III. Ecosmos: A Revolutionary Fertile, Habitable, Solar-Bioplanet Incubator Lifescape
H. Prolific ExoWorlds, Galactic Dynamics, Solar Orrerys, Habitable Zones, Biosignatures
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.
Heller, Rene and John Armstrong. Superhabitable Worlds. Astrobiology. Online January, 2014. McMaster University and Weber State University astrophysicists contend that earlier views of “habitable zones” for orbiting planets have been based on our earth alone. Rather a wider sense of where life can accrue by asking what kind of celestial object, such as exomoons, in an increasingly conducive spacescape can be home. A “terrestrial menagerie” is advised that considers many factors as surface area, land to ocean ratio, tectonics, magnetic flux, climate thermostat, panspermia, sun size, biological diversity, atmosphere, orbital dynamics, and so on. By this vista, a number of notable predictions accrue. The initial appearance of life on a planet will serve, as it evolves, to make it even more habitable over time. This inclusive 2013 scenario is seen to refute the 2000 Rare Earth hypothesis whence everything is so chancy that our sentient orb must be the only one in the cosmos.
To be habitable, a world (planet or moon) does not need to be located in the stellar habitable zone (HZ), and worlds in the HZ are not necessarily habitable. Here, we illustrate how tidal heating can render terrestrial or icy worlds habitable beyond the stellar HZ. Scientists have developed a language that neglects the possible existence of worlds that offer more benign environments to life than Earth does. We call these objects "superhabitable" and discuss in which contexts this term could be used, that is to say, which worlds tend to be more habitable than Earth. In an appendix, we show why the principle of mediocracy cannot be used to logically explain why Earth should be a particularly habitable planet or why other inhabited worlds should be Earth-like. Superhabitable worlds must be considered for future follow-up observations of signs of extraterrestrial life. Considering a range of physical effects, we conclude that they will tend to be slightly older and more massive than Earth and that their host stars will likely be K dwarfs. This makes Alpha Centauri B, member of the closest stellar system to the Sun that is supposed to host an Earth-mass planet, an ideal target for searches of a superhabitable world. (Abstract)
Hinkel, Natalie, et al. Stellar Characterization Necessary to Define Holistic Planetary Habitability. arXiv:1904.01089. Natalie H., Southwest Research Institute, Irina Kitiashvili, NASA along with Patrick Young and Ben Rackham, ASU propose an Astro2020 Science White Paper to study this vital interrelation. The significant insight is that prior views of planets and stars in separate isolation misses their integral, symbiotic interaction. In regard, a benign sun with an orbital Earth and planets as some manner of incubator-like solar system would be appreciated as the most characteristic cosmic feature.
It is a truism within the exoplanet field that "to know the planet, you must know the star." This pertains to the physical properties of the star (i.e. mass, radius, luminosity, age, multiplicity), the activity and magnetic fields, as well as the stellar elemental abundances which can be used as a proxy for planetary composition. In this white paper, we discuss important stellar characteristics that require attention in upcoming ground- and space-based missions, such that their processes can be understood and either detangled from that of the planet, correlated with the presence of a planet, or utilized in lieu of direct planetary observations. (Abstract)
Hoffmann, Volker, et al. Chaos in Terrestrial Planet Formation. arXiv:1508.00917. University of Zurich astrophysicists describe how planetary bodies seem to be formed by vicarious accretions and collisions. It is shown how that “highly chaotic behavior” can often result in wide variety of orbital arrangements. Companion papers could be Building Massive Compact Planetesimal Disks from the Accretion of Pebbles by John Moriarty and Debra Fischer (arXiv:1507.08215), and The Formation of the Solar System by Suzanne Pfalzner, et al (1501.03101). And for this website, it is amazing that upon a most favorable bioworld, a collaborative worldwide species can quantify and reconstruct how everything came to be.
Howard, Andrew, et al. A Rocky Composition for an Earth-sized Exoplanet. Nature. Online October 30, 2013. As the Abstract explains, in this awesome post-Kepler age, a ten person team including Debra Fischer and Geoffrey Marcy perceive and quantify orbital worlds similar to our own that seem to naturally proliferate around every star and in all galaxies. And we ought to notice how fantastic it is for us humankinder to be able to state into the 21st century that “Planets like Earth are common around Sun-like stars.”
