Evidence for geologic processes on comets. Issue 11 (7th November 2016)

• Record Type: Journal Article
• Authors: Sunshine, Jessica M.; Thomas, Nicolas; El‐Maarry, Mohamed Ramy; Farnham, Tony L.
• Is Part Of: Journal of geophysical research. Volume 121:Issue 11(2016:Nov.)
• Page Start: 2194
• Page End: 2210
• Publication Date: 2016-11-07
• Subjects: comets -- morphology -- surfaces -- Planetary sciences: Comets and small bodies -- surfaces -- erosion and weathering -- origin and evolution; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1002/2016JE005119
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: Spacecraft missions have resolved the nuclei of six periodic comets and revealed a set of geologically intriguing and active small bodies. The shapes of these cometary nuclei are dominantly bilobate reflecting their formation from smaller cometesimals. Cometary surfaces include a diverse set of morphologies formed from a variety of mechanisms. Sublimation of ices, driven by the variable insolation over the time since each nucleus was perturbed into the inner Solar System, is a major process on comets and is likely responsible for quasi‐circular depressions and ubiquitous layering. Sublimation from near‐vertical walls is also seen to lead to undercutting and mass wasting. Fracturing has only been resolved on one comet but likely exists on all comets. There is also evidence for mass redistribution, where material lifted off the nucleus by subliming gases is deposited onto other surfaces. It is surprising that such sedimentary processes are significant in the microgravity environment of comets. There are many enigmatic features on cometary surfaces including tall spires, kilometer‐scale flows, and various forms of depressions and pits. Furthermore, even after accounting for the differences in resolution and coverage, significant diversity in landforms among cometary surfaces clearly exists. Yet why certain landforms occur on some comets and not on others remains poorly understood. The exploration and understanding of geologic processes on comets is only beginning. These fascinating bodies will continue to provide a unique laboratory for examining common geologic processes under the uncommon conditions of very high porosity, very low strength, small particle sizes, and near‐zero gravity. Key Points: Cometary surfaces include a diverse range of landforms reflecting the variety of processes that formed them Among the key mechanisms active on cometary surfaces are sublimation, sedimentary processes, and fracturing All morphologies do not exist on all comets and certain landforms (e.g., flows and spires) are unique to specific nuclei