Nitrogen fixation on early Mars and other terrestrial planets: experimental demonstration of abiotic fixation reactions to nitrite and nitrate

Understanding the abiotic fixation of nitrogen is critical to understanding planetary evolution and the potential origin of life on terrestrial planets. Nitrogen, an essential biochemical element, is certainly necessary for life as we know it to arise. The loss of atmospheric nitrogen can result in an incapacity to sustain liquid water and impact planetary habitability and hydrological processes that shape the surface. However, our current understanding of how such fixation may occur is almost entirely theoretical. This work experimentally examines the chemistry, in both gas and aqueous phases, that would occur from the formation of NO and CO by the shock heating of a model carbon dioxide/nitrogen atmosphere such as is currently thought to exist on early terrestrial planets. The results show that two pathways exist for the abiotic fixation of nitrogen from the atmosphere into the crust: one via HNO and another via NO(2). Fixation via HNO, which requires liquid water, could represent fixation on a planet with liquid water (and hence would also be a source of nitrogen for the origin of life). The pathway via NO(2) does not require liquid water and shows that fixation could occur even when liquid water has been lost from a planet's surface (for example, continuing to remove nitrogen through NO(2) reaction with ice, adsorbed water, etc.).     

Hydrothermal simulation experiments as a tool for studies of the origin of life on Earth and other terrestrial planets: a review

The potential of life's origin in submarine hydrothermal systems has been evaluated by a number of investigators by conducting high temperature-high pressure experiments involving organic compounds. In the majority of these experiments little attention has been paid to the importance of constraining important parameters, such as the pH and the redox state of the system. This is particularly revealed in the apparent difficulties in interpreting experimental data from hydrothermal organic synthesis and stability studies. However, in those cases where common mineral assemblages have been used in an attempt to buffer the pH and redox conditions to geologically and geochemically realistic values, theoretical and experimental data seem to converge. The use of mineral buffer assemblages provides a convenient way by which to constrain the experimental conditions. Studies at high temperatures and pressure in the laboratory have revealed a number of reactions that proceed rapidly in hydrothermal fluids, including the Strecker synthesis of amino acids. In other cases, the verification of postulated abiotic reaction mechanisms has not been possible, at least for large molecules such as large fatty acids and hydrocarbons. This includes the Fischer-Tropsch synthesis reaction. High temperature-high pressure experimental methods have been developed and used successfully for a long time in, for example, mineral solubility studies under hydrothermal conditions. By taking advantage of this experimental experience new and, at times, unexpected directions can be taken in bioorganic geochemistry, one being, for instance, primitive two-dimensional information coding. This article critically reviews some of the organic synthesis and stability experiments that have been conducted under simulated submarine hydrothermal conditions. We also discuss some of the theoretical and practical considerations that apply to hydrothermal laboratory studies of organic molecules related to the origin of life on Earth and probably also to the other terrestrial planets.     

Microbial rock inhabitants survive hypervelocity impacts on Mars-like host planets: first phase of lithopanspermia experimentally tested

The scenario of lithopanspermia describes the viable transport of microorganisms via meteorites. To test the first step of lithopanspermia, i.e., the impact ejection from a planet, systematic shock recovery experiments within a pressure range observed in martian meteorites (5-50 GPa) were performed with dry layers of microorganisms (spores of Bacillus subtilis, cells of the endolithic cyanobacterium Chroococcidiopsis, and thalli and ascocarps of the lichen Xanthoria elegans) sandwiched between gabbro discs (martian analogue rock). Actual shock pressures were determined by refractive index measurements and Raman spectroscopy, and shock temperature profiles were calculated. Pressure-effect curves were constructed for survival of B. subtilis spores and Chroococcidiopsis cells from the number of colony-forming units, and for vitality of the photobiont and mycobiont of Xanthoria elegans from confocal laser scanning microscopy after live/dead staining (FUN-I). A vital launch window for the transport of rock-colonizing microorganisms from a Mars-like planet was inferred, which encompasses shock pressures in the range of 5 to about 40 GPa for the bacterial endospores and the lichens, and a more limited shock pressure range for the cyanobacterium (from 5-10 GPa). The results support concepts of viable impact ejections from Mars-like planets and the possibility of reseeding early Earth after asteroid cataclysms.     

From Halley's Comet to solar terrestrial science : The evolution of the Inter-Agency consultative group

The Inter-Agency Consultative Group (IACG) is an organization which seeks to maximize scientific returns from focused areas of space science through international cooperation. In its 11-year history the IACG has experienced both monumental success (with the collaborative exploration of Comet Halley) and, more recently, some serious growing pains in its second phase of operation, which focuses on solar terrestrial science. In this post-Cold War period, with increased interaction between countries offering greater opportunities for cooperation, the lessons to be learned from the IACG's experience will be valuable ones.     

