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As there are millions of rogue planets in the Milky Way, what would happen if one hit a planet in the Solar System.
For example, if the rogue planet hit Pluto, would Pluto fall in to the Sun due to to its gravity? What kind of catastrophic damage could it do in the Solar System?
It would depend entirely on the size, composition and trajectory of the two objects coming into the collision. They could annihilate each other leaving a mess of debris. Or one or both could survive the collisions in some form. And each of the surviving objects could be flung out of the solar system, flung into a spiral into the sun, flung into an elliptical orbit, or thrown into other objects. The space between planets is big so odds of direct and immediate collision of the "planets like billiard balls" variety you see on some sci-fi aren't likely. But anything the size of a planet would be seen well before any impact.
This really depends on the size, density and velocity the rogue planet was traveling before the collision and which planet it hit. As a side note, the possibility of this happening is quite rare.
If that rogue planet have sufficient velocity and under perfect conditions (such as the angle of collision), yes there is a possibility that it could reach the sun (bringing along with the 'planet' it collided say Pluto). The effect of that rogue planet would be enough to slightly disrupt other planets' orbit if it passes close and could disrupt the entire solar system. Pluto may not just fall to the sun based on the the pull of gravity, but also the velocity from the rouge planet.
Firstly addressing the 'sun' problem, yes if a sizable planet punches in to the sun, it'll create something like a mass coronal ejection which in return would bombard the solar system with harmful rays. Already this has affected the solar system.
If a sizable rouge planet hit one of the rocky planets such as Mars, large chunks of debris would come shooting out of the collision, a very high chance that a few pieces would land on Earth potentially creating another mass extinction; similarly to the other rocky planets such as Venus and Mercury. Similar to one of the solar system's gas giants if say, another gas giant hit it.
To summaries this, even a rogue planet entering our system would have already changed a few things not to mention a collision.
There are lot of ifs, buts, sizes, etc to answer: - Any sizable objects entering our solar system will disturb our orbital 'equilibrium'. - First the empty space between the planets is huge, So very unlikely a rogue planet will collide with a solar system planet but once it has entered in to the solar system gravity well it sure headed towards Sun. No 'Deep Impact' or 'Armageddon' please. - Second the rogue planet will have a high probability to alter the Oort Cloud objects sending them our way with multiple results. - Third it may get captured by the gas giants(Triton/Neptune). - Fourth if the rogue planets escapes the gas giants it will encounter Asteroid Belt altering the orbits there.
Finally any interaction direct or indirect with the inner planets is going to be catastrophic. Just think about the magnitude of tsunamis if a earth size planet comes anywhere close to us.
