"Voyager 1 has entered the final lap on its race to the edge of interstellar space," said Dr. Edward Stone, Voyager project scientist at the California Institute of Technology in Pasadena. Caltech manages NASA's Jet Propulsion Laboratory in Pasadena, which built and operates Voyager 1 and its twin, Voyager 2.
In November 2003, the Voyager team announced it was seeing events unlike any in the mission's then 26-year history. The team believed the unusual events indicated Voyager 1 was approaching a strange region of space, likely the beginning of this new frontier called the termination shock region. There was considerable controversy over whether Voyager 1 had indeed encountered the termination shock or was just getting close.
The termination shock is where the solar wind, a thin stream of electrically charged gas blowing continuously outward from the sun, is slowed by pressure from gas between the stars. At the termination shock, the solar wind slows abruptly from a speed that ranges from 700,000 to 1.5 million mph and becomes denser and hotter. The consensus of the team is Voyager 1, at approximately 8.7 billion miles from the sun, has at last entered the heliosheath, the region beyond the termination shock.
More information on this development, including some nice pictures, can be found at http://www.nasa.gov/vision/universe/solarsystem/voyager_agu.html.
Personal note: I grew up with the Voyager missions. When they were launched, I was seven years old. When they reached Jupiter, I was nine. They reached Saturn during my last year of elementary school. When Voyager 2 reached Uranus, I was in eleventh grade, and when it reached Neptune, I was right in the middle of my four years of college.
Looks like it may soon be time to bid them farewell.