Persistence is the most ambitious mission ever sent to Mars. The machine itself is a marvel of technology. The main goal of the rover is to take samples, which he packs and leaves behind as landmarks on his way to the Jezero crater. He is going at his own pace and this year he has just traveled three kilometers and collected seven of the more than 40 samples to be collected. More information Within a decade, it is estimated that this material will be transported back to Earth, completing the mission: searching for signs of life that supposedly existed on the red planet 3.5 billion years ago. Among its seven instruments are two microphones. They are far from basic, but they are the type that anyone could buy in a store. One is integrated into the camera system in the Input, Descent and Landing System (EDL) and records the noise made by the six wheels as they travel. The other comes with the SuperCam instrument, which is installed on its web Persistence and records ambient noise every few minutes. But someone from the University of Malaga (UMA) in southern Spain had an idea no one else had thought of: the rover could record the sound produced by its laser when it cuts the rocks of Mars. A team led by UMA professor Javier Laserna provided the NASA mission with a spectroscopy system to analyze the light emitted by the laser. The beam cuts for a few seconds and during this time it emits light. The spectrum of this light can be analyzed to find out what the rock is made of, but it also makes noise. As César vlvarez from the Laserna team points out, “the SuperCam microphone is synchronized with the laser, and during those seconds you can hear a sound as the rock cuts.” His colleague Javier Amorós, also from UMA and co-author of the study, says that “if you know the distance to the rock, you can measure the speed of sound.” The results of this year’s sound recording have just been published in the journal Science Nature. While this is not entirely new to acoustics experts, as it has already been done with models on Earth, the most striking finding is that the speed of sound varies with frequency. Mars is very quiet, and before the rovers, only the sound of the wind was heard José Antonio Rodríguez, from the Astrobiology Center of Spain According to the models, given the atmospheric pressure – which on Mars planes is about 100 times lower than the Earth at sea level – and the physical properties of the environment – carbon dioxide dominates the Martian atmosphere – the estimate was that the sound waves would travel at about 240 meters per second compared to 342 on Earth. Modeling was not far off. The speed of sound during the day ranges from 240m / s to 257m / s. And the fluctuations correspond to the frequency: the highest, above 2 kHz, travels up to 257 m / s. Meanwhile, the low frequencies, around 84 Hz, move more slowly, around 240 m / s. While hypothetical, a conversation between two people who are only five meters apart would simply cause an incomprehensible cacophony. For the study authors, the different attenuation relative to Earth is the most striking property of sound on Mars. The lower density of the planet’s atmosphere makes the attenuation much greater than on the Earth’s surface. It is understood as the loss of power of the original signal as it travels through a medium, the physics of this process is relatively simple: as the sound wave moves in the air, the molecules collide with each other, oscillating and producing heat. Part of the acoustic energy diffuses into the medium. The charm of this process is explained by physicist Manuel de la Torre, a researcher at NASA’s Jet Propulsion Laboratory, which is located behind the Persistence Mission. “I thought it was interesting how the microphone captured the rate of energy dispersion from the atmosphere into the heat in a very subtle atmosphere that is rich in CO₂. You can even hear the scale where the motion reaches the size of the distance between the molecules. It’s a dynamic system that is difficult to measure on Earth. “ But the sound of Mars is not only interesting. The recordings of the wind, the wheels and the laser serve as a mirror of the medium: the atmosphere of Mars. The Mars Environmental Dynamics Analyzer (MEDA), one of Persistence‘s instruments, is responsible for studying this. MEDA is an advanced meteorological station and its main researcher is José Antonio Rodríguez, from the Center for Astrobiology (CAB), which belongs to the National Institute of Aerospace Technology of Spain. “Mars is very quiet and before the rovers only the sound of the wind could be heard,” explains Rodríguez. During the day, in the layer closest to the surface, post-conduction disturbance occurs, characterized by the vertical movement of air caused by sunshine and an unstable thermal gradient. “The recordings allow us to study the variations in these bursts. We do the study of turbulence with MEDA, with data on temperature, pressure… but the sound allowed it on a small level “, adds the Spanish scientist. Compared to the millions of meteorological stations on Earth, there are only three – all of them Spanish. In addition to the other data we collect, we can now add the audio being recorded Persistence. As Rodríguez explains, “these stations and microphone data allow us to refine models and better understand the dynamics of the atmosphere to plan future missions.” English version by Simon Hunter.
