Martian North Polar Cap (NASA, Mars Global Surveyor, 09/12/98)
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 late-March 1999. 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 portrayed. 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.
Image credit: NASA/JPL/Malin Space Science Systems