[Illustration: 16. Photomosaic globe of Mars made of more than 1500
computer-corrected pictures taken by _Mariner 9_ in 1971 and 1972.
The residual North Pole ice cap is at the top.]
This 1.2-meter (4-foot) diameter globe of Mars was assembled from
photographs taken by _Mariner 9_, an unmanned spacecraft that orbited
the planet from November 14, 1971, until October 27, 1972. This globe is
the first such photomosaic ever made of a planet.
Launched on May 30, 1971, _Mariner 9_ succeeded in photographing the
entire surface of the planet. In its 349 days of orbit around Mars,
_Mariner 9_ circled the planet 698 times and took more than 7300
photographs.
In its highly elliptical orbit, _Mariner 9_ obtained a sequence of
overlapping wide-angle photographs. These were processed by a computer
to remove the known variations in _Mariner 9_ camera response and
geometric distortions, as well as to enhance surface detail. The mosaic
made from the processed photographs is a pictorial presentation of the
Martian surface which shows ridges and craters in the dark regions and
on the bright polar caps with equal clarity. Surface features are in
correct relationship and perspective, with only a minimum of shading
difference between individual photographs.
In assembling the photomosaic, each picture was taped in place on the
globe. Then, the match of adjacent pictures was assessed to determine
where to trim the edges so that sharp features would not be intersected.
The edges of each print were feathered so that when the prints were
glued into place, the lines between pieces were almost
indistinguishable. The complete globe received a thin protective
coating.
This globe and copies of it enable scientists to study the geology and
morphology of Mars from a perspective never before possible.
The photomosaic globe was designed and assembled at the Jet Propulsion
Laboratory, California Institute of Technology, Pasadena, California.
The Mars Globe is on loan from the National Aeronautics and Space
Administration.