The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
David C Catling - One of the best experts on this subject based on the ideXlab platform.
-
on detecting biospheres from chemical thermodynamic disequilibrium in Planetary Atmospheres
Astrobiology, 2016Co-Authors: Joshua Krissansentotton, David S Bergsman, David C CatlingAbstract:Abstract Atmospheric chemical disequilibrium has been proposed as a method for detecting extraterrestrial biospheres from exoplanet observations. Chemical disequilibrium is potentially a generalized biosignature since it makes no assumptions about particular biogenic gases or metabolisms. Here, we present the first rigorous calculations of the thermodynamic chemical disequilibrium in Solar System Atmospheres, in which we quantify the available Gibbs energy: the Gibbs free energy of an observed atmosphere minus that of atmospheric gases reacted to equilibrium. The purely gas phase disequilibrium in Earth's atmosphere is mostly attributable to O2 and CH4. The available Gibbs energy is not unusual compared to other Solar System Atmospheres and smaller than that of Mars. However, Earth's fluid envelope contains an ocean, allowing gases to react with water and requiring a multiphase calculation with aqueous species. The disequilibrium in Earth's atmosphere-ocean system (in joules per mole of atmosphere) ranges...
-
on detecting biospheres from chemical thermodynamic disequilibrium in Planetary Atmospheres
arXiv: Earth and Planetary Astrophysics, 2015Co-Authors: Joshua Krissansentotton, David S Bergsman, David C CatlingAbstract:Atmospheric chemical disequilibrium has been proposed as a method for detecting extraterrestrial biospheres from exoplanet observations. Chemical disequilibrium is potentially a generalized biosignature since it makes no assumptions about particular biogenic gases or metabolisms. Here, we present the first rigorous calculations of the thermodynamic chemical disequilibrium in Solar System Atmospheres, in which we quantify the available Gibbs energy: the Gibbs free energy of an observed atmosphere minus that of atmospheric gases reacted to equilibrium. The purely gas phase disequilibrium in Earth's atmosphere is mostly attributable to O2 and CH4. The available Gibbs energy is not unusual compared to other Solar System Atmospheres and smaller than that of Mars. However, Earth's fluid envelope contains an ocean, allowing gases to react with water and requiring a multiphase calculation with aqueous species. The disequilibrium in Earth's atmosphere-ocean system (in joules per mole of atmosphere) ranges from 20 to 2E6 times larger than the disequilibria of other Atmospheres in the Solar System. Only on Earth is the chemical disequilibrium energy comparable to the thermal energy per mole of atmosphere. Earth's disequilibrium is biogenic, mainly caused by the coexistence of N2, O2 and liquid water instead of more stable nitrate. In comparison, the O2-CH4 disequilibrium is minor. We identify abiotic processes that cause disequilibrium in the other Atmospheres. Our metric requires minimal assumptions and could potentially be calculated using observations of exoplanet Atmospheres. However, further work is needed to establish whether thermodynamic disequilibrium is a practical exoplanet biosignature, requiring an assessment of false positives, noisy observations, and other detection challenges. Our Matlab code and databases for these calculations are available, open source.
-
common 0 1 bar tropopause in thick Atmospheres set by pressure dependent infrared transparency
Nature Geoscience, 2014Co-Authors: Tyler D Robinson, David C CatlingAbstract:In many Planetary Atmospheres, including that of Earth, the base of the stratosphere—the tropopause—occurs at an atmospheric pressure of 0.1 bar. A physically based model demonstrates that the pressure-dependence of transparency to infrared radiation leads to a common tropopause pressure that is probably applicable to many Planetary bodies with thick Atmospheres.
