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Thread: Astrobiological papers from Arvix and everywhere

  1. #31
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    I admit I would never have thought of this one. Cannot get full paper, but this says enough.


    http://adsabs.harvard.edu/abs/2018MNRAS.481.2487O

    Biofluorescent worlds: global biological fluorescence as a biosignature

    O'Malley-James, Jack T.; Kaltenegger, L. (12/2018)

    In this paper, we analyse a new possible biological surface feature for habitable worlds orbiting other stars: biofluorescence. High ultraviolet (UV) and blue radiation fluxes drive the strongest biofluorescence in terrestrial fluorescent pigments and proteins. F stars emit more blue and UV radiation than the Sun, while planets and exomoons orbiting such stars remain in the habitable zone for 2-4 Gyr; a time span that could allow a complex biosphere to develop. Therefore, we propose biofluorescence as a new surface biosignature for F star planets. We investigate how the extra emission from surface fluorescence could cause observable signals at specific wavelengths in the visible spectrum. Using the absorption and emission characteristics of common coral fluorescent pigments and proteins, we simulate the increased emission at specific visible wavelengths caused by strong fluorescence, accounting for the effects of different (non-fluorescent) surface features, atmospheric absorption and cloud cover. Our model shows that exoplanets with a fluorescent biosphere could have characteristic surface colours that allow the presence of surface life to be inferred from observations with upcoming telescopes.

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    Attempts to replicate Martian environments with Earthly micro-critters living in them.


    http://adsabs.harvard.edu/abs/2018IJAsB..17..314C

    Anaerobic microorganisms in astrobiological analogue environments: from field site to culture collection

    Cockell, C. S., et al. (10/2018)

    Astrobiology seeks to understand the limits of life and to determine the physiology of organisms in order to better assess the habitability of other worlds. To successfully achieve these goals we require microorganisms from environments on Earth that approximate to extraterrestrial environments in terms of physical and/or chemical conditions. The most challenging of these environments with respect to sample collection, isolation and cultivation of microorganisms are anoxic environments. In this paper, an approach to this challenge was implemented within the European Union's MASE (Mars Analogues for Space Exploration) project. In this review paper, we aim to provide a set of methods for future field work and sampling campaigns. A number of anoxic environment based on characteristics that make them analogous to past and present locations on Mars were selected. They included anoxic sulphur-rich springs (Germany), the salt-rich Boulby Mine (UK), a lake in a basaltic context (Iceland), acidic sediments in the Rio Tinto (Spain), glacier samples (Austria) and permafrost samples (Russia and Canada). Samples were collected under strict anoxic conditions to be used for cultivation and genomic community analysis. Using the samples, a culturing approach was implemented to enrich anaerobic organisms using a defined medium that would allow for organisms to be grown under identical conditions in future physiological comparisons. Anaerobic microorganisms were isolated and deposited with the DSMZ (Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH) culture collection to make them available to other scientists. In MASE, the selected organisms are studied with respect to survival and growth under Mars relevant stresses. They are artificially fossilized and the resulting biosignatures studied and used to investigate the efficacy of life detection instrumentation for planetary missions. Some of the organisms belong to genera with medical and environmental importance such as Yersinia spp., illustrating how astrobiology field research can be used to increase the availability of microbial isolates for applied terrestrial purposes.

  2. #32
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    This paper, which I don't think I've noted yet (could be wrong), makes amusing comments on the search for smart aliens to date, concluding we've barely gotten underway.


    https://arxiv.org/abs/1809.07252v1

    How Much SETI Has Been Done? Finding Needles in the n-Dimensional Cosmic Haystack

    Jason T. Wright, Shubham Kanodia, Emily G. Lubar (Submitted on 19 Sep 2018)

    Many articulations of the Fermi Paradox have as a premise, implicitly or explicitly, that humanity has searched for signs of extraterrestrial radio transmissions and concluded that there are few or no obvious ones to be found. Tarter et al. (2010) and others have argued strongly to the contrary: bright and obvious radio beacons might be quite common in the sky, but we would not know it yet because our search completeness to date is so low, akin to having searched a drinking glass's worth of seawater for evidence of fish in all of Earth's oceans. Here, we develop the metaphor of the multidimensional "Cosmic Haystack" through which SETI hunts for alien "needles" into a quantitative, eight-dimensional model and perform an analytic integral to compute the fraction of this haystack that several large radio SETI programs have collectively examined. Although this model haystack has many qualitative differences from the Tarter et al. (2010) haystack, we conclude that the fraction of it searched to date is also very small: similar to the ratio of the volume of a large hot tub or small swimming pool to that of the Earth's oceans. With this article we provide a Python script to calculate haystack volumes for future searches and for similar haystacks with different boundaries. We hope this formalism will aid in the development of a common parameter space for the computation of upper limits and completeness fractions of search programs for radio and other technosignatures.

