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

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

Weinberger, Alycia. Building Planets in Disks of Chaos. Sky & Telescope. November, 2008. A Carnegie Institution of Washington astronomer explains how the ubiquitous presence of orbiting dust disks can be noticed as a signature of protoplanetary nurseries. (See also in the September S. & T. “Planetary Peculiarities” by Ken Croswell, and “Are Super-Sized Earths the New Frontier” by Ray Jayawardhana in the November 2008 issue of Astronomy.)

Giant collisions, rogue asteroid swarms – planet building is messy and unpredictable, and it sometimes leaves lots of debris. But one way or another, it seems to happen around most stars. (32) But I prefer to think of disks as signals rather than noise. They signal that planetary formation is common. Their constituents may tell us about how planets become hospitable for life. And they are beacons of the long-past era when our Sun came to host a place able to produce astronomers who look out and wonder. (37)

Weiss, Lauren, et al. Architectures of Compact Multi-planet Systems. arXiv:2203.10076. Seven astro-authorities contribute to this presentation to be made at the 2023 Protostars and Planets VII conference in Kyoto, Japan (see below). Some other coauthors are Fred C. Adams, Erik Petigura, and Konstantin Batygin. After a two year –demic hiatus, hopefully our EarthWise scientific endeavors to explore, quantify, describe and learn from this stellar spacescape.can proceed apace. For an earlier view see Peas in a Pod: Planets in a Kepler Multi-planet System are Similar in Size and Regularly Spaced by Lauren Weis, et al at 1706.06204.

One of the most important developments in exoplanet science in the past decade is the discovery of multi-planet systems with sub-Neptune-sized planets. This chapter explores their architectures, which often display a high degree of uniformity of similar sizes, regular orbital spacing, low eccentricities, and small inclinations. We begin with a critical review and find that these peas-in-a-pod planetary systems may be a common outcome of planet formation processes. Stars form along with circumstellar disks with a tendency to produce these planetary systems. In summary, interesting observational and theoretical challenges remain in order to understand how these surprisingly organized planetary systems arise from the relative disorder of their formation processes. (Abstract excerpt)

Taking a step back, we can think of the striking uniformity found in compact multi-planet systems as an example of self organization. In general, any self-organizing system has a primary driving force that acts to create structure and some “counter-force” that acts as a stabilizing influence. In the present context, the peas-in-a-pod architecture typical of compact multis contains close planet masses and regular orbital spacing. With the peas-in-a-pod pattern becoming well-established, the future work needs to identify the driving forces and counter-forces that lead to such interesting planetary systems. (18)

Protostars & Planets VII, twice postponed, this meeting will take place in Kyoto on April 10th – 15th of 2023. This conference series has provided an important opportunity for scientists working on the formation of stars and planets. We would like to have a series of review talks summarizing the development in our field in recent years. The Protostars & Planets Series by the University of Arizona Press will then publish a chapter volume of papers.

Werner, Michael and Michael Jura. Improbable Planets. Scientific American. June, 2009. Werner, chief NASA scientist for the Spitzer Space Telescope, and Jura, a UCLA astronomer, extol the rush of instrumental findings that reveal a new cosmos which proliferates worlds, planetary objects, stars, and solar systems of every possible variety. And on one earth, evidently as if a fertile seed or egg, life and mind evolves and quickens as if a planetary person being born to and exploring its nursery, as a genesis universe begins to witness and imagine itself.

Astronomers hardly expected the ubiquity of planetary systems, their hardiness and the apparent universality of the processes by which they form. (39)

Wiedner, Martina, et al. Origins Space Telescope: From First Light to Life: ESA Voyage 2050 White Paper. arXiv:2012.02731. A 27 member team from the European Space Agency posts their grant proposal which was one of four selected for this international project. It is based on three questions: How does the Universe work?, How did we get here?, Are we alone? And to take a philoSophia view, a nascent worldwise knowledgeable sapience becomes able to recreate and envision the whole vast scenario it arose from. Who are me/We beings that can altogether learn the the galactic baryon cycle? Might our Earthmost home be a fittest, optimum candidate? Here is another instance of a major personsphere transition proceeding to come to her/his own discoveries.

The Origins Space Telescope is one of four science and technology definition studies selected by NASA for the 2020 Astronomy and Astrophysics Decadal survey in the USA. Origins will trace our history from the time dust and heavy elements permanently altered the cosmic landscape to present-day life. It is designed to answer three major science questions: How do galaxies form stars, make metals, and grow their central supermassive black holes from reionization? How do the conditions for habitability develop during the process of planet formation? Do planets orbiting M-dwarf stars support life? (Abstract excerpt)

Winn, Joshua and Daniel Fabrycky. The Occurrence and Architecture of Exoplanetary Systems. arXiv:1410.4199. A chapter to appear by September in the Annual Review of Astronomy and Astrophysics, Volume 53, 2015, by an MIT physicist and a University of Chicago astronomer. This astronomical discovery of a cosmic neighborhood innately filled worlds of every kind was unimaginable before 1995, and a sporadic occurrence before the Kepler 2009 launch. Today a plethora of articles as this describe a radically new planetary nursery being revealed to our Earthly surveillance.

