In this solar system, Mercury and Venus have no moons. Mercury is the smallest planet in the solar system and only slightly larger than Earth's moon. It is the closest planet to the Sun. Venus is the second closest planet to the Sun and is slightly smaller than Earth.
In addition to Mercury and Venus, the dwarf planets Ceres and Makemake have no known moons.
A moon, also known as a natural satellite, is a celestial body orbiting another celestial body, such as a planet. The celestial body a moon orbits is known as its primary.
Planets outside the solar system probably have moons, but none have been confirmed as of 2014. There are also no known moons of moons.
Most of the planets in the solar system have at least one moon. Earth has one Moon. Mars has two moons. Jupiter has 67 confirmed moons. Saturn has 62 confirmed moons. Uranus has 27 confirmed moons. Neptune has 14 known moons. As for the dwarf planets with moons, Pluto has five confirmed moons, Haumea has two known moons and Eris has one confirmed moon.
Some scientists believe certain moons, such as those of Jupiter and Saturn, may support life. As of 2014, no direct evidence exists of life on any moons.