Periodic Reporting for period 3 - EXOCONDENSE (Climate Dynamics of Exoplanets with Condensible Atmospheres)
Période du rapport: 2020-10-01 au 2022-03-31
EXOCONDENSE is aimed at understanding the atmospheres of planets around stars other than our own, stimulated by the revolution in ability of astronomers to detect exoplanets and to characterize their climates and atmospheres. With the next generation of ground and space-based telescopes, smaller (potentially Earth-like) planets are coming into view. All planets deepen our understanding of the fundamental nature of planetary climate and its evolution, including planets that are not likely to be habitable for any form of life.
Condensible substances play a ubiquitous role in planetary atmospheres. Depending on the temperature of a planet, a range of substances other than water can condense. Phase change effects -- loosely speaking, condensation -- profoundly affect the dynamics of planetary climate, and the way we interpret astronomical observations. Condensation transports heat from one place to another , forms clouds which feed back on climate, and provides feedback on the energy balance of the planet even when in a gaseous state. Condensation and later precipitation affect the chemical evolution of an atmosphere.
It is the overall objective of this project to develop a comprehensive understanding of the effects of condensation in exoplanet atmospheres, through developing and carrying out a new suite of simulations of atmospheres involving condensible substances. There is an emphasis on developing predictions that can be tested against observations.
It is important for the same reason that understanding the Big Bang is important. It satisfies a deeply and widely held desire to understand our origins, and our place in the Universe. Up until twenty years ago, for all we knew planets are a very rare event in the Universe. Now, astronomy has opened a window into one of the deepest questions of all: Are We Alone?
Condensible substances play a ubiquitous role in planetary atmospheres. Depending on the temperature of a planet, a range of substances other than water can condense. Phase change effects -- loosely speaking, condensation -- profoundly affect the dynamics of planetary climate, and the way we interpret astronomical observations. Condensation transports heat from one place to another , forms clouds which feed back on climate, and provides feedback on the energy balance of the planet even when in a gaseous state. Condensation and later precipitation affect the chemical evolution of an atmosphere.
It is the overall objective of this project to develop a comprehensive understanding of the effects of condensation in exoplanet atmospheres, through developing and carrying out a new suite of simulations of atmospheres involving condensible substances. There is an emphasis on developing predictions that can be tested against observations.
It is important for the same reason that understanding the Big Bang is important. It satisfies a deeply and widely held desire to understand our origins, and our place in the Universe. Up until twenty years ago, for all we knew planets are a very rare event in the Universe. Now, astronomy has opened a window into one of the deepest questions of all: Are We Alone?
So far, we have achieved:
- A series of papers concerning basic aspects of exoplanet dynamics which provide the underpinning for understanding condensation processes, drawing on concepts in linear wave dynamics that were originally developed for understanding the Earth's tropical circulation, especially phenomena such as El Nino.
- A new theory of the atmospheric circulation of planets for which the source of the atmosphere is evaporation or sublimation from the hot dayside and the sink is condensation on the cold nightside. This model has recently been extended to include the temperature inversions created by absorption of ultraviolet light, and has been applied to the lava planet K2-141b.
- Publication of the first simulation of the lava planet 55 Cancri-e which took into account the possibility of a non-condensible background atmosphere, which appears to be necessary to explain the relatively warm night-side temperatures of the planet.
Extended potential vorticity analysis to the atmosphere of hot gas-giant exoplanets which are tide-locked (i.e. always present the same face to their star).
- Contributed to the first global simulation of the effects of a novel heat-transporting mechanism whereby on very hot planets, the hydrogen molecule breaks up into atoms, absorbing heat in the process and releasing that heat where the atoms recombine.
- The first simulation of the global circulation of a brown dwarf star in orbit around and irradiated by a host star. Brown dwarfs are an outstanding and highly observable laboratory for probing the effects of clouds and condensation. The EXOCONDENSE team has published a number of additional papers probing condensation behaviour on such objects, employing our generalized version of the CM1 three dimensional convection model.
- The first simulation of 3D convection in a condensing pure steam atmosphere (relevant to runaway greenhouse atmospheres, which play an important role in evolution of planetary habitability).
Adapted our general circulation model for sub-neptunes featuring water in a hydrogen atmosphere, and has published a paper describing the dynamics in the absence of condensation, as a preliminary to probing latent heat and compositional buoyancy effects. Results have been obtained including the latter effects, and are currently being analysed in preparation for publication.
- Atmospheric chemistry plays a significant role in generating condensable substances, so further results have been obtained with our chemistry modelling framework, based on the open-source VULCAN code. A validation of the code has been published, and the code has been applied to address questions relating to hydrogen atmospheres.
- Produced the first model of the outer edge of the habitable zone to incorporate modern advances in the understanding of geochemical weathering processes. This work has considerable bearing on the interpretation of observations which seek the signature of a chemical-weathering thermostat in action. Our recent work has improved upon our original one-dimensional model, by coupling the model of the carbon dioxide land sink to our three dimensional climate model, which provides the precipitation patterns needed to accurately determine the sink.
- A series of papers concerning basic aspects of exoplanet dynamics which provide the underpinning for understanding condensation processes, drawing on concepts in linear wave dynamics that were originally developed for understanding the Earth's tropical circulation, especially phenomena such as El Nino.