-
an analytic radiative convective model for Planetary Atmospheres
arXiv: Earth and Planetary Astrophysics, 2012Co-Authors: Tyler D Robinson, David C CatlingAbstract:We present an analytic 1-D radiative-convective model of the thermal structure of Planetary Atmospheres. Our model assumes that thermal radiative transfer is gray and can be represented by the two-stream approximation. Model Atmospheres are assumed to be in hydrostatic equilibrium, with a power law scaling between the atmospheric pressure and the gray thermal optical depth. The convective portions of our models are taken to follow adiabats that account for condensation of volatiles through a scaling parameter to the dry adiabat. By combining these assumptions, we produce simple, analytic expressions that allow calculations of the atmospheric pressure-temperature profile, as well as expressions for the profiles of thermal radiative flux and convective flux. We explore the general behaviors of our model. These investigations encompass (1) worlds where atmospheric attenuation of sunlight is weak, which we show tend to have relatively high radiative-convective boundaries, (2) worlds with some attenuation of sunlight throughout the atmosphere, which we show can produce either shallow or deep radiative-convective boundaries, depending on the strength of sunlight attenuation, and (3) strongly irradiated giant planets (including Hot Jupiters), where we explore the conditions under which these worlds acquire detached convective regions in their mid-tropospheres. Finally, we validate our model and demonstrate its utility through comparisons to the average observed thermal structure of Venus, Jupiter, and Titan, and by comparing computed flux profiles to more complex models.
-
an analytic radiative convective model for Planetary Atmospheres
The Astrophysical Journal, 2012Co-Authors: Tyler D Robinson, David C CatlingAbstract:We present an analytic one-dimensional radiative‐convective model of the thermal structure of Planetary Atmospheres. Our model assumes that thermal radiative transfer is gray and can be represented by the twostream approximation. Model Atmospheres are assumed to be in hydrostatic equilibrium, with a power-law scaling between the atmospheric pressure and the gray thermal optical depth. The convective portions of our models are taken to follow adiabats that account for condensation of volatiles through a scaling parameter to the dry adiabat. By combining these assumptions, we produce simple, analytic expressions that allow calculations of the atmosphericpressure‐temperature profile, as well as expressions for the profiles of thermal radiative flux and convective flux. We explore the general behaviors of our model. These investigations encompass (1) worlds where atmospheric attenuation of sunlight is weak, which we show tend to have relatively high radiative‐convective boundaries; (2) worlds with some attenuation of sunlight throughout the atmosphere, which we show can produce either shallow or deep radiative‐convective boundaries, depending on the strength of sunlight attenuation; and (3) strongly irradiated giant planets (including hot Jupiters), where we explore the conditions under which these worlds acquire detached convective regions in their mid-tropospheres. Finally, we validate our model and demonstrate its utility through comparisons to the average observed thermal structure of Venus, Jupiter, and Titan, and by comparing computed flux profiles to more complex models.
Stephen R Kane - One of the best experts on this subject based on the ideXlab platform.
-
phase modeling of the trappist 1 Planetary Atmospheres
The Astronomical Journal, 2021Co-Authors: Stephen R Kane, Franck Selsis, Tiffany Jansen, Thomas Fauchez, Alma Y CejaAbstract:Transiting compact multi-planet systems provide many unique opportunities to characterize the planets, including studies of size distributions, mean densities, orbital dynamics, and atmospheric compositions. The relatively short orbital periods in these systems ensure that events requiring specific orbital locations of the planets (such as primary transit and secondary eclipse points) occur with high frequency. The orbital motion and associated phase variations of the planets provide a means to constrain the atmospheric compositions through measurement of their albedos. Here we describe the expected phase variations of the TRAPPIST-1 system and times of superior conjunction when the summation of phase effects produce maximum amplitudes. We also describe the infrared flux emitted by the TRAPPIST-1 planets and the influence on the overall phase amplitudes. We further present the results from using the global circulation model ROCKE-3D to model the Atmospheres of TRAPPIST-1e and TRAPPIST-1f assuming modern Earth and Archean atmospheric compositions. These simulations are used to calculate predicted phase curves for both reflected light and thermal emission components. We discuss the detectability of these signatures and the future prospects for similar studies of phase variations for relatively faint M stars.
