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New Insights Into the Properties of the Cryptic Terrain of the South Polar Seasonal Cap of Mars through Laboratory Investigations and Orbital Data

Presentation #300.01 in the session Martian Ice, Climate, and Habitability (Oral Presentation)

Published onOct 23, 2023
New Insights Into the Properties of the Cryptic Terrain of the South Polar Seasonal Cap of Mars through Laboratory Investigations and Orbital Data

The seasonal caps of Mars grow from of meteoric precipitation and direct deposition of carbon dioxide ice (CO2), the primary constituent of the martian atmosphere, and lesser quantities of impurities like dust and water ice (H2O). The two seasonal caps, of the north and south, reach maximal extents of ~50° in either hemisphere during winter and retreat regularly throughout the spring and into early summer, when they disappear, until late summer or early fall when they return.

Expressed in the southern seasonal cap is an enigmatic “Cryptic Terrain”, an area bounded by ~60° - 210° E and ~75° - 85° S. Unlike the rest of the seasonal cap, which maintains a high albedo and low surface temperatures, the Cryptic Terrain remains cold enough for solid CO2 at the surface but with much lower albedo. The “Kieffer Model” posits that the CT ice is transparent, which permits sunlight to warm the ice-ground interface enough to cause gas pockets to grow and eventually explode into the air, trailing with it dust and other dark materials to form fans and morphological features called spiders.

Open questions about the CT are: how is it able to maintain the low albedo and low temperature, even as solar radiation increases throughout spring without sublimating fully? Also, why does the CT behave differently from the rest of the seasonal cap?

In this presentation, we will combine recent measurements of the Bi-directional Reflectance Distribution function of various phases of CO2 ice, made in the MARVIN chamber at York University, with observations made by the Mars Color Imager (MARCI) to elucidate the differential properties of the CT from the rest of the seasonal cap. Using experiments and observations, we will explain how the CT can maintain a low albedo and low temperature without radiation-driven runaway sublimation. Further, we will provide interpretations of what can cause these differential properties, related to surface pressure and temperature regimes that create the different phases of CO2 ice crystals that are expressed in the seasonal cap and CT. The Cryptic Terrain is a little less cryptic now.

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