  3. #33
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    A semi-depressing paper on the likelihood that SETI puts us in touch only with dead aliens.


    https://arxiv.org/abs/1802.09399v1

    Area Coverage of Expanding E.T. Signals in the Galaxy: SETI and Drake's N

    Claudio Grimaldi, Geoffrey W. Marcy, Nathaniel K. Tellis, Frank Drake (Submitted on 23 Feb 2018 (this version), latest version 8 Mar 2018 (v2))

    The Milky Way Galaxy contains an unknown number, N , of civilizations that emit electromagnetic radiation (of unknown wavelengths) over a finite lifetime, L. Here we are assuming that the radiation is not produced indefinitely, but within L as a result of some unknown limiting event. When a civilization stops emitting, the radiation continues traveling outward at the speed of light, c, but is confined within a shell wall having constant thickness, cL. We develop a simple model of the Galaxy that includes both the birthrate and detectable lifetime of civilizations to compute the possibility of a SETI detection at the Earth. Two cases emerge for radiation shells that are (1) thinner than or (2) thicker than the size of the Galaxy, corresponding to detectable lifetimes, L, less than or greater than the light-travel time, ∼100,000 years, across the Milky Way, respectively. For case (1), each shell wall has a thickness smaller than the size of the Galaxy and intersects the galactic plane in a donut shape (annulus) that fills only a fraction of the Galaxy's volume, inhibiting SETI detection. But the ensemble of such shell walls may still fill our Galaxy, and indeed may overlap locally, given a sufficiently high birthrate of detectable civilizations. In the second case, each radiation shell is thicker than the size of our Galaxy. Yet, the ensemble of walls may or may not yield a SETI detection depending on the civilization birthrate. We compare the number of different electromagnetic transmissions arriving at Earth to Drake's N, the number of currently emitting civilizations, showing that they are equal to each other for both cases (1) and (2). However, for L < 100,000 years, the transmissions arriving at Earth may come from distant civilizations long extinct, while civilizations still alive are sending signals yet to arrive.

    QUOTES: "Beyond the scope of this paper but certainly important is the possibility that a single civilization may multiply its emission of EM radiation by migration and colonization or by robotic (and perhaps self-replicating) probes, all of which could maintain transmitters of radiation (Gertz 2017). Colonization and probes imply that the lifetime, L, is related to the effective birthrate of new civilizations (or probes), augmenting b, rendering the two parameters mutually dependent. A proliferation of colonies and probes could be the dominant source of EM signals from "technological civilizations" in the Galaxy. Modeling such proliferation involves parametrization of the likelihood that a civilization can bodily migrate to new outposts, either within its planetary system or to neighboring stars, and modeling the probability and proliferation due to subsequent migrations, increasing exponentially the number of lineages like a genealogical tree. The changing luminosity of host stars may motivate such migrations (Zuckerman 1985, 1995). However, Gott (1995) has argued that migration of civilizations may be insignificant, otherwise we would likely be one of the migrants. Moreover, migration over interstellar distances is easily shown to be extraordinarily difficult from energy needs, centuries needed for transport, and technical challenges."

  4. #34
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    Will file this one under astrobiology. Apparently it isn't so hard to create highly complex hydrocarbons in low temperatures as we thought. Curiouser and curiouser...


    https://phys.org/news/2018-10-scient...mospheric.html

    Scientists present new clues to cut through the mystery of Titan's atmospheric haze
    October 8, 2018, Lawrence Berkeley National Laboratory

    Saturn's largest moon, Titan, is unique among all moons in our solar system for its dense and nitrogen-rich atmosphere that also contains hydrocarbons and other compounds, and the story behind the formation of this rich chemical mix has been the source of some scientific debate.

    Now, a research collaboration involving scientists in the Chemical Sciences Division at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) has zeroed in on a low-temperature chemical mechanism that may have driven the formation of multiple-ringed molecules—the precursors to more complex chemistry now found in the moon's brown-orange haze layer.

    The study, co-led by Ralf Kaiser at the University of Hawaii at Manoa and published in the Oct. 8 edition of the journal Nature Astronomy, runs counter to theories that high-temperature reaction mechanisms are required to produce the chemical makeup that satellite missions have observed in Titan's atmosphere.

  5. #35
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    Capturing an object like that interstellar asteroid that passed through a few month ago seems very unlikely, and transferring life from it to elsewhere is even a smaller possibility, but who knows.


    https://arxiv.org/abs/1801.10254

    Implications of Captured Interstellar Objects for Panspermia and Extraterrestrial Life

    Manasvi Lingam, Abraham Loeb (Submitted on 30 Jan 2018 (v1), last revised 13 Oct 2018 (this version, v3))

    We estimate the capture rate of interstellar objects by means of three-body gravitational interactions. We apply this model to the Sun-Jupiter system and the Alpha Centauri A&B binary system, and find that the radius of the largest captured object is a few tens of km and Earth-sized respectively. We explore the implications of our model for the transfer of life by means of rocky material. The interstellar comets captured by the "fishing net" of the Solar system can be potentially distinguished by their differing orbital trajectories and ratios of oxygen isotopes through high-resolution spectroscopy of water vapor in their tails.

