Geologic mapping of the Comet 67P/Churyumov–Gerasimenko's Northern hemisphere

Abstract

The Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS), the scientific imaging system onboard the Rosetta mission, has been acquiring images of the nucleus of the comet 67P/Churyumov-Gerasimenko since 2014 August with a resolution which allows a detailed analysis of its surface. Indeed, data reveal a complex surface morphology which is likely the expression of different processes which occurred at different times on the cometary nucleus. In order to characterize these different morphologies and better understand their distribution, we performed a geologic mapping of comet's 67P Northern hemisphere in which features have been distinguished based on their morphological, textural and stratigraphic characteristics. For this purpose, we used narrow-angle camera images acquired in 2014 August and September with a spatial scale ranging from 1.2 to 2.4 m pixel -1 . Several different geologic units have been identified on the basis of their different surface textures, granulometry and morphology. Some of these units are distinctive and localized, whereas others are more common and distributed all over the Northern hemisphere. Moreover, different types of linear features have been distinguished on the basis of their morphology. Some of these lineaments have never been observed before on a comet and can offer important clues on the internal structures of the nucleus itself. The geologic mapping results presented here will allow us to better understand the processes which affected the nucleus' surface and thus the origin and evolutionary history of comet 67P/Churyumov-Gerasimenko.

Constraints on cometary surface evolution derived from a statistical analysis of 67P’s topography

“…The surface is rich in land forms comparable to what is usually found on larger planetary bodies. Rosetta has mapped extensively the comet and its morphology has been described in many publications: Thomas et al (2015a); El-Maarry et al (2015; Giacomini et al (2016); Birch et al (2017). Among all morphological features, we focus our interest on the near-vertical walls of cliffs and pits, interpreted to result from of surface collapse (Vincent et al 2015b) and which clearly display ongoing regressive erosion due to ongoing activity/thermal stress (Vincent et al 2016b) or sudden outbursts (Vincent et al 2016a).…”

The Rocky‐Like Behavior of Cometary Landslides on 67P/Churyumov‐Gerasimenko

“…Moreover, the material constituting the landslide deposits appears composed of diamicton (Giacomini et al, ) with fragmented blocks with a general rocky appearance, deviating from the flow‐like morphologies found on icy bodies landslides. On icy satellites, temperature changes due to localized flash heating occur during landslide motion.…”

“…The global coverage and different viewing geometries of OSIRIS NAC (Narrow Angle Camera) and WAC (Wide Angle Camera) images allowed the identification of landslides located on different physiographic and geological regions on 67P (El‐Maarry et al, ; Giacomini et al, ). The landslide database was mainly built on NAC images taken at distance of 42–80 km, corresponding to a pixel scale of 1.12–1.49 m/px that allowed us to outline the identified landslide deposits.…”

“…This lack of landslides reflects the clear surface dichotomy characterizing the two hemispheres of 67P. Indeed, on the northern terrain large cliffs and consolidated terrains are coupled with dusty deposits and smooth terrains (Giacomini et al, ; Vincent et al, ) also due to the transport of fallback material, primarily from the southern hemisphere to the north (Lai et al, ), while on the southern hemisphere a much smoother topography is present and cliffs heights tend to be smaller (Vincent et al, ).…”

“…67P is characterized by an extremely diverse morphology comprising different surface features such as rough consolidated terrains, smooth plains, unconsolidated mantles, pits, fractures, cliffs, cuestas, ubiquitous boulders, and layers (Thomas et al, ). The peculiarity of 67P is also reflected by the widespread presence of landslides, whose deposits are typically identified in geomorphological maps as gravitational accumulation collapses (El‐Maarry et al, ; Giacomini et al, ).…”