Isotopic Fractionation by Gravitational Escape |
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Authors: | Lammer H MISSING END TAG SJ |
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Institution: | 1.Space Research Institute, Department of Extraterrestrial Physics, Austrian Academy of Sciences, Schmeidlstr. 6, A-8042 Graz, Austria ;2.Institute for Geophysics, Astrophysics and Meteorology, University of Graz, Universit?tsplatz 5, A-8010, Graz, Austria ; |
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Abstract: | Present natural data bases for abundances of the isotopic compositions of noble gases, carbon and nitrogen inventories can
be found in the Sun, the solar wind, meteorites and the planetary atmospheres and crustal reservoirs. Mass distributions in
the various volatile reservoirs provide boundary conditions which must be satisfied in modelling the history of the present
atmospheres. Such boundary conditions are constraints posed by comparison of isotopic ratios in primordial volatile sources
with the isotopic pattern which was found on the planets and their satellites. Observations from space missions and Earth-based
spectroscopic telescope observations of Venus, Mars and Saturn's major satellite Titan show that the atmospheric evolution
of these planetary bodies to their present states was affected by processes capable of fractionating their elements and isotopes.
The isotope ratios of D/H in the atmospheres of Venus and Mars indicate evidence for their planetary water inventories. Venus'
H2O content may have been at least 0.3% of a terrestrial ocean. Analysis of the D/H ratio on Mars imply that a global H2O ocean with a depth of ≤ 30 m was lost since the end of hydrodynamic escape. Calculations of the time evolution of the 15N/14N isotope anomalies in the atmospheres of Mars and Titan show that the Martian atmosphere was at least ≥ 20 times denser than
at present and that the mass of Titan's early atmosphere was about 30 times greater than its present value. A detailed study
of gravitational fractionation of isotopes in planetary atmospheres furthermore indicates a much higher solar wind mass flux
of the early Sun during the first half billion years.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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