Weather Movie, Mars South Polar Region, March-April 2009

This image is from a movie from NASA Mars Reconnaissance Orbiter showing the southern high-latitudes region of Mars from Mar. 19-Apr. 14, 2009, a period when regional dust storms occurred along the retreating edge of carbon-dioxide frost in the seasonal south polar cap. The movie combines hundreds of images from the Mars Color Imager (MARCI) camera on NASA's Mars Reconnaissance Orbiter. In viewing the movie, it helps to understand some of the artifacts produced by the nature of MARCI images when seen in animation. MARCI acquires images in swaths from pole-to-pole during the dayside portion of each orbit. The camera can cover the entire planet in just over 12 orbits, and takes about 1 day to accumulate this coverage. The indiviual swaths are assembled into a mosaic, and that mosaic is shown here wrapped onto a sphere. The blurry portions of the mosaic, seen to be "pinwheeling" around the planet in the movie, are the portions of adjacent images viewing obliquely through the hazy atmosphsere. Portions with sharper-looking details are the central part of an image, viewing more directly downward through less atmosphere than the obliquely viewed portions. MARCI has a 180-degree field of view, and Mars fills about 78 percent of that field of view when the camera is pointed down at the planet. However, the Mars Reconnaissance Orbiter often is pointed to one side or the other off its orbital track in order to acquire targeted observations by the higher-resolution imaging systems on the spacecraft. When such rolls exceed about 20 degrees, gaps occur in the mosaic of MARCI swaths. Also, dark gaps appear when data are missing, either because of irrecoverable data drops, or because not all the data have yet been transmitted from the spacecraft. It isn't easy to see the actual dust motion in the atmosphere in these images, owing to the apparent motion of these artifacts. However, by concentrating on specific surface features (craters, prominent ice deposits, etc.) and looking for the brownish clouds of dust, it is possible to see where the storms start and how they move around the planet. In additon to tracking the storms, it is also interesting to watch how the seasonal cap shrinks from the beginning to the end of the animation. This shrinkage results from subliming of the carbon-dioxide frost from the surface as the frost absorbs southern hemisphere mid-spring sunlight. The temperature contrast between the warm sunlit ground just north of the cap's edge and the cold carbon-dioxide frost generates strong winds, enhanced by the excess carbon dioxide subliming off the cap. These winds create the conditions that lead to the dust storms. http://photojournal.jpl.nasa.gov/catalog/PIA11987