Europa is a prime target for astrobiology and has been prioritized as the next target for a National Aeronautics and Space Administration flagship mission. It is important, therefore, that we advance our understanding of Europa, its ocean and physical environment as much as possible. Here, we describe observations of Europa obtained during its orbital eclipse by Jupiter using the Hubble Space Telescope. We obtained Advanced Camera for Surveys Solar Blind Channel far ultraviolet low-resolution spectra that show oxygen line emission both in and out of eclipse. We also used the Wide-Field and Planetary Camera-2 and searched for broad-band optical emission from fluorescence of the surface material, arising from the very high level of incident energetic particle radiation on ices and potentially organic substances. The high-energy particle radiation at the surface of Europa is extremely intense and is responsible for the production of a tenuous oxygen atmosphere and associated FUV line emission. Approximately 50% of the oxygen emission lasts at least a few hours into the eclipse. We discuss the detection limits of the optical emission, which allow us to estimate the fraction of incident energy reradiated at optical wavelengths, through electron-excited emission, Cherenkov radiation in the ice and fluorescent processes.

In SETI, when searching for ‘beacons’ – transmissions intended for us and meant to get our attention – one must guess the appropriate frequency to search by considering what frequencies would be universally obvious to other species. This is a well-known concept in game theory, where such solutions to a non-communicative cooperative game (such as a mutual search) are called ‘Schelling points’. It is noteworthy, therefore, that when developing his eponymous units, Planck called them ‘natural’ because they ‘remain meaningful for all times and also for extraterrestrial and non-human cultures’. Here, I apply Planck's suggestion in the context of Schelling points in SETI with a ‘Planck Frequency Comb’, constructed by multiplying the Planck energy by integer powers of the fine structure constant. This comb includes a small number of frequencies in regions of the electromagnetic spectrum where laser and radio SETI typically operates. Searches might proceed and individual teeth in the comb, or at many teeth at once, across the electromagnetic spectrum. Indeed, the latter strategy can be additionally justified by the transmitter's desire to signal at many frequencies at once, to improve the chances that the receiver will guess one of them correctly. There are many arbitrary and anthropocentric choices in this comb's construction, and indeed one can construct several different frequency combs with only minor and arbitrary modifications. This suggests that it may be fruitful to search for signals arriving in frequency combs of arbitrary spacing. And even though the frequencies suggested here are only debatably ‘better’ than others proposed, the addition of the Planck Frequency Comb to the list of ‘magic frequencies’ can only help searches for extraterrestrial beacons.

The search for Dyson Spheres has been propelled not only by the hope of discovering intelligent alien life, but by humanity's ever-increasing need for energy. However, the Dyson Sphere is not a practical design, requiring too much matter to build and too much energy to stabilize. Here we discuss the various designs of a Dyson Sphere and propose the Solar Wind Power (SWP) Satellite, a simplistic, self-sustaining system that draws power from the solar wind and uses a laser to fire energy to collectors (on space stations, bases, etc.) positioned anywhere in the Solar System. While a small SWP Satellite can provide an estimated 2 MW of power, larger (or networks of) satellites could provide terawatts of power or more. The cost of the SWP Satellite would be relatively cheap – it primarily consists of shaped copper, with only a few complex systems onboard. Detection of such a satellite would be difficult using current technology, because at this time we can only detect solar wind deviations of up to 10−13 MS yr−1, while a 2 MW satellite would only divert 10−34 MS yr−1. Thus, only very large SWP Satellites could possibly be detected.

The last few million years on planet Earth have witnessed two remarkable phases of hominid development, starting with a phase of biological evolution characterized by rather rapid increase of the size of the brain. This has been followed by a phase of even more rapid technological evolution and concomitant expansion of the size of the population that began when our own particular ‘sapiens’ species emerged, just a few hundred thousand years ago. The present investigation exploits the analogy between the neo-Darwinian genetic evolution mechanism governing the first phase, and the memetic evolution mechanism governing the second phase. From the outset of the latter until very recently – about the year 2000 – the growth of the global population N was roughly governed by an equation of the form dN/Ndt=N/T*, in which T* is a coefficient introduced (in 1960) by von Foerster, who evaluated it empirically as about 200 000 million years. It is shown here how the value of this hitherto mysterious timescale governing the memetic phase is explicable in terms of what happened in the preceding genetic phase. The outcome is that the order of magnitude of the Foerster timescale can be accounted for as the product of the relevant (human) generation timescale, about 20 years, with the number of bits of information in the genome, of the order of 10 000 million. Whereas the origin of our ‘homo’ genus may well have involved an evolutionary hard step, it transpires that the emergence of our particular ‘sapiens’ species was rather an automatic process.

