Mars Global Surveyor's Mars Orbiter Camera obtained its last
SPO-2 images of Mars on September 12, 1998. SPO-2, or 'Science
Phasing Orbit-2', took place between early June and mid-September
1998. Shown above are MOC wide angle (red and blue band) images
of the martian north polar region obtained around 3:15 a.m. PDT on
September 12, 1998. This color composite was made using red and
blue wide angle MOC images 55001 and 55002--these were the last
pictures taken of the planet until the camera resumes its work in
The north polar layered deposits, a terrain believed composed
of ice and dust deposited over millions of years, dominates this view.
The swirled pattern in the images above are channels eroded into this
deposit. The pattern is accentuated by the illumination and seasonal
frost differences that arise on sun-facing slopes during the summer.
The permanent portion of the north polar cap covers most of the region
with a layer of ice of unknown thickness.
At the time this picture was obtained, the martian northern
hemisphere was in the midst of the early Spring season. The margin
of the seasonal carbon dioxide frost cap was at about 67° N, so the
ground throughout this image is covered by frost. The frost appears
pink rather than white; this may result from textural changes in the
frost as it sublimes or because the frost is contaminated by a small
amount of reddish martian dust. Please note that these pictures have
not been 'calibrated' and so the colors are not necessarily accurately
In addition to the north polar cap, the pictures also show some
clouds (bluish-white wisps). Some of the clouds on the right side of the
images are long, linear features that cast similar long, dark shadows
on the ground beneath them.
When the MOC resumes imaging of Mars in March 1999, summer
will have arrived in the north polar regions and the area surrounding the
permanent polar cap will appear much darker than it does here. The
dark features surrounding the cap are sand dunes, and these are
expected to darken over the next several months as seasonal ice
sublimes and is removed from the surface.
Photo Credit: NASA/JPL/Malin Space Science Systems
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