Tracking the south polar seasonal cap retreat of Mars using computer vision

We use daily polar stereographic mosaics obtained from the Mars Color Imager (MARCI) to autonomously track the recession of the South Polar Seasonal Cap (SPSC) during Mars Years (MYs) 28 to 31, for the period Ls = 178° to Ls = 345°. Utilizing an autonomous approach, we can delineate the SPSC by fitting an ellipse, offering the advantage of faster processing. This allows us to monitor the recession with enhanced time sampling capabilities. The SPSC recession is divided into two segments separated by a discontinuity at Ls = ~260°, corresponding to the detachment of the Mountains of Mitchel seasonal cap from the main cap. Before the discontinuity, the SPSC exhibits variability where the recession rate can vary by up to 50%, with the fastest recession occurring at Ls = ~235° and the slowest at Ls = ~191°. After the discontinuity, the SPSC experiences reduced variability and undergoes a monotonic deceleration until Ls = ~319°, gradually approaching the stable latitude of ~86° S, consistent with the South Polar Residual Cap. MY 28 demonstrates distinct behavior in response to the Global Dust Storm (GDS), as the SPSC was smaller and sublimated faster before the onset of the storm compared to the 4-year average. Plain language summary The seasonal frost layer on Mars, consisting of frozen carbon dioxide, covers vast expanses during the winters. This frost forms as carbon dioxide gas in the atmosphere turns into solid ice on the surface, impacting the overall atmospheric pressure. We studied daily images captured by the Mars Color Imager (MARCI) to automatically monitor the retreat of the South Polar Seasonal Cap (SPSC) as it returns to the atmosphere during the spring over a span of four years. To achieve this, we employed a computer programming language called Python and a publicly available software library designed for visual analysis. By fitting an ellipse that most closely resembles the contour of the cap, we were able to trace and measure the change in the SPSC over time and determine how quickly SPSC shrinks. We discovered that our strategy produces results that are similar to those of previously published approaches, but in a lot less time and with increasing accuracy. We noticed new patterns in the seasonal retreat of the seasonal cap, including brief periods of faster shrinking, likely influenced by wind patterns. Additionally, we investigated a prominent icy area known as the Mountains of Mitchel seasonal cap and found that its behavior differed before and after a significant global dust storm in Mars Year 28.