The first manmade object to reach interstellar space was the NASA Voyager 1 probe. Voyager 1 was confirmed to have entered interstellar space back in September of 2013, 36-years after its launch. NASA’s Voyager 2 spacecraft was launched in 1977 and is about 11 billion miles from Earth right now.
Voyager 2 has been traveling in the outermost layer of the heliosphere, which is a massive bubble that is around the sun and planets. Scientists are waiting for Voyager 2 to reach the outer boundary of the heliosphere known as the heliopause. Once it exists the heliosphere it will become the second man-made object to do so.
Scientists at NASA say that since late August the Cosmic Ray Subsystem instrument fitted to Voyager 2 has measured a 5% increase in the rate of cosmic rays hitting the spacecraft compared to Early August. Since some of the cosmic rays are blocked by the heliosphere, an increase in impact with spacecraft signals that it is close to exiting the heliosphere. When Voyager 1 saw a similar increase in cosmic rays, it was about three months later when the spacecraft entered interstellar space.
Scientists note that Voyager 2 is in a different location in the heliosheath, the outer region of the heliosphere, than Voyager 1 was in and the exit timeline could look different for Voyager 2. Another interesting tidbit from the science team monitoring the Voyager 2 spacecraft is that the six-year gap between Voyager 1 and Voyager 2 reaching the heliopause is important.
The team notes that the heliopause moves inward and outward during the 11-year activity cycle of the sun. Scientists expect to learn a lot when Voyager 2 reaches the heliopause, but the spacecraft isn’t there yet.