Heliosphere Boundaries and Interactions

Scientific Investigation 3: Advance understanding of the temporal and spatial evolution of the boundary region in which the solar wind and the interstellar medium interact. 

IMAP will resolve the effects of physical processes within the heliosheath controlling global heliospheric structures and the interactions among the solar wind (SW), the local interstellar flow, and local interstellar magnetic field. The approach to this objective involves six synergistic sets of observations: 1) utilize interstellar neutral atom populations and PUI observations to probe the external properties of the interstellar medium imposed as boundary conditions on the global heliosphere; 2) resolve the complete ENA energy partition of ENA populations; 3) resolve evolution of ENAs down to 6 month scales; 4) resolve Ribbon and Belt connection to derive accurate direction and strength of the interstellar magnetic field; 5) utilize statistically resolved secondary neutral atom populations (H, He, O) to probe the properties of the interstellar flow as it is heated and deflected around the heliopause; and 6) relate in situ observations of the origin of suprathermal populations and energetic populations at 1 AU to the ENA energy distributions. IMAP addresses: 

  1. Requirements for primary interstellar neutral populations (H, He, O) for precise flow properties determine the outer boundary conditions on the global heliosphere. 
  2. The resolution of ENA populations from core SW through PUI, suprathermal and energetic particle ENAs requires statistically accurate measurements across a broad energy range. 
  3. Resolution of temporal evolution of the Ribbon, the Belt, and heliospheric regions are needed to understand temporal variability of global heliospheric structures. 
  4. Resolving the Ribbon and Belt connection and direction and the strength of the interstellar magnetic field requires a combination of high-angular-resolution ENA measurements and ENA energy distributions spanning a large energy range. 
  5. Maps of secondary interstellar neutral populations (H, He, and O) from IMAP-Lo are required to derive interstellar flow deflection and heating around the heliopause. IMAP must observe these secondary species from multiple vantage points over the year, which is essential in understanding 3D spatial structure of the interstellar flow near the nose. 
  6. Lastly, the physical processes mediating the plasma balance within the heliosheath rely on understanding the origin of suprathermal particles from highly variable in situ measurements at 1 AU covering populations from SW core protons through suprathermal and energetic protons.