Atmospheres as Habitats.

Abstract

The potential of planetary atmospheres as habitats is understudied and likely underestimated. Although planetary atmospheres can provide the fundamental physical, chemical, and energetic requirements for life, they also represent unique challenges to survival and biosphere stability. Atmospheric habitats, either self-contained or dependent on surface biospheres, may exist elsewhere in the solar system and on exoplanets. Four hypotheses essential to airborne habitats and their potential importance to astrobiology include: H-I: Earth can host fully airborne life. H-II: Fully airborne microbial life can be experimentally evolved and sustained in the laboratory. H-III: Atmospheres within our solar system can be assessed for a potential aerobiosphere, with Venus the most likely candidate. H-IV: Atmospheres around exoplanets can be modeled, simulated, and observed to assess the likelihood of aerobiospheres. New theory, modeling, observation, and experimentation are required to improve our understanding of the constraints and likelihood of airborne life. Notably, we can neither confirm nor rule out multigenerational airborne life on Earth yet.