Geomorphological study of the gullies in Penticton Crater, Mars: Classification and origin

Abstract

Penticton crater, a southern hemisphere mid-latitude crater on Mars, is covered with features that are typical examples of Martian gullies that resemble the terrestrial gullies on Earth. We studied the gullies present in the Penticton crater, classified them and interpreted their formation mechanism using a remote sensing approach. A wide variety of gullies, including the classic gullies, channel gullies, alcove-apron features, linear gullies and a distinct light-toned gully, were detected in the crater. With its diverse classes of gullies and absence of a preferential orientation trend between pole-facing and equator-facing slopes, the Penticton crater is ideal for observing present-day gully activity and studying the mechanism of modern gully formation. The geomorphological study points out prominent glacial features like lobate debris apron (LDA), lineated valley fill (LVF), and concentric crater fill (CCF) in the region. Extensive morphologic evidence suggests the previous existence of latitude-dependent mantle (LDM) on the pole-facing crater walls. The morphometric analysis using parameters like length, orientation, alcove and apron width of the gullies for all four Martian seasons suggests that the gullies are currently not active. The age estimated using crater size frequency distribution indicated that the study area is 5.5 ± 0.7 Ma, which falls in the range of the high obliquity period of Mars. We propose a rare scenario where there are multiple gully-forming mechanisms acting on the same crater. Our results imply that the gullies on the pole-facing slopes are formed on LDM due to destabilization triggered by the sublimation during the recent shift in Martian obliquity. However, morphometric parameters, including the apex slopes suggest that the gullies on the steeper equator-facing slope were most likely formed by the sliding of dry granular sand.