Did life begin on the beach?

Water is one of the prerequisites of life. Further requirements are the existence of a system of interacting organic molecules capable of capturing and converting the supply of external energy and elaborating the replicating function that is needed for propagation. None of this would be possible without the existence of some means of concentrating, selecting, and then containing these mutually interacting substances in proximity to one another, i.e., a primitive cell. Starting from this hypothesis we propose a model for the development of life on Earth. Our model embodies the following new features: (1) rapid cycles of catalysis and transport of material, (2) desegregation (separation by tidal action and degradation by catalysis) as well as segregation (by chromatography on tidal beaches), (3) cross-catalysis instead of auto-catalysis, as well as (4) compartmentalization, although the latter idea is of course not new. But our "lipid first" model, in contrast to earlier "peptide first" or "RNA first" models, provides for the compartments needed to act as a cradle for the subsequent development of information- rich molecules like peptides and RNA. If anything, the earliest information-rich molecules were probably membrane-spanning peptides/proteins.     

Did evolution select a nonrandom "alphabet" of amino acids?

The last universal common ancestor of contemporary biology (LUCA) used a precise set of 20 amino acids as a standard alphabet with which to build genetically encoded protein polymers. Considerable evidence indicates that some of these amino acids were present through nonbiological syntheses prior to the origin of life, while the rest evolved as inventions of early metabolism. However, the same evidence indicates that many alternatives were also available, which highlights the question: what factors led biological evolution on our planet to define its standard alphabet? One possibility is that natural selection favored a set of amino acids that exhibits clear, nonrandom properties-a set of especially useful building blocks. However, previous analysis that tested whether the standard alphabet comprises amino acids with unusually high variance in size, charge, and hydrophobicity (properties that govern what protein structures and functions can be constructed) failed to clearly distinguish evolution's choice from a sample of randomly chosen alternatives. Here, we demonstrate unambiguous support for a refined hypothesis: that an optimal set of amino acids would spread evenly across a broad range of values for each fundamental property. Specifically, we show that the standard set of 20 amino acids represents the possible spectra of size, charge, and hydrophobicity more broadly and more evenly than can be explained by chance alone.     

‘Did you see that,grandpa Mao?’ The prestige and propaganda rationales of the Chinese space program

China has seen a dramatic acceleration in the scope and capabilities of its space program in the past decade. This has been coupled with significantly increased global economic presence and influence as well as a steady improvement of its military capabilities. China's emergence as a major world actor has encouraged the emergence of a ‘China threat’ school of thought which interprets all Chinese policy, including its space program, as an evidence of a threatening challenge to US dominance in which the pursuit of a range of military space capabilities plays a central role. This article challenges that interpretation, arguing that China's space program is the product of a range of factors including powerful domestic political and developmental rationales and that the program is overwhelmingly driven by domestic rather than international considerations, particularly in terms of the use of the program for the purposes of enhancing prestige.     

Did mineral surface chemistry and toxicity contribute to evolution of microbial extracellular polymeric substances?

Abstract Modern ecological niches are teeming with an astonishing diversity of microbial life in biofilms closely associated with mineral surfaces, which highlights the remarkable success of microorganisms in conquering the challenges and capitalizing on the benefits presented by the mineral-water interface. Biofilm formation capability likely evolved on early Earth because biofilms provide crucial cell survival functions. The potential toxicity of mineral surfaces toward cells and the complexities of the mineral-water-cell interface in determining the toxicity mechanisms, however, have not been fully appreciated. Here, we report a previously unrecognized role for extracellular polymeric substances (EPS), which form biofilms in shielding cells against the toxicity of mineral surfaces. Using colony plating and LIVE/DEAD staining methods in oxide suspensions versus oxide-free controls, we found greater viability of wild-type, EPS-producing strains of Pseudomonas aeruginosa PAO1 compared to their isogenic knockout mutant with defective biofilm-producing capacity. Oxide toxicity was specific to its surface charge and particle size. High resolution transmission electron microscopy (HRTEM) images and assays for highly reactive oxygen species (hROS) on mineral surfaces suggested that EPS shield via both physical and chemical mechanisms. Intriguingly, qualitative as well as quantitative measures of EPS production showed that toxic minerals induced EPS production in bacteria. By determining the specific toxicity mechanisms, we provide insight into the potential impact of mineral surfaces in promoting increased complexity of cell surfaces, including EPS and biofilm formation, on early Earth. Key Words: Mineral toxicity-Bacteria-EPS evolution-Biofilms-Cytotoxicity-Silica-Anatase-Alumina. Astrobiology 12, 785-798.     

