Energetics of water in the Solar System

Abstract

Water is vital for space exploration, from drinking to fuel reformation, and is naturally abundant in the Solar System [1–16]. While in-situ resource utilization (ISRU) requires vastly less energy than transporting resources, the energetics has scarcely been explored besides on Earth and limited analysis on Mars’ vapor. Here, we develop a thermodynamic framework to quantify the energy requirements for resource extraction from 18 water sources on 11 planetary bodies. We find that desalinating saline liquid brines, where available, could be the most energetically favorable option and the energy required to access water vapor can be four to ten times higher than accessing ice deposits. While desalination energetics are highly sensitive to salt concentration, we show that desalination energetics only vary by a factor of 2 with respect to the type of salt present. Additionally, unlike chemical mixtures, the minimum energetics are insensitive to composition in physical mixtures (e.g., ice-regolith and inert vapor mixtures). Additionally, by deriving and computing the equation-of-state for pure water, we extend the least work estimates of atmospheric water harvesting by 94°C lower than previous studies that depend on predetermined databases. The presented approach and data may inform decisions regarding water harvesting, habitation, and resource reformation.