From NASA’s web site:
bq.. NASA’s Voyager 1 spacecraft has entered the solar system’s final frontier, a vast, turbulent expanse where the Sun’s influence ends and the solar wind crashes into the thin gas between stars.
“Voyager has entered the final lap on its race to the edge of interstellar space, as it begins exploring the solar system’s final frontier,” 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 encountered before 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 controversy at that time over whether Voyager 1 had indeed encountered the termination shock or was just getting close.
“The consensus of the team now is that Voyager 1, at 8.7 billion miles from the Sun, has at last entered the heliosheath, the region beyond the termination shock,” said Dr. John Richardson from MIT, Principal Investigator of the Voyager plasma science investigation.
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 its average speed of 300 to 700 km per second (700,000 – 1,500,000 miles per hour) and becomes denser and hotter.