Voyager 1 in the Foreshock, Termination Shock, and Heliosheath

Abstract

Voyager 1 (V1) began measuring precursor energetic ions and electrons from the heliospheric termination shock (TS) in July 2002. During the ensuing 2.5 years, average particle intensities rose as V1 penetrated deeper into the energetic particle foreshock of the TS. Throughout 2004, V1 observed even larger, fluctuating intensities of ions from 40 kiloelectron volts (keV) to >/=50 megaelectron volts per nucleon and of electrons from >26 keV to >/=350 keV. On day 350 of 2004 (2004/350), V1 observed an intensity spike of ions and electrons that was followed by a sustained factor of 10 increase at the lowest energies and lesser increases at higher energies, larger than any intensities since V1 was at 15 astronomical units in 1982. The estimated solar wind radial flow speed was positive (outward) at approximately +100 kilometers per second (km s(-1)) from 2004/352 until 2005/018, when the radial flows became predominantly negative (sunward) and fluctuated between approximately -50 and 0 km s(-1) until about 2005/110; they then became more positive, with recent values (2005/179) of approximately +50 km s(-1). The energetic proton spectrum averaged over the postshock period is apparently dominated by strongly heated interstellar pickup ions. We interpret these observations as evidence that V1 was crossed by the TS on 2004/351 (during a tracking gap) at 94.0 astronomical units, evidently as the shock was moving radially inward in response to decreasing solar wind ram pressure, and that V1 has remained in the heliosheath until at least mid-2005.

Observations of the magnetic field and plasma in the heliosheath by Voyager 2 from 2007.7 to 2009.4

“…The bulk speed V in the heliosheath [Richardson and Wang, 2010], observed by the plasma instrument on V2 [Bridge et al, 1977], has been twice as high as that observed by Voyager 1 (V1) when it crossed TS in December, 2004 [Stone et al, 2005;Gurnett and Kurth, 2005;Decker et al, 2005;Burlaga et al, 2005a]. These high speeds were observed from the last crossing of the TS in September 1, 2007September 1, (2007 to 2009.7.…”

Electrostatic shielding in plasmas and the physical meaning of the Debye length

“…Christon 1987;Collier and Hamilton 1995;Grabbe 2000;Mauk et al 2004;Schippers et al 2008;Dialynas et al 2009;Ogasawara et al 2013), outer heliosphere and inner heliosheath (e.g. Decker and Krimigis 2003;Decker et al 2005;Heerikhuisen et al 2008;Zank et al 2010;Livadiotis et al 2011Livadiotis et al , 2013, and other general plasma analyses (e.g. Milovanov …”

Implications of solar wind suprathermal tails for IBEX ENA images of the heliosheath

“…Also using WIND data, Chotoo et al [2000] analyzed power law tails associated with corotating interaction regions and extracted the values of k. The 2004 Voyager 1 termination shock crossing extends suprathermal tail observations into the heliosheath. The Voyager 1 LECP instrument observed a k = 1.6 power law tail for hydrogen ions at v ) v sw [Decker et al, 2005]. While the acceleration mechanism for the power law tail is under debate, the diversity of regimes in which it has been observed indicates that it is a universal characteristic of plasma throughout the heliosphere and heliosheath.…”

“…[4] Recently, the Voyager 1 and 2 Low Energy Charged Particle (LECP) detectors have established that a power law describes the heliosheath ions downstream of the termination shock in the energy range of $30 keV to 10 MeV [Decker et al, 2005; R. B. Decker et al, Voyager 2 encounter with an energetic-particle-mediated termination shock, submitted to Science, 2008]. Below 30 keV there is an unmeasured energy region, including the $0.01 -6 keV that will be investigated by IBEX.…”