-
the stellar activity of trappist 1 and consequences for the Planetary Atmospheres
The Astrophysical Journal, 2017Co-Authors: Rachael M Roettenbacher, Stephen R KaneAbstract:The signatures of planets hosted by M dwarfs are more readily detected with transit photometry and radial velocity methods than those of planets around larger stars. Recently, transit photometry was used to discover seven planets orbiting the late-M dwarf TRAPPIST-1. Three of TRAPPIST-1's planets fall in the Habitable Zone, a region where liquid water could exist on the Planetary surface given appropriate Planetary conditions. We aim to investigate the habitability of the TRAPPIST-1 planets by studying the star's activity and its effect on the planets. We analyze previously published space- and ground-based light curves and show the photometrically determined rotation period of TRAPPIST-1 appears to vary over time due to complicated, evolving surface activity. The dramatic changes of the surface of TRAPPIST-1 suggest that rotation periods determined photometrically may not be reliable for this and similarly active stars. While the activity of the star is low, we use the premise of the "cosmic shoreline" to provide evidence that the TRAPPIST-1 environment has potentially led to the erosion of possible Planetary Atmospheres by extreme ultraviolet stellar emission.
Franck Selsis - One of the best experts on this subject based on the ideXlab platform.
-
phase modeling of the trappist 1 Planetary Atmospheres
The Astronomical Journal, 2021Co-Authors: Stephen R Kane, Franck Selsis, Tiffany Jansen, Thomas Fauchez, Alma Y CejaAbstract:Transiting compact multi-planet systems provide many unique opportunities to characterize the planets, including studies of size distributions, mean densities, orbital dynamics, and atmospheric compositions. The relatively short orbital periods in these systems ensure that events requiring specific orbital locations of the planets (such as primary transit and secondary eclipse points) occur with high frequency. The orbital motion and associated phase variations of the planets provide a means to constrain the atmospheric compositions through measurement of their albedos. Here we describe the expected phase variations of the TRAPPIST-1 system and times of superior conjunction when the summation of phase effects produce maximum amplitudes. We also describe the infrared flux emitted by the TRAPPIST-1 planets and the influence on the overall phase amplitudes. We further present the results from using the global circulation model ROCKE-3D to model the Atmospheres of TRAPPIST-1e and TRAPPIST-1f assuming modern Earth and Archean atmospheric compositions. These simulations are used to calculate predicted phase curves for both reflected light and thermal emission components. We discuss the detectability of these signatures and the future prospects for similar studies of phase variations for relatively faint M stars.
-
evolution of the solar activity over time and effects on Planetary Atmospheres ii κ1 ceti an analog of the sun when life arose on earth
The Astrophysical Journal, 2010Co-Authors: I Ribas, G Porto F De Mello, Leticia D Ferreira, Eric Hebrard, Franck Selsis, S Catalan, A Garces, J Do D NascimentoAbstract:The early evolution of Earth's atmosphere and the origin of life took place at a time when physical conditions at the Earth were radically different from its present state. The radiative input from the Sun was much enhanced in the high-energy spectral domain, and in order to model early Planetary Atmospheres in detail, a knowledge of the solar radiative input is needed. We present an investigation of the atmospheric parameters, state of evolution, and high-energy fluxes of the nearby star κ1 Cet, previously thought to have properties resembling those of the early Sun. Atmospheric parameters were derived from the excitation/ionization equilibrium of Fe I and Fe II, profile fitting of Hα, and the spectral energy distribution. The UV irradiance was derived from Far-Ultraviolet Spectroscopic Explorer and Hubble Space Telescope data, and the absolute chromospheric flux from the Hα line core. From careful spectral analysis and the comparison of different methods, we propose for κ1 Cet the following atmospheric parameters: T eff = 5665 ± 30 K (Hα profile and energy distribution), log g = 4.49 ± 0.05 dex (evolutionary and spectroscopic), and [Fe/H] = +0.10 ± 0.05 (Fe II lines). The UV radiative properties of κ1 Cet indicate that its flux is some 35% lower than the current Sun's between 210 and 300 nm, it matches the Sun's at 170 nm, and increases to at least 2-7 times higher than the Sun's between 110 and 140 nm. The use of several indicators ascribes an age to κ1 Cet in the interval ~0.4-0.8 Gyr and the analysis of the theoretical Hertzsprung-Russell diagram (H-R) suggests a mass ~1.04 M ☉. This star is thus a very close analog of the Sun when life arose on Earth and Mars is thought to have lost its surface bodies of liquid water. Photochemical models indicate that the enhanced UV emission leads to a significant increase in photodissociation rates compared with those commonly assumed of the early Earth. Our results show that reliable calculations of the chemical composition of early Planetary Atmospheres need to account for the stronger solar photodissociating UV irradiation.
