ALBERT

Description: Infrared diffuse reflectance spectra (2.53-25 microns) of some carbonaceous (C) chondrites were measured. The integrated intensity of the absorption bands near 3 microns caused by hydrous minerals were compared with the modal content of hydrous minerals for the meteorites. The CM and CI chondrites show larger values of the intergated intensity than those of the unique C chondrites Y82162, Y86720 and B7904, suggesting that the amount of hydrous minerals in the CM and CI chondrites is larger, which supports the contention that hydrous minerals were dehydrated by thermal metamorphism in the unique chondrites. Orgueil (CI) has the largest value of the integrated intensity among the C chondrites we measured and shows a sharp absorption band at 3685/cm (2.71 microns) that is not seen in the spectra of the CM chondrites. There is an excellent correlation between the observed hydrogen content in C chondrites and the integrated intensity. The CM chondrites show a wide variation in the strength of absorption bands at 1470/cm (6.8 microns), despite the similarity in absorption features near 3 micron for all CM chondites. The 1470/cm band could be due to the presence of some hydrocarbons but may also be a result of terrestrial alteration processes.

Description: Crystals of halite and sylvite within the Monahans (1998) H5 chondrite contain aqueous fluid inclusions. The fluids are dominantly sodium chloride-potassium chloride brines, but they also contain divalent cations such as iron, magnesium, or calcium. Two possible origins for the brines are indigenous fluids flowing within the asteroid and exogenous fluids delivered into the asteroid surface from a salt-containing icy object.

Description: Aladdin is a remote sensing and sample return mission focused on the two small moons of Mars, Phobos and Deimos. Understanding the moons of Mars will help us to understand the early history of Mars itself. Aladdin's primary objective is to acquire well documented, representative samples from both moons and return them to Earth for detailed analyses. Samples arrive at Earth within three years of launch. Aladdin addresses several of NASA's highest priority science objectives: the origin and evolution of the Martian system (one of two silicate planets with satellites) and the composition and nature of small bodies (the building blocks of the solar system). The Aladdin mission has been selected as a finalist in both the 1997 and 1999 Discovery competitions based on the high quality of science it would accomplish. The equivalent of Aladdin's Phase A development has been successfully completed, yielding a high degree of technical maturity. Aladdin uses an innovative flyby sample acquisition method, which has been validated experimentally and does not require soft landing or anchoring. An initial phasing orbit at Mars reduces mission propulsion requirements, enabling Aladdin to use proven, low-risk chemical propulsion with good mass margin. This phasing orbit is followed by a five month elliptical mission during which there are redundant opportunities for acquisition of samples and characterization of their geologic context using remote sensing. The Aladdin mission is a partnership between Brown University, the Johns Hopkins University Applied Physics Laboratory, Lockheed Martin Astronautics, and NASA Johnson Space Center.

Description: Attempts to match the E asteroids with enstatite-rich meteorites universally conclude that the aubrites or enstatite chondrites are natural candidates, and accordingly conclude that E asteroids as a class are very water-poor. Accordingly, the highly reduced nature of typical enstatite-rich meteorites suggests that aqueous alteration was an improbable process on any E asteroid. However, there are spectroscopic observations of several E-class asteroids that suggest the presence there of hydrated phases. Examination of the Kaidun meteorite reveals the true situation.

Description: The ability of living organisms to survive on the smaller bodies in our solar system is examined. The three most significant sterilizing effects include ionizing radiation, prolonged extreme vacuum, and relentless thermal inactivation. Each could be effectively lethal, and even more so in combination, if organisms at some time resided in the surfaces of airless small bodies located near or in the inner solar system. Deep within volatile-rich bodies, certain environments theoretically might provide protection of dormant organisms against these sterilizing factors. Sterility of surface materials to tens or hundreds of centimeters of depth appears inevitable, and to greater depths for bodies which have resided for long periods sunward of about 2 A.U.

Description: Mineralogical constraints can be placed on the Martian surface by assuming chemical equilibria among the surface rocks, atmosphere and hypothesized percolating groundwater. A study was made of possible Martian surface mineralogy, as modified by the action of aqueous alteration, using the EQ3/6 computer codes. These codes calculate gas fugacities, aqueous speciation, ionic strength, pH, Eh and concentration and degree of mineral saturation for complex aqueous systems. Thus, these codes are also able to consider mineralogical solid solutions. These codes are able to predict the likely alteration phases which will occur as the result of weathering on the Martian surface. Knowledge of the stability conditions of these phases will then assist in the definition of the specifications for the sample canister of the proposed Martian sample return mission. The model and its results are discussed.

