Two 2001 images from the Mars Orbiter Camera on NASA's Mars Global Surveyor orbiter show a dramatic change in the planet's appearance when haze raised by dust-storm activity in the south became globally distributed.
At left, an image from late June 2001 shows clear conditions over much of the planet, with regional dust-storm activity occurring in the Hellas basin (bright oval feature) near the edge of the south polar cap. At right, a July 2001 image from the same perspective shows the planet almost completely enveloped. Dust extends to altitudes of more than 60 kilometers (37 miles) during global-scale storms.
The clearing phase can last for several months. An additional image from later during this global dust storm is included with these two at http://photojournal.jpl.nasa.gov/catalog/pia03170 .
Malin Space Science Systems (MSSS), San Diego, and Caltech built the Mars Orbiter Camera, which was operated by MSSS. NASA's Jet Propulsion Laboratory, Pasadena, California, managed the Mars Global Surveyor Project for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, built the orbiter and partnered with JPL in mission operations.