NASA's Voyager 2 probe has traveled through space for 41 years and is currently only less than 11 billion miles from the earth or more than 118 times the distance between the Earth and the sun.
Now, operators consider that Voyager 2, launched from the Kennedy Space Center in August 1977, can reach the edge of the solar system and get into interstellar space.
In the last decade, the probe has been fared through the outermost layer of the heliosphere – a large spherical region of space dominated by the sun's influence and its magnetic field.
When Voyager 2 passes through the border to the heliosphere, known as the heliopause, it becomes just the second man-made object, after its twin Voyager 1
Since the end of August this year, instruments on board have measured a 5 percent increase in cosmic beam velocity that hits the spacecraft compared to the beginning of the month.
Cosmic rays are high energy radiation stemming from the outside of the solar system, consisting of fast particles. Some of these cosmic rays are blocked by the heliosphere. Therefore, planning plans expect to discover more of them when the probe approaches and crosses the heliopause – much like the increase observed in May 2012 by Voyager 1 about three months before entering interstellar space.
However, the increase in detection of cosmic rays is not necessarily a definite sign that the probe is about to cross the heliopause, according to the Voyager team. Voyager 2 is located in a completely different region in the outermost lag of Voyager 1, so it is possible that the timeline of their solar system outputs varies.
Voyager 2 also approaches the heliopause six years after its twin, which is significant because this limit moves inward and outward during the 11-year-old activity cycle of the sun.
"We see a change in the environment around Voyager 2, there is no doubt about it," said Voyager Project Scientist Ed Stone, from Caltech in Pasadena, said in a statement. "We will learn a lot in the coming months, but we still do not know when we reach the heliopause. We are not there yet – that's one thing I can say with confidence."
Both Voyager spacecraft was built by NASA's Jet Propulsion Laboratory in Pasadena, California, which continues to drive them.
During their time in space, Voyagers revolutionized our understanding of the outer solar system. For example, Voyager 2 is the only spacecraft that has flown off all four of the outer planets. It was also the first to form the rings of Jupiter, Uranus and Neptune.
Meanwhile, the probes were the first to discover active volcanoes beyond the Earth on the Io, the first to discover tips for a sea beyond our planet under the ice-cold crust of Europe and the first to observe the flash of another world among the violent storms of Jupiter. They can also be credited with identifying several new planet months, including 11 around Uranus.
Although no-one will come close to another star system for at least 40,000 years, they still give us fascinating insights into the completely unexplored area where our sun's influence decreases and interstellar space begins. All the more remarkable given that they are running on technology with less power than an average 2018 smartphone.