Emerging Possibilities and Insuperable Limitations of Exogeophysics: The Example of Plate Tectonics

To understand the evolution and the habitability of any rocky exoplanet demands detailed knowledge about its geophysical state and history—such as predicting the tectonic mode of a planet. Yet no astronomical observation can directly confirm or rule out the occurrence of plate tectonics on a given exoplanet. Moreover, the field of plate tectonics is still young—questioning whether we should study plate tectonics on exoplanets at this point in time. In this work, we determine the limitations and the emerging possibilities of exogeophysics, the science of connecting geophysics to exoplanets, on the example of plate tectonics. Assuming current uncertainties in model and planet parameters, we develop a qualitatively probabilistic and conservative framework to estimate on what kind of planets and where in the Galaxy plate tectonics might occur. This we achieve by modeling how plate yielding, the most critical condition needed for plate mobility and subduction, is affected by directly observable (planet mass, size) or indirectly, to some degree, assessable planet properties (structure and composition). Our framework not only highlights the importance of a planet's chemistry for the existence of plate tectonics and the path toward practical exogeophysics but also demonstrates how exoplanet science can actually help to better understand geophysics and the fundamentals of plate tectonics on Earth itself

O_2 solubility in Martian near-surface environments and implications for aerobic life

Due to the scarcity of O_2 in the modern Martian atmosphere, Mars has been assumed to be incapable of producing environments with sufficiently large concentrations of O_2 to support aerobic respiration. Here, we present a thermodynamic framework for the solubility of O2 in brines under Martian near-surface conditions. We find that modern Mars can support liquid environments with dissolved O_2 values ranging from ~2.5 × 10^(−6) mol m^(−3) to 2 mol m^(−3) across the planet, with particularly high concentrations in polar regions because of lower temperatures at higher latitudes promoting O_2 entry into brines. General circulation model simulations show that O_2 concentrations in near-surface environments vary both spatially and with time—the latter associated with secular changes in obliquity, or axial tilt. Even at the limits of the uncertainties, our findings suggest that there can be near-surface environments on Mars with sufficient O_2 available for aerobic microbes to breathe. Our findings may help to explain the formation of highly oxidized phases in Martian rocks observed with Mars rovers, and imply that opportunities for aerobic life may exist on modern Mars and on other planetary bodies with sources of O_2 independent of photosynthesis

Follow the Oxygen: Comparative Histories of Planetary Oxygenation and Opportunities for Aerobic Life

Aerobic respiration—the reduction of molecular oxygen (O_2) coupled to the oxidation of reduced compounds such as organic carbon, ferrous iron, reduced sulfur compounds, or molecular hydrogen while conserving energy to drive cellular processes—is the most widespread and bioenergetically favorable metabolism on Earth today. Aerobic respiration is essential for the development of complex multicellular life; thus the presence of abundant O_2 is an important metric for planetary habitability. O_2 on Earth is supplied by oxygenic photosynthesis, but it is becoming more widely understood that abiotic processes may supply meaningful amounts of O_2 on other worlds. The modern atmosphere and rock record of Mars suggest a history of relatively high O2 as a result of photochemical processes, potentially overlapping with the range of O_2 concentrations used by biology. Europa may have accumulated high O_2 concentrations in its subsurface ocean due to the radiolysis of water ice at its surface. Recent modeling efforts suggest that coexisting water and O2 may be common on exoplanets, with confirmation from measurements of exoplanet atmospheres potentially coming soon. In all these cases, O_2 accumulates through abiotic processes—independent of water-oxidizing photosynthesis. We hypothesize that abiogenic O_2 may enhance the habitability of some planetary environments, allowing highly energetic aerobic respiration and potentially even the development of complex multicellular life which depends on it, without the need to first evolve oxygenic photosynthesis. This hypothesis is testable with further exploration and life-detection efforts on O_2-rich worlds such as Mars and Europa, and comparison to O_2-poor worlds such as Enceladus. This hypothesis further suggests a new dimension to planetary habitability: “Follow the Oxygen,” in which environments with opportunities for energy-rich metabolisms such as aerobic respiration are preferentially targeted for investigation and life detection

Comparison of Box-Behnken, Face Central Composite and Full Factorial Designs in Optimization of Hempseed Oil Extraction by n-Hexane: a Case Study

