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Diagram of the energy balance of the stratosphere and troposphere on Titan; 'rIR, oPtical depth in the infrared. Straight lines denote the solar radiation and the wavy lines the thermal infrared radiation. The flux units are the percent of the globaly averaged solar radiation at the top of Titan's atmosphere. The troposphere emission temperature (near the tropopause) is determined by the antigreenhouse effect and is 9 K cooler than the effective temperature. The increase in temperature from the tropopause to the surface is due to a greenhouse effect of 21 K resulting from thermal infrared radiation (113%) emitted from the lower atmosphere and warming the surface. The surface is not in radiative balance because convective motions account for an energy flux of 1%.
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There are many parallels between the atmospheric thermal structure of the Saturnian satellite Titan and the terrestrial greenhouse effect; these parallels provide a comparison for theories of the heat balance of Earth. Titan's atmosphere has a greenhouse effect caused primarily by pressure-induced opacity of N2, CH4, and H2. H2 is a key absorber be...
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Citations
... Aerosol absorption and reflectivity are wavelength-dependent (Adams et al. 2019;Feinstein et al. 2023). They therefore modify the thermal structure of the atmosphere (McKay et al. 1991(McKay et al. , 1999Heng et al. 2012;Keating & Cowan 2017), which, in turn, affects the formation rate of aerosols (Morley et al. 2015;Gao et al. 2018). Atmospheric properties such as metallicity, vertical mixing strength, and longitudinal transport also determine the abundance and composition of aerosols (Parmentier et al. 2013;Gao et al. 2018;He et al. 2018). ...
The presence of aerosols is intimately linked to the global energy budget and the composition of a planet’s atmosphere. Their ability to reflect incoming light prevents energy from being deposited into the atmosphere, and they shape the spectra of exoplanets. We observed five near-infrared secondary eclipses of WASP-80b with the Wide Field Camera 3 (WFC3) aboard the Hubble Space Telescope to provide constraints on the presence and properties of atmospheric aerosols. We detect a broadband eclipse depth of 34 ± 10 ppm for WASP-80b. We detect a higher planetary flux than expected from thermal emission alone at 1.6 σ , which hints toward the presence of reflecting aerosols on this planet’s dayside, indicating a geometric albedo of A g < 0.33 at 3 σ . We paired the WFC3 data with Spitzer data and explored multiple atmospheric models with and without aerosols to interpret this spectrum. Albeit consistent with a clear dayside atmosphere, we found a slight preference for near-solar metallicities and for dayside clouds over hazes. We exclude soot haze formation rates higher than 10 −10.7 g cm ⁻² s ⁻¹ and tholin formation rates higher than 10 −12.0 g cm ⁻² s ⁻¹ at 3 σ . We applied the same atmospheric models to a previously published WFC3/Spitzer transmission spectrum for this planet and found weak haze formation. A single soot haze formation rate best fits both the dayside and the transmission spectra simultaneously. However, we emphasize that no models provide satisfactory fits in terms of the chi-square of both spectra simultaneously, indicating longitudinal dissimilarity in the atmosphere’s aerosol composition.
... The estimates for the surface temperature of Titan range in the interval 90.6 − 94K [8,9]. It is interesting to note that the same temperatures are also found at higher altitudes, where a condensate haze forms at a pressure of 0.03 bar [25]. ...
We propose a formula for computing the average planetary surface temperatures based solely on the solar irradiance and the bond albedo. The formula is empirically derived from data on Earth, Venus and Titan, and a model is proposed to justify it. We introduce the concept of planetary inner albedo, as a complement to the usual bond albedo. A geometric proof is given for the main finding of the paper, which can be summarized as follows: the ratio of the inner to outer albedo is a constant, related to the universal parabolic constant. Furthermore, we extend the surface temperature formula to gas giants, giving the temperature at which condensates (e.g., of ammonia) start forming within their atmosphere, particularly for Jupiter, Saturn and Uranus. Based on model complexity, applicability and accuracy, the heating mechanism via atmospheric reflectivity (a mirror effect) performs much better than the alternatives. Responses to reviewers are included at the end.
... Aerosol absorption and reflectivity are wavelengthdependent (Adams et al. 2019;Feinstein et al. 2023). They therefore modify the thermal structure of the atmosphere (McKay et al. 1991(McKay et al. , 1999Heng et al. 2012;Keating & Cowan 2017), which in turn affects the formation rate of aerosols (Morley et al. 2015;Gao et al. 2018). Atmospheric properties like metallicity, vertical mixing strength and longitudinal transport also determine the abundance and composition of aerosols (Parmentier et al. 2013;Gao et al. 2018;He et al. 2018). ...
