Making predictions about aliens is not an easy task. Most previous work has focused on extrapolating from empirical observations and mechanistic understanding of physics, chemistry and biology. Another approach is to utilize theory to make predictions that are not tied to details of Earth. Here we show how evolutionary theory can be used to make predictions about aliens. We argue that aliens will undergo natural selection – something that should not be taken for granted but that rests on firm theoretical grounds. Given aliens undergo natural selection we can say something about their evolution. In particular, we can say something about how complexity will arise in space. Complexity has increased on the Earth as a result of a handful of events, known as the major transitions in individuality. Major transitions occur when groups of individuals come together to form a new higher level of the individual, such as when single-celled organisms evolved into multicellular organisms. Both theory and empirical data suggest that extreme conditions are required for major transitions to occur. We suggest that major transitions are likely to be the route to complexity on other planets, and that we should expect them to have been favoured by similarly restrictive conditions. Thus, we can make specific predictions about the biological makeup of complex aliens.

We use recent results from astrobiology, particularly the A-form of the Drake equation and combine it with data on the evolution of life on Earth to obtain a new assessment of the prevalence of technological species in our Universe. A species is technological if it is, in theory, capable of interstellar communication. We find that between seven and 300 technological species have likely arisen in the Milky Way until today, the current state of which however unknown. Assuming that we are currently alone in our Galaxy, we estimate that we would need to wait for roughly 26 million years for a 50% chance of another technological species to arise. By relating our results to the much-debated Fermi–Hart paradox, we discuss if and to what extent our results may help quantify the chances of humanity to manage the transition to a long-term sustainable path of existence.

We studied the radiolysis of a wide variety of N-heterocycles, including many of biological importance, and find that the majority are remarkably stable in the solid-state when subjected to large doses of ionizing gamma radiation from a 60Co source. Degradation of N-heterocycles as a function of dose rate and total dose was measured using high-performance liquid chromatography with UV detection. Many N-heterocycles show little degradation when γ-irradiated up to a total dose of ~1 MGy, which approximates hundreds of millions of years’ worth of radiation emitted in meteorite parent bodies due to slow radionuclide decay. Extrapolation of these results suggests that these N-heterocyclic compounds would be stable in dry parent bodies over solar system timescales. We suggest that the abundance of these N-heterocycles as measured presently in carbonaceous meteorites is largely reflective of their abundance at the time aqueous alteration stopped in their parent bodies and the absence of certain compounds in present-day samples is either due to the formation mechanisms or degradation which occurred during periods of aqueous alteration or thermal metamorphism.

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.

Surface mineral crusts on Earth are highly diverse and usually, contain microbial life. Crusts constitute an attractive target to search for life: they require water for their formation, they efficiently entrap organic matter and are relatively easy to sample and process. They hold a record of life in the form of microbial remains, biomolecules and carbon isotope composition. A miniaturized Raman spectrometer is included in the ExoMars 2020 payload as it is sensitive to a range of photosynthetic pigments. Samples from the Haughton Impact Structure, Canadian High Arctic and others, shows the preservation of pigments in a range of crust types, especially supra-permafrost carbonate crusts and cryptogamic crusts. The Raman spectral signatures of these crusts are shown along with biomarker analysis to showcase these techniques prior to the ExoMars 2020 mission. Carotenoids and other photoprotective microbial pigments are identified in the Haughton surface crusts using Raman spectroscopy. Gas chromatography-mass spectrometry analyses show a distribution of fatty acids which are most likely from a cyanobacterial source. The successful demonstration of these analyses in the Haughton Impact structure shows the biosignature of surface mineral crusts can be easily extracted and provides an excellent target for sampling evidence of life on Mars.

Two fundamental problems for extraterrestrial intelligences (ETIs) attempting to establish interstellar communication are timing and energy consumption. Humanity's study of exoplanets via their transit across the host star highlights a means of solving both problems. An ETI ‘A’ can communicate with ETI ‘B’ if B is observing transiting planets in A's star system, either by building structures to produce artificial transits observable by B, or by emitting signals at B during transit, at significantly lower energy consumption than typical electromagnetic transmission schemes. This can produce a network of interconnected civilizations, establishing contact via observing each other's transits. Assuming that civilizations reside in a Galactic Habitable Zone (GHZ), I conduct Monte Carlo Realization simulations of the establishment and growth of this network, and analyse its properties in the context of graph theory. I find that at any instant, only a few civilizations are correctly aligned to communicate via transits. However, we should expect the true network to be cumulative, where a ‘handshake’ connection at any time guarantees connection in the future via e.g. electromagnetic signals. In all our simulations, the cumulative network connects all civilizations together in a complete network. If civilizations share knowledge of their network connections, the network can be fully complete on timescales of order a hundred thousand years. Once established, this network can connect any two civilizations either directly, or via intermediate civilizations, with a path much less than the dimensions of the GHZ.

