Published on: 01.04.2022 – 12:18 Modified on: 01.04.2022 – 12:16
PARIS (AFP) – A quiet planet where sound travels slowly and at two distinct speeds, the red planet’s amazing acoustic landscape, captured by the Perseverance rover, reveals its secrets to earthlings.
Barely landed, just over a year ago, the NASA robot sent us the first audio ever recorded on Mars thanks to a microphone, at frequencies audible to the human ear, something previous missions had tried unsuccessfully.
A gust of wind could be clearly heard behind a shrill vehicle noise. The red planet, whose interplanetary probes have been sending us thousands of images for 50 years, has finally come out of its “sounding nothingness”, the CNRS welcomes on the occasion of the publication of a study in Nature on Friday.
That first recording revealed previously unknown turbulence regimes, recalls its lead author Sylvestre Maurice, scientific co-manager of the rover’s SuperCam instrument, where the microphone designed by Isae-Supaéro in Toulouse is installed.
But this “passive” listening wasn’t meaningful enough. And since Mars is very quiet most of the time, it was necessary to use two “active” sound sources from Earth on board, this astrophysicist from the Irap (Institute for Research in Astrophysics and Planetology) of the University of Toulouse explains to AFP.
Photo provided by NASA on June 25, 2021 of the Ingenuity helicopter taken with a Perseverance camera on Mars. Handout NASA/AFP/Archives
His team used the flights of the small Ingenuity helicopter, companion of the Perseverance rover, and lasers firing at the rocks to study their chemical composition (a “click-click” sound). “We had a very localized source of sound there that was between two and five meters from its target and we knew exactly when it would fire,” explains the researcher.
“Difficult Conversation”
The speed of sound could be measured on site: 240 meters per second compared to 340 meters per second on our planet. It’s nothing unusual that it’s slower, given the composition of the Martian atmosphere (96% CO2 versus 0.004% on Earth) and its very low pressure (170 times that of Earth).
The surprise came from the sound of the laser and its… 250 meters per second. “I kind of panicked! I told myself that one of the two measurements was wrong because there is only one speed of sound on Earth, near the surface,” Sylvestre Maurice recalls.
However, there are two speeds: one for the highs (the laser), the other for the lows (the helicopter). In addition, “the sound attenuation on Mars is stronger than on Earth, especially the high frequencies, which are lost very quickly, even at short distances”. This would make “a difficult conversation between two people who are only five meters apart,” according to CNRS.
The researcher even ventures the analogy with a concert: “On earth, you reach the sounds of the orchestra with the same speed, whether low or high. Imagine yourself on Mars, if you’re a little far from the stage… you’re going to have a hell of a time lag.”
In his eyes, the “scientific bet” to have a microphone installed on a space mission is a success. While this new tool is still in its infancy, continuing to listen to Mars should help better understand its atmosphere, which was similar to Earth’s in the past and may have supported life.
In particular, analyzing the sounds of turbulence such as these vertical winds called + convection plumes + will allow us “to refine our digital models for predicting the climate and weather” of Mars, expects Thierry Fouchet of the Paris Observatory – PSL, one of the authors.
Other atmospheres such as that of Venus or Titan, a moon of Saturn, could also be the subject of sound studies using the same type of instrument.
© 2022 AFP