The presence of aerosols is intimately linked to the global energy budget and composition of planet atmospheres. Their ability to reflect incoming light prevents energy from being deposited into the atmosphere, and they shape spectra of exoplanets. We observed one near-infrared secondary eclipse of WASP-80b with the Wide Field Camera 3 aboard the Hubble Space Telescope to provide constraints on the presence and properties of atmospheric aerosols. We detect a broadband eclipse depth of $34\pm10$ ppm for WASP-80b, making this the lowest equilibrium temperature planet for which a secondary eclipse has been detected so far with WFC3. We detect a higher planetary flux than expected from thermal emission alone at $1.6\sigma$ that hints toward the presence of reflecting aerosols on this planet's dayside. We paired the WFC3 data with Spitzer data and explored multiple atmospheric models with and without aerosols to interpret this spectrum. Albeit consistent with a clear dayside atmosphere, we found a slight preference for near-solar metallicities and for dayside clouds over hazes. We exclude soot haze formation rates higher than $10^{-10.7}$ g cm$^{-2}$s$^{-1}$ and tholin formation rates higher than $10^{-12.0}$ g cm$^{-2}$s$^{-1}$ at $3\sigma$. We applied the same atmospheric models to a previously published WFC3/Spitzer transmission spectrum for this planet and find weak haze formation. A single soot haze formation rate best fits both the dayside and the transmission spectra simultaneously. However, we emphasize that no models provide satisfactory fits in terms of chi-square of both spectra simultaneously, indicating longitudinal dissimilarity in the atmosphere's aerosol composition.
... The haze, primarily composed of organic-rich solid particles, absorbs at visible wavelengths and is transparent at infrared (IR) wavelengths. This leads to an anti-greenhouse effect in which solar radiation is absorbed in the upper atmosphere, whereas thermal IR radiation from the surface escapes easily, reducing the surface temperature by an estimated 9 K (McKay et al. 1991). ...
In this work, we present for the first time infrared spectra of Titan from the Spitzer Space Telescope (2004–2009). The data are from both the short wavelength–low resolution (SL; 5.13–14.29 μ m, R ∼ 60–127) and short wavelength–high resolution (SH; 9.89–19.51 μ m, R ∼ 600) channels showing the emissions of CH 4 , C 2 H 2 , C 2 H 4 , C 2 H 6 , C 3 H 4 , C 3 H 6 , C 3 H 8 , C 4 H 2 , HCN, HC 3 N, and CO 2 . We compare the results obtained for Titan from Spitzer to those of the Cassini Composite Infrared Spectrometer (CIRS) for the same time period, focusing on the 16.35–19.35 μ m wavelength range observed by the SH channel but impacted by higher noise levels in the CIRS observations. We use the SH data to provide estimated haze extinction cross sections for the 16.67–17.54 μ m range that are missing in previous studies. We conclude by identifying spectral features in the 16.35–19.35 μ m wavelength range that could be analyzed further through upcoming James Webb Space Telescope Cycle 1 observations with the Mid-Infrared Instrument (5.0–28.3 μ m, R ∼ 1500–3500). We also highlight gaps in the current spectroscopic knowledge of molecular bands, including candidate trace species such as C 60 and detected trace species such as C 3 H 6 , that could be addressed by theoretical and laboratory study.
... The haze, primarily composed of organicrich solid particles, absorbs at visible wavelengths and is transparent at infrared (IR) wavelengths. This leads to an anti-greenhouse effect in which solar radiation is absorbed in the upper atmosphere whereas thermal IR radiation from the surface escapes easily, reducing the surface temperature by an estimated 9 K (McKay et al. 1991 Since the 1970s, IR spectroscopy has been a useful tool for probing the composition of the neutral atmosphere of Titan. This has been conducted using ground-based telescopes, visiting spacecraft such as Voyager and Cassini, and space-based observatories including theInfrared Space Observatories. ...
