VII. Pedia Sapiens: A Genesis Future on Earth and in the Heavens
C. An Earthropic Principle: Novel Evidence About a Special Planet
Gardner, Andy and Joseph Conlon. Cosmological Natural Selection and the Purpose of the Universe. Complexity. Online May, 2013. To ponder, isn’t it fantastic that we brave creatures upon a conducive mote can yet, suddenly, collaboratively, expand our imaginations to roam the celestial reaches to ask whatever, whom are we, and maybe touch why? As the quotes convey, an Oxford University zoologist and a biophysicist consider, from their fields, some evolutionary reasons in support Lee Smolin’s (search 1999) title CNS theory. It is written in a usual arcane, abstract style, but offers a perceptive inkling and promise of an intended involvement of learned human volition and co-creativity of a truly universal significance.
The cosmological natural selection (CNS) hypothesis holds that the fundamental constants of nature have been fine-tuned by an evolutionary process in which universes produce daughter universes via the formation of black holes. Here, we formulate the CNS hypothesis using standard mathematical tools of evolutionary biology. Specifically, we capture the dynamics of CNS using Price’s equation, and we capture the adaptive purpose of the universe using an optimization program. We establish mathematical correspondences between the dynamics and optimization formalisms, confirming that CNS acts according to a formal design objective, with successive generations of universes appearing designed to produce black holes. (Abstract)
Georgakarakos, Nikolaos, et al. Giant Planets: Good Neighbors for Habitable Worlds?. arXiv:1804.02183. NYU Abu Dhabi and CalTech JPL astrophysicists add to growing perceptions that as large gaseous worlds vicariously course through solar systems, sometimes inward and back, they have a major impact upon their relative, long-term habitability by Earth-size bioworlds. See also the Astronomy article by Jesse Emspak herein for another view.
The presence of giant planets influences potentially habitable worlds in numerous ways. Massive celestial neighbors can facilitate the formation of planetary cores and modify the influx of asteroids and comets towards Earth-analogs later on. Furthermore, giant planets can indirectly change the climate of terrestrial worlds by gravitationally altering their orbits. Investigating 147 well characterized exoplanetary systems known to date that host a main sequence star and a giant planet we show that the presence of 'giant neighbors' can reduce a terrestrial planet's chances to remain habitable, even if both planets have stable orbits.. (Abstract excerpt)
Gribbin, John. Alone in the Milky Way. Scientific American. September, 2018. In a topical issue on The Science of Being Human, the veteran British science writer and author of the Alone in the Universe (2011) presents a succinct update with the same message as this new section. The case for extraterrestrial civilizations has long been based on the vast, statistical estimate of a 100 billion stars in a galaxy. Into the 21st century, it became known that solar systems with life-bearing orbital bodies are the common rule. But a wealth of astronomic findings about variable suns, radiation flows, planetary forms, motions, locales, chemistries, surfaces, atmospheres, meteors, moons, and more, has given rise to an unexpected realization. Our worldwide technological society able to learn this may be the result of a rarest cosmic and evolutionary concatenation of many critical steps. Here we read of Earth’s good position within a galactic habitable zone, favorable levels of metallic elements, many fortuitous timings, how early life passed dire tests, the chancy success of Homo sapiens, and more. If of a mind to ask and see, an awesome discovery of ultimate import appears in our midst. And akin to Michael Tomasello in this issue, Gribbin closes by saying that we peoples ought to peaceably and strive for a sustainable futurity.
Gribbin, John. Alone in the Universe: Why Our Planet is Unique. Hoboken, NJ: Wiley, 2011. The British science writer is amazed that with a prolific chancery of swirling galaxies, stellar chaos, askew orbits, hot Jupiters, metallicities, wandering continental plates, cometary impacts, a funny sun, toxic atmospheres, along with life’s episodic, contingent evolution, rife with extinctions, and more, it’s a wonder we inquisitive earthlings are here at all. So, once more, by this train, it is concluded We are It, and ought to decisively avail our cosmic lottery winnings to save the world and green the galaxy.
