Robert M. Walker Distinguished Lecture Series Colloqiuium
"Voyager Explores the Edge of Interstellar Space"
After a thirty-five year journey, Voyager 1 began observing the properties of the very local interstellar medium on August 25, 2012, at a radial distance of 121.6 AU. Now at 133 AU, Voyager 1 has been exploring the region where the interstellar and solar winds strongly interact and a "wall" of H atoms forms. The interstellar plasma density is ~100 times that in the outer heliosphere, and the intensity of galactic cosmic rays is ~ 4 times the highest level observed at 1 AU, with transient variations caused by the arrival of Merged Interaction Regions originating at the sun. Although the interstellar magnetic field is distorted as it wraps around the heliosphere, the turbulence in the field is <1% of the average field. This very weak turbulence leads to extremely low cosmic ray scattering rates and pitch angle anisotropies that persist for months. Now at 109 AU, Voyager 2 continues to explore the outer regions of the heliosphere where the solar wind flow has turned as it approaches contact with the interstellar wind.