Who are the SETI sceptics?

Search for ExtraTerrestrial Intelligence (SETI) is now more than half a century old and has provoked enough discussion on technical, philosophical, and popular level, much of it critical. Historically, the criticism of SETI has been strong enough to heavily influence the course of research, so that there is a significant interest in discerning the nuances and fine points of critical argumentation. In this paper, I outline the two major forms of SETI scepticism, “fundamentalist” and “instrumentalist,” which are often conflated in the published literature, both technical and popular. Precise delineation between these two types of scepticism is important for future research as a part of a wider taxonomic project, the build-up of SETI theory, as well as for smooth joining of SETI with the ongoing astrobiological revolution. Resolving the confusion in this respect is likely to lead to an improved atmosphere and heightened public image of future SETI searches and related activities.     

Biogenesis and early life on Earth and Europa: favored by an alkaline ocean?

Recent discoveries about Europa--the probable existence of a sizeable ocean below its ice crust; the detection of hydrated sodium carbonates, among other salts; and the calculation of a net loss of sodium from the subsurface--suggest the existence of an alkaline ocean. Alkaline oceans (nicknamed "soda oceans" in analogy to terrestrial soda lakes) have been hypothesized also for early Earth and Mars on the basis of mass balance considerations involving total amounts of acids available for weathering and the composition of the early crust. Such an environment could be favorable to biogenesis since it may have provided for very low Ca2+ concentrations mandatory for the biochemical function of proteins. A rapid loss of CO2 from Europa's atmosphere may have led to freezing oceans. Alkaline brine bubbles embedded in ice in freezing and impact-thawing oceans could have provided a suitable environment for protocell formation and the large number of trials needed for biogenesis. Understanding these processes could be central to assessing the probability of life on Europa.     

A comparison between the 19th century early proposals and the 20th–21st centuries realized projects intended to contact other planets

Methods dealing with how to contact other planets that are supposed to be inhabited by “intelligent” civilizations have begun more than one century and a half ago. The historical question has been already treated in several studies and the aim of this paper is not to provide details on that aspect. On the other hand, it could be interesting to make a comparison between the different approaches to contact planets, formulated at different epochs (even if obviously techniques were not in the same state of advancement). The most important characteristics of the earliest messages, remained only on a theoretical form, will be presented. The main features of modern messages, which have been concretely realized, will also be emphasized. Drawing a parallel between these two series of projects could demonstrate what has been considered as unavoidable by both pioneer and modern messages creators, while it has not been proved that the first ones have had any influence on the second ones. The common points emerging from this comparison could then (perhaps) help to select adequate models for an intelligible message intended to ETs, particularly concerning the language forms. Besides this, the differences could illustrate the human cultural advances in the field of METI and underline the tendencies that have been chosen in that field since the last decades.     

Should the Space Station be an ark?

This essay explores the pros and cons of maximizing the number of species that can be maintained on the Space Station. It reviews some of the history of comparative space biology to show that different cultures have different perspectives on the study of non-traditional research organisms (ie non-rodents) in space. Despite these differences, there are simple principles that all international partners in the Space Station endeavour should be able to uphold when deciding what facilities to build and what species to fly. As an argument for maximizing the taxonomic diversity on the Space Station, examples are given to show how very similar organisms may have different reactions to microgravity. At the same time the political pressure in the USA to make the Space Station an institution specifically servicing the 'health, well-being and economic benefits of people on earth', is acknowledged. Ultimately the justification for what species will be on the Space Station should rest with the quality of the scientific questions being asked.     

Planning the post-Apollo space program: Are there lessons for the present?

