Extraterrestrial Environments Research Articles

Physicochemical Salt Solution Parameters Limit the Survival of Planococcus halocryophilus in Martian Cryobrines.

Microorganisms living in sub-zero environments can benefit from the presence of dissolved salts, as they significantly increase the temperature range of liquid water by lowering the freezing point. However, high concentrations of salts can reduce microbial growth and survival, and can evoke a physiological stress response. It remains poorly understood how the physicochemical parameters of brines (e.g. water activity, ionic strength, solubility and hydration shell strength between the ions and the surrounding water molecules) influence the survival of microorganisms. We used the cryo− and halotolerant bacterial strain Planococcus halocryophilus as a model organism to evaluate the degree of stress different salts assert. Cells were incubated in liquid media at −15°C containing single salts at eutectic concentrations (CaCl2, LiCl, LiI, MgBr2, MgCl2, NaBr, NaCl, NaClO4 and NaI). Four of these salts (LiCl, LiI, MgBr2 and NaClO4) were also investigated at concentrations with a low water activity (0.635) and, separately, with a high ionic strength (8 mol/L). Water activity of all solutions was measured at −15°C. This is the first time that water activity has been measured for such a large number of liquid salt solutions at constant sub-zero temperatures (−15°C). Colony-Forming Unit (CFU) counts show that the survival of P. halocryophilus has a negative correlation with the salt concentration, molecular weight of the anion and anion radius; and a positive correlation with the water activity and anions’ hydration shell strength. The survival of P. halocryophilus did not show a significant correlation with the ionic strength, the molecular weight of the cation, the hydrated and unhydrated cation and hydrated anion radius, and the cations’ hydration bond length. Thus, the water activity, salt concentration and anion parameters play the largest role in the survival of P. halocryophilus in concentrated brines. These findings improve our understanding of the limitations of microbial life in saline environments, which provides a basis for better evaluation of the habitability of extraterrestrial environments such as Martian cryobrines.

The PANGAEA mineralogical database.

Future human missions to the surface of the Moon and Mars will involve scientific exploration requiring new support tools to enable rapid and high quality science decision-making. Here, we describe the PANGAEA (Planetary ANalogue Geological and Astrobiological Exercise for Astronauts) Mineralogical Database developed by ESA (European Space Agency): a catalog of petrographic and spectroscopic information on all currently known minerals identified on the Moon, Mars, and associated with meteorites. The catalog also includes minerals found in the analog field sites used for ESA's geology and astrobiology training course PANGAEA, to broaden the database coverage. The Mineralogical Database is composed of the Summary Catalog of Planetary Analog Minerals and of the Spectral Archive and is freely available in the public repository of ESA PANGAEA. The Summary Catalog provides essential descriptive information for each mineral, including name (based on the International Mineralogical Association recommendation), chemical formula, mineral group, surface abundance on planetary bodies, geological significance in the context of planetary exploration, number of collected VNIR and Raman spectra, likelihood of detection using different spectral methods, and bibliographic references evidencing their detection in extraterrestrial or terrestrial analog environments. The Spectral Archive provides a standard library for planetary in-situ human and robotic exploration covering Visual-Near-Infrared reflective (VNIR) and Raman spectroscopy (Raman). To populate this library, we collected VNIR and Raman spectra for mineral entries in the Summary Catalog from open-access archives and analyzed them to select the ones with the best spectral features. We also supplemented this collection with our own bespoke measurements. Additionally, we compiled the chemical compositions for all the minerals based on their empirical formula, to allow identification using the measured abundances provided by LIBS and XRF analytical instruments. When integrated into an operational support system like ESA's Electronic Fieldbook (EFB) system, the Mineralogical Database can be used as a real-time and autonomous decision support tool for sampling operations on the Moon, Mars and during astronaut geological field training. It provides both robust spectral libraries to support mineral identification from instrument outputs, and relevant contextualized information on detected minerals.

