Vastitas' Dust Devils - Sol 104

The Surface Stereo Imager on NASA's Phoenix Mars Lander caught this DD in action West-South/West of the Lander at 11:16 M.L.T. on Sol 104, such as Sept., 9, 2008.
Dust Devils (a.k.a. "DD") have not been detected in any Phoenix images from earlier in the Mission, but at least 6 were observed in a dozen images taken on Sol 104.
DD are whirlwinds that often occur when the Sun heats the surface of Mars, or some areas on Earth. The warmed surface heats the layer of atmosphere closest to it, and the warm air rises in a whirling motion, stirring dust up from the surface like a miniature tornado. The DD visible in the center of this image just below the horizon is estimated to be about 400 meters (about 1300 feet) from Phoenix, and 4 meters (13 feet) in diameter. It is much smaller than DD that have been observed by NASA's Mars Exploration Rover Spirit much closer to the Equator. It is closer in size to DD seen from orbit in the Phoenix landing region, though still smaller than those.

The image has been enhanced to make the dust devil easier to see.