The nature of cometary organic matter is of great interest to investigations involving the formation and distribution of organic matter relevant to the origin of life. We have used pyrolysis–Fourier transform infrared (FTIR) spectroscopy to investigate the chemical effects of the irradiation of naturally occurring bitumens, and to relate their products of pyrolysis to their parent assemblages. The information acquired has then been applied to the complex organic matter present in cometary nuclei and comae. Amalgamating the FTIR data presented here with data from published studies enables the inference of other comprehensive trends within hydrocarbon mixtures as they are progressively irradiated in a cometary environment, namely the polymerization of lower molecular weight compounds; an increased abundance of polycyclic aromatic hydrocarbon structures; enrichment in 13C; reduction in atomic H/C ratio; elevation of atomic O/C ratio and increase in the temperature required for thermal degradation. The dark carbonaceous surface of a cometary nucleus will display extreme levels of these features, relative to the nucleus interior, while material in the coma will reflect the degree of irradiation experienced by its source location in the nucleus. Cometary comae with high methane/water ratios indicate a nucleus enriched in methane, favouring the formation of complex organic matter via radiation-induced polymerization of simple precursors. In contrast, production of complex organic matter is hindered in a nucleus possessing a low methane/water ration, with the complex organic matter that does form possessing more oxygen-containing species, such as alcohol, carbonyl and carboxylic acid functional groups, resulting from reactions with hydroxyl radicals formed by the radiolysis of the more abundant water. These insights into the properties of complex cometary organic matter should be of particular interest to both remote observation and space missions involving in situ analyses and sample return of cometary materials.

The question about the stability of certain biomolecules is directly connected to the life-detection missions aiming to search for past or present life beyond Earth. The extreme conditions experienced on extraterrestrial planet surface (e.g. Mars), characterized by ionizing and non-ionizing radiation, CO2-atmosphere and reactive species, may destroy the hypothetical traces of life. In this context, the study of the biomolecules behaviour after ionizing radiation exposure could provide support for the onboard instrumentation and data interpretation of the life exploration missions on other planets. Here, as a part of STARLIFE campaign, we investigated the effects of gamma rays on two classes of fungal biomolecules–nucleic acids and melanin pigments – considered as promising biosignatures to search for during the ‘in situ life-detection’ missions beyond Earth.

The current advances in our exploration of Mars have made us think of the human species as a multiplanetary species. However, we have certain challenges before we can truly consider ourselves such a species, especially moral ones. Therefore, astrobioethics would be the right one to examine what it takes to consider ourselves a multiplanetary species. The purpose of this paper is to analyse the meaning and significance of being an inter- and multiplanetary species. To achieve this, a philosophical and critical analysis will be made, using as input aspects of biology, ethics and moral community. We conclude that to be a truly multiplanetary species, more than the technological aspects that allow us to reach other planets, a change at different levels will be needed.

A study was undertaken to determine if amber, coal and clay samples contain bacteria, in relation to the possibility that rocks ejected from Earth might contain microorganisms capable of colonizing other planets. A technique for isolating bacteria from rocks was developed which excluded the possibility that any of the rock isolates resulted from contamination. Two species of Bacillus were found in the amber sample, and a species of the same genus was found in coal; bacilli were also commonly found in clay. It is concluded that species of the spore-forming genus Bacillus could therefore be ejected from Earth in these geological substrates and possibly be transferred elsewhere.

