As the 28-year-old Voyagers 1 and 2 spacecraft approach the edge of interstellar space, they have found that the heliosphere, the “bubble” within which the sun dominates, bulges outward in the northern hemisphere and is pressed inward in the south. Voyager 1, flying about 34 degrees north of the equator, crossed the termination shock and entered the outermost layer of the heliosphere about 9 billion miles from the sun. Meanwhile Voyager 2, about 26 degrees south of the equator, finds that the shock may be nearly a billion miles closer to the sun.
Scientists believe that the observed discrepancies may be attributed to an interstellar magnetic field pressing inward on the southern hemisphere. Voyager 2 will determine the exact location of the shock in the south when it crosses it sometime before the end of next year. Then scientists will have a better idea of how strong the magnetic field is outside of the heliospheric bubble.
Voyager 2 is also finding that the shock in the south is a source of low energy ions as was discovered by Voyager 1 in the north. Contrary to earlier predictions, however, neither Voyager 1 nor 2 have found the source of higher energy anomalous cosmic rays.
Both Voyager spacecraft were launched from the Cape Canaveral Air Force Station in Florida: Voyager 2 on Aug. 20, 1977 and Voyager 1 on Sept. 5, 1977 on a faster, shorter trajectory than its twin. The mission is managed for NASA by the Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology.