THE 2-3 kHz HELIOSPHERIC RADIATION, THEIBEXRIBBON, AND THE THREE-DIMENSIONAL SHAPE OF THE HELIOPAUSE

Recent Interstellar Boundary Explorer ( IBEX ) observations indicate that the total dynamic pressure in the interstellar medium is closely partitioned between the plasma and the magnetic field, with an Alfvén Mach number M A ∼ 1 and a sonic Mach number ∼2. Observations of the IBEX Ribbon provide a unique determination of the orientation of the undraped interstellar magnetic field along the heliopause. There is also a striking correspondence between the Ribbon location and the source locations of 2–3 kHz radiation determined from Voyager observations: the radiation sources north of the ecliptic form a line parallel to but offset by about 30° from the Ribbon. A general Rankine–Hugoniot analysis is used to argue that the heliopause should not be symmetric about the velocity vector V ISM of the interstellar medium relative to the Sun (the nominal nose direction). Furthermore, the closest point on the heliopause to the Sun should be on the Ribbon for M A = 0 and at least 9° from the nominal nose direction toward the Ribbon for M A = 1. These new results are combined into a conceptual model of the heliopause that includes (1) a plasma depletion layer formed as the interstellar magnetic field drapes against the heliopause, (2) a minimum inner heliosheath thickness and closest point between the Sun and heliopause along (or close to) the Ribbon rather than in the nominal nose direction (along V ISM ), and (3) inference of an asymmetric heliopause shape from the angular offset of the radio sources and Ribbon and from the Rankine–Hugoniot analysis.