With the advent of modern astronomy, humans might now have acquired the technological and intellectual requirements to communicate with other intelligent beings beyond the solar system, if they exist. Radio signals have been identified as a means for interstellar communication about 60 years ago. And the Square Kilometer Array will be capable of detecting extrasolar radio sources analogous to terrestrial high-power radars out to several tens of light years. The ultimate question is: will we be able to understand the message or, vice versa, if we submit a message to extraterrestrial intelligence first, how can we make sure that they will understand us? Here I report on the largest blind experiment of a pretend radio message received on Earth from beyond the solar system. I posted a sequence of about two million binary digits (‘0’ and ‘1’) to the social media that encoded a configuration frame, two slides with mathematical content and four images along with spatial and temporal information about their contents. Six questions were asked that would need to be answered to document the successful decryption of the message. Within a month after the posting, over 300 replies were received in total, including comments and requests for hints, 66 of which contained the correct solutions. About half of the solutions were derived fully independently, the other half profited from public online discussions and spoilers. This experiment demonstrates the power of the world wide web to help interpreting possible future messages from extraterrestrial intelligence and to test the decryptability of our own deliberate interstellar messages.

Liquid water on Mars might be created by deliquescence of hygroscopic salts or by permafrost melts, both potentially forming saturated brines. Freezing point depression allows these heavy brines to remain liquid in the near-surface environment for extended periods, perhaps as eutectic solutions, at the lowest temperatures and highest salt concentrations where ices and precipitates do not form. Perchlorate and chlorate salts and iron sulphate form brines with low eutectic temperatures and may persist under Mars near-surface conditions, but are chemically harsh at high concentrations and were expected to be incompatible with life, while brines of common sulphate salts on Mars may be more suitable for microbial growth. Microbial growth in saturated brines also may be relevant beyond Mars, to the oceans of Ceres, Enceladus, Europa and Pluto. We have previously shown strong growth of salinotolerant bacteria in media containing 2M MgSO4 heptahydrate (~50% w/v) at 25°C. Here we extend those observations to bacterial isolates from Basque Lake, BC and Hot Lake, WA, that grow well in saturated MgSO4 medium (67%) at 25°C and in 50% MgSO4 medium at 4°C (56% would be saturated). Psychrotolerant, salinotolerant microbes isolated from Basque Lake soils included Halomonas and Marinococcus, which were identified by 16S rRNA gene sequencing and characterized phenetically. Eutectic liquid medium constituted by 43% MgSO4 at −4°C supported copious growth of these psychrotolerant Halomonas isolates, among others. Bacterial isolates also grew well at the eutectic for K chlorate (3% at −3°C). Survival and growth in eutectic solutions increases the possibility that microbes contaminating spacecraft pose a contamination risk to Mars. The cold brines of sulphate and (per)chlorate salts that may form at times on Mars through deliquescence or permafrost melt have now been demonstrated to be suitable microbial habitats, should appropriate nutrients be available and dormant cells become vegetative.

The detection of organic molecules that are indicative of past or present biological activity within the Solar System bodies and beyond is a key research area in astrobiology. Mars is of particular interest in this regard because of evidence of a (perhaps transient) warm and wet climate in its past. To date, space missions to Mars have primarily used pyrolysis technique to extract organic compounds from the Martian regolith, but it has not enabled a clear detection of unaltered native Martian organics. The elevated temperatures required for pyrolysis extraction can cause native Martian organics to react with perchlorate salts in the regolith, possibly resulting in the chlorohydrocarbons that have been detected by mass spectrometry, a commonly used in situ technique for space applications. Supercritical carbon dioxide (SCCO2) extraction technique is a powerful alternative to pyrolysis that may be capable of extracting and delivering unaltered native organic species to an analyser. In this study, we report the SCCO2 extraction of unaltered amino acids (AAs) with simple laboratory analyses of extracts by capillary electrophoresis laser-induced fluorescence (CE/LIF) and liquid chromatography with mass spectrometry (LC/MS) techniques. The extraction efficiencies of several representative AAs using SCCO2 with small amounts of pure water (~1–5%) as a co-solvent were determined. Glass beads were used as a model substrate to examine the effects of several experimental parameters and Johnson Space Center (JSC) Mars-1A Martian regolith simulant was used to study the effect of complex matrix on extraction efficiencies. With optimized experimental conditions (75C and 5% of water), extraction efficiencies from doped JSC Mars-1A were found to be ~40% for glycine, alanine and serine and ~10% for lysine. Extraction of native organics from undoped JSC Mars-1A suggests that SCCO2/water solvent system can extract both organics extractable with pure SCCO2 and those extractable with pure water. Additionally, species not extracted by either pure SCCO2 or pure water were extracted with SCCO2/water solvent. Despite the preliminary nature of this work, it paves the path for more comprehensive extraction studies of astrobiologically relevant samples with thorough analyses of resulting extracts.

