Phobos is the largest and innermost of Mars' two moons.

Temperatures

Measurements of the day and night sides of Phobos show such extreme temperature variations that the sunlit side of the moon rivals a pleasant winter day in Chicago, while only a few kilometers away, on the dark side of the moon, the climate is more harsh than a night in Antarctica. High temperatures for Phobos were measured at -4 degrees Celsius (25 degrees Fahrenheit) and lows at -112 Celsius (-170 degrees Fahrenheit). This intense heat loss is likely a result of the fine dust on Phobos' surface, unable to retain heat.

Atmosphere

Phobos has no atmosphere. Due to this, it may be a captured asteroid, but some scientists show evidence that contradicts this theory.

Movement

Phobos is nearing Mars at a rate of 1.8 meters every hundred years; at that rate, it will either crash into Mars in 50 million years or break up into a ring.

Surface

Its most prominent feature is the six-mile crater Stickney, its impact causing streak patterns across the moon's surface. Stickney was seen by Mars Global Surveyor to be filled with fine dust, with evidence of boulders sliding down its sloped surface.

based

1. Pictures - Courtesy of Windows to the Universe, http://www.windows.ucar.edu .
2. Nasa.gov website.