Microbiological activities can be detected in various extreme environments on Earth, which suggest that extraterrestrial environments, such as on Mars, could host life. There have been proposed a number of biomarkers to detect extant life mostly based on specific molecules. Because terrestrial organisms have catalytic proteins (enzymes), enzymatic activity may also be a good indicator to evaluate biological activities in extreme environments. Phosphatases are essential for all terrestrial organisms because phosphate esters are ubiquitously used in genetic molecules (DNA/RNA) and membranes. In this study, we evaluated microbial activity in soils of the Atacama Desert, Chile, by analysing several biomarkers, including phosphatase activity. Phosphatases extracted with Tris buffer were assayed fluorometrically using 4-methylumbelliferyl phosphate as a substrate. The horizontal distribution of phosphatase activity and other parameters in soils from the Atacama Desert showed that phosphatase activity was positively correlated with amino acid concentration and colony-forming units and negatively correlated with precipitation amount. We found consistent that biochemical indicators including phosphatase significantly decreased in the extreme hyper-arid zone where rainfall of <25 mm year−1. The results were compared with phosphatase activities detected in extreme environments, such as submarine hydrothermal systems and Antarctic soils, as well as soils from ordinary environments. Overall, our results suggested that phosphatase activity could be a good indicator for evaluating biological activities in extreme environments.

Xanthoria parietina is a widespread foliose lichen growing on barks and rocks showing a broad spectrum of tolerance to air pollutants such as NOX and heavy metals, and resistance to UV-radiation because of the screening properties provided by the secondary metabolite parietin. The aim of this study was to evaluate the ability of this lichen species to survive in the following simulated space conditions, UV-radiation in N2 atmosphere and UV-radiation in vacuum. The efficiency of the photosynthetic apparatus was used as an indicator of vitality, and was expressed in terms of chlorophyll a fluorescence (FV/FM) and Normalized Difference Vegetation Index (NDVI), which were measured within 72 h from the exposure. Additionally, during the irradiation, the IR reflectance spectrum of the lichen was monitored in situ to assess changes in spectral bands. The results showed significant differences in physiological recovery trends between the treatments, highlighting that UV-radiation in vacuum causes stronger effects on FV/FM values. The IR analysis revealed several spectral band changes in the fingerprint region. The most visible variation was the 5200 cm−1 water band that disappeared in the overtone region. Nevertheless, X. parietina was able to survive UV-radiation in N2 atmosphere and in vacuum, and for this reason it may be considered a candidate for further evaluations on its survival capacity in extreme conditions.

Planets that orbit M-class dwarf stars in their habitable zones are expected to become tidally-locked in the first billion years of their history. Simulations of potentially habitable planets orbiting K and G-class stars also suggest that many will become tidally-locked or become pseudo-synchronous rotators in a similar time frame where certain criteria are fulfilled. Simple models suggest that such planets will experience climatic regions organized in broadly concentric bands around the sub-stellar point, where irradiation is maximal. Here, we develop some of the quantitative, as well as the qualitative impacts of such climate on the evolutionary potential of life on such worlds, incorporating the effects of topography and ocean currents on potential biological diversity. By comparing atmospheric circulation models with terrestrial circulation and biological diversity, we are able to construct viable thought models of biological potential. While we await the generation of atmospheric circulation models that incorporate topography and varying subaerial landscape, these models can be used as a starting point to determine the overall evolutionary potential of such worlds. The planets in these thought-models have significant differences in their distribution of habitability that may not be apparent from simple climate modelling.

Advanced extraterrestrial civilizations may produce observable technosignatures when they migrate inside their planetary systems and to other planetary systems. Collectively, the search for technosignatures produced by migrating extraterrestrial civilizations can be described as the search for migrating extraterrestrial intelligence (SMETI). I propose that extraterrestrial civilizations may use free-floating planets as interstellar transportation to reach, explore and colonize planetary systems. I propose possible technosignatures and artefacts that may be produced by extraterrestrial civilizations using free-floating planets for interstellar migration and interstellar colonization, as well as strategies for the search for their technosignatures and artefacts. I discuss technosignatures that may be produced by extraterrestrial civilizations using other methods of interstellar migration and colonization. As an example, I discuss the star GJ 433, which experienced a close flyby a few thousand years ago. I divide possible technosignatures of migrating civilizations into groups to highlight similarities and differences among technosignatures produced by civilizations using different methods of migration and interstellar colonization. It follows from the comparison, for example, that interstellar migration using flybys of stars can blend with interstellar migration using free-floating planets.