- A new theory of the atmospheric circulation of planets for which the source of the atmosphere is evaporation or sublimation from the hot dayside and the sink is condensation on the cold nightside. This model has recently been extended to include the temperature inversions created by absorption of ultraviolet light, and has been applied to the lava planet K2-141b.
- Publication of the first simulation of the lava planet 55 Cancri-e which took into account the possibility of a non-condensible background atmosphere, which appears to be necessary to explain the relatively warm night-side temperatures of the planet.
Extended potential vorticity analysis to the atmosphere of hot gas-giant exoplanets which are tide-locked (i.e. always present the same face to their star).
- Contributed to the first global simulation of the effects of a novel heat-transporting mechanism whereby on very hot planets, the hydrogen molecule breaks up into atoms, absorbing heat in the process and releasing that heat where the atoms recombine.
- The first simulation of the global circulation of a brown dwarf star in orbit around and irradiated by a host star. Brown dwarfs are an outstanding and highly observable laboratory for probing the effects of clouds and condensation. The EXOCONDENSE team has published a number of additional papers probing condensation behaviour on such objects, employing our generalized version of the CM1 three dimensional convection model.
- The first simulation of 3D convection in a condensing pure steam atmosphere (relevant to runaway greenhouse atmospheres, which play an important role in evolution of planetary habitability).
Adapted our general circulation model for sub-neptunes featuring water in a hydrogen atmosphere, and has published a paper describing the dynamics in the absence of condensation, as a preliminary to probing latent heat and compositional buoyancy effects. Results have been obtained including the latter effects, and are currently being analysed in preparation for publication.
- Atmospheric chemistry plays a significant role in generating condensable substances, so further results have been obtained with our chemistry modelling framework, based on the open-source VULCAN code. A validation of the code has been published, and the code has been applied to address questions relating to hydrogen atmospheres.
- Produced the first model of the outer edge of the habitable zone to incorporate modern advances in the understanding of geochemical weathering processes. This work has considerable bearing on the interpretation of observations which seek the signature of a chemical-weathering thermostat in action. Our recent work has improved upon our original one-dimensional model, by coupling the model of the carbon dioxide land sink to our three dimensional climate model, which provides the precipitation patterns needed to accurately determine the sink.
So far, we have:
- Pioneered the use of the novel cube-sphere representation of atmospheres in exploration of the general circulation of tide-locked exoplanets.
- Developed a novel stochastic scheme for computing the electromagnetic radiation exiting from a planet's atmosphere, which has substantial advantages in the interpretation of astronomical data.
- Developed a new approach to computing transfer of energy by electromagnetic radiation in pure-steam (runaway greenhouse) atmospheres, which captures the essential aspects of the process, but is much more computationally efficient than full real-gas radiative transfer calculations. We have pioneered the use of advanced geochemical representations of the processes that control the amount of carbon dioxide in a planetary atmosphere.
- Developed one of the world’s few flexible three dimensional convection models suitable for a wide range of planetary atmospheres, and applied it to a range of atmospheres, including those of brown dwarfs.
By the end of the project, we will have developed a new understanding of convection including the effects of composition on buoyancy and the effects of condensible species that make up a major part of the mass of the convecting atmospheres; we also anticipate having used these insights to develop new representations of convection for use in global circulation models.
To that end, we will:
- Carry out three dimensional simulations of the climate and atmospheric evolution of planets which are undergoing a runaway greenhouse.
- Complete incorporating a model of mineral vapor clouds in our global circulation model, and will have applied this to lava planets, and compared simulations with data.
- Complete a study of the hydrological cycle on the temperate subNeptune exoplanet K2-18b, with emphasis on understanding the effects of latent heat release and compositional buoyancy on global circulation patterns.
- Pioneered the use of the novel cube-sphere representation of atmospheres in exploration of the general circulation of tide-locked exoplanets.
- Developed a novel stochastic scheme for computing the electromagnetic radiation exiting from a planet's atmosphere, which has substantial advantages in the interpretation of astronomical data.
- Developed a new approach to computing transfer of energy by electromagnetic radiation in pure-steam (runaway greenhouse) atmospheres, which captures the essential aspects of the process, but is much more computationally efficient than full real-gas radiative transfer calculations. We have pioneered the use of advanced geochemical representations of the processes that control the amount of carbon dioxide in a planetary atmosphere.
- Developed one of the world’s few flexible three dimensional convection models suitable for a wide range of planetary atmospheres, and applied it to a range of atmospheres, including those of brown dwarfs.
By the end of the project, we will have developed a new understanding of convection including the effects of composition on buoyancy and the effects of condensible species that make up a major part of the mass of the convecting atmospheres; we also anticipate having used these insights to develop new representations of convection for use in global circulation models.
To that end, we will:
- Carry out three dimensional simulations of the climate and atmospheric evolution of planets which are undergoing a runaway greenhouse.
- Complete incorporating a model of mineral vapor clouds in our global circulation model, and will have applied this to lava planets, and compared simulations with data.
- Complete a study of the hydrological cycle on the temperate subNeptune exoplanet K2-18b, with emphasis on understanding the effects of latent heat release and compositional buoyancy on global circulation patterns.