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

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

He, Matthias and Lauren Weiss. Inner Planetary System Gap Complexity is a Predictor of Outer Giant Planets. arXiv:2306.08846. University of Notre Dame describe further signs of natural mathematic lineaments which serve to “inform” and arrange whole solar systems. But these 2023 perceptions even more imply and require an intrinsic reality as it arrays, develops and may approach its ecosmic self-witness. See also On the Degree of Dynamical Packing in the Kepler Multi-planet Systems at 2306.12967,

The connection between inner small planets and outer giants is crucial to understand planet formation across a wide orbital range. While Kepler found many close-in multi-planet systems, little is known about giant populations and how they impact the architectures of the inner domain. Here, we use the Kepler Giant Planet Search (KGPS) catalog to study how small transiting planets correlate with outer giant planets. For systems with at least three small transiting planets, their distribution of gap complexity appears to differ between those with an outer giant planet and those without any outer giants. The larger gap complexities of inner systems with an outer giant hints that massive external planets play an important role in the formation and/or disruption of the inner systems. (Excerpt)

Heller, Rene and John Armstrong. Superhabitable Worlds. Astrobiology. Online January, 2014. McMaster University and Weber State University astrophysicists contend that earlier views of “habitable zones” for orbiting planets have been based on our earth alone. Rather a wider sense of where life can accrue by asking what kind of celestial object, such as exomoons, in an increasingly conducive spacescape can be home. A “terrestrial menagerie” is advised that considers many factors as surface area, land to ocean ratio, tectonics, magnetic flux, climate thermostat, panspermia, sun size, biological diversity, atmosphere, orbital dynamics, and so on. By this vista, a number of notable predictions accrue. The initial appearance of life on a planet will serve, as it evolves, to make it even more habitable over time. This inclusive 2013 scenario is seen to refute the 2000 Rare Earth hypothesis whence everything is so chancy that our sentient orb must be the only one in the cosmos.

To be habitable, a world (planet or moon) does not need to be located in the stellar habitable zone (HZ), and worlds in the HZ are not necessarily habitable. Here, we illustrate how tidal heating can render terrestrial or icy worlds habitable beyond the stellar HZ. Scientists have developed a language that neglects the possible existence of worlds that offer more benign environments to life than Earth does. We call these objects "superhabitable" and discuss in which contexts this term could be used, that is to say, which worlds tend to be more habitable than Earth. In an appendix, we show why the principle of mediocracy cannot be used to logically explain why Earth should be a particularly habitable planet or why other inhabited worlds should be Earth-like. Superhabitable worlds must be considered for future follow-up observations of signs of extraterrestrial life. Considering a range of physical effects, we conclude that they will tend to be slightly older and more massive than Earth and that their host stars will likely be K dwarfs. This makes Alpha Centauri B, member of the closest stellar system to the Sun that is supposed to host an Earth-mass planet, an ideal target for searches of a superhabitable world. (Abstract)

Terrestrial planets that are slightly more massive than Earth, that is, up to 2 or 3 M⊕, are preferably superhabitable due to the longer tectonic activity, a carbon-silicate cycle that is active on a longer timescale, enhanced magnetic shielding against cosmic and stellar high-energy radiation, their larger surface area, a smoother surface allowing for more shallow seas, their potential to retain atmospheres thicker than that of Earth, and the positive effects of non-intelligent life on a planet’s habitability, which can be observed on Earth. Higher biodiversity made Earth more habitable in the long term. If this is a general feature of inhabited planets, that is to say, that planets tend to become more habitable once they are inhabited, a host star slightly less massive than the Sun should be favorable for superhabitability. (10)

Hinkel, Natalie, et al. Stellar Characterization Necessary to Define Holistic Planetary Habitability. arXiv:1904.01089. Natalie H., Southwest Research Institute, Irina Kitiashvili, NASA along with Patrick Young and Ben Rackham, ASU propose an Astro2020 Science White Paper to study this vital interrelation. The significant insight is that prior views of planets and stars in separate isolation misses their integral, symbiotic interaction. In regard, a benign sun with an orbital Earth and planets as some manner of incubator-like solar system would be appreciated as the most characteristic cosmic feature.

