A predicted small and round heliosphere

The shape of the solar wind bubble within the interstellar medium, the so-called heliosphere, has been explored over six decades(1-7). As the Sun moves through the surrounding partially-ionized medium, neutral hydrogen atoms penetrate the heliosphere, and through charge-exchange with the supersonic solar wind, create a population of hot pick-up ions (PUIs). The Voyager 2 (V2) data demonstrated that the heliosheath pressure is dominated by PUIs. Here we use a novel magnetohydrodynamic model that treats the PUIs as a separate fluid from the thermal component of the solar wind. Unlike previous models (8-10), the new model reproduces the properties of the PUIs and solar wind ions based on the New Horizon(11) and V2(12) spacecraft observations. The model significantly changes the energy flow in the outer heliosphere, leading to a smaller and rounder shape than previously predicted, in agreement with energetic neutral atom observations by the Cassini spacecraft.Accepted manuscrip