"In a historical sense, the old idea that the solar wind will just be gradually whittled away as you go further into interstellar space is simply not true", said Don Gurnett, co-author of a second plasma density paper and a professor emeritus of physics and astronomy at The University of Iowa in the US.
Each paper has been dedicated to one of the five operating science instruments onboard Voyager 2. Here, the Sun no longer has any influence over the environment. The "bubble" of the heliosphere is continuously "inflated" by plasma, a gas of charged particles or ions, coming from the Sun. We had no quantitative idea of how big this bubble is that the sun creates around itself with its supersonic solar wind, made of ionized plasma, which is speeding away from the sun in all directions. The space between stars also contains cosmic rays, or particles accelerated by exploding stars. It then made for the southern hemisphere of the heliosphere (the outermost region of the solar system, sometimes referred to as "the bubble"), straight for interstellar space. Scientists say that the increased density of plasma is evidence that the vehicle is traveling out of the enclosure of warm and low-density plasma of solar winds into cold and high plasma density interstellar space. This was when scientists knew it had entered a different region in space.
We also now understand that the heliosphere is leaking particles.
Scientists expected that the edge of the heliosphere, called the heliopause, can move as the Sun's activity changes, sort of like a lung expanding and contracting with breath. Yet they crossed into the ISM at basically the same distances from the sun.
Both Voyager 1 and Voyager 2 were launched in 1977, designed for five-year missions. Though its transition shares similarities with Voyager 1's, these initial results have revealed a previously unobserved area of interaction between particles from space and particles from the Sun. Kurth is one of the study's authors and a scientist with the Voyager missions.
It is also similar to the plasma density jump experienced by Voyager 1 when it crossed into interstellar space, they said.
Artist impression of the solar system and interstellar space. This is the point where the solar wind piles up against the approaching wind of particles in interstellar space, which Prof Gurnett likens to the effect of a snow plow on a city street. Both probes are the only man-made objects that have sunk so far into the sparkling depth of the cosmos.
"Without the new Voyager 2data, we wouldn't know if what we were seeing with Voyager 1 was characteristic of the entire heliosphere or specific just to the location and time when it crossed". Another surprising revelation was the magnetic field in the region just beyond the heliopause is parallel to the magnetic field inside the heliosphere. "Even the formation of the solar system, most astronomers believe, was triggered by an interstellar shock wave from a supernova", he says.
The approximate positions of Voyager 1 and 2. Voyager 2 swung past Jupter, Saturn, Neptune, and Uranus.
It is unclear when or if a follow-up mission will again reach the distances the Voyager craft have achieved, but plans for an interstellar probe are being looked at by the COSPAR (Committee on Space Research) Panel on Interstellar Research. Voyager 1, the faster of the two probes, is now over 13.6 billion miles (22 billion kilometers) from the Sun, while Voyager 2 is 11.3 billion miles (18.2 billion kilometers) from the Sun.
The Voyager probes became world famous thanks to the gold plates they carry, full of music, sounds and images of the earth, meant as a kind of time capsule that tells the story of our world to any aliens they might encounter along the way. Scientists believe it would take Voyager 2,300 years to reach the inner edge of the cloud, and 30,000 years to fly past it completely.