How does Mars sound? The rover’s microphone recorded the red planet’s dust devils

A dust devil looks a bit like a tornado, but is weaker and rarely lasts more than a minute.

It’s a winding column of heated air hurtling across the sun-warmed ground, made visible by the dust it kicks upward. While usually benign, dust devils can occasionally kill.

Dust devils have been known to appear on Mars since the 1970s. They have been observed both from the ground and from orbit.

The more dust there is in the Martian atmosphere, the hotter and more agitated it becomes, and this can escalate into a global dust storm.

When the dust settles, it can coat and disable the solar arrays that are essential to many of the instruments we’ve landed on the planet.

There’s a lot we don’t know about how these devils work. But new research, published this week in Nature Communications, has recorded what dust devils sound like, providing new insights into how they operate.

But it also raises questions about how future astronauts would detect and interpret sounds on the red planet.

There has been a great deal of erosion on Mars since the last few rivers and lakes disappeared, including at the landing sites of NASA’s current rovers Curiosity and Perseverance.

While the erosive power of a single dust devil is tiny, a billion years of dust devil could potentially have washed away miles of rock.

There are therefore many reasons for wanting to better understand how dust devils work.

And now we know what a Martian dust devil sounds like thanks to a new study led by Naomi Murdoch of the University of Toulouse in France.

Many passing dust devils have been caught on cameras on Mars landers and rovers, but Murdoch and his team report a dust devil that luckily passed squarely over the Perseverance rover on Sept. 27, 2021, which was at the bottom of the Mars. Jezero crater.

The rover’s masthead camera, called the SuperCam, includes a microphone, and this recorded the sound of the wind rising and falling as the dust devil passed.

Specifically, the wind noise increased as the main vortex wall arrived, followed by a pause representing still air in the eye of the vortex, before a second episode of wind noise as it passed the rear vortex wall. vortex.

It took less than ten seconds and you can listen to the audio recording below (turn the volume up to max).

Other sensors also provided information. They showed that the pressure dropped to a minimum between the two bursts of wind noise — which to me is consistent with sucking rather than blowing — and they also recorded the impacts of individual dust grains on the rover.

The dust devil was about 25 meters in diameter, at least 118 meters high, and traveled over the ground at a speed of about five meters per second.

The maximum wind speed in the spinning vortex was probably just under 11 meters per second, equivalent to a “cool” to “strong” breeze on Earth.

Did it really sound like that? Hearing a recording that purports to be the sound of the Martian wind is fine, but is that really what we would hear if we were there ourselves?

The first thing to note is that this genuinely originates as “real sound”, as opposed to other data such as images or radio signals transformed into sound (a process known as sonification), such as the so-called sound of two black holes colliding or radio noise from the atmosphere of Venus.

The Dust Devil audio file contains real sound waves picked up by a microphone on Mars.

The atmosphere there is much thinner than on Earth (the pressure on the Martian surface is less than a hundredth of ours), so the high-frequency component of sound is hardly carried (scientists say it is “attenuated”).

The result is that the wind sounds much lower in pitch than a similar wind on Earth.

The only other planetary body from which we have authentic sound recordings is Venus, where in 1982 two Soviet “Venera” landers recorded wind and lander operation noises.

However, if you were on Mars you could never hear the wind directly with your ears.

If you were foolish enough to expose your ears to the Martian atmosphere, the low pressure outside would burst your eardrums and you would be instantly deaf as well as having no air to breathe.

If you were to go out in a pressurized space suit (a much more sensible idea), what you would hear would depend on how well the sound waves were transmitted through the solid shell of your helmet, and then how well these were transformed into sound waves in the air inside the helmet.

In other words, you would hear a distorted version of what an external microphone would pick up. Imagine walking the Earth with your head inside a goldfish bowl and you’ll get some of the idea.

If future human explorers to Mars want to hear what’s going on in the external environment, I suspect they’ll rely on a suit-mounted microphone that powers wireless earphones, although I can’t find any evidence that this has yet been factored in. Drawing of the suit of Mars.

This all boils down to a recording from an external microphone which is the best way to represent sounds on Mars, or indeed any other planet that has an atmosphere.

If you want to hear more sounds from Mars, NASA has a collection of audio recordings you can listen to.

By David RotheryProfessor of Planetary Geosciences, The Open University

(The conversation)