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The Venusian Lower Atmosphere Haze as a Depot for Desiccated Microbial Life: A Proposed Life Cycle for Persistence of the Venusian Aerial Biosphere.

Authors
  • Seager, Sara1, 2, 3
  • Petkowski, Janusz J1
  • Gao, Peter4
  • Bains, William1
  • Bryan, Noelle C1
  • Ranjan, Sukrit1
  • Greaves, Jane5, 6
  • 1 Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
  • 2 Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
  • 3 Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
  • 4 Department of Astronomy, University of California at Berkeley, California, USA.
  • 5 School of Physics and Astronomy, Cardiff University, Cardiff, United Kingdom. , (United Kingdom)
  • 6 Institute of Astronomy, Cambridge University, Cambridge, United Kingdom. , (United Kingdom)
Type
Published Article
Journal
Astrobiology
Publisher
Mary Ann Liebert
Publication Date
Oct 01, 2021
Volume
21
Issue
10
Pages
1206–1223
Identifiers
DOI: 10.1089/ast.2020.2244
PMID: 32787733
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

We revisit the hypothesis that there is life in the venusian clouds to propose a life cycle that resolves the conundrum of how life can persist aloft for hundreds of millions to billions of years. Most discussions of an aerial biosphere in the venusian atmosphere temperate layers never address whether the life-small microbial-type particles-is free floating or confined to the liquid environment inside cloud droplets. We argue that life must reside inside liquid droplets such that it will be protected from a fatal net loss of liquid to the atmosphere, an unavoidable problem for any free-floating microbial life forms. However, the droplet habitat poses a lifetime limitation: Droplets inexorably grow (over a few months) to large enough sizes that are forced by gravity to settle downward to hotter, uninhabitable layers of the venusian atmosphere. (Droplet fragmentation-which would reduce particle size-does not occur in venusian atmosphere conditions.) We propose for the first time that the only way life can survive indefinitely is with a life cycle that involves microbial life drying out as liquid droplets evaporate during settling, with the small desiccated "spores" halting at, and partially populating, the venusian atmosphere stagnant lower haze layer (33-48 km altitude). We, thus, call the venusian lower haze layer a "depot" for desiccated microbial life. The spores eventually return to the cloud layer by upward diffusion caused by mixing induced by gravity waves, act as cloud condensation nuclei, and rehydrate for a continued life cycle. We also review the challenges for life in the extremely harsh conditions of the venusian atmosphere, refuting the notion that the "habitable" cloud layer has an analogy in any terrestrial environment.

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