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The Evolution of Habitable Zones in Known Exoplanet Systems

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Everyday new exoplanets are being discovered; some of which are in the habitable zone around their star and each with a lifespan long enough for the potential of life to develop. The information presented in this paper is on notable main sequence stars and how they evolve through time. I show the evolution of habitable zones, how they grow and shrink throughout the lifecycle of their host star. After their time on the main sequence these stars will all reach their inevitable end; becoming red giants, asymptotic giant stars and white dwarf stars. Red dwarf stars will take longer than the age of the universe and will be the last remaining stars amongst the black holes. I make use of Rich Townsend's stellar evolutionary model to calculate the evolution of the habitable zone distances for nine main sequence stars of spectral type G, K and M with varying stellar metallicities. The evolution of each habitable zone is represented by its host star’s luminosity against time. All the star systems comprise planets: the number of exoplanets in the habitable zone, at any given time along the evolutionary track are shown. The inner and outer zones will change relative to the different variables used at any given age. The results show a pattern emerging between the different types of habitable zones. An Earth-like albedo of 0.3 produces a greater habitable zone distance than that of a Venusian albedo of 0.75 but less than the habitable zone of a tidally locked planetary system. The radius of the habitable zone will vary whilst a star is undergoing a change in phase. The habitable zone migrates inwards post main sequence.
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