THE ORIGIN OF LOW MASS STARS

Recent evidence indicates that most low mass stars in the Galaxy (<5 Msolar) form alongside massive stars in clusters embedded in giant molecular clouds. Once their parental gas is removed, the fate of these clusters is to disperse and blend into the field population of the galactic disk. The distribution of stellar masses in the solar neighborhood, called the Initial Mass Function, is discussed in the context of the origin of low mass stars. Arguments based on the production rate of field stars are presented that point to giant molecular clouds as the primary birth sites for low mass stars. The role of observations of molecular clouds at millimeter and infrared wavelengths in confirming this picture is reviewed. Millimeter-wave observations have revealed that molecular clouds consist of low-density gas interspersed with high-density cores. Near-infrared images of these clouds indicate that stars form preferentially in these cores, with the number of young stars roughly scaling with the mass of the core. Molecular-line and near-infrared observations which characterize star formation in the nearest giant molecular cloud complex in Orion are presented. The implications for the Sun forming in a cluster environment are briefly discussed.     

CIRCUMSTELLAR AND INTERSTELLAR SYNTHESIS OF ORGANIC MOLECULES

We review the formation and evolution of complex circumstellar and interstellar molecules. A number of promising chemical routes are discussed which may lead to the formation of polycyclic aromatic hydrocarbon molecules, fullerenes, and unsaturated hydrocarbon chains in the outflows from stars. Some of the problems with these chemical schemes are pointed out as well. We also review the role of grains in the formation of complex molecules in interstellar molecular clouds. This starts with the formation of simple molecules in an ice grain mantle. UV photolysis and/or thermal polymerization can convert some of these simple molecules into more complex polymeric structures. Some of these species may be released to the gas phase, particularly in the warm regions around newly formed stars. Methanol and formaldehyde seem to play an important role in this drive towards molecular complexity and their chemistry is traced in some detail.     

The Distribution of Particulate Organic Carbon in the Oceans: Ecological Implications

Distribution of participate organic carbon (POC) in the oceans appears to be in the form of small “clouds” high in POC superimposed on lower background values typical of depth and water mass. The background values display an exponential decrease with depth. Samples taken at close intervals, both vertical and horizontal, suggest that the extent of these clouds in water below the photic zone must be less than a meter in any dimension. The concentration of POC in the clouds is of the same order as that found in surface waters. Feeding behaviour of the larger zooplankton may involve active searching for these patches; the organisms should be examined for evidences of mechanisms for finding patches. The maximum distance between patches, even in deeper water, must be of the order of a few tens of meters.     

ANALOGS OF THE EARLY SOLAR SYSTEM

Within the last few decades, the existence of protoplanetary disks has been inferred on the basis of emission from T Tauri stars that does not arise from a stellar photosphere. More recently, high-resolution interferometric techniques have resolved the dust continuum emission, and millimeter arrays have imaged circumstellar molecular gas. These measurements corroborate the disk interpretation; many T Tauri stars are surrounded by centrifugally supported circumstellar disks with radial sizes of order 100 AU. Further proof issues from Hubble Space Telescope images of disks that are illuminated externally. The morphology of circumstellar dust is revealed in striking detail and affirms the prevalence and dimensions of disks imaged at longer wavelengths. The fate of circumstellar material around young stars must be understood in order to discern the degree to which these disks are proto-planetary. Observational studies of circumstellar disks which are in the beginning of a dispersal phase are challenging and place great demands on astronomical techniques. Nevertheless, the connection between disks and the formation of extra-solar planets is supported by increasing circumstantial evidence. Optically thin dust continuum emission persists in T Tauri stars and is detected around some young main sequence stars. Since the dust is subject to rapid dispersal by radiation pressure and Poynting-Robertson drag, some mechanism of replenishment is required. Disks around nearby young main sequence stars show evidence for inner voids and disk asymmetries that should also disappear on short timescales. The presence of large orbiting bodies which collide and interact with the resulting debris can explain both the persistence of optically thin dust and the maintenance of otherwise-ephemeral dynamical features. Together with recent detections of extra-solar planets, these observations lend some support to the hypothesis that circumstellar disks commonly give birth to planetary systems.     