Planets with sizes between that of Earth (with radius R⊕) and Neptune (about 4 R⊕) are now known to be common around Sun-like stars. Most such planets have been discovered through the transit technique, by which the planet's size can be determined from the fraction of starlight blocked by the planet as it passes in front of its star. Measuring the planet's mass-and hence its density, which is a clue to its composition-is more difficult. Planets of size 2-4 R⊕ have proven to have a wide range of densities, implying a diversity of compositions, but these measurements did not extend down to planets as small as Earth. Here we report Doppler spectroscopic measurements of the mass of the Earth-sized planet Kepler-78b, which orbits its host star every 8.5 hours. Given a radius of 1.20 ± 0.09 R⊕ and mass of 1.69 ± 0.41 M⊕, the planet's mean density of 5.3 ± 1.8 g cm−3 is similar to the Earth's, suggesting a composition of rock and iron. (Abstract)
Inutsuka, Shu-ichiro, editor in chief. Protostars & Planets VII. Tempe: University of Arizona Press, 2023. This entry will be about this latest series (search) volume, and the international conference in Japan in April 2023 from which its chapters are drawn. We note, for example, Offner, Stella, et al. The Origin and Evolution of Multiple Star Systems by Stella Offner, et al, Organic Chemistry in the First Phases of Solar-type Protostars by Ceccarelli, Cecilia, Ceccarelli,et al, Architectures of Compact Multi-Planet Systems by Lauren Weiss, et al and Chemical Habitability: Supply and Retention of Life's Essential Elements During Planet Formation by Krijt, Sebastiaan, Krijt, et al. Our EarthMost global and galactic quest picks up again going forward.
Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus and Sulfur (CHNOPS) play key roles in the origin and rise of life on Earth. We begin by citing the CHNOPS budget on Earth, their role in shaping our biosphere, and origins in the Solar Nebula. We then view how these elements are distributed in diverse astrophysical settings, tracing their journeys from synthesis in dying stars to molecular clouds, and onto temperate rocky planets around main sequence stars. (Krijt, S. excerpt)
Jones, Barrie. The Search for Life Continued: Planets Around Other Stars. Berlin: Springer, 2008. The Open University astronomer provides a thorough, illustrated guide to earth’s outward quest for animate neighbors across the galaxy and cosmos. This endeavor has lately taken on a new scope with the ability to search for and detect similar planets orbiting distant suns. Their apparent proliferation provides another good reason that we are not alone. And to gain such a vista for our precious home abode, so egg-like and pregnant in the celestial reaches, could inspire us to join in a common incentive and destiny, therefore choose Earth.
Kaltenegger, Lisa. How to Characterize Habitable Worlds and Signs of Life. Annual Review of Astronomy and Astrophysics. 55/433, 2017. The Cornell University, Carl Sagan Institute astronomer introduces and scopes out a novel field of “comparative planetology” as worldwide collaborations come upon and enter a revolutionary fertile cosmos graced by a profligate propensity to form globular bioworlds and incubator solar systems. Biochemical precursors, protocell rudiments, incipient microbes, and so on hence seem to inherently appear, evolve, wherever they can. An especial feature for initial studies would be signatures of biospheric atmospheres.
The detection of exoplanets orbiting other stars has revolutionized our view of the cosmos. First results suggest that it is teeming with a fascinating diversity of rocky planets, including those in the habitable zone. Even our closest star, Proxima Centauri, harbors a small planet in its habitable zone, Proxima b. With the next generation of telescopes, we will be able to peer into the atmospheres of rocky planets and get a glimpse into other worlds. Using our own planet and its wide range of biota as a Rosetta stone, we explore how we could detect habitability and signs of life on exoplanets over interstellar distances. The discussion on what makes a planet a habitat and how to detect signs of life is lively. This review will show the latest results, the challenges of how to identify and characterize such habitable worlds, and how near-future telescopes will revolutionize the field. For the first time in human history, we have developed the technology to detect potential habitable worlds. (Abstract)
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