Runaway and moist greenhouse atmospheres and the evolution of Earth and Venus

“Rayleigh scattering by water was also considered by Kasting (1988); Kasting et al. (1993), but these authors used the scattering coefficient for air because the coefficient for H2O was not available, or at least not known to them.”

“Although it is difficult to be quantitative, primarily because of uncertainties in cloud prediction, it is clear that this point is only achieved for temperatures that are far warmer than any relevant for the global warming debate (22).”

“This cooling process requires millions to tens of millions of years (Abe & Matsui 1986; Matsui & Abe 1986; Kasting 1988; Zahnle et al. 1988; Elkins-Tanton 2008, 2011).”

“The insulating atmosphere produces a surface temperature that remains above the solidus of the magma ocean liquids through N95% of the solidification process, maintaining a liquid surface to the planet, as similarly calculated by Abe (1997) and Kasting (1988) .”

“Many papers have explored the effects of a runaway greenhouse on Venus, arguing that it may have lost one or more Earth oceans of water as a consequence of an early runaway (Kasting et al. , 1984; Kasting, 1988; Chassefie`re, 1996a, 1996b; Kulikov et al. , 2006; Gillmann et al. , 2009).”

“Planets with magmas at the surface cool extremely quickly, even in the presence of an atmosphere (Abe, 1993, 1997; Abe and Matsui, 1985, 1986; Elkins-Tanton, 2008; Kasting, 1988).”

“Nonbiologi-cal oxygen might also become apparent on a hot planet undergoing a catastrophic greenhouse conversion (Kasting, 1988).”

“This is larger than the so-called “con uously habitable zone” (CHZ) defined as the semimajor realm for which a planet’s mean surface temperature wil above the water melting point, but not so high as to allow l of water by evaporation and subsequent photolysis (Kas et al., 1993; Kasting, 1988).”

“This was done previously by using a 1D radiative-convective model (Kasting 1988).”

“If the effective temperature of a planetary surface exceeds certain values, set by the energy received from its star and the greenhouse effect caused by the gases present in its atmosphere, then the water on the planet will evaporate at sufficient levels to supply the upper atmosphere with a moist greenhouse effect (K…”

“Water clouds would therefore have a weak greenhouse effect in this regime (Kasting 1988), but may significantly increase planetary albedo (Selsis et al. 2007; Kaltenegger et al. 2011).”

“We do not take into account water loss during giant impacts (Genda & Abe 2005; Canup & Pierazzo 2006) or via hydrodynamic escape (Matsui & Abe 1986; Kasting 1988).”

“6) set by the physical and optical properties of water (Kasting 1988; Abe 1988).”

“The globally atmosphere, increasing its greenhouse effect and possibly averaged water vapor concentration in such an atmosphere even raising T0 to the point where liquid water is once might then be expected to be far lower than purely onemore stable (Kasting 1988).”

“The prevailing theory for the formation of the Moon suggests that the Moon was created when a large (roughly Mars-sized) impactor hit the young Earth [Hartmann and Davis, 1975; Cameron and Ward , 1976; Canup, 2004], requiring the accumulation of a significant amount of material before the impact.”

“equivalent of 4 − 525 meters of liquid water if spread evenly across its surface [Donahue & Russell 1997], while the idea of an ancient Venus with oceans is hardly new [e.g. Kasting et al. 1984, Kasting 1988, Grinspoon & Bullock 2003]. At the same time, some planet formation scenarios for Venus-type objects cl…”

“…photochem build-up of O2 (Selsis et al., 2002): (i) CO2-rich atmospheres:PCO2 > 50 mbar for dry atmospheres,PCO2 > 0.5 bar for wet atmospheres, and (ii) water-rich atmospheres loosing hydrogen to space after H2O photolysis (for instance during a runaway greenhouse effect as describ Kasting, 1988).”

“Throughincrea-ses in stratospheric humidity, warming may also cause evaporative loss of the oceans to space before the runaway greenhouse state occurs 5,6 .”

“10; stratospheric water for aqua planets is taken from two competing non-gray one-dimensional radiative-convective models of the runaway greenhouse effect (Kasting, 1988; Abe and Matsui, 1988).”

“Note that the limit of condensation of water vapor obtained in our case is closer from Venus compared to previous work (grey line) [ Abe and Matsui , 1988; Kasting , 1988].”

“At that point, neglecting the effects of solar irradiance changes on the cloud cover, the water vapour content of the atmosphere will increase substantially and the oceans will start to evaporate (Kasting 1988).”

“Firstly, the ‘waterloss’ (or ‘moist greenhouse’ limit’) (Kasting, 1988) occurs where the planet’s entire ocean reservoir is lost via diffusion-limited escape within the lifetime of the planet (originally estimated to occur at = 0.95 AU for Earth (Kasting et al., 1993) and more recently at 0.99 AU…”

“This can happen if other gases are scarce (Wordsworth and Pierrehumbert 2013), or the planet could enter a “moist greenhouse” state (Kasting 1988; Kasting et al. 2015; Leconte et al. 2013a; Wolf and Toon 2015).)”

