The first audio recordings of Mars reveal a quiet planet where sound circulates slowly and at two different speeds, according to an article published in the journal Nature on Friday. The incredible acoustic landscape of the red planet is slowly being revealed by the microphones of the Perseverance robot, which has been circling its surface for just over a year.
The first sounds were recorded as soon as the rover started to walk. Under the screeching sound of the vehicle, a gust of wind could be clearly perceived. The lead author of the study published in Nature, Sylvestre Maurice, one of those responsible for the SuperCam installed on the robot, guarantees that the analyzes show turbulence hitherto unknown.
But the red planet held even more important surprises, such as the fact that the frequency of high-pitched and low-pitched sounds travel at different speeds. Maurice’s team used records from the small Ingenuity helicopter, which is accompanying Perseverance, and auditory results from laser firing at the rocks to probe their chemical composition.
With this specific instrument, which emits a kind of “clack clack”, “we had a very localized sound source, between two and five meters away from the target, and we knew exactly when it was going to fire”, explained the researcher. The results confirmed for the first time that the speed of sound is slower on Mars, at 240m per second, compared to 340m on Earth.
It was predictable, as the atmosphere of Mars contains 95% carbon dioxide, compared to 0.04% on Earth. The atmosphere of Mars causes the sound to be muffled, on the order of about 20 decibels, relative to our planet, the study indicates. But the surprise came when measuring the sound of the laser: 250 m per second.
“I panicked a little,” the specialist explained. “I said to myself: one of the two measurements is false, because on Earth, close to the surface, sound only has one speed.” But the results have been confirmed again and again: the highs of the laser have one speed, the bass of the helicopter blades another.
“Trebles are lost very quickly, even at close range,” Maurice explained. This implies that “a conversation between two people would be difficult, even five meters apart,” according to the French National Center for Scientific Research in commenting on the article.
“On Earth, the sounds of an orchestra come to you at the same time, whether they’re low or high. On Mars, if you’re a little farther from the scene . . . the range can be phenomenal.” The analysis of the sounds of turbulence, such as vertical winds, will allow in particular “to fine-tune our digital climate and weather forecast models”, explained Thierry Fouchet, from the Paris Observatory, another of the authors of the study. Venus and Titan could be the next candidates for sound research with microphones like those used on Mars.