Survival of the Halophilic Archaeon Halovarius luteus after Desiccation, Simulated Martian UV Radiation and Vacuum in Comparison to Bacillus atrophaeus

Extraterrestrial environments influence the biochemistry of organisms through a variety of factors, including high levels of radiation and vacuum, temperature extremes and a lack of water and nutrients. A wide variety of terrestrial microorganisms, including those counted amongst the most ancient inhabitants of Earth, can cope with high levels of salinity, extreme temperatures, desiccation and high levels of radiation. Key among these are the haloarchaea, considered particularly relevant for astrobiological studies due to their ability to thrive in hypersaline environments. In this study, a novel haloarchaea isolated from Urmia Salt Lake, Iran, Halovarius luteus strain DA50T, was exposed to varying levels of simulated extraterrestrial conditions and compared to that of the bacteria Bacillus atrophaeus. Bacillus atrophaeus was selected for comparison due to its well-described resistance to extreme conditions and its ability to produce strong spore structures. Thin films were produced to investigate viability without the protective influence of cell multi-layers. Late exponential phase cultures of Hvr. luteus and B. atrophaeus were placed in brine and phosphate buffered saline media, respectively. The solutions were allowed to evaporate and cells were encapsulated and exposed to radiation, desiccation and vacuum conditions, and their post-exposure viability was studied by the Most Probable Number method. The protein profile using High Performance Liquid Chromatography and Matrix Assisted Laser Desorption/Ionization bench top reflector time-of-flight are explored after vacuum and UV-radiation exposure. Results showed that the change in viability of the spore-forming bacteria B. atrophaeus was only minor whereas Hvr. luteus demonstrated a range of viability under different conditions. At the peak radiation flux of 105 J/m2 under nitrogen flow and after two weeks of desiccation, Hvr. luteus demonstrated the greatest decrease in viability. This study further expands our understanding of the boundary conditions of astrobiologically relevant organisms in the harsh space environment.

A Systematic Study of the Limits of Life in Mixed Ion Solutions: Physicochemical Parameters Do Not Predict Habitability.

This study investigated what defines the limits of life in mixed ion solutions. Better understanding these limits should allow us to better predict the habitability of extreme environments on the Earth and extraterrestrial environments. We systematically examined the response of Bacillus subtilis, a well characterized non-halophile model organism, to a range of solutions made from single and mixed salts up to their solubility limits and measured at what concentration growth was arrested, specifically exploring Na, Mg, and Ca cations and Cl, SO4, and ClO4 anions. We measured the physicochemical properties of the solutions to identify which properties correlated with the limits of growth. Individual salts imposed a growth limit specific to the combination of cation and anion, although we generally observe that chloride salts allow growth at lower water activity than sulfate salts, with perchlorate restricting growth even at the highest measured water activity. Growth was limited at a wide range of ionic strength, with no apparently correlation. Despite the theoretically counteracting disordering effects (chaotropic) of perchlorates and ordering effects (kosmotropic) effects of sulfates, when these salts were combined they instead additively narrowed the window for growth in both the Na and Mg cation systems, in the same manner as the combined effects of two chaotropic Ca salts. Our results imply that away from hard limits that might be imposed by physicochemical properties such as water activity, ionic strength or chaotropicity in highly concentrated brines, these properties do not set the limits of life. Instead these limits are highly specific to the salts and organisms in question. This specificity means that the habitability of extreme environments cannot be predicted, even with accurate measurements of the physicochemical conditions present.

Fitness of Outer Membrane Vesicles From Komagataeibacter intermedius Is Altered Under the Impact of Simulated Mars-like Stressors Outside the International Space Station.

