Abode Of Life Research Articles

Astrobiologists are rational but not Bayesian

AbstractThe 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.

A Precursor Balloon Mission for Venusian Astrobiology

Abstract The potential detection of phosphine in the atmosphere of Venus has reignited interest in the possibility of life aloft in this environment. If the cloud decks of Venus are indeed an abode of life, it should reside in the “habitable zone” between ∼50–60 km altitude, roughly coincident with the middle cloud deck, where the temperature and pressure (but not the atmospheric composition) are similar to conditions at the Earth’s surface. We map out a precursor astrobiological mission to search for such putative lifeforms in situ with instrument balloons, which could be delivered to Venus via launch opportunities in 2022–2023. This mission would collect aerosol and dust samples by means of small balloons floating in the Venusian cloud deck and directly scrutinize whether they include any apparent biological materials and, if so, their shapes, sizes, and motility. Our balloon mission would also be equipped with a miniature mass spectrometer that should permit the detection of complex organic molecules. The mission is augmented by contextual cameras to search for macroscopic signatures of life in the Venusian atmospheric habitable zone. Finally, mass and power constraints permitting, radio interferometric determinations of the motion of the balloons in Venusian winds, together with in situ temperature and pressure measurements, will provide valuable insights into the poorly understood meteorology of the middle cloud region.

They may not be out there

My colleagues Mario Livio and Joe Silk, in their article “Where are they?” (Physics Today, March 2017, page 50), have underplayed the most straightforward answer by far to the question Enrico Fermi posed. That answer is that if they exist, they are too far away to have made it here. The universe is big and getting bigger, and the speed of light places a strict constraint on travel times. Possible signals from aliens, even if intelligence were abundant throughout the cosmos, would typically take thousands or even millions of years to reach us—and their spacecraft would take even longer. The main conclusion to be drawn is that we will probably be unable to know for a very long time whether they even exist.Yes, some aliens might be nearby. Earth is located in a spiral arm of the Milky Way about 25 000 light-years from the center of the galaxy, whose disk spans 100 000 light-years. More precisely, the Sun lies in a cavity of interstellar gas called the Local Bubble, which extends over roughly 600 light-years.11. H. A. Smith, Am. Sci. 99, 320 (2011). https://doi.org/10.1511/2011.91.320 It in turn is located in the Gould belt, a spur of stars, star clusters, and molecular clouds between two of the galaxy’s spiral arms. The belt stretches to about 1200 light-years in its longest dimension. The approximate number of stars per cubic light-year in our immediate solar neighborhood is 0.004, to within a factor of two, so it holds about 30 million stars of all types.Our earliest broadcasts have only made it out to about 100 light-years. What are the chances of chatting with alien neighbors if we wait and listen for the next 1200 years, long enough for the farthest signals in the neighborhood to reach us? The combined chances need to be better than about 1 in 30 million. If the stars are too big or too small, if the planets’ orbit or obliquity are wrong, their sizes or chemical compositions unsuited, their surfaces ill equipped, their geologic and meteoritic history too inauspicious, then we are alone. Then add in the biological uncertainties, which are much less well understood: If the chemistry needed to generate life is too intricate or too slow, if evolution from proteins to intelligence is too often aborted or misdirected, or if civilizations die off quickly, then, too, we are alone.I support the search for extraterrestrial intelligence. If we don’t look, we won’t find them. But it is a risky endeavor, and nonprofessionals should keep in mind the complex and contingent evolutionary history of intelligence on Earth and the enormous limitations imposed by the finite speed of light. Livio and Silk end their discussion by asking, “Are we alone? The answer may affect nothing less than our claim for being special in the cosmos. . . . We shall never know unless we search!” That search, however, could very likely last an astronomically long time.I think my own community of scientists has hopped aboard an optimistic science fiction bandwagon while being insufficiently honest in highlighting the many cautions. Percival Lowell, famous for his search for Pluto and his studies of the canals of Mars, wrote in 1908, “From all we have learned of its constitution on the one hand, or of its distribution on the other, we know life to be as inevitable a phase of planetary evolution as is quartz or feldspar or nitrogenous soil. Each and all of them are only manifestations of chemical affinity.”22. P. Lowell, Mars as the Abode of Life, Macmillan (1908), p. 37.No one believes that today. Every schoolchild knows that Mars has no artificial canals and no Martians either. Lowell’s confident assumption was wishful thinking, and we should beware of making similar assumptions.A companion issue is not nearly as ambiguous: the ethical one. If the human race might be alone, with no one to talk with, then we face the possibility that neither we nor our planet are commonplace; we might even be rare. The implications are that Earth and its life have cosmic value, that we have concomitant responsibilities, and that we will have to solve our problems without advice from superintelligent beings from space. The prospect brings great urgency to the cause of protecting our rare planet and its precious inhabitants.ReferencesSection:ChooseTop of pageReferences <<1. H. A. Smith, Am. Sci. 99, 320 (2011). https://doi.org/10.1511/2011.91.320, Google ScholarCrossref2. P. Lowell, Mars as the Abode of Life, Macmillan (1908), p. 37. Google Scholar© 2017 American Institute of Physics.

