F. E.G. Butcher

Time will tell: temporal evolution of Martian gullies and palaeoclimatic implications.

Abstract To understand Martian palaeoclimatic conditions and the role of volatiles therein, the spatiotemporal evolution of gullies must be deciphered. While the spatial distribution of gullies has been extensively studied, their temporal evolution is poorly understood. We show that gully size is similar in very young and old craters. Gullies on the walls of very young impact craters (less than a few myr) typically cut into bedrock and are free of latitude-dependent mantle (LDM) and glacial deposits, while such deposits become increasingly evident in older craters. These observations suggest that gullies go through obliquity-driven degradation–accumulation cycles over time, controlled by: (1) LDM emplacement and degradation; and (2) glacial emplacement and removal. In glacially-influenced craters, the distribution of gullies on crater walls coincides with the extent of glacial deposits, which suggests that the melting of snow and ice played a role in the formation of these gullies. Yet, present-day activity is observed in some gullies on formerly glaciated crater walls. Moreover, in very young craters, extensive gullies have formed in the absence of LDM and glacial deposits, showing that gully formation can also be unrelated to these deposits. The Martian climate varied substantially over time, and the gully-forming mechanisms are likely to have varied accordingly.

The Hydrology of Mars Including a Potential Cryosphere

Abstract Water is one of the most common and important volatiles found throughout the Solar System, influencing both the geological evolution of planetary bodies and their potential habitability. The evidence for past and present water on Mars has been a main driver of its exploration. Ancient fluvial landforms indicate that Mars once had surficial conditions suitable for the presence of persistent liquid water on its surface. However, climate models of early Mars remain notably difficult to reconcile with these observations. The global inventory of water on Mars is critical to understanding how the planets potential habitability has varied over time. In this chapter, we review these topics, including the inventory of water, its various reservoirs, and potential loss mechanisms, and discuss how the planet’s hydrosphere evolved with time.