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PostPosted: Fri May 11, 2018 2:17 pm 
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Posts: 227
A Methane Extension to the Classical Habitable Zone

"... We use a single column radiative-convective climate model to assess the greenhouse effect of CH4 (10 to about 100,000 ppm) on the classical habitable zone (N2-CO2-H2O) for main-sequence stars with stellar temperatures between 2,600 to 10,000 K (about A3 to M8). ... We show that 10% CH4 can increase the width of the classical HZ of the hottest stars (TEFF = 10,000 K) by over 20%. In contrast, the CH4 anti-greenhouse can shrink the HZ for the coolest stars (TEFF = 2,600 K) by a similar percentage. ... We parameterize the limits of this N2-CO2-H2O-CH4 habitable zone and discuss implications in the search for extraterrestrial life."


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PostPosted: Mon May 21, 2018 1:01 pm 
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Long Term Planetary Habitability and the Carbonate-Silicate Cycle

"...We develop a model incorporating key aspects of Earth's short and long-term biogeochemical carbon cycle to explore the potential changes in the CO2 greenhouse due to variance in planet size and stellar insolation. We find that proposed changes in global topography, tectonics, and the hydrological cycle on larger planets results in proportionally greater surface temperatures for a given incident flux. For planets between 0.5 to 2 R_earth the effect of these changes results in average global surface temperature deviations of up to 20 K, which suggests that these relationships must be considered in future studies of planetary habitability."


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PostPosted: Mon May 21, 2018 11:42 pm 
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Joined: Sun Jul 06, 2008 1:04 pm
Posts: 1055
Location: the Retirement Coast, NSW, Australia
thrash wrote:

Excellent! The effect of the carbonate-silicate cycle in stabilising planetary temperatures in the liquid-water band is an important factor in increasing the the number of habitable planets , and I am very glad to have a quantitative fix on it.

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My SFRPG setting, Flat Black

© My posts on SFRPG must not be reproduced beyond the board except with explicit permission from me.


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PostPosted: Thu Jun 14, 2018 1:20 pm 
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Posts: 227
The Atmosphere

"These notes contain everything necessary to run a flipped course on "The Atmosphere" at an introductory undergraduate level. There are notes for the students to read before each course meeting and problems for them to work on in small groups during course meetings. Topics include (1) atmospheric composition, structure, and thermodynamics; (2) solar and terrestrial radiation in the atmospheric energy balance; (3) atmospheric dynamics and circulation. I include 10 problem sets, four practice midterms, and two practice finals. Problems are drawn from the atmospheres of modern and past Earth, solar system planets, and extrasolar planets...."


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PostPosted: Fri Jun 15, 2018 2:28 pm 
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Posts: 227
Formation of Giant Planets

"This Chapter [in the Handbook of Exoplanets] describes the principal route that, according to current knowledge, can lead to the formation of giant planets, the core nucleated accretion model, and an alternative route, the disk instability model, which may lead to the formation of planetary-mass objects on wide orbits."


A dynamical origin for planets in triple star systems

"Here, we explore the possibility that planets in triples are formed as a consequence of the dynamical interactions of binaries in star clusters. Our simulations show that the probability of forming triple star systems with a planet is in the range 0.5−3%, potentially accounting for most of the observed population."


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PostPosted: Mon Jun 18, 2018 5:04 pm 
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Posts: 227
Photochemistry beyond the red limit in chlorophyll f–containing photosystems

"... Chlorophyll a photochemistry, using red light (680 to 700 nm), is near universal and is considered to define the energy “red limit” of oxygenic photosynthesis. We present biophysical studies on the photosystems from a cyanobacterium grown in far-red light (750 nm). ... These photosystems function beyond the red limit using far-red pigments in only a few key positions."

In other words, photosynthetic life-as-we-know-it may be possible on worlds previously considered too dim (such as Mars) or with light too red (such as red dwarf stars).


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