Due to the lack of an atmosphere on the Moon, the Apollo lunar flags had an upper horizontal pole in order to make them fully hoisted, looking like floating in the wind. Now Mars does have an atmosphere but quite a thin one, and I wonder whether Martian winds are strong enough to make a flag on a vertical pole float. Surely, the flag would float when in a strong dust storm but such storms don't happen that often, do they?
In the movie Mission to Mars there's an ongoing strong storm that allegedly is able to cover most of the planet, or something like that (it's a long time I've seen the movie). Is the movie right? There, the Stars and Stripes float like on Earth in the storm, but aside from storms, when it's sunny (and I suppose it's sunny almost all the time on the crew's landing location) would the winds still be strong enough to make the Stars and Stripes float or would NASA/SpaceX play it safe and attach the flag to a horizontal pole too like on the Moon? Are there any specific considerations by NASA or SpaceX?