Historical Extent of Mars’ South Polar Massive CO2 Ice Deposit

Science/Technical/Management. Mars’ South Polar Massive CO2 Ice Deposit (‘CO2 Deposit’) has a mass comparable to its current, primarily CO2, atmosphere. It exchanges with the atmosphere and CO2 adsorbed in the regolith on ~100 kyr timescales in response to orbital obliquity variations. Recent work predicts that the total inventory of CO2 available to exchange between the CO2 Deposit, atmosphere, and regolith on obliquity timescales is 5-to-50× Mars’ current atmospheric mass (presently held mainly in the regolith). The prediction implies that during recent (<1 Myr ago) obliquity minima (~15°), polar CO2 ice deposition (sourced primarily from regolith CO2 desorption) would create a paleo-CO2 Deposit 5-50× more massive than the present-day (obliquity = ~25°) CO2 Deposit. We conducted a pilot study that identified never-before-reported morphologic markers previously only associated with the present-day CO2 Deposit that extend to ~81° S (~14× the current CO2 Deposit area), consistent with this prediction. Determining the mass of Mars’ obliquity-timescale exchangeable CO2 reservoir is critical for understanding many aspects of Mars’ climate, especially the availability of conditions necessary to sustain near-surface liquid water during the Noachian, Hesperian, and Amazonian.

Goals/Methodology. We have two objectives: Objective 1. Determine the 2-dimensional extent of the paleo-Massive CO2 Ice Deposit. Objective 2. Determine the mass of the paleo-Massive CO2 Ice Deposit. These objectives will be met with three Tasks:
Task 1. Map paleo-Massive CO2 Ice Deposit morphological markers. We will map the region 80° S to the pole on a 1-km grid to identify the complete distribution of paleo-CO2 Deposit terrain (e.g., terrains identified in our pilot study) and other terrain types (for contextualization).
Task 2. Analyze morphologic evolution of CO2-Deposit-related features and calculate extent of paleo-CO2 Deposit. We will perform morphologic analysis linking terrains on with present-day CO2 Deposit to their degraded state in paleo-CO2 Deposit terrain. This analysis will allow identification of the maximal areal extent of the paleo-CO2 Deposit based on Task 1 terrain mapping, in preparation for comparison to modeled paleo-CO2 glacial cycle extent (Task 3).
Task 3. Numerically model paleo-Massive CO2 Ice Deposit development to assess Mars’ obliquity-timescale CO2 budget. We will use a numerical model of CO2 global climate exchange and CO2 glacial flow to find the obliquity-timescale exchangeable CO2 inventory that yields a maximal CO2 glacial areal extent that most closely matches the observed extent (from Task 2).