In this work we present, for the first time, infrared spectra of Titan from the Spitzer Space Telescope ($2004-2009$). The data are from both the short wavelength-low resolution (SL, $5.13-14.29\mathrm{\mu m}, R\sim60-127$) and short wavelength-high resolution channels (SH, $9.89 - 19.51\mathrm{\mu m}, R\sim600$) showing the emissions of CH$_{4}$, C$_{2}$H$_{2}$, C$_{2}$H$_{4}$, C$_{2}$H$_{6}$, C$_{3}$H$_{4}$, C$_{3}$H$_{6}$, C$_{3}$H$_{8}$, C$_{4}$H$_{2}$, HCN, HC$_{3}$N, and CO$_{2}$. We compare the results obtained for Titan from Spitzer to those of the Cassini Composite Infrared Spectrometer (CIRS) for the same time period, focusing on the $16.35-19.35\mathrm{\mu m}$ wavelength range observed by the SH channel but impacted by higher noise levels in CIRS observations. We use the SH data to provide estimated haze extinction cross-sections for the $16.67-17.54\mathrm{\mu m}$ range that are missing in previous studies. We conclude by identifying spectral features in the $16.35-19.35\mathrm{\mu m}$ wavelength range, including two prominent emission features at 16.39 and $17.35\mathrm{\mu m}$, that could be analyzed further through upcoming James Webb Space Telescope Cycle 1 observations with the Mid-Infrared Instrument ($5.0-28.3\mathrm{\mu m}, R\sim1500-3500$). We also highlight gaps in current spectroscopic knowledge of molecular bands, including candidate trace species such as C$_{60}$ and detected trace species such as C$_{3}$H$_{6}$, that could be addressed by theoretical and laboratory study.
... We note that present-day Titan, where CH4 is a condensing gas, is too cold for its greenhouse effect to be dominated by CH4. Instead its greenhouse effect is largely due to collision-induced absorption between N2, H2, and CH4 plus absorption by photochemical hazes, with only a minor contribution from the CH4−CH4 continuum (30). Nevertheless, our results suggest that extrasolar planets with exotic condensable greenhouse gases, such as hot rocky planets covered with lava oceans and with atmospheres made of outgassed silicate-vapor species (31,32), would have radiative balances surprisingly similar to Earth's. ...
SE ADJUNTAN UNA SERIE DE GRÁFICAS Y UN ARTÍCULO PUBLICADO QUE DAN A ENTENDER CON CLARIDAD QUE EL PRINCIPAL GAS DE EFECTO INVERNADERO EN NUESTRA ACTUAL ATMÓSFERA ES EL VAPOR DE AGUA Y NO EL CO2 YA QUE AL SER UN GAS CONDENSABLE EL NÚMERO MEDIO DE MOLÉCULAS DE VAPOR DE AGUA QUE HAY EN LA ATMÓSFERA VARÍA MUY RÁPIDAMENTE CON LOS CAMBIOS DE LA TEMPERATURA SUPERFICIAL MEDÍA DEL AIRE Y AL SER EL PRINCIPAL GAS DE EFECTO INVERNADERO SI SE HACE UN USO INTENSIVO DEL H2 EN EL SECTOR DEL TRANSPORTE COMO SUSTITUTO DE LOS COMBUSTIBLES FÓSILES MUY PROBABLEMENTE TENDREMOS UN AUMENTO PROGRESIVO CON EL TIEMPO DEL VALOR MEDIO DEL NÚMERO DE MOLÉCULAS DE VAPOR DE AGUA EN NUESTRA ATMÓSFERA Y AL SER ACTIVA EN EL INFRARROJO Y SER EL GAS MAYORITARIO CON EFECTO INVERNADERO QUE HAY EN NUESTRA ATMÓSFERA SE PRODUCIRÁ UNA MAYOR ABSORCIÓN DE LA RADIACIÓN TÉRMICA SOLAR ENTRANTE Y EMITIDA POR LA TIERRA LO QUE PROVOCARÀ UN AUMENTO NO LINEAL DE LA TEMPERATURA MEDIA DEL AIRE DEBIDO A UN EFECTO DE REALIMENTACIÓN POSITIVA YA QUE AL AUMENTAR LA TEMPERATURA MEDIA DEL AIRE SE EVAPORARÁ MÁS AGUA DE LOS OCÉANOS AGRAVANDO EL PROBLEMA LA UNICA ALTERNATIVA VIABLE DESDE MI PUNTO DE VISTA PARA ESTABILIZAR LA TEMPERATURA