X-ray digital imaging petrography of lunar mare soils: modal analyses of minerals and glasses

It is essential that accurate modal (i.e., volume) percentages of the various mineral and glass phases in lunar soils be used for addressing and resolving the effects of space weathering upon reflectance spectra, as well as for their calibration such data are also required for evaluating the resource potential of lunar minerals for use at a lunar base. However, these data are largely lacking. Particle-counting information for lunar soils, originally obtained to study formational processes, does not provide these necessary data, including the percentages of minerals locked in multi-phase lithic fragments and fused-soil particles, such as agglutinates. We have developed a technique for modal analyses, sensu stricto, of lunar soils, using digital imaging of X-ray maps obtained with an energy-dispersive spectrometer mounted on an electron microprobe. A suite of nine soils (90 to 150 micrometers size fraction) from the Apollo 11, 12, 15, and 17 mare sites was used for this study. This is the first collection of such modal data on soils from all Apollo mare sites. The abundances of free-mineral fragments in the mare soils are greater for immature and submature soils than for mature soils, largely because of the formation of agglutinitic glass as maturity progresses. In considerations of resource utilization at a lunar base, the best lunar soils to use for mineral beneficiation (i.e., most free-mineral fragments) have maturities near the immature/submature boundary (Is/FeO approximately or = 30), not the mature soils with their complications due to extensive agglutination. The particle data obtained from the nine mare soils confirm the generalizations for lunar soils predicted by L.A. Taylor and D.S. McKay (1992, Lunar Planet Sci. Conf. 23rd, pp. 1411-1412 [Abstract]).     

Homochirality as the signature of life: the SETH Cigar

A characteristic hallmark of life is its homochirality: all biomolecules are usually of one hand, e.g. on Earth life uses only L-amino acids for protein synthesis and not their D mirror images. It is therefore suggested that a search for extra-terrestrial life can be approached as a Search for Extra-Terrestrial Homochirality (SETH). A novel miniaturized space polarimeter, called the SETH Cigar, is described which could he used to detect optical rotation as the homochiral signature of life on other planets. Moving parts are avoided by replacing the normal rotating polarizer by multiple fixed polarizers at different angles as in the eye of the bee. It is believed that homochirality will be found in the subsurface layers on Mars as a relic of extinct life.     

A sophisticated lander for scientific exploration of Mars: scientific objectives and implementation of the Mars-96 Small Station

A mission to Mars including two Small Stations, two Penetrators and an Orbiter was launched at Baikonur, Kazakhstan, on 16 November 1996. This was called the Mars-96 mission. The Small Stations were expected to land in September 1997 (Ls approximately 178 degrees), nominally to Amazonis-Arcadia region on locations (33 N, 169.4 W) and (37.6 N, 161.9 W). The fourth stage of the Mars-96 launcher malfunctioned and hence the mission was lost. However, the state of the art concept of the Small Station can be applied to future Martian lander missions. Also, from the manufacturing and performance point of view, the Mars-96 Small Station could be built as such at low cost, and be fairly easily accommodated on almost any forthcoming Martian mission. This is primarily due to the very simple interface between the Small Station and the spacecraft. The Small Station is a sophisticated piece of equipment. With the total available power of approximately 400 mW the Station successfully supports an ambitious scientific program. The Station accommodates a panoramic camera, an alpha-proton-x-ray spectrometer, a seismometer, a magnetometer, an oxidant instrument, equipment for meteorological observations, and sensors for atmospheric measurement during the descent phase, including images taken by a descent phase camera. The total mass of the Small Station with payload on the Martian surface, including the airbags, is only 32 kg. Lander observations on the surface of Mars combined with data from Orbiter instruments will shed light on the contemporary Mars and its evolution. As in the Mars-96 mission, specific science goals could be exploration of the interior and surface of Mars, investigation of the structure and dynamics of the atmosphere, the role of water and other materials containing volatiles and in situ studies of the atmospheric boundary layer processes. To achieve the scientific goals of the mission the lander should carry a versatile set of instruments. The Small Station accommodates devices for atmospheric measurements, geophysical and geochemical studies of the Martian surface and interior, and cameras for descent phase and panoramic views. These instruments would be able to contribute remarkably to the process of solving some of the scientific puzzles of Mars.     

Terraforming: making an Earth of Mars

As we understand more about life on Earth and about the chemical and biological potential of other planets and objects in our solar system, it's not too much of a leap to consider creating a habitable environment on another planet. Scientists have begun to ponder the possibility of transforming Mars, the most Earthlike of the nearby planets. Various scenarios have been proposed, and in many ways these scenarios duplicate the processes that transformed the early Earth. Here we look at some of the possibilities.     

