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PubMed2003

Modern and ancient extremely acid saline deposits: terrestrial analogs for martian environments?

Extremely acid (pH <1) saline lakes and groundwaters existed in the mid-Permian of the mid-continent of North America. Modern counterparts have been found in acid saline lake systems throughout southern Australia. We compare and contrast the Permian Opeche Shale of North Dakota and Nippewalla Group of Kansas to modern Australian salt lakes in southern Western Australia and in northwest Victoria. With the exception of some minor variations in pH, evaporite mineralogy, and water geochemistry, the Permian and modern systems are similar and characterized by: (1) ephemeral saline continental playas hosted by red siliciclastic sediments, (2) evaporite minerals, including abundant sulfates, (3) Al-Fe-Si-rich waters with low pH values, (4) acidophilic microbes, and (5) paucity of carbonates. The composition of these terrestrial systems is strikingly similar to compositional data returned from the martian surface. Specifically, both Earth and martian systems have high amounts of iron oxides and sulfates, and little, if any, carbonates. We propose that the modern and ancient terrestrial acid saline environments may be good analogs for possible environments on Mars.

Australia↗
PubMed1992

The seeding of life by comets.

The evidence that living organisms were already extant on the earth almost 4 Gyr ago and that early bombardment by comets and asteroids created a hostile environment up to about this time has revived the question of how it was possible for prebiotic chemical evolution to have provided the necessary ingredients for life to have developed in the short intervening time. The actual bracketed available temporal space is no more than 0.5 Gyr and probably much less. Was this sufficient time for an earth-based source of the first simple organic precursor molecules to have led to the level of the prokaryotic cell? If not, then the difficulty would be resolved if the ancient earth was impregnated by organic molecular seed from outer space. Curiously, it seems that the most likely source of such seeds was the same a one of the sources of the hostile enviroment, namely the comets which bombarded the earth. With the knowledge of comets gained by the space missions it has become clear that a very large fraction of the chemical composition of comet nuclei consists of quite complex organic molecules. Furthermore it has been demonstrated that comets consist of very fluffy aggregates of interstellar dust whose chemistry derives from photoprocessing of simple ice mixtures in space. Thus, the ultimate source of organics in comets comes from the chemical evolution of interstellar dust. An important and critical justification for assuming that interstellar dust is the ultimate source of prebiotic molecular insertion on the earth is the proof that comets are extremely fluffy aggregates, which have the possibility of breaking up into finely divided fragments when the comet impacts the earth's atmosphere. In the following we will summarize the properties of interstellar dust and the chemical and morphological structure of comets indicated by the most recent interpretations of comet observations. It will be shown that the suitable condition for comets having provided abundant prebiotic molecules as well as the water in which they could have further evolved are consistent with theories of the early earth environment.

Cosmic Dust↗
PubMed1995

Dust in the Universe: implications for terrestrial prebiotic chemistry.

In the present review we analyze the available literature on the distribution of dust in the Universe, methods of its observation and determination of the chemical composition, and the roles for terrestrial prebiotic chemistry. The most plausible natural sources of dust on the Earth in the prebiotic era are sedimentation of interplanetary dust, meteoritic and cometary impacts, volcanic eruptions, and soil microparticulates; the interplanetary medium being among the most powerful supplier of the dust matter. Two fundamental roles of dust particles for the origins of life are considered: (1) catalytic formation of prebiotic compounds; and (2) delivery of organic matter to the Earth by space dust particles. Due to the fact that there is only approximate information on the chemical composition and properties of interstellar, circumstellar, and major part of interplanetary dust, even the simulating experiments are difficult to perform. Until these gaps are filled, it seems reasonable to focus efforts of the scientists dealing with dust-driven catalytic formation of prebiotically important compounds on the volcanic and meteoritic/cometary impact environments.

Cosmic Dust↗
PubMed2003

Biological potential of Martian hydrothermal systems.

A source of energy to power metabolism may be a limiting factor in the abundance and spatial distribution of past or extant life on Mars. Although a global average of chemical energy available for microbial metabolism and biomass production on Mars has been estimated previously, issues of how the energy is distributed and which particular environments have the greatest potential to support life remain unresolved. We address these issues using geochemical models to evaluate the amounts of chemical energy available in one potential biological environment, Martian hydrothermal systems. In these models, host rock compositions are based upon the compositions of Martian meteorites, which are reacted at high temperature with one of three groundwater compositions. For each model, the values for Gibbs energy of reactions that are important for terrestrial chemosynthetic organisms and likely representative for putative Martian microbes are calculated. Our results indicate that substantial amounts of chemical energy may be available in these systems, depending most sensitively upon the composition of the host rock. From the standpoint of sources of metabolic energy, it is likely that suitable environments exist to support Martian life.

