QUESTION:
What are the main differences or similarities between the Martian soil and
the lunar soil, regarding their geotechnical properties? What do you mean
when saying that the Martian soil behaves like a lunar soil?

ANSWER from Jeff Plescia on June 24, 1998:
The principal difference between lunar and Martian soil is the manner in
which they are formed.  Before going further, it should be noted that soil
has a very specific meaning for the Earth and the term is only loosely
applied to Mars.  In many cases the term regolith is used, particularly for
the Moon.  In any event, lunar regolith/soil is formed by the physical
breakup of rocks due largely to the impact of meteorites.  The meteorites
range in size from dust grains to large objects and over millions to
billions of years the surface is simply ground up. When the soil is looked
at in detail it is made up of various size pieces of rock and small amounts
of material that was melted by the impacts.

For Mars, the soil is believed to be caused by weathering of rocks, as for
the Earth. Early in time, when there was water on the surface, presumably
the rocks were altered to other minerals like clay which make up the current
soil. But, we do not yet have definite mineralogic data for the martian
surface so the mineral composition is speculative.

When it is said that the Martian soil behaves like lunar or dense
terrestrial soil, it is only an analogy for the physical properties, not the
composition.