The current debate over the future of human spaceflight in the USA has been a fascinating, and troubling, exercise in futility for those inextricably committed to an expansive vision of human exploration and development of space. The retirement of the Space Shuttle, originally set for the end of 2010 but later extended into 2011, the technical and funding problems of the Constellation follow-on program that led to its cancellation in 2009, and the emergence of commercial vendors who might be able to offer human access to Earth orbit have all complicated the current environment. In view of this situation, the question may be legitimately asked: what might we learn from earlier efforts to develop a human spaceflight capability the last time such a transition took place? Using the post-Apollo transition from the ballistic capsule to a winged, reusable vehicle as a case study, this article seeks to illuminate the planning, decision-making, economic, and political issues that have arisen in this policy debate. It suggests that a web of interlocking issues—only one of which was technical—affected the course taken. Instead, politics, economics, social and cultural priorities, values, and institutional considerations all helped to frame the debate and shape the decision.     

Seeing the Forest or the Trees? Shifting Categorical Effects in Map Memory

People use spatial and nonspatial information to structure memory for an environment. Two experiments explored interactions between spatial and social categories on map memory when mediated by retrieval (Experiment 1) and encoding (Experiment 2) demands. Participants studied a map depicting business locations (including proprietors' race). In Experiment 1, participants completed two memory tasks, one globally focused and the other locally focused. The global task compressed, while the local task expanded, within-category similarity. Furthermore, processing styles carried over to the subsequent task. Experiment 2 emphasized either the spatial or social category during encoding, which increased that category's weighting in memory. These results extend the work of Maddox, Rapp, Brion, and Taylor, suggesting that retrieval and encoding demands can shift how these categories affect spatial memory.     

Why does the total pressure on the subsolar magnetopause differ from the solar wind dynamic pressure?

Based on analysis of MHD equations and the results of numerical simulation in the magneto-sheath it is demonstrated that the total pressure on the magnetopause differs from the solar wind dynamic pressure in the majority of cases. From the equation of motion it follows that the total pressure is reduced due to deflection from the Sun-Earth line. At the same time, it increases because of formation of a magnetic barrier. This result is consistent with experimentally observed expansion of the magnetosphere for the radial direction of the interplanetary magnetic field, when no magnetic barrier is formed. In this paper we compare the behavior of pressure along the Sun-Earth line for the northward and radial interplanetary field, using the results of numerical MHD simulation and observational data from THEMIS. In the isotropic MHD approximation, the difference between the total pressure on the subsolar magnetopause at northern and radial IMFs does not exceed 10–12 percent. However, in the anisotropic approximation this difference increases up to 15–20 percent. The results of anisotropic modeling well agree with observed averaged profiles of pressure components in the subsolar magnetosheath.     

The carbon or silicon colonization of the universe?

At the time of the Apollo Programme, a first human mission to Mars was proposed as early as 1984 with the argument that the higher costs of human exploration would be more than justified by the increased effectiveness of human explorers. This was based on the Apollo experience, where "ground truth" measurements and sampling provided the basis for subsequent unmanned exploration of the Solar System. A human Mars mission is now not seen until 2030, at the end of a series of increasingly sophisticated unmanned probes. Each robot mission not only teaches us something about Mars, but also through experience increases our capabilities for the unmanned exploration of that planet. As a consequence, what a human mission would have to do becomes progressively more demanding. Any extended plan for the human exploration of Space will tend to be overtaken by advances in technology, and if this is not factored into the scenario the proposals will become progressively unrealistic.     

Chemistry of the interstellar medium--an evolutionary dead end?

An analysis of the experimental data available and of the present theoretical concepts shows that even the initial physicochemical chemical precellular stages of biological evolution are impossible in the interstellar medium, while biomonomers possibly formed on asteroids and comets might have participated after transportation to the Earth in the final stages of the origin of the first precellular biological structures and then in the first living cells.     

How rare is complex life in the Milky Way?

An integrated Earth system model was applied to calculate the number of habitable Earth-analog planets that are likely to have developed primitive (unicellular) and complex (multicellular) life in extrasolar planetary systems. The model is based on the global carbon cycle mediated by life and driven by increasing stellar luminosity and plate tectonics. We assumed that the hypothetical primitive and complex life forms differed in their temperature limits and CO(2) tolerances. Though complex life would be more vulnerable to environmental stress, its presence would amplify weathering processes on a terrestrial planet. The model allowed us to calculate the average number of Earth-analog planets that may harbor such life by using the formation rate of Earth-like planets in the Milky Way as well as the size of a habitable zone that could support primitive and complex life forms. The number of planets predicted to bear complex life was found to be approximately 2 orders of magnitude lower than the number predicted for primitive life forms. Our model predicted a maximum abundance of such planets around 1.8 Ga ago and allowed us to calculate the average distance between potentially habitable planets in the Milky Way. If the model predictions are accurate, the future missions DARWIN (up to a probability of 65%) and TPF (up to 20%) are likely to detect at least one planet with a biosphere composed of complex life.     

