Plasma Sheet Thickness at Jupiter From Galileo Measurements of Electron Density and a New Model of Jupiter's Magnetic Field

Electron density has been determined throughout much of Galileo's primary mission at Jupiter (December 7, 1995 to November 6, 1997) by observing plasma waves measured by the plasma wave instrument on board the spacecraft. The density data set is used here to identify spacecraft encounters with Jupiter's magnetotail plasma sheet during the primary mission by assuming that electron density is highest at the center of the plasma sheet. As Jupiter rotates, the spacecraft encounters one pair of plasma sheet crossings during each ten-hour rotation period. Electron density is usually seen to increase as Galileo enters the plasma sheet, reach a maximum value near the center of the plasma sheet, and then decrease as the spacecraft exits the plasma sheet. This signature is clearest in the data at radial distances between 20 RJ, and 50 RJ from Jupiter. Plasma sheet thickness is determined by identifying the z-coordinate of the spacecraft as it enters and exits the plasma sheet. The z-position is measured with respect to a newer magnetic field model by Khurana and Kivelson. This work seeks to determine the plasma sheet thickness in Jupiter's magnetotail, where other instruments observe a thicker plasma sheet in the midnight and dusk sectors and a thinner, more distinct sheet in Jupiter's dawn sector.