A deep silence reigns on Mars

The first analysis of sound on Mars, based on recordings from the Perseverance rover, indicates that the speed of sound is slower than on Earth and that deep silence often prevails.

The research, published April 1 in the journal Nature, reveals the speed of sound through an extremely thin atmosphere, often carbon dioxide, what Mars might look like to human ears, and how scientists can use audio recordings to explore subtle changes in air pressure in Another world. Measurement of the condition of the rover.

“It’s a new sense of investigation that we’ve never used on Mars before,” Sylvester Morris, an astrophysicist at the University of Toulouse in France and lead author of the study, said in a statement. “I expect many more discoveries to come, using the atmosphere as a source of sound and a propagation medium.”

Most of the sounds in the studio were recorded by the microphone on Perseverance’s SuperCam, mounted to the rover’s header. The study also refers to sounds recorded by another microphone attached to the hull of the rover. This second microphone recently recorded the jets and whistles of the rover’s gaseous dust removal tool, or gDRT, that expels flakes from the rocks that the rover scraped for examination.

The result of the recordings: a new understanding of the peculiar features of the Martian atmosphere, in which the speed of sound is slower than on Earth and varies with pitch (or frequency). On Earth, sounds typically travel at a speed of 343 meters per second. But on Mars, low-pitched sounds travel at a speed of about 240 meters per second, while high-pitched sounds travel at 250 meters per second.

The changing speeds of sound on the Red Planet are the result of the influence of the cold thin atmosphere of carbon dioxide. Prior to the mission, scientists had predicted that the Martian atmosphere would affect the speed of sound, but this phenomenon was never noticed until these recordings were made. Another effect of this opaque atmosphere: the sounds travel a short distance, and the higher tones are barely carried at all. On the ground, the sound can reduce after about 65 meters; On Mars, it only misses 8 metres), and high-pitched sounds are completely lost at that distance.

The SuperCam microphone recordings also reveal previously unobserved pressure changes caused by turbulence in the Martian atmosphere as its energy changes on small scales. Martian winds were also measured for the first time on very short time scales.

One of the most striking features of the audio recordings, Morris said, is the silence that seems to prevail on Mars. “At one point, we thought the microphone was broken, and it was very quiet,” he added. This is also a result of Mars having such a thin atmosphere.

“Mars is very quiet because of the low atmospheric pressure,” said Baptiste Scheide of Los Alamos National Laboratory in New Mexico, who is also a study co-author. “But the pressure changes with the seasons on Mars.”

This means that in the coming autumn months on Mars, the sound of Mars can get louder and provide more information about the air and weather of another world. “We are entering a high pressure season,” Chadd said. “Perhaps the acoustic environment on Mars is less calm than when we landed.”

The acoustic team also studied what the SuperCam microphone picked up from the twin rotors of the Ingenuity, the Mars helicopter that is the rover’s airborne companion and explorer. It rotates at 2,500 revolutions per minute, Morris said, and produces a “distinctive low-pitched sound at 84 Hz,” referring to the standard acoustic measurement of vibrations per second and the speed of rotation of both rotors.

On the other hand, when a SuperCam laser, which vaporizes pieces of rock from a distance to study its composition, hits a target, it produces sparks that create a high-pitched noise above 2 kHz.

Studying the sounds recorded by the rover’s microphones not only reveals details of the Martian atmosphere, but also helps scientists and engineers assess the health and function of the rover’s many systems, in the same way that one might notice unpleasant noises when driving a car.