Topographically Influenced Evolution of Large-scale Changes in Comet 67P/Churyumov–Gerasimenko's Imhotep Region

Abstract

Large portions of comet 67P/Churyumov–Gerasimenko’s northern hemisphere are blanketed by fallback material consisting of centimeter-sized particles termed the smooth terrains. Observations from the Rosetta mission show that the most drastic transient changes during 67P’s 2015 perihelion passage occurred within a subset of these deposits. However, we still do not understand the processes driving these changes, limiting our overall understanding of how comets evolve over both seasonal and multiorbit timescales. Herein we provide a complete documentation of scarp-driven activity on 67P’s largest smooth terrain deposit, a highly active portion of the Imhotep region that is the southernmost of all smooth terrain basins on 67P. We also present a thermal model that accurately predicts when and where scarps originate during the course of the observed activity. Assuming a uniform surface composition, our model shows that activity is heavily controlled by local topography rather than the presence of ice-enhanced hot spots on the surface. Scarps within the smooth terrain deposits in central Imhotep also exhibit a peculiar behavior, where three scarps originate from the same location but at different times and migrate in opposite directions. This behavior indicates that the landscape retains a memory of previous cycles of erosion and deposition, reflected by the depth of the volatile-rich layer. Future work will need to couple our thermal model with a landscape evolution model in order to explain the complete dynamic evolution of these terrains.

Quantifying Morphological Changes & Sediment Transport Pathways on Comet 67P/Churyumov-Gerasimenko

“…2), all of which are bounded at least on one side by a migrating scarp wall. These depressions are typically observed migrating radially from a topographic discontinuity, although the genesis point is not always clear (Birch et al, 2019;Jindal et al, 2022). The radial migration of the scarps is key in differentiating between the processes of scarp migration and plains migration.…”

“…Each Scarp migration, boulder/nucleus exposure, boulder migration, increased surface roughness in honeycombs, and pit formation in Ash and Khonsu are all classified as erosional processes. All these processes act to remove granular smooth terrain material on the surface, most likely driven by the sublimation of near-surface volatile ices (Hu et al, 2017;El-Maarry et al, 2017;Birch et al, 2019;Jindal et al, 2022). We classify boulder burials, nucleus burials, and decreased surface roughness of honeycombs as indicators of deposition of new smooth terrain sediment.…”

“…We classify boulder burials, nucleus burials, and decreased surface roughness of honeycombs as indicators of deposition of new smooth terrain sediment. While other research classifies the burial of scarps as a depositional indicator (Jindal et al, 2022), we did not include them here due to the difficulty of classifying fading scarps with varying viewing geometries. However, we still used scarp fading/burial to better interpret trends in our data when appropriate.…”

“…6). Later, in Near-Perihelion 1, the energetic scarp-driven activity in the Imhotep 1 basin intra-regionally redistributed grains, burying a boulder, five scarps, and a pit in the process (Jindal et al, 2022). In Near-Perihelion 2, as scarp migrations continued in Imhotep 1, remobilized grains partially or completely buried six scarp fronts in Imhotep 1 and a consolidated cliff in Imhotep 2 (Fig.…”

“…Past work has documented several types of morphological units on 67P, including consolidated nucleus materials (a.k.a consolidated terrain), which often outcrop in the form of cliffs within smooth terrain regions, as well as bouldered terrains, talus deposits, smooth terrains, cauliflower plains, and pitted plains (Birch et al, 2017). Surface changes that have been examined in detail include depressions (Birch et al, 2017), scarps (Birch et al, 2017, El-Maarry, 2017Jindal et al, 2022), honeycomb features (Shi et al, 2016;Hu et al, 2017;El-Maarry et al, 2019), ripples (El-Maarry et al, 2017;Jia et al, 2017), pits (Deshapriya et al, 2016), and bright spots (Deshapriya et al, 2016;Fornasier et al, 2016). Although these many studies documented the evolution of isolated regions and features on 67P, a synthesis of the evolution of all of 67P's smooth terrains has remained unexplored.…”