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    A white paper on developing new life-detection methods, but it seems light on details. Still interesting, a short (9-p) read.


    https://arxiv.org/abs/1810.06026

    Life-Detection Technologies for the Next Two Decades

    Chaitanya Giri, et al. (Submitted on 14 Oct 2018)

    Since its inception six decades ago, astrobiology has diversified immensely to encompass several scientific questions including the origin and evolution of Terran life, the organic chemical composition of extraterrestrial objects, and the concept of habitability, among others. The detection of life beyond Earth forms the main goal of astrobiology, and a significant one for space exploration in general. This goal has galvanized and connected with other critical areas of investigation such as the analysis of meteorites and early Earth geological and biological systems, materials gathered by sample-return space missions, laboratory and computer simulations of extraterrestrial and early Earth environmental chemistry, astronomical remote sensing, and in-situ space exploration missions. Lately, scattered efforts are being undertaken towards the R&D of the novel and as-yet-space-unproven life-detection technologies capable of obtaining unambiguous evidence of extraterrestrial life, even if it is significantly different from Terran life. As the suite of space-proven payloads improves in breadth and sensitivity, this is an apt time to examine the progress and future of life-detection technologies.

  6. #36
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    Exclamation

    Article from a few years back showing diagrams of what a methane-based (vs. water-based) cell might look like. One of the very few articles on methane-based life.


    http://advances.sciencemag.org/content/1/1/e1400067

    Membrane alternatives in worlds without oxygen: Creation of an azotosome

    James Stevenson, Jonathan Lunine, Paulette Clancy
    Science Advances 27 Feb 2015: Vol. 1, no. 1, e1400067

    The lipid bilayer membrane, which is the foundation of life on Earth, is not viable outside of biology based on liquid water. This fact has caused astronomers who seek conditions suitable for life to search for exoplanets within the “habitable zone,” the narrow band in which liquid water can exist. However, can cell membranes be created and function at temperatures far below those at which water is a liquid? We take a step toward answering this question by proposing a new type of membrane, composed of small organic nitrogen compounds, that is capable of forming and functioning in liquid methane at cryogenic temperatures. Using molecular simulations, we demonstrate that these membranes in cryogenic solvent have an elasticity equal to that of lipid bilayers in water at room temperature. As a proof of concept, we also demonstrate that stable cryogenic membranes could arise from compounds observed in the atmosphere of Saturn’s moon, Titan, known for the existence of seas of liquid methane on its surface.

    ==============

    Science news article on same

    https://phys.org/news/2015-10-kind-life-titan.html

    What kind of life would we find on Titan?

    October 5, 2015 by Paul Patton, Universe Today
    Attached Images Attached Images
    Last edited by Roger E. Moore; 2018-Oct-16 at 05:42 PM.

  7. #37
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    Amid a sudden flood of papers indulging in wishful dreaming about next-generation VLA radio telescopes was this paper on its use for SETI. This is the only ngVLA paper I will mention, as they get tiresome after the first 20. I know it's for a good cause, but still...


    https://arxiv.org/abs/1810.06568

    Science with an ngVLA: SETI Searches for Evidence of Intelligent Life in the Galaxy

    Steve Croft, et al. (Submitted on 15 Oct 2018)

    Radio SETI experiments aim to test the hypothesis that extraterrestrial civilizations emit detectable signals from communication, propulsion, or other technologies. The unprecedented capabilities of next generation radio telescopes, including ngVLA, will allow us to probe hitherto unexplored regions of parameter space, thereby placing meaningful limits on the prevalence of technological civilizations in the Universe (or, if we are fortunate, making one of the most significant discoveries in the history of science). ngVLA provides critical capabilities in the 10 - 100 GHz range, and will be a valuable complement to SKA in the southern hemisphere, as well as surveying the sky at frequencies underexplored by previous SETI experiments.

  8. #38
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    Geology reveals when life was up between a rock and a hard place, i.e., being pounded by asteroids. Same everywhere else?


    https://phys.org/news/2018-10-geolog...ecks-life.html

    How geology tells the story of evolutionary bottlenecks and life on Earth

    October 16, 2018 by Sarah Wild, Astrobiology Magazine

    Evidence that catastrophic geological events could have created evolutionary bottlenecks that changed the course of life on Earth may be buried within ancient rocks beneath our feet. There is a 700-million year gap in Earth's history, and in that time one of the most transformative events happened: life appeared. This missing epoch could hold not just the secret of humanity's first ancestor, but could guide our search for life on other planets.

    To this end a recent paper, published in the scientific journal Astrobiology, tries to bring the worlds of geology and chemistry together by laying out what Earth's ancient geology tells us about when life began on the planet, and how geological constraints – such as those caused by an asteroid impact or evolutionary bottlenecks – can be used to vet the different theories about the evolution of life.

    "Geologists have only weakly constrained the time when the Earth became habitable and the later time when life actually existed to the long interval between about 4.5 billion years ago and 3.85 billion years ago," Norm Sleep, a geologist at Stanford University in the United States, writes in his paper.

    https://www.liebertpub.com/doi/10.1089/ast.2017.1778
    (actual paper)

  9. #39
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    Alien life might be capable of changing a planet's rotation just by existing. We might have done it ourselves ("we" meaning "earth life").


    https://phys.org/news/2018-11-life-a...-rotation.html

    How life could help atmospheric tides slow a planet's rotation

    November 5, 2018 by Joelle Renstrom, Astrobiology Magazine

    Resonating oscillations of a planet's atmosphere caused by gravitational tides and heating from its star could prevent a planet's rotation from steadily slowing over time, according to new research by Caleb Scharf, who is the Director of Astrobiology at Columbia University. His findings suggest that the effect is enhanced for a planet with an atmosphere that has been oxygenated by life, and the resulting 'atmospheric tides' could even act as a biosignature.

