Moons · Space Codex
Deimos
A 15 km lump of dark rock that circles Mars every 30 hours.
Mars's small, smooth outer moon
At a glance
Key points
A thick blanket of dust softens its craters, giving it a smoother face than Phobos.
- About 15 km across, smaller than many cities
- Covered by dust possibly 100 m deep
- Slowly drifting away from Mars
Surface
Deimos has no grooves and only small, partly buried craters. Its slightly reddish, dark surface resembles C-type asteroids. Debris knocked off by impacts can briefly form a thin ring around Mars before it falls back as dust.
Orbit
Unlike Phobos, Deimos orbits outside the synchronous distance, so tides push it slowly outward instead of drawing it in. From the Martian surface it would look like a bright star, rising in the east and taking more than two days to cross the sky.
What we still don't know
Whether Deimos shares Phobos's origin. MMX will observe it during its survey of the Martian system.
Missions
- 2005–
Mars Reconnaissance Orbiter
NASAActiveHiRISE camera and relay for surface missions.
- Launch 19 Oct 2026
H3 F10 from Tanegashima at 19:41 UTC (window to 7 Nov). Phobos operations 2027–2030, sample return 2031.
First-hand · our 3D model
How we render it
Deimos is a displaced triaxial mesh at its measured 15 × 12 × 11 km proportions, long axis towards Mars. Its surface map is our own procedural work, smoother than Phobos to suggest its deep dust blanket.
It is drawn at about 1.6% of Mars's radius, enlarged from its true 0.18% so it stays visible. It orbits in Mars's equatorial frame, inclined 1.8°, with a 1.26-day period kept in true ratio to its neighbours, and keeps one face towards Mars.
Moon sizes and orbits are compressed so a whole system fits on screen, but never reordered: each moon is drawn at 0.72 × (true size ratio)^0.6 of its planet, capped so no large moon is drawn bigger than it really is, and orbit distances are log-compressed into a band that clears the planet's rings. Orbital periods keep their true ratios, every moon is tidally locked, and on lighter devices only the two largest moons of each planet are drawn.
Related entries
- MarsCold desert with an ancient wet past
- PhobosMars's doomed inner moon
- Martian Moons eXploration (MMX)JAXA's Phobos sample return
Sources
- NASA Science: Deimos (opens in a new tab)
- JPL Solar System Dynamics: satellite physical parameters (opens in a new tab)
- JPL Solar System Dynamics: satellite mean orbital elements (opens in a new tab)
Last reviewed against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.