The phenomenon of formation of prebiological compounds in volcanic processes

Organic matter has been found in the juvenile ash of seven volcanoes in Kamchatka, the Kurile Island and Indonesia. Its amount in one eruption is of the order of 100 000 tons. This matter constitutes a multicomponent mixture (more than 150 components) of, mainly, high-boiling (b.p. over 250°C) organic compounds of a complex structure. These are represented by hydrocarbons of saturated and aromatic nature, and, among them, polycyclic hydrocarbons, amino acids, amino sugars and other heteroatomic molecules, also containing N, O, S and Cl. The formation of the above mentioned organic compounds is associated with volcanic processes—with abiogenous synthesis taking place in ash-gas clouds and, possibly, in the entrails of the Earth (hydrocarbons and their heteroatomic derivatives have also been found in volcanic bombs). On the strength of these facts, volcanic phenomena are regarded as the process which serves as the starting point of the chemical evolution from the inanimate to the animate matter.     

The phenomenon of formation of prebiological compounds in volcanic processes

Organic matter has been found in the juvenile ash of seven volcanoes in Kamchatka, the Kurile Islands and Indonesia. Its amount in one eruption is of the order of 1 00 000 tons. This matter constitutes a multicomponent mixture (more than 150 components) of, mainly, high boiling (b.p. over 250 degrees C) organic compounds of a complex structure. These are represented by hydrocarbons of saturated and aromatic nature, and, among them, polycyclic hydrocarbons, amino acids, amino sugars and other heteroatomic molecules, also containing N, O, S and C1. The formation of the above mentioned organic compounds is associated with volcanic processes--with abiogenous synthesis taking place in ash-gas clouds and, possibly, in the entrails of the Earth (hydrocarbons and their heteroatomic derivatives have also been found in volcanic bombs). On the strength of these facts, volcanic phenomena are regarded as the process which serves as the starting point of the chemical evolution from the inanimate to the animate matter.     

Processes accompanying the charging of dust grains in the ionospheric plasma

The influence of the neutral component of the dusty ionospheric plasma on the process of dust grain charging is analyzed. Microscopic ion fluxes onto a dust grain are calculated with allowance for the interaction with the neutral components of the ionospheric plasma for both negatively and positively charged dust grains. For the latter case, which takes place in the presence of intense UV or X-ray solar radiation, the electron heating caused by the photoelectric effect is also investigated. It is found that the efficiency of electron heating depends on the density of neutral particles. The altitudes at which these effects appreciably influence the charging of different types of nano- and microscale dust grains are determined. It is shown that these effects should be taken into account in describing noctilucent clouds, polar mesosphere summer echoes, and physical phenomena involving grains of meteoric origin.     

Characterisation of the Carbohydrate Fraction of the Temporary Adhesive Secreted by the Tube Feet of the Sea Star <Emphasis Type="Italic">Asterias rubens</Emphasis>

In sea stars, adhesion takes place at the level of a multitude of small appendages, the tube feet. It involves the secretion of an adhesive material which, after tube foot detachment, remains on the substratum as a footprint. It was previously reported that the two main organic components of this material are proteins and carbohydrates. The carbohydrate moiety of the adhesive secretion of Asterias rubens was investigated using a set of 16 lectins which were used on sections through tube feet, on footprints, and on the proteins extracted from these footprints. After gel electrophoresis, these proteins separate into eight protein bands which were named sea star footprint proteins (Sfps). Eleven lectins label the tube foot epidermis at the level of the adhesive cells, four react with footprints, and eight with two of the extracted footprint proteins, which are therefore classified as glycoproteins. Sfp-290 appears to bear mostly N-linked oligosaccharides and Sfp-210 principally O-linked oligosaccharides. The outer chains of both glycoproteins enclose galactose, N-acetylgalactosamine, fucose, and sialic acid residues. Another part of the carbohydrate fraction of the footprints would be in the form of larger molecules, such as sialylated proteoglycans. These two types of glycoconjugates are presumably key components of the sea star temporary adhesive providing both cohesive and adhesive contributions through electrostatic interactions by the polar and hydrogen-bonding functional groups of their glycan chains.     

Hailstones: A Window into the Microbial and Chemical Inventory of a Storm Cloud

Storm clouds frequently form in the summer period in temperate climate zones. Studies on these inaccessible and short-lived atmospheric habitats have been scarce. We report here on the first comprehensive biogeochemical investigation of a storm cloud using hailstones as a natural stochastic sampling tool. A detailed molecular analysis of the dissolved organic matter in individual hailstones via ultra-high resolution mass spectrometry revealed the molecular formulae of almost 3000 different compounds. Only a small fraction of these compounds were rapidly biodegradable carbohydrates and lipids, suitable for microbial consumption during the lifetime of cloud droplets. However, as the cloud environment was characterized by a low bacterial density (Me = 1973 cells/ml) as well as high concentrations of both dissolved organic carbon (Me = 179 µM) and total dissolved nitrogen (Me = 30 µM), already trace amounts of easily degradable organic compounds suffice to support bacterial growth. The molecular fingerprints revealed a mainly soil origin of dissolved organic matter and a minor contribution of plant-surface compounds. In contrast, both the total and the cultivable bacterial community were skewed by bacterial groups (γ-Proteobacteria, Sphingobacteriales and Methylobacterium) that indicated the dominance of plant-surface bacteria. The enrichment of plant-associated bacterial groups points at a selection process of microbial genera in the course of cloud formation, which could affect the long-distance transport and spatial distribution of bacteria on Earth. Based on our results we hypothesize that plant-associated bacteria were more likely than soil bacteria (i) to survive the airborne state due to adaptations to life in the phyllosphere, which in many respects matches the demands encountered in the atmosphere and (ii) to grow on the suitable fraction of dissolved organic matter in clouds due to their ecological strategy. We conclude that storm clouds are among the most extreme habitats on Earth, where microbial life exists.     

