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The landscape seen by the Viking landers was variable on a sol-to-sol basis, and over the succession of Martian seasons. (N.B., a sol on Mars is the Martian equivalent of a day on Earth). In this view, the sun is low in the sky casting shadows behind the rocks which are strewn everywhere across the plane. The sky is colored by airborne dust particles which are finer that talcum powder and lofted by thin, cold Martian winds. At various times throughout the Martian year, fierce dust storms arise filling the atmosphere with considerably more material than is evident in the photograph. (It is the opinion of the present author that tribo-electrostatic charging of the Martian dust occurs during such storms, and that this charging might provide a basis for Martian lightning, although actual lightning on Mars has not yet been seen.) Occasionally, ground frosts were recorded by the Viking lander cameras, substantiating the fact that Mars still has water, albeit very sparse. Ice crystal clouds were also recorded on occasion.
Slide 12 of 20