Friday, August 17, 2007

Viking 1's First Picture

Credit: NASA

The above photo is the first picture from the surface of Mars, taken by Viking 1 on July 20, 1976.
The camera began scanning the scene 25 seconds after touchdown and continued to scan for five minutes. The picture was assembled from left to right during the 20 minutes it took to transmit the data from the Orbiter relay station to Earth. The first segment to be displayed was a narrow strip at the far left. About all that could be determined was the presence of bright and dark areas in the scene, but even that was cause for elation. Ironically, some viewers were more impressed by the picture of the footpad than by the view of the martian surface, marveling at the fidelity with which the rivets were displayed.

The lower edge of the picture is at a slant range of about 1.5 m, the upper edge about 2 m. The larger rocks are about 10 cm across...

The vertical streaking in the left quarter of the picture stimulated a variety of explanations. Those of us familiar with camera operation doubted that it represented a camera malfunction. Instead, something was causing the light levels to vary during the first 1 1/2 minutes following touchdown. It was suggested that clouds were passing in front of the Sun, or, more improbably, that the deployed parachute was casting a shadow as it drifted between the Sun and the Lander. It seemed most likely that dust, kicked up at the time of the landing, was briefly entrained in the lower atmosphere between the camera and the surface. This argument was strengthened by the observation of a sizable accumulation of dirt in the upper concave part of the footpad. Demonstration of the transient nature of the effect is provided by a later picture of the same area taken with the same approximate lighting. Note that the streaks have disappeared.
-- The Martian Landscape - The First Picture

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