III. Ecosmos: A Revolutionary Fertile, Habitable, Solar-Bioplanet Incubator Lifescape
H. Prolific ExoWorlds, Galactic Dynamics, Solar Orrerys, Habitable Zones, Biosignatures
Franck, Siegfried, et al. Extraterrestrial Gaias. Schneider, Stephen, et al, eds. Scientists Debate Gaia. Cambridge: MIT Press, 2004. The detection of extrasolar, earth-like planets takes on a new dimension when viewed through the lens of the Gaia perspective. Whether they are life-bearing can be ascertained by the composition of their atmosphere.
The general question is whether an Earth-sized planet discovered outside the solar system can accommodate a self-regulating geosphere-biosphere system with homeorrhesis (i.e., sister of Gaia). (315)
Frank, Adam. How Nature Builds a Planet. Discover. July, 2005. The latest info on varieties of planetary formation as an intelligent earth learns about its own origin and those of its neighbors.
Gaidos, Eric, et al. New Worlds on the Horizon: Earth-Sized Planets Close to Other Stars. Science. 318/210, 2007. We are presently witness to a unique historical achievement, not imaginable any time sooner, when our sentient planet via telescope, satellite, and computer instrumentation, along with a global research network, can detect a plethora of kindred orbs around other stars throughout the galaxy. What then is an ovular bioplanet of which we should be mindful? Might human beings at once ‘therefore choose Earth’, and seek to begin a celestial conversation?
Gargaud, Muriel, et al. Habitability in the Universe from the Early Earth to Exoplanets. Origins of Life and Evolution of Biospheres. 46/4, 2016. An introduction to a special issue as a profligate cosmic vista opens to us Earthlings. Typical papers are Host Star Evolution for Planet Habitability, Review on the Role of Planetary Factors on Habitability, and The Logic of Life by Robert Pascal and Addy Pross, abstract below.
In this paper we propose a logical connection between the physical and biological worlds, one resting on a broader understanding of the stability concept. We propose that stability manifests two facets - time and energy, and that stability’s time facet, expressed as persistence, is more general than its energy facet. That insight leads to the logical formulation of the Persistence Principle, which describes the general direction of material change in the universe, and which can be stated most simply as: nature seeks persistent forms. Significantly, the principle is found to express itself in two mathematically distinct ways: in the replicative world through Malthusian exponential growth, and in the ‘regular’ physical/chemical world through Boltzmann’s probabilistic considerations. By encompassing both ‘regular’ and replicative worlds, the principle appears to be able to help reconcile two of the major scientific theories of the 19th century – the Second Law of Thermodynamics and Darwin’s theory of evolution – within a single conceptual framework. (Pascal, Pross)
Gaudi, B. Scott, et al. The Demographics of Exoplanets. arXiv:2011.04703. SG, Ohio State University, Jessie Christiansen, Caltech, and Michael Meyer, University of Michigan post a chapter to appear in ExoFrontiers: Big Questions in Exoplanetary Science (Bristol: IOP Publishing Ltd) AAS-IOP ebooks, 2021). It is a sign of a new maturity if this fast-moving, expansive field of exoplanetary science can begin to lay out a program for a near and farther census. Amongst many aspects are the shape of the explanet, host star interactions, multiple formation paths for gas giants, and so on. But as the second quote notes, these studies come up with more evidence of how special our own Sun – Earth system really is.
In the broadest sense, the primary goal of exoplanet demographic surveys is to determine the frequency and distribution of planets as a function of as many of the physical parameters that may influence planet formation and evolution as possible, over as broad of a range of these parameters as possible. By comparing these planet distributions to the predictions of planet formation theories, we can begin to both test and refine these theories. In this chapter, we review the major results on exoplanet demographics to date. (Abstract)
Gaudi, B. Scott, et al. The Habitable Exoplanet Observatory Mission Concept Report. arXiv:2001:06683. We note this 500 page mission statement by some 200 astroscientists with a main base at Jet Propulsion Laboratory as a premier example into the 2030s of our collaborative Earthkind personsphere beginning to explore, quantify and spread forth in a revolutionary genesis universe.
Gelino, Dawn and Jason Wright. NASA and the Search for Technosignatures. arXiv:1812.08681. The 70 page main report from a September 2018 Workshop on how we Earthlings might look for and validly detect the presence of exo-civilizations with technical capacities. Some sections are Pulsed Radio, Continuous Wave Radio, Laser, Searches, also Limits of Megastructures, Waste Heat for Stars and Galaxies, and much more as our human to Anthropo sapience is just beginning to explore cosmic neighborhoods.
Gerrit, Horstmann, et al. Tidally Forced Planetary Waves in the Tachocline of Solar-like Stars. arXiv:2208.00644. We cite this entry by German (Dresden), Georgian (Tbilisi) and Austrian (Graz) astrophysicists as a current worldwide finding about solar system phenomena to an extent that the composite sun and its orbital orrery appear to act as an integral whole unit.
The tachocline is the transition region of stars of more than 0.3 solar masses, between the radiative interior and the differentially rotating outer convective zone.
Gilbert, Gregory and Daniel Fabrycky. An Information Theoretic Framework for Classifying Exoplanetary System Architectures. arXiv:2003.11098. University of Chicago astronomers contribute to a growing sense that planetary arrays can be seen to exhibit innate mathematic patterns and regularities. By a novel application of nonlinear dynamics it is proposed that a sunny star with its orbital members could make up an active, composite system. Rather than looking at individual globes, the full orrery gains priority as a basic unit. In so doing they pose algorithmic, deterministic and aggregate modes of complexity drawn from disparate areas such as bird flocking, epidemic spreading, and message transmission. As this infinite frontier beckons, it would be a grand resolve of inklings from Kepler to Hubble that visible, audible harmonics and rhythms grace the celestial heavens. See Relative Habitability of Exoplanet Systems with Two Giant Planets by Nora Baily and DF at 2205.02777 for more perceptions of how solar orrerys act as whole, mathematical units.
