The magnetic properties experiments on Mars Pathfinder

The Mars Pathfinder lander carried two magnet arrays, each containing five small permanent magnets of varying strength. The magnet arrays were passively exposed to the wind borne dust on Mars. By the end of the Mars Pathfinder mission a bull's-eye pattern was visible on the four strongest magnets of the arrays showing the presence of magnetic dust particles. From the images we conclude that the dust suspended in the atmosphere is not solely single phase particles of hematite (α-Fe2O3) and that single phase particles of the ferrimagnetic minerals maghemite (γ-Fe2O3) or magnetite (Fe3O4) are not present as free particles in any appreciable amount. The material on the strongest magnets seems to be indistinguishable from the bright surface material around the lander. From X-ray fluorescence it is known that the soil consists mainly of silicates. The element iron constitutes about 13% of the soil. The particles in the airborne dust seem to be composite, containing a few percent of a strongly magnetic component. We conclude that the magnetic phase present in the airborne dust particles is most likely maghemite. The particles thus appear to consist of silicate aggregates stained or cemented by ferric oxides, some of the stain and cement being maghemite. These results imply that Fe2+ ions were leached from the bedrock, and after passing through a state as free Fe2+ ions in liquid water, the Fe2+ was oxidized to Fe3+ and then precipitated. It cannot, however, be ruled out that the magnetic particles are titanomagnetite (or titanomaghemite) occurring in palagonite, having been inherited directly from the bedrock.