RE-ANALYSIS OF MARTIAN CRATER EJECTA CHARACTERISTICS IN THE THERMAL INFRARED

Thermal infrared remote sensing has been used to explore the surface of Mars since the late 20th century, providing datasets that could contain information on surface changes over decadal time scales. Impact crater ejecta, in particular, exhibit characteristic variations in both albedo and thermophysical properties related to variations in particle size and packing that result from both primary impact processes and later modification. Our study is focused on craters examined in visible and infrared data from the Phobos and Viking missions [1] with the goal of extending these analyses to more recent datasets from Mars Global Surveyor (MGS), Mars Reconnaissance Orbiter (MRO), and Mars Odyssey to explore changes in the visible and thermophysical properties of the examined craters.

Re-analysis was completed via compilation of data into an ArcGIS database, beginning with initial results from the Viking Infrared Thermal Mapper (IRTM) and the geographic locations of craters examined previously [1]. Visual mapping of crater ejecta deposits was completed using more recent imagery (Odyssey's Thermal Emission Imaging Spectrometer - THEMIS and MRO's Context Camera). Ejecta maps were then used to verify that albedo and thermal inertia values derived from IRTM data were consistent with previous work and to extend these analyses to later datasets, beginning with thermal inertia maps from the Thermal Emission Spectrometer (MGS-TES) [2].

Preliminary results indicate that our re-analyses do a reasonable job of replicating Viking-era measurements and reproducing those results using MGS-TES data. This indicates that we have a valid comparison and any significant variations are likely due to surface changes. Examination of visible imagery indicates these are due to deposition/removal of dust: exposure of coherent ejecta correlates with increases in thermal inertia, while decreases in thermal inertia correspond to mantled ejecta. Ongoing work is focused on further examination of the visible morphologies of craters that exhibit changes between IRTM and MGS-TES to better identify the cause of these changes, and to extend our analyses to more recent results from THEMIS.

[1] Betts and Murray, 1993. JGR 98, p. 11043. doi: 10.1029/93je00107.

[2] Putzig,et al., 2005. Icarus 173, p. 325. doi:10.1016/j.icarus.2004.08.017.