The Solar System is a place of immense gravitational complexity, and determining the exact number of objects orbiting its planets is a surprisingly difficult task. While Earth possesses a single, large companion, the outer reaches of the Sun’s family are crowded with dozens, even hundreds, of smaller worlds. The total count is not fixed but is constantly being revised as technology allows astronomers to spot increasingly smaller objects in distant, dark orbits.
The Current Official Count
The most up-to-date census of the Solar System’s moons confirms a vast and growing population of natural satellites. As of early 2025, astronomical bodies like NASA and the International Astronomical Union (IAU) recognize a total of over 891 confirmed natural satellites orbiting larger bodies. This count includes every confirmed object orbiting planets, dwarf planets, and even the numerous smaller asteroids and trans-Neptunian objects. Out of this total, more than 420 satellites are officially recognized as orbiting the eight major planets and the recognized dwarf planets.
New discoveries around the gas giants routinely add to the list. The total is expected to continue climbing as new surveys are completed, particularly in the far-flung, dim regions of the outer Solar System.
Defining a Natural Satellite
A “moon” is an informal term for a natural satellite, which is simply any celestial body orbiting a planet, dwarf planet, or minor planet. Unlike the strict criteria for planet status, the IAU does not maintain a formal, universally agreed-upon definition that includes a minimum size or mass for a moon. The classification hinges primarily on the object maintaining a stable, repeating orbit around a larger body, rather than being a temporary capture or part of a ring system.
Moons exist on a vast spectrum of size and shape, from the large, spherical worlds like Ganymede and Titan to tiny, irregularly shaped space rocks measuring just a few kilometers across. The largest satellites are massive enough for their own gravity to pull them into a nearly round form, a state known as hydrostatic equilibrium. Smaller moons, often believed to be captured asteroids, retain their potato-like, asymmetrical shapes.
Distribution of Moons Across the Solar System
The vast majority of the Solar System’s moons are concentrated in the outer regions, dominated by the four gas and ice giants. Saturn currently holds the record, with a staggering count of approximately 274 confirmed moons, many of which are tiny, irregular bodies that orbit far from the planet. Jupiter follows closely with around 95 confirmed satellites, including the four massive Galilean moons first spotted by Galileo Galilei.
Further out, the ice giants also maintain large families of moons. Uranus is orbited by about 28 known satellites, while Neptune has 16 confirmed moons. The terrestrial planets of the inner Solar System possess very few; Earth has only one, and Mars has two small, irregularly shaped moons, Phobos and Deimos. The total count is rounded out by the moons of dwarf planets, such as Pluto, which has five satellites, including its large companion, Charon.
The outer planets’ dominance is largely due to their massive gravitational fields, which were powerful enough to sweep up and capture numerous passing asteroids and Kuiper Belt objects early in the Solar System’s history. These captured bodies typically settle into distant, highly inclined, and often retrograde orbits.
The Process of Discovery and Confirmation
The process of discovery and official confirmation is methodical and time-consuming. New moons are typically first spotted by powerful ground-based telescopes, which survey the faint light around the bright giant planets. Space probes, such as NASA’s Cassini mission at Saturn, have also played a significant role by identifying objects much closer to the planet.
Once a potential moon is detected, it is given a provisional designation, such as “S/2009 S 1,” which indicates it is the first satellite discovered at Saturn in 2009. Astronomers must then observe the object over an extended period to precisely calculate its orbital path. This confirmation process is necessary to ensure the object is a permanently bound satellite and not a temporary, passing asteroid. Only after the orbit is confirmed as stable is the body given an official name, a step that formalizes its addition to the Solar System’s census.