Metallicity and the Evolution of the Habitable Zone

The habitable zone around a star is defined as a region around the star where temperatures are just right for liquid water to exist on a planet’s surface. During the course of a star’s life, the location and width of the habitable zone changes as the luminosity of the star changes. As a consequence, a planet that is currently in the habitable zone of its host star only spends a finite amount of time there. The longer a planet spends in the habitable zone, the more time it has for life to develop and evolve.Danchi & Lopez (2013) present a study on the evolution of the habitable zone around stars with 1.0, 1.5 and 2.0 times the mass of the Sun, for metallicities ranging from 0.0001 to 0.070. A star’s metallicity is basically the fraction of a star’s mass that is comprised of elements heavier than hydrogen and helium. For comparison, the Sun’s metallicity is 0.017. The study shows that the metallicity of a star strongly affects the amount of time a planet spends in the star’s habitable zone.A star like the Sun spends the majority of its life producing energy by fusing hydrogen into helium in its core. This ...