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What would happen if a large non-gaseous body, equal to or greater than that of Jupiter hits with Jupiter?

My assumption is the larger body (name it as A) will have a large gravity and a large mass even if they are of same size, because Jupiter mainly consists of hydrogen and helium so the average mass will be less. A will cut through Jupiter and because A will have a high gravity an atmosphere of hydrogen and helium will be formed.

But I don't know to what percentage my assumption is correct. So what could be the answer?

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    $\begingroup$ According to current theories, once you get to about 10 Earth masses you start to look like Neptune. Once you get to about 0.6 Jupiter masses you start to look like Jupiter. Once you get to about 15 Jupiter masses you start to look like a brown dwarf. So this large body would have to be some sort of construct held apart by antigravitational forces, likely artificial. $\endgroup$ – called2voyage Jul 21 '15 at 15:15
  • $\begingroup$ This could be an interesting xkcd what if scenario. What happens when you slam increasingly large rocks at Jupiter. Hmmmm... $\endgroup$ – PearsonArtPhoto Jul 21 '15 at 19:18
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I'm working on the assumption that you mean equal in mass, and by "non-gaseous" you mean composed of elements heavier than hydrogen and helium (technically, Jupiter is mostly liquid or solid due to the extreme pressures). According to our current theories such a body could not evolve naturally, but lets ignore that little fact.

Lets say that the density of the impacting body is 8 times higher than Jupiter, this would make it denser than iron, I don't know if that is realistic at that level of compression by gravity. This would give the impactor a radius half that of Jupiter (If the density is 8 times higher, the volume must by 1/8th, and because volume is proportional to radius cubed, the radius would thus be the cube root of 1/8th, or 1/2).

According to Newton's Impact Depth theory, an impactor will penetrate to approximately it's own length * relative density before running out of momentum and this is true regardless of velocity.

Making the simplifying assumption that both bodies have uniform density, the impactor could thus punch 8 times it's own diameter into Jupiter, as Jupiter only has twice the diameter of the impactor, it could punch through 4 Jupiters before running out of momentum.

In reality, a disproportionate amount of Jupiter's mass will be in a dense rocky core. If it hits the core then more of its momentum will be absorbed, Jupiter's core will end up being punched out the far side of Jupiter in a great fiery bulge.

So far we haven't considered the energy of the impact. Since the body falls in from outside the solar system, it will be travelling at very least 70km/s, this is from a combination of Heliocentric escape velocity at Jupiter's orbit, and Jupiter escape velocity (the two giant masses will pull on each other very strongly and so come together at a great velocity).

The kinetic energy of a Jupiter mass at 70km/s is 4.65*10^36 J, while the gravitational binding energy of Jupiter is 2.086 * 10^36 J, so the impact could potentially yield a blast powerful enough to overcome the gravitational binding energy of both planets, although only just so - a lot of the mass could coalesce into a new planet.

That amount of energy is equal to the energy released by the sun in 390 years. Jupiter is 4x further from Earth than the Sun is, and thanks to the inverse square rule, we only get 1/16th of that, so we receive a blast equal to 24 years of sunlight—all in the matter of hours—now a lot of that energy will be absorbed in the process of blasting Jupiter to pieces but there would be plenty leftover to irradiate Earth (the blast would also be somewhat directional, if the site of impact is aimed towards Earth we are goners as soon as the radiation arrives, but even if the initial radiation doesn't get us, the blast wave of superheated Jupiter atmosphere will)

So the answer to your question, is that Jupiter is blown to pieces and we all die.

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