Geologic characteristics of relatively high thermal inertia intracrater deposits in southwestern Margaritifer Terra, Mars

Abstract

Twenty-one craters in southwestern Margaritifer Terra exhibit unusually warm interior deposits in nighttime Thermal Emission Imaging System (THEMIS) infrared images. These deposits exhibit nighttime temperatures as high as 223 K and are 5-18° warmer than the surrounding plain. Thermal inertia values, derived from Thermal Emission Spectrometer (TES) data, are greater for the deposits than the plains, with maximum values between ∼455 and 675 J m-2 K-1 s-1/2. Analysis of THEMIS thermal inertia data having nearly an order of magnitude better spatial resolution shows that the deposits can have a thermal inertia as high as ∼1060 J m-2 K-1 s-1/2. Albedo and dust cover index values suggest that both the deposits and the surrounding region are generally dust-free. Compositional analysis with TES and THEMIS data show that though a small number of the deposits may have isolated compositional differences, the majority of the deposits have a composition similar to that of the surrounding plains. The geomorphology of the craters as viewed from Mars Orbiter Camera (MOC) images shows that the deposits are coherent units, rather than sand deposits, an observation that is consistent with the relatively high thermal inertia values. If these deposits are coherent rock units, as the results of our study suggest, possible methods of formation include emplacement of primary igneous material or lithification of sediments from surrounding terrain. Copyright 2007 by the American Geophysical Union.