-
evolution of the solar activity over time and effects on Planetary Atmospheres ii kappa 1 ceti an analog of the sun when life arose on earth
arXiv: Solar and Stellar Astrophysics, 2010Co-Authors: I Ribas, G Porto F De Mello, Leticia D Ferreira, Eric Hebrard, Franck Selsis, S Catalan, A Garces, J Do D Nascimento, J R De MedeirosAbstract:The early evolution of Earth's atmosphere and the origin of life took place at a time when physical conditions at the Earth where radically different from its present state. The radiative input from the Sun was much enhanced in the high-energy spectral domain, and in order to model early Planetary Atmospheres in detail, a knowledge of the solar radiative input is needed. We present an investigation of the atmospheric parameters, state of evolution and high-energy fluxes of the nearby star kap^1 Cet, previously thought to have properties resembling those of the early Sun. Atmospheric parameters were derived from the excitation/ionization equilibrium of Fe I and Fe II, profile fitting of Halpha and the spectral energy distribution. The UV irradiance was derived from FUSE and HST data, and the absolute chromospheric flux from the Halpha line core. From careful spectral analysis and the comparison of different methods we propose for kap^1 Cet the following atmospheric parameters: Teff = 5665+/-30 K (Halpha profile and energy distribution), log g = 4.49+/-0.05 dex (evolutionary and spectroscopic) and [Fe/H] = +0.10+/-0.05 dex (Fe II lines). The UV radiative properties of kap^1 Cet indicate that its flux is some 35% lower than the current Sun's between 210 and 300 nm, it matches the Sun's at 170 nm and increases to at least 2-7 times higher than the Sun's between 110 and 140 nm. The use of several indicators ascribes an age to kap^1 Cet in the interval ~0.4-0.8 Gyr and the analysis of the theoretical HR diagram suggests a mass ~1.04 Msun. This star is thus a very close analog of the Sun when life arose on Earth and Mars is thought to have lost its surface bodies of liquid water. Photochemical models indicate that the enhanced UV emission leads to a significant increase in photodissociation rates compared with those commonly assumed of the early Earth. Our results show that reliable calculations of the chemical composition of early Planetary Atmospheres need to account for the stronger solar photodissociating UV irradiation.
R Freedman - One of the best experts on this subject based on the ideXlab platform.
-
comparative Planetary Atmospheres models of tres 1 and hd 209458b
The Astrophysical Journal, 2005Co-Authors: Jonathan J Fortney, M S Marley, Katharina Lodders, D Saumon, R FreedmanAbstract:We present new self-consistent atmosphere models for the transiting planets TrES-1 and HD 209458b. The planets were recently observed with the Spitzer Space Telescope in bands centered on 4.5 and 8.0 μm, for TrES-1, and 24 μm, for HD 209458b. We find that standard solar-metallicity models fit the observations for HD 209458b. For TrES-1, which has a Teff ~300 K cooler, we find that models with a metallicity 3-5 times enhanced over solar abundances can match the 1 σ error bar at 4.5 μm and 2 σ at 8.0 μm. Models with solar abundances that include energy deposition into the stratosphere give fluxes that fall within the 2 σ error bars in both bands. The best-fit models for both planets assume that reradiation of absorbed stellar flux occurs over the entire planet. For all models of both planets, we predict planet-to-star flux ratios in other Spitzer bandpasses.