Geology: Evidence of life in Earth's oldest rocks.

When did life first arise on Earth? Analysis of ancient rocks in Greenland that contain structures interpreted as bacterial in origin suggest that Earth might have been an abode for life much earlier than previously thought. See Letter p.535 Stromatolites are sedimentary formations created by the layered growth of microorganisms in shallow marine settings. Fossil stromatolites constitute some of the earliest evidence for life on Earth. Allen Nutman et al. describe metamorphosed stromatolites deposited around 3,700 million years ago in what is now Greenland. This is more than 200 million years older than the previous record-holders for earliest-known fossils, so these stromatolites rank as the Earth's earliest fossils by some margin. Although there is indirect evidence from isotope geochemistry that the pedigree of life on Earth is even older, this report is likely to be controversial.

Titan as the Abode of Life.

Titan is the only world we know, other than Earth, that has a liquid on its surface. It also has a thick atmosphere composed of nitrogen and methane with a thick organic haze. There are lakes, rain, and clouds of methane and ethane. Here, we address the question of carbon-based life living in Titan liquids. Photochemically produced organics, particularly acetylene, in Titan’s atmosphere could be a source of biological energy when reacted with atmospheric hydrogen. Light levels on the surface of Titan are more than adequate for photosynthesis, but the biochemical limitations due to the few elements available in the environment may lead only to simple ecosystems that only consume atmospheric nutrients. Life on Titan may make use of the trace metals and other inorganic elements produced by meteorites as they ablate in its atmosphere. It is conceivable that H2O molecules on Titan could be used in a biochemistry that is rooted in hydrogen bonds in a way that metals are used in enzymes by life on Earth. Previous theoretical work has shown possible membrane structures, azotosomes, in Titan liquids, azotosomes, composed of small organic nitrogen compounds, such as acrylonitrile. The search for a plausible information molecule for life in Titan liquids remains an open research topic—polyethers have been considered and shown to be insoluble at Titan temperatures. Possible search strategies for life on Titan include looking for unusual concentrations of certain molecules reflecting biological selection. Homochirality is a special and powerful example of such biology selection. Environmentally, a depletion of hydrogen in the lower atmosphere may be a sign of metabolism. A discovery of life in liquid methane and ethane would be our first compelling indication that the universe is full of diverse and wondrous life forms.

Astrobiology: a very short introduction

1. What is astrobiology? 2. From stardust to planets, the abodes for life 3. Origins 4. From slime to sublime 5. Life: a genome's way of making more and fitter genomes 6. Life in the solar system 7. Far-off worlds, distant suns 8. Controversies and prospects

Venus-Earth-Mars: comparative climatology and the search for life in the solar system.

Both Venus and Mars have captured the human imagination during the twentieth century as possible abodes of life. Venus had long enchanted humans—all the more so after astronomers realized it was shrouded in a mysterious cloak of clouds permanently hiding the surface from view. It was also the closest planet to Earth, with nearly the same size and surface gravity. These attributes brought myriad speculations about the nature of Venus, its climate, and the possibility of life existing there in some form. Mars also harbored interest as a place where life had or might still exist. Seasonal changes on Mars were interpreted as due to the possible spread and retreat of ice caps and lichen-like vegetation. A core element of this belief rested with the climatology of these two planets, as observed by astronomers, but these ideas were significantly altered, if not dashed during the space age. Missions to Venus and Mars revealed strikingly different worlds. The high temperatures and pressures found on Venus supported a “runaway greenhouse theory,” and Mars harbored an apparently lifeless landscape similar to the surface of the Moon. While hopes for Venus as an abode of life ended, the search for evidence of past life on Mars, possibly microbial, remains a central theme in space exploration. This survey explores the evolution of thinking about the climates of Venus and Mars as life-support systems, in comparison to Earth.

Star Measurements Hint at Many More Abodes for Life

Reexamining a group of stars observed by NASA's Kepler spacecraft, astronomers say they have identified a trove of candidate planets that are both Earth-sized and potentially habitable.

US planetary sciences to focus on smaller missions, research, and technology development

Heeding community advice, NASA’s planetary science division seeks to scale back its flagship missions while retaining strong international partnerships.

