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

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

Morbidelli, Alessandro, et al. Building Terrestrial Planets. Annual Review of Earth and Planetary Science. 40/251, 2012. Universite de Nice-Sophia Antipolis, Cornell University, Planetary Sciences Institute, Tucson, Universite de Bordeaux, and Southwest Research Institute astrophysicists study how disparate orbiting worlds proceed to agglomerate, coalesce and become gaseous or solidify with various liquid and chemical mantles. Isn’t it amazing then, after billions of years, as brave creatures form a collaborative noosphere, we can reconstruct how their earth, and all kinds of potential neighbors come to be? What for, whatever kind of a cosmos, what such great discovery and resolve awaits?

This article reviews our current understanding of terrestrial planet formation. The focus is on computer simulations of the dynamical aspects of the accretion process. Throughout the review, we combine the results of these theoretical models with geochemical, cosmochemical, and chronological constraints to outline a comprehensive scenario of the early evolution of our solar system. Given that the giant planets formed first in the protoplanetary disk, we stress the sensitive dependence of the terrestrial planet accretion process on the orbital architecture of the giant planets and on their evolution. This suggests a great diversity among the terrestrial planet populations in extrasolar systems. Issues such as the cause for the different masses and accretion timescales between Mars and Earth and the origin of water (and other volatiles) on our planet are discussed in depth. (Abstract)

Mordasini, Christoph, et al. Global Models of Planet Formation. International Journal of Astrobiology. 14/2, 2015. This Exoplanet edition indeed shows how much has been learned in the past few years about a galaxy and cosmos that is now understood as inherently filled with orbital worlds of every possible kind. German, Chinese, and Swiss astronomers can thus propose an initial census of planetary populations. But it is curious that this celestial propensity for solar incubators has not yet been invoked as a cosmic Copernican revolution from a Ptolemaic pointlessness to a natural nursery and heavenly hatchery.

Despite the strong increase in observational data on extrasolar planets, the processes that led to the formation of these planets are still not well understood. However, thanks to the high number of extrasolar planets that have been discovered, it is now possible to look at the planets as a population that puts statistical constraints on theoretical formation models. A method that uses these constraints is planetary population synthesis where synthetic planetary populations are generated and compared to the actual population. The key element of the population synthesis method is a global model of planet formation and evolution. With future global models addressing the geophysical characteristics of the synthetic planets, it should eventually become possible to make predictions about the habitability of planets based on their formation and evolution. (Abstract excerpts)

Moriarty, John and Sarah Ballard. The Kepler Dichotomy in Planetary Disks: Linking Kepler Observables to Simulations of Late-Stage Planet Formation. arXiv:1512.03445. We cite this entry by Yale University and MIT astrophysicists to convey the sophisticated, diverse range of exoplanet and exosolar system studies. Of note is a referral to the Kepler Dichotomy named for optional attractor modes that embryonic orbital worlds may settle into. See also Spin-Orbit Misalignment as a Driver of the Kepler Dichotomy (1607.03999), and A Flat Inner Disk Model as an Alternative to the Kepler Dichotomy in the Q1 to Q16 Planet Population (1702.08126).

NASA's Kepler Mission uncovered a wealth of planetary systems, many with planets on short-period orbits. These short-period systems reside around 50% of Sun-like stars and are similarly prevalent around M dwarfs. Their formation and subsequent evolution is the subject of active debate. In this paper, we simulate late-stage, in-situ planet formation across a grid of planetesimal disks with varying surface density profiles and total mass. We identify mixture models with different primordial planetesimal disk properties that self-consistently recover the multiplicity, period ratio and duration ratio distributions of the Kepler planets.

We draw three main conclusions: (1) We favor a "frozen-in" narrative for systems of short period planets, in which they are stable over long timescales, as opposed to metastable. (2) The "Kepler dichotomy", an observed phenomenon of the Kepler sample wherein the architectures of planetary systems appear to either vary significantly or have multiple modes, can naturally be explained by formation within planetesimal disks with varying surface density profiles. Finally, (3) we quantify the nature of the "Kepler dichotomy" for both GK stars and M dwarfs, and find that it varies with stellar type. While the mode of planet formation that accounts for highly multiplistic systems occurs in 24+/-7% of planetary systems orbiting GK stars, it occurs in 63+/-16% of planetary systems orbiting M dwarfs. (Abstract)

Naeye, Robert. Planetary Harmony. Sky & Telescope. January, 2005. To date 18 multiple-planet extrasolar systems have been found by astronomers, whose orbital properties bring a new dimension to the understanding of solar systems. There seem to be two general types – if Jupiter size planets are too proximate they tend to scatter smaller planets into wide elliptical orbits not conducive for life. But if their spacing is similar to our own solar system, a resonant condition sets in between large and small planets favorable for life and its temporal evolution. See also an article "Pictured at Last?" by Naeye in the August 2005 issue of the same journal which talks about advanced telescopes and computer enhancements which make it a matter of time until exoplanets can be visually seen.

Ollivier, Marc, et al. Planetary Systems: Detection, Formation, and Habitability of Extrasolar Planets. Berlin: Springer, 2009. A profoundly new kind of fertile cosmos is being revealed in our midst as earthkind her/his self proceeds to seek out and find an increasing natural propensity for and presence of orbital worlds.

Otegi, J. F., et al. The Similarity of Multi-Planet Systems. arXiv:2112.07413. We cite this entry by University of Geneva and University of Zurich astronomers because they post an early study of “exoplanet demographics” about inklings that solar systems may take on overall patterns and geometries of size, spacings, and more of their unitary own.

