Book of Abstracts- Lunar Regolith Simulant Materials Workshop
Book of Abstracts- Lunar Regolith Simulant Materials Workshop
Book of Abstracts- Lunar Regolith Simulant Materials Workshop
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grained material which is in turn a function <strong>of</strong> the regolith<br />
thickness (Fig 8).<br />
In regions <strong>of</strong> thin regolith, the supply <strong>of</strong> coarsegrained<br />
material will be greater and the steady-state<br />
grain size floor will be higher. No soil in that region is<br />
likely to be finer than a certain limiting value. Conversely,<br />
in regions <strong>of</strong> thick regolith, bedrock is reaching<br />
much less frequency by impacts so the supply <strong>of</strong><br />
fresh coarse ejecta is lower and the mean grain size<br />
may reach lower values. If no new coarse material<br />
were added, a result <strong>of</strong> an infinitely thick regolith, the<br />
equilibrium mean the balance between communition<br />
and agglutination would establish the mean grain size.<br />
This suggests a relationship between regolith thickness<br />
and mean grain size. Figure 9 shows the regolith<br />
thickness estimated by various techniques plotted<br />
against the mean grain size and the maximum and<br />
minimum grain size at each Apollo site.<br />
The correlation shown in Figure 10 can be used to<br />
predict the finest grain size from estimation <strong>of</strong> regolith<br />
thickness, something that can be done from orbit. It<br />
can also be used to estimate the regolith thickness if a<br />
number <strong>of</strong> grain size analyses is available for a site.<br />
In summary, the evolution <strong>of</strong> the lunar regolith has<br />
been complex and has resulted from a dynamic system<br />
producing several systematic correlations and relationships.<br />
Understanding those relationships may allow us<br />
to produce more appropriate simulants and allow us to<br />
understand how our simulants may differ from actual<br />
lunar regolith.<br />
References: All figures are from D. S. McKay et<br />
al., 1974, Grain size and the evolution <strong>of</strong> lunar soils,<br />
Proceedings <strong>of</strong> the Fifth <strong>Lunar</strong> Conference, Supplement<br />
5, Geochemica et Cosmochemica Acta, Vol. 1,<br />
pp 887-906.<br />
No correlation is obvious between mean grain size<br />
and regolith thickness. However if only the finestgrained<br />
soil sample at each site is used, a strong correlation<br />
is seen with regolith thickness. This finest grain<br />
size may represent the steady state baseline at each site<br />
as shown in Figure 8.<br />
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