VIII. Pedia Sapiens: A New Genesis Future
C. An Earthropic Principle: Novel Evidence for a Special Planet
We have reached the penultimate Natural Genesis section which appropriately posts an epic 21st century to 2020 realization. It has long been thought that the vast multitudes of galaxies, stars and now orbital planets would contain many life-bearing worlds. But as the number of certain check points or bottlenecks which it appears that biosphere to noosphere evolution need pass through grows in number (lately some 17) an awesome conclusion is starting to dawn. Verily, our home Earth may be the fittest first, optimum or last to attain a momentary singularity of cocreative self-selection.
Angier, Natalie. The Earth’s Shell has Cracked, and We’re Drifting on the Pieces. New York Times. December 18, 2018. The popular science writer draws upon a Royal Society meeting about plate tectonics and Philosophical Transactions A issue from it (see Robert Stern herein for more) about how our home planet has been distinguished and enlivened by mobile continental forms over a billion years, while Venus and many other worlds have not. It is noted that this ancient surface balance of land and sea is vitally crucial for a planet to become habitable for life and evolution. She consulted with R. Stern (UT Dallas), Jun Korenaga (Yale), Aubrey Zerkle (St. Andrews, Scotland)), and others as this rare Earth crustal and oceanic interplay grows in significance.
This volume brings together contributions from the Royal Society Discussion Meeting on ‘Earth dynamics and the development of Plate Tectonics’ held in March 2018. Plate tectonics is not seen on other planets, so why does it occur on Earth, and when did it start? The nature of tectonics depends on initial conditions, mantle thermal states, and an ability to weaken the lithosphere to allow plate boundaries to form. Geodynamic models, rock deformation experiments, models for growth of the continental crust, and evidence from the rock record are consistent with the development of plate tectonics from a single-lid state. Major changes occurred in the geological record near the end of the Archaean, suggesting that plate tectonics had become the dominant gobal regime by the Proterozoic. Modern plate tectonics and the generation of stable continents were key events in the evolution of the biosphere on Earth, and similar tectonic processes could be crucial for the development of habitability of exoplanets. (Synopsis)
Arnould, Jacques. Astrobiology, Sustainability and Ethical Perspectives. Sustainability. 1/4, 2009. In this online journal which has become a home for authoritative writings about saving the planet, a CNES French Space Agency philosopher contends that an expansive panorama that views earth and human in the context of a conducive, life friendly cosmos could be of much utility and incentive.
Astrobiology, a new field of research associating the prospects and constraints of prebiotic chemistry, mineralogy, geochemistry, astrophysics, theoretical physics, microbial ecology, etc., is assessed in terms of sustainability through the scientific and social functions it fulfils, and the limits it encounters or strives to overcome. In the same way as sustainable development, astrobiology must also take into account the temporal dimension specific to its field of investigation and examine its underlying conception of Nature. (Abstract)
Bach-Muller, Nanna and Uffe Jorgensen. Orbital Eccentricity: Multiplicity Correlation for Planetary Systems and Comparison to the Solar System. arXiv:2010.10371. As exoplanet findings grow in number and variety, Niels Bohr Institute, University of Copenhagen astroscientists can perceive another unusual aspect of our home orrery. With regard to most other systems with a few worlds, our 8 or 9 member planets as well as their relatively round orbit and even spacings is a quite rare confluence. As we post in late 2020 with our precious, precarious Earth beset by so many perils, this awesome significance grows in validity. See also Solid Tidal Friction in Multi-layer Planets by Emeline Bolmont, et al at 2010.04587.
The orbit eccentricities of the Solar System planets are unusually low compared to the average of known exoplanetary systems. A power law correlation has been found between the multiplicity of a planetary system and the orbital eccentricities of its components for systems above two worlds. In this study we investigate the correlation for an expanded data sample by way of planetary systems as units (unlike studies of individual planets). Our full survey contains 1171 exoplanets in 895 systems whence the correlation between eccentricity and multiplicity follows a clear power law. We find that Solar System orbits fit the general trend and suggest that the Solar System might not show uncommonly low eccentricities but rather more planets compared to a "standard" planetary system. Based on the power law correlation, we estimate that the probability of a system having 8 planets or more is of the order of 1%. (Abstract excerpt)
Balbi, Amedeo and Francesco Tombesi. The Habitability of the Milky Way during the Active Phase of its Central Supermassive Black Hole. Nature Scientific Reports. 7/16626, 2017. Vergata University of Rome astrophysicists add still another deleterious impediment due to excessive galactic radiations from the main galactic black hole which prohibit the long multi-million year span necessary for organisms to form, evolve and complexify.
