Studying CO2 Glaciers on Mars with Observations and Laboratory Experiments

Radar investigations have revealed that carbon dioxide ice deposits exist at the south polar layered deposits (SPLD) of Mars. The CO2 is spread across multiple units, each made up of two or three layers separated by water ice bounding layers. They measure up to 1 km thick and are covered by thin layers of water and CO2. Measurements of surface topography, along with surface features that resemble crevasses, support the interpretation that these deposits have undergone or currently undergo viscous flow – in the form of dry ice glaciers.

Glacial modeling is an effective way to constrain flow rates, basal friction, geothermal flux, and more (potentially depositional and thus climatic history), but the current state of the literature does not provide the necessary inputs for CO2 ice rheology or for the physical state of the glaciers themselves, especially related to the bounding layers. In order to successfully model the glaciers in 3D, those measurements must be made.

Scientific Goals: We aim to better constrain the flow of CO2 ice in martian conditions with laboratory studies of CO2 ice rheology. The eventual aim is to determine when the ice flowed and for how long. This in turn will help constrain the periods of deposition of CO2 ice, revealing important events in the recent climatic history of Mars.

Methodology: Previous studies only considered CO2 rheology in narrow stress and temperature conditions over a small range of grain sizes. These were important first steps but do not correspond well to CO2 ice at martian conditions at the SPLD. Dr. Goldsby and an unnamed post-doc will create CO2 ice using novel sample fabrication methods: condensing CO2 snow and frost onto a copper plate at liquid nitrogen temperatures. By fabricating ice of small grain size, these techniques will allow exploration of both grain size-sensitive flow mechanisms involving grain boundary sliding (the properties of which are unknown for CO2 ice) as well as dislocation creep. Samples thus prepared will be deformed in ways expected to occur on Mars.

Previous mapping only characterized the thickness and spatial extent of the CO2 deposits, but much more detail can be extracted from the topographic and radar measurements. Of critical importance are two bounding layers that separate the CO2 deposits into three well-defined vertical units. Those layers were mapped only approximately, but they must affect the stress-strain and friction relationships of the dry ice glaciers. Dr. Smith will map the thickness and extent of these layers in order to derive important boundary conditions for the CO2 glaciers. He will also map surface features resembling pressure ridges and crevasses that were not discussed

in previous studies of the CO2 units. Those features, and the water ice bounding layers, provide excellent information on the stress conditions of the glaciers, information that will be used in later 3D modeling. Dr. Smith will lead this effort.