Voyager 1, launched in 1977, has been struck by another "tsunami wave" from the sun, suggesting the vehicle may have finally reached interstellar space. In March of 2013, the craft was hit by one of these waves, causing some investigators to declare the spacecraft had left our family of planets.
Data from Voyager examining the wave provides further evidence the 37-year-old spacecraft has reached interstellar space. This region is filled with ionized gas, or plasma.
"Normally, interstellar space is like a quiet lake. But when our sun has a burst, it sends a shock wave outward that reaches Voyager about a year later. The wave causes the plasma surrounding the spacecraft to sing," Ed Stone, project scientist on the mission since 1972, said.
From time to time, the sun exhibits coronal mass ejections, or CME's, which throw vast quantities of particles into space. These create shock waves, that emanate out to furthest reaches of the solar system. Cosmic rays, produced by stars around the sun, are affected by pressure waves created by CME's. Voyager 1 is equipped with a plasma wave detector and a cosmic ray sensor which can detect when these shock waves are encountered.
Such an event was recorded in 2012, not not recognized until after the second wave hit in 2013. Plasma in the region of space where the spacecraft is flying is up to 40 times as dense as it is within the solar system. This is because solar wind is pushing up against the gas, concentrating it, like a bubble.
"The tsunami wave rings the plasma like a bell. While the plasma wave instrument lets us measure the frequency of this ringing, the cosmic ray instrument reveals what struck the bell - the shock wave from the sun," Stone said.
Voyager 1 has broken through a magnetic bubble known as the heliosphere, which completely contains the solar wind. However, this does not mean the mechanism has left the solar system. For that to happen, it would have to pass the final halo of comets surrounding our companion star.
This is the first man-made object to ever travel past the heliosphere. At 11.9 billion miles from Earth, the vehicle is more than 128 times further away from the Earth than we are from the Sun.
Voyager 1 explored the gas giants of Jupiter and Saturn. The craft is eventually headed toward a close encounter with a star named AC + 79 3888, located 17.6 light years from the Earth. Arrival at that alien star system will happen in about 40,000 years.
