The History of Dirt at the Phoenix Site

Images from the MECA microscopes directly demonstrated that: The color of the Phoenix soil is dominated by a small fraction of ubiquitous red dirt (URD); the mass is dominated by small sand-sized particles with evidence of aeolian transport; small white flakes may represent some of the salt content; and despite observation of submicron platy particles, the soil is deficient in clay-sized particles. This talk focuses, however, on indirect event of the soil history. Chemical findings from MECA constrain the salt and carbonate content. Humidity and temperature measurements suggest that water vapor moves over a diurnal cycle from the soil/ice boundary to the soil/atmosphere boundary. Both chemical and microscopic homogeneity suggest that aeolian mixing is on a faster scale than alteration processes or photochemical deposition. Observations of ice suggest that a fraction of the soil may be periodically embedded as pore-filled permafrost, but little evidence for active cryoturbation can be seen. [This work was performed at the Jet Propulsion Laboratory, Caltech, with funding from NASA.]