    Tides can distort a planet's mass, which in turn affects its rotation. We're most familiar with gravitational tides, which on Earth we feel from the gravity of the Moon and the Sun. These gravitational tides create bulges as Earth spins, and the Moon and Sun tug on those bulges, slowing the spin.

    By contrast, atmospheric tides, sometimes called thermal or solar tides, occur when sunlight heats the surface and air on Earth's daytime side. That heating shifts the atmosphere's mass from the hottest point to cooler points on the planet. As with gravitational tides, atmospheric tides cause bulges that are vulnerable to gravitational pulls. Those bulges subtly change the shape of Earth's atmosphere, stretching it from a sphere to something slightly less symmetrical and more elliptical. Scharf suggests imagining a 'handle' on Earth, and that forces pulling on the atmospheric handle can then help speed up or slow down the planet's rotation.

  10. #40
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    So, if Venus had life, it would have a shorter day? Good to know.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  11. #41
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    Quote Originally Posted by Noclevername View Post
    So, if Venus had life, it would have a shorter day? Good to know.
    That's funny, because I thought the SAME THING.

  12. #42
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    Not good news for M-dwarf worlds, if you are looking for life or a place to colonize. Let's hope this kind of superflare disappears after reaching the main sequence.


    https://arxiv.org/abs/1811.02008

    Detection of a giant flare displaying quasi-periodic pulsations from a pre-main sequence M star with NGTS

    James A. G. Jackman, et al. (Submitted on 5 Nov 2018)

    We present the detection of an energetic flare on the pre-main sequence M3 star NGTS J121939.5-355557, which we estimate as only 2 Myr old. The flare had an energy of 3.2 +0.4/-0.3 ×10^36 erg and a fractional amplitude of 7.2 ± 0.8, making it one of the most energetic flares seen on an M star. The star is also X-ray active, in the saturated regime with logLx/LBol = −3.1. In the flare peak we have identified multi-mode quasi-periodic pulsations formed of two statistically significant periods of approximately 320 and 660 seconds. This flare is one of the largest amplitude events to exhibit such pulsations. The shorter period mode is observed to start after a short-lived spike in flux lasting around 30 seconds, which would not have been resolved in Kepler or TESS short cadence modes. Our data shows how the high cadence of NGTS can be used to apply solar techniques to stellar flares and identify potential causes of the observed oscillations. We also discuss the implications of this flare for the habitability of planets around M star hosts and how NGTS can aid in our understanding of this.

  13. #43
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    Quote Originally Posted by Roger E. Moore View Post
    https://arxiv.org/abs/1811.02008

    Detection of a giant flare displaying quasi-periodic pulsations from a pre-main sequence M star with NGTS
    News report on this report, giving a plain-language overview. I do recall younger stars seem to be subject to severe flaring.

    Giant flare detected on a pre-main sequence M star
    November 13, 2018 by Tomasz Nowakowski, Phys.org report
    https://phys.org/news/2018-11-giant-...ence-star.html

  14. #44
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    A rather heavy thought about SETI.


    https://arxiv.org/abs/1811.06313

    Life Before Fermi - Back to the Solar System

    David L Clements (Submitted on 15 Nov 2018)

    The existence of intelligent, interstellar traveling and colonising life is a key assumption behind the Fermi Paradox. Until recently, detecting signs of life elsewhere has been so technically challenging as to seem almost impossible. However, new observational insights and other developments mean that signs of life elsewhere might realistically be uncovered in the next decade or two. We here review what are believed to be the basic requirements for life, the history of life on Earth, and then apply this knowledge to potential sites for life in our own Solar System. We conclude that the necessities of life - liquid water and sources of energy - are in fact quite common in the Solar System, but most potential sites are beneath the icy surfaces of gas giant moons. If this is the case elsewhere in the Galaxy, life may be quite common but, even if intelligence develops, is essentially sealed in a finite environment, unable to communicate with the outside world.

