THERMAL AND ALBEDO MAPPING OF THE POLAR-REGIONS OF MARS USING VIKING THERMAL MAPPER OBSERVATIONS .1. NORTH POLAR-REGION

We present the first maps of the apparent thermal inertia and albedo o f the north polar region of Mars. The observations used to create thes e maps were acquired by the infrared thermal mapper (IRTM) instruments on the two Viking orbiters over a 50-day period in 1978 during the Ma rtian early northern summer season. The maps cover the region from 60 degrees N to the north pole at a spatial resolution of 1/2 degrees of latitude. The analysis and interpretation of these maps is aided by th e results of a one-dimensional radiative convective model, which is us ed to calculate diurnal variations in surface and atmospheric temperat ures, and brightness temperatures at the top of the atmosphere for a w ide range of assumptions concerning aerosol optical properties and aer osol optical depths. The results of these calculations show that the e ffects of the Martian atmosphere on remote determinations of surface t hermal inertia are more significant than have been indicated in previo us studies. The maps of apparent thermal inertia and albedo show a gre at deal of spatial structure that is well correlated with surface feat ures. The north residual polar cap has a very high apparent thermal in ertia, and is interpreted to contain dense, coarse-grained, or solid w ater ice that extends from within 2 mm of the surface to depths of at least 1 m below the surface. Detached, bright water ice deposits surro unding the residual cap also have very high apparent thermal inertias, and are interpreted to have similar properties. Polar layered deposit s surrounding the north residual cap also have high apparent thermal i nertias, and are also interpreted to contain near-surface water ice. M ariner 9 images Of the north residual cap obtained in 1972 show much l ess bright water frost coverage than Viking images obtained three Mars years later in 1978, and it is suggested that layered deposits may be actively forming in these areas over interannual timescales. Dark tra nsverse dune deposits adjacent to the north residual cap have relative ly low apparent thermal inertias, as do arcuate scarp regions within t he polar layered deposits that appear to be major sources of polar dun e material. The apparent thermal inertias of these north polar dune de posits are significantly lower than those of intracrater dune deposits at lower latitudes. The north polar dunes are interpreted to be compo sed of dark unconsolidated material that is being eroded from the laye red deposits and transported away from the pole by saltation. The regi on poleward of 60 degrees N contains no large low thermal inertia regi ons, which is interpreted as evidence that atmospheric dust is not acc umulating in the north polar region under present climatic conditions.