Postimpact Evolution of the Southern Hale Crater Ejecta, Mars

摘要

As one of the youngest large (>100 km wide) impacts on Mars, Hale crater offers a unique opportunity to observe well-preserved deposits of Mars' former interior. We utilize visible imagery (Context Camera [CTX] and High Resolution Imaging Science Experiment [HiRISE]) and elevation data (Mars Orbiter Laser Altimeter [MOLA], High Resolution Stereo Camera [HRSC], and HiRISE stereo pairs) to examine the region south of Hale crater, which contains the greatest density of landforms caused by with the impact. Linear depressions, mounds, and polygons indicate that the ejecta material contained volatiles and underwent substantial postimpact geomorphic evolution after it was emplaced. Ejecta landform formation was facilitated by volatiles, likely water ice displaced from the subsurface during the impact, contained within the material. We suggest that the ejecta flowed into valleys where it acted in a manner similar to terrestrial debris flows, leaving mounds, high-standing deposits, lobate flow margins, and fan structures. Continued flow and settling of the ejecta then caused deposit dewatering, producing networks of linear depressions, particularly in places where the flows of ejecta were constricted. However, these landforms are not present everywhere, and their formation was likely influenced by topography. This work highlights that, while volatiles were present over much of Hale crater's ejecta blanket, the surface expression of them is spatially variable on local and regional scales.