NASA says the spacecraft has now detected an increase in cosmic rays - fast-moving particles that originate outside our solar system - which suggests that the spacecraft might be close to crossing into interstellar space.
It was launched in 1977, but since 2007 the probe has been traveling through the outermost layer of the heliosphere, including the bubble around the Sun and the planets dominated by solar material and magnetic fields.
In the month of May of 2012, Voyager 1 experienced an increase in the rate of cosmic rays which are similar to what Voyager 2 is as of now detecting. The duration takes for the data transmitted at the speed of light takes 19:57:03 hours to reach the Earth while the Voyager 2 is about 118.77 AU from the Earth and it takes 16:27:12 hours for the data to reach back on Earth. Once it exits the region, it will become the second human-made object, after its twin Voyager 1, to enter interstellar space.
Voyager 1 and Voyager 2 aren't traveling in exactly the same direction, so it's been hard for NASA to predict when each spacecraft would officially being an interstellar journey in relation to the other. At the time Voyager 1 left our solar system, it was in the heliosheath, which is the outer region of the heliosphere.
Since late August, the Cosmic Ray Subsystem instrument on Voyager 2 has measured about a 5 percent increase in the rate of cosmic rays hitting the spacecraft compared to early August. Well, after nearly 6 years after the Voyager 1 crossed what can be said the edge of our solar system and the start of interstellar space, Voyager 2 could join the wagon too. Voyager 2 is also lagging about six years behind its counterpart, so it will likely cross at a different point in the sun's 11 year cycle. This, however, does not necessarily mean that Voyager 2 will cross the border now, because every 11 years of a solar cycle, our Solar System is expanding and contracting a little bit.
We're seeing a change in the environment around Voyager 2, there's no doubt about that.
Scientists expect to learn a lot when Voyager 2 reaches the heliopause, but the spacecraft isn't there yet. However, when exactly it will reach the heliopause (beyond where the waning solar wind), scientists do not know.
The Voyager spacecraft were built by NASA's Jet Propulsion Laboratory in Pasadena, California, which continues to operate both. The Voyager missions are part of the NASA Heliophysics System Observatory.