ENERGETIC NEUTRAL HYDROGEN OBSERVATIONS DEMONSTRATE THAT VOYAGER 1 IS NOT OBSERVING THE EXTRAORDINARILY STRONG INTERSTELLAR MAGNETIC FIELD

Abstract

ABSTRACT It is generally believed that Voyager 1 (V1) is now in interstellar space, having crossed the heliopause at a heliocentric distance of 121.58 au in late August of 2012. Here we use recently published spectra of energetic neutral hydrogen, and the magnetic field and energetic particles directly measured by V1 to find the average pressure in the inner heliosheath (termination shock to 122 au). This pressure turns out to be surprisingly large, (3.57 ± 0.71) × 10−12 dyn cm−2, and is completely dominated by pressures of pickup ions (PUIs), created in the inner heliosheath, and their suprathermal tails (43%), and PUIs and their tails that are produced upstream of the termination shock and enter the heliosheath (46%). We compute the total particle pressure in the outer heliosheath near the heliopause from distribution functions of the interstellar plasma and locally created PUIs using profiles of proton density, proton temperature, and neutral hydrogen density from model 2 in Zank et al., and find it to be at most 7.7 × 10−13 dyn cm−2. Balancing pressure across the heliopause, thus requires an unusually large magnetic pressure (2.8 × 10−12 dyn cm−2). The resulting strength and 1σ uncertainty of the draped magnetic field in the outer heliosheath near the heliopause is 0.839 ± 0.106 nT. The 3σ lower limit field strength (0.52 nT) is greater than the field of ∼0.43 ± 0.02 nT measured by V1, implying that there is less than 1% probability that V1 is measuring the interstellar draped field.