"Sometime between September 8, 2012 and November 30, 2012, there was a major change in which the parachute extension to the southeast (lower right) was moved inward, so the parachute covers a smaller area," observes Alfred McEwen, planetary geologist at the University of Arizona in Tucson and HiRISE principal investigator. "In the same time interval some of the dark ejecta around the backshell brightened, perhaps from deposition of airborne dust."
McEwen also points to another windy event between Dec. 16, 2012 and Jan. 13, 2013, which caused the parachute to shift to the southeast.
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Apart from being a minor curiosity and a lovely reminder that we have satellites capable of observing temporal weather events on another planet, these flapping events may help explain why the Viking landers' parachutes still remain visible from orbit since their landing in 1976 - windy events dust-off the bright parachute material. Also, the motion of a large piece of fabric on the surface of Mars provides a direct view of the weather conditions on the ground, much like a windsock on an airfield provides pilots with general information about wind direction and speed.