Evidence for scalloped terrains on 67P

• Main Authors: Bouquety, Axel, Groussin, Olivier, Jorda, L., Séjourné, Antoine, Costard, François, Bouley, Sylvain
• Other Authors: Laboratoire d'Astrophysique de Marseille (LAM), Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2021
• Subjects: [SDU]Sciences of the Universe [physics]; Keller; Quadrangle; Ice; permafrost; Alaska
• Online Access: https://hal.science/hal-03585144; https://doi.org/10.5194/espc2021-25

Virtual meeting International audience The Rosetta mission provided detailed data of the surface of the nucleus of comet 67P/Churyumov-Gerasimenko. The analysis of these data, and especially the images of the Narrow Angle Camera (NAC) from the Optical Spectroscopic and Infrared Remote Imaging System (OSIRIS instrument; Keller et al., 2007), revealed the morphological diversity of the nucleus surface (El-Maarry et al., 2019). Among these morphologies, depressions have been observed in several regions (Fig.1).Figure 1: Example of studied depression located on Ma'at region (NAC image, 1 m/pixel). The white arrows indicate the depressionsThe origin of these structures remains unclear and several hypotheses have been proposed: (1) the depressions could be indicative of scarp retreat (Vincent et al., 2016; El-Maary et al., 2017), (2) they mark the location of future cliff collapses (Pajola et al., 2016d), and (3) they are seasonal structures shaped by the changes induced by perihelion approach (Groussin et al., 2015). In a previous study, we studied two of these depressions, located in the Ash region, by a comparative morphometrical analysis (Bouquety et al., 2021). We observed that the two depressions grew by several meters during the last perihelion passage, and that this growth is not necessarily linked with cliff collapses. Thus, in that case, the sublimation of ices certainly played a key role in shaping these depressions. On Earth and Mars, there are similar depressions with the same shape and geometry that are controlled by thaw processes. These depressions are called thermokarstic lakes on Earth and scallops depressions on Mars (Fig.2). On both planets, these periglacial structures result from the degradation of an ice rich permafrost (Costard and Kargel, 1995; Morgenstern et al., 2007; Séjourné et al., 2011). Figure 2: Example of thaw depressions. (a) Thermokarstic lakes in Alaska on Earth (Digital Orthophoto Quadrangle DOQ, 5 m/pixel). (b) Scalloped terrain in Utopia planitia on Mars (HiRISE image, 50 ...