Punctuated equilibrium, in the sense of Eldredge and Gould in 1972, and path dependence (Gould in 2002), dominate evolutionary processes, many of whose dynamics can be expressed in terms of interacting information sources (Wallace in 2010). Argument based on Feynman's (in 2000) characterization of information as a form of free energy leads to a close, if inverse, analogy between evolutionary transitions and economic ratchets. Driven by such a ‘self-referential’ mechanism, increases in available metabolic free energy – via the aerobic transition – led to the eukaryotic transition and to life as we know it. Formal analysis focuses on groupoid symmetries associated with the cognitive processes of gene expression, an extension of the symmetry breaking/making perspectives of physical science into biological phenomena. This suggests that understanding modalities of cognitive gene expression, as opposed to focus on genes themselves, provides the deepest insight into evolutionary phenomena, a perspective at some variance with current simplistic gene-centred views that constrain evolutionary theory.

The Stanley Miller experiment suggests that amino acid-based life is ubiquitous in our universe, although its varieties will not have followed the particular, highly contingent and path-dependent, evolutionary trajectory found on Earth. Are many alien organisms likely to be individually conscious in ways we would recognize? Almost certainly. Will alien consciousness require a ‘sleep cycle’? A strong argument suggests it will. Can some species develop analogs to culture and high-order technology? Less likely, but still fairly probable. If so, will we be able to communicate with them? Only on a basic level, and only with profound difficulty. The reasoning is fairly direct and involves convolution of a learned heritage system with individual and collective consciousness.

Candida lusitaniae and C. guilliermondii are perfect model organisms for the study of Candida genera behaviour in various conditions. Both of them are rare pathogens capable to cause candidiasis in the patients with weakened immune system and can undergo morphology switches related to the increased antifungal drug resistance. Candida genera yeasts are able to inhabit diverse range of ecological niches including space ships and space stations. During the long-term expeditions, astronauts are affected by various factors that can change the state immune system. In such conditions, the commensal usually non-pathogenic microorganisms can spread through the body of the host and cause infections. Weakened immune system and limited use of drugs in spaceships promote the search of the alternative methods for the biocontrol of microorganisms. Several studies demonstrate that microorganisms are altering their gene expression, physiology, morphology, pathogenicity and evolving resistance to the antifungals under microgravity conditions. Our research indicated that switch to the pseudohyphae morphology leads up 30-fold increased resistance to amphotericin B in C. lusitaniae and C. guilliermondii. Cultivation of yeasts in rotary cell culture system (RCCS) is related to the altered cell growth and resistance to the antifungal treatment. Our results showed that growth in the RCCS led to the extreme increase in cell resistance to amphotericin B as compared with the standard growth conditions. In our research, we applied electroporation for the biocontrol of two Candida species. C. lusitaniae and C. guilliermondii cells grown in RCCS exhibited significantly increased survivability after pulsed electric field (PEF) treatment in comparison with cells grown under routine conditions. We have shown that PEF bursts of 2.5–25 kV cm−1 of 100 µs × 8 duration display a dose-dependent permeabilization of both studied Candida species. Our research indicated that budding cells and pseudohyphae morphology cells, with increased resistance to amphotericin B, can be effectively inactivated after applying PEF higher than 15 kV cm−1.

If space explorers discover a biosphere supporting life on an off-Earth body, should they treat that life as possessing intrinsic value? This is an ethical quandary leading to a further question: how do we ground a universal moral norm to which the astroethicist can appeal? This article closely analyses various forms of responsibility ethics and finds them weak because they commit the naturalistic fallacy – that is, they ask nature to define the good. The good, however, is self-defining and not derivable from nature. Even so, a revised responsibility ethic could ground its universal norms on the fact that life and only life can experience and appreciate the good. Conclusion: living creatures possess intrinsic value both on Earth and elsewhere in the Universe.

