NASA/JPL/Malin Space Science Systems
The spiraling feature near the center of this Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image is known as a cycloidal marking. Patterns like this can also occur on Earth. On Mars, the cycloidal pattern---and all of the other dark streaks in this picture---are thought to have been formed by passing dust devils. On Earth, cycloidal markings have been observed to result from some tornadoes. The pattern is created when more than one vortex (spinning column of air) is travelling, and spinning, together. This picture is near 62.9°S, 234.7°W. Sunlight illuminates the scene from the upper left.
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, California. 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, California and Denver, Colorado.