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- Deimos on Wikipedia
Deimos
Details
Deimos is the smaller, outer moon of Mars, only about 12 kilometers across. Its dusty regolith softens many of its craters, giving this dark asteroid-like moon a smoother face than its larger sibling Phobos.
Deimos matters because it is a moon at the edge of the word's usual intuition. It is not a round companion world like Earth's Moon, or even a dramatic battered body like Phobos. It is a tiny, dark, irregular object only about a dozen kilometers across, orbiting Mars as a quiet outer satellite.
What makes Deimos visually different from Phobos is the way its surface has been softened. NASA describes a thick regolith layer that partly fills craters, so the moon looks smoother than its small size and impact history might suggest. On a body with such weak gravity, impact debris does not simply fall back in the ordinary way; Mars helps keep some of that material near the moon’s orbital region, where it can be redeposited over time.
That is why Deimos belongs on this scale. It shows the lower edge of what a planetary moon can feel like: not a world with atmosphere, oceans, or tectonics, but a dusty fragment held in a planetary system. Deimos is important because it makes the moon category stretch down to something close to asteroid scale.
5.24km
Key facts
- Scale fact
- 12 kmmean diameter
- Composition
- C-type asteroid-like material and regolith
Scale context
Where Deimos sits on the full axis
By size on the journey, Deimos sits between Halley's Comet and Crab Pulsar. The band below compares Deimos with nearby Small irregular moon objects so the size jump stays easy to read.
Together, these objects make the size change around Deimos easy to compare at a glance.
Sources
References for Deimos
Measurements and descriptive context are compiled by the Scale of Space team from the references below. If you find an error, please let us know.
- Deimos — Wikipedia
- Visual reference: Wikimedia Commons (NASA / JPL / University of Arizona, Public domain)
Between the smallest and the largest, perspective is everything.
About
Scale of Space is a scroll-based journey through the universe, placing objects on a single logarithmic scale so you can compare size across an unbroken range.
Guides turn parts of that scale into curated essays, while focused views let you explore the same range through specific groups of objects.