Postimpact Evolution of the Southern Hale Crater Ejecta, Mars. Issue 9 (14th September 2020)

• Record Type: Journal Article
• Authors: Collins‐May, J. L.; Carr, J. R.; Balme, M. R.; Ross, N.; Russell, A. J.; Brough, S.; Gallagher, C.
• Is Part Of: Journal of geophysical research. Volume 125:Issue 9(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-09-14
• Subjects: Hale crater -- dewatering -- ejecta -- volatiles; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1029/2019JE006302
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: 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. Plain Language Summary: When meteorites hit Mars, material from underground is brought to the surface. The appearance of this material on the surface provides clues about the Martian subsurface. Given its size, Hale crater is young compared to other craters on Mars. This means that its deposits are better preserved and may hold more clues about their formation than older crater deposits. Detailed reconstructions of how these deposits changed over time tell us about the material they were originally made of and what was in the subsurface before Hale crater formed. This work provides the first detailed description of the ejecta deposits to the south of Hale crater and analyzes how features within the ejecta may have been created. The appearance of the Hale crater deposits suggests that the deposits once contained water, which most likely came from ice that was in the ground when the meteor that formed Hale crater impacted. In some locations, so much water was present in the Hale crater deposits that water flowed across the surface and carved channels, as well as formed mounds and cracked surfaces. However, these features are found only in certain locations, suggesting that the processes that formed them did not occur everywhere. Key Points: Ejecta deposits south of Hale crater exhibit a variety of previously undocumented landforms Ejecta surface morphology is the result of water incorporated into the ejecta, facilitating a diverse range of geomorphic processes Some landforms (e.g. mounds) may be unique to this region of Hale crater's ejecta