Nucleobases are nitrogenous bases composed of monomers that are a major constituent of RNA and DNA, which are an essential part of any cellular life on the Earth. The search for nucleobases in the interstellar medium remains a major challenge, however, the recent detection of nucleobases in meteorite samples and laboratory synthesis in simulated analogue experiments have confirmed their abiotic origin and a possible route for their delivery to the Earth. Nevertheless, cellular life is based on the interacting network of complex structures, and there is substantial lack of information on the possible routes by which such ordered structures may be formed in the prebiotic environment. In the current study, we present the evidence for the synthesis of complex structures due to shock processing of nucleobases. The nucleobases were subjected to the reflected shock temperature of 3500–7000 K (estimated) and pressure of about 15–34 bar for over ~2 ms timescale. Under such extreme thermodynamic conditions, the nucleobases sample experiences superheating and subsequent cooling. Electron microscopic studies of shock processed residue show that nucleobases result in spontaneous formation of complex structures when subjected to extreme conditions of shock. These results suggest that impact shock processes might have contributed to the self-assembly of biologically relevant structures and the origin of life.

Many rocky exoplanets are heavier and larger than the Earth and have higher surface gravity. This makes space-flight on these worlds very challenging because the required fuel mass for a given payload is an exponential function of planetary surface gravity, exp(g0). We find that chemical rockets still allow for escape velocities on Super-Earths up to 10× Earth mass. More massive rocky worlds, if they exist, would require other means to leave the planet, such as nuclear propulsion. This is relevant for space colonization and the search for extraterrestrial intelligence.

There is increased interest in exploring planetary bodies that have ocean worlds, and planetary protection (PP) practices for spacecraft are important to avoid harmful biological contamination of these sensitive environments. In the autumn of 2018 a diverse set of subject matter experts were assembled to examine the environmental input parameters (e.g. space radiation, Europa surface turnover) and biological input parameters that are referenced by the Europa Clipper project probabilistic risk model, to assess the < 1 × 10−4 probability of contamination requirement derived from NASA Procedural Requirements 8020.12D. A joint NASA–JPL lead workshop entitled, ‘Europa Clipper Planetary Protection Workshop’ was convened on 13–15 November 2018, to validate probability model input values, current Europa Clipper PP requirements and implementation strategy, and identify future PP research topics. The three objectives for the 3 day workshop were: (1) to validate the probability of contamination modelling framework for Europa Clipper PP; (2) to agree on probability of contamination model input values, or on a plan to derive/identify appropriate model inputs and (3) to develop workshop concurrence regarding future PP research plans and their priority. Workshop participants engaged in detailed scientific and engineering discussions focusing on Clipper mission objectives and trajectories, Europan ice shell geophysics and understanding the impact of initial microbial bioburdens and spacecraft cleanliness with all three objectives being successfully completed by the end of the workshop.

Recent studies postulated the viability of a suite of metabolic pathways in Enceladus’ ocean motivated by the detection of H2 and CO2 in the plumes – evidence for available free energy for methanogenesis driven by hydrothermal activity at the moon's seafloor. However, these have not yet been explored in detail. Here, a range of experiments were performed to investigate whether microbial iron reduction could be a viable metabolic pathway in the ocean by iron-reducing bacteria such as Geobacter sulfurreducens. This study has three main outcomes: (i) the successful reduction of a number of crystalline Fe(III)-bearing minerals predicted to be present at Enceladus was shown to take place to differing extents using acetate as an electron donor; (ii) substantial bacterial growth in a simulated Enceladus ocean medium was demonstrated using acetate and H2(g) separately as electron donors; (iii) microbial iron reduction of ferrihydrite was shown to partially occur at pH 9, the currently accepted value for Enceladus’ ocean, whilst being severely hindered at the ambient ocean temperature of 0°. This study proposes the possibilities for biogeochemical iron cycling in Enceladus’ ocean, suggesting that a strain of iron-reducing bacteria can effectively function under Enceladus-like conditions.

