Voyager 1 detects plasma "hum" in interstellar space
More than 40 years after launch, Voyager 1 is still making new discoveries. The latest achievement by the craft is the detection of a faint, plasma “hum,” indicating that there may be more activity in interstellar gas than previously thought.
When it took off in 1977, Voyager 1 was carrying an instrument called the Plasma Wave System (PWS), which measures electron density. The craft used this to study the magnetospheres of Jupiter and Saturn, and recorded radio waves coming from the gas and ice giants on its tour of the solar system.
But it wasn’t until it left the solar system that the PWS really earned its keep. One of the few instruments still operational after all these decades, NASA was able to use the PWS to measure the plasma shock waves as Voyager 1 passed out of the heliosphere, the bubble that marks the Sun’s influence. Using this data, NASA confirmed that in 2012 Voyager 1 became the first human-made object to enter interstellar space.
Since then, the craft has been relaying data back about this new frontier. And now, the PWS has detected a steady background signal from the plasma, which seems to suggest that there’s a higher baseline of activity going on in interstellar space than was thought.
"It's very faint and monotone, because it is in a narrow frequency bandwidth," says Stella Ocker, an author of the study. "We're detecting the faint, persistent hum of interstellar gas.”
Picking up this signal was trickier than it may seem. While the solar winds don’t reach beyond the edge of the heliosphere, it turns out that the Sun’s influence can sometimes extend into interstellar space when it throws off coronal mass ejections (CMEs). These energetic outbursts were first detected by the PWS in 2014, which registered them like “tsunamis” and made it hard to pick up anything else. But given enough time, the instrument has been able to listen closely in between these events.
"The interstellar medium is like a quiet or gentle rain," says James Cordes, senior author of the study. "In the case of a solar outburst, it's like detecting a lightning burst in a thunderstorm and then it's back to a gentle rain.”
The new study is a monument to the incredible ongoing work of the Voyager mission, and helps us learn more about the universe beyond our solar system. It could even inform the design of upcoming missions headed for interstellar space.
The research was published in the journal Nature Astronomy.