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  • Exo II: Modelling Phase Curves of Hot Jupiter Planets and Implications for Habitable Planets



    For centuries, humans have wondered if there is intelligent life elsewhere in the universe. With the advent of telescopes capable of detecting planets around other stars, exoplanets, we would like to determine if these planets are capable of harboring life. In our solar system, spacecrafts and landers have been sent to our terrestrial neighbors to look for life. Sample return missions, though costly in both time and money, are one sure fire way to discover if a material ever has, ever could, or contains any familiar life. Barring that, in situ measurement from landers are next best. For exoplanets, these methods are impossible. Therefore, we use remote sensing techniques. What light should we look for to detect life?

    Life, as we know it, requires certain surface and atmospheric conditions. We require oxygen to breathe, ozone to protect us from harmful rays, and liquid water on the surface to serve as a catalyst for biochemical reactions. These signatures of life can be detected in the spectrum of a planetary atmosphere. To understand how biology can affect the atmosphere it is critical to understand atmospheres in habitable and non-habitable situations. Ideally a spectrum would reveal features related to water and ozone. Direct imaging of a planet would be ideal. Both of these techniques rely on the planet being bright enough and distant enough from its star to resolve them separately. The systems for which these techniques have been applied are few in number. Conversely, there are a number of photometric surveys searching for and characterizing exoplanets.

    Kepler’s high-precision light curves have provided a cornucopia of information buried within the noise of other surveys. Not only are they able to provide a measure of stellar limb darkening, the period of the planet, the size of the planet, and the orbital semi-major axis, but these light curves may also provide information about the temperature, albedo, and even mass of the planet.

    In our project, we will demonstrate what can be learned from the albedo and temperature for several well-known exoplanets. We will introduce the components of light curves and their relationship to the geometry of the system. We later discuss the atmospheric implications for these planets, and finally what a potentially habitable terrestrial planet would look like.

    Geometry of Phase Curves

    As a planet orbits its host star, from our perspective, interesting situations can arise. These situations include transits, when the planet crosses in front of the star from our perspective, occultations, when the planet passes behind the star, and other phase effects caused by the planet reflecting stellar light, that lead to fluctuations in the brightness of the system over time. These fluctuations can be quantified and are governed by properties of bodies in the system. Figure \ref{fig:geometry} demonstrates an example light curve and the geometry of a planet similar to the situations of the planet presented in this report.