Mars is a primary target of astrobiological interest: its past environmental conditions may have been favourable to the emergence of a prebiotic chemistry and, potentially, biological activity. In situ exploration is currently underway at the Mars surface, and the subsurface (2 m depth) will be explored in the future ESA ExoMars mission. In this context, BIOlogy and Mars EXperiment was performed to evaluate the stability and detectability of organic biomarkers under space and Mars-like conditions. Our data suggested that some target molecules, namely melanin, azelaic acid and nucleic acids, can be detected even after 16 months exposure to Low Earth Orbit conditions by multidisciplinary approaches. We used the same techniques as onboard the ExoMars rover, as Raman and infrared spectroscopies and gas chromatograph-mass spectrometer, and polymerase chain reaction even if this is not planned for the imminent mission to Mars. These results should be taken into account for future Mars exploration.

Bacillus pumilus SAFR-032, an endospore-forming bacterial strain, was investigated to determine its methylation pattern (methylome) change, compared to ground control, after direct exposure to space conditions onboard the International Space Station (ISS) for 1.5 years. The resulting ISS-flown and non-flown strains were sequenced using the Nanopore MinION and an in-house method and pipeline to identify methylated positions in the genome. Our analysis indicated genomic variants and m6A methylation increased in the ISS-flown SAFR-032. To complement the broader omics investigation and explore phenotypic changes, ISS-flown and non-flown strains were compared in a series of laboratory-based chamber experiments using an X-ray irradiation source (doses applied at 250, 500, 750, 1000 and 1250 Gy); results show a potentially higher survival fraction of ISS-flown DS2 at the two highest exposures. Taken together, results from this study document lasting changes to the genome by methylation, potentially triggered by conditions in spaceflight, with functional consequences for the resistance of bacteria to stressors expected on long-duration missions beyond low Earth orbit.

Corrosion of aluminium (Al) is a potential problem for spacecraft as this metal is used for various mechanical parts due to its strength, durability, etc. However, it can be corroded by certain factors including microbes. Studying microbes which can be implicated in microbiologically influenced corrosion (MIC) due to their extremophilic nature is of vital importance. In this current study, Al and acid-tolerant microbes were isolated from the samples of China space station assembly cleanroom surfaces; acidic environments can accelerate the corrosion process on metal surfaces. Nine bacterial and 10 fungal strains were identified with 16S ribosomal RNA gene/internal transcribed spacer region sequencing and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The dominant bacteria were of Bacillus, fungi of Penicillium and Aspergillus genera. Knowing the microbes which may be conveyed from the cleanrooms to the space stations with a potential capacity of Al degradation is important for long-term maintenance of station components. This study might aid in designing further researches of the aforementioned microorganisms and, therefore, contribute to the prevention of MIC.

Planetary habitability may be affected by exposure to γ radiation from supernovae (SNe). Records of Earth history during the late Quaternary Period (40 000 years to present) allow testing for specific SN γ radiation effects. SNe include Type Ia white dwarf explosions, Type Ib, c and II core collapses, and many γ burst objects. Surveys of galactic SNe remnants offer a nearly complete accounting for this time and including SN distances and ages. Terrestrial changes in records of the cosmogenic isotope 14C are here compared to SN-predicted changes. SN γ emission occurs mainly within 3 years; average per-event total emissions of 4 × 1049 erg are used for comparison of close events There are 18 SNe ≤ 1.5 kpc, and brief 14C anomalies are reported for eight of the closest. Four are notable (BP is year before 1950 CE): the older Vela SNR and an abrupt 30‰ del 14C rise at 12 740 BP; S165 and a 20‰ rise at 7431 BP; Vela Jr. and a 14‰ rise at 2765 BP; and HB9 and a 9‰ rise at 5372 BP. Rapid-increase anomalies in 14C production have been attributed to cosmic rays from exceptionally large solar flares. However, the proximity and ages of these SNe, the probable size and duration of their γ emissions, the predicted effects on 14C, and the agreement with 14C records together support SNe causation. Also, the supposed solar-caused 14C anomalies at CE 774 and 993 may instead have been caused by the SNe associated with the G190.9-2.2 and G347.3-00.5 remnants. Both are of appropriate age and distance.

