III. Ecosmos: A Revolutionary Fertile, Habitable, Solar-Bioplanet, Incubator Lifescape

H. Stellar Planetary Systems: A Diverse Profusion of Galaxies, Solar Orrerys and Habitable Zones

Shields, Aomawa. The Climates of Other Worlds: A Review of the Emerging Field of Exoplanet Climatology. Astrophysical Journal Supplement Series. 243/2, 2019. A UC Irvine astrophysicist adds another important detectable feature for exoplanet searches across near and far Milky Way environs. Just as here, atmospheric weather patterns are a good indicator of relative habitability.

While climate models have often used to analyze and predict climate and weather on Earth, a growing community of researchers has begun to apply relative models to extrasolar planets. This work has provided a better understanding of how orbital, surface, and atmospheric properties affect planetary climate and habitability; how these climatic effects might change for different stellar and planetary environments; and how observational signatures of newly discovered planets might be influenced by these climatic factors. This review summarizes the active field of exoplanet climatology thus far, recent work using a hierarchy of computer models to identify planets most capable of supporting life, and offers a glimpse into future directions for exoplanet science. (Abstract excerpt)

Shorttle, Oliver, et al. Why Geosciences and Exoplanetary Sciences Need Each Other. arXiv:2108.08382. In an article to appear in a special Geoscience Beyond the Solar System issue (17/4) of Elements: An International Magazine of Mineralology, Geochemistry and Petrology, Cambridge University and Southwest Research Institute astrogeologists including Cayman Unterborn contribute to this grand project going forward as our fittest global genius begins to explore and quantify near and farther orbital environs. A glossary from Abiogenesis Zone and Albedo to Tidal Lock and White Dwarf suits the wild frontier. See also Compositional Diversity of Rocky Exoplanets at 2108.08383, and The Diversity of Exoplanets: From Interior Dynamics to Surface Expressions st 2198L09385, for this issue. See Blue Marble, Stagnant Lid: Could Dynamic Topography avert a Waterworld? by this group at 2201.05636 for more considerations.

The study of planets outside our solar system may lead to major advances in our understanding of the Earth, and provide insight into the universal set of rules by which planets form and evolve. To achieve these goals requires applying geoscience's wealth of Earth observations to fill in the blanks left by the necessarily minimalist exoplanetary observations. In turn, Earth's many one-offs, e.g., plate tectonics, surface liquid water, a large moon, and life - which have long presented chicken and egg type conundrums for geoscientists - may find resolution in the study of exoplanets possessing only a subset of these phenomena. (Abstract)

Shostak, Seth. Searching for Smart Life around Small Stars. Astronomy. February, 2014. The SETI Institute astronomer and advocate contends that “red dwarfs” ought to be an especially favorable locale for bioworlds with intelligence. Article illustrations go on to depict a Residential Areas around a G type stars (our sun) and this K type, dubbed No Fry Zones or habitable areas. But by displaying both a planetary band and the host star, one is led to wonder if they altogether are “solar incubator” systems, which would be conceivable from a revolutionary conducive spacescape, heavenly hatchery, vista. See How Did Life Begin? by SS in The Search for Alien Life issue from Scientific American (Summer 2022).

A red dwarf is a small and relatively cool star on the main sequence, either late K or M spectral type. Because of their small size, they burn their fuel slowly, which allows them to live a very long time. (Internet)

Sibony, Yves, et al. The Rotation of Planet-Hosting Stars. arXiv:2204.01421. University of Geneva and University of Zurich researchers perform initial analyses that indicate the presence of whole solar system interactivities between physical stellar forces and nascent orbital worlds.

Simpson, Fergus. An Anthropic Prediction for the Prevalence of Waterworlds. arXiv:1607.03095. As myriad orbital objects of every possible kind are being detected, the University of Barcelona, Institute for Cosmic Sciences, researcher notes that in contrast to a default state of wholly wet or dry surfaces, Earth’s mottled mantle of ocean and land is a rare anomaly. By way of a “planetary fecundity,” life has been able to evolve from primitive rudiments to human observers, thus an anthropic explanation. We include longish quotes to catch the gist, which appends another reason why this home Earth is so uniquely precious.

Should we expect most habitable planets to share the Earth's marbled appearance? Terrestrial planets within the habitable zone are thought to display a broad range of water compositions, due to the stochastic nature of water delivery. Such diversity, taken at face value, implies that the surfaces of most habitable planets will be heavily dominated by either water or land. Convergence towards the Earth's equitably partitioned surface may occur if a strong feedback mechanism acts to regulate the exposure of land. It is therefore feasible that the Earth's relatively balanced division of land and sea is highly atypical amongst habitable planets. We construct a simple model for the anthropic selection bias that may arise from an ensemble of surface conditions. Across a broad class of models we consistently find that (a) the Earth's ocean coverage of 71% can be readily accounted for by observational selection effects, and (b) due to our proximity to the waterworld limit, the maximum likelihood model is one where the majority of habitable planets are waterworlds. This 'Dry Earth' scenario is consistent with results from numerical simulations, and could help explain the apparently low-mass transition in the mass-radius relation. (Abstract)