DE NUESTRA ATMÓSFERA ES UTILIZAR AIRE LÍQUIDO O COMPRIMIDO Y NO SUSTITUIR UN GAS MINORITARIO EN NUESTRA ATMÓSFERA QUE GENERA UN PEQUEÑO EFECTO INVERNADERO Y REALIMENTACIÓN POSITIVA EN CUANTO A QUE CONTRIBUYE A AUMENTAR LENTAMENTE EL NÚMERO MEDIO DE MOLÉCULAS DE VAPOR DE AGUA QUE HAY EN NUESTRA ATMÓSFERA POR EL PRINCIPAL GAS DE EFECTO INVERNADERO QUE ES EL VAPOR DE AGUA QUE ES LA MOLECULA RESPONSABLE DE LA MAYORÍA DE LA ABSORCIÓN DE LA RADIACIÓN TÉRMICA ENTRANTE QUE PROVIENE DEL SOL Y DE LA EMITIDA POR LA TIERRA O SEA EN OTRAS PALABRAS QUE LA MAYOR CONTRIBUCIÓN AL AUMENTO DE LA TEMPERATURA DEL AIRE SE DEBE AL VAPOR DE AGUA QUE ACTUALMENTE Y EN EL FUTURO SERÁ EL PRINCIPAL GAS DE EFECTO INVERNADERO EN NUESTRA ATMÓSFERA HAY QUE TENER EN CUENTA QUE LA TEMPERATURA MEDIA DEL AIRE AUMENTA PORQUE PARTE DE LA RADIACIÓN TÉRMICA SOLAR ES ABSORVIDA POR LAS MOLÉCULAS DE AGUA Y LO MISMO OCURRE CON LA RADIACIÓN TÉRMICA EMITIDA POR LA TIERRA.SE ADJUNTA UN ARTICULO EN DONDE SE EXPLICA UNA CORRELACIÓN LINEAL OBSERVADA ENTRE EL FLUJO NETO DE SALIDA DE RADIACIÓN TÉRMICA TERRESTRE Y LA TEMPERATURA SUPERFICIAL MEDIA TENIENDO SOLO EN CUENTA AL VAPOR DE AGUA HECHO QUE CONFIRMA QUE ES EL PRINCIPAL GAS DE EFECTO INVERNADERO EN LA TIERRA Y HAY QUE EVITAR A TODA COSTA QUE SU CONCENTRACIÓN SIGA AUMENTANDO POR LOS PERNICIOSOS EFECTOS DE REALIMENTACIÓN POSITIVA QUE PROVOCA AL SER UN GAS CONDENSABLE Y CUYA EVAPORACIÓN OCEÁNICA ES MUY SENSIBLE A LA TEMPERATURA SUPERFICIAL DEL AGUA EN LOS MISMOS APARTE DE SER LA CINÉTICA DE EVAPORACIÓN O CONDENSACIÓN RAPIDA CUANDO SE PRODUCE UNA VARIACIÓN DE LA TEMPERATURA SUPERFICIAL DEL AGUA EN LOS OCÉANOS DE TODO EL PLANETA .
... Methane (CH 4 ) plays a fundamental role for the climate of Saturn's moon Titan in that it importantly contributes to the greenhouse effect in the troposphere (McKay et al., 1991) and is the most abundant condensable species (Niemann et al., 2005). Furthermore, methane can exist in the troposphere in liquid (rain) or solid (hail, snow) form depending on altitude, or more precisely, temperature and pressure (Graves et al., 2008;Lorenz & Lunine, 2002;Tokano et al., 2006). ...
... The model of calculates the absorption and scattering of solar radiation by the stratospheric organic haze, absorptions by permitted transitions of C 2 H 6 (ethane) and C 2 H 2 (acetylene) in the stratosphere and collision-induced absorption by various combinations of CH 4 , N 2 and H 2 molecules by a spectrally resolved radiative transfer code. This model approximately reproduced the temperature profiles measured by Voyager 1 and helped understand the greenhouse effect and anti-greenhouse effect in Titan's atmosphere (McKay et al., 1991). Furthermore, the vertical profile of the solar flux measured by the Huygens Probe (Tomasko et al., 2008) was found to be roughly consistent with that predicted by the model of . ...
... Several model parameters of the radiative transfer model are adjusted to make the model applicable to past methane-rich conditions. The haze production rate and H 2 abundance are expected to linearly scale with the CH 4 photolysis rate (McKay et al., 1991). Therefore, these two parameters are scaled with the solar luminosity, neglecting possible deviation of the linear relationship when the methane abundance is not optically thick enough in Lyman α. ...