Statistical multivariate methods like Box-Behnken, face central composite and full factorial designs (BBD, FCCD and FFD, respectively) in combination with the response surface methodology (RSM) were compared when applied in modeling and optimization of the hempseed oil (HSO) extraction by n-hexane. The effects of solvent-to-seed ratio, operation temperature and extraction time on HSO yield were investigated at the solvent-to-seed ratio of 3:1, 6.5:1 or 10:1 mL/g, the extraction temperature of 20, 45 or 70 °C and the extraction time of 5, 10 or 15 min. All three methods were efficient in the statistical modeling and optimization of the influential process variables and led to almost the same optimal process conditions and predicted HSO yield. Having better statistical performances and being economically advantageous over the FFD with repetition, the BBD or FCCD combined with the RSM is recommended for the optimization of liquid-solid extraction processes

Korišćenje otpadnih koštica šljive kao izvora ulja i katalizatora za proizvodnju biodizela

Possibilities of using waste plum stones in biodiesel production were investigated. The plum kernels were used as a source to obtain oil by the Soxhlet extraction method, while the whole plum stones, the plum stone shells that remained after the crashing, and the plum kernel cake that remained after the oil extraction, were burned off to obtain ashes. The collected ashes were characterized by elemental composition, porosity, and base strength and tested for catalytic activity in transesterification of esterified plum kernel oil. Dominant elements were potassium, calcium, and magnesium at different contents in the three obtained ashes. The most active catalyst was the plum stone shell ash, so the effect of temperature (40, 50, and 60°C) on the reaction rate was investigated. The reaction rate constant increased with the reaction temperature with the activation energy value of 58.8 kJ mol-1. In addition, the plum stone shell ash can be reused as a catalyst after recalcination.U ovom radu istraživana je mogućnost korišćenja otpadnih koštica šljive u proizvodnji biodizela. Jezgra šljive su iskorišćena kao sirovina za dobijanje ulja primenom Soxhlet-ove metode ekstrakcije. Cele koštice, ljuske koštica šljive i pogača dobijena nakon ekstrakcije ulja iz jezgra šljive spaljeni su da bi se dobio pepeo, koji je korišćen kao katalizator. Dobijene tri vrste sakupljenog pepela su najpre okarakterisane u pogledu hemijskog sastava, poroznosti i baznosti, a zatim je testirana katalitička aktivnost u transesterifikaciji esterifikovanog ulja koštica šljive. Dominantni elementi u pepelu, kao što su kalijum, kalcijum i magnezijum, imali su različit sadržaj u sve tri vrste pepela. Najveću katalitičku aktivnost pokazao je pepeo koštica šljive, zbog čega je dalje istraživan uticaj temperature (40, 50 i 60 °C) na brzinu reakcije katalizovane ovim pepelom. Konstanta brzine reakcije povećavala se sa porastom temperature reakcije, a vrednost energije aktivacije je 58,8 kJ mol-1 . Pored toga, pepeo koštica šljive može se ponovo koristiti kao katalizator nakon rekalcinacije

O_2 solubility in Martian near-surface environments and implications for aerobic life

Due to the scarcity of O_2 in the modern Martian atmosphere, Mars has been assumed to be incapable of producing environments with sufficiently large concentrations of O_2 to support aerobic respiration. Here, we present a thermodynamic framework for the solubility of O2 in brines under Martian near-surface conditions. We find that modern Mars can support liquid environments with dissolved O_2 values ranging from ~2.5 × 10^(−6) mol m^(−3) to 2 mol m^(−3) across the planet, with particularly high concentrations in polar regions because of lower temperatures at higher latitudes promoting O_2 entry into brines. General circulation model simulations show that O_2 concentrations in near-surface environments vary both spatially and with time—the latter associated with secular changes in obliquity, or axial tilt. Even at the limits of the uncertainties, our findings suggest that there can be near-surface environments on Mars with sufficient O_2 available for aerobic microbes to breathe. Our findings may help to explain the formation of highly oxidized phases in Martian rocks observed with Mars rovers, and imply that opportunities for aerobic life may exist on modern Mars and on other planetary bodies with sources of O_2 independent of photosynthesis

Follow the Oxygen: Comparative Histories of Planetary Oxygenation and Opportunities for Aerobic Life

