To learn more about Saturn's outer atmosphere, scientists use radio occultation, a method where radio signals are sent through Saturn's ionosphere to Earth from a nearby spacecraft.
The characteristics of the received signal help to determine densities of ionospheric material. Past occultation data from Pioneer 11 and Voyager spacecraft revealed a highly variable Saturnian ionosphere.
Moore et al. studied similar measurements recently reported by the Cassini radio science team. These new measurements not only reinforced the presence of ionospheric variability, but also provided enough data to clearly identify a dawn/dusk asymmetry in Saturn's equatorial ionosphere.
Based on suggestions that water vapor in Saturn's upper atmosphere might originate from its satellites and rings, the authors used a new three-dimensional model that includes water diffusion to demonstrate the catalytic effect of water. They show that molecules of water can exchange charge with free protons to create short-lived molecular ions that combine quickly with electrons, thereby depleting Saturn's ionosphere. Such corrections better predict the dawn/dusk asymmetry in densities measured by Cassini.
Title: Cassini radio occultations of Saturn's ionosphere: I. model comparisons using a constant water flux
Authors: Luke Moore and Michael Mendillo: Center for Space Physics, Boston University, Boston, Massachusetts, U.S.A.; Andrew F. Nagy: Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan, U.S.A.; Arvydas J. Kliore: California Institute of Technology/Jet Propulsion Laboratory, Pasadena, California, U.S.A.; Ingo Müller-Wodarg: Center for Space Physics, Boston University, Boston, Massachusetts, U.S.A.; Department of Physics and Astronomy, Imperial College, London, United Kingdom; John D. Richardson: Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, Massachusetts, U.S.A.
Source Geophysical Research Letters (GRL) paper 10.1029/2006GL027375, 2006
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