Artist's impression of the planet Mars as seen from one of its two satellites, either Phobos or Deimos. The white polar regions seen on Mars are ice caps; there is an apparently permanent cap of water ice at the North pole, while seasonal polar caps of carbon dioxide can grow to middle latitudes by the end of the Martian winter. Both the Martian moons reflect only a few percent of the incident sunlight. The spectrum of reflected light suggests a composition similar to that of bodies in the outer asteroid belt. One theory is that both moons were originally asteroid-like bodies near Jupiter, which perturbed their orbits and allowed their capture by Mars.