Surface sediment chemistry

Participants: Svend Knak Jensen, Haraldur Páll Gunnlaugsson, Jonathan P. Merrison, Per Nørnberg.

Pictures of the tracks left by the Rovers driving around on the dusty surface of Mars show that while the surface layer is red, the material below is dark grey. These colours are interpreted as originating from Fe(III)- and Fe(II) compounds, respectively. It would be straightforward to explain the oxidation of Fe(II) to Fe(III) if water was abundant on Mars. However, Mars is a very dry planet, and the question arises as to how Fe(II) may be oxidized in the Martian environment without involving water.

Heterogeneous oxidation of Fe(II) in a Mars-like environment could contribute to an explanation. This is followed up in wind mediated chemistry experiments

The research concentrates on exploring the chemical consequences of material transport in an atmosphere with very low concentrations of water and oxygen. Since the chemical reactions are slow, it is impractical to conduct the experiments using the wind tunnel for month-long experiments. Instead, the wind motion is mimicked by slow rotation (about one Hz) of a reaction chamber, which is a closed container with various minerals in a well-defined atmosphere. The motion makes the mineral grains rub against each other and collide with the wall of the reaction chamber, which may facilitate a chemical reaction.

The technique has been used to investigate the oxidation of magnetite (Fe3O4) to hematite (Fe2O3) [1]. Figure 1 shows a glass reaction chamber initially containing magnetite (black), which after several months of rotation has been partially turned into hematite (reddish). The presence of hematite is confirmed by Mössbauer- and XRD-measurements. The reaction does not require water and oxygen to proceed, which makes it a putative mechanism for the reddish color of Mars that is known from in situ measurements to be due to hematite formed in an environment without water [2].

Current research focuses on finding mechanisms that can explain the presence of oxidants on the Martian surface. 

Figure 1. A reaction chamber with magnetite (black) and hematite (reddish).

[1] Merrison J. P. et al., (2010) Icarus 205(2), 716.
[2] Goetz et al., (2005) Nature (236), 62.