“(A11) as before.tures exceed p360 K, and the stratospheric H2O mixing ratio becomes large (Kasting 1988).”

“It is easier to understand how this process works by examining a somewhat simpler calculation described by Kasting (1988), the results of which are summarized in Fig.”

“Not to be confused with an ocean planet for which, in addition, water must represent a significant fraction of the bulk mass (Léger et al. 2004). equilibrium balance and is heated until the surface can radiate at optical wavelength around a temperature of 1400 K (Kasting et al. 1984; Kasting 1988).”

“Extensive atmospheric O2 buildup due to H2O photolysis followed by H escape may also occur on planets that enter a runaway greenhouse state (Ingersoll 1969; Kasting 1988; Leconte et al. 2013).”

“…intensity of the magnetic field, solar wind erosion, each of which has clearly played a role on atmosphere evolution (Pepin, 2006; Lammer et al., 2008; Raymond et al., 2004; Chassefiere et al., 2012; Jakosky and Phillips, 2001; Kasting, 1988; Kasting and Catling, 2003; Wordsworth et al., 2013).”

“Shaviv (2003) suggested a link between the cosmic ray flux and average global temperatures on Earth.”

“A good example is a planet interior to the habitable zone that loses its water by way of a runaway or moist greenhouse (Kasting 1988, 1997, 2010; Wordsworth & Pierrehumbert 2013).”

“H 2 O photodissociation and H escape might have provided oxygen to the Hadean Earth, as water vapor can reach the upper atmosphere during magma ocean conditions (Kasting, 1988), subsequent to giant impacts.”

“On Venus, these clouds are even more reflective than surface ice, and with an albedo of 0.75, 581g would only absorb 56 W m −2 averaged over the surface.”

“The results are almost identical to those in Kasting (1988), demonstrating that the inclusion of the non-ideality terms discussed in Section 2 makes little difference to the results for this range of surface pressures.”

“…in such scenarios, the hypothetical wet and “habitable” Venus, approaches at some time a moist stage and a runaway greenhouse effect finally transforms the planet to an extremely hot and dry body with growing solar luminosity (e.g., Rasool and de Bergh 1970; Kasting 1988; Salvador et al. 2017).”

“For Earth’s present inventory of water, a runaway greenhouse would have a surface pressure of several hundred bars and surface temperatures well in excess of the critical temperature for water [Kasting, 1988].”

“Water is now absent from the atmosphere of Venus, but it may have been present earlier and removed by a runaway greenhouse effect (Rasool & De Bergh 1970; Kasting 1988).”

“This elevated D/H ratio could result from H2O photolysis following ocean evaporation, with preferential loss of hydrogen to space compared to the twice-heavier deuterium (e.g., Donahue et al. 1982; Kasting 1988; Donahue & Russell 1997).”

“…results from the differing amount of Rayleigh scattering in the ELP atmospheres (which is greatest where there is the most incident blue parent starlight) and from the greater atmospheric absorption by water vapour (see Appendix B of Kasting 1988) at near-infrared as opposed to visible wavelengths.”

“Ideal gas behavior was assumed when calculating the dry adiabat, which is a reasonable approximation for the range of temperatures and pressures studied (Kasting 1988; Wordsworth et al. 2013).”

“Photolysis of the unprotected H2O and the subsequent loss of hydrogen to space would allow atmospheric O2 to accumulate (Ingersoll, 1969; Kasting, 1988).”

“Matsui and Abe (1986) and Kasting (1988) showed that if Earth and Venus had the same starting water content, Venus would lose most of its water post-accretion via hydrodynamic escape during a post-collision, hot water vapor atmosphere phase.”

“…water content, acquired via collisions with material originating beyond the ”water line” at 0.29 AU, but note that the effects of water depletion during impacts (Genda & Abe 2005; Canup & Pierazzo 2006) and hydrodynamic escape (Matsui & Abe 1986; Kasting 1988) have not been accounted for.”

“Previous work suggested that early Venus was close to the threshold for a runaway greenhouse[9]—our new lower radiation limit and enhanced solar absorption imply that, given the same amount of nitrogen in the atmosphere as Earth, Venus may not have had a habitable period.”

“…case, the inner edge of the HZ is restricted by the runaway greenhouse effect and/or escape of water from the atmosphere (e.g., Rasool & de Bergh 1970; Hart 1978; Abe & Matsui 1988; Kasting 1988; Leconte et al. 2013; Wolf & Toon 2015; Ribas et al. 2016; Bolmont et al. 2017; Kopparapu et al. 2017).”

