.jpg)
Photograph of Mars obtained on August 24, 1956 (18 days before the opposition on September 11, 1956) by R. B. Leighton of the California Institute of Technology. The distance between Earth and Mars at the time the photograph was taken was about 35,000,000 miles. The Mt. Wilson 60-inch reflector was used with its aperture cut to 21 inches by an off-axis diaphragm. The exposure time, on Kodachrome Type A film, was 20 seconds. The positive, used in making the print, was composed by George Emmerson at the Jet Propulsion Laboratory.
This color photograph suggests that the darker areas of Mars are not necessarily “green” in color as they are often described, but may be a darker shade of the prevailing yellow-orange light areas. It is noted that the photograph as it appears here has been subjected to duplication in the course of which some minor color changes occurred. The brilliant white south polar cap is clearly evident. Rather surprisingly, this cap is probably just what it looks like—a thin layer of frozen water, perhaps in the form of hoarfrost. As the polar cap recedes, the dark areas (especially those in the same hemisphere) become darker. The dark area near the lower right-hand limb of Mars is Syrtis Major, one of the most prominent and well-known features of the planet. This feature, among others of its kind, has been of increasing interest to exobiologists in recent years. The extremely light-colored area to the right and just below the ice cap is Hellas, one of the most prominent Martian desert areas.