Titan's paleoclimate after the onset of the putative last major methane outgassing event 700 Myr ago is simulated by a global climate model. If the atmosphere was methane‐depleted prior to outgassing, outgassed methane initially causes warming due to increased greenhouse effect. Further outgassing leads to methane snowfall, which in turn cools the troposphere and surface by an ice‐albedo feedback and thereby initiates a lengthy ice age. Formation of ice sheets begins in the polar region, but with increasing methane inventory the entire globe is eventually covered by surface methane frost as thick as 100 m, with local accumulation on elevated terrains. Among various time‐dependent input parameters the methane inventory by far exerts the greatest control over the climate evolution. As Titan's climate transitions from a dry state via a partially ice‐covered state to a globally ice‐covered state, the circulation and precipitation pattern change profoundly and the tropospheric temperature further decreases. Globally ice‐covered snowball Titan is characterized by weak meridional circulation, weak seasonality and widespread snowfall. Frost ablation begins after the end of outgassing due to photochemical destruction of atmospheric methane. It is conceivable that Titan's polar seas resulted from melting of the polar caps within the past 10 Myr and subsequent drainage to the polar basins. Surface methane frost could only melt when the frost retreated to the polar region, which led to global warming by lowering of the surface albedo at low latitudes and increased greenhouse effect.
... So, the energy imbalance revealed in the Cassini epoch and the possible long-term energy imbalance most likely come from the behaviors of emitted power. The hazes and greenhouse gases play important roles in modifying the thermal structure of Titan's atmosphere and surface by anti-greenhouse and greenhouse effects (McKay et al., 1991), respectively. The hazes and the greenhouse gases vary at Titan's seasons (Aharonson et al., 2009;West et al., 2018) and longer timescales (Lorenz et al., 1997), in which the temporal variations of haze distribution and methane abundance are driven by not only the eccentricity of Titan's orbit around the Sun but also the long-term interaction between Titan's atmosphere and surface. ...
Radiant energies of planets and moons are of wide interest in the fields of geoscience and planetary science. Based on long‐term multiinstrument observations from the Cassini spacecraft, we provide here the first observational study of Titan's global radiant energy budget and its seasonal variations. Our results show that Titan's radiant energy budget is not balanced over the Cassini era (2004–2017) with the absorbed solar energy (1.208 ± 0.008) × 10²³ J larger than the emitted thermal energy (1.174 ± 0.005) × 10²³ J. The energy imbalance is 2.9 ± 0.8% of the emitted thermal energy. Titan's global radiant energy budget is not balanced either at the timescales of Earth's years and Titan's seasons. In particular, the energy imbalance can be beyond 10% of the emitted thermal energy at the timescale of an Earth year. The energy imbalance revealed in this study has important impacts on Titan, which should be examined further by theories and models.
... The bright red arrow shape may be from the anvil head of fro en methane cirrus clouds located above an ac vely raining polar cell convec on storm see also challer et al. . . [7]. The application of the Vacuum Planet equation to the moon Titan shows that there is an atmospheric greenhouse effect of +10.8 Kelvin at the base of its atmosphere (Table 1). ...
... The application of the Vacuum Planet equation to the moon Titan shows that there is an atmospheric greenhouse effect of +10.8 Kelvin at the base of its atmosphere (Table 1). We are not able to confirm by our re-analysis presented here that the atmosphere of Titan has an antigreenhouse effect of 9 Kelvin, caused by the absorption of radiative ultra violet energy during the diabatic processes of Tholin formation in Titan's lower stratosphere [7]. ...
... That the global average surface temperature of Titan is 94 Kelvin[7].2. That the tropopause global minimum temperature of Titan is 71.6 Kelvin (Courtin and Kim, 2002)[6], and that this temperature occurs at a height of 42.3 km and at a pressure of 131.7 hPa (mbar)[18].3. ...
Abstract:
In this paper we present the results of a modelling analysis of the climate of Titan [2], in which we apply the techniques presented by Kiehl and Trenberth (1997) [3], and that were used by them to study the climate of the Earth. Our purpose here is to follow the fundamental concept that a terrestrial body that supports the surface presence of a volatile liquid, is cooled by the meteorological processes of Thermals, Evaporation, and Radiative loss. We have applied this precept to Titan and suggest that a system energy drain will be created within its troposphere. Because it has episodes of liquid precipitation of methane, evaporation of this liquid volatile, both from the surface of the moon and also by virga processes will cool the tropics of Titan. The supply of the energy for this latent heat of evaporation of liquid methane will create both surface and atmospheric cooling within the meteorological processes of Titan.
