Plasma density contours from a 3D magnetohydrodynamic model of the heliosphere. The interstellar plasma (orange) increases in density at the bow shock (red). The lower density (blue) solar wind plasma increases in density at the termination shock (blue-turquoise interface). Charge exchange processes involving shock-heated solar wind ions produce energetic neutral atoms that can be imaged to provide information on the 3D structure of the termination shock. Higher energy neutral atoms resulting from the charge-exchange of anomalous cosmic rays with interstellar hydrogen can also be imaged. Shock accelerated particles are ubiquitous in the universe and the termination shock provides a unique opportunity to study the detailed properties of a large-scale shock, in situ, including its effect on the plasma, magnetic fields, and energetic particles that encounter it.

• What is the size and structure of the heliosphere?

  
  

• How do the termination shock and heliopause respond to solar variations and interstellar pressure?

  
  

• How does the interstellar medium effect the inner heliosphere and solar wind dynamics?

  
  

• What roles do thermal plasma, pickup ions, waves, and anomalous cosmic rays play in determining the structure of the termination shock?

  
  

• What are the properties of interstellar gas and dust that penetrate into the heliosphere?