The Impact of Kinetic Neutrals on the Shape of the Heliosphere and Structure of the Heliotail

The solar wind fills interplanetary space and forms the heliosphere, a region surrounding the Sun that protects the Solar System from high-energy particles permeating interstellar space. The canonical view of the shape of the heliosphere resembles a long comet tail, however, our research group at BU, led by Dr. Merav Opher, has suggested that the heliosphere is tailless with a two-lobe structure. This study was done with a state-of-the-art 3D magnetohydrodynamic (MHD) code that treats the ionized and neutral H atoms as fluids. One shortcoming of this description is that the neutral H atoms should be described kinetically. We will use the newly developed OH-PT model that employs a kinetic description for the neutral hydrogen streaming through the heliosphere. The OH-PT model couples the Outer Heliosphere (OH) and Particle Tracker (PT) components within the Space Weather Modeling Framework (SWMF). The OH component utilizes the Block-Adaptive Tree Solarwind Roe-type Upwind Scheme (BATS-R-US) MHD code, a highly parallel, 3D, and block-adaptive solver. The PT component is based on the Adaptive Mesh Particle Simulator (AMPS) model, a 3D, direct simulation Monte Carlo model that solves the Boltzmann equation to model the neutral distribution function throughout the domain. We will study the effects the kinetic treatment of the neutrals has on the heliosphere, in particular, the consequences on its shape and global structure. Results from this research will not only be important for our fundamental understanding of the heliosphere but can also be expanded to study the consequences for high-energy particles streaming into the heliosphere as well.