Habitable Environments Research Articles

Macroautophagy and its Role in the Pathogenesis of Tuberculosis

Tuberculosis is a widespread disease worldwide that is caused by various mycobacterium tuberculosis (MTB). The main feature of this pathogen is the ability to persist inside the cells, carrying out phagocytosis. The pathogenesis of tuberculosis includes both inherent and adaptive immunity.The specific role in the genesis of the disease is played by macrophages, which are not only the first line of defense of macroorganism, but also they are habitable environment for MTB. Persistence inside alveolar macrophages is the absolute prerequisite to human disease. Another effector mechanism has come to the scientists’ attention, which could potentially be a kind of «key» in the treatment of mycobacterial infection. This process is called macroautophagy, its feature is the regulated isolation of the pathogen inside macrophages into special phagophores and also the formation of an autophagosome. Then comes the fusion of the autophagosome with the lysosome and intracellular degradation of the pathogen. Meanwhile, MTB has developed strategies to avoid macroautophagy. Here is the list: increased expression of the Eis (enhanced intracellular survival) gene; inhibition of Ras-related protein-Rab-7a; suppression of IFN-γ exposure to interlikin-6 produced by MTB-infected macrophages; and microRNA regulation. All these mechanisms reflect a well-coordinated process of autophagy avoiding. They are potential points to affect combating against MTB. Research objective. To summarize and analyze the data presented in PubMed, eLIBRARY, CyberLeninka databases on macroautophagy as a process that maintains intracellular homeostasis and its potential use against mycobacterial infection. This review also highlighted the factors that mycobacterium use to evade macroautophagy, which contributes to the persistence of this microorganism inside macrophages and complicates the process of recuperation. Materials and methods. The macroautophagy process and its peculiarities in MTB control were the object of study and searches in the PubMed, eLIBRARY, and CyberLeninka databases. We analyzed data presented in the open press for the last 27 years (1994-2020), the inquiry included the pathogenesis of MTB and strategies of MTB evasion of macroautophagy. Results. It was found that macroautophagy can potentially be a component of treatment of mycobacterial infection, but this aspect requires more detailed study. We also examined those strategies that ensure MTB survival inside phagocytic cells. These mechanisms of macroautophagy evasion can be points of application of pathogenetic therapy as well as host targeting therapy.

The Biological Study of Lifeless Worlds and Environments

Astrobiology is focused on the study of life in the universe. However, lifeless planetary environments yield biological information on the variety of ways in which physical and chemical conditions in the universe preclude the possibility of the origin or persistence of life, and in turn this will help explain the distribution and abundance of life, or lack of it, in the universe. Furthermore, many places that humans wish to explore and settle in space are lifeless, and studying the fate of life in these environments will aid our own success in thriving in them. In this synthetic review, I have three objectives, as follows: (1) To discuss the biological value and use of lifeless environments, (2) To explore the diverse planetary bodies and environments that can be lifeless and to categorize them, and (3) To propose sets of biological experiments that can be undertaken in different categories of lifeless worlds and environments and suggest concepts for mission ideas to realize these goals. They include origin of life and microbial inoculation experiments in lifeless but habitable environments. I suggest that the biological study of lifelessness is an underappreciated area in planetary sciences.

A 571 million-year-old alkaline volcanic lake photosynthesizing microbial community, the Anti-atlas, Morocco.

