Evolution of the Imhotep Basin on Comet67P/Churyumov-Gerasimenko

Abstract:

The smooth terrains of comet 67P/Churyumov-Gerasimenko are primarily formed by air-falling debris liberated during erosion of the consolidated nucleus and represent sedimentary basins of ice-rich regolith materials. Over course of the Rosetta mission, the smooth terrains exhibited the most drastic transient changes, and so understanding their evolution is paramount to understanding the evolution of 67P’s surface in general. The largest smooth terrain deposit resides in the Imhotep region, which has been shown to erode primarily via sublimation-driven scarp retreat.

Using image data from the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) narrow angle camera (NAC) onboard the Rosetta spacecraft, we track decameter-scale changes across the smooth terrains of the Imhotep basin during the course of the mission and provide a model of smooth terrain erosion on comets to explain our observations. By combining existing shape models with photoclinometry, we have generated dozens of high-resolution (cm-scale vertical accuracy) digital terrain models (DTMs) across the Imhotep region. Using these DTMs, we have measured both the erosion and subsequent restoration of the smooth terrains. By performing these measurements on multiple OSIRIS images acquired throughout the mission, we map the temporal evolution of the depth of Imhotep’s smooth terrains. These measurements are a precise measure of fallback volumes on 67P, and lay the groundwork for future measurements of fallback on all other smooth terrains across the nucleus. Our work shows that while there is net erosion of material in some regions of the Imhotep basin during the course of the mission, other regions in the same basin experience a net fallback of material. We will discuss these measurements and their resulting implications.