  15. #45
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    A "Hilda" planet is in 3:2 MMR with the nearest gas giant outward, as our asteroid Hilda is with Jupiter. Interesting possibility for an exo-Earth.

    https://arxiv.org/abs/1811.09579

    Exocomets in the 47 UMa System: Theoretical Simulations including Water Transport

    Manfred Cuntz, Birgit Loibnegger, Rudolf Dvorak (Submitted on 23 Oct 2018)

    Motivated by ongoing discoveries of features (most likely) attributable to exocomets in various systems, this study examines the dynamics of possible comets around 47 UMa. Based on the assumption that most systems hosting planets should also harbor leftovers from planet formation processes, comets are thus also expected to exist in the system of 47 UMa. This system is known to host three Jupiter-type planets; however, based on stability analyses, additional terrestrial planets in stable orbits might also be able to exist, including planets in 47 UMa's habitable zone. Furthermore, we also consider a possible 'Hilda'-planet. The aim of our study is to explore the interaction of exocomets with the Jupiter-type planets in the system and examine the probability of cometary collisions with the planets, including possible Earth-mass planets located in the habitable zone. Moreover, we investigate the transport of water onto the Earth-mass planets, including quantitative estimates. It is found that the Earth-mass planets would be able to receive some water, but much less than currently present on Earth. We also checked if the comets form families, but no families were found. Finally, the capture of comets in close orbits and the possibility of small clouds formed when comets come too close to the star and disintegrate are also part of our work.

  16. #46
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    More on a tardigrade-based index for possible exo-Earths - can a tardigrade survive there? (yes/no)

    http://adsabs.harvard.edu/abs/2018LSSR...19...13J

    Tardigrade indexing approach on exoplanets

    Jagadeesh, Madhu Kashyap; Roszkowska, Milena; Kaczmarek, Lukasz
    Life Sciences in Space Research, Volume 19, p. 13-16.
    Publication Date: 11/2018

    Finding life on other worlds is a fascinating area of astrobiology and planetary sciences. Presently, over 3800 exoplanets, representing a very wide range of physical and chemical environments, are known. Scientists are not only looking for traces of life outside Earth, but they are also trying to find out which of Earth's known organisms (ex: tardigrades (water bears)) would be able to survive on other planets. In our study, we have established a metric tool for distinguishing the potential survivability of active and cryptobiotic tardigrades on rocky-water and water-gas planets in our solar system and exoplanets, taking into consideration the geometrical means of six physical parameters such as radius, density, escape velocity, revolution period, surface temperature, and surface pressure of the considered planets. More than 3800 exoplanets are available as the main sample from Planetary Habitable Laboratory - Exoplanet Catalog (PHL-EC), from which we have chosen 57 exoplanets in our study including Earth and Mars, with water composition as reference. The Active Tardigrade Index (ATI) and Cryptobiotic Tardigrade Index (CTI) are two metric indices with minimum value 0 (= tardigrades cannot survive) and maximum 1 (= tardigrades will survive in their respective state). Values between 0 and 1 indicate a percentage chance of the active or cryptobiotic tardigrades surviving on a given exoplanet. Among known planets some of the exoplanets are tabulated as ATI and CTI indices for sample representation like: Kepler-100d, Kepler-48d, Kepler-289b, TRAPPIST-1 f and Kepler-106e. The results with Mars as the threshold indicates that Mars could be the only rock-water composition planet that could be more suitable for tardigrades than other considered exoplanets.

  17. #47
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    An older article I discovered, may be of interest to fans of Titan.


    https://phys.org/news/2017-07-scient...membranes.html

    Scientists find moon of Saturn has chemical that could form 'membranes'
    July 28, 2017 by Elizabeth Zubritsky, NASA's Goddard Space Flight Center

    NASA scientists have definitively detected the chemical acrylonitrile in the atmosphere of Saturn's moon Titan, a place that has long intrigued scientists investigating the chemical precursors of life. On Earth, acrylonitrile, also known as vinyl cyanide, is useful in the manufacture of plastics. Under the harsh conditions of Saturn's largest moon, this chemical is thought to be capable of forming stable, flexible structures similar to cell membranes. Other researchers have previously suggested that acrylonitrile is an ingredient of Titan's atmosphere, but they did not report an unambiguous detection of the chemical in the smorgasbord of organic, or carbon-rich, molecules found there. Now, NASA researchers have identified the chemical fingerprint of acrylonitrile in Titan data collected by the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. The team found large quantities of the chemical on Titan, most likely in the stratosphere—the hazy part of the atmosphere that gives this moon its brownish-orange color.

    ....The cells of Earth's plants and animals would not hold up well on Titan, where surface temperatures average minus 290 degrees Fahrenheit (minus 179 degrees Celsius), and lakes brim with liquid methane.

    In 2015, university scientists tackled the question of whether any organic molecules likely to be on Titan could, under such inhospitable conditions, form structures similar to the lipid bilayers of living cells on Earth. Thin and flexible, the lipid bilayer is the main component of the cell membrane, which separates the inside of a cell from the outside world. This team identified acrylonitrile as the best candidate.

  18. #48
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    Combining different types of SETI.

    https://arxiv.org/abs/1807.08879

    Relative Likelihood of Success in the Searches for Primitive versus Intelligent Extraterrestrial Life

    Manasvi Lingam, Abraham Loeb (Submitted on 24 Jul 2018 (v1), last revised 20 Dec 2018 (this version, v3))

    We estimate the relative likelihood of success in the searches for primitive versus intelligent life on other planets. Taking into account the larger search volume for detectable artificial electromagnetic signals, we conclude that both searches should be performed concurrently, albeit with significantly more funding dedicated to primitive life. Based on the current federal funding allocated to the search for biosignatures, our analysis suggests that the search for extraterrestrial intelligence (SETI) may merit a federal funding level of at least $10 million per year, assuming that the average lifetime of technological species exceeds a millennium.