We propose descriptive measures to characterize the arrangements of planetary masses, periods, and mutual inclinations within exoplanetary systems. They are based in complexity theory so to discern global, system-level trends of each architecture. Our approach considers all planets in a system simultaneously, facilitating both intra-system and inter-system analysis. We find that Kepler's high-multiplicity systems can be explained if most systems belong to a single intrinsic population. We confirm prior findings that planets within a system tend to be roughly the same size and coplanar. We apply this classification scheme to (1) quantify the similarity between systems, (2) resolve observational biases from physical trends, and (3) identify which systems to search for additional planets and where to look for these planets. (Abstract excerpt)
Gobat, Raphael and S. E. Hong. Evolution of Galaxy Habitability. Astronomy & Astrophysics. 592/A96, 2016. (arXiv:1605.06627) Korea Institute for Advanced Study cosmologists provide an intricate quantification of galactic environs from metallicity levels to stellar initial mass function, supernova rate, active galactic nuclei and more. These findings can then inform relative numbers of conducive biospheres, and after a billion year, an occurrence of intelligent civilizations. Just a decade or so into discoveries of myriad orbital worlds, estimates of a plurality of actual Earths remains dependent on many not well quantified variables. In any event, the solar, galactic, and cosmic habitability of life and intelligence are quite chancy, thus we might be among multitudes, or more likely uniquely rare.
We combine a semi-analytic model of galaxy evolution with constraints on circumstellar habitable zones and the distribution of terrestrial planets to probe the suitability of galaxies of different mass and type to host habitable planets, and how it evolves with time. We find that the fraction of stars with terrestrial planets in their habitable zone (known as habitability) depends only weakly on galaxy mass, with a maximum around 4e10 Msun. We estimate that 0.7% of all stars in Milky Way type galaxies to host a terrestrial planet within their habitable zone, consistent with the value derived from Kepler observations. On the other hand, the habitability of passive galaxies is slightly but systematically higher, unless we assume an unrealistically high sensitivity of planets to supernovae. We find that the overall habitability of galaxies has not changed significantly in the last ~8 Gyr, with most of the habitable planets in local disk galaxies having formed ~1.5 Gyr before our own solar system. (Abstract)
Gowanlock, Michael, et al. A Model of Habitability within the Milky Way Galaxy. Astrobiology. 11/9, 2011. The profusion of recent exoplanet discoveries has created a new climate and support for imagining a conducive, fertile cosmos for life-bearing and evolving bioworlds. In this paper Trent University and University of Hawaii astro-informaticians proceed to research and quantify the possibilities across our home galaxy. What vistas and choices await our own Great Earth?
We present a model of the galactic habitable zone (GHZ), described in terms of the spatial and temporal dimensions of the Galaxy that may favor the development of complex life. The Milky Way galaxy was modeled using a computational approach by populating stars and their planetary systems on an individual basis by employing Monte Carlo methods. We began with well-established properties of the disk of the Milky Way, such as the stellar number density distribution, the initial mass function, the star formation history, and the metallicity gradient as a function of radial position and time. We varied some of these properties and created four models to test the sensitivity of our assumptions. To assess habitability on the galactic scale, we modeled supernova rates, planet formation, and the time required for complex life to evolve. Our study has improved on other literature on the GHZ by populating stars on an individual basis and modeling Type II supernova (SNII) and Type Ia supernova (SNIa) sterilizations by selecting their progenitors from within this preexisting stellar population. In the model that most accurately reproduces the properties of the Galaxy, the results indicate that an individual SNIa is 5.6× more lethal than an individual SNII on average. In addition, we predict that 1.2% of all stars host a planet that may have been capable of supporting complex life at some point in the history of the Galaxy. Of those stars with a habitable planet, 75% of planets are predicted to be in a tidally locked configuration with their host star. The majority of these planets that may support complex life are found toward the inner Galaxy, distributed within, and significantly above and below, the galactic midplane. (855)
Haghighipour, Nader. Super-Earths: A New Class of Planetary Bodies. Contemporary Physics. 52/5, 2012. With over 200 references, a NASA astrobiologist provides a current summary as our own “super” collaborative earthkind comes to discover a conducive universe filled with every variety of analog neighbors. Whom is the intelligent planetary person collectively learning all this, and whatever does it mean?
Super-Earths, a class of planetary bodies with masses ranging from a few Earth-masses to slightly smaller than Uranus, have recently found a special place in exoplanetary science. Being slightly larger than a typical terrestrial planet, super-Earths may have physical and dynamical characteristics similar to those of Earth whereas unlike terrestrial planets, they are relatively easier to detect. Because of their sizes, super-Earths can maintain moderate atmospheres and possibly dynamic interiors with plate tectonics. They also seem to be more common around low-mass stars where the habitable zone is in closer distances. This article presents a review of the current state of research on super-Earths, and discusses the models of the formation, dynamical evolution, and possible habitability of these objects. Given the recent advances in detection techniques, the detectability of super-Earths is also discussed, and a review of the prospects of their detection in the habitable zones of low-mass stars is presented. (Abstract, 403)
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