Space weathering of ice layers in lunar cold traps

Abstract

There are several mechanisms acting at the cold traps that can alter the inventory of volatiles there, including micrometeoroid bombardment, solar wind and magnetospheric ion sputtering, photon-stimulated desorption, and sublimation. We investigate the effects of these space weathering processes on ice layers in a lunar cold trap. We simulate the development of hydrogen content in a column of material near the surface of the Moon by a Monte Carlo model. Each column is initialized with an ice layer existing within otherwise very immature soil. Time is allowed to run for 1 billion years and all changes to the column are calculated. We find that an ice layer must be > 10 cm thick or > 10 cm deep to have a detectable water enhancement.After 1 billion years, the ice layer is buried below the range of the neutron detection technique.For thinner or shallower deposits, the ice becomes indistinguishably mixed with the enriched soil from steady source delivery. A total of 40 cm deposit of water ice at a concentration of 10% is required to equal the hydrogen content resulting from the solar-wind steady source alone. The saturation level of the regolith is 3.7% water ice by mass.