Abodes for life in carbonaceous asteroids?

Thermal evolution models for carbonaceous asteroids that use new data for permeability, pore volume, and water circulation as input parameters provide a window into what are arguably the earliest habitable environments in the Solar System. Plausible models of the Murchison meteorite (CM) parent body show that to first-order, conditions suitable for the stability of liquid water, and thus pre- or post-biotic chemistry, could have persisted within these asteroids for tens of Myr. In particular, our modeling results indicate that a 200-km carbonaceous asteroid with a 40% initial ice content takes almost 60 Myr to cool completely, with habitable temperatures being maintained for ∼24 Myr in the center. Yet, there are a number of indications that even with the requisite liquid water, thermal energy sources to drive chemical gradients, and abundant organic “building blocks” deemed necessary criteria for life, carbonaceous asteroids were intrinsically unfavorable sites for biopoesis. These controls include different degrees of exothermal mineral hydration reactions that boost internal warming but effectively remove liquid water from the system, rapid (1–10 mm yr −1) inward migration of internal habitable volumes in most models, and limitations imposed by low permeabilities and small pore sizes in primitive undifferentiated carbonaceous asteroids. Our results do not preclude the existence of habitable conditions on larger, possibly differentiated objects such as Ceres and the Themis family asteroids due to presumed longer, more intense heating and possible long-lived water reservoirs.

The Search for Worlds Like Our Own

The direct detection of Earth-like exoplanets orbiting nearby stars and the characterization of such planets-particularly, their evolution, their atmospheres, and their ability to host life-constitute a significant problem. The quest for other worlds as abodes of life has been one of mankind's great questions for several millennia. For instance, as stated by Epicurus approximately 300 BC: "Other worlds, with plants and other living things, some of them similar and some of them different from ours, must exist." Demokritos from Abdera (460-370 BC), the man who invented the concept of indivisible small parts-atoms-also held the belief that other worlds exist around the stars and that some of these worlds may be inhabited by life-forms. The idea of the plurality of worlds and of life on them has since been held by scientists like Johannes Kepler and William Herschel, among many others. Here, one must also mention Giordano Bruno. Born in 1548, Bruno studied in France and came into contact with the teachings of Nicolas Copernicus. He wrote the book De l'Infinito, Universo e Mondi in 1584, in which he claimed that the Universe was infinite, that it contained an infinite amount of worlds like Earth, and that these worlds were inhabited by intelligent beings. At the time, this was extremely controversial, and eventually Bruno was arrested by the church and burned at the stake in Rome in 1600, as a heretic, for promoting this and other equally confrontational issues (though it is unclear exactly which idea was the one that ultimately brought him to his end). In all the aforementioned cases, the opinions and results were arrived at through reasoning-not by experiment. We have only recently acquired the technological capability to observe planets orbiting stars other than 6 our Sun; acquisition of this capability has been a remarkable feat of our time. We show in this introduction to the Habitability Primer that mankind is at the dawning of an age when, by way of the scientific method and 21(st)-century technology, we will be able to answer this fascinating controversial issue that has persisted for at least 2500 years.

Other Worlds, Other Civilizations?

AbstractGalileo's work had a profound influence on our understanding of the question of “other worlds” and the possibility of other intelligent life in the universe. When he saw the Moon with its mountains, and Jupiter with its moons, he implicitly recognized that these were physical places and thus could themselves be possible abodes for life. But some ancient and medieval scholars had already suggested as much, though without the empirical backing that Galileo's observations provided. Thus perhaps an even more important influence on the development of these ideas is that Galileo made them popular with the educated public, rather than merely the speculations of specialists. By inciting the popular imagination to take seriously the possibility of other worlds, he engaged subsequent generations of philosophers and storytellers to explore the possibilities and implications of life on those worlds.

Planet Earth – our oasis in space

Planet Earth is unique in our solar system as an abode of life. In contrast to its planetary neighbours, the presence of liquid water, a benign atmospheric environment, a solid surface and an internal structure providing a protective magnetic field make it a suitable habitat for man. While natural forces have shaped the Earth over millennia, man through his technological prowess may become a threat to this oasis of life in the solar system.

Europa as an abode of life.

Life as we know it on Earth depends on liquid water, a suite of 'biogenic' elements (most famously carbon) and a useful source of free energy. Here we review Europa's suitability for life from the perspective of these three requirements. It is likely, though not yet certain, that Europa harbors a subsurface ocean of liquid water whose volume is about twice that of Earth's oceans. Little is known about Europa's inventory of carbon, nitrogen, and other biogenic elements, but lower bounds on these can be placed by considering the role of commentary delivery over Europa's history. Sources of free energy are challenging for a world covered with an ice layer kilometers thick, but it is possible that hydrothermal activity and/or organics and oxidants provided by the action of radiation chemistry at Europa's surface and subsequent mixing into Europa's ocean could provide the electron donors and acceptors needed to power a Europan ecosystem. It is not premature to draw lessons from the search for life on Mars with the Viking spacecraft for planning exobiological missions to Europa.