During the peak of their accretion phase, supermassive black holes in galactic cores are known to emit very high levels of ionizing radiation, becoming visible over intergalactic distances as quasars or active galactic nuclei (AGN). Here, we quantify the extent to which the supermassive black hole at the center of the Milky Way may have affected the habitability of Earth-like planets. We focus on the amount of atmospheric loss and biological damage suffered by planets exposed to X-ray and extreme ultraviolet radiation. We find that terrestrial planets could lose a total atmospheric mass comparable to that of present day Earth even at large distances from the galactic center. (Abstract excerpt)
Testing the Multiverse: Bayes, Fine-Tuning and Typicality.
Reviewed more in Anthropic Principle, the University of Sydney astronomer (search) posts his presentation at a 2014 London Philosophy of Cosmology conference. As a coauthor with Geraint Lewis of A Fortunate Universe (2016), this entry discusses anthropic themes along with Bayesian “theory testing” methods for better iterations of “relative certainties or credences.” For this Greatest Earth section, it is wondrous that inquisitive, globally cognizant peoples can imagine whole cosmoses at all. With 400th anniversary events underway for Galileo, what can these expansive vistas from our moon to a multiverse ever portend? As latest currents seem to presage, human beings ought to have a significant purpose in the actual scheme of things.
Barnes, Rory. Tidal Locking of Habitable Exoplanets. Celestial Mechanics and Dynamical Astronomy. 129/4, 2017. A University of Washington astronomer quantifies one more crucial condition as to whether a candidate orbital world could harbor living, evolving systems, or be prohibitively hostile to it. Since this Earth has been benign long enough to reach our global observation, its tidal regime, in accord with the moon and sun, must have been fortuitous. See also Niche Amplitude, Tidal Locking and Fermi’s Paradox and Evolutionary Exobiology II by David Stevenson in the International Journal of Astrobiology (Each online July 2018).
Potentially habitable planets can orbit close enough to their host star that the differential gravity across their diameters can fix the rotation rate at a specific frequency, a process called tidal locking. Tidally locked planets on circular orbits will rotate synchronously, but those on eccentric orbits will either librate or rotate super-synchronously. Lower mass stellar hosts will induce stronger tidal effects on potentially habitable planets, and tidal locking is possible for most planets in the habitable zones of GKM dwarf stars. These results suggest that the process of tidal locking is a major factor in the evolution of most of the potentially habitable exoplanets to be discovered in the near future. (Abstract excerpt)
Batygin, Konstantin and Greg Laughlin. Jupiter’s Decisive Role in the Inner Solar System’s Early Evolution. Proceedings of the National Academy of Sciences. 112/4214, 2015. As the rush of Kepler satellite findings become assimilated, radical new understandings of near and far stellar-planetary topological and dynamical arrays are being realized. Here Cal Tech and UC Santa Cruz astronomers report another way that our home system is unusual because this gas giant served to sweep away an original phase of close in worlds that often wreak instabilities. A commentary in the same issue by Smadar Naoz notes that our “unique” arrangement is a “second generation” sequence. Along with nine planets in the same plane with circular orbits for over a billion years, it is dawning that we Earthlings abide in a rare, especially conducive, habitable zone.
The Solar System is an unusual member of the galactic planetary census in that it lacks planets that reside in close proximity to the Sun. In this work, we propose that the primordial nebula-driven process responsible for retention of Jupiter and Saturn at large orbital radii and sculpting Mars’ low mass is also responsible for clearing out the Solar System’s innermost region. Cumulatively, our results place the Solar System and the mechanisms that shaped its unique orbital architecture into a broader, extrasolar context. (Significance)
Batygin, Konstantin, et al. Born of Chaos. Scientific American. May, 2016. Astrophysicists Batygin, Gregory Laughlin and Alessandro Morbidelli (search) write a popular article about the dynamic formation of the solar system and of our planet Earth just now being reconstructed, which all leads to an auspicious realization. In this post-Kepler satellite and worldwide collaborative era, it has been found that prolific arrays of orbital objects typically exhibit a contingent jumble of small rocky to giant gaseous planets in every which disordered location, especially close in to the host star. But our home solar community has a rare, well-spaced procession from one small Mercury to Venus, Earth and Mars onto larger outer worlds. Over its history, the planet Jupiter first moved toward the sun which cleaned out planetesimals and super-Earths, except for Mercury. It then tacked outward which led to further destructions or expulsions. See also Jupiter’s Decisive Role in the Inner Solar System’s Early Evolution by Batygin and Laughlin in the Proceedings of the National Academy of Sciences (112/4214, 2015) and the third quote.
