Saturn's hinge parameter from Cassini magnetotail passes in 2013–2014

Abstract

AbstractObservations of energetic charged particles (>40 keV) and magnetic fields were made by Cassini instruments during eight passes through Saturn's magnetotail in 2013 and 2014. These passes are unique because the spacecraft crossed the magnetotail plasma sheet at nearly perpendicular incidence, thus allowing an accurate cross‐section measurement. For each tail pass, Cassini/Magnetosphere Imaging Instrument detectors recorded fluxes that maximized at the center of the magnetotail while the Cassini/Magnetometer recorded magnetic field components in spherical coordinates for which BR = 0 at the center. These sheet encounters can be organized using the Arridge “bowl” model, an axially symmetric paraboloid surface for the neutral sheet that is characterized by a “hinge” distance rH. This hinge parameter can be computed for each pass and each observable by interpolating the observed encounter time between those times expected for rH = 10, 20, 30, and 40 Rs. The hinge distances vary considerably, although all values of rH are the same within statistical variation. The BR = 0 crossings yield an average rH = 26.8 ± 6.0 Rs. However, the 41–64 keV electrons exhibit a mean rH = 23.2 ± 9.2 Rs (if using flux peaks to mark disk crossings) or rH = 22.3 ± 5.7 Rs (if using flux centroids). On the other hand, the 56–106 keV ions display rH = 27.2 ± 6.4 Rs (peaks) and rH = 26.2 ± 8.1 Rs (centroids). Thus, the electrons have hinge distances slightly smaller than those of the magnetic field and ions. This behavior suggests that there may be one magnetotail for electrons and another for the ions and magnetic field.