The Ediacaran period coincides with the emergence of ancestral animal lineages and cyanobacteria capable of thriving in nutrient deficient oceans which together with photosynthetic eukaryotic dominance, culminated in the rapid oxygenation of the Ediacaran atmosphere. However, ecological evidence for the colonization of the Ediacaran terrestrial biosphere by photosynthetic communities and their contribution to the oxygenation of the biosphere at this time is very sparse. Here, we expand the repertoire of Ediacaran habitable environments to a specific microbial community that thrived in an extreme alkaline volcanic lake 571Myr ago in the Anti-atlas of Morocco. The microbial fabrics preserve evidence of primary growth structures, comprised of two main microbialitic units, with the lower section consisting of irregular and patchy thrombolytic mesoclots associated with composite microbialitic domes. Calcirudite interbeds, dominated by wave-rippled sandy calcarenites and stromatoclasts, fill the interdome troughs and seal the dome tops. A meter-thick epiclastic stromatolite bed grading upwards from a dominantly flat to wavy laminated base, transitions into low convex laminae consisting of decimeter to meter-thick dome-shaped stromatolitic columns, overlies the thrombolitic and composite microbialitic facies. Microbialitic beds constructed during periods of limited clastic input, and underlain by coarse-grained microbialite-derived clasts and by the wave-rippled calcarenites, suggest high-energy events associated with lake expansion. High-resolution microscopy revealed spherulitic aggregates and structures reminiscent of coccoidal microbial cell casts and mineralized extra-polymeric substances (EPS). The primary fabrics and multistage diagenetic features, represented by active carbonate production, photosynthesizing microbial communities, photosynthetic gas bubbles, gas escape structures, and tufted mats, suggest specialized oxygenic photosynthesizers thriving in alkaline volcanic lakes, contributed toward oxygen variability in the Ediacaran terrestrial biosphere.

Larval Zebrafish Use Olfactory Detection of Sodium and Chloride to Avoid Salt Water

Salinity levels constrain the habitable environment of all aquatic organisms. Zebrafish are freshwater fish that cannot tolerate high-salt environments and would therefore benefit from neural mechanisms that enable the navigation of salt gradients to avoid high salinity. Yet zebrafish lack epithelial sodium channels, the primary conduit land animals use to taste sodium. This suggests fish may possess novel, undescribed mechanisms for salt detection. In the present study, we show that zebrafish indeed respond to small temporal increases in salt by reorienting more frequently. Further, we use calcium imaging techniques to identify the olfactory system as the primary sense used for salt detection, and we find that a specific subset of olfactory receptor neurons encodes absolute salinity concentrations by detecting monovalent anions and cations. In summary, our study establishes that zebrafish larvae have the ability to navigate and thus detect salinity gradients and that this is achieved through previously undescribed sensory mechanisms for salt detection.

Knowledge management model for effective technology transfer at universities

Industry engagement and the application of universities’ research outcomes for shaping society to achieve a habitable environment are possible as a result of technology transfer. With reference to universities in the Czech Republic, this paper proposes a model of effective knowledge management for intellectual property created by university employees according to the structure of individual faculties and their main research focus. The ultimate goal is to achieve effective technology transfer through knowledge management. A review of previous technology transfer models, such as appropriability, dissemination, knowledge utilization, communication, use of a university technology transfer office, and the Triple Helix, shows that these models cannot effectively transfer technology individually but can do so in combination at different levels. Consequently, a knowledge management model is introduced in this study for the transfer of technology from universities. The introduction of technology transfer offices (TTOs) is expected to protect intellectual property, generate new knowledge and create access to valuable knowledge, among other benefits.