Extraterrestrial Environment↗
PubMed2006

The photochemical stability of carbonates on Mars.

Carbonates, predominately MgCO3, have been spectroscopically identified at a level of 2-5% in martian dust. However, in spite of this observation, and a large number of climate studies that suggest 1 to several bars of CO2 should be sequestered in carbonate rocks, no outcrop-scale exposures of carbonate have been detected anywhere on Mars to date. To address one hypothesis for this long-standing puzzle, the effect of ultraviolet (UV) light on the stability of calcium carbonate in a simulated martian atmosphere was experimentally investigated. Using 13C-labeled calcite, we found no experimental evidence of the UV photodecomposition of calcium carbonate in a simulated martian atmosphere. Extrapolating the lower limit of detection of our experimental system to an upper limit of carbonate decomposition on Mars yields a quantum efficiency of 3.5 x 10(-8) molecules/photon over the wavelength interval of 190-390 nm and a maximum UV photodecomposition rate of 1.2 x 10(-13) kg m(-2) s(-1) from a calcite surface. The maximum loss of bulk calcite due to this process would be 2.5 nm year(-1) (Mars year). However, calcite is expected to be thermodynamically stable on the surface of Mars, and potential UV photodecomposition reaction mechanisms indicate that, though calcium carbonate may decompose under vacuum, it would be stable in a CO2 atmosphere. Given the expected stability of carbonate on Mars and our inability to detect carbonate decomposition, we conclude that it is unlikely that the apparent absence of extensive carbonate deposits on the martian surface is due to UV photodecomposition in the current environment.

Calcium Carbonate↗
PubMed2001

Simulation of the low-Earth-orbit dose rates using secondary radiations from the HZE particles at NIRS-HIMAC.

In order to study biological effects from cyclic dose rates encountered at the low-Earth orbit (LEO), an experimental facility was designed in the Biology room of the Heavy Ion Medical Accelerator in Chiba (NIRS-HIMAC). An incubator placed in this facility is irradiated repeatedly by secondary radiations from HZE-particle beams supplied for independent users. The daily-average dose rate (1.4 mGy d-1) measured for 223 days and short-term dose rates measured for selected beam conditions were comparable to the dose rates observed in past LEO missions. Severe solar particle events can be simulated with hourly maximum dose rate of 2.8 mGy h-1. Preliminary measurements using CR-39 and TLD indicated that the dominant LET range is less than 5 keV micrometers-1. These results demonstrate the possibility of this facility for radiobiology studies of the effects of low dose rates comparable to the LEO environment.

Cesium Radioisotopes↗
PubMed1996

Food intake and nutritional status during EXEMSI. Experimental Campaign for the European Manned Space Infrastructure.

Modifications of food intake by astronauts during long-duration spaceflights have been observed. Various psychological stress factors, such as isolation, confinement, constrained community and boredom, are thought to play a role in this phenomenon. For this reason it was decided to include a nutritional investigation in the EXEMSI simulation study, in which four crew members (1 female and 3 males) were isolated and confined for 60 days in a space station-like environment. The Food and Nutritional Management System, developed for this experiment, provided on-line analysis of all available foods in terms of their nutrient content (macronutrients, water, minerals, vitamins). It permitted to keep an accurate record of the daily food intake of each crew member. The system has been shown to be a powerful tool for future missions, either simulations or actual spaceflights. It permits optimal management of food and eating on board, and offers the possibility of online analysis of the nutritional status of the crew. It can provide readily usable data for future analysis of nutritional variables in relation to other physiological and metabolic parameters. It could also supply a periodic feedback to the subject for the purpose of adjusting food intake. Eating and nutrition during the experiment were not a problem, but a pleasure, and therefore played an important role in its success. Confinement and isolation apparently had no effect on either the eating habits or the nutritional status of the crew members. The good food rather helped to decrease the potentially induced stress by providing daily periods of pleasure and of social activities. Detailed analysis of food intake showed erratic eating patterns, both before and during the experiment. However, the weekly averages of macro- and micronutrient intakes were in the normal range, except for vitamins B1 and B6 that were rather low and showed the need for supplements. Food appreciation was assessed by daily questionnaires. Satisfaction with the food provided during isolation was rated very high, and there was no feeling of hunger or monotony. The satisfaction with the food was mainly due to its high palatability, the adequate selection made with direct prior involvement of the crew, the large variety, and the extra supply that allowed the crew to choose and feel free regarding food intake. Comments from the crew afterwards clearly demonstrated that food had not been considered critical during the 60 days of isolation. This is an important fact considering the importance of food in such a restricted living environment.

Adult↗