Voyager 1 Tastes Interstellar Space
Dec. 4, 2012: Eleven billion miles from Earth, NASA's Voyager 1 spacecraft has entered a "magnetic highway" that connects our solar system to interstellar space. This could be one of Voyager 1's last steps on its long journey to the stars.
"Although Voyager 1 still is inside the sun's environment, we now can taste what it's like on the outside because the particles are zipping in and out on this magnetic highway," said Edward Stone, Voyager project scientist based at the California Institute of Technology, Pasadena. "We believe this is the last leg of our journey to interstellar space. Our best guess is it's likely just a few months to a couple years away. The new region isn't what we expected, but we've come to expect the unexpected from Voyager."
The new results were described on Dec. 3rd at the American Geophysical Union meeting in San Francisco.
The "magnetic highway" is a place in the far reaches of the solar system where the sun's magnetic field connects to the magnetic field of interstellar space. This connection allows charged particles from inside the heliosphere (the magnetic bubble that surrounds the sun) to zoom out; and it allows charged particles from outside to stream in. When Voyager 1 is in the magnetic highway, onboard particle sensors can directly sample material from beyond our solar system.
Since December 2004, when Voyager 1 crossed a point in space called the termination shock, the spacecraft has been exploring the heliosphere's outer layer or "heliosheath." In recent years, the speed of the solar wind around Voyager 1 has slowed to zero, and the intensity of the magnetic field has increased.
According to data from two onboard instruments that measure charged particles, Voyager 1 first entered the magnetic highway on July 28, 2012. The region ebbed away and flowed toward Voyager 1 several times. The spacecraft entered the region again Aug. 25 and the environment has been stable since.
Spacecraft data revealed the magnetic field became stronger each time Voyager entered the highway region; however, the direction of the magnetic field lines did not change, as researchers would expect if Voyager 1 had truly entered interstellar space.
"We are in a magnetic region unlike any we've been in before -- about 10 times more intense than before the termination shock -- but the magnetic field data show no indication we're in interstellar space," said Leonard Burlaga, a Voyager magnetometer team member based at NASA's Goddard Space Flight Center in Greenbelt, Md.
Voyager 1's exit from the solar system is, apparently, yet to come. But the magnetic highway is giving it a taste of what lies ahead.
Stay tuned to Science@NASA for updates from the edge of the solar system.
Voyager 1 and 2 were launched 16 days apart in 1977. After touring the outer planets in the 1980s, the two spacecraft have made a dash for the stars. Voyager 1 is now the most distant human-made object: 11 billion miles (18 billion kilometers) away from the sun. The signal from Voyager 1 takes approximately 17 hours to travel to Earth. Voyager 2, the longest continuously operated spacecraft, is about 9 billion miles (15 billion kilometers) away from the sun. While Voyager 2 has seen changes similar to those seen by Voyager 1, the changes are much more gradual. Scientists do not think Voyager 2 has reached the magnetic highway.
The Voyager spacecraft were built and continue to be operated by NASA's Jet Propulsion Laboratory, in Pasadena, Calif. Caltech manages JPL for NASA. The Voyager missions are a part of NASA's Heliophysics System Observatory, sponsored by the Heliophysics Division of the Science Mission Directorate at NASA Headquarters in Washington.