Determination of Jupiter's electron density profile from plasma wave observations


  • D. A. Gurnett,

  • F. L. Scarf,

  • W. S. Kurth,

  • R. R. Shaw,

  • R. L. Poynter


This paper summarizes the electron density measurements obtained in the Jovian magnetosphere from the plasma wave instruments on the Voyager 1 and 2 spacecraft. Three basic techniques are discussed for determining the electron density: (1) local measurements from the low-frequency cutoff of continuum radiation, (2) local measurements from the frequency of upper hybrid resonance emissions, and (3) integral measurements from the dispersion of whistlers. The limitations and advantages of each technique are critically reviewed. In all cases the electron densities are unaffected by spacecraft charging or sheath effects, which makes these measurements of particular importance for verifying in situ plasma and low-energy charged particle measurements. In the outer regions of the dayside magnetosphere, beyond about 40 RJ, the electron densities range from about 3 × 10−3 to 3 × 10−2 cm−3. On Voyager 2, several brief excursions apparently occurred into the low-density region north of the plasma sheet with densities less than 10−3 cm−3. Approaching the planet the electron density gradually increases, with the plasma frequency extending above the frequency range of the plasma wave instrument (56 kHz, or about 38 electrons cm−3) inside of about 8 RJ. Within the high-density region of the Io plasma torus, whistlers provide measurements of the north-south scale height of the plasma torus, with scale heights ranging from about 0.9 to 2.5 RJ.