Do H2O Ice Layers Stabilize Mars’ Massive CO2 Ice Deposit?

Scientific/Technical/Management

Mars has a massive, up to 1 km-thick CO2 ice deposit buried beneath a ~10 m-thick layer of H2O ice at its south pole. If released, the Buried CO2 ice could double Mars’ atmospheric pressure and significantly alter Mars’ climate. The Buried CO2 ice deposit arises from deposition of atmospheric CO2 at times of low obliquity (less polar sunlight) that is subsequently buried by a layer of H2O ice. The manner and frequency in which the Buried CO2 is released into the atmosphere is an open question with profound implications for Mars’ climate. One hypothesis proposes that the H2O ice layer is permeable to CO2 gas flow, such that the Buried CO2 freely and gradually equilibrates with the atmosphere as Mars’ obliquity evolves. An alternative hypothesis proposes that the H2O layer physically and thermally sequesters the Buried CO2 from the atmosphere, such that the Buried CO2 is released only rarely, when the H2O layer is ablated at times of critically high obliquity. Importantly, Mars’ mean pressure throughout all of the Amazonian would be significantly lower if H2O ice layers typically sequester a portion of Mars’ CO2 inventory as Buried CO2 ice. Thus, determining whether H2O layers sequester the Buried CO2 has significant consequences for understanding Amazonian Mars’ climate, habitability, and surface geologic processes. Each of the two hypotheses predicts different morphologic development and seasonal temperature behavior of the H2O ice layer. Therefore, we will analyze the morphologic and thermal characteristics of the H2O ice layer in order to determine whether the H2O ice layer sequesters the Buried CO2.

Methodology

To achieve our goal we will:

1. Use Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) images and digital terrain models to map the morphology and structure of the topmost H2O layer.
2. Use CTX to observe the spatiotemporal exposure of the H2O layer through overlying seasonal CO2 frost and holes in the RSPC, coupled with Thermal Emission Imaging System (THEMIS) data to map the seasonal temperature cycle of the exposed H2O regions. 3. Quantitatively model the morphological development of the H2O layer and heat transfer through the H2O layer, matched to observation, to determine whether CO2 sublimes through the H2O layer.
4. Model sintering rates of the H2O layer based on the observed thermal environment to determine whether the H2O layer will become impermeable to CO2 gas flow.