The basic geometry of the Solar System -- the shapes, spacings, and orientations of the planetary orbits -- has long been a subject of fascination as well as inspiration for planet formation theories. For exoplanetary systems, those same properties have only recently come into focus. Here we review our current knowledge of the occurrence of planets around other stars, their orbital distances and eccentricities, the orbital spacings and mutual inclinations in multiplanet systems, the orientation of the host star's rotation axis, and the properties of planets in binary-star systems. (Abstract)

Winter, Andrew, et al. Stellar Clustering Shapes the Architecture of Planetary Systems. Nature. 586/528, 2020. University of Heidelberg and University of Leichester astrophysicists review observational and experimental studies about the ways that solar systems may form and arrange themselves. A propensity for sunny stars to bunch together in groups then becomes a factor with regard to the relative habitability of orbital worlds.

Conclusions:Our results show that stellar clustering is a key factor setting the architectures of planetary systems. This environment represents a fundamental axis along which exoplanetary and atmospheric properties may vary, and which has implications for planetary habitability and the likelihood of life in the Universe. Star formation was likely more clustered in the past, so that an influence on older planetary systems may have been even greater. (532)

wolf, Eric, et al. Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model. arXiv:1702.03315. Astrophysicists from the University of Colorado (Wolf and Owen Toon), UC Irvine (Aomawa Shields), NASA Goddard (Ravi Kopparapu), and Jacob Haqq-Misra (NASA Astrobiology) study which fluidly interactive surface and atmospheric parameters might favor or constrain evolutionary life forms. Thermodynamic forces are seen to cause sharp transitions between certain snowball, waterbelt, temperate, and moist greenhouse states. Radiation, convection, clouds, ocean heat transport, sea ice, and more are implicated in a relative suitability and sustainability. See also, for example Atmospheric Tides in Earth-like Planets by Pierre Auclair-Desrotour, et al in Astronomy & Astrophysics (Online December, 2016).

wood, J. M., et al. Terrestrial planet formation from a ring: long-term simulations accounting for the giant planet instability. arXiv:2404.17259. Université Cote d’Azur, CNRS, Southwest Research Institute, Boulder, CO and University of Toronto astronomers including Alessandro Morbidelli discuss the latest Earthuman studies about how global worlds of all great and small kinds come to form and reside in vicarious solar systems. These origins are not readily revealing themselves so more finesse is required. But one wonders over the whole scenario whence. a collaborative sapiensphere carries out a retrospective task of scientific self-representation. Whom are we all to do this and for what reason?

The process leading to the formation of the terrestrial planet remains elusive. In a previous publication, we have shown that, if the first generation of planetesimals forms in a ring at about 1 AU and the gas disk's density peaks at the ring location, planetary embryos of a few Martian masses can grow. In this work, we extend our simulations beyond the gas-disk stage to account for the phase of giant planet instability. About half of the model forms a pair of Venus and Earth analogues and about 10% form a Mars analogue. The timing of the giant planet instability affects the terrestrial system's excitation state and the last giant impacts. The best-case scenario is that the Moon-forming event occurred between 50 and 80 My. (Excerpt)

Yang, Sheng, et al. The stability of unevenly spaced planetary systems. arXiv:2308.16798. We first post this paper about solar system by seven astrophysicists across China so that it is online. A longer review will follow.

Studying the orbital stability of multi-planet systems is essential to understand planet formation, estimate the stable time of an observed planetary system, and advance population synthesis models. Although previous studies have primarily focused on ideal systems characterized by uniform orbital separations, in reality a diverse range of orbital separations exists among planets within the same system. This study focuses on investigating the dynamical stability of systems with non-uniform separation. We considered a system with 10 planets with masses of 10−7 solar masses around a central star with a mass of 1 solar mass. We conclude that when estimating the orbital crossing time and colliding pairs in a realistic situation, updating the formula derived for evenly spaced systems would be necessary. (Excerpt)

The N-body simulation results are as follows:
• Orbit crossing times become shorter in the case of pairs with shorter initial orbital separations.
• There is a correlation between the closest separation pair and the first close encounter or collision.
• The orbital crossing time for systems with uneven orbital separation could be expressed based on the orbital periods of the closest separation pair. (5)

Zackrisson, Erik, et al. Terrestrial Planets Across Space and Time. arXiv:1602.00690. As a sign of the robust maturity of exoworld studies, Uppsala University, Stockholm University, Carnegie Observatories, and Lund University astronomers achieve a spacescape inventory which includes galaxy formation, cosmological parameters, stellar mass functions, planetary accretion, and so on. See also The Quest for Cradles of Life by Pratika Dayal, et al at 1507.04345 for a “cosmobiological” survey of galaxies.

