Galileo Radio Occultation Measurements of Jupiter's Ionosphere

Mosaic Image of Jupiter's Belt Zone (False
 Color) False Color Mosaic of Jupiter's Belt-Zone Boundary

The references given below provide a detailed account of the results derived from the Galileo radio occultation experiments at Jupiter. The abstracts are included here to summarize the main findings. Further information about the experiment geometry may be found in the accompanying table and figure. A compressed tar archive of the electron density profile data files and associated labels from the Jupiter radio occultation experiments is available for download. The false color image of Jupiter shown above was produced at the California Institute of Technology with data provided by the Galileo Imaging Team.


D. P. Hinson, F. M. Flasar, A. J. Kliore, P. J. Schinder, J. D. Twicken, and R. G. Herrera, Jupiter's ionosphere: Results from the first Galileo radio occultation experiment, Geophys. Res. Lett., Vol. 24, No. 17, 2107-2110, 1997.

Abstract: The Galileo spacecraft passed behind Jupiter on December 8, 1995, allowing the first radio occultation measurements of its ionospheric structure in 16 years. At ingress (24 deg S, 68 deg W), the principal peak of electron density is located at an altitude of 900 km above the 1-bar pressure level, with a peak density of 100,000 per cubic centimeter and a thickness of about 200 km. At egress (43 deg S, 28 deg W), the main peak is centered near 2000 km altitude, with a peak density of 20,000 per cubic centimeter and a thickness of about 1000 km. Two thin layers, possibly forced by upwardly propagating gravity waves, appear at lower altitudes in the ingress profile. This is the first in a two-year series of observations that should help to resolve long-standing questions about Jupiter's ionosphere.

D. P. Hinson, J. D. Twicken, and E. T. Karayel, Jupiter's ionosphere: New results from Voyager 2 radio occultation measurements, J. Geophys. Res., Vol. 103, No. A5, 9505-9520, 1998.

Abstract: High-quality radio occultation data were acquired as the Voyager 2 spacecraft flew behind Jupiter on July 10, 1979. We have conducted a thorough analysis of dual-frequency data from the ionosphere using a new method of data processing based on scalar diffraction theory. The method is capable of deciphering the effects of multipath propagation, which had not previously been possible for these data. This allows retrieved vertical profiles of electron number density to be extended downward throughout the lower ionosphere. The electron density profile at occultation entry (66 deg S, 258 deg W) has a topside scale height of 1020 km, consistent with previous results. New results include a peak density of 350,000 per cubic centimeter at a height of 640 km above the 1-bar pressure level. In addition, the lower side of the main peak contains quasi-sinusoidal density oscillations with a vertical spacing of 25-40 km at altitudes of 450-600 km. These appear to signal the presence of upward propagating gravity waves. The electron density profile at occultation exit (51 deg S, 148 deg W) exhibits a peak density of 230,000 per cubic centimeter at an altitude of 1900 km, and the topside has a uniform scale height of 850 km. These characteristics of the upper ionosphere, where the principal ion is believed to be H+, are consistent with earlier results. New results include two secondary peaks at lower altitudes. An intermediate layer, where the principal ion may be H3+, is centered near 1000 km with a peak density of 46,000 per cubic centimeter. A lower layer, possibly composed of metallic ions, is situated between 200 and 550 km with densities of 20,000-120,000 per cubic centimeter. The latter contains multiple, thin layers of ionization at altitudes of 300-450 km, which may be the result of vertical shear in the zonal wind or plasma instabilities. The height-integrated Pedersen conductivity is about 0.5 and 0.4 mho at entry and exit, respectively.

Locations of Radio Occultation Measurements

Jupiter's magnetic field magnitude at the 1-bar pressure level, as computed from the GSFC O4 model [cf. Acuna et al., Jupiter's magnetic field and magnetosphere, in Physics of the Jovian Magnetosphere, pp. 1-50, Cambridge University Press, 1983]. Contours are labeled in gauss. Latitudes are planetocentric. Locations of radio occultation experiments are indicated by red stars (Galileo orbiter) and red diamonds (Voyager 2). The labels adjacent to the symbols consist of a 2-digit orbit number for Galileo or "V2" for Voyager 2, followed by "N" for entry or "X" for exit.

Locations of Radio Occultation

Download Electron Density Profiles

The Galileo Radio Propagation Team has generated profiles of electron number density versus radius in Jupiter's ionosphere. A compressed tar archive (in .tgz format) of five electron density profile (EDS) data files and associated labels from experiments with the Galileo spacecraft may be downloaded by clicking here. Two analogous profiles derived from previous experiments with the Voyager 2 spacecraft may be downloaded by clicking here. The profiles and labels have been delivered to NASA's Planetary Data System (PDS). The accompanying table indicates the name of the electron density profile data file for each occultation event. The format of each EDS file is described in the label associated with it.

Last updated: October 17, 2003
David Hinson / Joe Twicken