Six of the eight major planets in our solar system have at least one moon, and so do several dwarf planets, asteroids, and other small bodies. Mercury and Venus are the only planets without any moons at all. Beyond the planets, the list of moon-bearing objects keeps growing as telescopes improve and spacecraft visit new targets.
The Planets and Their Moon Counts
Earth has one moon. Mars has two, both small and irregularly shaped. After that, the numbers jump dramatically. Jupiter has 95 known moons. Saturn holds the record at 274 confirmed moons as of March 2025, more than any other planet. Uranus has 28, and Neptune has 16.
The gap between the inner rocky planets and the outer gas and ice giants is enormous. Mercury and Venus orbit the Sun with zero natural satellites, while the four outer planets collectively account for over 400 moons. The sheer gravitational pull of the giant planets allows them to capture passing objects and hold onto material that coalesces into moons during formation. Saturn’s count has risen especially fast in recent years because many of its moons are tiny, some less than 10 kilometers across, and only became detectable with modern instruments.
Why Mercury and Venus Have None
Mercury sits so close to the Sun that the Sun’s gravity dominates the space around it, making it nearly impossible for a small object to settle into a stable orbit. Any would-be moon would either crash into Mercury or get pulled away by the Sun. Venus likely faces a similar problem, compounded by its slow, retrograde rotation. Simulations suggest that even if Venus once captured a moon, tidal interactions would have eventually dragged it inward to destruction.
Dwarf Planets With Moons
Pluto is the best-known example. It has five moons: Charon (so large relative to Pluto that the two are sometimes called a double system), plus the much smaller Nix, Hydra, Kerberos, and Styx. Eris, the most massive dwarf planet, has one moon called Dysnomia. Haumea has two, named Hi’iaka and Namaka. Makemake has one small, faint moon nicknamed MK2.
Farther out, other large trans-Neptunian objects also carry companions. Quaoar has a moon called Weywot, and Orcus has one named Vanth. These distant pairings are common enough that astronomers now consider binary or satellite systems a normal feature of the outer solar system, not an oddity.
Asteroids and Small Bodies
Moons aren’t exclusive to planets and dwarf planets. Dozens of asteroids have their own natural satellites. The first confirmed example was Dactyl, a tiny moon orbiting the asteroid Ida, discovered by the Galileo spacecraft in 1993. Since then, surveys have found binary and even triple asteroid systems. The asteroid Sylvia, for instance, has two moons.
These asteroid moons tend to be irregularly shaped, sometimes resembling lumpy boulders rather than spheres. Research into systems like Didymos (the target of NASA’s DART mission) suggests many of these small moons formed from debris disks around their parent asteroids, with fragments merging at low speeds to produce elongated or bilobed shapes. The upcoming ESA Hera mission will revisit the Didymos system to study exactly how these tiny satellites form and evolve.
How Celestial Bodies Get Their Moons
There are three main ways a body ends up with a moon. The first is co-accretion: the moon forms alongside its parent from the same cloud of dust and gas, much like how many of Jupiter’s and Saturn’s larger moons likely formed within disks of material swirling around the young planets. The second is capture, where a passing object gets snared by gravity. Many of the small, irregularly shaped moons of the outer planets are thought to be captured asteroids or comets. Neptune’s largest moon, Triton, orbits in the opposite direction of the planet’s rotation, a strong sign it was captured from the outer solar system.
The third mechanism is a giant impact. Earth’s Moon almost certainly formed this way. Early in the solar system’s history, a Mars-sized body collided with the young Earth, and the resulting debris coalesced into the Moon. Pluto’s moon Charon may have a similar origin story.
What About Moons Outside Our Solar System
No exomoon (a moon orbiting a planet around another star) has been confirmed yet, though astronomers are actively searching. The James Webb Space Telescope recently surveyed a Jupiter-like exoplanet called Kepler-167e specifically looking for signs of a moon, and results from that search are still being analyzed. The challenge is immense: detecting a moon around a planet that is itself just a speck of dimmed starlight requires extraordinary precision. Given that moons are so common in our own solar system, most astronomers expect exomoons exist in large numbers, but proving it remains one of the next big milestones in planetary science.
Quick Reference by Object Type
- Mercury: 0 moons
- Venus: 0 moons
- Earth: 1 moon
- Mars: 2 moons (Phobos, Deimos)
- Jupiter: 95 known moons
- Saturn: 274 known moons
- Uranus: 28 known moons
- Neptune: 16 known moons
- Dwarf planets: Pluto (5), Eris (1), Haumea (2), Makemake (1), plus moons around Quaoar, Orcus, and others
- Asteroids: Dozens of known binary and triple systems
The total number of known moons in the solar system continues to climb. Improved telescopes and dedicated surveys keep turning up small, faint satellites around planets and minor bodies alike. Saturn alone has gained hundreds of newly confirmed moons in the past few years, and similar discoveries are expected as astronomers push deeper into the outer solar system.