The feasibility of immunological detection using antibodies as an approach to detect and study alien life forms is examined. The latter could either mean alternative forms of life on planet Earth or extraterrestrial life. As a detection reagent for biological substances, antibodies have the advantage of being conformational, rather than sequence-dependent. Their high affinity to cognate antigens allows detection at picomolar levels. Antibodies could serve both as tools for detection as well as for the concentration of samples. Panels of highly specific antibodies could be made against a plethora of natural or synthetic biomarkers, for example stereoisomers of amino acids, nucleotide analogues, lipids, polysaccharides and polycyclic aromatic hydrocarbons. With detection reagents efficiently packaged and miniaturized as immunosensor chips in analytical panels, antibody microarrays could serve as the first line of detection and identification of biological remnants in situ during exploratory missions. Specific antibodies could also be used for affinity concentration of possible biomarkers obtained from sample return missions. Furthermore, antibodies raised against any alien biological samples could be the first specific probes made for further detection of, or investigations on, alien biology.

This paper outlines hypotheses relevant to the evolution of intelligent life and encephalization in the Phanerozoic. If general principles are inferable from patterns of Earth life, implications could be drawn for astrobiology. Many of the outlined hypotheses, relevant data, and associated evolutionary and ecological theory are not frequently cited in astrobiological journals. Thus opportunity exists to evaluate reviewed hypotheses with an astrobiological perspective. A quantitative method is presented for testing one of the reviewed hypotheses (hypothesis i; the diffusion hypothesis). Questions are presented throughout, which illustrate that the question of intelligent life's likelihood can be expressed as multiple, broadly ranging, more tractable questions.

Photosynthetic life requires sufficient photosynthetically active radiation to metabolize. On Earth, plant behaviour, physiology and metabolism are sculpted around the night–day cycle by an endogenous biological circadian clock. The evolution of life was influenced by the Earth–Sun orbital dynamic, which generates the photo-environment incident on the planetary surface. In this work, the unusual photo-environment of an Earth-like planet (ELP) in 3 : 2 spin–orbit resonance is explored. Photo-environments on the ELP are longitudinally differentiated, in addition to differentiations related to latitude and depth (for aquatic organisms) which are familiar on Earth. The light environment on such a planet could be compatible with Earth's photosynthetic life although the threat of atmospheric freeze-out and prolonged periods of darkness would present significant challenges. We emphasize the relationship between the evolution of life on a planetary body with its orbital dynamics.

An organic macromolecular residue, prepared from the Murchison meteorite by treatment with hydrofluoric and hydrochloric acids, was subjected to online thermochemolysis with tetramethylammonium hydroxide (TMAH). The most abundant compound released by thermochemolysis was benzoic acid. Other abundant compounds include methyl and dimethyl benzoic acids as well as methoxy benzoic acids. Short chain dicarboxylic acids (C4–8) were also released from the organic macromolecule. Within the C1 and C2 benzoic acids all possible structural isomers are present reflecting the abiotic origin of these units. The most abundant isomers include 3,4-dimethylbenzoic acid (DMBA), 3,5-DMBA, 2,6-DMBA and phenylacetic acid. Thermochemolysis also liberates hydrocarbons that are not observed during thermal desorption; these compounds include naphthalene, methylnaphthalenes, biphenyl, methylbiphenyls, acenaphthylene, acenaphthene, phenanthrene, anthracene, fluoranthene and pyrene. The lack of oxygen containing functional groups in these hydrocarbons indicates that they represent non-covalently bound, occluded molecules within the organic framework. This data provides a valuable insight into oxygen bound and physically occluded moieties in the Murchison organic macromolecule and implies a relative order of synthesis or agglomeration for the detected organic constituents.

The Rio scale is a tool for communicating the significance of a signal to the general public. It assigns scores to signals detected in searches for extraterrestrial intelligence (SETI), which characterizes both the consequences of a signal and the probability the signal is truly from ETI, in an easily digestible format for laypeople to interpret. In the 17 years since its construction, the number of groups actively conducting searches for evidence of intelligent life beyond the Earth has increased significantly, and theoretical work has established a new suite of observables that are capable of revealing the presence of ETI in a range of astronomical observations. In this paper, we revise the Rio scale, with the aim of (i) achieving consensus across academic disciplines on a scheme for classifying signals potentially indicating the existence of advanced extraterrestrial life, (ii) supplying a pedagogical tool to help inform the public about the process scientists go through to develop an understanding of a signal and (iii) providing a means of calibrating the expectations of the world at large when signals are discussed in the media. We also present (and encourage the SETI community to adopt) a single set of consistent terminology for discussing signals.

