After spending more than 7 years analyzing the outer layer of the solar system, the Voyager 1 spacecraft may finally be approaching interstellar space. New readings from its instruments have researchers at the NASA Jet Propulsion Laboratory (JPL), in Pasadena, California, very excited.
Scientists say that reaching the boundary of interstellar space should be accompanied by three key signs, two of which may have already been detected. However, it is very difficult to tell for sure when this will happen, since the signals were proposed theoretically.
Figuring out the exact size of the boundary is also very difficult, since the outer layer of the solar system may in fact be very thick. It represents an area where the magnetic influence of the Sun begins to be counterbalanced by influences from interstellar space.
Both Voyager spacecraft have to get out into this environment. Launched decades ago, they traveled over extensive distances. Voyager 1, which was launched on September 5, 1977, is currently more than 11 billion miles (18 billion kilometers) from the Sun.
The vehicle has traveled the most extensive distance of any man-made spacecraft. It now flies through the heliosheath, the outermost layer of the heliosphere (the envelope surrounding the Sun). Solar winds in this layer travel much slower, are more compressed, and more turbulent.
This happens because the influence of the interstellar environment is getting more intense. Eventually, it will overpower that of solar winds, and that is when and where Voyager 1 will have exited the solar system.
JPL scientists say that there are three tell-tale signs that should indicate Voyager 1's success – an increase in the amount of cosmic rays originating from interstellar space, a decrease in the lower-energy particle count originating within the system, and a change in the direction of the magnetic field.
On July 28, experts monitoring data the spacecraft relays back through the NASA Deep Space Network found that Voyager 1's instruments were detecting a 5 percent higher amount of high-energy cosmic rays from outside the solar system.
During the second half of the same day, researchers also noticed a 50 percent decrease in the amount of low-energy particles originating from the Sun. A change in the magnetic field direction was not observed. Over the next couple of days, all values returned close to normal.
“These are thrilling times for the Voyager team as we try to understand the quickening pace of changes as Voyager 1 approaches the edge of interstellar space,” Voyager project scientist Edward Stone says.
“We are certainly in a new region at the edge of the solar system where things are changing rapidly. But we are not yet able to say that Voyager 1 has entered interstellar space,” adds the expert, who is based at the California Institute of Technology, also in Pasadena.