Neptune has 13 known satellites to this date.
They are:
There are no known satellites of Mercury.
The Neptunes was created in 1990.
Mercury does not have any known natural satellites or moons. It is one of the few planets in our solar system that does not have a moon orbiting around it.
Venus has no known natural satellites or moons.
neptunes gravity is high
Venus has no known natural satellites (moons).
Venus has no known natural satellites or moons.
Mercury, Venus, Earth, Mars, Neptune and Pluto.
Mercury and Venus have no known natural satellites (moons).
there are currrently 2 known satellites oribiting mars
100
I don't know of any planet with exactly 21 known moons. The best answer is probably "Uranus" with 27 moons (natural satellites).