Valles Marineris, the largest canyon system in the Solar System, preserves 3.7 billion years of Martian history. It also contains abundant evidence of past water. This NASA FINESST-funded project aims to improve our understanding of the history of surface water in Valles Marineris. This will offer key insights into how liquid water persisted over time, and help constrain Mars' transition from a wetter past to its current arid state and key windows of habitability.