Paleolakes and life on early Mars

Two distinct directions have begun to elucidate key parameters in the search for extinct life on Mars. Carbonate sediments, deposited about 10,000 years ago in association with biological activity, have been sampled from the paleolake beds of Lake Vanda and Meirs in the McMurdo Dry Valleys in Antarctica. These samples are being analyzed for simple biological signatures that remain in cold and dry paleolake sediments, namely microfossils, percent carbonate, and total organic carbon. Our second initiative is the study of Colour Lake, in the Canadian Arctic, that periodically maintains a perennial ice cover. Physical measurements started this year will be used to determine one end point for ice covered lake environments and will be compared to continuous measurements from Antarctic lakes started in November 1985. Interestingly, Colour Lake also supports benthic mat communities, but the low pH precludes carbonate deposition. This research will broaden our knowledge base for what conditions are necessary for ice covered lake formation and what biological signatures will remain in paleolake deposits

Operation of an experimental algal gas exchanger for use in a CELSS

Concepts of a Closed Ecological Life Support System (CELSS) anticipate the use of photosynthetic organisms (higher plants and algae) for air revitalization. The rates of production and uptake of carbon dioxide and oxygen between the crew and the photosynthetic organisms are mismatched. An algal system used for gas exchange only will have the difficulty of an accumulation or depletion of these gases beyond physiologically tolerable limits (in a closed system the mismatch between assimilatory quotient (AQ) and respiratory quotient (RQ) is balanced by the operation of the waste processor). The results are given of a study designed to test the feasibility of using environmental manipulations to maintain physiologically appropriate atmospheres for algae and mice in a gas closed system. Specifically, the atmosphere behavior of this system is considered with algae grown on nitrate or urea and at different light intensities and optical densities. Manipulation of both allow operation of the system in a gas stable manner. Operation of such a system in a CELSS may be useful for reduction of buffer sizes, as a backup system for higher plant air revitalization and to supply extra oxygen to the waste processor or during crew changes

Exobiology site selection for future Mars missions: Martian paleolake sediments and terrestrial analogs

This research was conducted to establish the scientific framework for the exobiological study of sediments on Mars and to encourage the selection of these sedimentary deposits as sampling sites for future Mars missions. A study was completed on the Antarctic Dry Valley Lakes (terrestrial analogs of the purported Martian paleolakes) and their sediments that allowed the development of quantitative models relating environmental factors to the nature of the biological community and sediment forming processes. The publications presented include: (1) Diversity of micro-fungi isolated in an Antarctic dry valley; (2) Lake Hoare, Antarctica--sedimentation through a thick perennial ice cover; (3) The possibility of life on Mars during a water-rich past; (4) An Antarctic research outpost as a model for planetary exploration; (5) Early Martian environments--the Antarctic and other terrestrial analogs; (6) Lipophilic pigments from the benthos of a perennially ice-covered Antarctic lake; and (7) Perennially ice-covered Lake Hoare, Antarctica--physical environment, biology, and sedimentation

Lifetime performance characteristics of screen-printed potentiometric Ag/AgCl chloride sensors

Ag/AgCl chloride sensors were fabricated using thick-film technology. A number of different formulations were prepared and chloride responses were investigated over time. Near Nernstian, identical responses were observed over the first 160 days with an average chloride sensitivity of -51.8 ± 0.4 mV per decade change in chloride concentration (pCl), irrespective of paste formulation. After 6- months continuous immersion in tap water, pastes formulated with a glass binder began to exhibit a loss in sensitivity whilst those formulated from a commercial thickfilm dielectric paste remained functional for the best part of a year. The difference is attributed to the inclusion of proprietary additives in the commercial paste aiding adhesion and minimising AgCl leaching

Screen-printed platinum electrodes for the detection of cupric and ferric ions in high chloride backgrounds

Screen-printed platinum electrodes developed for use in corrosion monitoring applications have been used to detect cupric and ferric ions both individually and as mixtures in a background of 3.5% by weight sodium chloride and in the presence of dissolved oxygen. In single species detection linear responses for the Fe3+/Fe2+ couple were observed over the concentration range 0.3 to 100mM. By contrast, the small size of the working electrode caused a current limiting response for cupric ions over the same concentration range. In mixtures of these ions, the sensors show good differentiation and are able to separate the individual metal ion responses