Studies on the interaction of biomolecules with inorganic compounds, mainly mineral surfaces, are of great concern in identifying their role in chemical evolution and origins of life. Metal oxides are the major constituents of earth and earth-like planets. Hence, studies on the interaction of biomolecules with these minerals are the point of concern for the study of the emergence of life on different planets. Zirconium oxide is one of the metal oxides present in earth's crust as it is a part of several types of rocks found in sandy areas such as beaches and riverbeds, e.g. pebbles of baddeleyite. Different metal oxides have been studied for their role in chemical evolution but no studies have been reported about the role of zirconium oxide in chemical evolution and origins of life. Therefore, studies were carried out on the interaction of ribonucleic acid constituents, 5′-CMP (cytidine monophosphate), 5′-UMP (uridine monophosphate), 5′-GMP (guanosine monophosphate) and 5′-AMP (adenosine monophosphate), with zirconium oxide. Synthesized zirconium oxide particles were characterized by using vibrating sample magnetometer, X-Ray Diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy. Zirconia particles were in the nanometre range, from 14 to 27 nm. The interaction of zirconium oxide with ribonucleic acid constituents was performed in the concentration range of 5 × 10−5–300 × 10−5 M. Interaction studies were carried out in three mediums; acidic (pH 4.0), neutral (pH 7.0) and basic (pH 9.0). At neutral pH, maximum interaction was observed. The interaction of zirconium oxide with 5′-UMP was 49.45% and with 5′-CMP 67.98%, while with others it was in between. Interaction studies were Langmurian in nature. Xm and KL values were calculated. Infrared spectral studies of ribonucleotides, metal oxide and ribonucleotide–metal oxide adducts were carried out to find out the interactive sites. It was observed that the nitrogen base and phosphate moiety of ribonucleotides interact with the positive charge surface of metal oxide. SEM was also carried out to study the adsorption. The results of the present study favour the important role of zirconium oxide in concentrating the organic molecules from their dilute aqueous solutions in primeval seas.

The formation mechanism of linear and isopropyl cyanide (hereafter n-PrCN and i-PrCN, respectively) in the interstellar medium (ISM) has been proposed from the reaction between some previously detected small cyanides/cyanide radicals and hydrocarbons/hydrocarbon radicals. n-PrCN and i-PrCN are nitriles therefore, they can be precursors of amino acids via Strecker synthesis. The chemistry of i-PrCN is especially important since it is the first and only branched molecule in ISM, hence, it could be a precursor of branched amino acids such as leucine, isoleucine, etc. Therefore, both n-PrCN and i-PrCN have significant astrobiological importance. To study the formation of n-PrCN and i-PrCN in ISM, quantum chemical calculations have been performed using density functional theory at the MP2/6-311++G(2d,p)//M062X/6-311+G(2d,p) level. All the proposed reactions have been studied in the gas phase and the interstellar water ice. It is found that reactions of small cyanide with hydrocarbon radicals result in the formation of either large cyanide radicals or ethyl and vinyl cyanide, both of which are very important prebiotic interstellar species. They subsequently react with the radicals CH2 and CH3 to yield n-PrCN and i-PrCN. The proposed reactions are efficient in the hot cores of SgrB2 (N) (where both n-PrCN and i-PrCN were detected) due to either being barrierless or due to the presence of a permeable entrance barrier. However, the formation of n-PrCN and i-PrCN from the ethyl and vinyl cyanide always has an entrance barrier impermeable in the dark cloud; therefore, our proposed pathways are inefficient in the deep regions of molecular clouds. It is also observed that ethyl and vinyl cyanide serve as direct precursors to n-PrCN and i-PrCN and their abundance in ISM is directly related to the abundance of both isomers of propyl cyanide in ISM. In all the cases, reactions in the ice have smaller barriers compared to their gas-phase counterparts.

