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PostPosted: Wed Dec 05, 2018 12:44 pm 
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Posts: 259
Solar System Formation in the Context of Extra-Solar Planets

"...The statistics of exo-Jupiters indicate that the Solar System is unusual at the ~1% level among Sun-like stars (or ~0.1% among all stars). But why are we different? ... We identify bifurcation points in planetary system formation. We present a series of events to explain why our Solar System is so weird. Jupiter's core must have formed fast enough to quench the growth of Earth's building blocks by blocking the flux of inward-drifting pebbles. The large Jupiter/Saturn mass ratio is rare among giant exoplanets but may be required to maintain Jupiter's wide orbit. The giant planets' instability must have been gentle, with no close encounters between Jupiter and Saturn, also unusual in the larger (exoplanet) context. Our Solar System system is thus the outcome of multiple unusual, but not unheard of, events. "


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PostPosted: Fri Feb 08, 2019 8:23 am 
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Joined: Sun Jul 06, 2008 1:04 pm
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Location: the Retirement Coast, NSW, Australia
Here's a paper indicating another strike against the likelihood of habitable tide-locked worlds and habitable worlds of low-luminosity stars:

Barnes, R. Mullins, Goldblatt, C., Meadows, V.S.,Kasting, J.F., & Heller, R. "Tidal Venuses: Triggering a Climate Catastrophe via Tidal Heating", Astrobiology. 2013 Mar; 13(3): 225–250

"…we show that terrestrial exoplanets orbiting low-mass stars may be tidally heated at high-enough levels to induce a runaway greenhouse for a long-enough duration for all the hydrogen to escape. Without hydrogen, the planet no longer has water and cannot support life. We call these planets “Tidal Venuses” and the phenomenon a “tidal greenhouse.” Tidal effects also circularize the orbit, which decreases tidal heating. Hence, some planets may form with large eccentricity, with its accompanying large tidal heating, and lose their water, but eventually settle into nearly circular orbits (i.e., with negligible tidal heating) in the habitable zone (HZ)."

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PostPosted: Mon Feb 11, 2019 7:51 pm 
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Occurrence Rates of Planets orbiting FGK Stars: Combining Kepler DR25, Gaia DR2 and Bayesian Inference

"We characterize the occurrence rate of planets, ranging in size from 0.5-16 R⊕, orbiting FGK stars with orbital periods from 0.5-500 days.... For planets with sizes 1-1.75 R⊕ and orbital periods of 237-500 days, we find a rate of planets per FGK star of 0.24 [+0.11/−0.10] (68.3% credible interval). While the true rate of such planets could be lower by a factor of ∼ 2 (primarily due to potential contamination of planet candidates by false alarms), the upper limits on the occurrence rate of such planets are robust to ∼ 10%...."


Speeding past planets? Asteroids radiatively propelled by giant branch Yarkovsky effects

"Understanding the fate of planetary systems through white dwarfs which accrete debris crucially relies on tracing the orbital and physical properties of exo-asteroids during the giant branch phase of stellar evolution. Giant branch luminosities exceed the Sun's by over three orders of magnitude, leading to significantly enhanced Yarkovsky and YORP effects on minor planets...."


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PostPosted: Tue Feb 12, 2019 4:03 pm 
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Tidal Heating and the Habitability of the TRAPPIST-1 Exoplanets

"... We show that TRAPPIST-1d and e can avoid entering a runaway greenhouse state. Planet e is the most likely to support a habitable environment, with Earth-like surface temperatures and possibly liquid water oceans. Planet d also avoids a runaway greenhouse, if its surface reflectance is at least as high as that of the Earth. Planets b and c, closer to the star, have heat fluxes high enough to trigger a runaway greenhouse and support volcanism on the surfaces of their rock layers, rendering them too warm for life. Planets f, g, and h are too far from the star to experience significant tidal heating, and likely have solid ice surfaces with possible subsurface liquid water oceans."


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PostPosted: Sun Feb 17, 2019 3:26 pm 
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A limited habitable zone for complex life

"... We use 1-D radiative-convective climate and photochemical models to circumscribe the Habitable Zone for Complex Life (HZCL) based on known toxicity limits for a range of complex organisms. We find that for CO2 tolerances of 0.005-0.05 bar, the HZCL is only ~20-28% as wide as the traditional [CO2-extended] HZ for a Sun-like star and that CO concentrations may limit complex life throughout the entire HZ of the coolest M dwarfs...."


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