From 2008 to 2010, a series of discoveries led to a surprising conclusion: there is water on the Moon! Water and other volatile elements were detected in lunar volcanic glasses, suggesting hydration of the mantle. Infrared spectrometers observed OH/H2O on the sunlit side of the Moon. The LCROSS impactor confirmed the presence of water ice in the permanently shadowed regions of the Moon. These findings now demand integration for understanding the history and evolution of volatiles on the Moon and throughout the inner solar system.
Sources of lunar water may include:
1) internal mantle water, present at formation and released by subsurface geologic processes
2) external water, delivered by asteroids and comets over lunar history
3) in situ, created on the surface by interactions with solar wind plasma.
Trailblazer places advanced infrared sensors in orbit for spatial and temporal characterization of water and cold traps. Our knowledge of the ‘lunar water cycle’ is in its infancy, and Trailblazer remote sensing is the next step to resolve current questions about the character and origin of water in the Earth-Moon system, and characterize resources for future landed exploration.
The goal of Lunar Trailblazer is to understand the form, abundance, and distribution of water on the Moon, and the lunar water cycle.
Objective 1: Determine the form, abundance, and distribution of H2O and OH in sunlit terrains.
Credit: Lunar Trailblazer Team, after Pieters et al 2009/Dyar et al 2010.
Trailblazer will determine the form of water (OH vs. bound H2O vs. H2O ice), how much is present, and its distribution on the sunlit side of the Moon. A correlation between localized enhancements of water with silicic domes, pyroclastic glasses, and deeply sourced norites and anorthosites could suggest that the water is endogenic, providing a global assessment of which magmatic reservoirs are enriched in water, and whether they are correlated with other incompatible elements. These results would provide new information for understanding the thermal evolution of the Moon.
Objective 2: Assess time variability of lunar volatiles.
Credit: Li and Milliken, 2017.
Prior measurements suggest that a portion of the water or hydrated products on the surface of the moon is time-dependent, implying active creation and destruction of chemical bonds. Such activity could be driven by solar processes and/or mobility of volatiles on the surface today, in response to thermal gradients. Trailblazer seeks to characterize modern temporal variability and its possible correlation with mineralogy and soil maturity.
Objective 3: Determine the form and abundance of ice, bound H2O, and OH in permanently shadowed regions (PSRs)
Credit: Li et al., 2018.
At the poles of the Moon are regions that are permanently in shadow, which have been hypothesized to contain water ice that could potentially host organic content. Understanding the amount of water ice present, its form, purity, and geologic and topographic context are crucial to understanding the role of these reservoirs in the lunar water cycle, or as resources for future explorers.
Objective 4: Understand how localized gradients in albedo and surface temperature affect ice and OH/H2O concentration
Credit: ISRO/NASA/JPL-Caltech/Brown Univ./USGS.
Possible co-variation of temperature and volatile type and abundance can help explain the behavior of lunar water and constrain the lifetime of ice deposits. In addition, the small-scale topography and surface thermophysical parameters may influence the properties of the water and its stability and accessibility. Trailblazer's spatially high-resolution temperature data will help determine how water cycles function on airless bodies.
Exploration zone reconnaissance for landed missions and mapping crust lithologic composition.