How Many Moons Are in the Solar System?
More than 440 confirmed moons orbit the planets and Pluto — and Saturn alone has about 293, more than all the other planets combined. But there’s a catch worth knowing: nobody has ever agreed on what officially counts as a moon, and the number climbs almost every year.
Tap a planet for its moon count and biggest moon. Switch modes to see how the total collapses when you only count the large, round moons — there’s no official rule for which tiny chunks make the list.
So how many moons are in the solar system — really?
It depends on two things: what you count, and when you ask. Add up the confirmed moons of the eight planets and the dwarf planet Pluto and you get more than 440. Widen the net to include the moons of asteroids and other dwarf planets and the confirmed total passes 890. Narrow it instead to only the large, round moons — the handful of worlds big enough to pull themselves into a sphere — and you’re down to barely twenty. The widget above lets you flip between those views. There is no single right number, because there’s no single right definition — and whatever figure you settle on was probably lower last year.
Saturn, king of the moons
For most of history Jupiter, the biggest planet, was assumed to have the most moons. Not any more. Saturn pulled ahead in 2019, the two traded the lead for a few years, and then Saturn ran away with it: a single discovery of 128 new moons in March 2025 took its count to 274, and further finds have since pushed it to roughly 293. That’s more moons than every other planet in the solar system put together. The reasons are subtle — Saturn’s zone of gravitational control reaches comparatively far out, its environment lets captured moons settle into stable orbits, and old collisions seem to have shattered larger moons into swarms of small fragments. Its trajectory tells the story on its own:
What even counts as a moon?
Here’s the surprise at the heart of the question. The word "planet" has a strict, voted-on definition — it’s what cost Pluto its planethood in 2006. The word "moon" has none. A moon is just a natural body that orbits a planet, with no lower size limit at all. So the same label covers Ganymede, which is larger than the planet Mercury, and a dark lump of ice and rock only two or three kilometres across — about the size of a small town. Most of Saturn’s haul are exactly that: tiny "irregular" moons on tilted, far-flung orbits, the leftovers of captured or shattered bodies. Saturn has just 24 regular, well-behaved moons and around 250 irregular ones. Because there’s no cutoff, every improvement in telescopes simply finds more — which is why the count has no natural ceiling.
From a planet-sized giant to a chunk of ice
The range of these worlds is staggering. At the top end, Jupiter’s Ganymede and Saturn’s Titan are both bigger than Mercury; Titan even has a thick atmosphere and lakes of liquid methane. Several moons are among the most promising places to look for life: Jupiter’s Europa and Saturn’s Enceladus both hide liquid-water oceans beneath their icy crusts, and Enceladus visibly sprays that ocean into space through cracks at its south pole. Neptune’s Triton orbits backwards, a captured world from the outer solar system. And against all of that, Earth has exactly one moon — but ours is remarkably large for our planet, steadying Earth’s tilt and raising the tides. The giants count their moons in the dozens and hundreds; we have a single, well-loved one.
How sure are we — and why the number keeps moving
Every figure here is a snapshot. A moon is only "confirmed" once astronomers have tracked it across enough nights to pin down its orbit and have it accepted by the International Astronomical Union’s Minor Planet Center; until then it’s provisional. That’s why different sources quote slightly different totals at any moment — NASA’s headline page may still show 274 for Saturn while the IAU’s running tally has already passed 290, simply because they updated at different times. The deeper truth is that this is a question with a date stamp built in. New batches of moons are announced every year or two, almost always small ones, almost always around the giant planets. Whatever number you take away from this page, treat it as "at least this many, for now."
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A census that isn’t finished
Most "how many" questions feel like they ought to have a fixed answer waiting to be looked up. The moons of the solar system quietly refuse. Four hundred years ago the count was one — our Moon. Then Galileo found four more around Jupiter, and the number has been climbing ever since, in fits and starts, every new telescope pulling a few more small dark worlds out of the black.
That’s a different kind of answer, and a more honest one. The solar system isn’t a finished inventory; it’s a place we’re still surveying. "How many moons" is one of those rare questions whose truest reply is a direction rather than a number: more than we knew last year, fewer than we’ll know next year — and every one of them a world in its own right.
So how many moons are in the solar system? Over 440 today — and a number that has never once stopped growing.
Sources
- NASA Science & NASA Space Place, Moons — per-planet counts, the ~890 total, and the largest moons.
- Wikipedia, Moons of Saturn — Saturn’s running total (~293), the regular/irregular split, and the discovery timeline.
- The Conversation & BBC Sky at Night — the March 2025 batch of 128 moons, the lack of an official "moon" definition, and why Saturn leads.
- IAU Minor Planet Center — the confirmation process behind the official counts.
Counts are mid-2026 snapshots and rise over time; sources may differ slightly depending on when they were last updated.