Why O2 is required by complex life on habitable planets and the concept of planetary "oxygenation time"

Life is constructed from a limited toolkit: the Periodic Table. The reduction of oxygen provides the largest free energy release per electron transfer, except for the reduction of fluorine and chlorine. However, the bonding of O2 ensures that it is sufficiently stable to accumulate in a planetary atmosphere, whereas the more weakly bonded halogen gases are far too reactive ever to achieve significant abundance. Consequently, an atmosphere rich in O2 provides the largest feasible energy source. This universal uniqueness suggests that abundant O2 is necessary for the high-energy demands of complex life anywhere, i.e., for actively mobile organisms of approximately 10(-1)-10(0) m size scale with specialized, differentiated anatomy comparable to advanced metazoans. On Earth, aerobic metabolism provides about an order of magnitude more energy for a given intake of food than anaerobic metabolism. As a result, anaerobes do not grow beyond the complexity of uniseriate filaments of cells because of prohibitively low growth efficiencies in a food chain. The biomass cumulative number density, n, at a particular mass, m, scales as n (> m) proportional to m(-1) for aquatic aerobes, and we show that for anaerobes the predicted scaling is n proportional to m (-1.5), close to a growth-limited threshold. Even with aerobic metabolism, the partial pressure of atmospheric O2 (P(O2)) must exceed approximately 10(3) Pa to allow organisms that rely on O2 diffusion to evolve to a size approximately 10(3) m x P(O2) in the range approximately 10(3)-10(4) Pa is needed to exceed the threshold of approximately 10(2) m size for complex life with circulatory physiology. In terrestrial life, O(2) also facilitates hundreds of metabolic pathways, including those that make specialized structural molecules found only in animals. The time scale to reach P(O(2)) approximately 10(4) Pa, or "oxygenation time," was long on the Earth (approximately 3.9 billion years), within almost a factor of 2 of the Sun's main sequence lifetime. Consequently, we argue that the oxygenation time is likely to be a key rate-limiting step in the evolution of complex life on other habitable planets. The oxygenation time could preclude complex life on Earth-like planets orbiting short-lived stars that end their main sequence lives before planetary oxygenation takes place. Conversely, Earth-like planets orbiting long-lived stars are potentially favorable habitats for complex life.     

Discovery of abundant cellulose microfibers encased in 250 Ma Permian halite: a macromolecular target in the search for life on other planets

In this study, we utilized transmission electron microscopy to examine the contents of fluid inclusions in halite (NaCl) and solid halite crystals collected 650 m below the surface from the Late Permian Salado Formation in southeastern New Mexico (USA). The halite has been isolated from contaminating groundwater since deposition approximately 250 Ma ago. We show that abundant cellulose microfibers are present in the halite and appear remarkably intact. The cellulose is in the form of 5 nm microfibers as well as composite ropes and mats, and was identified by resistance to 0.5 N NaOH treatment and susceptibility to cellulase enzyme treatment. These cellulose microfibers represent the oldest native biological macromolecules to have been directly isolated, examined biochemically, and visualized (without growth or replication) to date. This discovery points to cellulose as an ideal macromolecular target in the search for life on other planets in our Solar System.     

UV photochemistry of DNA in vitro and in Bacillus subtilis spores at earth-ambient and low atmospheric pressure: implications for spore survival on other planets or moons in the solar system

Two major parameters influencing the survival of Bacillus subtilis spores in space and on bodies within the Solar System are UV radiation and vacuum, both of which induce inactivating damage to DNA. To date, however, spore survival and DNA photochemistry have been explored only at the extremes of Earth-normal atmospheric pressure (101.3 kPa) and at simulated space vacuum (10(-3)-10(-6) Pa). In this study, wild-type spores, mutant spores lacking alpha/beta-type small, acid-soluble spore proteins (SASP), naked DNA, and complexes between SASP SspC and DNA were exposed simultaneously to UV (254 nm) at intermediate pressure (1-2 Pa), and the UV photoproducts cis,syn-thymine-thymine cyclobutane dimer (c,sTT), trans,syn-thymine-thymine cyclobutane dimer (t,sTT), and "spore photoproduct" (SP) were quantified. At 101.3 kPa, UV-treated wild-type spores accumulated only SP, but spores treated with UV radiation at 1-2 Pa exhibited a spectrum of DNA damage similar to that of spores treated at 10(-6) Pa, with accumulation of SP, c,sTT, and t,sTT. The presence or absence of alpha/beta-type SASP in spores was partly responsible for the shift observed between levels of SP and c,sTT, but not t,sTT. The changes observed in spore DNA photochemistry at 1-2 Pa in vivo were not reproduced by irradiation of naked DNA or SspC:DNA complexes in vitro, suggesting that factors other than SASP are involved in spore DNA photochemistry at low pressure.     

