In diretta
moon · orbits Mars

Phobos

A 22-km rock in a decaying orbit, and the cheapest handhold in the Mars system.
Viking Orbiter VIS
48.7/100 · Hard
Escape velocity
11 m/s

A hard sprint would put you into orbit. A good throw leaves Phobos entirely.

Surface conditions on Phobos

Every figure below is tagged with where it came from. Measured means an instrument read it on or at the body; modeled means it was computed and never directly observed.

GravityMeasured
0.01 m/s²
0.001 g
Mean temperatureMeasured
-40 °C
-112 to -4 °C
Surface pressureMeasured
Vacuum
None
RadiationModeled
0.700 mSv/day
Interplanetary GCR, roughly half-shielded by the body
Solar fluxModeled
586 W/m²
0.43x Earth
Day / night cycleMeasured
7.7 h
Tidally locked; it orbits Mars three times a day
Water
Unknown
Travel timeModeled
7 months
Same transfer as Mars
Delta-v from LEOModeled
4.1 km/s
Cheaper than the Martian surface — there is almost no gravity well to climb out of
Radius
11.267 km
0.002x Earth

What it would take to settle Phobos

No world off Earth is habitable — the honest habitable fraction of every surface here is zero. What can be answered is how far each one sits from Earth along the seven axes a habitat has to buy its way out of. Phobos scores 48.7 out of 100, on 100% coverage of the axes. The single worst axis here is pressure (Vacuum); the one that most sets Phobos apart from the other thirteen is water.

Radiation30
Pressure100
Temperature19
Gravity65
Water70
Available energy17
Access32
Pressure
Vacuum

Below the Armstrong limit (0.062 bar) body fluids boil at body temperature — the difference between needing a mask and needing a pressure vessel. Above 1 bar the problem inverts into containment, and Venus at 92 bar has never let a lander live two hours.

Water
Unknown

Water is drinking water, breathing oxygen and rocket propellant in one deposit. A world without it has to import all three forever.

Gravity
0.01 m/s² — 0.001 g

Nobody has ever measured long-term human health at any gravity between 0 and 1 g. Below about 0.1 g, anchoring anything — including yourself — becomes the design driver.

Radiation
0.700 mSv/day — 106x Earth background

Shielding is mass, and mass is the single most expensive thing to move. Above roughly 1 mSv/day a surface habitat has to be buried.

Who has been to Phobos

Human landings
0
People who walked
0
Robotic landings
0
Named features
20

Never landed on. Fobos-Grunt failed in Earth orbit in 2011; JAXA MMX is due to land and return a sample.

Unprotected survival: Seconds, as in any vacuum.

Water

Possible buried ice inferred from low density, never confirmed. Phobos may be captured asteroid or re-accreted Mars ejecta — the sample return mission MMX is meant to settle it.

The named places on Phobos

The IAU has approved 20 names on Phobos, each drawn from a theme the naming committee chose for this world. Every name in the scene above is one of them, placed at its catalogued coordinates.

All 20 named places on PhobosWhat these terms mean, across every world →

Sources

Imagery is public-domain NASA/USGS mission data, streamed live from NASA Trek as a plate-carrée tile pyramid and draped on our own sphere — no third-party globe library and no cached copy of anyone else's map.