Aerobic respiration—the reduction of molecular oxygen (O_2) coupled to the oxidation of reduced compounds such as organic carbon, ferrous iron, reduced sulfur compounds, or molecular hydrogen while conserving energy to drive cellular processes—is the most widespread and bioenergetically favorable metabolism on Earth today. Aerobic respiration is essential for the development of complex multicellular life; thus the presence of abundant O_2 is an important metric for planetary habitability. O_2 on Earth is supplied by oxygenic photosynthesis, but it is becoming more widely understood that abiotic processes may supply meaningful amounts of O_2 on other worlds. The modern atmosphere and rock record of Mars suggest a history of relatively high O2 as a result of photochemical processes, potentially overlapping with the range of O_2 concentrations used by biology. Europa may have accumulated high O_2 concentrations in its subsurface ocean due to the radiolysis of water ice at its surface. Recent modeling efforts suggest that coexisting water and O2 may be common on exoplanets, with confirmation from measurements of exoplanet atmospheres potentially coming soon. In all these cases, O_2 accumulates through abiotic processes—independent of water-oxidizing photosynthesis. We hypothesize that abiogenic O_2 may enhance the habitability of some planetary environments, allowing highly energetic aerobic respiration and potentially even the development of complex multicellular life which depends on it, without the need to first evolve oxygenic photosynthesis. This hypothesis is testable with further exploration and life-detection efforts on O_2-rich worlds such as Mars and Europa, and comparison to O_2-poor worlds such as Enceladus. This hypothesis further suggests a new dimension to planetary habitability: “Follow the Oxygen,” in which environments with opportunities for energy-rich metabolisms such as aerobic respiration are preferentially targeted for investigation and life detection

Optimizacija proizvodnje biodizela kukuruznog ulja metanolizom katalizovanom pepelom kurdeljke

The use of low-cost or priceless feedstocks such as byproducts in biodiesel production results in a reduced overall process costs. The present paper reports the use of corn germs and corn cobs as byproducts from corn-based starch production in the biodiesel production by the methanolysis of the oil extracted from corn germs, catalyzed by the ash produced by combustion of corn cobs. The major aim was to optimize the methanol-to-oil molar ratio, catalyst loading, and reaction time in a batch stirred reactor with respect to the content of methyl ester fatty acids (FAME). The statistical modeling and optimization were carried out using a second-order polynomial (quadratic) model developed by the response surface methodology combined with a 33 factorial design with 3 central points. The FAME content was determined by a high-pressure liquid chromatography method. The analysis of variance showed that only the catalyst amount, the reaction time, the catalyst amount interaction with reaction time and all three quadratic terms were the significant model terms with the confidence level of 95 %. The optimum reaction conditions (the catalyst amounts of 19.8 %, the methanol-to-oil molar ratio of 9.4 mol/mol and the reaction time of 31 min) provided the FAME content of 98.1 %, which was in an excellent agreement with the predicted FAME content (98.4 %). Thus, both corn germs and corn cobs may be suitable feedstocks for biodiesel production.Upotreba jeftinih ili bezvrednih sirovina, kao što su sporedni proizvodi, u proizvodnji biodizela ima za rezultat smanjene ukupne troškove procesa. U ovom radu su prikazani rezultati upotrebe kukuruznih klica i okrunjenog kukuruznog klipa (kurdeljke, krudeljke) kao sporednih proizvoda iz proizvodnje kukuruznog skroba u proizvodnji biodizela metanolizom ulja izdvojenog iz kukuruznih klica, katalizovane pepelom dobijenim sagorevanjem kurdeljke. Glavni cilj je bila optimizacija molskog odnosa metanol-ulje, količine katalizatora i reakcionog vremena u šaržnom reaktoru sa mešanjem u odnosu na sadržaj metilestra masnih kiselina (MEMK). Statističko modelovanje i optimizacija izvršeni su korišćenjem kvadratnog modela, razvijenog metodologijom odzivne površine, u kombinaciji sa 33 faktorijelnim planom sa 3 centralne tačke. Sadržaj MEMK-a je određen metodom tečne hromatografije pod visokim pritiskom. Analiza varijanse je pokazala da su samo uticaji količine katalizatora, reakcionog vremena, interakcije količine katalizatora sa reakcionim vremenom i sva tri kvadratna člana statistički značajni sa nivoom pouzdanosti od 95 %. Pod optimalnim reakcionim uslovima (količina katalizatora 19,8 %, molski odnos metanol/ulje 9,4 mol/mol i reakciono vreme 31 min) dobijen je sadržaj MEMK-a od 98,1 %, koji se slaže sa predviđenim sadržajem MEMK-a (98,4 %). Prema tome, i kukuruzne klice i kurdeljka mogu biti pogodne sirovine za proizvodnju biodizela

A triethanolamine:choline chloride deep eutectic solvent as a cosolvent in the ethanolysis of Brassica nigra L. seed oil