With a grain of salt: what halite has to offer to discussions on the origin of life

This experimental study investigated how the dynamics of the crystallization of the evaporite mineral halite could affect the accumulation and preservation of organic macromolecules present in the crystallizing solution. Halite was grown under controlled conditions in the presence of polymer nanoparticles that acted as an analog to protocellular material. Optical microscopy, atomic force microscopy, and laser scanning confocal fluorescence microscopy were used to trace the localization of the nanoparticles during and after growth of halite crystals. The present study revealed that the organic nanoparticles were not regularly incorporated within the halite, but were very concentrated on its surfaces. Their distribution was controlled dominantly by the morphologic surface features of the mineral rather than by specific molecular interactions with an atomic plane of the mineral. This means that the distribution of organic molecules was controlled by surfaces like those of halite's evaporitic growth forms. The experiments with halite also demonstrated that a mineral need not continuously incorporate organic molecules during its crystallization to preserve those molecules: After rejection by (non-incorporation into) the crystallizing halite, the organic nanoparticles increased in concentration in the evaporating brine. They ultimately either adsorbed in rectilinear patterns onto the hopper-enhanced surfaces and along discontinuities within the crystals, or they were encapsulated within fluid inclusions. Of additional importance in origin-of-life considerations is the fact that halite in the natural environment rapidly can change its role from that of a protective repository (in the absence of water) to that of a source of organic particles (as soon as water is present) when the mineral dissolves.     

The art and science of interstellar message composition: a report on international workshops to encourage multidisciplinary discussion

Throughout the history of the Search for Extraterrestrial Intelligence (SETI), there has been widespread recognition of the profound societal implications of detecting intelligence beyond Earth. At the SETI Institute, interstellar message construction serves as the focus of a multidisciplinary attempt to prepare for the cultural impact of signal detection and the critical events that would follow. Interstellar message construction at the SETI Institute builds upon the recommendations of the 1991–1992 Workshops on the Cultural Aspects of SETI, while also exploring opportunities for multidisciplinary contributions on new topics. Through a series of international workshops in Toulouse, Paris, Zagreb, Washington, and Bremen, the SETI Institute and partner organizations have fostered broad-based discussion about some of the most important decisions that would follow detection of extraterrestrial intelligence, including “should we reply?” and if so, “what should we say, and how might we say it?”. Several of the themes addressed at these workshops will be highlighted, including the relationship between art and science in designing messages, the value of interactive messages, and the importance of better understanding the nature of language.     

Analysis of volatile lunar compounds: The study of gas retention time on Carbosieve SIII adsorbent with respect to temperature

This work presents the study of the characteristic retention times on Carbosieve SIII adsorbent for several permanent gases CO₂, CO, CH₄, N₂ with respect to the temperature of cooling of adsorption accumulators. To perform this work, a laboratory model of a gas chromatograph that included all key components of a standard instrument has been designed.     

R3DE: Radiation Risk Radiometer-Dosimeter on the International Space Station--optical radiation data recorded during 18 months of EXPOSE-E exposure to open space

Radiation Risk Radiometer-Dosimeter E (R3DE) served as a device for measuring ionizing and non-ionizing radiation as well as cosmic radiation reaching biological samples located on the EXPOSE platform EXPOSE-E. The duration of the mission was almost 1.5 years (2008-2009). With four channels, R3DE detected the wavelength ranges of photosynthetically active radiation (PAR, 400-700?nm), UVA (315-400?nm), UVB (280-315?nm), and UVC (<280?nm). In addition, the temperature was recorded. Cosmic ionizing radiation was assessed with a 256-channel spectrometer dosimeter (see separate report in this issue). The light and UV sensors of the device were calibrated with spectral measurement data obtained by the Solar Radiation and Climate Experiment (SORCE) satellite as standard. The data were corrected with respect to the cosine error of the diodes. Measurement frequency was 0.1?Hz. Due to errors in data transmission or temporary termination of EXPOSE power, not all data could be acquired. Radiation was not constant during the mission. At regular intervals of about 2 months, low or almost no radiation was encountered. The radiation dose during the mission was 1823.98 MJ m(-2) for PAR, 269.03 MJ m(-2) for UVA, 45.73 MJ m(-2) for UVB, or 18.28 MJ m(-2) for UVC. Registered sunshine duration during the mission was about 152 days (about 27% of mission time).The surface of EXPOSE was most likely turned away from the Sun for considerably longer. R3DE played a crucial role on EXPOSE-EuTEF (EuTEF, European Technology Exposure Facility), because evaluation of the astrobiology experiments depended on reliability of the data collected by the device. Observed effects in the samples were weighted by radiation doses measured by R3DE.     

Distribution of Plasma Pressure in the Geomagnetic Tail in the Transition Region from Dipole to Quasidipole and Stretched Magnetic Field Lines: Events on October 13, 1995 and March 13, 1996

The results of an analysis of the pressure distribution of the hot magnetosphere plasma and transverse currents in the plasma at distances from 8R _E to 12R _E are presented. The data were taken in the vicinity of the equatorial plane onboard the Interball-1 satellite during its passages on October 13, 1995 and March 13, 1996. The pressure was determined from the measurements of particle fluxes by the CORALL, DOK-2, and SKA-2 instruments. The specific features of this experiment made it possible to calculate the pressure with a high accuracy and to determine the distribution of the magnetostatically equilibrium currents in the plasma. It is shown that at the parts of the monotonous increase of the pressure in the earthward direction one can detect regions of plateau in the plasma pressure. A possible origin of the small-scale variations and regions with plateau are discussed. A comparison of the measured pressure profiles with the pressure profiles in the Tsyganenko and Mukai-2003 model is performed. Transverse currents flowing in the plasma are calculated assuming magnetostatic equilibrium.