The study of cosmology, galaxy formation and exoplanetary systems has now advanced to a stage where a cosmic inventory of terrestrial planets may be attempted. By coupling semi-analytic models of galaxy formation to a recipe that relates the occurrence of planets to the mass and metallicity of their host stars, we trace the population of terrestrial planets around both solar-mass (FGK type) and lower-mass (M dwarf) stars throughout all of cosmic history. We find that the mean age of terrestrial planets in the local Universe is 8±1 Gyr and that the typical planet of this type is located in a spheroid-dominated galaxy with total stellar mass about twice that of the Milky Way. When looking at the inventory of planets throughout the whole observable Universe (i.e. in all galaxies on our past light cone) we argue for a total of ≈2×1019 and ≈7×1020 terrestrial planets around FGK and M stars, respectively. Due to the hierarchical formation of galaxies and lookback-time effects, the average terrestrial planet on our past light cone has an age of just 1.7±0.2 Gyr and is sitting in a galaxy with a stellar mass a factor of ≈2 lower than that of the Milky Way. These results are discussed in the context of cosmic habitability, the Copernican principle and the prospects of searches for extraterrestrial intelligence at cosmological distances. (Abstract)

This means, that if Earth had been randomly drawn from the cosmological population of TPs, the most likely outcome would seemingly have been for it not to be located in a Milky Way-type system. This, by itself, indicates a mild violation of the Copernican/mediocrity principle (mild, because our position isn’t extremely improbable), but the balance could potentially be shifted back in favour of disk-dominated galaxies by habitability arguments. This requires that there is a mechanism that reduces the fraction of habitable TPs in spheroid-dominated systems compared to disk-dominated ones. (7)

Zeng, Li, et al. Growth Model Interpretation of Planet Size Distribution. Proceedings of the National Academy of Sciences. 116/9723, 2019. A 16 member team based at Harvard including Dimitar Sasselov provide a good example of how later 2010s exoplanet studies, now an intense global activity (search Astro2020), have begun to identify topological features across an array from rocky asteroids to gas giants. As the Abstract alludes, it is noted again how chancy and rare the presence of just the right size and location might be so to hold a benign atmosphere without becoming all dry or wet. A concurrent entry As Planetary Discoveries Pile Up, a Gap Appears in the Pattern by Rebecca Boyle in Quanta Magazine (May 16, 2019) which links to a similar Astrophysical Journal paper.

The radii and orbital periods of 4,000+ confirmed/candidate exoplanets have been precisely measured by the Kepler mission. The radii show a bimodal distribution, with two peaks corresponding to smaller planets (likely rocky) and larger intermediate-size planets, respectively. While only the masses of the planets orbiting the brightest stars can be determined by ground-based spectroscopic observations, these observations allow calculation of their average densities placing constraints on the bulk compositions and internal structures. However, an important question about the composition of planets ranging from 2 to 4 Earth radii (R⊕) still remains. They may either have a rocky core enveloped in a H2–He gaseous envelope (gas dwarfs) or contain a significant amount of multicomponent, H2O-dominated ices/fluids (water worlds). Planets in the mass range of 10–15 M⊕, if half-ice and half-rock by mass, have radii of 2.5 R⊕, which exactly match the second peak of the exoplanet radius bimodal distribution. (Abstract excerpt)

Zhu, Wei and Subo Dong. Exoplanet Statistics and Theoretical Implications. arXiv:2103.02127. For a paper to appear in the 2021 Annual Review of Astronomy and Astrophysics, Tsinghua University, Beijing and Peking University researchers contribute to this new phase of collective Earthwise studies all about every quantifiable aspect of myriad exo-solar systems. At issue is how they formed by accretive processes, their present arrays by mass/radii forces, and so on. Into the 2020s, a grand initiative opens for our home world, if we can come to our senses in time, to continue the ecosmic question and answer project.

In the last few years, significant advances have been made in understanding the distributions of exoplanet populations and the architecture of planetary systems. We review the recent progress of planet statistics, with a focus on the inner <~ 1 AU region of the planetary system that has been fairly thoroughly surveyed by the Kepler mission. We also discuss the theoretical implications of these statistical results for planet formation and dynamical evolution. (Abstract)

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