If we could see Our Heliosphere, What would our Home in the Galaxy look like?
The Sun and solar system move through a part of the galaxy referred to as the local interstellar medium. It is built up from material released from the stars of our galaxy through stellar winds, novae, and supernovae. The interstellar medium has considerable structure as illustrated here. IBEX images reveal global properties of the interstellar boundaries that separate our heliosphere from the local interstellar medium. Image courtesy of L. Huff/P. Frisch; The box shows an astrosphere at the binary star BZ Cam (photo courtesy of R. Casalegno, C. Conselice et al., WIYN, NOAO).
Relation to Voyager
The Voyager 1 (V1) satellite crossed the Termination Shock (TS) on December 16th, 2004 at a distance of 94 AU
Before crossing the TS, Voyager 1 observed increases in the intensity of the lowest energy energetic particles it could observe. On December 16th, Voyager 1 recorded a variety of observations that support a shock crossing (Stone et al., 2005; Decker et al., 2005, Burlaga et al., 2005). As shown in the figure below (top left) from Decker et al. (2005), the intensities of the low-energy energetic particles increased as Voyager 1 approached the TS, consistent with beaming along magnetic field lines connected to the TS (Burlaga et al., 2005). Near day 355, V1 also observed an abrupt increase in the magnetic field strength (as shown in the figure below to the right from Burlaga et al., 2005) as well as increased levels of compressive turbulence. The simultaneous jumps in magnetic field strength and energetic particle intensities proved to the scientific community that Voyager 1 had in fact crossed the termination shock.
Based on Voyager 1's magnetic field and energetic particle observations, and our knowledge of solar wind shocks, it is inferred that the bulk velocity of the solar wind must have also dropped suddenly when Voyager 1 crossed the TS. Unfortunately the plasma detector on Voyager 1 failed early in the mission, so it is impossible to get a direct measurement of the decrease in velocity. Voyager 2 is, however, approaching the termination shock and it continues to provide accurate plasma velocity measurements. It is hoped, and highly likely, that Voyager 2 will soon make the first direct measurements of the flows in the heliosheath.
The Voyager in situ measurements are known at one specific location and time. Though Voyager 1 has recorded the first measurement of the TS and heliosheath properties, single-point measurements do not give a global understanding of the system. Because IBEX provides global maps of the interstellar interaction, IBEX observations are highly complimentary to, and synergistic with, the detailed single direction measurements provided by the Voyager satellites.
Stone, E.C, et al, Voyager 1 Explores the Termination Shock Region and the Heliosheath Beyond, Science, 309, 2017 2005.
Decker, R.B, et al, Voyager 1 in the Foreshock, Termination Shock, and Heliosheath, Science, 309, 2020, 2005.
Burlaga, L.F, et al, Crossing the Termination Shock into the Heliosheath: Magnetic Fields, Science, 309, 2027, 2005