Structure of Carbon Dioxide Crystals (Martian Snow) as Observed in TEM Replicas and Low Temperature SEM Images

Abstract Earth and Mars are the only planets in our solar system having polar ice caps that expand and contract in response to changes in the seasons. On Earth, the polar caps are composed of water-ice (snow crystals). Whereas, on Mars the extreme low temperatures at the polar cap regions result in the precipitation of CO2 ice (Martian snow) in addition to water-ice. Viking spacecraft have recorded various spectral data on this CO2 mantle and the transmission spectra for solid CO2 have been measured in the laboratory; however, little is known about the structural features of the crystals. Because previous studies have shown that low temperature SEM could be used to image structural variation of snow crystals34 and because data on the structure of CO2 crystals are needed to develop scattering and emission models of CO2 ice, we have attempted to image CO2 crystals. Freeze-etch replicas were made from frozen-fractured plasma membranes of yeast cells that were used as a substrate for CO2 crystal growth.