Mars 2020 Mission Overview

The Mars 2020 mission will seek the signs of ancient life on Mars and will identify, prepare, document, and cache a set of samples for possible return to Earth by a follow-on mission. Mars 2020 and its Perseverance rover thus link and further two long-held goals in planetary science: a deep search for evidence of life in a habitable extraterrestrial environment, and the return of martian samples to Earth for analysis in terrestrial laboratories. The Mars 2020 spacecraft is based on the design of the highly successful Mars Science Laboratory and its Curiosity rover, but outfitted with a sophisticated suite of new science instruments. Ground-penetrating radar will illuminate geologic structures in the shallow subsurface, while a multi-faceted weather station will document martian environmental conditions. Several instruments can be used individually or in tandem to map the color, texture, chemistry, and mineralogy of rocks and regolith at the meter scale and at the submillimeter scale. The science instruments will be used to interpret the geology of the landing site, to identify habitable paleoenvironments, to seek ancient textural, elemental, mineralogical and organic biosignatures, and to locate and characterize the most promising samples for Earth return. Once selected, ∼35 samples of rock and regolith weighing about 15 grams each will be drilled directly into ultraclean and sterile sample tubes. Perseverance will also collect blank sample tubes to monitor the evolving rover contamination environment. In addition to its scientific instruments, Perseverance hosts technology demonstrations designed to facilitate future Mars exploration. These include a device to generate oxygen gas by electrolytic decomposition of atmospheric carbon dioxide, and a small helicopter to assess performance of a rotorcraft in the thin martian atmosphere. Mars 2020 entry, descent, and landing (EDL) will use the same approach that successfully delivered Curiosity to the martian surface, but with several new features that enable the spacecraft to land at previously inaccessible landing sites. A suite of cameras and a microphone will for the first time capture the sights and sounds of EDL. Mars 2020’s landing site was chosen to maximize scientific return of the mission for astrobiology and sample return. Several billion years ago Jezero crater held a 40 km diameter, few hundred-meter-deep lake, with both an inflow and an outflow channel. A prominent delta, fine-grained lacustrine sediments, and carbonate-bearing rocks offer attractive targets for habitability and for biosignature preservation potential. In addition, a possible volcanic unit in the crater and impact megabreccia in the crater rim, along with fluvially-deposited clasts derived from the large and lithologically diverse headwaters terrain, contribute substantially to the science value of the sample cache for investigations of the history of Mars and the Solar System. Even greater diversity, including very ancient aqueously altered rocks, is accessible in a notional rover traverse that ascends out of Jezero crater and explores the surrounding Nili Planum. Mars 2020 is conceived as the first element of a multi-mission Mars Sample Return campaign. After Mars 2020 has cached the samples, a follow-on mission consisting of a fetch rover and a rocket could retrieve and package them, and then launch the package into orbit. A third mission could capture the orbiting package and return it to Earth. To facilitate the sample handoff, Perseverance could deposit its collection of filled sample tubes in one or more locations, called depots, on the planet’s surface. Alternatively, if Perseverance remains functional, it could carry some or all the samples directly to the retrieval spacecraft. The Mars 2020 mission and its Perseverance rover launched from the Eastern Range at Cape Canaveral Air Force Station, Florida, on July 30, 2020. Landing at Jezero Crater will occur on Feb 18, 2021 at about 12:30 PM Pacific Time.

Hydrothermal Activity at a Cretaceous Seamount, Canary Archipelago, Caused by Rejuvenated Volcanism

Our knowledge of venting at intraplate seamounts is limited. Almost nothing is known about past hydrothermal activity at seamounts, because indicators are soon blanketed by sediment. This study provides evidence for temporary hydrothermal circulation at Henry Seamount, a re-activated Cretaceous volcano near El Hierro island, close to the current locus of the Canary Island hotspot. In the summit area at around 3000–3200 m water depth, we found areas with dense coverage by shell fragments from vesicomyid clams, a few living chemosymbiotic bivalves, and evidence for sites of weak fluid venting. Our observations suggest pulses of hydrothermal activity since some thousands or tens of thousands years, which is now waning. We also recovered glassy heterolithologic tephra and dispersed basaltic rock fragments from the summit area. Their freshness suggests eruption during the Pleistocene to Holocene, implying minor rejuvenated volcanism at Henry Seamount probably related to the nearby Canary hotspot. Heat flow values determined on the surrounding seafloor (49 ± 7 mW/m2) are close to the expected background for conductively cooled 155 Ma old crust; the proximity to the hotspot did not result in elevated basal heat flow. A weak increase in heat flow toward the southwestern seamount flank likely reflects recent local fluid circulation. We propose that hydrothermal circulation at Henry Seamount was, and still is, driven by heat pulses from weak rejuvenated volcanic activity. Our results suggest that even single eruptions at submarine intraplate volcanoes may give rise to ephemeral hydrothermal systems and generate potentially habitable environments.

