The Evolution of Climate and a Possible Biosphere on Venus
Abstract
Of the three local terrestrial planets with atmospheres, two have lost their oceans either to a subsurface cryosphere or to space, and one has had liquid oceans for most of its history. Understanding the sources and sinks for surface water and characterizing the longevity of oceans and the magnitude of loss mechanisms on terrestrial planets of differing size, composition and proximity to stars of various stellar types, and the range of physical parameters which facilitates plate tectonics is key to defining stellar habitable zones.
Venus almost surely experienced a transition, early in its history, from a wet, more Earth-like environment to its current hot and highly desiccated state. The timescale is disputed, but recent results using 3D GCM's suggest that, depending on ancient rotation rate and topography, an ancient ocean may have persisted for 2 GY. A more recent global transition is indicated by the sparse, randomly distributed and relatively pristine crater population, which implies a decrease in volcanic resurfacing rate between 300 and 1000 Myr ago. These two transitions may have been causally related if the loss of atmospheric and interior water caused the transition from plate tectonics to single plate behavior. For much of solar system history Earth may have had a neighboring planet with life-supporting oceans. During this time the terrestrial planets were not isolated. Rather, due to frequent impact transport, they represented a continuous environment for early microbial life. Life, once established in the early oceans of Venus, may have migrated to the clouds which, on present day Venus, may represent a habitable niche. Though highly acidic, this aqueous environment enjoys moderate temperatures, surroundings far from chemical equilibrium, and potentially useful radiation fluxes. Observations of unusual chemistry in the clouds, puzzling patterns of unidentified solar absorbers, and particle populations that are not well characterized, suggest that this environment must be explored much more fully before biology can be ruled out. A sulfur-based metabolism for cloud-based life on Venus has been proposed. While speculative, these arguments, along with the discovery of terrestrial extremophile organisms that might survive in the Venusian clouds, establish the credibility of astrobiological exploration of Venus.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.P43G3837G
- Keywords:
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- 5210 Planetary atmospheres;
- clouds;
- and hazes;
- PLANETARY SCIENCES: ASTROBIOLOGYDE: 5215 Origin of life;
- PLANETARY SCIENCES: ASTROBIOLOGYDE: 5225 Early environment of Earth;
- PLANETARY SCIENCES: ASTROBIOLOGYDE: 6207 Comparative planetology;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS