In the abyssal depths of interstellar space, a NASA probe launched from the U.S. in 1977 is still passively exploring the galaxy, returning all data to its makers, here on Earth. Called Voyager 1, the craft is far beyond the heliopause — an invisible "shield" that marks our solar system's border with the rest of the galaxy.
Out there, in the interstellar medium, Voyager 1's instruments have detected the haunting hum of interstellar gas — plasma waves moving through a region of space far beyond the human imagination, according to a new study published in the journal Nature Astronomy.
Voyager 1 can help scientists study the composition of interstellar space
New data slowly returned from Voyager 1's position more than 14 billion miles away has revealed the new interstellar emission. "It's very faint and monotone, because it is in a narrow frequency bandwidth," said Stella Koch Ocker, a doctoral student in astronomy at Cornell, who is part of the study. "We're detecting the faint, persistent hum of interstellar gas." This new discovery helps scientists comprehend how the interstellar medium interacts with the solar wind, and how the solar system's heliosphere — which is a type of protective "shield" — is reshaped and modified by the environment of deep space.
Voyager 1 was launched in 1977, and made a flyby of Jupiter in 1979 and Saturn in 1980. Moving at unconscionable speeds of 38,000 mph (61,155 km/h), the spacecraft penetrated the heliopause in August of 2012. But once the craft made it to interstellar space, Voyager 1's Plasma Wave System picked up minute perturbations in the gas, and between the eruptions our sun creates, the researchers discovered a steady, continual signature — and it's coming from the near-vacuum of space itself.
"The interstellar medium is like a quiet or gentle rain," said James Cordes, senior author of the study and George Feldstein Professor of Astronomy, in a Phys.org report. "In the case of a solar outburst, it's like detecting a lightning burst in a thunderstorm and then it's back to gentle rain." Ocker thinks more low-level activity in interstellar gas exists than scientists previously believed, which means researchers can track and analyze the distribution of plasma — at least when it isn't roiled by solar flares.
Voyager 1 is a marvel of human ingenuity
Shami Chatterjee, a research scientist at Cornell, said the perpetual tracking of the density of interstellar space is significant. "We've never had a chance to evaluate it. Now we know we don't need a fortuitous event related to the sun to measure interstellar plasma," explained Chatterjee in the Phys.org report. "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."
NASA's Voyager 1 departed the Earth with a golden record stowed aboard — one created by the late Cornell Professor Carl Sagan — in addition to state-of-the-art technology of the mid-1970s. NASA's Jet Propulsion Laboratory says it takes 22 Watts to send a signal back to Earth, and the probe has just 70 kilobytes of computer memory. When it started on its way out of our solar system, Voyager 1 could send data at 21 kilobits per second — but now that it's 14 billion miles away, its transfer rate has slowed drastically, to 160 bits/second. All to say: it's way, way out there, but we're still learning a lot about the universe from a 1970s-era spacecraft.