Black mustard (Brassica nigra L.) seeds oil (BMSO), characterized by a high content of erucic acid (C22:1), belongs to inedible oils. Since BMSO has a high percentage of monounsaturated and branched fatty acids, it is a suitable raw material for biodiesel production. Also, green cosolvents, like deep eutectic solvents (DESs), can improve the biodiesel production process. This study reports the influence of the triethanolamine:choline chloride DES (2:1 mol/mol) on the BMSO ethanolysis over calcined CaO as a catalyst, under the following reaction conditions: temperature of 50, 60, and 70 ºC, ethanol-to-oil molar ratio of 12:1, as well as TEOA:ChCl DES and calcined CaO content of 20% and 10%, respectively. At 70 ºC, the ChCl:TEOA DES provided a high content of fatty acid ethyl esters (FAEE) (98.46±0.7%) after 1.5 min, compared to the control reaction (without the presence of DES), where the maximum FAEE content (98.05±0.6%) was achieved within 4 h. BMSO ethanolysis was described by the kinetic model of the pseudo-first order and the model of variable reaction order concerning TAG and the autocatalytic behavior of the ethanolysis reaction. Both kinetic models, with great accuracy, fitted the experimental data. As a result, physicochemical properties of the obtained biodiesel were within the limit values prescribed by the quality standard EN 14214. Also, the reusability of calcined CaO was proven even in four cycles with the FAEE content of over 90%

Pepeo pšenične slame kao katalizator u proizvodnji biodizela

Wheat straw ash (WSA) was investigated as a new catalyst in biodiesel production from sunflower oil. The catalyst was characterized by temperature-programmed decomposition, X-ray powder diffraction, Hg porosimetry, N2 physisorption, and scanning electron microscopy - energy dispersive X-ray spectroscopy methods. The methanolysis reaction was tested in the temperature range of 55–65 oC, the catalyst loading range 10–20 % of the oil weight, and the methanol-to-oil molar ratio range 18 : 1–24 : 1. The reaction conditions of the sunflower oil methanolysis over WSA were optimized by using the response surface methodology in combination with the historical experimental design. The optimum process conditions ensuring the highest fatty acid methyl esters (FAME) content of 98.6 % were the reaction temperature of 60.3 oC, the catalyst loading of 11.6 % (based on the oil weight), the methanol-to-oil molar ratio of 18.3 :1, and the reaction time of 124 min. The values of the statistical criteria, such as coefficients of determination (R2 = 0.811, R2pred = 0.789, R2adj = 0.761) and the mean relative percent deviation (MRPD) value of 10.6 % (66 data) implied the acceptability and precision of the developed model. The FAME content after 4 h of reaction under the optimal conditions decreased to 37, 12, and 3 %, after the first, second, and third reuse, respectively.Pepeo pšenične slame (PPS) je korišćen kao katalizator u proizvodnji biodizela iz sunco-kretovog ulja. Karakterizacija katalizatora je izvršena primenom metoda tempera-turski programiranom razgradnjom (temperature-programmed decomposition, TPDe), rentgenskom difrakcijom (X-ray diffraction, XRD), Hg porozimetrijom, N2 fizi-sorpcijom i skenirajućom elektronskom mikrosopijom sa energo-disperzivnom spek-trometrijom (scanning electron microscopy and energy dispersive X-ray spectroscopy, SEM-EDS). Reakcija metanolize istraživana je pri sledećim reakcionim uslovima: tem-peraturni opseg 55-65 °C; količina katalizatora 10-20 % (računato na masu ulja) i opseg molskog odnosa methanol : ulje 18 : 1 – 24 : 1. Optimizacija reakcionih uslova izvršena je metodologijom površine odziva u kombinaciji sa istorijskim eksperimentalnim planom. Maksimalni prinos metil estara masnih kiselina (MEMK) od 98,6 % postignut je pri sledećim optimalnim reakcionim uslovima: temperatura 60,3 oC, količina katalizatora 11,6 % (računato na masu ulja), molski odnos methanol : ulje 18,3 : 1 i vreme trajanja reakcije 124 min. Vrednosti koeficijenata determinacije (R2 = 0,811, R2pred = 0,789, R2adj = 0,761) i srednjeg relativnog odstupanja (10,6 %, 66 podataka) ukazali su na prihvatljivost i pouzdanost razvijenog modela. Sadržaj MEMK nakon 4 h reakcije pri optimalnim uslovima smanjen je na 37, 12 i 3 % nakon prve, druge i treće upotrebe katalizatora, redom