Outer membrane vesicles (OMVs), produced by nonpathogenic Gram-negative bacteria, have potentially useful biotechnological applications in extraterrestrial extreme environments. However, their biological effects under the impact of various stressors have to be elucidated for safety reasons. In the spaceflight experiment, model biofilm kombucha microbial community (KMC) samples, in which Komagataeibacter intermedius was a dominant community-member, were exposed under simulated Martian factors (i.e., pressure, atmosphere, and UV-illumination) outside the International Space Station (ISS) for 1.5 years. In this study, we have determined that OMVs from post-flight K. intermedius displayed changes in membrane composition, depending on the location of the samples and some other factors. Membrane lipids such as sterols, fatty acids (FAs), and phospholipids (PLs) were modulated under the Mars-like stressors, and saturated FAs, as well as both short-chain saturated and trans FAs, appeared in the membranes of OMVs shed by both post-UV-illuminated and “dark” bacteria. The relative content of zwitterionic and anionic PLs changed, producing a change in surface properties of outer membranes, thereby resulting in a loss of interaction capability with polynucleotides. The changed composition of membranes promoted a bigger OMV size, which correlated with changes of OMV fitness. Biochemical characterization of the membrane-associated enzymes revealed an increase in their activity (DNAse, dehydrogenase) compared to wild type. Other functional membrane-associated capabilities of OMVs (e.g., proton accumulation, interaction with linear DNA, or synaptosomes) were also altered after exposure to the spaceflight stressors. Despite alterations in membranes, vesicles did not acquire endotoxicity, cytotoxicity, and neurotoxicity. Altogether, our results show that OMVs, originating from rationally selected nonpathogenic Gram-negative bacteria, can be considered as candidates in the design of postbiotics or edible mucosal vaccines for in situ production in extreme environment. Furthermore, these OMVs could also be used as promising delivery vectors for applications in Astromedicine.

Reactions of translationally cold trapped CCl+ with acetylene (C2H2).

Ion-neutral chemical reactions are important in several areas of chemistry, including in some regions of the interstellar medium, planetary atmospheres, and comets. Reactions of CCl+ with C2H2 are measured, and the main products include C3H2 + and C3H+, both relevant in extraterrestrial environments. Accurate branching ratios are obtained, which favor the formation of C3H2 + over C3H+ by a factor of four. The measured rate constants are on the order of Langevin, and complementary electronic structure calculations are used to aid in the interpretation of experimental results.

Improving Limitations of Rover Missions in the Moon and Planets by Unifying Vehicle–Terrain Interaction Models

This paper extends the analysis of empirical methods for describing vehicle–terrain interactions in lunar terrain. Given analytical formulation to predict mobility performance in extraterrestrial environments requires reliable in situ testing campaigns, this imposes fundamental restrictions to conceive a more consolidated theory, and further any possibility to use improved empirical methods to design better space hardware. Hence, we propose an analytical approach to extrapolate data taken in parabolic flights to model vehicle performance in multiple gravity regimes. The extrapolation technique and respective reported uncertainties can be used, therefore, to tune fitting parameters of a set of general formulas in the domain of Terramechanics, allowing to have empirical estimates of the wheel mobility in cases where testing is inherently very complex. Finally, by the analysis of previous Moon and Mars rover missions with the fitted equations, we report an empirical design criterion that allows to generate first estimates of the optimal wheel dimensions, taking into account the eventual longitudinal slip of the rover and including the desired mass of the payload. The introduced rules for geometry optimization can be important for future space rover missions in remote soils.

Growth on Carbohydrates from Carbonaceous Meteorites Alters the Immunogenicity of Environment-Derived Bacterial Pathogens.

The last decade has witnessed a renewed interest in space exploration. Public and private institutions are investing considerable effort toward the direct exploration of the Moon and Mars, as well as more distant bodies in the solar system. Both automated and human-crewed spacecraft are being considered in these efforts. As inevitable fellow travelers on the bodies of astronauts, spaceships, or equipment, terrestrial microorganisms will undoubtedly come into contact with extraterrestrial environments, despite stringent decontamination. These microorganisms could eventually adapt and grow in their new habitats, where they might potentially recolonize and lead to the infection of the human space travelers. In this article, we demonstrate that clinically relevant bacterial species found in the environment are able to grow in minimal media with sugar compounds identified in extraterrestrial carbon sources. As a surrogate model, we used carbohydrates previously isolated from carbonaceous meteorites. The bacteria underwent an adaptation process that caused structural modifications in the cell envelope that sparked changes in pathogenic potential, both in vitro and in vivo. Understanding the adaptation of microorganisms exposed to extraterrestrial environments, with subsequent changes in their immunogenicity and virulence, requires a comprehensive analysis of such scenarios to ensure the safety of major space expeditions in the decades to come.