The Canova Association: “Historical Continuation” and the Rebirth of Two Northern Italian Villages

The Canova Association is an international non-profit organization founded in 2001 in the medieval village of Canova, in Oira di Crevoladossola (Verbano-Cusio-Ossola, Italy). The main purpose and the goal of the association are the re-evaluation of local stone architecture and raising awareness and appreciation of its importance, all of it through educational, cultural and artistic events and activities. During these years, Mauricio Cesprini and Ken Marquardt have witnessed the gradual transformation of this historic enclave into a habitable environment following the teachings of the local building tradition.

Sustainable urban mobility: An approach to urbanization and motorization challenges in Nigeria, a case of Lagos state

In Lagos state, the relationship between urbanization and motorization is unbalanced because the present transportation interventions of the state do not commensurate with her growing population and migration rate. However, the state cannot be said to be totally insensitive to these challenges as witnessed in her renewed effort by providing suitable public transportation system with a dedicated lane and the expansion of other modes of transport such as rail and inland water transport. Through content analysis, this research examined the present situation of Lagos state public transport system with her prevailing population size, sustainable urban mobility approach and the future of public transport in Lagos State in line with global practices. The study reviewed the Lagos state non-motorized transport policy and the impact thus far. It was revealed that unless certain strategic decisions and policies are made, the state will continue to experience the current traffic congestion on her roads as well as increased vehicular pollution and waste of resources. Also, for Lagos state to attain her acclaimed position of a 21st century economy, she must as a matter of policy initiate and implement interventions that align with the principle of urban mobility where cycling, walking, high capacity buses operation is effectively operational and open up of other modes of transportation in the state. It was further recommended that the Lagos state government should take a bold step as recently done in the restriction of motorcycles and tricycles operation on certain routes within the state, hence, initiating interventions that will best enhance public transportation, improve habitable environment and safety of lives and properties in the state.

The Effect of Learning Habit and Learning Environment at School to The Students’ Achievement at Madrasah Tsanawiyah Insan Qur’ani Aceh Besar

The title of this research was “the effect of learning habit and learning environment at school to the students’ achievement at Madrasah Tsanawiyah Insan Qur’ani Aceh Besar”, which aimed to know the effect of learning habit and learning environment at school to the students’ achievement both partially and simultaneously at Madrasah Tsanawiyah Insan Qur'ani Aceh Besar. The research used a quantitative approach with the kind of descriptive research. The population of research was the students in grade VIII that contain 128 students in the class and as the sample were 25 students. The sample was obtained by using Proportionate Stratified Random Sampling. The technique of collecting data will be obtained from observation, questionnaire, and documentation. The techniques of data analysis are used multiple linear regression analysis with t-test and f-test at a significant level of 0.05. The result of research showed that there was a significant effect of learning habit and learning environment to the students’ achievement.

Dynamic aperture factor analysis/target transformation (DAFA/TT) for Mg-serpentine and Mg-carbonate mapping on Mars with CRISM near-infrared data

Serpentine and carbonate are products of serpentinization and carbonation processes on Earth, Mars, and other celestial bodies. Their presence implies that localized habitable environments may have existed on ancient Mars. Factor Analysis and Target Transformation (FATT) techniques have been applied to hyperspectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) to identify possible serpentine and Mg-carbonate-bearing outcrops. FATT techniques are capable of suggesting the presence of individual spectral signals in complex spectral mixtures. Applications of FATT techniques to CRISM data thus far only evaluate whether an entire analyzed image (≈ 3 × 105 pixels) may contain spectral information consistent with a specific mineral of interest. The spatial distribution of spectral signal from the possible mineral is not determined, making it difficult to validate a reported detection and also to understand the geologic context of any purported detections. We developed a method called Dynamic Aperture Factor Analysis/Target Transformation (DAFA/TT) to highlight the locations in a CRISM observation (or any similar laboratory or remotely acquired data set) most likely to contain spectra of specific minerals of interest. DAFA/TT determines the locations of possible target mineral spectral signals within hyperspectral images by performing FATT in small moving windows with different geometries, and only accepting pixels with positive detections in all cluster geometries as possible detections. DAFA/TT was applied to a hyperspectral image of a serpentinite from Oman for validation testing in a simplified laboratory setting. The mineral distribution determined by DAFA/TT application to the laboratory hyperspectral image was consistent with Raman analysis of the serpentinite sample. DAFA/TT also successfully mapped the spatial distribution of Mg-serpentine and Mg-carbonate previously detected in CRISM data using band parameter mapping and extraction of ratioed spectra. We applied DAFA/TT to CRISM images in some olivine-rich regions of Mars to characterize the spatial distribution of Mg-serpentine and Mg-carbonate-bearing outcrops.