The theory of lithopanspermia proposes the natural exchange of organisms between solar system bodies through meteorites. The focus of this theory comprises three distinct stages: planetary ejection, interplanetary transit and planetary entry. However, it is debatable whether organisms transported within the ejecta can survive all three stages. If the conjecture is granted, that life can indeed be safely transmitted from one world to another, then it is not only a topic pertaining to planetary science but also biological sciences. Hence, these stages are only the first three factors of the equation. The other factors for successful lithopanspermia are the quality, quantity and evolutionary strategy of the transmitted organisms. When expanding into new environments, invading organisms often do not survive in the first attempt and usually require several attempts through propagule pressure to obtain a foothold. There is a crucial difference between this terrestrial situation and the one brought about by lithopanspermia. While invasive species on Earth repeatedly enters a new habitat, a species pragmatically arrives on another solar system body only once; thus, an all-or-nothing response will be in effect. The species must survive in the first attempt, which limits the probability of survival. In addition, evolution sets a boundary through the existence of an inverse proportionality between the exchanges of life between two worlds, thus further restricting the probability of survival. However, terrestrial populations often encounter unpredictable and variable environmental conditions, which in turn necessitates an evolutionary response. Thus, one evolutionary mode in particular, bet hedging, is the evolutionary strategy that best smooth out this inverse proportionality. This is achieved by generating diversity even among a colony of genetically identical organisms. This variability in individual risk-taking increases the probability of survival and allows organisms to colonize more diverse environments. The present analysis to understand conditions relevant to a bacterial colony arriving in a new planetary environment provides a bridge between the theory of bet hedging, invasive range expansion and planetary science.

One principal challenge in biology is defining a postulate by which the habitability of other planets can be assessed. Current assessments suffer from two potential weaknesses. With respect to other planets, either assumptions are made about the physical and chemical conditions of environments that err on the side of biological optimism without empirical constraint by spacecraft observations or novel physiologies of microorganisms are invented to fit extraterrestrial environmental conditions with no demonstrated microbiological counterparts on Earth. Attempts to assess the habitability of the early Earth suffer from similar problems. We discuss the following postulate: ‘the proposition that a planet is or was habitable requires that the physiological requirements of microorganisms on Earth known at the time of assessment match the empirically determined combined physical and chemical conditions in the extraterrestrial or early Earth environment being assessed’ as a means of evaluating ‘habitability’. We use as tests for our postulate the early Earth and the cloud deck of Venus (a habitat that has been a source of optimistic debate for forty years). We conclude that, although the early Earth was habitable, Venus is a dead world.

Mars has surely been scrutinised since the dawn of humankind. Its appearance every couple of years like a drop of blood in the sky led to warlike attributes in the ancient world. In the 16th century Tycho Brahe made accurate observations of the position of Mars that enabled Johannes Kepler to obtain his first two laws of planetary motion. These in turn were explained by Newton's laws of motion and gravity. In the 17th century the first telescope observations were made, but Mars is small and very little surface detail could be discerned.

Throughout the 18th and 19th centuries telescopes improved, revealing many dark areas on the red tinted surface. During the close opposition of 1877 sufficient detail could be seen that enabled Giovanni Schiaparelli to announce that he could see about 40 canali on Mars. This led to the saga of the canals of Mars, finally laid to rest in 1971 when Mariner 9 made observations from Martian orbit showing that the canali/canals do not exist.

Belief that there was life on Mars was widespread in the 19th century. However, the majority of astronomers never believed in Martian intelligence. Least controversial was the view that the dark areas were some form of plant life. This view persisted until Mariner 4 flew past Mars in 1965 and discovered a far thinner atmosphere than previously thought. This was a low point, with impact craters dominating the images. It was Mariner 9 that revealed much more promising landscapes, including volcanic features, and others indicating that water had flowed across the surface, particularly when Mars was young. Thus, the contemporary era of Mars exploration began.