The modification of minerals with metals can promote changes in their surface and, consequently, in their physicochemical properties. Minerals could have played an important role in the origin of life as they can protect molecules against degradation by radiation and hydrolysis, pre-concentrate molecules from dilute solutions and catalyse the formation of polymers. Thus, the current work studied the modification of montmorillonite with Cu2+ and Fe3+ ions. These modified montmorillonites were used to study the interaction with adenine dissolved in distilled water and artificial seawater 4.0 Gy (Gy = billion years ago). The most important result of this work is that the adsorption of adenine onto modified montmorillonites is a complex interaction among adenine, salts in seawater and Cu2+/Fe3+-montmorillonite (Cu2+/Fe3+-Mont) . The adsorption of Cu2+ and Fe3+ onto montmorillonite decreased its surface area and pore volume. The Sips isotherm model showed the best fit of the data and n values indicate that the adenine adsorption process was homogeneous. The highest adenine adsorption was obtained in artificial seawater 4.0 Gy onto Fe3+-Mont at 60°C and the lowest in distilled water or artificial seawater 4.0 Gy onto montmorillonite [montmorillonite washed with distilled water (Mont-STD)] at 60°C. Adenine adsorption onto Mont-STD/montmorillonite modified with 500 ml of 0.1 mol l−1 of CuCl2 and Fe3+-Mont was an exothermic process and an endothermic process, respectively. For all adsorptions ΔG was negative. The adsorption of adenine onto Fe3+-Mont was ruled out by entropy and the other samples by enthalpy and entropy, being a major contribution for Gibbs free energy from enthalpy. The Fourier transform-infrared data indicate that the interaction of adenine with minerals may occur through the NH2 functional group.

Interstellar travel in the Milky Way is commonly thought to be a long and dangerous enterprise, but are all galaxies so hazardous? I introduce the concept of galactic traversability to address this question. Stellar populations are one factor in traversability, with higher stellar densities and velocity dispersions aiding rapid spread across a galaxy. The interstellar medium (ISM) is another factor, as gas, dust grains and cosmic rays all pose hazards to starfarers. I review the current understanding of these components in different types of galaxies, and conclude that red quiescent galaxies without star formation have favourable traversability. Compact elliptical galaxies and globular clusters could be ‘super-traversable’, because stars are packed tightly together and there are minimal ISM hazards. Overall, if the ISM is the major hindrance to interstellar travel, galactic traversability increases with cosmic time as gas fractions and star formation decline. Traversability is a consideration in extragalactic surveys for the Search for Extraterrestrial Intelligence (SETI).

A free-floating planet (FFP) is a planetary-mass object that orbits around a non-stellar massive object (e.g. a brown dwarf) or around the Galactic Centre. The presence of exomoons orbiting FFPs has been theoretically predicted by several models. Under specific conditions, these moons are able to retain an atmosphere capable of ensuring the long-term thermal stability of liquid water on their surface. We model this environment with a one-dimensional radiative-convective code coupled to a gas-phase chemical network including cosmic rays and ion-neutral reactions. We find that, under specific conditions and assuming stable orbital parameters over time, liquid water can be formed on the surface of the exomoon. The final amount of water for an Earth-mass exomoon is smaller than the amount of water in Earth oceans, but enough to host the potential development of primordial life. The chemical equilibrium time-scale is controlled by cosmic rays, the main ionization driver in our model of the exomoon atmosphere.

To ensure long-term survival of humans and Earth life generally, strategies need to be in place to recolonize Earth after global catastrophes and to colonize exoplanets. In one strategy of space colonization, the physical barriers erected by time and space are circumvented by sending cryopreserved human and animal embryos to exoplanets rather than adult crews. There the embryos would be developed to neonates in artificial uterus (AU) systems. A similar strategy could also be used to repopulate Earth after human extinction events. In this paper, we review the status and future prospects of these embryonic survival strategies. A critical requirement in each scenario is an AU system for complete ectogenesis, i.e. complete development of embryos to neonates outside the natural womb. While such systems do not yet exist, they may soon be developed to afford clinical assistance to infertile women and reproductive choices to prospective parents. In human survival schemes, AU systems would likely first be used to extend conventional survival missions (e.g. subterranean bunkers) by replacing some adult crew members with cryopreserved embryos. For major mass extinctions and all far future events, adult crews would be entirely replaced by embryos and androids. The most advanced missions would feature orbiting embryo spacecraft for Earth recolonization and analogous interstellar spacecraft for colonizing exoplanets. We conclude that an advanced civilization using such an integrated, embryonic approach could eventually colonize distant parts of its home galaxy and potentially the wider universe.