Screen-printed platinum electrodes for measuring crevice corrosion: Nickel aluminium bronze as an example

Screen-printed platinum electrodes were used to monitor crevice corrosion processes. The electrodes, printed on an inert alumina substrate, formed the bottom of an artificial crevice when mechanically clamped to a rectangular block of nickel-aluminium bronze (NAB). Cyclic differential pulse voltammetry was used to detect corrosion products over time whilst the assembly was immersed in a 3.5% by weight aqueous solution of sodium chloride. Cupric (Cu2+), ferric (Fe3+) and ferrous (Fe2+) ions were detected with evolution profiles indicative of selective phase corrosion

Fourth Symposium on Chemical Evolution and the Origin and Evolution of Life

This symposium was held at the NASA Ames Research Center, Moffett Field, California, July 24-27, 1990. The NASA exobiology investigators reported their recent research findings. Scientific papers were presented in the following areas: cosmic evolution of biogenic compounds, prebiotic evolution (planetary and molecular), early evolution of life (biological and geochemical), evolution of advanced life, solar system exploration, and the Search for Extraterrestrial Intelligence (SETI)

Novel fabrication method for rapid creation of channels using PDMS for microfluidic networks on planar substrates

A novel and simple method for the rapid fabrication of microfluidic networks is presented. A silicone elastomer (PDMS - poly(dimethylsiloxane)) is cured around formers, which are then removed post-cure, resulting in a microstructure suitable for fluidic applications. The limiting factors in the fabrication method are in the materials and tools used for the development of the formers. If the methods used cannot produce a structure of accurate dimensions then the microstructure formed will be limited. For creating very narrow fluidic channels, the material used needs to be strong so that even with narrow dimensions it can be removed without damage but the use of sacrificial materials has been investigated as this overcomes this requirement. The principle of the technique is demonstrated with an unusual material (caramelised sugar – which can be easily dissolved in water) to fabricate channels with diameters down to 16μm

A Closed-loop, Non-linear, Miniaturised Capillary Electrophoresis System Enabled by Control of Electroosmotic Flow

The miniaturisation of capillary electrophoresis (CE) systems makes separation of ionic species with similar electrophoretic mobilities challenging. We report on a novel closed-loop system that does not rely on migration time to identify ionic species unlike many conventional CE systems. To aid miniaturisation our method requires the sample undergoing separation to travel back and forth along the short channel multiple times. For each consecutive cycle the sample becomes increasingly separated until it is deemed sufficiently separated such that it can be reliably identified by any appropriate detection system. As the sample approaches either of the channel ends, contactless conductivity detectors detect the presence of the sample and trigger the modification of the electroosmotic flow (EOF) to reverse the direction of flow in the channel. After sufficient separation the identification is performed in-channel using, in our case, an electrochemical detection scheme. Incorporation of a closed-loop control system means that unpredictable variation in migration time does not present an issue for ionic species identification. This new method of non-linear CE is demonstrated in a microfluidic channel formed in PDMS (polydimethylsiloxane), reversibly sealed to a glass wafer on which metal electrodes are patterned in gold. The sample movement in both directions along the channel occurs without affecting the electrophoretic separation already achieved during each cycle by changing the EOF in magnitude and direction. The EOF is changed by modifying the zeta-potential along the channel wall through the application of a voltage on a zeta-potential modification (ZPM) electrode placed close to the channel surface. Depending on the magnitude and polarity of the voltage applied to the ZPM electrode our experiments have shown the ability to increase, decrease or reverse the EOF

Life on ice, Antarctica and Mars

The study of the origin of life and the prospects for human exploration of Mars are two themes developed in a new 57-minute film, Life on Ice, Antarctica, and Mars, produced by the InnerSpace Foundation and WHRO Television for broadcast by the Public Broadcasting System (PBS). A brief explanation of the film and how it relates to the future human exploration of space is presented