Cycles of Deposition and Erosion in Eastern Arabia Terra, Mars

The erosion, transport, and deposition of dust are pervasive and active global processes, yet current and past cycles of dust deposition and possible erosion are poorly understood. Eastern Arabia Terra is an ideal location to characterize current dust deposits and assess rates, cycles, and the history of dust accumulation because dust is likely currently accumulating in this region [1], and higher thermal inertia material is observed within craters that may offer a window into a previous depositional environment. In addition moderate elevations and atmospheric pressures, rather than the extreme elevations present in Tharsis Montes and Elysium Planitia, provide a more straightforward interpretation of thermal inertia, wind velocities, and dust deposition rates. MOC and THEMIS visible images, THEMIS day and night infrared images, THEMIS and TES thermal inertia, TES albedo, and MOLA topographic profiles were analyzed to produce a thermophysical unit map of eastern Arabia Terra. THEMIS thermal inertias are critical for this effort because it provides quantitative information used to characterize each unit at a higher spatial resolution than previous datasets. THEMIS thermal inertia [2] is calculated from THEMIS band 9 nighttime temperatures using a 7 dimensional look-up table and interpolating on a pixel-by-pixel basis. The primary sources of error include uncertainties in the nighttime temperature of the surface (10%), slopes along crater walls (5%, assuming an uncertainty of 5 degrees), and variations in albedo (2%, assuming an uncertainty of 0.01) and elevation (2%, assuming an uncertainty of 200 meters) that are not resolved in the TES and MOLA data sets, respectively. This region has been mapped into 5 thermophysical units: 1) dust; 2) intracrater sand; 3) wind streaks associated with craters; 4) resistive material within craters; and 5) relatively high inertia material surrounding Arabia Terra dust deposits. The dust unit is constrained to be 5 cm to several meters thick because the albedo and thermal inertia of this material is uniform [3], while topographic features are clearly observed through this mantle [1]. Estimates of dust deposition rates imply young ages of less than 105 years for these deposits [1], so there must be a current process of dust removal that is preventing a thicker deposit from forming. In addition, resistive material within craters are the highest thermal inertia material in the region (400-450 J m-2 K-1 s-1/2), and often contain layers or preserved dunes that appear etched or scoured, suggesting current erosion of this material. The presence of resistive layers and duneforms that are currently undergoing erosion indicate that there have been multiple cycles of deposition and erosion in Arabia Terra, and also suggests that past climates on Mars circulated dust in a manner much different than is currently observed. References: [1] Christensen, P. R. (1986), Regional dust deposits on Mars: Physical properties, age, and history, J. Geophs. Res., 91(B3) 3533-3545. [2] Fergason, R. L., P. R. Christensen, H. H. Kieffer, High-resolution thermal inertia derived from THEMIS: Thermal model and applications, to be submitted. [3] Wells, E. N., J. Veverka, and P. Thomas (1984), Mars: Experimental study of albedo changes caused by dust fallout, Icarus, 58(3), 331-338.