August 2, 1999, marks the spring equinox for the martian southern hemisphere. It is also the start of autumn for regions north of the equator. Winter in the south has finally come to a close, and the seasonal frosts of the wintertime south polar cap are retreating. Small, local dust storms frequently occur along the margins of the polar cap, as the colder air blowing off the cap moves northward into warmer regions.
The wide angle camera view of Mars shown here was obtained by the Mars Global Surveyor Mars Orbiter Camera in late July 1999, about 1 week before the start of southern spring. The frosty, retreating south polar cap (white) is seen in the lower quarter of the image, and wisps of dust storm clouds (grayish-orange in this view) occur just above the cap at the lower left. The southernmost of the large Tharsis volcanoes, Arsia Mons, is seen at the upper left. Arsia Mons is about 350 kilometers (~220 miles) across.
Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.