And that chain (of coincidences) has so many weak links that it may mean that, for all the proliferation of stars and planets in the Universe, as an intelligent species we may be unique. (xiii) Whether or not you see the hand of God in any of this, it would mean that we are the most technologically advanced civilization in the Universe, and the only witnesses with an understanding of the origin and nature of the Universe itself. If humankind and Gaia can survive the present crises, the whole of the Milky way may become our home. If not, the death of Gaia may be an event of literally universal significance. (xv)
Hall, Shannon. Summer Solstice Mystery: Does the Earth’s Tilt Hold the Secret to Life? New York Times. June 21, 2018. With this timely article, one more special feature of our conducive bioplanet comes to scientific and public notice. Earth’s axial tilt or obliquity of 23.5 degree which gifts seasonal variations is well within a 10 to 40 degree range seen as necessary. Life’s biochemistry and developmental evolution to literate intelligence requires a steady, benign climate that does not lock into hot, gaseous or cold, frozen states. Bioastronomers Rene Heller, Rory Barnes, David Ferreira and others comment, along with citations such as Climate at High-Obliquity in Icarus (243/236, 2014) and Exo-Milankovitch Cycles II: Climates of G-dwarf Planets at arXiv:1805.00283. For more see Statistical Trends in the Obliquity Distribution of Exoplanet Systems at arXiv:1805.03654. Many exoworlds, and also their sunny stars, wobble but at lower or higher deleterious angles, which often change over time.
Milankovitch cycles describe the collective effects of changes in the Earth's movements on its climate over thousands of years. The term is named for Serbian geophysicist and astronomer Milutin Milanković. In the 1920s, he hypothesized that variations in eccentricity, axial tilt, and precession of the Earth's orbit resulted in cyclical variation in the solar radiation reaching the Earth, and that this orbital forcing strongly influenced climatic patterns on Earth. (Wikipedia)
Hall, Shannon. The Recipe for Other Earths. Nature. 552/20, 2017. A science writer reports upon efforts by geologists to understand our world make up so as to better evaluate whether exoplanet conditions might aid or inhibit a relative habitability.
But Earth has a lot more going for it than its size, mass and favourable orbit, says Cayman Unterborn (search), an exogeologist at Arizona State University in Tempe. Its churning molten core, for example, creates and sustains a magnetic field that shields the planet’s fragile atmosphere from the solar wind. And the motion of tectonic plates helps regulate global temperatures, by cycling carbon dioxide between rocks and the atmosphere. (21)
Haqq-Misra, Jacob. Does the Evolution of Complex Life Depend on the Stellar Spectral Energy Distribution?. arXiv:1905.07343. The Blue Marble Space Institute, Seattle astrobiologist (search) adds another measured condition which is vital for biospheric life to develop into complex organisms. As the Abstract notes, the right intensity of solar radiation is needed over a sufficiently long span (a billion years for Earth), so that a global species as our own can appear.
This paper presents the proportional evolutionary time hypothesis, which posits that the mean time required for the evolution of complex life is a function of stellar mass. The "biological available window" is defined as the region of a stellar spectrum between 200 to 1200 nm that generates free energy for life. Over the ∼4 Gyr history of Earth, the total energy incident at the top of the atmosphere and within the biological available window is ∼1034 Joules. The hypothesis assumes that the rate of evolution from the origin of life to complex life is proportional to this total energy, which would suggest that planets orbiting other stars should not show signs of complex life if the total energy incident on the planet is below this energy threshold. (Abstract)
Hatzes, Artie. The Architecture of Exoplanets. Space Science Reviews. 205/1-4, 2016. A Friedrich Schiller University, Jena astronomer divides this Earthwise study of a prolific cosmos known since 1995 to fill itself with orbital worlds into two phases. Before the 2009 Kepler satellite launch, our own home orrery was still used as the standard model. In the years since, all possible manner of celestial objects from planetesimals to small rocky orbs, super Earths, gas giants, and solar systems will a large range of stellar modes, often as binary pairs. But a analog of the familiar museum icon of nine planets in an orderly, circular series has not been found. Search Konstantin Batygin, et al for scientific reports, and The Way Forward at arXiv:1603.08238 about how studies might proceed as this auspicious finding sinks in.