Approximately 22% of sun-like stars have Earth-like exoplanets. Advanced civilizations may exist on these, and significant effort has been expended on the theoretical analysis of planetary systems, and accompanying practical detection instruments.

The longevity of technological civilizations is unknown, as is the probability of less advanced societies becoming technological. Accordingly, searching for pre-industrial extra-terrestrial societies may be more productive.

Using the earth as a model, a consideration of possible detectible proxies suggests that observation of seasonal agriculture may be possible in the near future – particularly in ideal circumstances, for which quantitative analysis is provided. More speculatively, other detectible processes may include: species introduction; climate change; large urban fires and land-use or aquatic changes.

Primitive societies may be both aware that their activities may be observed from other planets, and may deliberately adjust these activities to aid or conceal detection.

The search for biosignatures is likely to generate controversial results, with no single biosignature being clear proof of the presence of life. Bayesian statistical frameworks have been suggested as a tool for testing the effect that a new observation has on our belief in the presence of life on another planet. We test this approach here using the tentative discovery of phosphine on Venus as an example of a possible detection of a biosignature on an otherwise well-characterized planet. We report on a survey of astrobiologists' views on the likelihood of life on Enceladus, Europa, Mars, Titan and Venus before the announcement of the detection of phosphine in Venus' atmosphere (the Bayesian Prior Probability) and after the announcement (the Posterior Probability). Survey results show that respondents have a general view on the likelihood of life on any world, independent of the relative ranking of specific bodies, and that there is a distinct ‘fans of icy moons’ sub-community. The announcement of the potential presence of phosphine on Venus resulted in the community showing a small but significant increase in its confidence that there was life on Venus; nevertheless the community still considers Venus to be the least likely abode of life among the five targets considered, last after Titan. We derive a Bayesian formulation that explicitly includes both the uncertainty in the interpretation of the signal as well as uncertainty in whether phosphine on Venus could have been produced by life. We show that although the community has shown rational restraint about a highly unexpected and still tentative detection, their changing expectations do not fit a Bayesian model.

Lipids are among the organic substances that can work as biosignatures, indicating life in an environment. We present an experimental investigation concerning analysis of lipids from a microbial source deposited on the Mars Global Simulant (MGS-1) regolith by geomatrix-assisted laser desorption/ionization-mass spectrometry (GALDI-MS). Our results indicate that lipids from intact microbial cells of a black yeast strain can be detected in these mimetic samples of Martian soil. These lipid molecules are predominantly associated with the occurrence of adducts in the GALDI-MS spectra. The results can be helpful in the planning of future planetary missions.

The origin of life from inanimate matter is still an open question, and our knowledge is still very limited. In this sense, prebiotic chemistry seeks to study and understand how chemical reactions may have contributed to the origin of life. Minerals are of great relevance to prebiotic chemistry, as they may have preconcentrated precursors of biomolecules or biomolecules from diluted solutions, provided protection for biomolecules against UV radiation and hydrolysis, catalysing their reactions and played the role of a primitive genetic code. Montmorillonite, a prebiotic mineral, was shown to be able to adsorb adenine and later also histidine. In addition, histidine adsorption did not displace adenine from the montmorillonite. Kinetic experiments showed that using a whole period of time (7 days) it was not possible to adjust the data to any mathematical kinetic model. Thus, the data were separated into four different adsorption ranges: range 1 (0–60 min), range 2 (60–4320 min), range 3 (4320–7200 min) and range 4 (7200–10 080 min). Range 1 showed adsorption that was too fast, meaning no variations in the adsorption data, and the data of range 3 did not fit in any model used in this work. Thus, range 2 (60–4320 min) and range 4 (7200–10 080 min) were analysed. The adsorption kinetics of histidine adsorption indicated two reaction steps, a quick step (60–4320 min), following the pseudo-first-order model, followed by a slower step (7200–10 080 min) of the pseudo-second order. With these results, isotherms were constructed with times of 1 h and 7 days. The results of the quick step (1 h) showed a reaction that was not thermodynamically favoured. For this time range, Gibbs energy values obtained ranged between 5 and 10 kJ mol−1 at temperatures of 20, 35 and 50°C, and the adsorption occurred due to the balance shift of increase in histidine concentrations. The isotherms of the slow step (7 days) presented negative values, showing a more favourable reaction with Gibbs energy values ranging between −5 and −11 kJ mol−1. The mathematical modelling of the data indicates that seawater ions are crucial in the adsorption process. Thus, the study provided essential information for prebiotic chemistry, showing that time and the reaction medium should always be taken into account.

