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. This has to be an incredibly fine powder formed from impacts over millions of years, and it looks like the whole surface is made up of fine dust. New images from the spacecraft's Mars orbiter camera show many never-before seen features on Phobos, and are among the highest resolution ever obtained of the Martian satellites.
Large boulders appear to be partly buried in the surface material.
The instrument has been able to obtain the first global-scale infrared spectra of Earth and Mars in addition to the new Phobos data, bringing new insights about the composition of these three very different worlds. Mars, which is much colder than Earth because of its distance from the Sun, is less complex and shows only significant amounts of carbon dioxide. The spectrum of Phobos, however, has little structure because it has no atmosphere and the energy it emits is coming entirely from its surface. On Monday, September 14, Mars Global Surveyor begins its second phase of aerobraking, using the friction from repeated passes through Mars' atmosphere to lower and circularize the spacecraft's orbit. The magnetometer and thermal spectrometer will be turned on through December to gather data each time the spacecraft passes closest to Mars' surface.