It is a truism within the exoplanet field that "to know the planet, you must know the star." This pertains to the physical properties of the star (i.e. mass, radius, luminosity, age, multiplicity), the activity and magnetic fields, as well as the stellar elemental abundances which can be used as a proxy for planetary composition. In this white paper, we discuss important stellar characteristics that require attention in upcoming ground- and space-based missions, such that their processes can be understood and either detangled from that of the planet, correlated with the presence of a planet, or utilized in lieu of direct planetary observations. (Abstract)

Hoffmann, Volker, et al. Chaos in Terrestrial Planet Formation. arXiv:1508.00917. University of Zurich astrophysicists describe how planetary bodies seem to be formed by vicarious accretions and collisions. It is shown how that “highly chaotic behavior” can often result in wide variety of orbital arrangements. Companion papers could be Building Massive Compact Planetesimal Disks from the Accretion of Pebbles by John Moriarty and Debra Fischer (arXiv:1507.08215), and The Formation of the Solar System by Suzanne Pfalzner, et al (1501.03101). And for this website, it is amazing that upon a most favorable bioworld, a collaborative worldwide species can quantify and reconstruct how everything came to be.

Howard, Andrew, et al. A Rocky Composition for an Earth-sized Exoplanet. Nature. Online October 30, 2013. As the Abstract explains, in this awesome post-Kepler age, a ten person team including Debra Fischer and Geoffrey Marcy perceive and quantify orbital worlds similar to our own that seem to naturally proliferate around every star and in all galaxies. And we ought to notice how fantastic it is for us humankinder to be able to state into the 21st century that “Planets like Earth are common around Sun-like stars.”

Planets with sizes between that of Earth (with radius R⊕) and Neptune (about 4 R⊕) are now known to be common around Sun-like stars. Most such planets have been discovered through the transit technique, by which the planet's size can be determined from the fraction of starlight blocked by the planet as it passes in front of its star. Measuring the planet's mass-and hence its density, which is a clue to its composition-is more difficult. Planets of size 2-4 R⊕ have proven to have a wide range of densities, implying a diversity of compositions, but these measurements did not extend down to planets as small as Earth. Here we report Doppler spectroscopic measurements of the mass of the Earth-sized planet Kepler-78b, which orbits its host star every 8.5 hours. Given a radius of 1.20 ± 0.09 R⊕ and mass of 1.69 ± 0.41 M⊕, the planet's mean density of 5.3 ± 1.8 g cm−3 is similar to the Earth's, suggesting a composition of rock and iron. (Abstract)

Inutsuka, Shu-ichiro, editor in chief. Protostars & Planets VII. Tempe: University of Arizona Press, 2023. This entry will be about this latest series (search) volume, and the international conference in Japan in April 2023 from which its chapters are drawn. We note, for example, Offner, Stella, et al. The Origin and Evolution of Multiple Star Systems by Stella Offner, et al, Organic Chemistry in the First Phases of Solar-type Protostars by Ceccarelli, Cecilia, Ceccarelli,et al, Architectures of Compact Multi-Planet Systems by Lauren Weiss, et al and Chemical Habitability: Supply and Retention of Life's Essential Elements During Planet Formation by Krijt, Sebastiaan, Krijt, et al. Our EarthMost global and galactic quest picks up again going forward.

Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus and Sulfur (CHNOPS) play key roles in the origin and rise of life on Earth. We begin by citing the CHNOPS budget on Earth, their role in shaping our biosphere, and origins in the Solar Nebula. We then view how these elements are distributed in diverse astrophysical settings, tracing their journeys from synthesis in dying stars to molecular clouds, and onto temperate rocky planets around main sequence stars. (Krijt, S. excerpt)

Jones, Barrie. The Search for Life Continued: Planets Around Other Stars. Berlin: Springer, 2008. The Open University astronomer provides a thorough, illustrated guide to earth’s outward quest for animate neighbors across the galaxy and cosmos. This endeavor has lately taken on a new scope with the ability to search for and detect similar planets orbiting distant suns. Their apparent proliferation provides another good reason that we are not alone. And to gain such a vista for our precious home abode, so egg-like and pregnant in the celestial reaches, could inspire us to join in a common incentive and destiny, therefore choose Earth.

Kaltenegger, Lisa. How to Characterize Habitable Worlds and Signs of Life. Annual Review of Astronomy and Astrophysics. 55/433, 2017. The Cornell University, Carl Sagan Institute astronomer introduces and scopes out a novel field of “comparative planetology” as worldwide collaborations come upon and enter a revolutionary fertile cosmos graced by a profligate propensity to form globular bioworlds and incubator solar systems. Biochemical precursors, protocell rudiments, incipient microbes, and so on hence seem to inherently appear, evolve, wherever they can. An especial feature for initial studies would be signatures of biospheric atmospheres.

