Voyager 1, a spacecraft launched by NASA in 1977 to study the outer solar system, has sent back information about a faint background hum in interstellar space, likely caused by plasma, Space.com reports.
A groundbreaking mission, Voyager 1 became the first manmade craft to travel past the heliosphere, considered the “border” of our solar system. Since 2012, with Voyager 1 more than 14 billion miles from Earth, NASA has collected information from an uncharted region of space, even as the vehicle’s plutonium energy source dwindles to less than a decade’s worth of operation power.
The hum, described as like the sound of a light rain, comes from plasma material found throughout the universe. The constant hum is interrupted by jolts from a burst of solar wind which, as one astronomer put it, hits the spacecraft like a clap of thunder in an otherwise calm space.
“Now we know we don’t need a fortuitous event related to the sun to measure interstellar plasma,” Shami Chatterjee, a Cornell astronomer, said in the same statement. “Regardless of what the sun is doing, Voyager is sending back detail. The craft is saying, ‘Here’s the density I’m swimming through right now. And here it is now. And here it is now. And here it is now.’ Voyager is quite distant and will be doing this continuously.”