Our picture of Mars today is not only much more complete than that before Mariner 4, in several ways it is quite different. The belief, however, that there might be life on Mars persists – subsurface life cannot be ruled out and, failing that, there might be ancient fossils on Mars.

This paper proposes a long-term scheme for robotic exploration of the galaxy, and then considers the implications in terms of the ‘Fermi paradox’ and our search for extraterrestrial intelligence (ETI). We discuss the ‘Galactic ecology’ of civilizations in terms of the parameters T (time between ET civilizations arising) and L, the lifetime of these civilizations. Six different regions are described.

In this paper, we revisit the Dysonian approach and assume that a superadvanced civilization is capable of building a cosmic megastructure located closer than the habitable zone (HZ). Then such a Dyson Sphere (DS) might be visible in the optical spectrum. We have shown that for typical high melting point metamaterial – Graphene, the radius of the DS should be of the order of 1011 cm, or even less. It has been estimated that energy required to maintain the cooling system inside the DS is much less than the luminosity of a star. By considering the stability problem, we have found that the radiation pressure might stabilize dynamics of the megastructure and as a result it will oscillate, leading to interesting observational features – anomalous variability. The similar variability will occur by means of the transverse waves propagating along the surface of the cosmic megastructure. In the summary, we also discuss the possible generalization of the definition of HZs that might lead to very interesting observational features.

Mars' total atmospheric nitrogen content is 0.2 mbar. One-dimensional (1D) photochemical simulations of Mars' atmosphere show that nitric acid (HNO3(g)), the most soluble nitrogen oxide, is the principal reservoir species for nitrogen in its lower atmosphere, which amounts to a steady-state value of 6×10−2 kg or 4 moles, conditions of severe nitrogen deficiency. Mars could, however, support ∼1015 kg of biomass (∼1 kg N m−2) from its current atmospheric nitrogen inventory. The terrestrial mass ratio of nitrogen in biomass to that in the atmosphere is ∼10−5; applying this ratio to Mars yields ∼1010 kg of total biomass – also, conditions of severe nitrogen deficiency. These amounts, however, are lower limits as the maximum surface-sink of atmospheric nitrogen is 2.8 mbar (9×1015 kg of N), which indicates, in contradistinction to the Klingler et al. (1989), that biological metabolism would not be inhibited in the subsurface of Mars. Within this context, we explore HNO3 deposition on Mars' surface (i.e. soil and ice-covered regions) on pure water metastable thin liquid films. We show for the first time that the negative change in Gibbs free energy increases with decreasing HNO3(g) (NO3−(aq)) in metastable thin liquid films that may exist on Mars' surface. We also show that additional reaction pathways are exergonic and may proceed spontaneously, thus providing an ample source of energy for nitrogen fixation on Mars. Lastly, we explore the dissociation of HNO3(g) to form NO3−(aq) in metastable thin liquid films on the Martian surface via condensed phase simulations. These simulations show that photochemically produced fixed nitrogen species are not only released from the Martian surface to the gas-phase, but more importantly, transported to lower depths from the Martian surface in transient thin liquid films. A putative biotic layer at 10 m depth would produce HNO3 and N2 sinks of −54 and −5×1012 molecules cm−2 s−1, respectively, which is an ample supply of available nitrogen that can be efficiently transported to the subsurface. The downward transport as well as the release to the atmosphere of photochemically produced fixed nitrogen species (e.g. NO2−, NO and NO2) suggests the existence of a transient but active nitrogen cycle on Mars.

The majority of extra-solar planets have been discovered (or confirmed after follow-up) through radial-velocity (RV) surveys. Using ground-based spectrographs such as High Accuracy Radial Velocity Planetary Search (HARPS) and HARPS-North, it is now possible to detect planets that are only a few times the mass of the Earth. However, the presence of dark spots on the stellar surface produces RV signals that are very similar in amplitude to those caused by orbiting low-mass planets. Disentangling these signals has thus become the biggest challenge in the detection of Earth-mass planets using RV surveys. To do so, we use the star's lightcurve to model the RV variations produced by spots. Here we present this method and show the results of its application to CoRoT-7.

