The number of natural satellites, commonly called moons, orbiting the planets in our solar system varies dramatically, reflecting the diverse formation histories and gravitational environments of each world. The count of these celestial bodies is far from uniform, ranging from terrestrial planets with no moons or a single companion, to massive gas giants surrounded by dozens of captured worlds. The distinct populations of moons reveal a fundamental difference in how systems formed in the inner and outer regions of our solar neighborhood.
The Direct Answer: Zero Planets with Three Moons
The question of which planet has exactly three moons has a straightforward answer: currently, none of the eight major planets in our solar system possess precisely three natural satellites. Planetary moon populations tend to fall into distinct groups, making the number three an anomaly. Inner planets have either one, two, or zero moons, while the outer gas and ice giants host satellite systems that number in the dozens.
The lack of a three-moon system is a statistical quirk tied to the mechanics of satellite capture and formation. While a planet’s moon count is generally dynamic, systems tend to be stable at the low end (one or two) or at the high end (many dozens). This pattern suggests that having three moons is a configuration that may be less gravitationally stable over the billions of years of solar system history.
Contextualizing the Count: Earth and Mars
The planets closest to the number three are the two rocky worlds just beyond the Sun: Earth and Mars. Earth hosts a single, unusually large satellite, simply called the Moon or Luna. This solitary companion is thought to have formed from a massive impact early in Earth’s history, resulting in a system that is unique in its planet-to-moon size ratio.
Mars, in contrast, orbits the Sun accompanied by two small, irregularly shaped moons named Phobos and Deimos. These two satellites are small, dark, and heavily cratered, with compositions that strongly resemble C-type asteroids found in the outer asteroid belt. Scientists widely believe that Phobos and Deimos are not indigenous to Mars but are instead asteroids that were gravitationally captured by the planet.
Phobos is only about 14 miles across at its longest dimension, illustrating the small size of these Martian moons. Their small size and likely captured origin illustrate the low-end limit of stable satellite systems for terrestrial planets.
The Abundance of Satellites in the Outer Solar System
Moving beyond Mars, the moon counts jump dramatically, further demonstrating why three is a rare number. Jupiter, the largest planet, has over 95 confirmed moons, while Saturn currently holds the record with over 140. The massive size of these gas giants gives them an immense gravitational reach. This powerful gravity allows them to easily capture orbiting bodies, which accumulate over time into complex, crowded satellite systems.
Even the ice giants, Uranus and Neptune, maintain large families of moons, with counts exceeding two dozen each. These systems are populated by both large, spherical, internally active moons and numerous smaller, irregularly shaped bodies.