Abstract DGP2026-48

Planet Four: Inter- and Intra-annual Variability of Dark Regolith on Ice Coverage at the Martian South Polar Region

K.-Michael Aye (1), Tom Ihro (1), Tim Michaels (2), Ganna Portyankina (3), Megan E. Schwamb (4) and Candice J. Hansen (5)

(1) Freie Universität Berlin, Germany, (2) University of Wisconsin–Madison, Madison, Wisconsin, USA, (3) Deutsches Zentrum für Luft- und Raumfahrt (DLR), Berlin, Germany, (4) Astrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, UK, (5) Planetary Science Institute, Tucson, AZ, USA

The seasonal deposition of dark regolith material on Mars' south polar ice cap through CO2 gas jet eruptions significantly influences the regional albedo and consequently affects the surface-atmosphere energy budget. Understanding the spatial and temporal evolution of this dark material coverage is crucial for accurately modeling the thermal balance and sublimation dynamics of the polar regions during spring and summer seasons. Previous studies have estimated a surface coverage of approximately 20%, and our Planet Four dataset allows us to update these estimates.

We present a comprehensive analysis of dark regolith coverage derived from HiRISE observations spanning six Mars-years (MY 28-33), utilizing citizen scientist classifications from the Planet Four project. Our dataset comprises 463 HiRISE observations analyzed using tile-based statistical methods, revealing coverage fractions ranging from less than 1% to over 30%, with a mean coverage of 6.89% ± 6.13% across all observations.

The multi-year dataset enables both interannual comparisons, revealing year-to-year variations in coverage extent and distribution, and intra-annual analysis tracking the seasonal progression of regolith deposition throughout individual Mars-years. By binning observations according to solar longitude that span a range of Ls = 160-340°, we characterize the temporal evolution of surface coverage as CO2 ice sublimation proceeds and jet activity deposits material onto the seasonal ice cap. Our analysis reveals remarkable repeatability between different martian years, with interesting variations for MY 33.

The statistical characterization includes measures of coverage heterogeneity and homogeneity across observed tiles (i.e., HiRISE observation subframes that are identified as one Planet Four study tile). Note that each of these HiRISE observations cover a surface area sufficiently large enough to observe a highly varying CO2 gas jet activity within many of the HiRISE images (so, across all subframe tiles for the whole image). Our introduced measures for surface coverage homogeneity allows us to quantify if the coverage is more or less uniform across one large HiRISE observation or highly heterogeneous. These differences reflect the complex interplay between jet eruption dynamics, local topography, and prevailing wind conditions during deposition.

We will show that this kind of analysis drastically benefits from improved image coregistration of existing datasets, as that would enable automated, large-scale surface change detection studies at the precise locations of individual eruption sites, facilitating detailed investigations of multi-year surface evolution and time-series analysis of the surface changes caused by the deposited regolith.