Exploring Jupiter with Radio Waves W S Kurth

Exploring Jupiter with Radio Waves W. S. Kurth The University of Iowa City, IA

Juno Science Objectives Origin Determine O/H ratio (water abundance) and constrain core mass to decide among alternative theories of origin. Interior Understand Jupiter's interior structure and dynamical properties by mapping its gravitational and magnetic fields Atmosphere Map variations in atmospheric composition, temperature, cloud opacity and dynamics to depths greater than 100 bars at all latitudes. Magnetosphere Characterize and explore three-dimensional structure of Jupiter's polar magnetosphere and auroras.

A Useful Analogy (hopefully) Vibrating string = Plasma Sound Waves = Radio Waves

History: Before Spacecraft Measurements • Jovian decametric radiation (auroral) discovered from groundbased measurements in 1955 (Burke and Franklin) • Period (IAU) 9 h 55 m 29. 37 +/- 0. 04 s • Maximum frequency of decametric radiation (39. 5 MHz) yields estimate of magnetic field strength (14. 1 Gauss) • Study of decimetric radiation (from the radiation belts) provided information on the tilt of the magnetic dipole (about 10 degrees) from the rotation axis and with a small offset from the center. • Io influence on Jupiter’s decametric radiation (Bigg, 1964)

Jupiter’s Magnetosphere Solar Wind

Periodicities in radio emissions allow us to determine the rotation period of a planet.

Bigg’s discovery of an Io influence on the visibility of Jovian radio emissions foreshadowed the Voyager discovery of volcanoes on Io in 1979.

Radio waves allow us to ‘see’ Jupiter’s radiation belts. Janssen et al. , Planetary Radio Emissions V, 2001.

Auroras are a visible manifestation of a magnetized planet’s interaction with it’s space environment.

Jupiter has the brightest auroras in the solar system.

Juno will provide an opportunity to determine how Jupiter’s auroras are generated.

Jupiter produces a veritable ‘zoo’ of radio emissions.

Auroral radio emissions are composed of a plethora of fine structure.

Juno will allow us to fly through the source of Jupiter’s auroral radio emissions.

Radio waves allow us to look for lightning in Jupiter’s atmosphere.

Radio Planets: Comparing Earth & Jupiter Earth Jupiter Planetary Radius 6378 km 71, 400 km Earth x 11 Rotation Period 24 Hr ~ 10 Hr Earth x 0. 4 Magnetic Moment 0. 3 4. 3 Earth x 14 Frequency Range 30 k. Hz to 800 k. Hz Like AM radio 10 k. Hz to 40 MHz Like Shortwave Radio Total Power ~ 30 Mega. Watts ~ 10 Giga. Watts Earth x 300 Radio Emissions Most Influenced By: Sun Io, Rapid Rotation Scale of Magnetosphere 65, 000 km 4, 300, 000 km Earth x 65

Galopeau et al. , Planetary Radio Emissions VI, 2005 Gurnett and Goertz, J. Geophys. Res. , 1981.

Both Earth and Jupiter produce intense radio emissions as part of the process of generating auroras. Earth de Feraudy et al. , Planetary Radio Emissions V, 2001. Ladreiter & Le. Blanc, Planetary Radio Emissions III, 1991.