![Click here for movie of PIA11988](https://webarchive.library.unt.edu/eot2008/20090513050110im_/http://photojournal.jpl.nasa.gov/figures/PIA11987_fig1.jpg)
Click on the image for movie
This movie shows the southern high-latitudes region of Mars from March 19
through April 14, 2009, a period when regional dust storms occurred along
the retreating edge of carbon-dioxide frost in the seasonal south polar
cap. Compared with a full-hemisphere view (see PIA11987), this view shows more
details of where the dust clouds formed and how they moved around the
planet.
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.
Malin Space Science Systems, San Diego, provided and operates the Mars
Color Imager. NASA's Jet Propulsion Laboratory, a division of the
California Institute of Technology in Pasadena, manages the Mars
Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington.
Lockheed Martin Space Systems, Denver, is the prime contractor for the
project and built the spacecraft.