Anaerobic biodegradation of TCE in laboratory columns of fractured saprolite

An experiment was conducted to determine if biodegradation of trichloroethylene (TCE) can occur in previously uncontaminated ground water in saturated fractured saprolite (highly weathered material derived from sedimentary rocks). Two undisturbed columns (0.23 m diameter by 0.25 m long) of fractured saprolite were collected from approximately 2 m depth at an uncontaminated site on the Oak Ridge Reservation, Oak Ridge, Tennessee. Natural, uncontaminated ground water from the site, which was degassed and spiked with dissolved phase TCE, was continuously pumped through one column containing the natural microbial communities (the biotic column). In a second column, the microorganisms were inhibited and the dissolved phase TCE was added under aerobic conditions (dissolved oxygen conditions > 2 ppm). In effluent from the biotic column, reducing conditions rapidly developed and evidence of anaerobic biodegradation of TCE, by the production of cDCE, first appeared approximately 31 days after addition of TCE. Reductive dechlorination of TCE occurred after iron-reducing conditions were established and about the same time that sulfate reduction began. There was no evidence of methanogenesis. Analyses using polymerase chain reaction with specific primers sets detected the bacteria Geothrix, Geobacter, and Desulfococcus-Desulfonema-Desulfosarcina in the effluent of the biotic column, but no methanogens. The presence of these bacteria is consistent with iron- and sulfate-reducing conditions. In the inhibited column, there were no indicators of TCE degradation. Natural organic matter that occurs in the saprolite and ground water at the site is the most likely primary electron donor for supporting reductive dechlorination of TCE. The relatively rapid appearance of indicators of TCE dechlorination suggests that these processes may occur even in settings where low oxygen conditions occur seasonally due to changes in the water table.     

A Unifying Concept of Water Purification Kinetics

Conclusion This paper is, in a sense, a search for meaningful measurements of those internal and external forces or factors that shape the progress of water purification both in nature and in treatment works. Progress is related to time or distance.Internal factors are expressed in terms of (I) a fundamental reaction rate of a specific impurity exposed to a specific treatment process, (2) temperature itself or temperature-dependent properties of the water undergoing treatment, (3) longitudinal variation in treatment response, and (4) longitudinal change in the concentration of the impurity.External factors are measured in terms of (I) extent of contact surface relative to the volume of water treated or, for packed treatment columns or fixed contact media, relative to the volume of the contact media, and (2) contact opportunity in terms of the induced mobility of the contact surfaces or their sweep through the treatment unit as a product of time and velocity gradient. Structural longitudinal changes in relative contact surface and operational longitudinal changes in contact opportunity as well as relative contact surface require that these measurements be stated as functions to be evaluated specifically for each purification unit and its method of operation. Longitudinal change in interfacial activity itself is made part of the measurement of treatment response. The mounting competition for water by municipalities, agriculture, and industry has placed water in short supply in many parts of the world and led to its increased pollution by ever more numerous and complex waste substances. Water purification, both for the prevention of the pollution of receiving bodies of water and for the production of safe and satisfactory water supplies for home, farm, and industry, thereby, has become ever more pressing and important. Needed progress in purification methods and economy can be insured, in the long run, only by a more fundamental understanding of the kinetics of water purification. For this understanding, we must look to the research and observational talents marshalled in institutions such as the ‘Eidgen?ssische Anstalt für Wasserversorgung, Abwasserreinigung und Gew?sserschutz an der ETH Zürich’ and to the leadership given these institutions by scientists such as Professor Dr. O. JAAG. The present special issue of this Journal pays tribute to the past accomplishments of this institution and its director and thereby expresses to both of them also the good wishes of sister institutions and their staffs for ‘the years that are waiting before’.     

Radiative heating of interstellar grains falling toward the solar nebula: 1-D diffusion calculations

As the dense molecular cloud that was the precursor of our Solar System was collapsing to form a protosun and the surrounding solar-nebula accretion disk, infalling interstellar grains were heated much more effectively by radiation from the forming protosun than by radiation from the disk's accretion shock. Accordingly, we have estimated the temperatures experienced by these infalling grains using radiative diffusion calculations whose sole energy source is radiation from the protosun. Although the calculations are 1-dimensional, they make use of 2-D, cylindrically symmetric models of the density structure of a collapsing, rotating cloud. The temperature calculations also utilize recent models for the composition and radiative properties of interstellar grains (Pollack et al. 1994. Astrophys. J. 421, 615-639), thereby allowing us to estimate which grain species might have survived, intact, to the disk accretion shock and what accretion rates and molecular-cloud rotation rates aid that survival. Not surprisingly, we find that the large uncertainties in the free parameter values allow a wide range of grain-survival results: (1) For physically plausible high accretion rates or low rotation rates (which produce small accretion disks), all of the infalling grain species, even the refractory silicates and iron, will vaporize in the protosun's radiation field before reaching the disk accretion shock. (2) For equally plausible low accretion rates or high rotation rates (which produce large accretion disks), all non-ice species, even volatile organics, will survive intact to the disk accretion shock. These grain-survival conclusions are subject to several limitations which need to be addressed by future, more sophisticated radiative-transfer models. Nevertheless, our results can serve as useful inputs to models of the processing that interstellar grains undergo at the solar nebula's accretion shock, and thus help address the broader question of interstellar inheritance in the solar nebula and present Solar System. These results may also help constrain the size of the accretion disk: for example, if we require that the calculations produce partial survival of organic grains into the solar nebula, we infer that some material entered the disk intact at distances comparable to or greater than a few AU. Intriguingly, this is comparable to the heliocentric distance that separates the C-rich outer parts of the current Solar System from the C-poor inner regions.     

