J. M. Knudsen

Mineralogic and compositional properties of Martian soil and dust: Results from Mars Pathfinder

Mars Pathfinder obtained multispectral, elemental, magnetic, and physical measurements of soil and dust at the Sagan Memorial Station during the course of its 83 sol mission. We describe initial results from these measurements, concentrating on multispectral and elemental data, and use these data, along with previous Viking, SNC meteorite, and telescopic results, to help constrain the origin and evolution of Martian soil and dust. We find that soils and dust can be divided into at least eight distinct spectral units, based on parameterization of Imager for Mars Pathfinder (IMP) 400 to 1000 nm multispectral images. The most distinctive spectral parameters for soils and dust are the reflectivity in the red, the red/blue reflectivity ratio, the near-IR spectral slope, and the strength of the 800 to 1000 nm absorption feature. Most of the Pathfinder spectra are consistent with the presence of poorly crystalline or nanophase ferric oxide(s), sometimes mixed with small but varying degrees of well-crystalline ferric and ferrous phases. Darker soil units appear to be coarser-grained, compacted, and/or mixed with a larger amount of dark ferrous materials relative to bright soils. Nanophase goethite, akaganeite, schwertmannite, and maghemite are leading candidates for the origin of the absorption centered near 900 nm in IMP spectra. The ferrous component in the soil cannot be well-constrained based on IMP data. Alpha proton X-ray spectrometer (APXS) measurements of six soil units show little variability within the landing site and show remarkable overall similarity to the average Viking-derived soil elemental composition. Differences exist between Viking and Pathfinder soils, however, including significantly higher S and Cl abundances and lower Si abundances in Viking soils and the lack of a correlation between Ti and Fe in Pathfinder soils. No significant linear correlations were observed between IMP spectral properties and APXS elemental chemistry. Attempts at constraining the mineralogy of soils and dust using normative calculations involving mixtures of smectites and silicate and oxide minerals did not yield physically acceptable solutions. We attempted to use the Pathfinder results to constrain a number of putative soil and dust formation scenarios, including palagonitization and acid-fog weathering. While the Pathfinder soils cannot be chemically linked to the Pathfinder rocks by palagonitization, this study and McSween et al. [1999] suggest that palagonitic alteration of a Martian basaltic rock, plus mixture with a minor component of locally derived andesitic rock fragments, could be consistent with the observed soil APXS and IMP properties.

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 bulls-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.

Magnetic enhancement on the surface of Mars

The magnetic properties experiments on the Viking missions and the Pathfinder mission indicate that the Martian soil and airborne dust are somewhat magnetic (average saturation magnetization, σS ∼ 4 A m2kg−1). While hematite, superparamagnetic or macrocrystalline, is not sufficiently magnetic to yield the results obtained, pyrogenetic titaniferous magnetite (TiMt) might conceivably be the cause. However, the σS of the dust is considerably higher than that in any of the known Martian meteorites, some of which may be representative of the bedrock from which the Mars soil formed. Furthermore if the reported TiO2 content of Mars soil (∼1% by weight) was entirely present as TiMt of composition Usp 60 (that typical of terrestrial ocean floor basalts), the calculated abundance (<4%) would yield σS of only 1.2 A m2kg−1. As the Pathfinder magnetic properties experiment results pertain only to the airborne dust particles on Mars, the likelihood of aeolian concentration of such TiMt grains is minimal. Ferrous iron in the bedrock silicates must have been converted to maghemite (γ-Fe2O3) by some unknown oxidative mechanism; this “magnetic enhancement” should be incorporated in any process envisioned for the origin of Martian soil.

Simulation of the Martian dust aerosol at low wind speeds

[1] Performing realistic simulations is crucial for developing, testing, and subsequently analyzing results of experiments sent to the surface of Mars. A wind tunnel has been constructed, in which the atmospheric conditions of pressure and wind speed are controlled to match those observed by the Pathfinder mission to Mars. Injection into the wind tunnel of an analogue dust from Salten Skov in Denmark allows simulation of the Martian aerosol. Here experiments can be tested in preparation for a planned mission to the planet (Mars Exploration Rovers to be launched in 2003). Observations of adhesion and cohesion effects have been made in the wind tunnel, which are relevant to particle transport and of significance for validating the performance of specific experiments on Mars. Preliminary studies have been made, at Mars atmospheric pressure, of dust capture on magnet arrays similar to those flown on the Mars Pathfinder mission.

Mössbauer spectroscopy on the surface of Mars. Why

A Mössbauer spectrometer is included in the preliminary payload of a rover to be placed on the surface of Mars in the Soviet mission to the planct in 1996/1,2/. In counection with the American planctary program it has also been suggested to construct a Mössbauer spectrometer to be landed on Mars /3, 4/. The objective is to study the iron compounds of the Martian soil and rocks by backscattering Mössbauer spectroscopy. The paper describes the significance of the element iron in the study of the evolution of the planetary system and what we might expect to learn from Mössbauer spectroscopy of the surface materials of Mars. The study of Mars is expected to expand substantially in the coming decades, probably culminating with a manned flight to the planet. The international Mössbauer community may contribute significantly to the preparation of these events.

Instruments for the Magnetic Properties Experiments on Mars Pathfinder

Abstract The paper gives a description of two instruments, the Magnet Array (MA) and the Tip Plate Magnet (TPM), that are part of the Magnetic Properties Experiments on board the U.S. Mars Pathfinder spacecraft, which was launched 4 December 1996, and is expected to land on Mars 4 July 1997. Both instruments consist of permanent magnets of varying strength that are designed to capture airborne dust. The instruments will be imaged by the Lander camera and the pictures transmitted to Earth. The pictures are the data on which conclusions about the magnetic properties of the Martian dust will be based. As an addition to the description of the construction of the instruments, we give a brief discussion of the background for the interpretation of the results of the Magnetic Properties experiment.

Titanium and the magnetic phase on Mars

The significance of the element titanium for the study of the magnetic mineral in the surface dust of Mars is described.

A Mössbauer study of an impactite from the Monturaqui crater

The iron mineralogy of samples of the Monturaqui impactite has been studied by Mössbauer spectroscopy. Magnetite, maghemite, goethite and a ferrous glass phase were identified. In a magnetic separate a bcc-structured iron-nickel alloy was identified in addition to the oxide phases. The oxides have formed by weathering of iron-nickel alloys.

Extraterrestrial magnetite studied by Mössbauer spectroscopy

The meteorite Orgueil is a carbonaceous chondrite of type CI. Carbonaceous chondrites contain Fe(III), Fe(II) and in some cases metallic iron, indicating that they are in a state far from thermodynamic equilibrium. In Orgueil about 40% of the iron is present in magnetite (Fe3O4). In this work a sample of magnetite grains extracted from Orgueil has been studied by Mössbauer spectroscopy. It has been found that the magnetic phase contains about 11% of maghemite and that the remaining magnetite has a vacancy concentration smaller than 0.006, corresponding to the formula Fe2.994O4.

Rotation of a Rigid Body

The general treatment of the motion of a rigid body is rather involved and we shall in this book consider only certain special cases. The insights to be gained can be applied in virtually all of theoretical physics, and have important technological ramifications. Applications of the theorems derived stretch from studies of the spin of the electron and rotating atomic nuclei, to investigations of the motion of planets and galaxies.