Evidence for reconnection at Saturn's magnetopause

Abstract

Observations of Saturn's magnetopause by the Cassini Plasma Spectrometer (CAPS) and magnetometer have revealed clear instances of magnetic reconnection signatures, two of which are described here. Both encounters occurred at the equator in the prenoon sector as Cassini was exiting the magnetosphere. Evidence of heating in the electrons and ions is highly suggestive of energization comparable to that associated with the reconnection process at Earth. In one case, the fields are strongly antiparallel and the magnetic data indicate the presence of a locally open magnetic field. In the other example, magnetic data indicate a locally closed magnetic field compatible with the field lines being locally parallel, but the particle signatures lead to the conclusion of a distant reconnection site poleward of the cusps being active. The reconnection voltage for the first case is calculated to be 48 kV, which is of the same order as previous estimates at Saturn. This is lower than the corotational voltage but is not insignificant.