How the martian residual south polar cap develops quasi-circular and heart-shaped pits, troughs, and moats

For the first time, we report the development of dark fans on the sides of the CO2 mesas and the fracturing and deterioration of the initially smooth upper surface of CO2 mesas. We interpret these features as indicating the sublimation and subsequent escape of CO2 from the interiors of mesas, which undermines structural support of mesa tops, causing them to collapse. The collapse of mesa tops, along with uneven deposition of CO2 ice, creates steep scarps that erode during the summer due to preferential sunlight absorption. During the winter, CO2 deposition acts to smooth topography, creating gently sloping ramps. We propose that the interplay between the steep scarps and gentle slopes leads to either quasi-circular pits, heart-shaped pits, linear troughs, or moats, depending on local conditions.