Bombardment of the Hadean Earth: wholesome or deleterious?

Graham Ryder died in January 2002 at the age of 53. He was a Staff Scientist at the Lunar and Planetary Science Institute in Houston, TX for most of his professional life, studying lunar petrology and planetary impacts. For many years he was the senior editor of the Proceedings of the Lunar and Planetary Science Conference, and he was the senior editor of Geological Society of America Special Paper 307, The Cretaceous-Tertiary Event and Other Catastrophes in Earth History. He was the major advocate for the 3.8 Ga lunar impact cataclysm and was just beginning to publish on correlations of the early lunar impact record to that of the other inner planets at the time of his death. Graham's abstract to the Rubey Colloquium was never presented. Although Graham made many of the points in this abstract to lunar science audiences, he certainly would have wanted these views to be shared with the Astrobiology community. We have taken the liberty of publishing this abstract with the Rubey proceedings, with only a few minor revisions to include reference to some recently published papers. These revisions were recommended by Gary R. Byerly, who reviewed this abstract for publication.     

Why Raman spectroscopy on Mars?--a case of the right tool for the right job

We provide a scientific rationale for the astrobiological investigation of Mars. We suggest that, given practical constraints, the most promising locations for the search for former life on Mars are palaeolake craters and the evaporite deposits that may reside within them. We suggest that Raman spectroscopy offers a promising tool for the detection of evidence of former (or extant) biota on Mars. In particular, we highlight the detection of hopanoids as long-lived bacterial cell wall products and photosynthetic pigments as the most promising targets. We further suggest that Raman spectroscopy as a fibre optic-based instrument lends itself to flexible planetary deployment.     

Which way is the bookstore? A closer look at the judgments of relative directions task

We present a detailed analysis of a widely used assay in human spatial cognition, the judgments of relative direction (JRD) task. We conducted three experiments involving virtual navigation interspersed with the JRD task, and included confidence judgments and map drawing as additional metrics. We also present a technique for assessing the similarity of the cognitive representations underlying performance on the JRD and map-drawing tasks. Our results support the construct validity of the JRD task and its connection to allocentric representation. Additionally, we found that chance performance on the JRD task depends on the distribution of the angles of participants’ responses, rather than being constant and 90 degrees. Accordingly, we present a method for better determining chance performance.     

Does the rapid appearance of life on Earth suggest that life is common in the universe?

It is sometimes assumed that the rapidity of biogenesis on Earth suggests that life is common in the Universe. Here we critically examine the assumptions inherent in this if-life-evolved-rapidly-life-must-be-common argument. We use the observational constraints on the rapidity of biogenesis on Earth to infer the probability of biogenesis on terrestrial planets with the same unknown probability of biogenesis as the Earth. We find that on such planets, older than approximately 1 Gyr, the probability of biogenesis is > 13% at the 95% confidence level. This quantifies an important term in the Drake Equation but does not necessarily mean that life is common in the Universe.     

Why go to the moon? The many faces of lunar policy

What is it about the Moon that captures the fancy of humankind? A silvery disk hanging in the night sky, it conjures up images of romance and magic. It has been counted upon to foreshadow important events, both of good and ill, and its phases for eons served humanity as its most accurate measure of time. This paper discusses the Moon as a target for human exploration and eventual settlement. This paper will explore the more than 50-year efforts to reach the Moon, succeeding with space probes and humans in Project Apollo in the 1960s and early 1970s. It will then discuss the rationales for spaceflight, suggesting that human space exploration is one of the least compelling of all that might be offered. The paper will then discuss efforts to make the Moon a second home, including post-Apollo planning, the Space Exploration Initiative, and problems and opportunities in the 2004 Vision for Space Exploration, and cancellation of that program in 2010.