How many moons does Mars have?
Guess before you scroll — the answer is below
The answer
2 moons
Mars has 2 small moons, Phobos and Deimos, both named after the sons of the Greek war god Ares. Phobos is so close to Mars and orbits so fast that it rises and sets twice in a single Martian day — and it is slowly spiraling inward, expected to eventually break apart or crash into the planet in tens of millions of years.
How to get close to this number
Reason from size and position. A small planet next to the asteroid belt has weak capture gravity but a supply of nearby debris, so it should have a few captured rocks rather than the dozens that a giant planet accumulates or the large formed moon that Earth has. Two is exactly what that reasoning predicts.
The contrast with Jupiter on this site is the useful one: a hundred-plus moons versus two, for planets in the same region of the solar system. Moon counts scale with mass far more steeply than with anything else, because capture depends on gravitational reach — and Jupiter's is enormously larger.
The Phobos detail in the explanation is the genuinely strange one. It orbits so fast and so low that it rises and sets twice in a Martian day, and it is spiralling inward toward eventual destruction. A moon on a decaying orbit is a reminder that orbital configurations are temporary, even when the timescales are tens of millions of years.
Where this number comes from
| Source | NASA Science |
|---|---|
| Figure refers to | 2023 |
| Last checked | |
| Unit | moons |
Numbers move. If this one has drifted from its source, let us know.
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