Recent Energetic Particle Activity at Voyagers 1 and 2
Abstract
We present energetic particle measurements made at Voyager 2 (helioradius 119 AU, lat S32°, long 218°) in the heliosheath and at Voyager 1 (helioradius 144 AU, lat N35°, long 175°) in the local interstellar medium. Data are from the LECP instruments on the two spacecraft during mainly the 2017-18 period. Voyager 2 is now 35 AU beyond its termination shock crossing (at 84 AU in August 2007), indicating a heliosheath at Voyager 2 at least 7-8 AU wider than that (28 AU) traversed by Voyager 1. This is not surprising, since Voyager 1 penetrated the heliosheath near the heliosphere's nose, while Voyager 2 is doing so more toward its flank, i.e., at a longitude tailward from nose by about 45° (see Dialynas et al., this session, for discussion of heliosheath thickness and the Voyagers). At Voyager 2 during 2015-18, intensities of heliosheath electrons >20 keV and low-energy ions >30 keV remain elevated, with the latter showing broad transient variations, with intensities a factor ≈5 or more above those measured during the 2013 intensity minimum. Pressure in the low-energy ions during 2015-18 is (1.2 ± 0.2) × 10-13 dyne cm-2, comparable to high levels measured in the heliosheath at Voyager 2 during 2009 through 2011. Data taken through mid-2018 show no signs that Voyager 2 has, or very soon will, cross the heliopause, particularly when compared to data from Voyager 1 taken prior to and during its heliopause crossing (at 122 AU in August 2012). Voyager 1 is now about 22 AU upstream of where it crossed the heliopause nose. Intensities of low-energy ions and electrons and of anomalous cosmic rays remain at background levels. Angular distributions of galactic cosmic ray protons >211 MeV continue to depart from isotropy, showing broad (0.3-0.8 year) episodes of intensity depletions of protons gyrating nearly perpendicular to the magnetic field. Data taken during August 2017 through early February 2018 show small, irregular departures from isotropy. Thereafter, the anisotropy increases steadily, but remains relatively small, reaching an amplitude ≈3% by mid-2018. These data are relevant to plasma oscillation events measured by the Voyager 1 Plasma Wave (PWS) instrument during August 2017 and early June 2018 (see Gurnett et al., this session, for discussion of these PWS data).
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMSH11A..02D
- Keywords:
-
- 2124 Heliopause and solar wind termination;
- INTERPLANETARY PHYSICSDE: 2126 Heliosphere/interstellar medium interactions;
- INTERPLANETARY PHYSICSDE: 2152 Pickup ions;
- INTERPLANETARY PHYSICSDE: 7845 Particle acceleration;
- SPACE PLASMA PHYSICS