Penetration and relaxation behavior of JSC-1A lunar regolith simulant under cryogenic conditions

Lunar in situ resource utilization discussions have recently been focused on the presence and distribution of ice in the upper layers of surface regolith, in particular within the confines of the permanently shadowed regions. Extraction ideas - ranging from simple scooping to percussive drilling and thermal (optical) mining utilizing cold-trap volatile capture – require detailed knowledge of the mechanical properties of icy regolith as we are likely to encounter. Penetrometers provide a robust and straightforward measurement technique for determining soil properties, but previous research fails to reliably show measurement sensitivity to increasing ice content due to difficulties in experimentation at cryogenic conditions. To display the capability of a simple conical penetrometer to discern saturation levels of icy regolith simulant within an expected range, we conducted laboratory penetration and subsequent relaxation measurements of JSC-1A lunar simulant using a specially-designed cryogenic apparatus which minimizes sample temperature fluctuation as well as the thermal mismatch between the penetrating probe and tested sample. We measured penetration resistance and force relaxation behavior for JSC-1A lunar simulant under constant displacement rate penetration at ~300 mTorr pressure, ~110 K sample temperature, 170 K to 190 K probe temperature, and ice contents of 0% to 12% and 100%. Penetration resistance and relaxation behavior both showed sensitivity to ice content, with parameters of best-fit curve models offering simple empirical predictors of saturation. A critical ice content of 1% to 3%, wherein a significant increase in penetration resistance occurs, is identified as being fundamentally influenced by the filling of substantial pore space with grouting ice. A decrease in viscoelastic behavior of high ice content samples at cryogenic temperatures is noted, and inhibition of relaxation mechanisms due to activation-energy-based temperature effects is also demonstrated in dry, ice-free simulant. Additional research across the spectrum of ice saturations, temperatures, and pressure environments likely to be found in extraterrestrial environments is suggested to improve upon these results, in particular using cryogenic systems even more specialized to reduce thermal issues and increase load capacities and apparatus stiffness. Such additional information will serve to advance the potential use of these results and this technology in future exploratory missions.

The MaMBA-concept for an extraterrestrial base and its first module mock-up

Habitats must enable astronauts to survive in an extraterrestrial environment, but the challenge is not only a technological one: architecture and engineering should be brought together to create an environment in which a crew can perform optimally. With missions to Mars in mind, crew mental health becomes a design driver equally important to the support of physiological functions. We here suggest a habitat concept, MaMBA (short for Moon and Mars Base Analog), which combines the two requirements. In its basic configuration, MaMBA consists of six upright cylindrical, hard-shell pressure vessels as main modules and two airlocks, which are all connected with inflatable corridor modules. We present the current state of the design and particularly focus on the laboratory module, of which we have constructed a mock-up equipped with scientific instrumentation. In the long-term, we plan to develop this laboratory module into a functional prototype including subsystems such as the life support system. Eventually, we aim to create a habitat which can serve as a test platform (for technologies, operations, and procedures) and whose usability is continually validated through iterative testing with human inhabitants. The habitat is open to international partners for simulations.

The Radiation Stability of Thymine in Solid H2O.

Nucleobases are of significant importance to all known organisms, may be an important building block of life, and could be important biosignatures of current or past life. Given their potential significance to the field of astrobiology, it is important to understand the survival of these molecules when subjected to ionizing radiation as is present in a range of extraterrestrial environments. In this work, we present data on the kinetics of the radiolytic destruction of pure thymine and water + thymine ice mixtures at temperatures from 13 to 150 K. Rate constants were measured using in situ infrared spectroscopy, and radiolytic half-lives for thymine were computed for different planetary and interstellar environments. Our results demonstrate that the survival of thymine decreases as the dilution of thymine in water increases. Additionally, we find that thymine survival increases with ice temperature and that this decrease may be related to structure of the ice matrix.

