Martian soil analogue

As samples of the red dust from Mars are not available, background studies and tests of experiments to be carried out on Mars missions have to take place on Earth by using Mars analogue samples. These are samples of which none have all the properties of the Martian dust.

One dust analogue is found in Denmark (Salten Skov I). First of all, it has the right grain size distribution (about 2-3 µm particles) and magnetic properties (3.9 Am2/kg) not too far from the Mars dust (~2 Am2/kg). The near UV spectrum of the dust is comparable to spectra from the surface material of Mars. Electrification, adhesion and cohesion properties are as we expect the Mars dust to have under the cold and dry planetary conditions. However, the mineralogy is goethite (~75%), Hematite (~19%), Maghemite (~6%) and thus far from the Martian dust with a basaltic chemistry.

Salten Skov Mars-analog

Experimental facilities
Mars sample analogues have been used in scientific experiments related to Martian surface processes (magnetic capture, electrification, adhesion, aerodynamics, Mars mission instrument and solar panel tests). The main facility used for these experiments are two Mars wind tunnels.

Mars tank and wind tunnel AWTS I
Mars tank and wind tunnel AWTS II

However, a number of other analytical instruments are necessary for characterization of the mineralogical composition of the samples used. Particle size of the dust is determined by laser diffraction. Mineralogy is determined by x-ray diffraction (XRD) and Mössbauer spectroscopy (MS), and morphology and chemical composition by scanning (SEM) and transmission electron microscopy (TEM), both with EDX analyzers (energy dispersive x-ray analysis), and total chemical analyses of bulk samples by x-ray fluorescence (XRF).

Iron oxides

Magnetite Fe3O4 [ FeIII (FeII , FeIII) O4 ]

Magnetite is a strongly magnetic iron oxide, which deviates from most other iron oxides by containing both divalent and trivalent iron. Magnetite is often found in beach sand in Denmark as small black magnetic grains.

Maghemite γ- Fe2O3

Maghemite is also strongly magnetic and has a structure like magnetite. It deviates from magnetite by almost all the iron being trivalent. Empty places in the structure compensate for the iron in oxidation state +III. Maghemite, known from burned sites, is very strongly red-brownish. It was found in the Salten Skov I soil from Mid Jutland, Denmark, although this was never a burned site.

Hematite α- Fe2O3

Hematite is only very weakly magnetic. The grains are fine, almost blood-red (Greek: haima = blood). It is also known as bloodstone which is almost black and used for jewelry. Hematite is utilized as a dye (e.g. Swedish red). Nor this mineral belongs in temperate moist climate zones.

Goethite α- FeOOH

Goethite is almost non-magnetic. The colour is yellow to yellow-orange and also used as a dye. Goethite is a very common mineral in Danish soils. It is named after Wolfgang von Goethe the German writer and scientist.

Titanomagnetite (ulvöspinel) Fe2TiO4 [FeII (FeII, TiIV) O4]

Ulvöspinel is different from magnetite by not being a strong magnetic mineral.
Like magnetite it has a cubic structure, and transitions between the two are common.
Most likely, the mineral is part of the volcanic rocks on Mars.