Mercury & Venus have no natural satellites.
You probably mean to ask about natural satellites as opposed to artificial satellites. In terms of neutrality, all satellites are neutral. In any event, the planet Jupiter has the most natural satellites, of any planet in our solar system. The planet Earth has the most artificial satellites.
No.
have any robots or satellites ever landed on pluto
Betelgeuse is a star, not a planet, so it does not have any satellites. Satellites, also known as moons, typically orbit planets, not stars.
Yes, any planet can have satellites. Gas planets actually have the most satellites due to their large masses.
Saturn
Venus is the biggest planet in our solar system that has no known satellites (moons).
I don't know of any planet with exactly 21 known moons. The best answer is probably "Uranus" with 27 moons (natural satellites).
a planetary satellite is any object that orbits a planet
non made satellites are those which orbits any planet or star such as earth,moon.
Earth
As far as is known in mid-2011, that would be Jupiter.