Life in the near space and implications for astrobiology

Near space is a region that lies between 20 and 100 km above sea level, which includes the major region of the stratosphere, the mesosphere and the lower thermosphere. Near space comprises a harsher physical environment which contains high ultraviolet light levels, subzero temperatures, desiccation and low atmospheric pressure, in comparison to the low-altitude atmosphere. This provides a unique analogue environment that resembles the surface conditions of Mars, the high-altitude atmospheric environments of Venus and the high radiation environments of early Earth. Microorganisms can enter the lower atmosphere and the near space through weather systems like wind, geological activities like earthquake and volcanic eruption and human activities like air transportation. In recent years, methodological and technological advances have deepened our understanding of the diversity and survival strategies of organisms in near space. Payload systems and methods for exposing organisms and for in situ collecting microbial samples in near space have been designed and developed. Consequently, a growing number of studies investigate the microbial survival strategies in near space by exposing model microorganisms (e.g., bacteria, archaea and yeasts) to near space extreme environments through flight exposures. A diverse group of microorganisms have been isolated, identified and characterized from near space, suggesting that it may potentially contain a vast unknown microbial biosphere. The dispersal of life in near space may play an essential role in shaping global patterns of microbial biodiversity and biogeography. The ability of these microbes to survive under near space extreme environments has prompted researchers from different disciplines to study them to better understand their diversity, distribution and survival strategies. Near space not only provides great opportunities to investigate some basic biological questions such as the biological effects of radiations, but it also has a wide application potential since microorganisms in near space, as extremophiles, are a valuable source of a variety of new genes and enzymes. Astrobiology is the study of the origin, evolution, habitability and future of life on Earth and beyond in the context of cosmic evolution. One promising research field in astrobiology is planetary analogue research which conducts experiments and tests in specific environments on Earth that have physical/chemical similarities to the extraterrestrial environments. Analogue research has offered new insights into the planetary habitability and the search for extraterrestrial life. Near space as a natural laboratory can provide hard evidence for important astrobiology topics including the limits to life on Earth, the upper boundary of Earth’s biosphere, the possibility of interplanetary transport of life, the assessment of panspermia hypothesis and the planetary protection. With the recent development of the Chinese Space Station and deep-space exploration, the study of near space biology will provide support for future space station related research and will further promote the development of astrobiology in China. Here I review the major advances in biodiversity in near space and their survival strategies, with emphases on key astrobiology questions associated with the research of near space. I also highlight major challenges that will be necessary to address in future research and discuss possible perspectives in the study of near space biology.

Non-terrestrial Material Agency

We are interested in discussing and exploring the intermingling of non-human agency, degrees of aliveness and alien life. Through the Proto-Alien Project (Proto-A), we investigate the synthesis and use of extraterrestrial organic matter (ETOM) as an active medium for artistic expression. We particularly focus on the ability to self-assemble, the morphogenetic tendencies and the non-linear behaviour of non-terrestrial material assemblages in liquids other than water. Largely, this project is a framework, a multi-disciplinary laboratory of ideas and experiments at the intersection of astrobiology, chemistry and media art. Our aim is to use ETOM to grow soft, kinetic and intelligent agents: autonomous ‘others’ that thrive and avoid equilibrium on extraterrestrial environments —a new type of alien material agency, yet unknown to humankind.

The discovery of cosmic fullerenes

In 2010, the Spitzer Space Telescope detected evidence of a complex form of carbon that had never been seen in extraterrestrial environments. Jan Cami recounts the discovery of buckminsterfullerene in space.