The aggregation of interstellar grains as a result of ballistic collisions produces loosely packed structures with much of their internal volume composed by vacuum (cavities). The molecular material present on the surfaces of the cavities gives rise to a series of reactions induced by cosmic rays, UV radiation, thermal shocks, etc., in high reducing conditions. Thus, a terrestrial type chemistry is given the possibility to evolve inside these cavities. The resulting products are different and of a wider range than those from gas-phase or surface chemistry in molecular clouds. Under conditions similar to those in the aggregate cavities, laboratory experiments have produced amino acids, sugars and other organic compounds from simple precursors. In dense star-forming regions, the molecular species inside aggregates are efficiently shielded against the local UV field. The same molecules were incorporated in the material which formed the Earth, as well as other planets, during the process of its formation and afterwards fell on the surface via comets, meteorites, interstellar dust, etc. This was the source material that can produce, under favorable circumstances, the biopolymers needed for life. The astronomical observations of organic molecules in star-forming regions and the results of analyses of meteorites and cometary dust seem to support the present hypothesis that complex prebiotic molecules form inside dust aggregates and therein survive the journey to planetary systems. The Miller experiment is revisited through innumerable repetitions inside dust grain aggregates.

At the beginning of the 21st century we witness considerable global developments in space exploration and a new era has begun: the New Space Age. The principal symbols of that age are firstly internationalization of space activities, secondly commercial utilization of space technologies, and lastly emergence of outer space economy. This paper presents selected signposts of the New Space Age. Three cases of recent outer space enterprises: recovery of asteroid resources (exo-mining), post-cremation memorial spaceflight (exo-burials) and first extraterrestrial advert (exo-marketing), are introduced in order to emphasize the monetary and social dimension of commercial application of space technologies. To give an illustration of these trends, this paper provides a brief socioculturally minded account of three outer space undertakings that are interpreted as signposts of the new era.

Life on Earth spans a range of temperatures and exhibits biological growth rates that are temperature dependent. While the observation that growth rates are temperature dependent is well known, we have recently shown that the statistical distribution of specific growth rates for life on Earth is a function of temperature (Corkrey et al., 2016). The maximum rates of growth of all life have a distinct limit, even when grown under optimal conditions, and which vary predictably with temperature. We term this distribution of growth rates the biokinetic spectrum for temperature (BKST). The BKST possibly arises from a trade-off between catalytic activity and stability of enzymes involved in a rate-limiting Master Reaction System (MRS) within the cell. We develop a method to extrapolate quantile curves for the BKST to obtain the posterior probability of the maximum rate of growth of any form of life on Earth. The maximum rate curve conforms to the observed data except below 0°C and above 100°C where the predicted value may be positively biased. The deviation below 0°C may arise from the bulk properties of water, while the degradation of biomolecules may be important above 100°C. The BKST has potential application in astrobiology by providing an estimate of the maximum possible growth rate attainable by terrestrial life and perhaps life elsewhere. We suggest that the area under the maximum growth rate curve and the peak rate may be useful characteristics in considerations of habitability. The BKST can serve as a diagnostic for unusual life, such as second biogenesis or non-terrestrial life. Since the MRS must have been heavily conserved the BKST may contain evolutionary relics. The BKST can serve as a signature summarizing the nature of life in environments beyond Earth, or to characterize species arising from a second biogenesis on Earth.

30 years after the Viking Mission landed on Mars (20 July 1976) to search for life, despite the positive findings of the Labelled Release (LR) experiment, the issue remains unresolved. The controversial history, following the immediate dismissal of the LR’s evidence for microbial activity in the Martian soil, and the later claim to its having found living microorganisms are reviewed. The bearing of post-Viking-to-current data on the issue is discussed in the context of the scientific community’s growing interest in the long-dismissed possibility of microbial life on Mars. Objections raised over the years to the biological interpretation of the Mars LR, those currently maintained, and their rebuttals are reviewed. A case is presented that enough evidence now exists for an objective review by astrobiologists to resolve this key issue, a review, surprisingly, not yet held. The results could greatly influence NASA’s currently shifting plans for Mars exploration. A variation of the LR experiment to test for chiral specificity in the metabolism of substrates by the active agent found in the Martian soil, and thus having the capability of obtaining an unambiguous answer to the life question, is proposed. Confirmation of life on Mars by this experiment can also determine whether Martian and Earth life forms share a common heritage. Together with mounting evidence for the viable transfer of microorganisms between the two planets, this would be evidence for panspermia, and establish the presence of a common biosphere in which the two planets participate. Should Martian microorganisms show a different chiral specificity than that of Earth life then this would indicate separate origins of the two neighbouring life forms, thereby strongly implying that life occurs widely throughout the cosmos. Any one of these possible outcomes would be a paradigm-breaking event.

