The breakthrough means the spacecraft has become the second human-made object to travel so far. The boundary where the hot solar winds of the heliosphere end and give way to the cold interstellar medium is known as the heliopause, and it's also the border of interstellar space. But Voyager project scientist Ed Stone said in October that "we're not there yet".
Our star system is surrounded by a hotchpotch of small objects called the Oort Cloud which are still affected by the sun's gravity. That likely won't happen for another 300 years, and it will take 30,000 years for Voyager 2 to fly beyond it.
Voyager 2 carries something unique: the Plasma Science Experiment instrument. With the help of Voyager 2's PSE, we can better understand the remote observations made by IBEX.
They showed a dramatic change on November 5, indicating the spacecraft was between the stars.
The ship is now at a distance of more than 11 billion miles (18 billion kilometers) from Earth, but despite the gap now being greater than that between Earth and the Sun, the ship is still within reach of our planet's communications systems.
"Voyager has a very special place for us in our heliophysics fleet", NASA's Nicola Fox said in a statement.
"It would be super-exciting to have a 50-year mission still operating", she added, describing the probes as "pioneers" of interstellar space".
A major concern is power and NASA has to keep shutting down instruments to reserve power.
Both Voyager probes are powered by radioisotope thermal generators, which convert heat from the radioactive decay of plutonium into electricity. Only Voyager 2, however, continues to have a functioning plasma instrument, which could tell us much more about this unexplored region, including the temperature, density and velocity of any electrically charged material flowing around the spacecraft. "The next months ahead could be very revealing as well.More to come!" "My personal goal is to get them to last 50 years total".
The two spacecraft were launched in the summer of 1977, fitted with instruments and cameras that astronomers hoped would provide them with information on Jupiter and Saturn over the course of five years.
"The mission is uncovering new mysteries", Opher said. After visiting all four gas giants, it followed Voyager 1 on a path to interstellar space, carrying one of two of the famous Golden Records, which contain messages "intended to communicate a story of our world to extraterrestrials", along with sounds and music from Earth (including Chuck Berry's "Johnny B. Goode", because aliens need to understand rock 'n roll).
"I think we're all happy and relieved that the Voyager probes have both operated long enough to make it past this milestone", said Suzanne Dodd, Voyager project manager at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.