-
comparative Planetary Atmospheres models of tres 1 and hd209458b
arXiv: Astrophysics, 2005Co-Authors: Jonathan J Fortney, M S Marley, Katharina Lodders, D Saumon, R FreedmanAbstract:We present new self-consistent atmosphere models for transiting planets TrES-1 and HD209458b. The planets were recently observed with the Spitzer Space Telescope in bands centered on 4.5 and 8.0 $\mu$m, for TrES-1, and 24 $\mu$m, for HD209458b. We find that standard solar metallicity models fit the observations for HD209458b. For TrES-1, which has an T_eff ~300 K cooler, we find that models with a metallicity 3-5 times enhanced over solar abundances can match the 1$\sigma$ error bar at 4.5 $\mu$m and 2$\sigma$ at 8.0$\mu$m. Models with solar abundances that included energy deposition into the stratosphere give fluxes that fall within the 2$\sigma$ error bars in both bands. The best-fit models for both planets assume that reradiation of absorbed stellar flux occurs over the entire planet. For all models of both planets we predict planet/star flux ratios in other Spitzer bandpasses.
Tyler D Robinson - One of the best experts on this subject based on the ideXlab platform.
-
common 0 1 bar tropopause in thick Atmospheres set by pressure dependent infrared transparency
Nature Geoscience, 2014Co-Authors: Tyler D Robinson, David C CatlingAbstract:In many Planetary Atmospheres, including that of Earth, the base of the stratosphere—the tropopause—occurs at an atmospheric pressure of 0.1 bar. A physically based model demonstrates that the pressure-dependence of transparency to infrared radiation leads to a common tropopause pressure that is probably applicable to many Planetary bodies with thick Atmospheres.
-
an analytic radiative convective model for Planetary Atmospheres
arXiv: Earth and Planetary Astrophysics, 2012Co-Authors: Tyler D Robinson, David C CatlingAbstract:We present an analytic 1-D radiative-convective model of the thermal structure of Planetary Atmospheres. Our model assumes that thermal radiative transfer is gray and can be represented by the two-stream approximation. Model Atmospheres are assumed to be in hydrostatic equilibrium, with a power law scaling between the atmospheric pressure and the gray thermal optical depth. The convective portions of our models are taken to follow adiabats that account for condensation of volatiles through a scaling parameter to the dry adiabat. By combining these assumptions, we produce simple, analytic expressions that allow calculations of the atmospheric pressure-temperature profile, as well as expressions for the profiles of thermal radiative flux and convective flux. We explore the general behaviors of our model. These investigations encompass (1) worlds where atmospheric attenuation of sunlight is weak, which we show tend to have relatively high radiative-convective boundaries, (2) worlds with some attenuation of sunlight throughout the atmosphere, which we show can produce either shallow or deep radiative-convective boundaries, depending on the strength of sunlight attenuation, and (3) strongly irradiated giant planets (including Hot Jupiters), where we explore the conditions under which these worlds acquire detached convective regions in their mid-tropospheres. Finally, we validate our model and demonstrate its utility through comparisons to the average observed thermal structure of Venus, Jupiter, and Titan, and by comparing computed flux profiles to more complex models.
-
an analytic radiative convective model for Planetary Atmospheres
The Astrophysical Journal, 2012Co-Authors: Tyler D Robinson, David C CatlingAbstract:We present an analytic one-dimensional radiative‐convective model of the thermal structure of Planetary Atmospheres. Our model assumes that thermal radiative transfer is gray and can be represented by the twostream approximation. Model Atmospheres are assumed to be in hydrostatic equilibrium, with a power-law scaling between the atmospheric pressure and the gray thermal optical depth. The convective portions of our models are taken to follow adiabats that account for condensation of volatiles through a scaling parameter to the dry adiabat. By combining these assumptions, we produce simple, analytic expressions that allow calculations of the atmosphericpressure‐temperature profile, as well as expressions for the profiles of thermal radiative flux and convective flux. We explore the general behaviors of our model. These investigations encompass (1) worlds where atmospheric attenuation of sunlight is weak, which we show tend to have relatively high radiative‐convective boundaries; (2) worlds with some attenuation of sunlight throughout the atmosphere, which we show can produce either shallow or deep radiative‐convective boundaries, depending on the strength of sunlight attenuation; and (3) strongly irradiated giant planets (including hot Jupiters), where we explore the conditions under which these worlds acquire detached convective regions in their mid-tropospheres. Finally, we validate our model and demonstrate its utility through comparisons to the average observed thermal structure of Venus, Jupiter, and Titan, and by comparing computed flux profiles to more complex models.