I compare three methods for transmitting signals over interstellar distances: radio transmitters, lasers and artificial transits. The quantitative comparison is based on physical quantities depending on energy cost and transmitting time L, the last parameter in the Drake equation. With our assumptions, radio transmitters are the most energy-effective, while macro-engineered planetary-sized objects producing artificial transits seem effective on the long term to transmit an attention-getting signal for a time that might be much longer than the lifetime of the civilization that produced the artefact.

The Zoo Hypothesis posits that we have not detected extraterrestrial intelligences (ETIs) because they deliberately prevent us from detecting them. While a valid solution to Fermi's Paradox, it is not particularly amenable to rigorous scientific analysis, as it implicitly assumes a great deal about the sociological structure of a plurality of civilizations. Any attempt to assess its worth must begin with its most basic assumption – that ETIs share a uniformity of motive in shielding Earth from extraterrestrial contact. This motive is often presumed to be generated by the influence of the first civilization to arrive in the Galaxy. I show that recent work on inter-arrival time analysis, while necessary, is insufficient to assess the validity of the Zoo Hypothesis (and its related variants). The finite speed of light prevents an early civilization from exerting immediate cultural influence over a later civilization if they are sufficiently distant. I show that if civilization arrival times and spatial locations are completely uncorrelated, this strictly prevents the establishment of total hegemony throughout the Galaxy. I finish by presenting similar results derived from more realistic Monte Carlo Realization (MCR) simulations (where arrival time and spatial locations are partially correlated). These also show that total hegemony is typically broken, even when the total population of civilizations remains low. The Zoo Hypothesis is therefore only justifiable on weak anthropic grounds, as it demands total hegemony established by a long-lived early civilization, which is a low probability event. In the terminology of previous studies of solutions to Fermi's Paradox, this confirms the Zoo Hypothesis as a ‘soft’ solution. However, an important question to be resolved by future work is the extent to which many separate hegemonies are established, and to what extent this affects the Zoo Hypothesis.

Formaldehyde is a precursor of sugars, which are compounds essential in all forms of life and a necessary molecule for prebiotic processes. This work focuses on evaluating the stability of formaldehyde exposed to a high radiation field simulating prebiotic conditions on primitive Earth, such as the ocean or shallow waters. Formaldehyde may have been formed from reactions in the atmosphere and from rainout processes reached water bodies. In our experiments, we employed γ radiation and found that formaldehyde was labile towards radiation and decomposed even at low irradiation doses due to the fact that aldehyde/hydrate groups present in formaldehyde structure are very reactive under irradiation. However, after exposing this molecule to several doses of irradiation, we detected the formation of formic acid and glycolaldehyde – both of which are of prebiotic interest. We also observed formaldehyde regeneration by one of its radiolytic products: formic acid.

In the early 1930s, Alfonso L. Herrera proposed his so-called sulfocyanic theory on the origin of life, an autotrophic proposal on the first living beings according to which NH4SCN and H2CO acted as raw materials for the synthesis of bio-organic compounds inside primordial photosynthetic protoplasmic structures. Although the work of Herrera is frequently cited in historical analysis of the development of the origin of life studies, very little attention has been given to the chemical significance of the reactions he published. In this paper we report the results of our search for amino acids obtained from a reactive mixture used by Herrera from 1933 onwards. Chromatograms using the high-pressure liquid chromatography (HPLC) technique suggest the presence of several amino acids, the total yield being 2% of the initial thiocyanate used. Preliminary identification based on HPLC retention times suggests the presence of glycine, alanine, cysteine and methionine. Alanine was the most abundant amino acid in all samples of fractionated material analysed. Although the starting materials used by Herrera were determined by his autotrophic hypothesis on the origin of cells, our results show that his experiments may provide insights into the abiotic synthesis of sulfur-containing amino acids within the framework of a heterotrophic emergence of life.