On a purely statistical basis, one naıvely expects to find a highly asymmetric division of land and ocean surface areas. A natural explanation for the Earth’s equitably partitioned surface is an anthropic selection process. We have highlighted two mechanisms which could be responsible for driving this selection effect. First of all, planets with highly asymmetric surfaces (desert worlds or waterworlds) are likely to produce intelligent species at a much lower frequency. Secondly, planets with larger habitable areas are capable of sustaining larger populations. Both of these factors imply that our host planet has a greater habitable area than most life-bearing worlds. (7) It has been argued that the apparently unique and special properties of the Earth is indicative of the sparsity of life in the Universe - the so-called ‘Rare Earth hypothesis’. However this interpretation fails to account for one of the factors which controls the fecundity: the number of observers produced by each planet. This amplifies the already considerable observational selection effects associated with the emergence of life. The parameters of an observer’s host planet are heavily skewed in favour of those conditions which maximize the abundance of life, not just the probability of its emergence. The apparent fine-tuning of the Earth’s parameters need not reflect the sparsity of life in the cosmos, but on the contrary, it may be driven precisely because we are a small piece within a vast ensemble. (8)

Simpson, Fergus. The Longevity of Habitable Planets and the Development of Intelligent Life. International Journal of Astrobiology. 16/3, 2017. The University of Barcelona cosmologist adds one more qualification for organisms to evolve, develop, proceed so as to reach a stage of global, knowledgeable sentience. It is not so much a “difficult” process as a necessarily “slow” pathway that seems to requires some billion years from microbes to cities to play out.

Why did the emergence of our species require a timescale similar to the entire habitable period of our planet? Our late appearance has previously been interpreted by Carter (2008) as evidence that observers typically require a very long development time, implying that intelligent life is a rare occurrence. Here we present an alternative explanation, which simply asserts that many planets possess brief periods of habitability. We also propose that the rate-limiting step for the formation of observers is the enlargement of species from an initially microbial state. In this scenario, the development of intelligent life is a slow but almost inevitable process, greatly enhancing the prospects of future search for extra-terrestrial intelligence (SETI) experiments such as the Breakthrough Listen project. (Abstract)

Smith, Harrison and Lana Sinapayen. Smith, Harrison and Lana Sinapayen. An Agnostic Biosignature Based on Modeling Panspermia and Terraformation. arXiv:2403.14195. Earth-Life Science Institute, Tokyo Institute of Technology and National Institute for Basic Biology, Okazaki, Japan astroscientists consider novel perceptions that ought to be factored in when it comes to assessing whether bio-friendly worlds have actually been found.

A main goal of astrobiology is to detect life outside of Earth. Our approach shows that as life propagates across the galaxy, correlations emerge between planetary types and location. This biosignature is agnostic because it is independent of assumptions about any particular instantiation. Rather it focuses on a specific hypothesis of what life may do, rather than what life may be. By clustering planets based on their observed properties we propose a way to prioritize specific planets for further observation. We identify various ways in which better understandings of astrophysical and planetary processes would improve our ability to detect life. (Excerpt)

Sramek, Ondrej, et al. Thermal Evolution and Differentiation of Planetesimals and Planetary Embryos. Icarus. 217/339, 2012. Czech, American, and French astrogeologists contribute to Great Earth’s discovery of myriad worlds such as our own across galactic and cosmic celestial ages, could one muse as if a uterine universe. And it is always intriguing in such studies how often gestational imageries are employed.

Stevenson, David and Sean Large. Evolutionary Exobiology: Towards the Qualitative Assessment of Biological Potential on Exoplanets. International Journal of Astrobiology. Online October, 2017. A Carlton le Williams Academy, Nottinghamshire, UK (search DS and the school) biologist and a University of Exeter physics consider this READ nascent exploratory phase of Earthkind’s cosmic census of potential near and far neighbors. A novel parameter of the relative “information density” of planetary life is added, along with tidal-locking from a good moon. See also Evolutionary Exobiology II by D. Stevenson in this journal (July 2018), and his 2017 Springer book The Nature of Life and Its Potential to Survive, which develops this informational essence.

A planet may be defined as habitable if it has an atmosphere and is warm enough to support the existence of liquid water. These are a basic set of conditions that allow it to develop life similar to ours, which is carbon-based and has water as its universal solvent. While this definition can allow a broad range of possibilities, it does not address whether any life forms will become complex or intelligent. In this paper, we seek a qualitative definition of which subset of these ‘habitable worlds’ might develop complex and interesting life forms. We identify two key principles in determining the capacity of life to breach certain transitions on route to developing intelligence. The first is the number of potential niches a planet provides. Secondly, the complexity of life will reflect the information density of its environment, which in turn is influenced by available niches. We use these criteria to place the evolution of terrestrial life in a mathematical framework based on environmental information content. Our model links the development of complex life to the physical properties of the planet, something currently lacking in all evolutionary theory. (Abstract edits)

