How many moons are there in the solar system?
Roughly 900 moons are confirmed, of which about 420 orbit the eight planets and the rest orbit dwarf planets and asteroids. Saturn overtook Jupiter decisively in 2025 when a single survey added 128 new moons at once, taking it to 274 against Jupiter's 95. Almost all of the new ones are irregular satellites a few kilometres across — captured objects on distant, tilted, often retrograde orbits, not the round bodies people picture. Earth has one; Mercury and Venus have none.
How the figure is arrived at
Take many long exposures of the space around a planet while tracking at the planet's rate, then stack the images so that a faint moving object builds up signal while the streaked background stars do not. Confirming a moon requires recovering it on later nights to prove the orbit is bound, which is why announcements come in batches years after the discovery images.
How confident it is
- Low estimate
- 850
- High estimate
- 950
- Spread
- 1.1× between the bounds
Other space and the universe counts
- How many stars are there in the universe? about 200 billion trillion
- How many stars are there in the Milky Way? between 100 billion and 400 billion
- How many atoms are there in the universe? about 10^80
- How many galaxies are there? hundreds of billions — possibly 2 trillion
- How many satellites are in orbit? about 12,000 active satellites
- How many planets are there in the galaxy? at least 100 billion — probably more planets than stars
- How many stars can you see with the naked eye? about 9,000 over the whole sky; roughly 2,500 at once
- How many constellations are there? exactly 88
- How much space junk is there? about 40,000 tracked objects, and over 130 million fragments too small to track
- How many asteroids are there? about 1.4 million catalogued
Common questions
- How many moons are there in the solar system?
- about 900 confirmed, and the number keeps moving
- How is that estimated?
- Take many long exposures of the space around a planet while tracking at the planet's rate, then stack the images so that a faint moving object builds up signal while the streaked background stars do not. Confirming a moon requires recovering it on later nights to prove the orbit is bound, which is why announcements come in batches years after the discovery images.
Related pages
- How many stars are there in the universe? about 200 billion trillion
- How many stars are there in the Milky Way? between 100 billion and 400 billion
- How many atoms are there in the universe? about 10^80
- How many galaxies are there? hundreds of billions — possibly 2 trillion
- How many satellites are in orbit? about 12,000 active satellites
- How many planets are there in the galaxy? at least 100 billion — probably more planets than stars
- How many stars can you see with the naked eye? about 9,000 over the whole sky; roughly 2,500 at once
- How many constellations are there? exactly 88
- How many people are there in the world? Living things and the natural world
- How many countries are there in the world? Things people built
- How many bones are in the human body? The human body
- How many grains of sand are there on Earth? Living things and the natural world
- How many ants are there in the world? Living things and the natural world
- How many trees are there in the world? Living things and the natural world
Sources
- NASA — National Aeronautics and Space Administration (Public domain (US Government))