Remote Radio Sounding Science For JIMO

J. L. Green (1), B. W. Reinisch (2), P. Song (2), S. F. Fung (1), 
R. F. Benson (1), W. W. L. Taylor (1), J. F. Cooper (1), L. Garcia (1), 
T. Markus (1), D. Gallagher (3), P. Gogineni (4)

(1) NASA/GSFC, Greenbelt, MD 20771 
(2) Center for Atmospheric Research, University of Mass. Lowell, Lowell, MA 01854
(3) NASA/MSFC, Huntsville, AL, 35812
(4) Remote Sensing Laboratory, University of Kansas, 66045


Radio sounding of the EarthÕs topside ionosphere and magnetosphere is a proven
technique from geospace missions such as the International Satellites for
Ionospheric Studies (ISIS) and the Imager for Magnetopause-to-Aurora Global
Exploration (IMAGE). Application of this technique to the Jupiter Icy Moons
Orbiter (JIMO) mission will provide unique remote sensing observations of the
plasma and magnetic field environments, and the subsurface structures of Europa,
Ganymede, and Callisto. Spatial structures of ionospheric plasma above the
surfaces of these bodies will vary in response to magnetic field perturbations
from magnetospheric plasma flows, ionospheric currents from ionization of
sputtered surface material, and induced electric currents in salty subsurface
oceans. Radio sounding at 3 kHz to 10 MHz will provide globally-determined
electron densities necessary for the extraction of the oceanic current signals
and will supplement in-situ plasma and magnetic field measurements. Long-range
magnetospheric sounding, pioneered by the radio plasma imager (RPI) instrument on
IMAGE, has provided electron density distributions along magnetic field lines and
in radial directions on time scales of minutes. RPI has also been able to measure
the entire electron plasma density distributions (in the orbit plane) of the
EarthÕs polar cap and the plasmasphere within one pass of the spacecraft. In a
similar manner, a radio sounder orbiting an icy moon would be able to measure the
electron density along the magnetic field into each hemisphere and provide
information on the Jovian magnetospheric background, the magnetospheric
influences on the moonÕs ionospheres, and distortions of magnetic field line
geometry from model predictions. The higher-power source available from JIMO
would allow radio sounding transmissions at much higher powers than those used on
ISIS or IMAGE making subsurface sounding of the Jovian icy moons possible at
frequencies above the ionosphere peak plasma frequency from ~5 MHz to 40 MHz.
Subsurface variations in dielectric properties, can be investigated by radio
sounding allowing the detection of dense and solid-liquid phase boundaries
associated with oceans and related structures in overlying ice crusts.

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Presentation, Fall Meeting, American Geophysical Union, San Francisco, USA, 
8-12 December 2003