VIII. Pedia Sapiens: A New Genesis Future
C. An Earthropic Principle: Novel Evidence for a Special Planet
Morbidelli, Alessandro and Sean Raymond. Challenges in Planet Formation. arXiv:1610.07202.. Universite de Nice Sophia-Antipoli, and CNRS, Laboratoire d'Astrophysique de Bordeau astrophysicists provide a latest update about how object worlds might have formed. As we report this active literature, an auspicious realization is that our own solar system is a rarest case (one in a thousand herein) with a relatively benign, long lived conducive order. A philosophical reflection ought to note how incredible it is that a global sapience can look back and reconstruct how this special planet and people came to be.
Over the past two decades, large strides have been made in the field of planet formation. Yet fundamental questions remain. Here we review our state of understanding of five fundamental bottlenecks in planet formation. These are: 1) the structure and evolution of protoplanetary disks; 2) the growth of the first planetesimals; 3) orbital migration driven by interactions between proto-planets and gaseous disk; 4) the origin of the Solar System's orbital architecture; and 5) the relationship between observed super-Earths and our own terrestrial planets. (Abstract)
Morbidelli, Alessandro, et al.
Topical Collection on the Delivery of Water to Proto-Planets, Planets and Satellites.
Space Science Reviews.
Eleven editors including Sean Raymond and Helmut Lammer introduce a special issue with this title about the occurrence, locales, and quantities of life’s ultimate biochemical through galactic, solar and planetary ages. Click on the issue citation for papers such as The Importance of Water for Life by Frances Westall and Andre Brack, The Delivery of Water during Terrestrial Planet Formation by David O.Brien, et al, Water in the Earth’s Interior by Anne Peslier, et al, and Water in Extrasolar Planets and Implications for Habitability by Lena Noack, et al.
Murchie, Guy. The Seven Mysteries of Life. Boston: Houghton Mifflin, 1978. We restate here Guy Murchie’s thoughtful perception of bioplanet Earth as an embryonic superorganism.
Sixth is the germination of worlds, a critical event that seems to happen once to every celestial organism and, after her billions of years of slow evolution, is occurring right now to Earth, as evidenced by many fundamental changes during what we call modern times - things that, as far as we know, never happened before and can never happen again on our planet. (7)
Naganuma, Takeshi. An Astrobiological View on Sustainable Life. Sustainability. 1/4, 2009. A Hiroshima University, Graduate School of Biosphere Science, environmentalist, who could not be in a more appropriate place, imaginatively views matter, evolution and its human frontier as a vectorial vortex of thermodynamic energies. In regard, it is asked whether such knowledge from its collective humankind scale can come to a common fore to save and sustain us.
In the Japanese language, the Sun is hi, and heat (fire) is also hi (originally ho or fo); water is mi or mizu; and, life is i-no-chi meaning energy of breath. The coincidence of two hi has impressed me, and I might say that split of mi by hi nourishes chi, at least, on the Earth. Both hi, that is the Sun’s radiation and the Earth’s interior heat, contribute to life. The degrees of contributions vary according to major modes of autotrophy, i.e., photosynthesis or chemolithoautotrophy. Examples of chemolithoautotrophic communities that depend primarily on geothermal hi are found in deep-sea hydrothermal vents and deep subsurface, respectively [4,5]. The idea that non-solar splitting of water nourishes life thus derives from the studies of deep-sea and deep subsurface biospheres, and is extended to possible extra-terrestrial biospheres. The concept of planetary biospheres should accommodate a more universal notion of life than traditional ones. The “non-solar splitting of water” idea is applicable to possible astrobiological biospheres. (835-836)
Olson, Stephanie, et al. Oceanographic Constraints on Exoplanet Life. arXiv:1909.02928. With our favorable tectonic balance of land and sea as a reference, University of Chicago geophysicists including Dorian Abbot consider variable exoworld oceanic conditions with regard to the presence of living systems. This liquid, amniotic surface hydrosphere is also seen as a major factor in their relative biological detectability. See also Scaling Relations for Terrestrial Exoplanet Atmospheres from Baroclinic Criticality by this extended group at 1908.02661 for more vital properties.
Liquid water oceans are crucial to our search for life on exoplanets because water is essential for life as we know it. However, oceans are dynamic habitats and some may be better hosts for life than others. In Earth's oceanic circulation conveys nutrients such as phospourous which affects the distribution and productivity of life. Of importance is upwelling due to wind-driven divergence in surface layers, which returns nutrients that tend to accumulate at depth. We address these aspects by using ROCKE-3D, a fully coupled ocean-atmosphere GCM, to investigate ocean dynamics on a diversity of habitable planets. Efficient nutrient recycling favors greater biological activity for better biosignature detection. Our results demonstrate the importance of oceanographic phenomena for exoplanet life detection and the emerging field of exo-oceanography. (Abstract excerpt)
Pacetti,, 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 far interstellar reaches will be deleterious in various ways 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)
Paradise, Adiv, et al. Climate Diversity in the Habitable Zone due to Varying pN2 Levels. arXiv:1910.02355. As if we did not already have enough finely tuned conditions which serve to make this home habitable Earth so very special, here University of Toronto astrophysicists and a biologist point out that an optimum band and pressure of atmospheric nitrogen is another vital parameter. For our bioplanet, it nominally is 79% and 21% oxygen within a tight zone of a few percent either way. In addition this range which has remained relatively stable for millions of years.
