Two planets, Venus and Mercury, are the only planets in the solar system that do not have any natural satellites or moons. Mercury, Venus, Mars and Earth are inner planets.
The outer planets are Jupiter, Uranus, Saturn and Neptune. All of these planets do have satellites or celestial bodies that orbit them. While the Earth has one moon, Mars has two small moons named Deimos and Phobos.
The outer planets have numerous moons. For example, Uranus has 27 moons, Neptune has 13 known moons, and Jupiter and Saturn have over 50 moons each.
In 1610, Galileo Galilei observed four moons of Jupiter, and Asaph Hall discovered the moons of Mars.