Sound of space: interstellar mission reveals previously undetected background noise

It is said that in space no one can hear you scream as sound is prevented from travelling through a vacuum.

Yet new data sent back from Nasa’s Voyager 1 probe has shown that interstellar space actually sounds like gentle rain.

The quiet, continual "hum" comes from clouds of interstellar gas, which can be detected as a faint background noise in between the crashing of solar flares from the Sun bursting through the heliopause, which makes the boundary of our Solar System.

"The interstellar medium is like a quiet or gentle rain," said senior author James Cordes, Professor of Astronomy at Cornell University in the US.

"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."

Voyager 1 set off from Earth in 1977 and became the first man-made object to leave the Solar System in August 2012.

Since then, it has been travelling through interstellar space, and sending regular messages back to scientists 14 billion miles away.

After entering interstellar space, the spacecraft's Plasma Wave System detected large disturbances caused by our own Sun. But in between the eruptions, they also detected the steady, persistent signature produced in the near-vacuum of space.

Stella Koch Ocker, a Cornell doctoral student in astronomy, who uncovered the emission, said: "It's very faint and monotone, because it is in a narrow frequency bandwidth.

"We're detecting the faint, persistent hum of interstellar gas."

Our Sun sends out a constant solar wind which creates a bubble in space, known as the heliosphere.

Scientists say the new discovery will help them understand how this protective bubble is shaped and modified by what is happening outside of the Sun’s reach.

Cornell research scientist 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'."

Voyager 1 left Earth carrying a gold record encoded with information about our history, geography, maths, physics, our greatest musical compositions and even the sound of someone falling in love, in the hope it may be found by an alien civilisation.

A second probe, Voyager 2, left Earth 16 days before Voyager 1, but did not get gravity assist from Jupiter or Saturn and so is moving more slowly. It left the Solar System in 2018.

Both the probes are powered using heat from the decay of radioactive material, contained 

in a device called a radioisotope thermal generator (RTG).

Their original five-year lifespans have stretched to 41 years, making Voyager 2 Nasa’s longest running mission.

However, some experts say that the probes will not have officially left the Solar System until they are beyond the Oort Cloud, a band of comets which are still trapped in the Sun’s gravitational pull.

It will take about 300 years for Voyager 2 to reach the inner edge of the Oort Cloud and possibly 30,000 years to fly beyond it.

The research was published in the journal Nature Astronomy.