Electron Plasma Oscillations and Related Effects Observed By Voyager 1 in the Interstellar Plasma during 2014
Monday, 15 December 2014: 2:25 PM
It is now well known that the Voyager 1 spacecraft crossed the heliopause into interstellar space in late August 2012. A key observation supporting this conclusion was the detection of electron plasma oscillations in October-November 2012, and again in April-May 2013. These observations showed the local electron density was consistent with the expected density of the local interstellar plasma. Such plasma oscillations are believed to be excited by electron beams originating from shocks associated with global merged interaction regions (GMIRs) propagating outward from the Sun. Now, another series of plasma oscillation events has been observed starting in early February 2014, and continuing to the present time (late July 2014). These events show a clear association with changes in the cosmic ray intensities and anisotropies that are suggestive of a solar disturbance propagating outward through the interstellar plasma. The interpolated radial density profile inferred from these and the previous plasma oscillations shows that after crossing the heliopause the electron density increased rapidly from 0.055 cm-3 in late October 2012, at 122 AU, to a broad maximum of about 0.090 to 0.095 cm-3 in July-August 2013, at about 125 AU, followed by a slow decrease to about 0.085 cm-3 in the most recent data, at 128 AU. This density profile is consistent with a large-scale compression (i.e., pileup) of the interstellar plasma near the nose of the heliosphere, together with a smaller scale plasma depletion layer immediately adjacent to the heliopause, as suggested by Fuselier and Cairns .