We hardly know yet. Planets other than those in our own solar system (called "extrasolar" planets or "exoplanets") have only been discovered in the last ten years or so. About a thousand are known, but astronomers feel there must be many, many more.
The planets we know of, some 300 now, are all in the Milky Way galaxy.
Planets orbit stars, stars orbit a galaxy. Planets are not "on" anything. A lot of stars out there have planets - we are just finding out how many now that we have better techniques to find them. So probably all galaxies have at least some stars with planets.
It is not known. Scientists are still not sure how many dwarf planets are in the solar system or how many true planets are in the galaxy. If estimates from our solar system apply elsewhere, however, the number is probably in the trillions.
All the planets we know of... even those orbiting other stars... are in the Milky Way Galaxy.
The closest galaxy that has planets is the Andromeda galaxy. It is the nearest galactic neighbor to the earth. The Milky Way has other planets too.
The planets were formed in the Milky Way. Our Galaxy (Milky Way) is older than the planets of our solar system.
There are eight planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The Milky Way is our galaxy, which contains billions of stars with their own solar systems.
You first have to get past the planets of our solar system (which is IN our galaxy) in order to then make movements to get out of the entire Milky Way galaxy.
The Andromeda galaxy is a separate galaxy from our Milky Way and has its own set of planets. However, due to the vast distance between our galaxies, we are currently unable to observe individual planets in the Andromeda galaxy.
Probably, but impossible to tell as we are only just seeing planets within our own galaxy.
There are billions of planets and moons in the Star Wars galaxy.
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