Regolith

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Regolith visible on picture "Postcard Above Tennessee Valley"

Regolith is the layer of rocky or icy debris, sand, and dust made by meteoritic impact that forms the uppermost surface of planets, satellites and asteroids. It is a possible construction material in the form of bricks. Loose regolith may also be used as a radiation shield.

Landscapes with regolith formation have been found that look like they were shaped by the flow of water. Those formations were probably created by "gas-supported density flows". [1]

Composition

The below table gives estimates of mineral composition based on the soil sample measurements performed by two Mars probes. Only the 6 most abundant minerals are listed.

Estimated abundance (weight %) of main components of Martian soil[2]
SiO2 Fe2O3 Al2O3 MgO CaO SO3
Viking 46.3 19.4 7.7 6.4 6.2 7.9
Pathfinder 48.6 17.5 8.3 7.5 6.3 5.4

The following table shows the results of an analysis of 11 igneous meteorites of Martian origin, which were divided into 5 standard geological categories based on their composition.

Atomic density values from a sample of Martian meteorites[3]
Element Atoms/gram
Basalt Lherzolite Clinopyroxenite Orthopyroxenite Dunite
O 1.60 X 1022 1.58 X 1022 1.54 X 1022 1.65 X 1022 1.51 X 1022
Na 2.35 X 1020 9.15 X 1019 1.13 X 1020 2.66 X 1019 2.51 X 1019
Mg 1.61 X 1021 4.07 X 1021 1.79 X 1021 3.77 X 1021 4.81 X 1021
Al 8.50 X 1020 3.34 X 1020 1.94 X 1020 1.45 X 1020 8.23 X 1019
Si 5.01 X 1021 4.50 X 1021 4.88 X 1021 5.38 X 1021 3.87 X 1021
P 5.60 X 1019 2.00 X 1019 3.76 X 1018 0 6.41 X 1018
K 1.23 X 1019 3.31 X 1018 2.93 X 1019 1.95 X 1018 5.31 X 1018
Ca 1.06 X 1021 4.04 X 1020 1.56 X 1021 1.98 X 1020 6.52 X 1019
Ti 8.21 X 1019 3.28 X 1019 2.59 X 1019 1.53 X 1019 7.60 X 1018
Mn 4.42 X 1019 3.91 X 1019 5.69 X 1019 4.04 X 1019 4.51 X 1019
Fe 1.58 X 1021 1.67 X 1021 1.79 X 1021 1.46 X 1021 2.29 X 1021

Open Issues

  • How radioactive is regolith?
  • What are the compositions of the regolith near possible settlement sites?

References

  1. How the landscape is formed to the shape of floods: THE COLLAPSE ORIGIN OF DENSITY FLOWS ON MARS
  2. Bell JF, McSween HY, Crisp JA, Morris RV, Murchie SL, Bridges NT,...Soderblom L. (2000). Mineralogic and compositional properties of Martian soil and dust: Results from Mars Pathfinder. Journal of Geophysical Research, 105(E1), 1721-1755. https://doi.org/10.1029/1999JE001060
  3. Kim MY, Thibeault SA, Simonsen LC, Wilson JW. (1998). Comparison of Martian Meteorites and Martian Regolith as Shield Materials for Galactic Cosmic Rays. NASA TP-1998-208724. http://hdl.handle.net/2060/19980237030