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Chemical Evolution in the Saturnian System

This article explores the Miller/Urey experiment and its implications for the origin of life. It discusses the molecules involved in the experiment and their role in the emergence of life on Earth.

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Chemical Evolution in the Saturnian System

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  1. Chemical Evolution in the Saturnian System Yuk L. Yung C. D. Parkinson Division of Geological and Planetary Sciences California Institute of Technology 1/4/2005

  2. Miller/Urey Experiment By the 1950s, scientists were in hot pursuit of the origin of life. Around the world, the scientific community was examining what kind of environment would be needed to allow life to begin. In 1953, Stanley L. Miller and Harold C. Urey, working at the University of Chicago, conducted an experiment which would change the approach of scientific investigation into the origin of life. Miller took molecules which were believed to represent the major components of the early Earth's atmosphere and put them into a closed system

  3. Purines Pyrimidines Sugars Fatty acids Amino acids Nucleotides Lipids (Membranes) Proteins (Catalysts) Nucleic acids (Information)

  4. The chiral Molecules of Life

  5. Barrier ~ 5.0 kcal mol-1 + Barrier ~ 3.9 kcal mol-1 + ΔHrxn ~ -1.6 kcal mol-1

  6. Atmospheric Densities N2 density from mass 28 peak N2 density from mass 14 peak

  7. INMS Hydrocarbons 1200 km(preliminary) • C2H2 (acetylene) ~5000 ppm • C2H6 (ethane) ~300 ppm • C3H4 (propyne) ~100 ppm • C3H8 (propane) ~30 ppm • C4H2 (diacetylene) (10 ppm) ? • C2N2 (cyanogen) (10 ppm) ? • C6H6 (benzene) (10 ppm) ?

  8. Isotopic ratios • Nitrogen • INMS from N2: 14N/15N = 182 (+74, -41) • Gurwell submillimeter (HCN) = 94+/-13 (T dependent) • Jupiter:430 (Owen et al., 2001), H-B:320,Terrestrial:272 • HCN enriched relative to N2 in ISM - Terzieva&Herbst, 2000 • Carbon • INMS from CH4: 12C/13C = 93 +/- 1 • ISO(HCN) = 89 +/- 9 • Gurwell submillimeter (HCN) = 130+/-29 • Terrestrial:89 • No evidence of 36Ar ==>less than 10-4

  9. Hydrodynamic Escape from Planetary Atmospheres In Jean’s escape, particles at the exobase moving in the outward direction with sufficient velocity (i.e. high enough kinetic energy) can escape from the planet…typically the vertical flow from the atmosphere is small HDE arises when the flow speed becomes large

  10. HDE also differs from gas-kinetic evaporation in that in some circumstances a substantial fraction of the entire thermospheric energy budget is used to power escape of gas from the atmosphere; it is possible that heavier species can be “dragged” along during HDE Under this circumstance, it is expected that atmospheric expansion due to HDE will be the dominant loss process

  11. HDE is an important process in atmospheric evolution of the terrestrial planets and CEGPs and can change the composition of planetary atmospheres from primordial values irreversibly hydrogen escape is of particular importance as it affects the oxidation state of the atmosphere and because it results in the loss of water vapour

  12. For Instance…(outstanding problems) Did early Venus initially have an ocean? HDE modelling using a water-rich atmosphere on Venus can help assess this problem (Kasting and Pollack, 1983) Isotopic ratios (i.e. fractionation: D/H, N, and noble gases) are very different on terrestrial planets even though they are believed to be formed from similar material (Hunten et al., 1987; Pepin, 1991)

  13. and… Greenhouse warming by methane in the atmosphere of the early Earth? CH4 density on early Earth dependent on HDE, strongly influencing its atmospheric climate and composition, i.e. (Pavlov et al., 2000; 2001) “blow-off” on HD209458b (Osiris) (Vidal-Madjar et al., 2003; 2004)

  14. Hydrodynamic Escape By Vidal-Madjar, A.

  15. HD Escape Equations

  16. Some Previous Models Watson et al. (1981): shooting method or trial-and-error method to solve steady state HDE equation for early Earth and Venus Set of solutions at the critical point (exobase) selected which can match the zero temperature at infinity and set temperature at the lower boundary. Calculated temperature and density at the boundary very sensitive to initial settings and I couldn’t reproduce cases using that method

  17. Kasting and Pollack (1983) numerically solve the steady state HDE problem for Venus Use an iterative method in which the momentum and energy equations are simultaneously solved Not able to get an exact sol’n at the critical point obtaining the supersonic solution Instead, they obtained subsonic solutions and argued that the escape flux can be close to the critical escape flux Method included infrared cooling by H2O and CO2 while only EUV absorption considered by Watson

  18. Chassefiere (1996) solves steady state HDE problem from lower boundary to exobase level Position of exobase level is determined when the mean free path becomes greater than the scale height Outgoing flow at exobase is set to be equivalent to a modified Jean’s escape (ionization and interaction between escaping particles and solar wind considered) Application to water-rich early Cytherian atmosphere

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