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Phobos
Position on the route: 5/45 · level needed 12 · journey (Mk0 engine) 5.4 h
By the numbers
| Diameter | 22 km (mean) |
|---|---|
| Distance from Mars | 9,376 km |
| Orbital period | 7 h 39 min |
| Gravity | ≈ 0.0057 m/s² |
| Origin | a captured asteroid or debris from an impact at Mars |
The story
Mars’s inner moon orbits closer to its planet than any other moon in the Solar System: it rises in the west and sets in the east twice a day. Its orbit shrinks about two metres a century; in time it will either break up into a ring or hit Mars.
Gravity is so weak that a speed of about 100 m/s takes you off the surface. That makes Phobos a candidate base for collecting fuel and resources before landing on Mars; Russia’s Fobos-Grunt (2011) tried to bring back a sample and failed.
Missions
- Mariner 9 (1971): the first close photographs
- Fobos-Grunt (2011): a sample-return attempt, failed after launch
- MMX (Japan, planned 2026): a Phobos sample return
Colony note
No gravity to speak of and no atmosphere; dusty regolith, poor radiation shielding. A fuel and observation outpost for Mars.
What probes bring back
- Its orbit sinks 2 m a century; in 30–50 million years it will break up or hit Mars.
- The grooves around Stickney may have been cut by ejecta that fell to Mars and bounced back.