The subsurface habitability of small, icy exomoons

Context. Assuming our Solar System as typical, exomoons may outnumber exoplanets. If their habitability fraction is similar, they would thus constitute the largest portion of habitable real estate in the Universe. Icy moons in our Solar System, such as Europa and Enceladus, have already been shown to possess liquid water, a prerequisite for life on Earth. Aims. We intend to investigate under what thermal and orbital circumstances small, icy moons may sustain subsurface oceans and thus be “subsurface habitable”. We pay specific attention to tidal heating, which may keep a moon liquid far beyond the conservative habitable zone. Methods. We made use of a phenomenological approach to tidal heating. We computed the orbit averaged flux from both stellar and planetary (both thermal and reflected stellar) illumination. We then calculated subsurface temperatures depending on illumination and thermal conduction to the surface through the ice shell and an insulating layer of regolith. We adopted a conduction only model, ignoring volcanism and ice shell convection as an outlet for internal heat. In doing so, we determined at which depth, if any, ice melts and a subsurface ocean forms. Results. We find an analytical expression between the moon’s physical and orbital characteristics and the melting depth. Since this expression directly relates icy moon observables to the melting depth, it allows us to swiftly put an upper limit on the melting depth for any given moon. We reproduce the existence of Enceladus’ subsurface ocean; we also find that the two largest moons of Uranus (Titania and Oberon) could well sustain them. Our model predicts that Rhea does not have liquid water. Conclusions. Habitable exomoon environments may be found across an exoplanetary system, largely irrespective of the distance to the host star. Small, icy subsurface habitable moons may exist anywhere beyond the snow line. This may, in future observations, expand the search area for extraterrestrial habitable environments beyond the circumstellar habitable zone.

From Neolithic towards space revolution: emergence of a new means of socio-natural interaction

The subject of this research is the ongoing drastic transformations in interactions between nature and humankind at the stage of space exploration. Earth’s material production will continue being developed, but at the same time, a completely new process will emerge, brought about by human interaction with extraterrestrial natural environment. This means predictions of taking production into outer space, especially heavy industry, which was even conceptualized by Konstantin Tsiolkovsky. Special importance in its development will be played by extraterrestrial mining industry. The author demonstrates that sustainable mining will continue to on Earth even after development of space mining, and these processes will be closely connected. Without development of space mining, it would be practically impossible to continue exploring space or ensure space security. It will be space mining that will play the defining role in formation of a new, space means of socio-natural interaction, which will define further evolution of our civilization in broad exploration of the Universe.

Functional Organization of extraterrestrial underground base on Mars

In the article relevant problems of colonization of other planets by mankind and development of extraterrestrial settlements are examined, in particular colonization of Mars and creation of Martian multifunctional base. Modern projects of leading space agencies for research and Mars colonization, shipping of equipment and the first settlers to the planet, and also projects of the first Martian habitats within the modern space technologies are discussed. In response to that natural and climatic conditions of the planet Mars which could substantially influence the formation and development of extraterrestrial multifunctional base are analyzed. Main natural and climatic factors such as high radiation background, absence of atmosphere, extreme temperature profile, low gravity, that have significant influence on formation of the Martian settlement on functional architectural and organizational levels are determined in the study. Functional model for establishment of an autonomic multifunctional base in extraterrestrial environment under the surface of the planet is proposed like the most fully satisfying the requirements for organization of extraterrestrial artificial environment for human's long-term stay considering extreme climate conditions of planet Mars and the desire to create comfortable conditions for livelihood of Martian pioneers. Basic blocks are determined and zones being parts of these blocks, which form the basis of the functional organization of extraterrestrial multifunctional complexes are detected. Possible options for functional connections between blocks and zones are analyzed.

High-resolution mass spectrometry for future space missions: Comparative analysis of complex organic matter with LAb-CosmOrbitrap and laser desorption/ionization Fourier transform ion cyclotron resonance.