Titan's stratospheric temperature asymmetry: a radiative origin?

During the 1981 Voyager encounter, Titan's stratosphere exhibited a large thermal asymmetry, with high northern latitudes being colder than comparable southern latitudes. Given the short radiative time constant, this asymmetry would not be expected at the season of the Voyager observations (spring equinox), if the infrared and solar opacity sources were distributed symmetrically. We have investigated the radiative budget of Titan's stratosphere, using two selections of Voyager IRIS spectra recorded at symmetric northern and southern latitudes. In the region 0.1-1 mbar, temperatures are 7 K colder at 50 degrees N than at 53 degrees S and the difference reaches approximately 13 K at 5 mbar. On the other hand, the northern region is strongly enriched in nitriles and hydrocarbons, and the haze optical depth derived from the continuum emission between 8 and 15 micrometers is twice as large as in the south. Cooling rate profiles have been computed at the two locations, using the gas and haze abundances derived from the IRIS measurements. We find that, despite lower temperatures, the cooling rate profiles in the pressure range 0.15-5 mbar are 20 to 40% larger in the north than in the south, because of the enhanced concentrations of infrared radiators. Because the northern hemisphere appears darker than the southern one in the Voyager images, enhanced solar heating is also expected to take place at 50 degrees N. Solar heating rate profiles have been calculated, with two different assumptions on the origin of the hemispheric asymmetry. In the most likely case where it results from a variation in the absorbance of the haze material, the heating rates are found to be 12-15% larger at the northern location than at the southern one, a smaller increase than that in the cooling rates. If the lower albedo in the north results from an increase in the particle number density, a 55 to 75% difference is found for the pressure range 0.15-5 mbar, thus larger than that calculated for the cooling rates. Considering the uncertainties in the haze model, dynamical heat transport may significantly contribute to the meridional temperature gradients observed in the stratosphere. On the other hand, the latitudinal variation in gas and haze composition may be sufficient to explain the entire temperature asymmetry observed, without invoking a lag in the thermal response of the atmosphere due to dynamical inertia.     

Oxygenic photosynthesis and the oxidation state of Mars

The oxidation state of the Earth's surface is one of the most obvious indications of the effect of life on this planet. The surface of Mars is highly oxidized, as evidenced by its red color, but the connection to life is less apparent. Two possibilities can be considered. First, the oxidant may be photochemically produced in the atmosphere. In this case the fundamental source of O2 is the loss of H2 to space and the oxidant produced is H2O2. This oxidant would accumulate on the surface and thereby destroy any organic material and other reductants to some depth. Recent models suggest that diffusion limits this depth to a few meters. An alternative source of oxygen is biological oxygen production followed by sequestration of organic material in sediments--as on the Earth. In this case, the net oxidation of the surface was determined billions of years ago when Mars was a more habitable planet and oxidative conditions could persist to great depths, over 100 m. Below this must be a compensating layer of biogenic organic material. Insight into the nature of past sources of oxidation on Mars will require searching for organics in the Martian subsurface and sediments.     

Reviews

THE DICTIONARY OF HUMAN GEOGRAPHY edited by R. J. Johnston. 20 x 13 cm, xix and 411 pages. Blackwell: Oxford 1983 (ISBN 0 631 13465 4) $A13.95 (limp).

THE GEOGRAPHY OF AUSTRALIAN CORPORATE POWER edited by Michael Taylor. 22 x 14 cm, ix and 230 pages. Croom Helm Australia: Sydney 1984 (ISBN 0 949614 06 8) $A24.95 (cloth).

MULTINATIONALS AS MUTUAL INVADERS: Intra‐industry Direct Foreign Investment edited by A. Erdilek. 14 x 22 cm, xii and 217 pages. Croom Helm: London 1985 (ISBN 0 7099 0935 7) $A39.95 (cloth).

UNEVEN DEVELOPMENT: Nature, Capital and the Production of Space by N. Smith. 15 x 22 cm, xv and 198 pages. Basil Blackwell: Oxford 1984 (ISBN 0 631 13564 2) $A59.95 (cloth); (ISBN 0 631 13685 1) $A18.95 (limp).

SOCIAL THEORY AND THE AUSTRALIAN CITY (Studies in Society No. 26) by L. Kilmartin, D. Thorns and T. Burke. 14 x 21 cm, ix and 218 pages. George Allen and Unwin: Sydney 1985 (ISBN 0 86861 405) $A24.95 (cloth); (ISBN 0 86861 413 0) $A12.95 (limp).

THE FUTURE OF URBAN FORM: The Impact of New Technology edited by J. Brotchie, P. Newton, P. Hall and P. Nijkamp. 14 x 22 cm, xiii and 374 pages. Croom Helm: London 1985 (ISBN 0 7099 3255 3) $A44.95 (cloth).