Book of Abstracts- Lunar Regolith Simulant Materials Workshop

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