A large number of studies have responded to the growing body of confirmed terrestrial habitable zone exoplanets by presenting models of various possible climates. However, the impact of the partial pressure of gases such as N2 has been poorly-explored, despite the abundance of N2 in Earth's atmosphere. We use PlaSim, a fast 3D climate model, to simulate hundreds of climates with varying N2 pressures, insolations, and surfaces to identify the impact of the gas partial pressure on the climate. We find that the climate's response is nonlinear and highly sensitive to this factor. We identify CO2 and H2O absorption lines, warming or cooling by the water vapor greenhouse positive feedback, heat transport, and more as competing mechanisms that determine the equilibrium climate. (Abstract excerpts)
Pilat-Lohinger, Elke. The Role of Dynamics on the Habitability of an Earth-like Planet. International Journal of Astrobiology. 14/2, 2015. In an Exoplanet issue, a University of Vienna astrophysicist reaches a notable conclusion about our own solar system. It seems especially conducive because the orbital planets all lie in the same plane, and have basically circular orbits. Such a relative stability over a long time period is most favorable for a suitable biosphere upon which life can evolve and emerge to a noosphere able to observe itself and a planetary neighborhood.
Prantzos, Nikos. A Probabilistic Analysis of the Fermi Paradox in Terms of the Drake Formula. arXiv:2003.04802. Two decades after his Our Cosmic Future book, the Institute of Astrophysics, Paris, research director provides a new update of this equation estimate of how many Earth-like worlds might exist. It is also cast another response to Enrico’s 1950s concern that no one actually seems to be there. An underrated factor may have been the lifetime duration of a technical civilization. This would have a major winnowing effect if they could not get their common act together so as to save their home bioworld. Based on our own terminal perils, this situation could imply that a decisive planetary self-realization and selection, indeed a sustainability singularity, is a critical. imperative step. In Prantzos’ expansive view, civilizations are seen to randomly come and go, some for a short period, others may be longer. Earth is not the first, nor the last, but at the present time is alone for these reasons.
In evaluating the number of technological civilizations N in the Galaxy through the Drake formula, emphasis is mostly put on astrophysical and biotechnological factors describing the emergence of a civilization and less on its lifetime L, which is strongly related to its demise. It is argued that this factor is in fact the most important regarding the practical implications of the Drake formula, because it determines the extent of the "sphere of influence" of any technological civilization. The Fermi paradox is then studied by way of a simplified Drake version through Monte Carlo simulations of N civilizations expanding in the Galaxy during their space faring lifetime. In that frame, the probability of "direct contact" is set as the fraction of the Galactic volume occupied collectively by N civilizations. The results are used to find regions in the parameter space where the Fermi paradox holds. (Abstract excerpt)
Provenzale, Murante, et al. Climate Bistability of Earth-like Planets. arXiv:1912.05392. Eleven astroscientists from Torino to Trieste report that our own world seems to have passed through both colder, icy states and warmer, watery times. By these findings, this prior occasion appears as dual climatic options, depending on relative levels of energetic forcings. And as noted, such dynamic shiftings may play a serious role as evolutionary organisms may proceed on their course.
About 500 million years ago, our planet seems to have experienced snowball conditions, with continental and sea ices covering a large fraction of its surface. This situation points to a potential bistability of Earth's climate, that can have at least two equilibrium states for the same external solar radiation forcing. Here we explore the probability of bistable climates in earth-like exoplanets, and the properties of planetary climates obtained by varying the semi-major orbital axis, eccentricity, obliquity, and atmospheric pressure. To this goal, we use the Earth-like surface temperature model (ESTM) to provide a climate estimator for parameter sensitivity and long climatic simulations. An intriguing result of the present work is that the planetary conditions that support climate bistability are remarkably similar to those required for the sustenance of complex, multicellular life on the planetary surface. (Abstract excerpt)
Quarles, Billy, et al. Obliquity Evolution of Circumstellar Planets in Sun-like Stellar Binaries. arXiv:1911.08431. We add this report by Georgia Tech and NASA astronomic researchers including Jack Lissauer because it broaches another vicarious variable which could influence for better or worse life’s chances to evolve and reach global abilities to retrospectively perceive realize this reality.
Changes in planetary obliquity, or axial tilt, influence the climates on Earth-like planets. In the solar system, the Earth's obliquity is stabilized due to our moon which causes small amplitude variations beneficial for advanced life. Most Sun-like stars have at least one stellar companion and the habitability of their exoplanets is shaped by these pairings. We show that a stellar companion dramatically effects whether an Earth-like obliquity stability is possible. We present a new formalism for the planetary spin precession that accounts for orbital misalignments between the planet and binary. Thus, Earth-like planets likely experience much larger obliquity variations, with more extreme climates, unless they are in specific favorable states. (Abstract excerpt)
Ramirez, Rodrigo, et al. New Numerical Determination of Habitablility in the Galaxy. International Journal of Astrobiology. Online March, 2017. Universidad Nacional Autonoma de Mexico and Instituto de Estudios Avanzados de Baja, California astrophysicists finesse quantifications of the relative galactic and cosmic occurrence of planetary life. While rudimentary organisms may likely proliferate, a global evolution of technological civilizations may be less common and hardly detectable.