The ultraviolet history of the terrestrial planets — implications for biological evolution

A radiative transfer model is employed to investigate the comparative surface ultraviolet (UV) radiation histories of Earth, Mars and Venus from 4.5 Ga to the present and thus their comparative theoretical photobiological histories. Earth probably began with a period of higher ultraviolet radiation fluxes during the anoxic Archean. During the early Proterozoic UV fluxes declined as oxygen partial pressures and thus ozone column abundance rose, but the ozone column became subject to stochastic depletion events caused principally by impact events and possibly large-scale volcanism and less frequently, close cosmic events such as supernovae. In contrast Mars has been subject to a history dominated by a slow increase in solar luminosity and a reduction in partial pressures of CO 2, both of which have resulted in an increase in UV flux. The UV radiation history of Venus has been dominated by the greenhouse effect through which high partial pressures of CO 2 made the surface UV radiation environment clement. These distinct histories influence the potential comparative evolutionary photobiology of the three planets. On Earth, life transitioned from the Archean, when tolerance to UV radiation, particularly for exposed organisms, must have been high to a more photobiologically clement era. In this latter era the predominant evolutionary selection pressure is one that allows for tolerance of sudden and unpredictable increases in UVB radiation above seasonal and diurnal maxima caused by exogenous perturbation of the ozone column. In the case of Mars, the UV radiation flux has increased over time. Today the biologically effective irradiances to DNA are not considerably different from those that are calculated for Archean Earth. If the planet suffered an atmospheric collapse then it may have been subject to an ultraviolet crisis at some point in its past when DNA-weighted irradiance would have increased three to five-fold. Venus transitioned into a photobiologically clement era soon after late bombardment. The lifeless surfaces of Mars and Venus, when in the former case DNA-weighted irradiances are not much greater than Archean Earth and in the latter case, insignificant, are testament to the unimportance of UV radiation as an evolutionary selection pressure when other physical factors, particularly lack of liquid water, become limiting to life. Understanding the comparative evolutionary differences in surface UV flux of the terrestrial planets can help us understand the influence, and lack of influence, of UV radiation in determining their suitability as abodes for life at different stages in their past.

Meteorological, Geological, and Biological Conditions on Venus

THE absence of oxygen in the atmosphere of Venus, as shown by St. John's spectroscopic observations, and the consequent absence of life such as we know, are scarcely what one would expect at first sight on a planet so much like the earth in size and mass and having a mean temperature within the range of terrestrial abodes of life. An explanation, however, is suggested by further consideration of what might happen to the earth and its inhabitants if it could be transferred to the orbit of Venus, and also have its axial rotation speed reduced to one revolution in several weeks.

Prof. Percival Lowell

BY the death, on November 12, of Percival Lowell, who equipped the Observatory at Flagstaff, Arizona, and planned its work with such conspicuous success, astronomy loses one of its most ardent disciples and enthusiastic observers. Prof. Lowell was born in Boston on March 13, 1855, and took his degree at Harvard in 1876. He lived in Japan at intervals from 1883 to 1893, and in the former year was appointed Counsellor and Foreign Secretary to the Korean Special Mission to the United States. His experiences of Eastern life were described in several memorable volumes, namely, “Chosön: a Sketch of Korea,” “The Soul of the Far East,” “Noto: an Unexplored Corner of Japan,” and “Occult Japan.” His other publications include “Mars,” published in 1895, “The Solar System,” “Mars and its Canals,” “Mars as the Abode of Life,” “The Evolution of Worlds,” and several fine volumes of “Annals of the Lowell Observatory.” In 1902 he was appointed non-resident professor of astronomy of the Massachusetts Institute of Technology, and in 1904 he received the Janssen medal of the French Astronomical Society for his researches on Mars. He had many admirers in this country, and was always ready to assist enterprises having the advancement of knowledge as their object. An illustration of this characteristic was the support which he gave to the Hill Observatory, Sidmouth; and he had the distinction of being the only one outside Great Britain who contributed financially to the endowment of this new observatory.

Book Review: II. Philosophy and Religion: The Evolution of Worlds

Book Review: II. Philosophy and Religion: The Evolution of Worlds

Mars as the Abode of Life

Mars as the Abode of Life

Mars as the Abode of Life

Mars as the Abode of Life