Habitable Zones for Planets with Pre-Industrial Earthlike Biospheres orbiting Main Sequence Stars

Abstract

We investigate the general case of a "natural" Earth without manmade influence. To do this we switch off anthropogenic sources in our model and investigate the biomarkers and Habitable Zone (HZ) limits for three main sequence stars. The HZ around a star is usually defined as the range of distances over which liquid water can exist on the surface of an orbiting planet. This assumes to be a requirement for the formation of life as we know it. In this work we define the HZ more conservatively to be suitable for complex life with a surface temperature range from 0°C to 30°C. With these constraints we determine the width of the HZ around main sequence stars (Sun, F2V and K2V) in which an earthlike biosphere would exist, i.e. we do not consider here terrestrial planets with enhanced CO2 atmospheres. We neglect anthropogenic influences and take a pre-industrial composition (1850) of the Earth atmosphere as starting conditions for our model. We have used a coupled radiative-convective photochemical column model to investigate the effect on atmospheric biomarkers across the HZ.