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To study this, we created a pressure profile curve for the atmosphere of Titan based on an application of Boyle’s law and Newton’s gravity law of spherical shells. The temperature lapse rate used in our analysis is based on data [6] that constrains three predictive equations, one each for the troposphere, tropopause and lower stratosphere respectively. With this atmospheric pressure profile model, we are then able to explore the results of the previous application of our Dynamic Atmosphere Energy-Transport (DAET) climate model to Titan [2].
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Finally, a sensitivity test was made of our DAET climate model by creating a zero-albedo version of Titan which we have called Clarity. With this model we are able to establish the dynamic limits of extreme albedo induced climate change for the moon Titan.
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In studying the science of atmospheres that are gravitationally bound to the surface of an orbiting, rotating, solar illuminated, terrestrial body, we must first establish the key mechanisms of atmospheric dynamics and apply these to Titan. The questions addressed are how the processes of high-frequency radiant energy capture, mechanical energy storage of specific heat and low-frequency radiant energy loss occur, and where they take place within the mobile fluid atmosphere that surrounds Titan. Our analysis using the traditional tools of climate science fully confirms that there is a greenhouse effect in the climate of Titan, and that it is located in the troposphere of that moon. Our formulation of a pressure temperature profile for Titan built on data and first principles, has established that the vast bulk of the methane within its atmosphere occurs in solid particulate form.
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Our climate model of Titan, that we have now calibrated against the results of the traditional climate science approach, shows that the lack of application of the tools of meteorology, namely the study of CAPE (convectively available potential energy) has resulted in a focus on only half of the story. Our modelling analysis has demonstrated both the existence and the effect of two complementary and opposing processes within an atmosphere that dynamically stabilise and ensure its long-term existence within tightly controlled thermal limits.
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These two processes are, the diabatic thermal radiant process of an equipartition flux cascade that manifests in the thermal radiant clarity of the low-pressure stratosphere, and the adiabatic thermal mass motion process of solar radiant forced convection. It is the adiabatic process of mass motion energy flux transport that manifests in and defines the troposphere. This is because it requires an environment where mass motion pressure forcing is the dominant energy flux process. The adiabatic process acts as a unidirectional energy gate, either removing energy from or delivering energy back to the site of thermal radiant disequilibrium within the troposphere.
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The results of our analysis demonstrate that the Greenhouse Effect in the thermally opaque, frozen methane particulate containing atmosphere of Titan is a tropospheric mass motion pressure induced adiabatic thermal effect, and not a diabatic atmospheric thermal radiant effect.
... At high pressure, N 2 and H 2 can absorb thermal radiation through collision-induced absorption (CIA). CIA of N 2 -N 2 , H 2 -N 2 and N 2 -CH 4 are responsible for most of the greenhouse effect on Titan [McKay et al., 1991], while H 2 -H 2 and H 2 -He play a significant role in the thermal structure of giant planets. Wordsworth and Pierrehumbert [2013] suggested that the early Earth could have been warmed by N 2 -H 2 CIA. ...
Stellar evolution models predict that the solar luminosity was lower in the past, typically 20-25% lower during the Archean (3.8-2.5 Ga). Despite the fainter Sun, there is strong evidence for the presence of liquid water on Earth’s surface at that time. This “faint young Sun problem” is a fundamental question in paleoclimatology, with important implications for the habitability of the early Earth, early Mars and exoplanets. Many solutions have been proposed based on the effects of greenhouse gases, atmospheric pressure, clouds, land distribution and Earth’s rotation rate. Here we review the faint young Sun problem for Earth, highlighting the latest geological and geochemical constraints on the early Earth’s atmosphere, and recent results from 3D global climate models and carbon cycle models. Based on these works, we argue that the faint young Sun problem for Earth has essentially been solved. Unfrozen Archean oceans were likely maintained by higher concentrations of CO2, consistent with the latest geological proxies, potentially helped by additional warming processes. This reinforces the expected key role of the carbon cycle for maintaining the habitability of terrestrial planets. Additional constraints on the Archean atmosphere and 3D fully coupled atmosphere-ocean models are required to validate this conclusion.
