This color picture of Mars was taken July 21--the day following
Viking l's successful landing on the planet. The local time on Mars is
approximately noon. The view is southeast from the Viking. Orange- red
surface materials cover most of the surface, apparently forming a thin
veneer over darker bedrock exposed in patches, as in the lower right.
The reddish surface materials may be limonite (hydrated ferric oxide).
Such weathering products form on Earth in the presence of water and
an oxidizing atmosphere. The sky has a reddish cast, probably due to
scattering and reflection from reddish sediment suspended in the lower
atmosphere. The scene was scanned three times by the spacecraft's
camera number 2, through a different color filter each time. To assist in
balancing the colors, a second picture was taken of z test chart
mounted on the rear of the spacecraft. Color data for these patches
were adjusted until the patches were an appropriate color of gray. The
same calibration was then used for the entire scene.
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