The detection of exoplanets orbiting other stars has revolutionized our view of the cosmos. First results suggest that it is teeming with a fascinating diversity of rocky planets, including those in the habitable zone. Even our closest star, Proxima Centauri, harbors a small planet in its habitable zone, Proxima b. With the next generation of telescopes, we will be able to peer into the atmospheres of rocky planets and get a glimpse into other worlds. Using our own planet and its wide range of biota as a Rosetta stone, we explore how we could detect habitability and signs of life on exoplanets over interstellar distances. The discussion on what makes a planet a habitat and how to detect signs of life is lively. This review will show the latest results, the challenges of how to identify and characterize such habitable worlds, and how near-future telescopes will revolutionize the field. For the first time in human history, we have developed the technology to detect potential habitable worlds. (Abstract)

Kaltenegger, Lisa and Zifan Lin. Finding Signs of Life in Transits: High-resolution Transmission Spectra of Earth-Like Planets around FGKM Host Star. Astrophysical Journal Letters. 909/1, 2021. (arXiv:2102.12011) Cornell University astronomers contribute to this frontier field of how to detect and distinguish biosignatures as our exoplanet neighborhood census proceeds apace. Subject topics are high resolution and transmission spectroscopy, atmosphere compositions, observational views, and more as our Earthomo sapience takes up the exploratory task of quantifying and learning all about whom or what might, or may not, be out there. The grand project then feeds back to situate and identify we valiant Earthlings.

Thousands of transiting exoplanets have already been detected orbiting a wide range of host stars, including the first planets that could potentially be similar to Earth. The upcoming Extremely Large Telescopes and the James Webb Space Telescope will enable the first searches for signatures of life in transiting exoplanet atmospheres. Here, we quantify the strength of spectral features that could indicate a similar biosphere on exoplanets orbiting a wide grid of host stars (F0 to M8). In the search for life in the cosmos, transiting planets provide the first opportunity to discover whether or not we are alone, with this database as one of the keys to optimize the search strategies. (Abstract)

Kaltenegger, Lisa, et al. TESS Habitable Zone Star Catalog. Astrophysical Journal Letters. 874/1, 2019. (TESS = Transiting Exoplanet Survey Satellite). We cite this report by Cornell, Lehigh, and Vanderbilt University researchers as an example of an initial EarthKinder cosmic census going forward.

Kane, Stephan. Worlds Without Moons: Exomoon Constraints for Compact Planetary Systems. arXiv:1704.01688. As the rush of Kepler findings and journal reports grow, a San Francisco State University astronomer can study the presence of these companion orbs as they may orbit around a host planet. While in occurrence, moons do not seem to be common. Our Earth, however, is then seen to have a most favorable moon, both in size and placement, which serves to stabilize its oblique tilt and provide tidal currents.

One of the primary surprises of exoplanet detections has been the discovery of compact planetary systems, whereby numerous planets reside within ~0.5 AU of the host star. Many of these kinds of systems have been discovered in recent years, indicating that they are fairly common orbital architecture. Of particular interest are those systems for which the host star is low-mass, thus potentially enabling one or more of the planets to lie within the Habitable Zone of the host star. One of the contributors to the habitability of the Earth is the presence of a substantial moon whose tidal effects can stabilize axial tilt variations and increase the rate of tidal pool formation. Here we explore the constraints on the presence of moons for planets in compact systems based on Hill radii and Roche limit considerations. We apply these constraints to the TRAPPIST-1 system and demonstrate that most of the planets are very likely to be worlds without moons. (Abstract)

Much has been written about the detection of exomoons and their potential habitability. It is also commonly held that the presence of a moon with substantial mass played a key role in Earth’s habitability through obliquity stabilization. Early work by indicated that a moonless Earth would have extreme variations in obliquity resulting in dramatic climate changes. A study by expanded the chaotic obliquity calculations by included the effects of the tidal expansion of the moon. Further simulations demonstrated that the Moon does indeed stabilize the Earth’s obliquity, though not at the previously determined amplitude and thus a moonless Earth does not necessarily preclude habitability. (1)

Kane, Stephen and Dawn Gelino. The Habitable Zone Gallery. Publications of the Astronomical Society of the Pacific. 124/4, 2012. As a good example of how far this project has come, NASA Exoplanet Science Institute researchers post a website that graphically displays a radically revised cosmos filled with as many planets as stars. Some 100 billion worlds are attributed to our Milky Way galaxy alone. While this window has just opened, it begs an imagination of an innately “habitable universe” that seeds itself with myriad brethren and sisteren planetary abodes.

The Habitable Zone Gallery is a new service to the exoplanet community which provides Habitable Zone (HZ) information for each of the exoplanetary systems with known planetary orbital parameters. The service includes a sortable table with information on the percentage of orbital phase spent within the HZ, planetary effective temperatures, and other basic planetary properties. In addition to the table, we also plot the period and eccentricity of the planets with respect to their time spent in the HZ. The service includes a gallery of known systems which plot the orbits and the location of the HZ with respect to those orbits. Also provided are animations which aid in orbit visualization and provide the changing effective temperature for those planets in eccentric orbits. Here we describe the science motivation, the underlying calculations, and the structure of the web site. (Abstract, 323)

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