It is time to rebalance the risk equation

The fear of unintended consequences is frequently used to argue against conservation interventions that range from climate engineering, to genetic editing of imperiled species, to actions as seemingly mundane as using seeds from non-local sources in restoration projects. There is no denying that unintended consequences are real and worthy of concern. Indeed, environmental textbooks are filled with descriptions of past interventions gone awry (such as the introduction of cane toads to Australia for biocontrol, the impacts of long-term wildfire suppression, or the use of DDT to control insect pests). However, there are also numerous counterexamples of interventions turning out as planned (for instance, barging salmon smolts around Snake River dams and human-assisted hybridization rescuing the depleted gene pool of Florida panthers). For actions under consideration, the question is how to weigh the possible unintended consequences versus the highly likely intended benefits. A June 2020 workshop (https://reviv​erest​ore.org/inten​ded-conse​quences), organized by Revive & Restore, assembled an international group of conservationists (including wildlife biologists, restoration scientists, geneticists, ethicists, and social scientists) to re-examine the precautionary principle and its associated focus on unintended and unanticipated consequences. Two observations make apparent the need for this reassessment. First, accelerating anthropogenic climate change and the expanding human footprint create ever-greater urgency for actions that could avert disasters or prevent human-driven extinctions. With most rivers dammed, a nitrogen cycle dominated by human alterations, and such severe global warming that within 50 years as many as one in three humans could be forced to migrate in search of a habitable environment (https://nyti.ms/2E5a0Wi), conservationists do not have the luxury of “doing nothing” out of fear of unintended consequences. Caution is prudent, but paralysis is unconscionable. Second, the science of risk assessment has advanced so that, although it is impossible to eliminate uncertainty, the likelihood of horrific ecological surprises is much less now than in previous decades. Ecologists today better understand ecosystems and indirect effects than they did in the 1960s and 1970s when several well-intended, but ill-fated, introductions were conducted (eg introducing the American red squirrel to Newfoundland to augment the diet of pine martens; introducing the seed weevil Rhinocyllus conicus to control exotic thistles in North America). Lessons learned with each intervention reduce the chance for future errors. Not only is risk assessment improving, but some of the tools for intervention are becoming refined. For example, the genomic and phenotypic changes that result from gene editing are much more precise than those wrought by more widely accepted techniques like hybridization and mutagenesis. Obviously, the answer is not to blithely ignore unintended consequences and adopt an “anything goes” attitude. However, it is time to recalibrate our traditional cautionary approach to environmental decision making with fine-tuning in four dimensions. First, the intended consequences of proposed interventions must carry more weight in analyses. Consider the public debate over transgenic Bt crops. The intended benefit of reducing the application of broadly toxic insecticides has largely been overshadowed by fears of environmental harms, for which there is no convincing evidence. Second, scientists should avoid being overly influenced by examples of disaster from generations ago and give more credit to recently accumulated empirical evidence. From reintroductions to genetic rescues, the vast majority of contemporary environmental interventions have produced their intended positive outcomes, yet a few historical cases of problematic outcomes continue to dominate public perception. Moreover, all actions, including inaction, entail the potential for unintended consequences. For instance, growing evidence shows that protected area creation – an intervention largely embraced by conservationists – typically displaces, rather than curtails, environmental harms and can prove counterproductive if local communities are alienated. Third, risk assessment relies on tools ranging from controlled experiments and practical experience to models and simulations. All of these tools help characterize risk, but empirical data should be far more reassuring than theoretical, but untested, models. Thirty years of globally widespread Bt crops with no ill-effects ought to inspire confidence, whereas speculative interventions such as solar geoengineering warrant greater precaution. Lastly, and most importantly, scientists need to recognize that the worst unintended consequences may not be environmental or ecological, but rather social. A carbon tax might be a great way to reduce greenhouse-gas emissions and a protected area may secure a remnant population of a declining species, but such actions disproportionately impose costs on marginalized human communities. A wider variety of voices must be invited to weigh in on what intended outcomes are desired, and how best to achieve them. While risk reduction efforts now better recognize and minimize unintended environmental harms, much work remains to address unintended social and cultural consequences. MICHELLE MARVIER Santa Clara University, Santa Clara, CA PETER KAREIVA Aquarium of the Pacific, Long Beach, CA