Prior to the discovery of exoplanets our expectations of their architecture were largely driven by the properties of our solar system. We expected giant planets to lie in the outer regions and rocky planets in the inner regions. Planetary orbits should be circular, prograde and in the same plane. The reality of exoplanets have shattered these expectations. Jupiter-mass, Neptune-mass, Superearths, and even Earth-mass planets can orbit within 0.05 AU of the stars, sometimes with orbital periods of less than one day. Exoplanetary orbits can be eccentric, misaligned, and even in retrograde orbits. This was put on a firm statistical basis with the Kepler mission that clearly demonstrated that there were more Neptune- and Superearth-sized planets than Jupiter-sized planets. These are often in multiple, densely packed systems where the planets all orbit within 0.3 AU of the star, a result also suggested by radial velocity surveys. Exoplanets also exhibit diversity along the main sequence. Giant planets around low mass stars are rare, but these stars show an abundance of small (Neptune and Superearth) planets in multiple systems. We have yet to find a planetary system that is analogous to our own solar system. The question of how unique are the properties of our own solar system remains unanswered. Advancements in the detection methods of small planets over a wide range of orbital distances is needed before we gain a complete understanding of the architecture of exoplanetary systems. (Abstract)
Holmes, Bob. The Goldilocks Planet. New Scientist. March 23, 2019. A science writer makes a case that the presence of a Gaian self-maintaining biosphere should be seen as another major reason why this Earth is uniquely viable in the cosmos. Three properties are here cited that help this to happen – redundancy, diversity, and modularity – along with niche construction, group selection, and more.
As far as we know, Earth is a one-off: there is no population of competing, reproducing planets for natural selection to choose between to form the next generation. And yet, like a superorganism honed by evolution, Earth seems to self-regulate in ways that are essential for life. Oxygen levels have remained relatively constant for hundreds of millions of years, as has the availability of key building blocks of life such as carbon, nitrogen and phosphorus. Crucially, Earth’s surface temperature has remained with the narrow range that allows liquid water to exist. (35)
Hong, Yu-Cian, et al. Innocent Bystanders: Orbital Dynamics of Exomoons during Planet-Planet Scattering. arXiv:1712.06500. We note this entry by Hong, Philip Nicholson, and Jonathan Lunine, Cornell University, and Sean Raymond, University of Bordeaux because, as the Abstract cites, it gives a sense of how involved, chancy and chaotic the formation of long duration, evolutionary bioworlds seems to be. This may be why, we muse, on a statistical basis the universe needs a quintillion candidates so that at least one fittest Earth-like planet might be able to self-discover, realize and select.
Horner, Jonathan, et al. The Influence of Jupiter, Mars and Venus on Earth’s Orbital Evolution. arXiv:1708.03448. Australian and British astroscientists including David Waltham consider still another closely finessed attribute of this solar system which is necessary for an extended benign period of Earth life evolution.
n the coming years, it is likely that the first potentially Earth-like planets will be discovered orbiting other stars. Once found, the characterisation of those planets will play a vital role in determining which will be chosen as the first targets for the search for life beyond the Solar System. One of the plethora of factors to be considered in that process is the climatic variability of the exo-Earths in question. In the Solar System, the Earth's long-term climate is driven by several factors, including the modifying influence of life on our atmosphere, and the temporal evolution of solar luminosity. The gravitational influence of the other planets in the Solar System adds an extra complication, driving the Milankovitch cycles (2nd quote) that are thought to have caused the on-going series of glacial and interglacial periods that have dominated Earth's climate for the past few million years. Our results illustrate how small changes to the architecture of a given planetary system can result in marked changes in the potential habitability of the planets therein, and are an important first step in developing a means by which the nature of climate variability on planets beyond our Solar System can be characterised. (Abstract)
Jones, Barrie. The Search for Life Continued: Planets Around Other Stars. Berlin: Springer, 2008. The Open University astronomer provides a thorough, illustrated guide for the outward quest for animate worlds and entities across the galaxy and cosmos. This endeavor has taken on a new dimension with the ability to search for and detect similar earths orbiting distant suns. Their apparent proliferation provides another good reason that we are not alone and could inspire us earthlings to join in a sustainable initiative and destiny.