Supernovae, neutron stars and biomolecular chirality

Recent theoretical and experimental investigations of the origin of biomolecular chirality are reviewed briefly. Biotic and abiotic theories are evaluated critically with the conclusion that asymmetric photochemical processes with circulary polarized light (CPL), particularly asymmetric photolyses, constitute the most viable mechanisms. Solar CPL sources appear too weak and random to be effective. We suggest an alternative CPL source, namely, the synchrotron radiation from the neutron star remnants of supernova explosions. This could asymmetrically process racemic compounds in the organic mantles of the dust grains in interstellar clouds, and the resulting chiral molecules could be transferred to Earth by cold accretion as the solar system periodically traverses these interstellar clouds.     

Polyynes and Cyanopolyynes: Their Synthesis with the Carbon Arc Gives the Same Abundances Occurring in Carbon-Rich Stars

Carbon vapour generated from a carbon arc or by laser ablation of graphite is reactive with simple molecules and atoms producing end-capped polyyne chains. With these techniques both hydrogen-terminated polyynes as well as monocyano- and dicyanopolyynes have been produced. Experiments based on arcing graphite electrodes can reproduce the molecular distribution of polyynes existing around carbon-rich AGB stars. In fact, it has been found that the relative abundances of the polyynes produced in carbon arc in vacuum decreases by a factor between 3 and 5 as the chain length increases by a C₂ unit. An analogous trend has been observed both for polyynes and cyanopolyynes in the circumstellar environment around carbon-rich stars. This fact suggests that the mechanism of formation of the polyynes in the carbon arc may be similar to that occurring in the surroundings of the carbon-rich stars. Polyynes and cyanopolyynes represent authentic prebiotic molecules which appear quite ubiquitous in the cosmos and should have played a role in the early organic chemistry preceding the appearance of life. Presented at: National Workshop on Astrobiology: Search for Life in the Solar System, Capri, Italy, 26 to 28 October, 2005.     

Fitness in the universe: Choices and necessities

We live in a universe of chance, but not of accident. Repeatedly in the course of its development choices have been made for which one can ask the reasons. One such choice is fundamental: if the proton had not so much greater mass than the electron, all matter would be fluid; and if the proton did not have exactly the same numerical charge as the electron — or some simple multiple of that charge — virtually all matter would be charged. If a universe were started with charged hydrogen, it could expand, but probably nothing more. Hydrogen, carbon, nitrogen and oxygen play as fundamental — and irreplaceable — roles in the metabolism of stars as of living organisms. Both metabolisms are coupled, through radiation from the stars providing the energy on which life must come ultimately to run on the planets. In the course of their evolution on the Earth, living organisms have found their way repeatedly and exclusively to certain types of organic molecule to perform specific functions; so, for example, the chlorophylls for photosynthesis, and carotenoids for plant phototropism and for vision. It is argued that some measure of necessity has governed these choices; and that an extended principle of natural selection has operated at all levels of material organization to produce such elements of order and compatibility in the universe.     

Tacticity control in the synthesis of poly(lactic acid) polymer stars with dipentaerythritol cores

The synthesis of a family of polymer stars with arms of varied tacticities is discussed. The effect of polymer tacticity on the physical properties of these polymer stars is presented. Dipentaerythritol cores support six poly(lactic acid) (PLA) arms. Lewis acidic tin and aluminum catalysts control the polymerization to afford polymer stars of variable tacticity. The analysis of these polymers by NMR spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and differential scanning calorimetry reveals the effects of tacticity control on the physical properties of the polymer stars. Preliminary decomposition studies suggest that the biodegradation profile of a polymer star may also be tuned by stereochemical control. This is the first systematic altering of tacticity in PLA polymer stars, showing that polymer tacticity can have a great impact on star properties.     