“The Venusian and Martian atmospheres are enriched by a factor of 150 and 6, respectively, in D/H relative to that of Earth (1), suggesting water on Venus was almost entirely lost early in its evolution (74).”

“…stable liquid surface water through the runaway or moist greenhouse processes [Ingersoll, 1969; Kasting and Pollack, 1983; Kasting et al., 1984; Kasting, 1988; Goldblatt and Watson, 2012; Goldblatt et al., 2013] is expected to operate interior to the inner edge of the habitable zones of…”

“A planet with a strong greenhouse effect could be hot enough to enter a moist greenhouse state, where dissociation of water in the upper atmosphere and hydrogen escape to space leads to rapid water loss (e.g. Kasting 1988; Abbot et al. 2012).”

“in the form of sedimenting aerosols that will take the place of, or even adsor”

“eres have finite lifetimes, because once the upper atmosphere becomes water-rich, the water can be lost in a few tens of millions of years by photodissociation followed by escape of hydrogen to space [18,19]. However, a planet can also lose its water to space at much lower temperatures. Once the surface temperature ex…”

“Values for F crit from the literature are typically 285 W m - 2 to 310 W m - 2 for a 1 M Earth planet (Pollack, 1971; Watson et al., 1984; Abe and Matsui, 1988; Kasting, 1988; Pierrehumbert, 2010).”

“High stellar fluxes during planetary accretion can prove detrimental to volatile retention, particularly when insolation levels exceed the runaway greenhouse threshold (see Figure 2, Kasting 1988; Abe & Matsui 1988; Goldblatt et al. 2013; Ramirez et al. 2014).”

“Venus is at the inner edge of the stellar HZ and has undergone a runaway greenhouse effect (Walker 1975; Kasting 1988) that vaporized any past oceans (Hasimoto et al .”

“The critical, orbit-averaged energy flux for an exomoon to turn into a runaway greenhouse is around 300W/m2, depending on the moon’s surface gravity and atmospheric composition (Kasting 1988; Kasting et al. 1993; Selsis et al. 2007; Pierrehumbert 2010; Goldblatt & Watson 2012).”

“4!10(21) l, liquid water can persist at temperatures up to the critical point, 374 8C (Kasting 1988), or even higher if the effects of salinity are taken into account.”

“Second-generation models that greatly improved on the radiative transfer in runaway and near-runaway greenhouse atmospheres were developed independently by Kasting (1988) and Abe & Matsui (1988).”

“Still, desiccation of exoplanets with liquid water by the runaway greenhouse mechanism (Ingersoll, 1969; Kasting and Pollack, 1983; Kasting et al., 1984b; Kasting, 1988; Goldblatt and Watson, 2012; Goldblatt et al., 2013) is likely a common process.”

“Only the top of the atmosphere—where pressures are less than a few 10ths of a bar—radiates into space (Kasting, 1988), thus by expanding the volume of the top of the atmosphere, more radiation can escape.”

“The used model is based on a T (P ) profile prescription (Kasting 1988) starting from the 1000-bar level (unsaturated since T (1000 bar) > Tcritical) upwards, assuming a dry adiabat, and switching optionally to a moist adiabat (where T (P ) = Tsaturation(P )) if/when saturation reaches unity.”

“It has been understood for some time that changes to the strength of the greenhouse effect are fundamental to our understanding of the climate of earth and how it can change (Arrenhius 1896; Callendar 1938; Kasting 1989).”

“A planet on the inner edge of the habitable zone (see Chapter 5) could conceivably have a large abiotic buildup of oxygen through a runaway greenhouse effect while the oceans evaporate; after photodissociation of water in the atmosphere, hydrogen could escape, leaving oxygen behind (Kasting, 1988).”

“Informed by the ‘habitable zone’ first defined by Kasting (1988), we have searched for planets where liquid water, so fundamental to Earth-life, might be present on the planetary surface.”

“Were the moon to orbit its planet too closely, then it might be undergoing a moist or runaway greenhouse effect (Kasting, 1988; Kasting et al., 1993) and be temporarily uninhabitable or even desiccated and uninhabitable forever (Heller and Barnes, 2013, 2014).”

“…and habitability of planets other than modern Earth have been carried out primarily with one-dimensional (1D) radiative-convective models (e.g., Kasting 1988; Kasting et al. 1993; Pavlov et al. 2001; Segura et al. 2003; Domagal-Goldman et al. 2008, 2011; Kitzmann et al. 2010; Zsom et al. 2012;…”

“…model with the interior model at a pressure P = Pb = 300 bar (slightly above the critical pressure Pcrit = 220.67 bar) and at a temperature T = Tb. (P, T, ρ) profiles are then integrated upward via the prescription from Kasting (1988) in the case of an adiabat at hydrostatic equilibrium.”