Response of soil faunal communities to tea tree cultivars in the hilly region of western Sichuan, China

Soil fauna is vitally important to all soil ecosystems due to its significant role in humification and mineralization of plant residues, cycling of nutrients, improvement of soil porosity and structure, etc. Soil fauna is sensitive to land-use changes, fertilizer use, tillage, and land degradation. Tea production is one of the most important agricultural industries in China. However, very few studies have investigated the responses of soil fauna to tea tree (Camellia sinensis L.) cultivars; understanding these responses is crucial to maintaining soil health and biological diversity stability in such agricultural ecosystems. This paper concentrates on the impacts of tea trees on soil faunal community composition and diversity, forming the background of an evaluation of the land-use sustainability associated with various cultivars. Soil samples were collected at a depth of 0−20 cm from four major tea plantations in western Sichuan, China, with different cultivars (“Chuannong Huangyazao” - CH, “Fuding Dabai” - FD; “Chuanmu No.217” - CM, and “Chuancha No.3” - CC). The results showed that different tea tree cultivars in this study had significant (p < 0.05) influences on soil chemical properties. The soil at the FD plantation had the lowest pH, total nitrogen (TN), and available phosphorus (AP) but the highest available nitrogen (AN), while the soil at the CM plantation had the highest pH, AP and available potassium (AK). The highest soil faunal abundance (as indicated by the number of individuals per unit area) and community diversity (as indicated by Shannon and Margalef indices) occurred at the CC plantation. This result illustrated that compared to the other plantations, the CC plantation provided a more habitable environment and more nutrient resources for the soil faunal community development. The diversity of the soil faunal community was highly associated (p < 0.05) with variations in soil pH, organic carbon (OC), TN, AP and AK. The effects of tea tree cultivars on the rare soil faunal composition differed among the four tea plantations, but no significant difference in the composition of dominant and common taxa was observed. The relative abundance of the top ten soil faunal taxa was strongly associated with environmental variables. The two most important environmental factors (AP and AN) accounted for 57 % of the changes in soil faunal composition. This study highlighted cultivation and land-use management practices to promote soil health sustainability and soil faunal stability on land degraded by tea tree cultivars in western Sichuan, China.

3D Printed Minerals as Astrobiology Analogs of Hydrothermal Vent Chimneys.

Hydrothermal vents, which are highly plausible habitable environments for life and of interest for some origin-of-life scenarios, may exist on icy moons such as Europa or Enceladus in addition to Earth. Some hydrothermal vent chimney structures are extremely porous and friable, making their reconstruction in the lab challenging (e.g., brucite or saponite in alkaline hydrothermal settings). Here, we present the results from our efforts to reconstruct a simplified chimney structure directly out of mineral powder using binder jet additive manufacturing. Olivine sand was chosen for this initial method development effort since it represents a naturally occurring seafloor material and is inexpensively available in large quantities in powder form. The crystal structure of olivine used for the print was not modified during the process, as confirmed by powder X-ray diffraction (XRD). To characterize the microstructure of our 3D printed precipitates, we used computed tomography (CT) X-ray scan techniques. We also evaluated a chimney precipitate from a sample collected from the Prony Hydrothermal Field (PHF), southern New Caledonia, an alkaline system driven by serpentinization with mineralogy composed of brucite and carbonates. While not directly comparable from a mineralogical point of view, the microstructure and porosity of both precipitates was similar, suggesting that our 3D printing technique may be a valuable tool for future astrobiology research on hydrothermal vent precipitates.

