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

H. Prolific ExoWorlds, Galactic Dynamics, Solar Orrerys, Habitable Zones, Biosignatures

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)

Kaspi, Yohai and Adam Showman. Atmospheric Dynamics of Terrestrial Exoplanets over a Wide Range of Orbital and Atmospheric Parameters. Astrophysical Journal. 804/60, 2015. Weizmann Institute and University of Arizona planetary scientists find that exoworld enveloping climates and currents usually form and shift within attractor modes from snow/ice to hot/gaseous. Add the solar orientations, polar angles, and other variables, a precarious instability often appears.

The recent discoveries of terrestrial exoplanets and super-Earths extending over a broad range of orbital and physical parameters suggest that these planets will span a wide range of climatic regimes. Characterization of the atmospheres of warm super-Earths has already begun and will be extended to smaller and more distant planets over the coming decade. The habitability of these worlds may be strongly affected by their three-dimensional atmospheric circulation regimes, since the global climate feedbacks that control the inner and outer edges of the habitable zone including transitions to Snowball-like states and runaway-greenhouse feedbacks depend on the equator-to-pole temperature differences, patterns of relative humidity, and other aspects of the dynamics. Our simulations demonstrate that equator-to-pole temperature differences, meridional heat transport rates, structure and strength of the winds, and the hydrological cycle vary strongly with these parameters, implying that the sensitivity of the planet to global climate feedbacks will depend significantly on the atmospheric circulation. (Abstract excerpts)

Kasting, James. How to Find a Habitable Planet. Princeton: Princeton University Press, 2009. A complete guide by the Penn State University geoscientist that ranges from why our home earth is so fit for life to evidently conducive solar and galactic zones. Four chapters then survey detection methods for orbiting worlds, while a final chapter broaches thoughts on extraterrestrial intelligence.

Kempton, Eliza. Window on a Watery World. Nature. 513/493, 2014. A report on Water Vapour Absorption in the Clear Atmosphere of a Neptune-sized Exoplanet by Jonathan Fraine, et al, in the same issue. While many exoworlds are cloud-covered, for the first time a candidate, HAT-P-11b, has been found which is cloud free so as to allow spectrum analysis of its surface composition. In this case, water molecules have been detected as a good sign that this crucial media for evolving life is widely prevalent.

Kipping, David. Do Planets Remember How They Formed?. arXiv:1709.04987. As a fresh galactic and cosmic expanse becomes prolifically filled with planetary and solar phenomena, our Earthly exploration is entering a new era of quantifying, cataloging, and explaining. Here a Columbia University astronomer (view website) considers entropic histories as a novel way to retrace their evolution. One result is that Extrasolar planetary systems reveal a rich diversity of architectures, most of which do not directly resemble our own by way of planet-metallicities, mutual inclinations, orbital eccentricities, host star correlations, and more.

One of the most directly observable features of a transiting multi-planet system is their size-ordering when ranked in orbital separation. Kepler has revealed a rich diversity of outcomes, from perfectly ordered systems, like Kepler-80, to ostensibly disordered systems, like Kepler-20. Under the hypothesis that systems are born via preferred formation pathways, one might reasonably expect non-random size-orderings reflecting these processes. However, subsequent dynamical evolution, often chaotic and turbulent in nature, may erode this information and so here we ask - do systems remember how they formed? To address this, we devise a model to define the entropy of a planetary system's size-ordering, by first comparing differences between neighboring planets and then extending to accommodate differences across the chain. We find that the observed Kepler multis display a highly significant deficit in entropy compared to a randomly generated population. Put together, our work establishes that Kepler systems do indeed remember something of their younger years and highlights the value of information theory for exoplanetary science. (Abstract excerpts)

Knezevic, Zoran and Andrea Milani, eds. Dynamics of Populations of Planetary Systems. Cambridge: Cambridge University Press, 2005. Proceedings of an IAU Colloquium held in Belgrade, September 2004, noted as an example of our breakthrough ability to detect extrasolar systems and planets – then some 150, by November 2008 over 300 of all kinds and sizes. Surely an earthwide, collaborative endeavor as we instrument and scan the skies with an intuition of a life-conducive cosmos filled with neighbors and cousins.

Knezevic, Zoran and Anne Lemaitre, eds. Complex Planetary Systems. Cambridge: Cambridge University Press, 2015. This volume 310 in the International Astronomical Union IAU symposium series contributes to the nascent scientific project to explore a novel profligate universe which seeds and fills itself with all manner of potentially life-bearing orbital worlds. Typical papers are Dynamic Study of Possible Host Stars for Extrasolar Planetary Systems and The Grand Tack Model: A Critical Review.

IAU Symposium 310 takes a broad look at the complexity of planetary systems, in terms of the formation and dynamical evolution of planets, their satellites, minor bodies and space debris, as well as to the habitability of exoplanets, in order to understand and model their physical processes. The main topics covered are diverse, including: studies of the rotation of planets and satellites, including their internal structures; the long term evolution of space debris and satellites; planetary and satellite migration mechanisms; and the role of the Yarkovsky effect on the evolution of the rotating small bodies. Intended for researchers and advanced students studying complex planetary systems, IAU S310 appeals to non-specialists interested in problems such as the habitability of exoplanets, planetary migration in the early Solar System, or the determination of chaotic orbits.

Kouvenhoven, M. B. N, et al. Planetary Systems in Star Clusters. arXiv:1609.00898. After two decades of scientific realizations of a radically different cosmos that fills itself with planetary objects of all manner of types, sizes and stellar locales, a team of astrophysicists with joint Chinese and Dutch postings add another observation of how our own sun system is uniquely special. Most stars, as also galaxies, actually tend to collect and bunch together, so that planets in these jumbled environs are not in circular orbits but “scatter and disperse” widely.

Thousands of confirmed and candidate exoplanets have been identified in recent years. Consequently, theoretical research on the formation and dynamical evolution of planetary systems has seen a boost, and the processes of planet-planet scattering, secular evolution, and interaction between planets and gas/debris disks have been well-studied. Almost all of this work has focused on the formation and evolution of isolated planetary systems, and neglect the effect of external influences, such as the gravitational interaction with neighbouring stars. Most stars, however, form in clustered environments that either quickly disperse, or evolve into open clusters. Under these conditions, young planetary systems experience frequent close encounters with other stars, at least during the first 1-10 Myr, which affects planets orbiting at any period range, as well as their debris structures. (Abstract)

Kovacs, Tamas. Recurrence Network Analysis of Exoplanetary Observables. . We cite this entry by an Eotvos University, Budapest physicist as an example of how network complexity researchers are beginning to detect and quantify an intrinsic, independent, self-organizing mathematics which seems to apply even to the cosmic realm of dynamic solar systems.

Recent advancements of complex network representation among several disciplines motivated the investigation of exoplanetary dynamics by means of recurrence networks. We are able to recover different dynamical regimes by means of various network measures obtained from synthetic time series of a model planetary system. The framework of complex networks is also applied to real astronomical observations acquired by recent state-of-the-art surveys. The outcome of the analysis is consistent with earlier studies opening new directions to investigate planetary dynamics.

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