VIII. Pedia Sapiens: A New Genesis Future
C. An Earthropic Principle: Novel Evidence for a Special Planet
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.
Raymond, Sean. Sculpting Our Planetary System. American Scientist. September-October, 2018. In an issue on the many ways that Big Data/AI methods are bringing new capabilities to astronomical studies, a Laboratoire d’ Axtrophysique de Bordeaux researcher describes a novel, quite chaotic picture of how orbital worlds and solar systems form and evolve. Our familiar, orderly array, which was long taken as a norm, now seems a rare benign state as we learn about a usual crush of super-Earths, gas giants and rocky worlds in wildly shifting transits. See also by Formation of Terrestrial Planets by Raymond and Andre Izidoro at arXiv:1803.08830 and The Excitation of a Primordial Cold Asteroid Belt as an Outcome of the Planetary Instability by their group (1808.00609). The issue contains many entries from computations and astrochemistry to gravity waves and exoplanets.
The discovery of thousands of planets orbiting other stars has given us three surprising insights about our Solar System. First, we are weird: Our Solar System is a 1-in-2,000 rarity. Second, planet formation is a dynamic process, characterized by large-scale orbital drift as well as violent collisions and the ejection of young planets into interstellar space. Lastly, the second point may explain the first one—that is, how our Solar System formed is likely the root cause of our weirdness. (280)
Raymond, Sean, et al. Solar System Formation in the Context of Extra-Solar Planets. arXiv:1812.01033. Senior astrophysicists SR, University of Bordeaux, Andre Izidoro, Sao Paulo State University and Alessandro Morbidelli, University of Nice (search each) post a strongest analysis to date that our home Earth-Sun spatial and temporal array seems to be a rarest long term orderly, benign, conducive milieu for life to evolve and develop to a personsphere intelligence able to reach this auspicious conclusion. At the cusp of 2020, here is an incredible finding in our midst with implications for the fate and future not only of a geonate EarthKinder, but on to a self-chosen Ecosmos.
Exoplanet surveys have confirmed one of humanity's worst fears: we are weird. If our Solar System were observed with present-day Earth technology -- to put our system and exoplanets on the same footing -- Jupiter is the only planet that would be detectable. The statistics of exo-Jupiters indicate that the Solar System is unusual at the ~1% level among Sun-like stars (or ~0.1% among all stars). But why are we different? We argue that most Earth-sized habitable zone exoplanets are likely to form much faster than Earth, with most of their growth complete within the disk lifetime. Their water contents should span a wide range, from dry rock-iron planets to water-rich worlds with tens of percent water. Jupiter-like planets on exterior orbits may play a central role in the formation of planets with small but non-zero, Earth-like water contents.
Raymond, Sean, et al. Solar System Formation in the Context of Extrasolar Planets. Meadows, Victoria, et al, eds. Planetary Astrobiology. Tempe: University of Arizona Press, 2020. SR, University of Bordeaux, with coauthors Andre Isidora, Sao Paulo State University and Alessandro Morbidelli, University of Nice astrophysicists (search SR, AM) are leading expositors of the arduous, stochastic formation of stellar objects and their myriad rocky, gaseous, oceanic, icy, arid orbital worlds. Two decades into the 21st century, stars and planets have been found across every possible size, shape and kind as they traverse solar systems and fill diverse galaxies. In regard, sun and bioworld are coming to appear as unitary incubators for evolutionary habitation. But another august finding has grown in evidential veracity, whence our home system and planet Earth is a rarest optimum confluence by way of passing through many critical check-points, as this section reports.
Exoplanet surveys have confirmed one of humanity’s worst fears: We are weird. If our solar system were observed with present-day Earth technology — to put our system and exoplanets on the same footing — Jupiter is the only planet that would be detectable. The statistics of exo-Jupiters indicate that the solar system is unusual at the ~1% level among Sun-like stars (or ~0.1% among all main-sequence stars). But why are we different? This review focuses on global models of planetary system formation. Successful formation models for both the solar system and exoplanet systems rely on two key processes: orbital migration and dynamical instability. Systems of close-in “super-Earths” or “sub-Neptunes” cannot have formed in situ, but instead require substantial radial inward motion of solids either as drifting millimeter- to centimeter-sized pebbles or migrating Earth-mass or larger planetary embryos. (Abstract excerpt)
Rees, Martin. Is There Life Beyond Earth? New Scientist. July 12, 2003. More considerations by the Cambridge University astronomer about the future options and august purpose for an integral earthkind in the universe.
More time lies ahead than has elapsed in the entire course of biological evolution. In those aeons, Earth could be the “seed” from which post-human life spreads through the galaxy. The fate of humanity could then have an importance that is truly cosmic: what happens here might conceivably make the difference between a near eternity filled with ever more complex and subtle forms of life and one filled with nothing but base matter. (27)
Rees, Martin. Living in a Multiverse. Ellis, George F. R., ed. The Far-Future Universe: Eschatology from a Cosmic Perspective. Philadelphia: Templeton Foundation Press, 2002. In his many universe scenario, only those finely tuned for life can contain intelligent planetary beings who are able to learn, contemplate and creatively carry forth this genesis. (Noted again in The Greening of the Galaxy)
Our Earth may have cosmic importance, as the one place form which life could spread through the universe. This realization raises the stakes from the earth to the entire cosmos. This new century, on this planet may be a defining moment for the cosmos. In the entire domain that cosmologists explore – ten billion years of time, ten billion light-years of space – the most crucial space-time location of all could be here and now. (84)
Reinhold, Timo, et al. The Sun is Less Active that Other Solar-like Stars. Science. 368/516, 2020. A seven person team with postings in Germany, Korea, and Australia find that our starry sun to have a relatively benign magnetic field compared to a majority of similar solar types. Since higher magnetic activity may be averse to habitability, here may still be another feature that favors our home Earth.
The magnetic activity of the Sun and other stars causes their brightness to vary. Here, we investigate how typical the Sun’s variability is compared with other solar-like stars. By combining 4 years of photometric observations from the Kepler space telescope with astrometric data from the Gaia spacecraft, we were able to measure photometric variabilities of 369 solar-like stars. Most of those with well-determined rotation periods showed higher variability than the Sun and are considerably more active. These stars appear nearly identical to the Sun except for their higher variability. (Abstract)