This movie shows the temperature of the surface of Mars as measured by the Thermal Emission Spectrometer (TES) instrument on the Mars Global Surveyor orbiter. These temperatures clearly show the growth and retreat of the martian northern and southern polar ice caps. These caps grow in winter and are composed of carbon dioxide (CO2) ice with temperatures as low as -125° C (-195° F). In the summer these caps retreat to relatively small areas around the poles. This movie also demonstrates the large difference in summertime temperatures between the northern (Ls 90°) and southern hemisphere (Ls 270°). This difference is due to the fact that the orbit of Mars around the Sun is elliptical, and Mars is closest to the Sun, and therefore the warmest, during the summer season in the south.
Seasons on Mars are measured by the position of Mars in its orbit around the Sun. This system is measured in degrees of aerocentric longitude (Ls) around the orbit, beginning at 0° Ls at the northern spring equinox, progressing to 90° Ls at the start of northern summer, 180° Ls at the fall equinox, 270° Ls at the start of northern winter, and finally back to 360°, or 0°, Ls at the spring equinox.