An Advanced Radio Sounder for a Mission to Jupiter and its Icy Moons

Bodo W. Reinisch, James L. Green, and the PARS Team

A new planetary advanced radio sounder (PARS) for the radio sounding of
JupiterÕs icy moons and the surrounding Jovian magnetosphere is under
development. It will provide unique remote sensing observations of the plasma
and magnetic field environments and the subsurface conductivities of Europa,
Ganymede, and Callisto. The instrument will cover the frequency range from 1 kHz
to 40 MHz in order to make it possible to automatically assess the spatial
structures of ionospheric plasma above the moons from the orbiting spacecraft,
and then select the most suitable frequencies for radio probing of the icy moons
surfaces. In-situ plasma and magnetic field resonance measurements will
supplement the remote sounding measurements similar to the Radio Plasma Imager
(RPI) observations from the Imager for Magnetopause-to-Aurora Global Exploration
(IMAGE) satellite. Local measurements of induced magnetic fields from salty
subsurface oceans are significantly affected by contributions from ionospheric
current systems, particularly along inclined moon orbits, so remote imaging of
the associated plasma density structures will be critical to modeling of the
ionospheric backgrounds for magnetic sensing of oceans below the icy surfaces of
these three moons.

The electron densities in the moonsÕ ionospheres are expected to be lower than
~7 MHz, which will allow frequencies from 9 to 40 MHz to be used for subsurface
probing. Precision group height techniques based on the phase difference on
echoes at two closely spaced, simultaneously transmitted frequencies will
measure the accurate depths of subsurface stratifications. The ionospheric
(topside) profile measurements will be used to determine the diurnal variations
in the sources and sinks of plasma, and will also allow estimating the
ionospheric retardation and correct the propagation delays of subsurface echoes. 

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General Assembly of International Union of Radio Science, New Delhi, India, 
23-29 October 2005