A Climatic Investigation of Ammonia as a Remote Biosignature on Cold Haber Worlds

The study of exoplanet atmospheres for possible biosignatures will continue to dominate our understanding of surface-based habitability on planets outside our solar system over the coming decades. In one set of these studies, ammonia has been proposed as biologically significant on planets with atmospheres primarily composed of hydrogen and nitrogen, dubbed “cold Haber Worlds.” Previous modeling efforts have suggested that cold Haber Worlds should be able to photochemically produce enough ammonia to be detectable from Earth, but these efforts have not quantified the long term temperature profiles nor atmospheric lifetimes for these types of planets. Failing to understand these parameters calls into question ammonia’s ability to act as a remote biosignature. To explore these limits, we used a one-dimensional radiative-convective climate model to determine the atmospheric concentrations and surface temperatures for several cold Haber World cases. Here, we report on the results of these investigations and include a discussion regarding the atmospheric lifetimes for these planets along with a presentation on other possible explanations for ammonia in a planet's atmosphere. We also present a plan for future studies to further investigate the use of ammonia as a remote biosignature.Type: Bachelor's Thesi