Charting the heliosphere in three dimensions

Abstract

Space physicists continue their exploration of the solar system's home in the galaxy—that bubble of space, called the heliosphere, carved out of the interstellar medium by the solar wind. Studies of the heliospheric plasma are driven by the search for answers to questions such as: What mechanisms are responsible for the acceleration of the solar wind? How do the properties of the solar wind evolve with distance from the Sun? What is the nature of the interaction of the solar wind with the interstellar medium? The principal progress made in the last four years has come from data obtained by the Pioneer and Voyager spacecraft moving away from the Sun at roughly 3 AU/year, from the first measurements at high latitudes currently being made by the joint European-NASA mission named Ulysses, and from continued remote sensing of the inner heliosphere. This review focuses on the average values of the plasma velocity, density, and temperature and the magnetic field in different regions of the heliosphere, leaving discussion of the details of many important structures and processes to other papers.