Photosynthetic Potential of Planets in 3:2 Spin Orbit Resonances

Abstract: Photosynthetic life requires sufficient photosynthetically active radiation (PAR) to metabolise. On Earth, plant behaviour, physiology and metabolism are sculpted around the night-day cycle by an endogenous biological circadian clock. The evolution of life was influenced by the Earth-Sun orbital dynamic, which generates the photo-environment incident on the planetary surface. In this work the unusual photo-environment of an Earth-like planet (ELP) in 3:2 spin orbit resonance is explored. Photo-environments on the ELP are longitudinally differentiated, in addition to differentiations relating to latitude and depth (for aquatic organisms) which are familiar on Earth. The light environment on such a planet could be compatible with Earth's photosynthetic life although the threat of atmospheric freeze-out and prolonged periods of darkness would present significant challenges. We emphasise the relationship between the evolution of life on a planetary body with its orbital dynamics.