A planet may be defined as habitable if it has an atmosphere and is warm enough to support the existence of liquid water on its surface. Such a world has the basic set of conditions that allow it to develop life similar to ours, which is carbon-based and has water as its universal solvent. While this definition is suitably vague to allow a fairly broad range of possibilities, it does not address the question as to whether any life that does form will become either complex or intelligent. In this paper, we seek to synthesize a qualitative definition of which subset of these ‘habitable worlds’ might develop more complex and interesting life forms. We identify two key principles in determining the capacity of life to breach certain transitions on route to developing intelligence. The first is the number of potential niches a planet provides. Secondly, the complexity of life will reflect the information density of its environment, which in turn can be approximated by the number of available niches. We seek to use these criteria to begin the process of placing the evolution of terrestrial life in a mathematical framework based on environmental information content. This is currently testable on Earth and will have clear application to the worlds that we are only beginning to discover. Our model links the development of complex life to the physical properties of the planet, something which is currently lacking in all evolutionary theory.

We study the prospects for life on planets with subsurface oceans, and find that a wide range of planets can exist in diverse habitats with ice envelopes of moderate thickness. We quantify the energy sources available to these worlds, the rate of production of prebiotic compounds, and assess their potential for hosting biospheres. Life on these planets is likely to face challenges, which could be overcome through a combination of different mechanisms. We estimate the number of such worlds, and find that they may outnumber rocky planets in the habitable zone of stars by a few orders of magnitude.

The recent announcement of a Neptune-sized exomoon candidate orbiting the Jupiter-sized object Kepler-1625b has forced us to rethink our assumptions regarding both exomoons and their host exoplanets. In this paper, I describe calculations of the habitable zone for Earth-like exomoons in the orbit of Kepler-1625b under a variety of assumptions. I find that the candidate exomoon, Kepler-1625b-i, does not currently reside within the exomoon habitable zone, but may have done so when Kepler-1625 occupied the main sequence. If it were to possess its own moon (a ‘moon–moon’) that was Earth-like, this could potentially have been a habitable world. If other exomoons orbit Kepler-1625b, then there are a range of possible semi-major axes/eccentricities that would permit a habitable surface during the main sequence phase, while remaining dynamically stable under the perturbations of Kepler-1625b-i. This is however contingent on effective atmospheric CO2 regulation.

Recent paper by Robert Klee in this journal argues that we should endorse a form of cosmic pessimism due to the inevitable destruction of Earth and humanity, allegedly meaning the complete and total annihilation of all traces of humanity's existence (‘human expunction’). It could be shown that both the physical basis and philosophical methodology used by Klee to reach those bleak conclusions are at best premature and at worst unwarranted and misleading. Even worse, they reflect a mindset of unjustified and narrow-minded technological and societal pessimism, which contributes to the erosion of the Enlightenment values, the loss of public interest in space research and colonization, and could indeed increase vulnerability to real – as opposed to uncertain eschatological – global risks humanity is facing in this millennium.

Haughton crater in the Canadian Arctic has been extensively used as a Mars (and lunar) analogue over the past 20 years. Here we report on small scale, dark, semi-seasonal slope streaks formed by melt water flowing down the crater walls that we observed during the Mars Society-sponsored M160 expedition to the F-MARS facility on the NW rim of the crater. The streaks are formed by biofilms colonizing snow melt flowing from semi-permanent snow patches in Haughton crater on Devon Island and elsewhere in the Canadian Arctic. These features superficially resemble the dark slope streaks and recurring slope lineae (RSL) observed on Mars and may serve as analogues for wet models for their formation and a contrast with dry formation models. Their significance to astrobiology and planetary science is three-fold: (1) as examples of dark recurring streaks known to be associated with water they provide a benchmark to compare with Martian slope streaks and RSL. (2) The melt streaks may have potential as astrobiological analogues for wet models of slope streaks and RSL. (3) They are natural laboratories to study planetary protection issues associated with robotic and astronaut exploration of potential water-related slope features on Mars.

Biogenesis can be understood as the final process of the Universe's evolution, from Planck scale down to nuclear scale to atomic scale to molecular scale, then finally to bioscale, with the breaking of relevant symmetries at every step. By assuming the simplest definition of life, that life is just a molecular system which can reproduce itself (auto-reproducing molecular system – ARMS) and has such kinetic ability (kineto-molecular system), at least for its microscopic level, as to respond actively to its surrounding environments, we tried to explain the origin of life, taking the final step of the Universe evolution. We found a few clues for the origin of life, such as: (1) As the Universe expands and gets extremely cold, biogenesis can take place by ARMS, new level of stabilization may be achievable only at ‘locally cold places’ (LCPs), such as comets. (2) There must be the parity breaking in the bioscale stabilization process, which can be violated spontaneously, or dynamically by the van der Waals forces possible only at LCPs. (3) The rule of bioparity breaking is universal within the biohorizon. So we will find, e.g. only left-handed amino acids in all living beings dwelling within our Galaxy. (4) The idea of biogenesis through the bioscale stabilization in the evolution of the Universe looks very consistent with Panspermia hypothesis and supports it by providing a viable answer for life's origin at such LCPs.