Description: A recent investigation of C2M carbonaceous chondrite meteorite matrices using electron microscopy and High-Resolution Transmission Electron Microscopy (HRTEM) has provided data on the structure and chemistry of Poorly Characterized Phases (PCP). It is suggested that a dominant matrix variety (10 A PCP) has a structure equivalent to iron-rich tochinilite (6Fe0.9S5/Fe, Mg//OHO2/), which consists of coherently intrastratified mackinawite and brucite sheets. In addition, it is proposed that 17 A PCP is a commensurate intergrowth of serpentine and tochinilite layers. Various forms of PCP observed in carbonaceous chondrites appear to be intergrowths of tochinilite, serpentine, and tochinilite-serpentine minerals.

Description: A fragment of a carbonaceous chondrite (#53.12, maximal dimension about 2 mm) containing a phyllosilicate-sulfide vein was found during an inspection of small pieces of the Kaidun meteorite. Phyllosilicate veins are apparently rare in carbonaceous chondrites and have so far only been reported from the Y82162 CI chondrite. In hand sample the vein was visible on two perpendicular faces. The polished section prepared from one side displays a complex structure. A single vein, 150 microns in width, bifurcates, and each branch narrows toward a large rounded object (RO). The section contains abundant ROs, most of them less than or equal to 100 microns in diameter. The vein has sharp contacts to the surrounding matrix, whereas the RO contacts are diffuse. The phyllosilicate in the main vein has a massive texture along the contact, which becomes platy toward the vein center where the crystals protrude into an open space. The texture of the largest RO resembles that of a barred olivine (BO) chondrule. Some of the smaller ROs also texturally resemble chondrules. The BO chondrule contains rounded sulfide-silicate objects and small metal grains covered by oxides. Phyllosilicates of the main vein consist mainly of serpentine. The phyllosilicate near the contact with the matrix has low contents of minor elements and a high Mg/Fe ratio. The composition changes in a regular manner toward the center: Al, Na, Ca, Ni, and S increase, indicating increasing amounts of sulfates admixed. The phyllosilicate vein could only have formed after a substantial rock was formed. Mechanical stress probably opened a crack that was subsequently filled by phyllosilicate, pyrrhotite, and finally by a (Fe,Mg)-sulfate. The source of the matter mobilized to form the vein could have been within the rock itself or outside. No compositional or mineralogical zoning is apparent at the vein-rock contacts. The nature of the transporting agent (liquid H2O or vapor) must also remain an enigma. M. Zolensky has recently observed similar phyllosilicate-filled veins in dark, wet clasts in the Al Rais CR chondrite.

Description: The debate about fossil life on Mars includes the origin of magnetites of specific sizes and habits in the siderite-rich portions of the carbonate spheres in ALH 84001 [1,2]. Specifically [2] were able to demonstrate that inorganic synthesis of these compositionally zoned spheres from aqueous solutions of variable ion-concentrations is possible. They further demonstrated the formation of magnetite from siderite upon heating at 550 C under a Mars-like CO2-rich atmosphere according to 3FeCO3 = Fe3O4 + 2CO2 + CO [3] and they postulated that the carbonates in ALH 84001 were heated to these temperatures by some shock event. The average shock pressure for ALH 84001, substantially based on the refractive index of diaplectic feldspar glasses [3,4,5] is some 35-40 GPa and associated temperatures are some 300-400 C [4]. However, some of the feldspar is melted [5], requiring local deviations from this average as high as 45-50 GPa. Indeed, [5] observes the carbonates in ALH 84001 to be melted locally, requiring pressures in excess of 60 GPa and temperatures 〉 600 C. Combining these shock studies with the above inorganic synthesis of zoned carbonates it seems possible to produce the ALH 84001 magnetites by the shock-induced decomposition of siderite.

Description: A population of ferrous silicate spherules composed of cryptocrystalline ol-px-normative material, +/-SiO2-rich glass and rounded-to-euhedral Fe,Ni-metal grains preserved a condensation signature of the precursors formed under oxidizing conditions.