by Matthew Hilburn Eleven billion miles and 36 years after its launch, some researchers say the Voyager 1 spacecraft has finally left our solar system and entered interstellar space.

Researchers at the University of Maryland who made the claim realize it's a controversial view, but they say their model indicates the spacecraft left the solar system over a year ago - on July 27, 2012, to be exact.

Voyager "is truly beginning its travels through the Milky Way," said University of Maryland research scientist Marc Swisdak, lead author of a new paper published online this week in The Astrophysical Journal Letters.

The U.S. space agency, NASA, which operates Voyager, has recently published papers saying Voyager 1 is still in a zone influenced by the Sun called the heliopause, something the Maryland researchers call a "fuzzily defined" transition zone that is "both of unknown structure and location."

The controversy lies over the importance in the shift of the magnetic field as the probe passes out of the Sun's influence compared to the level of solar particles and galactic particles measured by the spacecraft.

Swisdak says looking at the magnetic field difference - as NASA is doing - may be the wrong indicator. He says that while you might expect a shift in the magnetic field once outside the solar system, "there's no reason to think the magnetic fields should have anything to do with one another."

"What we're arguing is that a lack of shift is consistent with going outside [the solar system," he said.

Swisdak says that while magnetic data should not be ignored, the particle data is more compelling.

According to Swisdak's research, there were successive "dips" in the solar particles with a corresponding increase in galactic electrons and protons. Researchers say that last summer, the solar particle counts disappeared and only galactic particles remained.

"The magnetic data is consistent with [leaving the solar system]," he said.

Swisdak argues that the NASA's heliopause "is not a surface neatly separating "outside" and "inside." His research concludes rather that it's "both porous to certain particles and layered with complex magnetic structure."

At the edges of the heliopause, Swisdak's research showed that there is a complex set of nested magnetic "islands" that he says, "spontaneously arise in a magnetic field due to a fundamental instability."

Within these "magnetic islands," drops in solar particle counts and surges in galactic particle counts can occur even without changes in the magnetic fields.

Swisdak calls the longevity of Voyager "impressive" considering that is computers are less powerful than the average smart phone or pocket calculator.

Talking about the controversy over whether or not the space probe has left the solar system, Swisdak says that on one level, it's important because Voyager 1 is providing humanity's first measurements outside the "cocoon" of the sun.

On a scientific level, he says "a lot of astronomy is done on an indirect basis."

"This gives us our first [direct] measurements of what it's like out there," he said.

Launched in 1977, Voyager 1's primary mission was the exploration of Jupiter and Saturn. The probe discovered active volcanoes on Jupiter's moon Io and showed the intricacies of Saturn's rings.

Voyager is also well-known for carrying greetings from Earth on a gold plated phonograph record containing sounds and images selected to portray the diversity of life and culture on Earth.

Voyager 1 continues to send back data and has enough power to keep operating until 2020. But given its vast distance, that data takes almost 18 hours to get back to Earth.