  19. #49
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    Doesn't rule out the evolution of plants that generate energy by means other than photosynthesis, but a good point anyway.


    https://arxiv.org/abs/1901.01270

    Photosynthesis on habitable planets around low-mass stars

    Manasvi Lingam, Abraham Loeb (Submitted on 4 Jan 2019)

    We show that planets around M-dwarfs with M⋆ ≲ 0.2 M⊙ may not receive enough photons in the photosynthetically active range of 400-750 nm to sustain Earth-like biospheres. As a result of the lower biological productivity, it is likely that biotic molecular oxygen will not build up to detectable levels in the atmospheres of habitable planets orbiting low-mass stars.

  20. #50
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    Potentially disastrous news from space... red dwarf planets might be lifeless because they are dried up.


    https://phys.org/news/2019-01-young-...ed-dwarfs.html

    Young planets orbiting red dwarfs may lack ingredients for life
    January 8, 2019

    Rocky planets orbiting red dwarf stars may be bone dry and lifeless, according to a new study using NASA's Hubble Space Telescope. Water and organic compounds, essential for life as we know it, may get blown away before they can reach the surface of young planets. This hypothesis is based on surprising observations of a rapidly eroding dust-and-gas disk encircling the young, nearby red dwarf star AU Microscopii (AU Mic) by Hubble and the European Southern Observatory's Very Large Telescope (VLT) in Chile. Planets are born in disks like this one.

    https://www.aanda.org/articles/aa/ab...a32462-17.html

  21. #51
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    More a philosophical paper than anything else, it makes its point very well. Short and recommended.


    https://arxiv.org/abs/1801.09146

    Different is More: The Value of Finding an Inhabited Planet that is Far From Earth 2.0

    Adrian Lenardic, Johnny Seales (Submitted on 27 Jan 2018 (v1), last revised 8 Jan 2019 (this version, v2))

    The search for an inhabited planet, other than our own, is a driver of planetary exploration in our solar system and beyond. Using information from our own planet to inform search strategies allows for a targeted search. It is, however, worth considering some span in the strategy and in a priori expectation. An inhabited Earth-like planet is one that would be similar to Earth in ways that extend beyond having biota. To facilitate analysis, we introduce a metric that extends from zero, for an inhabited planet that is like Earth in all other regards (i.e., zero differences), toward positive or negative values for planets that differ from Earth. The analysis shows how assessment of life potential in our galaxy changes more significantly if we find an inhabited planet that is less Earth-like (i.e., it quantifies how probability assessments improve with deviations from Earth-likeness). Discovering such planets could also provide a test of the strong form of the Gaia hypothesis - a test that has proved difficult using only the Earth as a laboratory. Lastly, we discuss how an Earth2.0 narrative, that has been presented to the public as a search strategy, comes with nostalgia-laden philosophical baggage that does not best serve exploration.

  22. #52
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    Like this paper as it expands the definition of what we would consider an "inhabited" or "habitable" planet to include very old systems.


    http://cdsads.u-strasbg.fr/abs/2019AAS...23343202K

    Habitability of Post-Main Sequence Planetary Systems

    Kozakis, Thea; Kaltenegger, Lisa
    American Astronomical Society, AAS Meeting #233, id.#432.02 (01/2019)

    During the post-main sequence phase of stellar evolution the habitable zone moves out past the system's original frost line, introducing an opportunity for outer planetary system habitability. We model the evolution of star-planet systems with hosts ranging from 1-3.5 Solar masses throughout the post-main sequence, calculating stellar mass loss and its effects on planetary orbital evolution and atmospheric erosion. The maximum amount of time in the evolving habitable zone is calculated, and for several mass cases we use a coupled climate/photochemistry code to study the impact of the stellar environment on the planetary atmosphere throughout its time in the habitable zone. Particular focus is put on studying the ground UV environments Europa-like planets/moons that could have developed subsurface life on the main sequence, have is uncovered during the red giant branch, and then experience a relatively stable environment on the horizontal branch before heating up past runaway greenhouse conditions on the asymptotic giant branch.

  23. #53
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    On the other hand, maybe you get lucky with a red dwarf's planet once in a while.

    https://phys.org/news/2019-01-potent...per-earth.html

    A new, potentially inhabitable super-Earth
    January 10, 2019, Instituto de Astrofísica de Canarias

    Researchers at the University of Oviedo, in collaboration with the Instituto de Astrofísica de Canarias (IAC) have discovered and characterized a planet in the habitability zone of a red dwarf star. It was detected using the method of transits. A team of researchers at the University of Oviedo and the Instituto de Astrofísica de Canarias (IAC) have discovered and characterized a super-Earth exoplanet orbiting at the inner limit of the habitability zone of a red dwarf star of type M0 called K2-286. They used data from the 15th campaign of the Kepler Space Telescope during its extended mission (K2).

    https://academic.oup.com/mnras/advan...ty3467/5259110

  24. #54
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    Is it real or manufactured?


