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PostPosted: Fri May 11, 2018 2:17 pm 
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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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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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PostPosted: Thu Jun 14, 2018 1:20 pm 
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Posts: 233
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: 233
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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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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PostPosted: Thu Jul 12, 2018 1:17 pm 
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Giant planet effects on terrestrial planet formation and system architecture

"...We find a correlation between the mass of the exterior giant planets and the collision history of the resulting planets, which holds implications for the planet's properties. More massive giants also produce terrestrial planets that are on smaller, more circular orbits. We do not find a strong correlation between exterior giant planet mass and the number of Earth-analogs (analogous in mass and semi-major axis) produced in the system."


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PostPosted: Tue Jul 17, 2018 2:39 am 
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The Inner Solar System's Habitability Through Time

"Earth, Mars, and Venus, irradiated by an evolving Sun, have had fascinating but diverging histories of habitability. Although only Earth's surface is considered to be habitable today, all three planets might have simultaneously been habitable early in their histories.

We consider how physical processes that have operated similarly or differently on these planets determined the creation and evolution of their atmospheres and surfaces over time. These include the geophysical and geochemical processes that determined the style of their interior dynamics and the presence or absence of a magnetic field; the surface-atmosphere exchange processes that acted as a source or sink for atmospheric mass and composition; the Sun-planet interactions that controlled escape of gases to space; and the atmospheric processes that interacted with these to determine climate and habitability. The divergent evolutions of the three planets provide an invaluable context for thinking about the search for life outside the Solar System."

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PostPosted: Thu Jul 19, 2018 2:24 pm 
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Evolution of Earth-like extrasolar planetary atmospheres: Assessing the atmospheres and biospheres of early Earth analog planets with a coupled atmosphere biogeochemical model

"... In this work, we present results from our newly developed Coupled Atmosphere Biogeochemistry model in which atmospheric O2 concentrations are fixed to values inferred by geological evidence...."

Edit to add (by the same authors):

Evolution of Earth-like planetary atmospheres around M-dwarf stars: Assessing the atmospheres and biospheres with a coupled atmosphere biogeochemical model

"...this is the first study to our knowledge which applies an automated chemical pathway analysis quantifying the production and destruction pathways of O2 for an Earth-like planet with an Archean O2 abundance orbiting in the habitable zone of the M-dwarf AD Leo. ... the net primary productivity (NPP) required to produce the same amount of atmospheric O2 at the surface is reduced. This implies that a possible Great Oxidation event, analogous to that on Earth, would have occurred earlier in time in analog atmospheres around M-dwarfs."


Last edited by thrash on Sat Aug 04, 2018 12:03 am, edited 2 times in total.

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PostPosted: Thu Jul 26, 2018 1:37 pm 
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A more comprehensive habitable zone for finding life on other planets

"... Here, I review the planetary and stellar processes considered in both classical and newer HZ formulations...."


Chemistry During the Gas-rich Stage of Planet Formation

"In this chapter [of the Handbook of Exoplanets] we outline some of the basic understanding of the chemistry that accompanies planet formation. We discuss the basic physical environment which dictates the dominant chemical kinetic pathways for molecule formation...."


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