III. Ecosmos: A Revolutionary Fertile, Habitable, Solar-Bioplanet, Incubator Lifescape
H. Stellar Planetary Systems: A Stochastic Profusion of Galaxies, Solar Orrerys, and Habitable Zones
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)
Goyal, Armaan, et al. Enhanced Size Uniformity for Near-resonant Planets. arXiv:2307.15875. Indiana University and California Institute of Technology astrophysicists contribute more evidence that whole solar-systems actually have overall spatial and temporal qualities.
Super-Earths within the same close-in, compact planetary system tend to exhibit a striking degree of uniformity in their radius, mass, and orbital spacing, and this 'peas-in-a-pod' phenomenon itself serves to provide one of the strongest constrains on planet formation at large. Here we provide a novel comparative size uniformity analysis for 48 near-resonant and 251 nonresonant multi-planet systems evaluating uniformity both across systems and between planetary pairs within the same system. We find that while multiplanet configurations exhibit strong peas-in-a-pod size uniformity regardless of their proximity to resonance. These results are broadly consistent with a variety of formation paradigms for multiplanet systems, such as convergent migration within a turbulent protoplanetary disk or planet-planet interactions incited by postnebular dynamical instabilities.
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)
Hall, Shannon. The Secrets of Super Earths. Sky & Telescope. March, 2017. A science journalist extols new evidence about larger cousins some five to ten times larger. But while they seem to be common across the galaxy, there is no parallel in our solar system, past or present. Into the later 2010s, as a flood of such findings continues, here is another reason why our Earth’s environs is an unusual occurrence.
Hansimeier, Arnold, et al, eds. Life on Earth and other Planetary Bodies. Berlin: Springer, 2012. Volume 24 in the Cellular Origin, Life in Extreme Habitats and Astrobiology series, due by November. With Stephan Kempe and Joseph Seckbach as coeditors, wide ranging chapters again evoke a true animate, fertile cosmos which by its innate nature seeks to bear forth complex, evolving, awakening creatures. For example: “Glaciopanspermia: Seeding the Terrestrial Planets with Life?” by Joop M. Houtkooper, and “Origin of the Genetic Code and Abiotic Synthesis of Organic Compounds” by Zita Martins.
This volume covers aspects of life on Earth with all its diversity and the possibilities of extraterrestrial life. It presents contributions by experts from 20 countries who discuss astrobiology emphasizing life “as we know it” to extraterrestrial places. On Earth, life also exists at the edge with harsh limitations. Some chapters address the extremophiles in niches of microbial life in terrestrial halo-environments, the local life without water, and the dormancy of polar cyanobacteria, while others focus on microorganisms dwelling in severe conditions such as lava caves. All those conditions of harsh environments, including the Antarctic biota, could serve as analogues for other planets. Special stress is given to the frozen worlds of Mars; Europa, the satellite of Jupiter; and life in the Saturn neighborhood with its moon Titan. Other chapters discuss the habitability of exoplanets, Galacticpanspermia, molecules, and prokaryotes below the planetary surface, halophile life in the Universe, and the SETI search for extraterrestrial intelligence in the Cosmos. (Publisher)
Haqq-Misra, Jacob, et al. Limit Cycles can Reduce the Width of the Habitable Zone. arXiv:1605.07130. NASA Astrobiology scientists including Natasha Batalha and James Kasting proceed to study a range of geospheres and atmospheres with regard to how conducive they might be for life to form and evolve. After twenty pages, it is said that our own global CO2 inventory is atypical, thus Earth might be uncommon in its ability to sustain a stable warm climate. See also Turbet, Martin, et al herein for further evidence.
The liquid water habitable zone describes the orbital distance at which a terrestrial planet can maintain above-freezing conditions through regulation by the carbonate-silicate cycle. Recent calculations have suggested that planets in the outer regions of the habitable zone cannot maintain stable, warm climates, but rather should oscillate between long, globally glaciated states and shorter periods of climatic warmth. Such conditions, similar to 'Snowball Earth' episodes experienced on Earth, would be inimical to the development of complex land life, including intelligent life. We argue that an abiotic Earth would have a greater CO2 partial pressure than today because plants and other biota help to enhance the storage of CO2 in soil. For G stars like the Sun, limit cycles occur only for planets with CO2 outgassing rates less than that on modern Earth. Our results suggest that host star type, planetary volcanic activity, and seafloor weathering are all important factors in determining whether planets will be prone to limit cycling. (Abstract excerpts)
Haqq-Misra, Jacob, et al. Why do we find ourselves around a yellow star instead of a red star? International Journal of Astrobiology. Online May, 2017. Blue Marble Space Institute, NASA Astrobiology Institute, and University of Colorado researchers consider why Earth happens to be orbiting a certain kind of star rather than another. By way of Bayesian inference, it appears as a slight “statistical fluke or anomaly.”
M-dwarf stars are more abundant than G-dwarf stars, so our position as observers on a planet orbiting a G-dwarf raises questions about the suitability of other stellar types for supporting life. If we consider ourselves as typical, in the anthropic sense that our environment is probably a typical one for conscious observers, then we are led to the conclusion that planets orbiting in the habitable zone of G-dwarf stars should be the best place for conscious life to develop. But such a conclusion neglects the possibility that K-dwarfs or M-dwarfs could provide more numerous sites for life to develop, both now and in the future. (Abstract excerpt)
Haswell, Carole. Transiting Exoplanets. Cambridge: Cambridge University Press, 2010. As another example of this epochal realization just coming of age, an Open University, London, astrophysicist provides a comprehensive textbook about orbiting worlds which proliferate through their daily discovery. But as noted for Sara Seager’s edited volume, such a cosmic Copernican revolution has not yet occurred.