    http://cdsads.u-strasbg.fr/abs/2018AcAau.152..289C

    Astroengineering, Dysonian SETI, and naturalism: A new Catch-22

    Cirkovic, Milan M.
    Acta Astronautica, Volume 152, p. 289-298 (11/2018)

    A methodological problem is inherent in any discussion of extraterrestrial engineering and its detectability: how to distinguish detection signatures of such astroengineering from "natural", non-intentional, albeit exotic, processes? In practice, searches for traces and manifestations of advanced technological civilizations have been reduced so far to searching for outliers in the allegedly well-known regularities expected from natural astrophysical sources. This procedure, however, is an epistemological minefield, for at least two reasons: (i) prior datasets on which the regularities are based might be contaminated by artefacts, and (ii) the procedure of computation of unobservable quantities usually contains the implicit assumption of the non-intentional nature of sources. In other words, we are facing a Catch-22-type problem: in order to prove the artificial nature of a source, we seemingly need to first assume that it is not artificial. In contrast to most problems in science, this one could possibly be aggravated, rather than reduced, with the progress of our scientific understanding. Some possible recourses, as well as directions for further work toward building a comprehensive methodology of the Dysonian SETI, are discussed.

  25. #55
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    Project OZMA lives on.


    https://arxiv.org/abs/1901.04057

    A search for technosignatures from TRAPPIST-1, LHS 1140, and 10 planetary systems in the Kepler field with the Green Bank Telescope at 1.15-1.73 GHz

    Pavlo Pinchuk, et al. (Submitted on 13 Jan 2019)

    As part of our ongoing search for technosignatures, we collected over three terabytes of data in May 2017 with the L-band receiver (1.15-1.73 GHz) of the 100 m diameter Green Bank Telescope. These observations focused primarily on planetary systems in the Kepler field, but also included scans of the recently discovered TRAPPIST-1 and LHS 1140 systems. We present the results of our search for narrowband signals in this data set with techniques that are generally similar to those described by Margot et al. (2018). Our improved data processing pipeline classified over 98% of the ∼ 6 million detected signals as anthropogenic Radio Frequency Interference (RFI). Of the remaining candidates, 30 were detected outside of densely populated frequency regions attributable to RFI. These candidates were carefully examined and determined to be of terrestrial origin. We discuss the problems associated with the common practice of ignoring frequency space around candidate detections in radio technosignature detection pipelines. These problems include inaccurate estimates of figures of merit and unreliable upper limits on the prevalence of technosignatures. We present an algorithm that mitigates these problems and improves the efficiency of the search. Specifically, our new algorithm increases the number of candidate detections by a factor of more than four compared to Margot et al. (2018).

  26. #56
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    Life, the multiverse, and everything.

    https://arxiv.org/abs/1901.04614

    Multiverse Predictions for Habitability: The Number of Stars and their Properties

    McCullen Sandora (Submitted on 15 Jan 2019)

    In a multiverse setting, we expect to be situated in a universe that is exceptionally good at producing life. Though the conditions for what life needs to arise and thrive are currently unknown, many will be tested in the coming decades. Here we investigate several different habitability criteria, and their influence on multiverse expectations: Does complex life need photosynthesis? Is there a minimum timescale necessary for development? Can life arise on tidally locked planets? Are convective stars habitable? Variously adopting different stances on each of these criteria can alter whether our observed values of the fine structure constant, the electron to proton mass ratio, and the strength of gravity are typical to high significance. This serves as a way of generating predictions for the requirements of life that can be tested with future observations, elevating the multiverse scenario to a predictive scientific framework.

    ====

    With all the negative news lately about the probability of life around M-dwarf planets, one has to hope for the best.

    https://arxiv.org/abs/1901.04739

    A transiting super-Earth close to the inner edge of the habitable zone of an M0 dwarf star

    E. Díez Alonso, et al. (Submitted on 15 Jan 2019)

    We present a super-Earth orbiting close to the inner edge of the habitable zone of the cool dwarf star K2-286 (EPIC 249889081), detected with data from the K2 mission in its 15 th campaign. The planet has radius of 2.1±0.2 R ⊕ , near the 1.5 - 2.0 R ⊕ gap in the radii distribution. The equilibrium temperature is 347 +21 −11 K, cooler than most of the small planets with well measured masses, and the orbital period is 27.359±0.005 days. K2-286, located at a distance of 76.3±0.3 pc, is an M0V star with estimated effective temperature of 3926±100 K, less active than other M dwarf stars hosting exoplanets. The expected radial velocity semi-amplitude induced by the planet on the star is 1.9 +1.3 −1.2 m⋅ s −1 , and the amplitude of signals in transit transmission spectroscopy is estimated at 5.0±3.0 ppm. Follow-up observations for mass measurements and transit spectroscopy should be desirable for this relatively bright target (m V =12.76,m Ks =9.32 ) hosting a transiting super-Earth within the inner edge of the habitable zone.

