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Chemical Mysteries and Biological Potential: (Some of the) Reasons to Return to Venus

Presentation #500.03 in the session “Plenary Panel: Venus-Sized Planets”.

Published onOct 26, 2020
Chemical Mysteries and Biological Potential: (Some of the) Reasons to Return to Venus

Some have called Venus “Earth’s evil twin” and, indeed, many of Venus’s environs appear quite hellish by terrestrial standards. This includes Venus’s atmosphere, famous for its thick global cloud/haze layer. There, the photochemical production of sulfuric acid (H2SO4) results in the condensation of liquid droplets composed of a ~85:15 ratio of H2SO4:H2O, by volume. While the general mechanism behind the formation of H2SO4 aerosols is now understood, many major mysteries about the chemistry of Venus’s atmosphere remain. For example, Bierson & Zhang (2020) demonstrated that it is difficult to reconcile the sharp decrease in SO2 abundance from the lower atmosphere (~100 ppm) to the middle atmosphere (~0.1 ppm) by conventional photochemistry and transport. This implies that a first-order process limiting the SO2 abundance in Venus’s middle atmosphere has yet to be discovered. SO2 is the dominant S-bearing species in Venus’s atmosphere and, along with OCS, is thought to be sourced from the planet’s surface/interior. However, the mechanism controlling the SO2 abundance near the surface of Venus is debated as well. Some have argued that volcanism is the main driver, while others have suggested that mineral buffers (e.g., pyrite-magnetite) are responsible (Hashimoto & Abe, 2005). Finally, an enigmatic UV absorber, responsible for attenuation in the 320-400 nm range, remains to be identified. Laboratory results from Wu et al. (2018) and modeling by Pinto et al. (2020) lend credence to the suggestion that OSSO and its photochemical products could be the long-sought culprits. But there is also the speculative hypothesis that this mysterious UV feature is related to the energy-capture mechanism of a hitherto unknown life form. Despite Venus’s hellish association, a steady stream of research stretching from the 1960s to today has continued to conjecture about Venus’s clouds as an abode for life that not only circumvents but thrives under such environmental challenges. Recently, Limaye et al. (2018) reviewed the potential for an iron- and sulfur-centered metabolism in the clouds of Venus, and Seager et al. (2020) proposed a Venusian life cycle involving a desiccated spore phase, where dormant life forms wait in the stagnant lower haze layer “depot” until they are lofted to the upper cloud layer where metabolic and replicative functions can resume. These tantalizing chemical mysteries, spanning from the surface to the upper atmosphere, along with the potential for extant Venusian life motivate further laboratory work, theoretical modeling, astronomical observations, and spacecraft missions to our sister world, Venus.


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