Heat Production and Tidally Driven Fluid Flow in the Permeable Core of Enceladus

AbstractSaturn's moon Enceladus has a global subsurface ocean and a porous rocky core in which water‐rock reactions likely occur; it is thus regarded as a potentially habitable environment. For icy moons like Enceladus, tidal heating is considered to be the main heating mechanism, which has generally been modeled using viscoelastic solid rheologies in existing studies. Here we provide a new framework for calculating tidal heating based on a poroviscoelastic model in which the porous solid and interstitial fluid deformation are coupled. We show that the total heating rate predicted for a poroviscoelastic core is significantly larger than that predicted using a classical viscoelastic model for intermediate to large (&gt;1014 Pa·s) rock viscosities. The periodic deformation of the porous rock matrix is accompanied by interstitial pore fluid flow, and the combined effects through viscous dissipation result in high heat fluxes particularly at the poles. The heat generated in the rock matrix is also enhanced due to the high compressibility of the porous matrix structure. For a sufficiently compressible core and high permeability, the total heat production can exceed 10 GW—a large fraction of the moon's total heat budget—without requiring unrealistically low solid viscosities. The partitioning of heating between rock and fluid constituents depends most sensitively on the viscosity of the rock matrix. As the core of Enceladus warms and weakens over time, pore fluid motion likely shifts from pressure‐driven local oscillations to buoyancy‐driven global hydrothermal convection, and the core transitions from fluid‐dominated to rock‐dominated heating.

Abiotic redox reactions in hydrothermal mixing zones: Decreased energy availability for the subsurface biosphere

Subseafloor mixing of high-temperature hot-spring fluids with cold seawater creates intermediate-temperature diffuse fluids that are replete with potential chemical energy. This energy can be harnessed by a chemosynthetic biosphere that permeates hydrothermal regions on Earth. Shifts in the abundance of redox-reactive species in diffuse fluids are often interpreted to reflect the direct influence of subseafloor microbial activity on fluid geochemical budgets. Here, we examine hydrothermal fluids venting at 44 to 149 °C at the Piccard hydrothermal field that span the canonical 122 °C limit to life, and thus provide a rare opportunity to study the transition between habitable and uninhabitable environments. In contrast with previous studies, we show that hydrocarbons are contributed by biomass pyrolysis, while abiotic sulfate (SO42-) reduction produces large depletions in H2 The latter process consumes energy that could otherwise support key metabolic strategies employed by the subseafloor biosphere. Available Gibbs free energy is reduced by 71 to 86% across the habitable temperature range for both hydrogenotrophic SO42- reduction to hydrogen sulfide (H2S) and carbon dioxide (CO2) reduction to methane (CH4). The abiotic H2 sink we identify has implications for the productivity of subseafloor microbial ecosystems and is an important process to consider within models of H2 production and consumption in young oceanic crust.

Returning Samples From Enceladus for Life Detection

Evidence suggests that Saturn’s icy moon Enceladus has a subsurface ocean that sources plumes of water vapor and ice vented to space from its south pole. In situ analyses of this material by the Cassini spacecraft have shown that the ocean contains key ingredients for life (elements H, C, N, O and possibly S; simple and complex organic compounds; chemical disequilibria at water-rock interfaces; clement temperature, pressure, and pH). The Cassini discoveries make Enceladus’ interior a prime locale for life detection beyond Earth. Scant material exchange with the inner Solar System makes it likely that such life would have emerged independently of life on Earth. Thus, its discovery would illuminate life’s universal characteristics. The alternative result of an upper bound on a detectable biosphere in an otherwise habitable environment would likewise considerably advance our understanding of the prevalence of life beyond Earth. Here we outline the rationale for returning vented ocean samples, accessible from Enceladus’ surface or low altitudes, to Earth for life detection. Returning samples allows analyses using laboratory instruments that cannot be flown, with decades or more to adapt and repeat analyses. We describe an example set of measurements to estimate the amount of sample to be returned and discuss possible mission architectures and collection approaches. We then turn to the challenges of preserving sample integrity and implementing planetary protection policy. We conclude by placing such a mission in the broader context of Solar System exploration.

Groundwater Flow to Gale Crater in an Episodically Warm Climate

AbstractOrbiter and rover data have revealed a complex and intermittent hydrological history in Gale Crater on Mars, where habitable environments appear to have endured for at least thousands of years. The intermittency may be the result of a dominantly cold climate punctuated by geologically brief periods of warmth and active hydrology. However, the time required to establish an integrated hydrological cycle in a warming climate is difficult to ascertain and has not been thoroughly investigated. Here we model the transient evolution of groundwater flow and subsurface temperature, the slowest evolving components of the hydrological cycle, during a warm departure from cold conditions. We find that tens of thousands of years are likely required before groundwater could be a meaningful source for large lakes in Gale. With highly favorable conditions, primarily high permeability, significant flow might develop in thousands of years. This implies that surface water dominates during the beginning of a warm phase. Annual mean surface temperatures in Gale below 290 K would likely leave the nearby highlands frozen at the surface. In that case, deep aquifers beneath a highlands permafrost layer could deliver water to Gale, where low temperatures would have reduced evaporation.

Ice-Ocean Exchange Processes in the Jovian and Saturnian Satellites

A growing number of satellites in the outer solar system likely have global oceans beneath their outer icy shells. While the presence of liquid water makes these ocean worlds compelling astrobiological targets, the exchange of heat and materials between the deep interior and the surface also plays a critical role in promoting habitable environments. In this article, we combine geophysical, geochemical, and geological observations of the Jovian satellites Europa, Ganymede, and Callisto as well as the Saturnian satellites Enceladus and Titan to summarize our current state of understanding of their interiors and surface exchange processes. Potential mechanisms for driving exchange processes upward from the ocean floor and downward from the satellite surface are then reviewed, which are primarily based on numerical models of ice shell and ocean dynamics and complemented by terrestrial analog studies. Future missions to explore these exo-oceans will further revolutionize our understanding of ice-ocean exchange processes and their implications for the habitability of these worlds.

Forecasting Rates of Volcanic Activity on Terrestrial Exoplanets and Implications for Cryovolcanic Activity on Extrasolar Ocean Worlds

Like the planets and moons in our solar system, the surfaces of terrestrial exoplanets may be shaped by volcanic activity. The magnitudes and rates of volcanic activity on terrestrial exoplanets will be intimately linked to their sizes and internal heating rates and can either facilitate or preclude the existence of habitable environments. In order to place bounds on the potential for such activity, we estimate total internal heating rates for 53 exoplanets with masses and radii up to ∼8M⊕ and 2R⊕, respectively, assuming that internal heating is drawn from both radiogenic and tidal sources. We then compare these internal heating rates to those of the planets and moons in our solar system in an attempt to constrain the expected rates of volcanic activity on these extrasolar worlds. We find that all 53 of the exoplanets surveyed are likely to have volcanic activity at their surfaces, and that at least 26% of these planets may be extrasolar ocean worlds. The majority of these ocean worlds may be similar in structure to the icy moons of the giant planets, having internal oceans beneath layers of surface ice. If so, these planets may exhibit cryovolcanism (i.e., icy volcanism) at their surfaces. Recent studies have shown that extrasolar volcanism could be detected by high-resolution spectrographs on existing ground-based telescopes. In the case of planets with densities and/or effective temperatures that are consistent with H2O-rich compositions, spectral identification of excess water vapor and other molecules that are explosively vented into space during cryovolcanic eruptions could serve as a way to infer the presence of subsurface oceans, and therefore indirectly assess their habitability. Considering the implications for habitability, our results suggest that continued characterization of terrestrial exoplanets in terms of their potential for volcanic activity should be a priority in the coming years.