  27. #57
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    Back to the Fermi Paradox, with alien Manifest Destiny across the Galaxy.

    https://arxiv.org/abs/1902.04450

    The Fermi Paradox and the Aurora Effect: Exo-civilization Settlement, Expansion and Steady States

    Jonathan Carroll-Nellenback, Adam Frank, Jason Wright, Caleb Scharf (Submitted on 12 Feb 2019)

    We model the settlement of the galaxy by space-faring civilizations in order to address issues related to the Fermi Paradox. We explore the problem in a way that avoids assumptions about the intent and motivation of any exo-civilization seeking to settle other planetary systems. We first consider the speed of an advancing settlement via probes of finite velocity and range to determine if the galaxy can become inhabited with space-faring civilizations on timescales shorter than its age. We also include the effect of stellar motions on the long term behavior of the settlement front which adds a diffusive component to its advance. The results of these models demonstrate that the Milky Way can be readily 'filled-in' with settled stellar systems under conservative assumptions about interstellar spacecraft velocities and launch rates. We then consider the question of the galactic steady-state achieved in terms of the fraction of settled planets. We do this by considering the effect of finite settlement civilization lifetimes on the steady states. We find a range of parameters for which the galaxy supports a population of interstellar space-faring civilizations even though some settleable systems are uninhabited. Both results point to ways in which Earth might remain unvisited in the midst of an inhabited galaxy. Finally we consider how our results can be combined with the finite horizon for evidence of previous settlements in Earth's geologic record. Our steady-state model can constrain the probabilities for an Earth visit by a settling civilization before a given time horizon. These results break the link between Hart's famous "Fact A" (no interstellar visitors on Earth now) and the conclusion that humans must, therefore, be the only technological civilization in the galaxy.

  28. #58
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    UV radiation should not be a problem for habitable planets around M dwarfs.

    https://arxiv.org/abs/1902.04086

    Stellar Activity Effects on Moist Habitable Terrestrial Atmospheres Around M dwarfs

    Mahmuda Afrin Badhan, et al. (Submitted on 11 Feb 2019)

    Transit spectroscopy of terrestrial planets around nearby M dwarfs is a primary goal of space missions in coming decades. 3-D climate modeling has shown that slow-synchronous rotating terrestrial planets may develop thick clouds at the substellar point, increasing the albedo. For M dwarfs with Teff > 3000 K, such planets at the inner habitable zone (IHZ) have been shown to retain moist greenhouse conditions, with enhanced stratospheric water vapor (fH2O > 1E-3) and low Earth-like surface temperatures. However, M dwarfs also possess strong UV activity, which may effectively photolyze stratospheric H2O. Prior modeling efforts have not included the impact of high stellar UV activity on the H2O. Here, we employ a 1-D photochemical model with varied stellar UV, to assess whether H2O destruction driven by high stellar UV would affect its detectability in transmission spectroscopy. Temperature and water vapor profiles are taken from published 3-D climate model simulations for an IHZ Earth-sized planet around a 3300 K M dwarf with an N2-H2O atmosphere; they serve as self-consistent input profiles for the 1-D model. We explore additional chemical complexity within the 1-D model by introducing other species into the atmosphere. We find that as long as the atmosphere is well-mixed up to 1 mbar, UV activity appears to not impact detectability of H2O in the transmission spectrum. The strongest H2O features occur in the JWST MIRI instrument wavelength range and are comparable to the estimated systematic noise floor of ~50 ppm.

  29. #59
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    Another version of the Drake Equation? I don't know if this is good or bad.

    https://arxiv.org/abs/1902.06784

    Multiverse Predictions for Habitability: Number of Habitable Planets

    McCullen Sandora (Submitted on 18 Feb 2019)

    How good is our universe at making habitable planets? The answer to this depends on which factors are important for life: Does a planet need to be Earth mass? Does it need to be inside the temperate zone? Are systems with hot Jupiters habitable? Adopting different stances on the importance of each of these criteria, as well as the underlying physical processes involved, can affect the probability of being in our universe; this can help to determine whether the multiverse framework is correct or not.

  30. #60
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    Is there intelligent life elsewhere, or are we it? As the comic-strip character Pogo once observed regarding this very issue, either way it's a mighty soberin' thought.

    https://arxiv.org/abs/1902.08035

    Introduction: Detectability of Future Earth

    Jacob Haqq-Misra (Submitted on 11 Feb 2019)

    Earth's future detectability depends upon the trajectory of our civilization over the coming centuries. Human civilization is also the only known example of an energy-intensive civilization, so our history and future trajectories provide the basis for thinking about how to find life elsewhere. This special issue of Futures features contributions that consider the future evolution of the Earth system from an astrobiological perspective, with the goal of exploring the extent to which anthropogenic influence could be detectable across interstellar distances. This collection emphasizes the connection between the unfolding future of the Anthropocene with the search for extraterrestrial civilizations. Our rate of energy consumption will characterize the extent to which our energy-intensive society exerts direct influence on climate, which in turn may limit the ultimate lifetime of our civilization. If the answer to Fermi's question is that we are alone, so that our civilization represents the only form of intelligent life in the galaxy (or even the universe), then our responsibility to survive is even greater. If we do find evidence of another civilization on a distant exoplanet, then at least we will know that our trajectory can be managed. But as long as our searches turn up empty, we must stay vigilant to keep our future secure.

    [[emphasis mine -- REM]]

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