THE HELIOSPHERIC PLASMA SHEET

High-resolution magnetic field and plasma data gathered by ISEE 3/ICE during several sector boundary crossings are used to investigate the n arrow heliospheric current sheet (almost-equal-to 3 x 10(3) km to 10(4 ) km thick), together with the heliospheric plasma sheet in which it i s embedded. The heliospheric plasma sheet region is identified by a si gnificantly enhanced plasma beta caused by density enhancements and di minished magnetic field strength and is about 20 to 30 times the thick ness of the current sheet. The thickness of the heliospheric plasma sh eet is found to increase exponentially with its average proton density . The heliospheric current sheet is often displaced to one edge or the other of the heliospheric plasma sheet. Further, the point of maximum plasma beta in the plasma sheet, where the magnetic field strength is at a broad local minimum, is not colocated with the heliospheric curr ent sheet. Within the plasma sheet, changes in the magnetic pressure a re balanced by corresponding changes in the plasma thermal pressure as expected for a convected solar wind feature. In addition, observation s show small pressure differences between the regions upstream and dow nstream of the plasma sheet, which are interpreted as causing the plas ma sheet to move across the spacecraft.