Part 4

The Magnetosphere

Perhaps the largest structure in the solar system is the magnetosphere of Jupiter. This is the region of space which is filled with Jupiter’s magnetic field and is bounded by the interaction of that magnetic field with the solar wind, which is the Sun’s outward flow of charged particles. The plasma of electrically charged particles that exists in the magnetosphere is flattened into a large disk more than 4.8 million kilometers (3 million miles) in diameter, is coupled to the magnetic field, and rotates around Jupiter. The Galilean satellites are located in the inner regions of the magnetosphere where they are subjected to intense radiation bombardment. It appears that Io is a source of the sulfur and oxygen ions which fill the magnetosphere. Another magnetospheric interaction is the electrical connection between Io and Jupiter along the magnetic field lines that leave Jupiter and intersect Io. This magnetic flux tube was examined by Voyager 1 and a flow of about five million amperes of current was measured, which was considerably more than anticipated. Voyager also discovered a new low-frequency radio emission coming from Jupiter, which is possibly associated with the Io torus.

Scientific investigations of the Voyager mission

Investigation Typical Jovian encounter objectives

Imaging science High-resolution reconnaissance over large phase angles; atmospheric dynamics; geologic structure of satellites Infrared radiation Atmospheric composition, thermal structure and dynamics; satellite surface composition and thermal properties Photopolarimetry Atmospheric aerosols; satellite surface texture and sodium cloud Radio science Atmospheric and ionospheric structure, constituents, and dynamics Ultraviolet spectroscopy Upper atmospheric composition and structure; auroral processes; distribution of ions and neutral atoms in the Jovian system Magnetic fields Planetary magnetic field; magnetospheric structure; Io flux tube currents Plasma particles Magnetospheric ion and electron distribution; solar wind interaction with Jupiter; ions from satellites Plasma waves Plasma electron densities; wave-particle interactions; low-frequency wave emissions Planetary radio astronomy Polarization and spectra of radio frequency emissions; Io radio modulation process; plasma densities Low-energy charged particles Distribution, composition, and flow of energetic ions and electrons; satellite-energetic particle interactions Cosmic ray particles Distribution, composition, and flow of high-energy trapped nuclei; energetic electron spectra

National Aeronautics and Space Administration

Jet Propulsion Laboratory California Institute of Technology Pasadena, California

JPL 400-24 7/79

Transcriber’s Notes

—Retained publication information from the printed edition: this eBook is public-domain in the country of publication.

—Silently corrected a few palpable typos.

—Moved captions nearer the relevant images; tweaked image references within captions accordingly.

—Added a Table of Contents.

—In the text versions only, text in italics is delimited by underscores.