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Effects of Roughness on Diurnal Hydration Transportation on the Lunar Surface

Presentation #119.02 in the session Moon & Earth (Poster + Lightning Talk)

Published onOct 23, 2023
Effects of Roughness on Diurnal Hydration Transportation on the Lunar Surface

Previous observations of the lunar surface revealed signatures of hydration, majorly in the form of hydroxyl [i.e., 1] with a small contribution from molecular water [2]. Recent work revealed a diurnal variability in the band strength, suggestive of localized migration of molecules [3,4]. Modeling of the transportation of lunar hydration has shown a dependence on surface roughness [5], and results in cold trapping near the poles. Here, we explore how transport of water across a lunar day is affected by surface roughness.

To test this, we developed a ballistic transport model with relevant loss mechanisms for H2O. Given a particle’s latitude, longitude, and time of day, we sampled the surface temperatures from [6]’s diviner hourly maps based on Diviner radiometer data. This dataset has a resolution of 0.5° latitude x 0.5° longitude by 0.26 lunar hours. The temperature was used to determine a launch velocity, and a landing location was found given a random launch angle and direction. Each particle was also subjected to a chance of being lost to the system through photolysis, sputtering, and Jeans escape [7, 8]. The model is run for one full lunar day, with a total of 96 timesteps.

We initiated our model with a random distribution of 1000 particles across the surface. We find that only 10% of the particles are retained through one lunar day, with 80% of the remaining particles migrating to within 10 degrees latitude of the poles. Of all the particles lost within the lunar day, nearly all of them (>99%) were destroyed by photolysis. The resolution of the temperature dataset is relatively large, and sub-pixel temperatures are known to vary widely. Assuming a moon with meter scale roughness, there may be sub-pixel regions with enough shadow to create cold spot regions where particles may land and be retained for longer. In conclusion, our model of the smooth moon results in 90% of particles being retained through a lunar day, with a rough moon model being expected to increase this amount.

[1] Pieters et al. (2009), Sci, 326, 5952.

[2] Honniball et al. (2020), Nat Astro, 5, 2.

[3] Hendrix et al. (2019), GRL, 46(5).

[4] Laferriere et al. (2022), JGR Planets, 127.

[5] Prem et al. (2018), Icarus, 299.

[6] Williams et al. (2017) Icarus, 283.

[7] Schorghofer (2014), GRL, 41.

[8] Grumpe et al. (2019), Icarus, 321.

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