  The springtime sublimation process of Mars' southern seasonal polar CO$_2$
ice cap features dark fan-shaped deposits appearing on the top of the thawing
ice sheet. The fan material likely originates from the surface below the ice
sheet, brought up via CO$_2$ jets breaking through the seasonal ice cap. Once
the dust and dirt is released into the atmosphere, the material may be blown by
the surface winds into the dark streaks visible from orbit. The location, size
and direction of these fans record a number of parameters important to
quantifying seasonal winds and sublimation activity, the most important agent
of geological change extant on Mars. We present results of a systematic mapping
of these south polar seasonal fans with the Planet Four online citizen science
project. Planet Four enlists the general public to map the shapes, directions,
and sizes of the seasonal fans visible in orbital images. Over 80,000
volunteers have contributed to the Planet Four project, reviewing 221 images,
from Mars Reconnaissance Orbiter's HiRISE (High Resolution Imaging Science
Experiment) camera, taken in southern spring during Mars Years 29 and 30. We
provide an overview of Planet Four and detail the processes of combining
multiple volunteer assessments together to generate a high fidelity catalog of
$\sim$ 400,000 south polar seasonal fans. We present the results from analyzing
the wind directions at several locations monitored by HiRISE over two Mars
years, providing new insights into polar surface winds.
