Using an energy balance model to determine exoplanetary climates that support liquid water.

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Sullivan, Macgregor
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Undergraduate research. , Undergraduate thesis.
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Spine label: Using an energy balance model to determine exoplanetary climates.
The purpose of this thesis is to modify an energy balance atmospheric model created by R. Pierrehumbert (Pierrehumbert 2011). His energy balance model gave an estimate of Gliese 581g’s, a tidally locked exoplanet, atmosphere. Using an energy balance model, the surface and air temperatures can be found for a planet in equilibrium, when the amount incoming energy is equal to the amount of outgoing energy. Starting from Pierrehumbert’s model, we have added for a greenhouse effect and an ice-albedo feedback. We have also modified the model to test a rotating planet (similar to Earth) in addition to a tidally locked planet. This model, by varying the planet’s surface pressure, stellar flux, and the atmosphere's emissivity, can find which conditions leads to the planet having the temperatures needed to support liquid water. Surface pressure affects how efficient the planet is at redistributing heat leading to uniform temperatures across its surface. As the incoming stellar flux or the emissivity increase, the planet’s surface temperatures rise due the increase in absorbed energy from the planet’s surface. We have also found that the orbital distances that are able to support liquid water depend heavily on the pressure of the planet’s atmosphere. In future work, this model will produce the planet’s IR emission to determine if the planet is detectable using telescopes like the James Webb Space Telescope.
i, 80 leaves: color illustrations.
Includes bibliographical references: leaves 79-80.
Section 1: Introduction – 1.1 Detection Methods & Measurable Values – 1.1.1 Transits and Atmospheric Composition - HD 209458b -- 1.1.2 - Secondary Eclipse and Temperature Difference Detection - HD 189733b -- 1.1.3 - Radial Velocity Method and the Mass, Radius, and Period - Gliese 581g -- 1.2 - What is the Habitable Zone -- 1.3 - Previous Atmospheric Models -- 1.4 - Looking at Eyeball Earths -- Section 2: Weak Temperature Gradient Energy Balance Model – 2.1 - What is an Energy Balance? --2.2 - The Weak Temperature Gradient Energy Balance Model -- 2.2.1 - Incoming Solar Energy -- 2.2.2 - Emitted Thermal Energy -- 2.2.3 - Turbulent Mixing -- 2.2.4 - The Greenhouse Effect -- 2.2.5 - Non Tidally Locked Planet -- Section 3: Methods -- 3.1 - Solving for Ta and Tg(θ) -- 3.1.1 - The Newton’s Method -- 3.1.2 - The Secant Method -- 3.2 - How does the Code Work? -- 3.2.1 - GroundTemp -- 3.2.2 - Albedo -- 3.2.3 - Roots -- 3.2.4 - WTG_EBM -- Section 4: Results -- 4.1 - The Model’s Output --4.2 - Identify Stable and Unstable Roots -- 4.3 - Changing the Model Parameters -- 4.3.1 - What happens as Stellar Flux is Changed? -- 4.3.2 - What happens as Emissivity is Changed? -- 4.3.3 - What happens as Surface Pressure is Changed? -- 4.3.4 - What are the differences between Tidally Locked and Rotating Planets? -- 4.3.5 - How does Introducing an Atmosphere affect the Planet? -- Section 5: Conclusions -- 5.1 - Effect of Pressure on Habitability -- 5.2 - How well does the Model Work? -- 5.2.1- Effect from the Approximations -- 5.3 - Future Work
Wheaton College (MA).
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