The embryo space colonization (ESC) concept is an interesting, very rational and quite effective way to guarantee the survival of the human species, as long as the technology is achieved and no unforeseen complications arise during even many millions of years journey to an exoplanet. Despite these formal advantages of the concept, this paper points to a number of arguments against its validity. These arguments revolve around two issues. One is to point out that while the concept of saving the Homo sapiens species is noble and should be supported, the way of saving humanity envisioned by the ESC departs from what should be understood by the concept of saving humanity through space colonization. The second issue is to draw attention to the ethical controversies that make this concept perhaps unsuitable for implementation at all. At least some of these objections do not address the concept of saving humanity by sending adult living persons on space missions.

The unique environment of space is characterized by several stress factors, including intense radiation, microgravity, high vacuum and extreme temperatures, among others. These stress conditions individually or in-combination influence genetics and gene regulation and bring potential evolutionary changes in organisms that would not occur under the Earth's gravity regime (1 × g). Thus, space can be explored to support the emergence of new varieties of microbes and plants, that when selected for, can exhibit increased growth and yield, improved resistance to pathogens, enhanced tolerance to drought, low nutrient and disease, produce new metabolites and others. These properties may be more difficult to achieve using other approaches under 1 × g. This review provides an overview of the space microgravity and ionizing radiation conditions that significantly influence organisms. Changes in the genomics, physiology, phenotype, growth and metabolites of organisms in real and simulated microgravity and radiation conditions are illustrated. Results of space biological experiments show that the space environment has significant scientific, technological and commercial potential. Combined these potentials can help address the future of life on Earth, part of goal e of astrobiology.

We propose that retinal-based phototrophy arose early in the evolution of life on Earth, profoundly impacting the development of photosynthesis and creating implications for the search for life beyond our planet. While the early evolutionary history of phototrophy is largely in the realm of the unknown, the onset of oxygenic photosynthesis in primitive cyanobacteria significantly altered the Earth's atmosphere by contributing to the rise of oxygen ~2.3 billion years ago. However, photosynthetic chlorophyll and bacterio chlorophyll pigments lack appreciable absorption at wavelengths about 500–600 nm, an energy-rich region of the solar spectrum. By contrast, simpler retinal-based light-harvesting systems such as the haloarchaeal purple membrane protein bacteriorhodopsin show a strong well-defined peak of absorbance centred at 568 nm, which is complementary to that of chlorophyll pigments. We propose a scenario where simple retinal-based light-harvesting systems like that of the purple chromoprotein bacteriorhodopsin, originally discovered in halophilic Archaea, may have dominated prior to the development of photosynthesis. We explore this hypothesis, termed the ‘Purple Earth,’ and discuss how retinal photopigments may serve as remote biosignatures for exoplanet research.

Assuming that securing the long-term survival of humans and Earth life is a valid goal, we briefly compare the strategies of building standard space colonies, such as on Mars, and embryo space colonization (ESC). In ESC embryos of humans and other Earth species would be sent to exoplanets and raised there via ectogenesis and android assistants. We find that the potential for securing long-term survival is far greater for ESC than for standard colonies, while the bioethical and other risks are far fewer.