Phobos: Mars's Larger Moon

Phobos is the larger and closer of Mars's two moons. It orbits Mars rapidly and appears to move across the Martian sky in an unusual way. Mars's two small moons add another layer to the study of how planets and their satellite systems form and evolve.

Mars is a world where apparently simple questions often lead to larger scientific problems. Researchers combine spacecraft images, measurements from orbit, surface observations and laboratory analysis of Martian material to build explanations that can be tested. As with all planetary science, the strongest conclusions come from multiple observations that agree with one another.

The value of studying phobos: mars's larger moon is not limited to one isolated fact. Mars is a rocky planet with a long geological history, a thin atmosphere and evidence that its environment changed substantially over time. Individual observations become more useful when they are placed into that larger planetary context.