Voyager-1 records the ‘hum’ of interstellar gas
Image: Los Angeles Times
NASA‘s Voyager-1 spacecraft, travelling outside the solar system, has sent back new data revealing a ‘hum’ given off by interstellar gas 14 billion miles from the Earth. The spacecraft, currently further away from the Earth than any human-made object before it, launched 44 years ago to study the gas giants of the outer solar system.
Its instruments have now recorded the ‘constant drone’ of plasma – the fourth state of matter that makes up 99.9 per cent of the universe – while in interstellar space.
The very faint and monotone sound has been sent back to Earth by Voyager-1 in a ‘narrow frequency bandwidth‘.
Cornell University astronomers, who carried out the analysis of the interstellar hum, say the signal carrying the data was so weak it isn’t audible without manipulation.
It’s hoped that the discovery of a constant hum will help astronomers understand more about how the medium interacts with the very edges of the Sun’s solar winds.
Examining data slowly sent back from more than 14 billion miles away, Stella Koch Ocker, a Cornell doctoral student in astronomy, uncovered the emission.
‘It’s very faint and monotone, because it is in a narrow frequency bandwidth,‘ Ocker said. ‘We’re detecting the faint, persistent hum of interstellar gas.‘
Voyager 1 crossed into interstellar space in August 2012 – and is continuing to collect data.
No manmade object has travelled further than NASA’s iconic spacecraft.
It carries a copy of the Golden Record – a ‘message to aliens’ compiled by legendary astronomer Carl Sagan. There are greetings in 55 languages, pictures of people and places on Earth and music ranging from Beethoven to Chuck Berry’s ‘Johnny B. Goode.’
Crossing into interstellar space involved going through the heliopause – the theoretical boundary where the Sun’s solar wind meets the interstellar medium.
The study published in Nature Astronomy shows how the heliosphere is shape and modified, say the New York team.
After entering interstellar space in 2012, Voyager’s Plasma Wave System detected gas bursts caused by our own sun, with a steady, persistent signature from the tenuous near-vacuum of space between the bursts.
Senior author Professor James Cordes said: ‘The interstellar medium is like a quiet or gentle rain,‘ adding that when there is a solar outburst it is like detecting a lightning burst in a thunderstorm, then going back to gentle rain.
Ocker believes there is more low-level activity in the interstellar gas than scientists had previously thought, which allows researchers to track the spatial distribution of plasma – that is, when it’s not being perturbed by solar flares.
Co-author Shami Chatterjee said: ‘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. 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,‘ said Chatterjee, or at least until it runs out of power required to send data back to the Earth.
The extremely weak, narrowband plasma wave emission the team detected seemed to continue for about 10 AU (929 million miles) of interstellar space.
The emission appears to be distinct from shock-generated plasma oscillations, that is those created by strong solar winds, that were previously used to measure the local density of plasma outside the heliopause.
Study authors predict the ‘hum’ may be generated by thermally or suprathermally excited plasma oscillations – very energetic particles.
The persistence of the emission through the most recent data published from Voyager-1 suggests that it may continue to be detectable by Voyager-1.
‘This future work will improve our understanding of the large-scale structure of the VLISM (Very Local Interstellar Medium) and may reveal the extent of the Sun’s role mediating interstellar turbulence,‘ the authors wrote.
Launched in September 1977, Voyager 1 flew by Jupiter in 1979 and then Saturn in late 1980. Travelling at about 38,000 mph, it crossed the heliopause in August 2012.
While it will continue on its voyage even after its power runs out due to momentum, by 2025 the spacecraft will no longer be able to send signals back to Earth.
So the scientists involved in the mission are taking every opportunity to study the data, learn more about interstellar space and prepare for the next mission.
The findings have been published in the journal Nature Astronomy.
WHERE ARE THE VOYAGERS NOW?
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Wisenox
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Interesting article. I wanted to know how it was still being powered, so I looked into the plasma wave detector:
https://rfengineer.net/rf-antenna/still-working-after-all-these-years-the-voyager-plasma-wave-subsystem/
However, that also led me to another site that tells us how we can listen to VLF waves on earth:
“Of course if you just want to poke around on VLF and listen to some of the higher-powered man-made VLF signals, like the aforementioned submarine communications, you can accomplish that with nothing but a hunk of wire attached to the audio input jack of a PC with a decent sound card.”
There’s also a video:
https://hackaday.com/2017/11/06/sferics-whistlers-and-the-dawn-chorus-listening-to-earth-music-on-vlf/
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Andy
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The RTG power pack is still operating, and will be able to power the instruments and transmitter for another four or five years.
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Wisenox
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Thanks, that’s actually what I was trying to find. Impressive, especially considering that it has already been going for 44 years. Does the cold temperature of space add to the lifespan?
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Andy
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I can’t recall ever hearing if the cold might affect the RTG, but as it uses radioactive decay to produce electricity, I would say the temperature would have no effect.
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