Mass spectrometers are regularly boarded on spacecraft for the exploration of the Solar System. A better understanding of the origin, distribution and evolution of organic matter and its relationships with inorganic matter in different extra-terrestrial environments requires the development of innovative space tools, described as Ultra-High-Resolution Mass Spectrometry (UHRMS) instruments. Analyses of a complex organic material simulating extraterrestrial matter (Titan's tholins) are performed with a homemade space-designed Orbitrap™ equipped with a laser ablation ionization source at 266 nm: the LAb-CosmOrbitrap. Mass spectra are obtained using only one laser shot and transient duration of 838 ms. A comparison is made on the same sample with a laboratory benchmark mass spectrometer: a Fourier Transform Ion Cyclotron Resonance equipped with a laser desorption ionization source at 355 nm (LDI-FTICR) allowing accumulation of 20,000 laser shots. Mass spectra and attributions of molecular formulae based on the peaks detected by both techniques show significant similarities. Detection and identification of the same species are validated. The formation of clusters ions with the LAb-CosmOrbitrap is also presented. This specific feature brings informative and unusual indirect detections about the chemical compounds constituting Titan's tholins. In particular, the detection of HCN confirms previous results obtained with laboratory Electrospray Ionization (ESI)-UHRMS studies about the understanding of polymeric patterns for the formation of tholins. The capabilities of the LAb-CosmOrbitrap to decipher complex organic mixtures using single laser shot and a short transient are highlighted. In agreement with results provided by a commercial FTICR instrument in the laboratory, we demonstrate in this work the relevance of a space laser-CosmOrbitrap instrument for future planetary exploration.

Persistence of Habitable, but Uninhabited, Aqueous Solutions and the Application to Extraterrestrial Environments.

In most environments on Earth, habitable environments contain life. Experiments were conducted to investigate the decoupling of the presence of habitable conditions and life. A set of microcosms habitable for known groups of organisms, but uninhabited (i.e., uninhabited habitats), was exposed to external environmental conditions to test the hypothesis that extreme habitable environments can remain uninhabited for sustained time periods. These microcosms were made of tubes containing liquid water and inorganic N, P, and S. Organics (used as electron donors and as a C source) were provided as L and D amino acids. One set of uninhabited habitats contained no additional salts, one set contained saturated NaCl, and one set contained saturated MgSO4. A ddH2O control and a complex medium for Halobacterium were used as controls. The presence of organisms was tested by enumeration of colonists and sequencing of extracted DNA. At each time point, inoculation into fresh medium was used to test for growth of organisms. After 1 week, the "no salt" and saturated MgSO4 solutions were colonized. After 6 months, both the NaCl-saturated and Halobacterium solutions remained uninhabited, but all other samples were colonized. These experiments demonstrate that certain types of habitable liquid water environments exposed to microbial atmospheric inoculation, even on Earth, can remain devoid of reproducing life for many months. On other planetary bodies, such as Mars, these data imply the possibility of preserved transient water bodies that would record habitable conditions, but no evidence of life, even if life existed elsewhere on the planet.

Thermal Heads for Melt Drilling to Subglacial Lakes: Design and Testing.

Antarctic subglacial lakes are often considered suitable analogues to extraterrestrial subglacial aqueous environments. Recently, an environmentally friendly RECoverable Autonomous Sonde (RECAS) was designed at the Polar Research Center of Jilin University (JLU) to sample the water of subglacial lakes without contamination. In this regard, the development of a fast-penetration thermal head is the key issue for RECAS. Two different prototypes were designed and tested at the JLU ice-well to determine the optimal design and operation parameters of the thermal heads. Practical top and bottom thermal heads were then designed based on one of the prototypes, which can penetrate ice at an average rate of 1.88 m/h. The test results for the RECAS thermal heads show that the rate of penetration (ROP) can be 1.80-1.95 m/h in -10°C ice, and the axial load on the thermal head only affects the ROP when it is lower than a specified threshold. The decrease of the ice temperature from -10°C to -30°C leads to a decrease of 17% in the ROP. The bottom thermal head can drill into dirty ice, and a simple collector positioned above the head can collect solid particles suspended in the melted ice. The top thermal head exhibited a long lifetime and stable heating performance after being powered in water for 2 weeks. In addition, the ice temperature near the borehole was monitored to evaluate the range of heat disturbance caused by the thermal head.