Chemical evolution in space

The bulk of complex molecules in the space between the stars is probably contained in small frozen interstellar dust grains. A typical grain is about as old as the earth and has, as a result of photochemical processing, converted a large fraction of its oxygen, carbon and nitrogen bearing mantle into large organic molecules whose maximum molecular weights are limited only by the grain size of about 0.1 m. Laboratory and theoretical methods provide the basis for explaining the evolution of interstellar grains from the time they are formed as seedlings in the atmospheres of cool evolved stars to the time they are destroyed by being incorporated into the material of new stars. The organic dust constitutes about one tenth of a percent of the total mass of the Milky Way and far outweighs any estimates of the total mass of all the planets. A planet like the earth is continually and directly accreting interstellar dust from space. Primitive carbonaceous meteorites show evidence of containing interstellar dust. Since comets are possibly almost pure aggregated interstellar dust they also provide a source of interstellar organic material on the earth.     

Palatability and Chemical Defenses of Macroalgae in the Antarctic Peninsula

We examined palatability of 37 species of nonencrusting macroalgae from the Antarctic Peninsula. This represents approximately 30% of the entire antarctic macroalgal flora and 75% of the 49 nonencrusting species we collected. Organic extracts from most species were also prepared and mixed into artificial foods. We examined palatability using feeding bioassays with three common, macroalga‐consuming animals (an omnivorous antarctic rockfish, Notothenia coriiceps; an omnivorous sea star, Odontaster validus; and a herbivorous amphipod, Gondogenia antarctica). Thallus pieces from 23 of 34 macroalgal species tested with the fish (68%) were rejected. Of the 23 species rejected as thallus, organic extracts of 16 were bioassayed using the fish with 9 (56%) unpalatable. Thallus pieces from 21 of 36 macroalgal species tested with the sea star (58%) were rejected. Of the 21 species rejected as thallus, organic extracts of 20 were bioassayed using the sea stars and 14 (70%) were unpalatable. Overall, 28 of the 37 species assayed as thallus (76%) were rejected by either or both the fish and sea stars. The amphipod assay was not suitable for use with thallus but was utilized with organic extracts of 23 macroalgal species that were rejected as thallus by either or both the fish and sea stars. Of these, 14 (61%) of the species' extracts were rejected by the amphipods. Unpalatability was highest among the brown algae examined with only an ephemeral, ectocarpoid species not rejected as thallus out of 10 species tested. Of the remaining nine brown algal species, six of seven tested were also unpalatable as extracts, including all the ecologically dominant, perennial species in the area. We conclude that unpalatability to herbivores is common in antarctic macroalgae and that chemical defenses may play an important role in the unpalatability of many algal species (NSF OPP9814538, OPP9901076).     

Specific dynamic action in the sunflower star, Pycnopodia helianthoides

The effects of meal size and meal type on specific dynamic action (SDA) were investigated in a large, active asteroid, the sunflower star, Pycnopodia helianthoides. When the sunflower stars were fed clam flesh totalling 5%, 10%, or 20% of their body weight there was a step-wise increase in the scope, time to peak oxygen consumption, duration of the response and total SDA. The change in the rate of oxygen consumption was slower than other organisms, and oxygen uptake remained elevated for over 12 d following consumption of the largest meal. There were also differences in the characteristics of the SDA if sunflower stars consumed a whole clam versus the shucked flesh of a clam. The time to reach peak oxygen consumption was greater for sunflower stars consuming a whole clam. This occurred because the clam had to be opened before they could digest the flesh; a smaller initial peak comprising 3.5% of the total SDA represented the energy require to open the clam valves. When the sunflower stars were fed different prey items (e.g. butter clam, purple urchin and herring) of similar wet organic mass, there was no difference in the time to peak, peak oxygen uptake or total SDA despite the fact that the prey items differed in protein, lipid and caloric content. There was an increased duration for which oxygen uptake remained elevated for sea stars that consumed the urchin meal. Five of the seven sunflower stars that consumed urchins exhibited a smaller second peak in oxygen uptake, totalling approximately 8.5% of the SDA energy budget. This likely represented the energy required to eject the urchin test from the stomach. Although the sunflower star is much larger and more active than other sea stars, it displayed similar SDA responses to other members of the Asteroidea, indicative of the low metabolic rate of this class.     