We describe an image-comparison technique of Heidemann and Ritter (2008a, b), which uses image compression, and is capable of: (i) detecting novel textures in a series of images, as well as of: (ii) alerting the user to the similarity of a new image to a previously observed texture. This image-comparison technique has been implemented and tested using our Astrobiology Phone-cam system, which employs Bluetooth communication to send images to a local laptop server in the field for the image-compression analysis. We tested the system in a field site displaying a heterogeneous suite of sandstones, limestones, mudstones and coal beds. Some of the rocks are partly covered with lichen. The image-matching procedure of this system performed very well with data obtained through our field test, grouping all images of yellow lichens together and grouping all images of a coal bed together, and giving 91% accuracy for similarity detection. Such similarity detection could be employed to make maps of different geological units. The novelty-detection performance of our system was also rather good (64% accuracy). Such novelty detection may become valuable in searching for new geological units, which could be of astrobiological interest. The current system is not directly intended for mapping and novelty detection of a second field site based on image-compression analysis of an image database from a first field site, although our current system could be further developed towards this end. Furthermore, the image-comparison technique is an unsupervised technique that is not capable of directly classifying an image as containing a particular geological feature; labelling of such geological features is done post facto by human geologists associated with this study, for the purpose of analysing the system's performance. By providing more advanced capabilities for similarity detection and novelty detection, this image-compression technique could be useful in giving more scientific autonomy to robotic planetary rovers, and in assisting human astronauts in their geological exploration and assessment.

The eclectic range of artefacts and ‘messages’ we dispatch into the vast expanse of space may become one of the most enduring remnants of our present civilization, but how does his protracted legacy adequately document the plurality of societal values and common, cultural heritage on our heterogeneous world? For decades now, this rendition of the egalitarian principle has been explored by the Search for Extra-Terrestrial Intelligence community in order to draft theoretical responses to ‘who speaks for Earth?’ for hypothetical extra-terrestrial communication strategies. However, besides the moral, ethical and democratic advancements made by this particular enterprise, there remains little practical exemplars of implementing this garnered knowledge into other experimental elements that could function as mutual emissaries of Earth; physical artefacts that could provide accessible details about our present world for future archaeological observations by our space-faring progeny, potential visiting extrasolar denizens or even for posterity. While some initiatives have been founded to investigate this enduring dilemma of humanity over the last half-century, there are very few comparative studies in regards to how these objects, time capsules and transmission events collectively disseminate content about the aggregate of our species and the Earth system it inhabits. This catalogue, assembled for extended study as part of the Beyond the Earth foundation, is intended as an initial, dialogic step towards evaluating such a ‘profile of humanity’. This investigation will endeavour to collate all cultural resources that can presently be garnered from spacecraft (non-mission orientated, cultural material that conveys an impression of Earth) and non-terrestrial transmissions (electromagnetic signals that are intentionally aimed off-world to embody humanities’ evolving, philosophical identity) in the expanse beyond our planetary borders in order to cross-analyse how we presently illustrate the diversity of our planet before, subsequently, deducing how we could appropriately depict our collective human civilization [and biosphere] within deep space and cosmic time.

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.

The earliest functional living system on Earth should have been able to reproduce an ordered configuration and a self-organization dynamics. It was capable of resisting a random variability in time and space to keep the functionality. Amino acids (AAs) and nucleobases generated from abiotic reactions as seen in laboratory-based experiments have demonstrated that molecular elements for life can be obtained by predictable physicochemical processes. However, a functional, self-organized living system needs complex molecular interactions to endure. In this paper, we address the transference of spatial information on highly enantiopure polymers as a critical condition to support the dynamics in a self-organized biogenic system. Previous scenarios have considered almost exclusively the information encoded in sequences as the suitable source of prebiotic information. But the spatial information transference has been poorly understood thus far. We provide the supporting statements which predict that the ordered configuration in a biogenic system should be significantly influenced by spatial information, instead of being exclusively generated by sequences of polymers. This theoretical approach takes into consideration that the properties of mutation and inheritance did not develop before definition of the structures that allow the management of information. Rather, we postulate that the molecular structures to store and transfer information must exist at first, in order to retain particular functional ‘meaning’, and subsequently, such information can be ‘inherited’ and eventually modified. Thus, the present contribution follows the theory that life was originated from an unstable prebiotic environment that involves the early spatial information transference based on large chiral asymmetry.