In Brief: A wealth of new evidence from computer simulations as well as observations of planets throughout the galaxy is revealing new details of our solar system’s dynamic and violent history. The solar system’s configuration of small inner rocky worlds and large outer giants is anomalous in comparison with most other planetary systems, which have different architectures. (30)
Beech, Martin. On Special Epochs, the Copernican Principle and Future Astronomy. Journal of the Royal Astronomical Society of Canada. April, 2015. The University of Regina, Saskatchewan astronomer and author (search) takes issue with the popular overuse of this “principle” which has come to designate a steady historic removal of human beings, planet Earth, its solar system, and even the Milky Way from any central, unique location or import. As a starter Nikolai himself would not agree nor would he approve this version in his name. From circa 2015, the latest cosmological findings, not possible earlier, are in fact finding people, bioplanet, sun, and galaxy to be unusually favorable in orbital geometries and benign duration. See also Since When Was the Sun a Typical Star? by MB in this journal for December 2011. Here is one more instance of a cosmic paradigm shift in our midst (e.g. Giulio Tononi, Cadell Last, many others) from denunciations of human and universe to realizations of a phenomenal place and purpose.
As described in an earlier article (Beech 2011), for example the blind acceptance of the Copernican Principle has resulted in the entirely wrong concept being propagated within popuar astronomy texts that the Sun and Solar System are in every way average, even bland and/or typical. They patently are not average in many demonstrable ways, and our seemingly modern fear of allowing for special circumstances and the existence of unique structures, events, epochs and has, in effect, led our collective understanding astray. Not only, in fact, is the Solar System located at a very specific and special place within our galaxy, we also live in a very special epoch within the history of the Universe. Indeed, we live in the epoch in which humanity is able to determine and at least partially comprehend the full scale of the observable Universe. (63-64)
Bonavita, Elenia, et al. The Impact of Tidal Disruption Events on Galactic Habitability. arXiv:2008.09988. University of Rome and Florida Institute of Technology astroresearchers including Amedeo Balbi and Manasvi Lingam add another impediment to planetary habitations by pointing out that perilous radiations which seem to suffuse interstellar domains could be quite deleterious to living systems. See also The Habitability of the Galactic Bulge at 2008.07586.
Tidal Disruption Events (TDEs) are characterized by the emission of a short burst of high-energy radiation. We analyze the cumulative impact of TDEs on galactic habitability using the Milky Way as a proxy. We show that X-rays and extreme ultraviolet (XUV) radiation emitted during TDEs can cause hydrodynamic escape and instigate biological damage. In particular, we show that planets within distances of ∼0.1-1 kpc could lose Earth-like atmospheres over the age of the Earth. We conclude by highlighting potential ramifications of TDEs and argue that they should be factored into analyses of inner galactic habitability. (Abstract)
Broad, William. In Secrets of Coral Spawning, Hope for Endangered Reefs. New York Times. June 21, 2016. We note this Science Times piece about large coral reefs which engage in an annual procreative event of spewing trillions of eggs at once into the ocean so that at least some may become fertile and grow anew. This is a stretch, but might one then imagine a coral cosmos whence trillions of vicarious bioworlds might take on a similar ovular guise, so that a few fittest might succeed?
Bryson, Steve, et al. The Occurrence of Rocky Habitable Zone Planets around Solar-like Stars from Kepler Data. Astrophysical Journal. Online November 5, 2020. This document with some 46 coauthors from the USA and beyond is the main report from the copious Kepler planet hunter project launched in 2009. While NASA statistical estimates may seem to allow millions of potentially habitably worlds, as per the second quote, it is said to be too early to firm up. In addition, no real Earth analogs have yet been found. See also Looking for Another Earth? Here are 300 Million, Maybe by Dennis Overbye in the New York Times for Nov. 5, 2020.
We present occurrence rates for rocky planets in the habitable zones (HZ) of main-sequence dwarf stars based on the Kepler DR25 planet candidate catalog and Gaia-based stellar properties. We provide the first analysis in terms of star-dependent instellation flux, which allows us to track HZ planets. These bounds reflect two extreme assumptions about the extrapolation of completeness beyond orbital periods where DR25 completeness data are available. The large uncertainties are due to the small number of detected small HZ planets. We also present occurrence rates for various stellar populations and planet size ranges. (Abstract excerpt)