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PostPosted: Wed Jul 15, 2020 1:03 am 
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Posts: 323
The New Generation Planetary Population Synthesis (NGPPS). I. Bern global model of planet formation and evolution, model tests, and emerging planetary systems

"... We have developed a combined global planetary formation and evolution model that solves as directly as possible the underlying differential equations for the structure and evolution of the gas disc, the dynamical state of the planetesimals, the internal structure of the planets yielding their gas accretion rate and internal structure, the accretion rate of planetesimals, disc-driven orbital migration, and the gravitational interaction of concurrently forming planets via a full N-body calculation. Importantly, the model now also follows the long-term evolution of the planets on Gigayear timescales after formation including the effects of cooling and contraction, atmospheric escape, bloating, and stellar tides...."


The New Generation Planetary Population Synthesis (NGPPS). II. Planetary population of solar-like stars and overview of statistical results

"We want to understand the global observable consequences of different physical processes and the initial system properties on the demographics of the planetary population. We select distributions of initial conditions that are representative of known protoplanetary discs and we use the Bern model to synthesise five planetary populations around 1 Sun-mass stars. Each population has a different initial number of Moon-mass embryos per disc to test for convergence: 1, 10, 20, 50, and 100. The last one is our nominal planetary population...."


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PostPosted: Thu Aug 13, 2020 12:55 pm 
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Effects of Flux Variation on the Surface Temperatures of Earth-like Circumbinary Planets

"The Kepler Space telescope has uncovered around thirteen circumbinary planets (CBPs) that orbit a pair of stars and experience two sources of stellar flux. We characterize the top-of-atmosphere flux and surface temperature evolution in relation to the orbital short-term dynamics between the central binary star and an Earth-like CBP analog. We compare the differential evolution of an Earth-like CBP's flux and surface temperature with that of an equivalent single-star (ESS) system to uncover the degree by which the potential habitability of the planet could vary. For a Sun-like primary, we find that the flux variation over a single planetary orbit is greatest when the dynamical mass ratio is ~0.3 for a G-K spectral binary. Using a latitudinal energy balance model, we show that the ice-albedo feedback plays a substantial role in Earth-like CBP habitability due to the interplay between flux redistribution (via obliquity) and changes in the total flux (via binary gyration). We examine the differential evolution of flux and surface temperature for Earth-like analogs of the habitable zone CBPs (4 Kepler and 1 hypothetical system) and find that these analogs are typically warmer than their ESS counterparts."


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PostPosted: Wed Sep 02, 2020 1:10 pm 
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Habitable Zones in Binary Star Systems: A Zoology

"Several concepts have been brought forward to determine where terrestrial planets are likely to remain habitable in multi-stellar environments. Isophote-based habitable zones, for instance, rely on insolation geometry to predict habitability, whereas Radiative Habitable Zones take the orbital motion of a potentially habitable planet into account. Dynamically Informed Habitable Zones include gravitational perturbations on planetary orbits, and full scale, self consistent simulations promise detailed insights into the evolution of select terrestrial worlds. All of the above approaches agree that stellar multiplicity does not preclude habitability. Predictions on where to look for habitable worlds in such environments can differ between concepts. The aim of this article is to provide an overview of current approaches and present simple analytic estimates for the various types of habitable zones in binary star systems."


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PostPosted: Fri Sep 04, 2020 1:03 pm 
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The High-Energy Radiation Environment Around a 10 Gyr M Dwarf: Habitable at Last?

"High levels of X-ray and UV activity on young M dwarfs may drive rapid atmospheric escape on temperate, terrestrial planets orbiting within the liquid water habitable zone. However, secondary atmospheres on planets orbiting older, less active M dwarfs may be stable and present more promising candidates for biomarker searches. We present new HST and Chandra observations of Barnard's Star (GJ 699), a 10 Gyr old M3.5 dwarf, acquired as part of the Mega-MUSCLES program...."

(Mostly for the Traveller relevance.)


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PostPosted: Thu Oct 29, 2020 12:52 pm 
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The Occurrence of Rocky Habitable Zone Planets Around Solar-Like Stars from Kepler Data

"We present occurrence rates for rocky planets in the habitable zones (HZ) of main-sequence dwarf stars based on the Kepler DR25 planet candidate catalog and Gaia-based stellar properties. We provide the first analysis in terms of star-dependent instellation flux, which allows us to track HZ planets. We define η⊕ as the HZ occurrence of planets with radius between 0.5 and 1.5 R⊕ orbiting stars with effective temperatures between 4800 K and 6300 K. We find that η⊕ for the conservative HZ is between 0.37+0.48−0.21 (errors reflect 68% credible intervals) and 0.60+0.90−0.36 planets per star, while the optimistic HZ occurrence is between 0.58+0.73−0.33 and 0.88+1.28−0.51 planets per star. These bounds reflect two extreme assumptions about the extrapolation of completeness beyond orbital periods where DR25 completeness data are available. The large uncertainties are due to the small number of detected small HZ planets. We find similar occurrence rates using both a Poisson likelihood Bayesian analysis and Approximate Bayesian Computation. Our results are corrected for catalog completeness and reliability. Both completeness and the planet occurrence rate are dependent on stellar effective temperature. We also present occurrence rates for various stellar populations and planet size ranges. We estimate with 95% confidence that, on average, the nearest HZ planet around G and K dwarfs is about 6 pc away, and there are about 4 HZ rocky planets around G and K dwarfs within 10 pc of the Sun."


An Integrated Analysis with Predictions on the Architecture of the tau Ceti Planetary System, Including a Habitable Zone Planet

"tau Ceti is the closest single Sun-like star to the solar system and hosts a multi-planet system with four confirmed planets. ... Our analysis suggests the presence of four additional planets, three of which match closely with the periods of three tentative planet candidates reported previously. We also predict at least one more planet candidate with an orbital period between ∼270−470 days, in the habitable zone for tau Ceti. ... The least massive planets and candidates are likely to be rocky, while the other planets and candidates could either be rocky or contain a significant gaseous envelope. The RV observable signature from the predicted habitable zone planet candidate would likely be at or just above the noise level in current data, but should be detectable in future extremely high-precision radial velocity and direct imaging studies. "


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