Remote Characterization of Physical Surface Characteristics of Mars Using Diurnal Variations in Apparent Thermal Inertia

Analysis of the Martian surface today can provide insight into the processes that may have affected it over its history. Information about the physical surface characterization of a region can help determine the degree of sorting it has experienced and/or its geologic maturity. Sub-resolved “checkerboard” mixtures of materials with different horizontal thermal inertia mixtures can lead to differences in the apparent thermal inertia values inferred from night and day radiance observations. Standard methods for deriving thermal inertia from orbit via the THermal EMission Imaging System (THEMIS) can give values for the same location that vary by as much as 20% between images (Fergason et al., 2006b). Such methods assume that each pixel contains material of a single, uniform thermal inertia. Here, it is proposed that if a mixture of low and high apparent thermal inertias is present within a pixel, the inferred thermal inertia will be strongly dominated by the thermal inertia of whichever surface is warmer at the time of the measurement. This effect will result in a change in thermal inertia values inferred from measurements taken at different times of day and night. Therefore, a correlation is hypothesized between the magnitude of diurnal variations in apparent thermal inertia values and the degree of non-uniformity of thermal inertias present in a given pixel location.Preliminary work has shown that the magnitude of such diurnal variation in inferred thermal inertias is sufficient to detect geologically useful differences in surfaces mixtures. Mapping the difference in apparent thermal inertias from day and night THEMIS observations may prove to be a new way of distinguishing surfaces that have relatively uniform thermal inertias from those that have mixed thermal inertias.