Voyager 1 may finally be reaching the end of the Solar System, 11 billion miles from Earth. The craft has entered a previously unexplored region of space called the "heliosheath depletion region."
Once Voyager 1 crosses that boundary, it will become the first man-made object to ever leave the Solar System. Although astronomers do not know exactly when this might happen, estimates range anywhere from a few months to a few years in the future.
There is no instant defining mark or instance at which objects are said to have left the Solar System. However, the Sun is surrounded by several layers of different conditions which denote how far from our home star a natural or man-made object travels. The outermost of these is called the heliosphere, and that is where Voyager 1 is currently located.
When the spacecraft entered the so-called "magnetic highway" within the heliosphere in August 2012, the flow of cosmic rays from outside our planetary system increased, while the flow of charged particles from the Sun disappeared.
Astronomers will consider Voyager 1 to have left the Solar System when three conditions are met. The first two are the increase of particles from outside the Solar System and a lack of particles from the Sun. The only condition which is not yet met is a sudden change in the magnetism in space, denoting the point where the magnetic field of the Sun gives way to that between the stars.
"If you looked at the cosmic ray and energetic particle data in isolation, you might think Voyager had reached interstellar space, but the team feels Voyager 1 has not yet gotten there because we are still within the domain of the sun's magnetic field." Ed Stone, Voyager project scientist at the California Institute of Technology, said.
One of the tasks aboard the 36-year-old space mission is to measure how far beyond our home star the heliosphere extends. Measurements of that distant region of our solar system were recorded by the cosmic ray and low-energy charged particle experiments aboard the craft along with reading from Voyager 1's magnetometer, beginning in May 2012 and extending through April 2013.
"What a triumph for Voyager and modern technology, to be able to observe these events as they were taking place (plus 17 hours of light travel-time over 11 billion miles away)," Bill Webber of New Mexico State University said.
Although Voyager 1 has given hints before that it has left the Solar System, once the magnetic field shifts for good, the $250 million dollar craft, launched September 5, 1977, will be in interstellar space.
Data collected by Voyager 1 revealing details of the edge of the Solar system has been published in the three articles carried in the journal Science on June 27.