of Earth and 5-15 times its mass. So if all of Jupiter's gas went away the liquid core would remain as an ocean planet. An ocean of liquid metal and the remnant core having a surface gravity of 5-15 g. The Galilean moons would get ejected into a solar orbit. $\endgroup$– user35272Commented May 8, 2020 at 8:45
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1$\begingroup$ @DaveGremlin Yes, the NS (and white dwarves) can be so small because it is so massive, and the gravity compresses it into degenerate matter. But the Jupiter is not enough massive for that. My comment asks, how exactly the OP thinks this "condensation". $\endgroup$– peterhCommented May 8, 2020 at 9:05
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1 Answer
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I know I shouldn't answer such an unrealistic hypothetical question but here goes...
What would happen if Jupiter became solid like Earth and condensed to the size of Earth?
Well at these densities the transition from gas at the edge to whatever you'd call it at the center of Jupiter is a bit complicated, there aren't distinct gas/liquid and liquid/solid boundaries.
So really Jupiter could not ever be "solid like Earth" and simultaneously "condensed to the size of earth".
...if Jupiter was... the size of earth... would... it's... gravity, orbit, rotation... stay the same, or would it adopt new ones?
Surface gravity is given by $GM/R^2$. With $GM=\text{1.266} \times 10^{17} \text{m}^3/\text{s}^2$ and $R=\text{6.378} \times 10^{6} \text{m}$ it would be 3112 m/s^2 or about 317 times Earth's surface gravity
Its orbit around the Sun would not change much at all; as far as the Sun is concerned it's already essentially a point mass.
Its rotation would certainly speed up! I thought this might come in to relevance some day; Jupiter's angular momentum is about $4.30\times 10^{38}$ kg m$^2$ s$^{-1}$. If we changed the shape of the density profile to match Earth's then we'd use the profile and mass to get a new moment of inertia and use that to get a new rotational period. However, if we kept the same profile shape we can just increase the rotation rate by the inverse square of the change in the radius. It would spin about 120 times faster.
The problem with that is that it would distort into an absurdly oblate spheroid and probably blow up. I say that because if it remained a sphere the centripetal acceleration $R \omega^2$ would be about 2840 m/s$^2$ or nearly equal and opposite to its surface gravity.
So this is an untenable situation and the planet would likely break up.
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1$\begingroup$ Sounda a lot like Mesklin en.wikipedia.org/wiki/Mesklin $\endgroup$ Commented May 8, 2020 at 10:02
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$\begingroup$ @SteveLinton or more likely, mescaline $\endgroup$ Commented May 8, 2020 at 12:09
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1$\begingroup$ For a less extreme version of the rotation issue, see Haumea. Strange things happen when a fast rotating object seeks hydrostatic equilibrium. $\endgroup$ Commented May 10, 2020 at 12:36