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Evolution/Alteration of Venus Isotope Ratios in the Venusian Atmosphere (A Wish List…) The Many Morphings of Venus • The terrestrial planets likely formed in similar conditions, yet today they look very different. • The evolution of Venus must have been very different than that of Earth: - No global magnetic field (but likely in the past) - No plate tectonics (also likely in the past) - Enormous surface pressure and temperature (94 bar, 700K) - Atmosphere almost entirely CO2 - Incredibly dry atmosphere (water content 1000x below Earth) • One way to understand this evolution is through studying isotopes.. Isotopes as a Tracer of Evolution McKeegan et al. (2011) Isotopes as a Tracer of Evolution δ H218O(‰) Lee et al. (2005) Cias et al. (1995) D/H - Did Venus Have an Ocean? • D/H ratio is a tracer of planetary water loss. H —Out to Space— D H 2O HDO O • —Down into Crust(?)— O Venus’ atmospheric D/H ratio is very high (~250x Earth) - At one point, Venus was wet. But how wet? Owen, Tobias, et al. (2001) D/H - Did Venus Have an Ocean? • To find out how much water was present, you need: - Current D/H Ratio - Primordial D/H Ratio • - Fractionation factor • - Same as Earth? Same as Comets? Relative efficiency of H and D loss Current Absolute Abundance • H2O and H2 are fairly well measured Current calculations give a global ocean depth of 5-500 meters. Owen, Tobias, et al. (2001) D/H - Did Venus Have an Ocean? • To find out how much water was present, you need: - Current D/H Ratio - Primordial D/H Ratio • - Fractionation factor • - Same as Earth? Same as Comets? Relative efficiency of H and D loss Current Absolute Abundance • H2O and H2 are fairly well measured Current calculations give a global ocean depth of 5-500 meters. Owen, Tobias, et al. (2001) Atmospheric Escape - Nitrogen Owen, Tobias, et al. (2001) Atmospheric Escape - Nitrogen Stronger escape on Mars due to low gravity Owen, Tobias, et al. (2001) Atmospheric Escape - Nitrogen Stronger escape on Mars due to low gravity Jupiter system formed from a different source Owen, Tobias, et al. (2001) Atmospheric Escape - Nitrogen Stronger escape on Mars due to low gravity What about Venus? Jupiter system formed from a different source Owen, Tobias, et al. (2001) Atmospheric Replenishment - Ar and Ne • The strength of degassing processes is a clue to geologic activity. • Argon - 40Ar is produced radiogenically from 40K, while 36Ar is primordial. Turcotte and Schubert (1988) - Low 40Ar/36Ar indicates low level of current outgassing. Less active geology. • Helium - 4He produced radiogenically, 3He primordial. - Currently no accurate measurements of He isotopes. Current Geological Processes • 33S/32S and 34S/32S are good tracers of volcanic processes. • Isotope ratios are largely determined in planetary interiors and volcanism. • They therefore are a clue to the current state of geologic activity. • Deviations from the average level inform you of both surface chemistry and the atmospheric sulfur cycle δ 34S(‰) Measurements at ~1% accuracy are needed to provide useful constraints on atmospheric chemistry Thode, H.G. (1991) Questions? References • Baines, Kevin H., et al. "Experiencing Venus: Clues to the Origin, Evolution, and Chemistry of Terrestrial Planets Via In‐Situ Exploration of Our Sister World." Exploring Venus as a Terrestrial Planet (2007): 171-189. • Baines, Kevin H., et al. "The Atmospheres of the Terrestrial Planets: Clues to the Origins and Early Evolution of Venus, Earth, and Mars." Comparative Climatology of Terrestrial Planets 137 (2014). • Ciais, P., et al. "A large northern hemisphere terrestrial CO2 sink indicated by the 13C/12C ratio of atmospheric CO2." SCIENCE-NEW YORK THEN WASHINGTON- (1995): 1098-1098. • Donahue, T. M., and C. T. Russell. "The Venus atmosphere and ionosphere and their interaction with the solar wind: An overview." Venus II (1997): 3-31. • Farquhar, James, and Boswell A. Wing. "Multiple sulfur isotopes and the evolution of the atmosphere." Earth and Planetary Science Letters 213.1 (2003): 1-13. • Fedorova, A., et al. "HDO and H2O vertical distributions and isotopic ratio in the Venus mesosphere by Solar Occultation at Infrared spectrometer on board Venus Express." Journal of Geophysical Research: Planets (1991– 2012) 113.E5 (2008). • Owen, Tobias, et al. "Protosolar nitrogen." The Astrophysical Journal Letters 553.1 (2001): L77. • Thode, H. G. Sulphur isotopes in nature and the environment: an overview. Wiley, 1991. • Turcotte, D. L., and G. Schubert. "Tectonic implications of radiogenic noble gases in planetary atmospheres." Icarus 74.1 (1988): 36-46.