Stojkovic, Neda, et al. Galactic Habitability Re-Examined: Indications of Bimodality. arXiv:1909.01742. Astronomical Observatory, Belgrade astrophysicists including Milan Cirkovic post an extensive contribution which seeks ways to better to quantify preferential places for living systems to form and evolve. As the quotes allude, this requires factoring in a range of stellar and galactic types, sizes and active shapes. See also Habitability of Galaxies and Application of Merger Trees in Astrobiology at arXiv:1908.05935 and What can Milky Way Analogues Tell us About the Star Formation Rate of Our Own Galaxy? at 1909.01654 for concurrent papers. Again how fantastic is it that homo to anthropo sapiens, phoenix-like out of war zones, can come together and move on to learn about our celestial neighborhood. The paper merits some extended quotes.

The problem of the extent of habitable zones in different kinds of galaxies is one of the outstanding challenges for contemporary astrobiology. In the present study, we investigate habitability in a large sample of simulated galaxies from the Illustris Project in order to at least roughly quantify the hospitality to life of different galactic types. In particular, we find a tentative evidence for a second mode of galactic habitability comprising metal-rich dwarfs similar to IC 225, LMC or M32. The role of the galactic environment and the observation selection effects is briefly discussed and prospects for further research on the topic outlined. (Abstract)

Hence, we have essentially two major views on the habitability of galaxies so far: (i) the conventional view based to a large degree on the “rare Earth” thinking of Gonzalez, Ward, and Brownlee limiting life to large spiral discs analogous to the Milky Way Population I, and (ii) the radical view, emerging since about 2015, that it is mostly quiescent early-type galaxies and dwarfs more similar to the local Population II that are the best abodes for life. Details may vary from study to study, but this dilemma is quickly becoming one of the central issues of astrobiology.(3)

Studies of galactic habitability are obviously in their infancy. There is a large number of galactic properties which may influence the habitability score in ways currently ill-understood, and even those whose influence is somewhat understood (like the mean metallicity or the global star-formation rate in the present study) are still only roughly represented in the models. Thus, we hereby propose an emerging picture of galactic habitability which is bimodal: high-metallicity dwarfs on one hand, and quiescent spiral discs on the other hand, represent the peaks of galactic habitability in the local universe at present. (15)

If the emerging picture is correct, one mode of habitability is based upon the following factors: large galaxies with active star formation, similar to the Milky Way, with habitable planets forming around the Pop I analog stars with high metallicities. This mode is characterized by many different kinds of planetary systems, a high level of chemical evolution and, presumably, easier routes for advancement of prebiotic chemistry in both interstellar/circumstellar medium and on planetary surfaces. Once life appears, however, it is subject to strong abiotic selection pressure of its astrophysical environment in form of frequent irradiations by supernovae and GRBs, perturbations due to the spiral-arm and galactic-plane crossings, higher cosmic-ray fluences, and other astrobiological regulation mechanisms. Part of these perturbing influences may overflow into the “Gaian windows”, which are likely to be shorter for biospheres in the giant spiral systems. (17)

Tamayo, Daniel, et al. A Criterion for the Onset of Chaos in Compact, Eccentric Multiplanet Systems. arXiv:2106.14863. We cite this June entry by Princeton University and University of Toronto astrophysicists including Scott Tremaine and Joshua Winn as another frontier instance whereof whole host star and orbital arrays are being treated as a unified assembly.

We derive a semi-analytic criterion for the presence of chaos in compact, eccentric multiplanet systems. We show that the onset of chaos is due to the overlap of two-body mean motion resonances (MMRs), like it is in two-planet systems and the secular evolution causes the MMR widths to expand and contract. For closely spaced two-planet systems, a near-symmetry suppresses this secular modulation. We make routines for evaluating the chaotic boundary available to the community through the open-source SPOCK package. (Abstract excerpt)

Teixeira, Joana, et al. Where in the Milky Way Do Exoplanets Preferentially Form?.. arXiv:2501.11660.. We note this entry by University of Porto and University of Padova astronomers as an example of the sophisticated extent and degree that our Earthuman astropocene survey as it becomes able to view whole galaxies in our ecosmichood canvas.

Exoplanets are detected around stars of different ages and times within the Galaxy. Our aim is to infer the Galactic birth radii of stars and their planets by projecting them back to their original positions based on an estimated metallicity [Fe/H]. We find that stars hosting planets have higher [Fe/H] and are younger. We show that the formation efficiency of planets decreases with the galactocentric distance, which relationship is stronger for high-mass planets than for low-mass planets. We conclude that the location of exoplanets follows the Galactic chemical evolution. (Excerpt)

Our analysis serves as an initial step toward understanding the galactic aspects of planet formation. With the upcoming PLATO mission, we anticipate a significant increase in both the sample size and, more importantly, the accuracy of age determinations. These advancements will pave the way for a deeper understanding of the connection between stellar populations and planetary systems across the Galaxy. (9)

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