Reduction of attractiveness to the sea star Asterias forbesi (Desor) by the clam Mercenaria mercenaria (Linnaeus)

Both in field and laboratory choice tests, the sea star, Asterias forbesi (Desor), was attracted to distant upstream clams, Mercenaria mercenaria (Linnaeus). Clams exposed to upstream sea stars were chosen less frequently by downstream sea stars than clams without sea stars upstream. Sea stars neither attracted nor repelled downstream conspecifics.When clams were exposed to upstream sea stars, their oxygen consumption decreased, as did their pumping rate and activity (as measured by number of visible siphons). The former may result from one or both of the latter.It is concluded that clam and sea star sense each other over a distance by chemical cues. The response of the clam is a general lowering of activity which may result in decreased attractiveness to sea star predators. This response may serve as a defensive measure against distance detection by Asterias forbesi.     

Japanese Organic Farmers: Strategies of Uncertainty after the Fukushima Disaster

This ethnographic study of organic farmers affected by radioactive contamination in Japan illuminates responses to situated uncertainty as an everyday mode of subjectivity and practice. The farmers' strategies vary along a continuum from accommodation with dominant institutions to precautions of possible uncertainty to innovations and oppositions of potential uncertainty. Significantly these strategies are contradictory and they show variations in power and morality. The data indicate a subjective- and practice-oriented response that I call localized, relational uncertainty. It is contextualized in farms and villages with responsibility for family, consumers, and organic agriculture itself and it enables farmers to embrace multiple strategies. Thus, uncertainty brings loss and limitations, but also produces opportunities through, for example, expanded trust in relationships, deepened commitment to place, reinterpretation of organic agriculture, and sharpened critique of Japan's trajectory of economic growth.     

Biological feedbacks as cause and demise of the Neoproterozoic icehouse: astrobiological prospects for faster evolution and importance of cold conditions

Several severe glaciations occurred during the Neoproterozoic eon, and especially near its end in the Cryogenian period (630-850 Ma). While the glacial periods themselves were probably related to the continental positions being appropriate for glaciation, the general coldness of the Neoproterozoic and Cryogenian as a whole lacks specific explanation. The Cryogenian was immediately followed by the Ediacaran biota and Cambrian Metazoan, thus understanding the climate-biosphere interactions around the Cryogenian period is central to understanding the development of complex multicellular life in general. Here we present a feedback mechanism between growth of eukaryotic algal phytoplankton and climate which explains how the Earth system gradually entered the Cryogenian icehouse from the warm Mesoproterozoic greenhouse. The more abrupt termination of the Cryogenian is explained by the increase in gaseous carbon release caused by the more complex planktonic and benthic foodwebs and enhanced by a diversification of metazoan zooplankton and benthic animals. The increased ecosystem complexity caused a decrease in organic carbon burial rate, breaking the algal-climatic feedback loop of the earlier Neoproterozoic eon. Prior to the Neoproterozoic eon, eukaryotic evolution took place in a slow timescale regulated by interior cooling of the Earth and solar brightening. Evolution could have proceeded faster had these geophysical processes been faster. Thus, complex life could theoretically also be found around stars that are more massive than the Sun and have main sequence life shorter than 10 Ga. We also suggest that snow and glaciers are, in a statistical sense, important markers for conditions that may possibly promote the development of complex life on extrasolar planets.     

The biochemical composition, energy content, and chemical antifeedant defenses of the common Antarctic Peninsular sea stars Granaster nutrix and Neosmilaster georgianus

The sea stars Granaster nutrix and Neosmilaster georgianus are conspicuous members of benthic communities along the Antarctic Peninsula. An analysis of the proximate composition of somatic body components of nonreproductive adults indicates the nutrient storage organs (pyloric caeca) are rich in both protein (60.7 and 60.6% mean dry wt, respectively) and lipid (25.4 and 29.8% mean dry wt, respectively). Body-wall tissues, while containing small inconspicuous skeletal ossicles, are also comprised of significant levels of organic matter (33.5 and 55.7% mean dry wt, respectively), attributable primarily to protein. Both the pyloric caeca and body-wall tissues are relatively rich in energy (mean energy levels=24.8 and 26.5 kJ g⁻¹ dry wt; 8.4 and 14.1 kJ g⁻¹ dry wt, respectively). Despite the availability of these nutrients and energy neither sea star is preyed upon by the sympatric omnivorous sea star Odontaster validus, a common predator of other Antarctic sea stars. Laboratory feeding bioassays indicate that O. validus rejects live intact individuals and body-wall tissues of both sea star species while readily consuming dried krill. Alginate food pellets containing a krill powder and tissue level concentrations of organic methanol extracts of body-wall tissues were also rejected by O. validus. Moreover, the copious mucus released from the body wall of N. georgianus was deterrent in O. validus food pellet bioassays. Thus, both sea stars evidently possess defensive secondary metabolites that defend against predation and are likely to play a role in mediating materials and energy transfer in the Antarctic benthos.