Suggestion for extended Viking magnetic properties experiment on future Mars missions

Introduction: A remarkable result from the Viking missions was the discovery that the Martian soil is highly magnetic, in the sense that the soil is attracted by a small magnet [I]. The soil was found to adhere almost equally well to a strong and a weak SmCo magnet in the Viking lander backhoe at both landing sites. The strong magnet had a magnetic field and field gradient of 0.25 T and 100 Tm-', respectively, whereas the corresponding values for the weak magnet were 0.07 T and 30 Tm-l. Besides the backhoe magnets the Viking landers also carried a strong magnet situated at the Reference Test Chart (RTC). This magnet was exposed solely to the airborne dust. The RTC magnets of both landers attracted a substantial amount of airborne dust. Based on the pictures returned of the soil clinging to the magnets, it was estimated that the particles in the Martian dust contain between 1% and 7% of a strongly magnetic phase, probably a ferrimagnetic oxide intimately dispersed throughout the soil. Chemical analyses by means of the Viking X-ray fluorescence spectrometer indicate a content of about 18% by weight of Fe203. The limits of the saturation magnetization, a, of the soil may be given approximately as: 5 Am2(kg Fe203)-' < a < 38 Am2(kg Fe20s)-'. A significant observation was that both the weak and the strong backhoe magnets were essentially saturated with magnetic soil throughout the whole Viking mission. The results were the same for both landing sites. A notable result was that the dust on the RTC magnets, the dust on the backhoe magnets and the dust on the surface of Mars were optically very similar, if not identical. It seems that the attracted airborne dust and the attracted surface dust were of the same composition and probably also in the same grain size range.