Previous studies using Kepler data suggest that planets orbiting the same star tend to have similar sizes. However, due to the faintness of the stars, only a few of the planets were detected with radial velocity follow-ups. It is yet unknown whether planetary systems indeed behave as "peas in a pod". In this work we explore the radii, masses, densities, and period ratios of orbital planets. We find that planets that are slike in radii could be rather different in mass.

Using a similarity metric defined as distance in logarithmic space, we find that planetary systems tend to be more similar in radius than in mass. This could be linked to the fact that the radius has a greater impact on the density and, hence, on the planetary composition than the mass. We also find a strong correlation between densities of adjacent planets. If the density is the main physical quantity that tends to be similar within a planetary system, it would explain that the stronger similarity in radius than in mass. (9)

Overbye, Dennis. 3 New Planet Are Found, and Their Size, Close to Earth’s, Makes Scientists Think ‘Life'. New York Times. September 1, 2004. Previously the over 120 extrasolar planets found so far have been large, Jupiter-like objects. At a NASA conference in Washington, DC has now been reported the detection of smaller, Neptune or Uranus size worlds. These findings are seen to give much credence to an expected proliferation of earth-like planets as suitable abodes for the evolution of life and intelligence.

The universe looked a little more familiar and friendlier yesterday. (A16)

Overbye, Dennis. A Planetary System That Looks Familiar. New York Times. November 7, 2007. A team led by Debra Fischer of San Francisco State University, which included veteran researcher Geoff Marcy, reports for the first time the detection of a multi-planet solar system. Five worlds have so far been identified by wobbles induced in the star they orbit. Although by such inference not quite of earth size and location, more Venus-like, a life-temperate habitable zone around this sun can be specified. Marcy was interviewed this day by Jim Lehrer on The News Hour where he noted its historic significance which implies that conducive solar systems may abound across the celestial cosmos.

Overbye, Dennis. Cast Adrift in the Milky Way, Billions of Planets, All Alone. New York Times. May 19, 2011. A report on an announcement in Nature (473/349, 2011) by the Microlensing Observations in Astrophysics project, a New Zealand and Japan collaborative, together with the Optical Gravitational Lensing Experiment, based at the University of Warsaw, about new research that appears to reveal a celestial space filled with myriad adrift worlds. These lonely planets may have been ejected from the solar systems that gave them birth, or were only distantly related to a stellar origin. As a consequence, planets are now considered to outnumber stars. A commentary in the same Nature issue by Joachim Wambsganss of Heidelberg University avers: “The implications of this discovery are profound. We have a first glimpse of a new population of planetary-mass objects in our Galaxy.” Whatever might we earthlings make of a prolific, gravid cosmos that seems to seed itself with such ovular orbs?

Overbye, Dennis. From Kepler Data, Astronomers Find Galaxy Filled with More but Smaller Worlds. New York Times. February 27, 2014. A science report the latest findings of a plethora of earth-like planets by international teams who analyze Kepler satellite data. The news is based on several arXiv postings: Marcy, Geoffrey, et al. “Masses, Radii, and Orbits of Small Kepler Planets: The Transition from Gaseous to Rocky Planets” by Geoffrey Marcy, et al (arXiv:1401.4195); Jason Rowe, et al. “Validation of Kepler's Multiple Planet Candidates. III: Light Curve Analysis & Announcement of Hundreds of New Multi-planet Systems” by Jason Rowe, et al (arXiv:1402.6534); and “Validation of Kepler's Multiple Planet Candidates. II: Refined Statistical Framework and Descriptions of Systems of Special Interest” by Jack Lissauer, et al (arXiv:1402.6352).

The result is a deluge of small planets that has tipped the cosmic balance from the giant Jupiter-size worlds that were the earliest discovered to smaller, friendlier worlds. “Small planets from the size of Neptune to Earth make up the majority of the planets in the galaxy,” said Douglas Hudgins, exoplanet program scientist at NASA headquarters. (Overbye)

Conclusions about Planet Composition and Formation: In general, the distribution of planet masses for a given planet radius may be a function of orbital period and the type of host star, stemming from the complex processes of planet formation in a protoplanetary disk. The distribution of planet masses surely depends on planet radius, stellar mass, orbital semi-major axis and eccentricity, and on the chemical and thermodynamic properties of the protoplanetary region where they form. Thus, the measured planet masses and radii here inform only one plane of a multi-dimensional space that characterizes planet properties. (Marcy, et al, 28-29)

Overbye, Dennis. In the Hunt for Planets, Who Owns the Data? New York Times. June 15, 2010. The Kepler satellite search team is said to be holding back the release of findings lest they turn out to be premature and open to misinterpreted, which some have an issue with. But may we add after 15 years and some 500 planets, this epochal discovery of a universe which by its creative propensities is filled with earth-like bio-planets, similar to the 1930s realization of myriad galaxies, ought to be broadly admitted. And maybe inspire a better, wholesome appreciation of our precious home.

On Tuesday, astronomers operating NASA’s Kepler spacecraft will release a list of about 350 stars newly suspected of harboring planets, including five systems with multiple candidate planets. That data could dramatically swell the inventory of alien worlds, which now stands at 461, none of them habitable by the likes of us. Astronomers everywhere, who have been waiting since Kepler’s launch in March 2009 to get their hands on this data, will be rushing to telescopes to examine these stars in the hopes of advancing the grand quest of finding Earthlike planets capable of harboring life out there. (D 1)

Overbye, Dennis. Now in Sight: Far-Off Planets. New York Times. November 11, 2008. A news report on the order of magnitude advances in observational techniques, along with better data and pixel analysis, which are beginning to visually observe remote planetary objects.

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