3 I think.
1 moon they know of
Mercury has no satellites.
it makes it very hot and oncreases the amount of radiation
No satellites have been discovered yet in orbit around Mercury. As of now, the answer to the question is zero.
Neptune has 13 moons.
the planet that has the most amount of moons is Jupiter which has 67 moons
the inner plants have a total of three moons. our moon, and two moons of mars. Phobos, and Deimos. but the out planets have many more moons. Neptune has the least amount of moons out of all the outer planets. it has 13 moons. but, the other outer planets have way more. Jupiter even has 63. of course, there are probably many more moons still to be discovered. well, not for earth and mars. in total, the outer planets must have at least 100 moons.
Moons do not orbit the Milky Way because they Milky Way is a galaxy. But if you are thinking about the amount of moons in the Milky Way total, it is around 1-2million. Probably even more.
mercurys period number is 80
Toledo Mercurys was created in 1947.
Toledo Mercurys ended in 1962.
Venus, both have zero moons.