For generations, the acoustic environment of Mars remained a mystery, forcing scientists to model and predict the soundscape based only on atmospheric data. Recent technological advancements finally provided the means to place sensitive instruments directly onto the surface of Mars. The successful deployment of these listening devices now offers an entirely new dimension to planetary exploration. This achievement allows us to move beyond silent images and experience the subtle soundscape of an alien world for the first time.
The Unique Physics of Martian Sound
Sound propagation on Mars is radically different from Earth due to the planet’s unique atmospheric conditions. The Martian atmosphere is extremely thin, with a surface pressure less than one percent of Earth’s sea-level pressure, and is composed of over 95% carbon dioxide (CO2). This low density and high CO2 concentration cause sound waves to lose energy much faster, resulting in heavy acoustic dampening. Consequently, sounds on Mars are much quieter and travel only a few meters before becoming inaudible.
The speed of sound is not a single constant value as it is on Earth, but varies significantly depending on the frequency of the sound. Low-frequency sounds, below about 240 Hertz, travel at approximately 240 meters per second. Sounds with a higher frequency travel faster, around 250 meters per second, a difference of about 10 meters per second. This phenomenon is caused by the way CO2 molecules react to sound waves at very low pressure, creating two distinct speeds of sound.
The Sounds Captured on Mars
The acoustic environment of Mars, recorded by the Perseverance rover, is often muffled and subdued compared to Earth. One of the first sounds captured was the Martian wind, which registers as a gentle whoosh or gust, rather than the intense howling often imagined. This faint wind sound is filtered by the atmosphere, which quickly attenuates the higher-pitched frequencies, leaving behind a more bass-heavy auditory experience.
The rover itself contributes a significant amount of noise to the Martian soundscape. Recordings reveal the mechanical sounds of the six metallic wheels crunching and rattling over the rugged terrain of the Jezero Crater. These noises, alongside the whirring of internal motors and the movement of the robotic arm, offer engineers an auditory diagnostic tool for monitoring the rover’s health.
Scientists have also captured the sharp, high-frequency “snap” produced when the SuperCam instrument fires its laser at a rock target. The characteristics of this snap are used to determine the hardness and physical properties of the target rock. Other recordings include the whirring of the Ingenuity Mars Helicopter blades and the faint crackle of electrical sparks within dust devils, offering new insights into atmospheric phenomena.
Listening Devices: The Microphones of Rovers
The ability to hear Mars is a direct result of specialized engineering and the inclusion of two distinct microphones aboard the Perseverance rover. One microphone is integrated into the SuperCam instrument, which is mounted on the rover’s mast. This device is designed primarily for scientific observations, recording the shock waves from the laser pulses and monitoring atmospheric acoustics to help determine wind speed and direction.
The second device is a commercial, off-the-shelf microphone originally intended to capture the sounds of the rover’s entry, descent, and landing phase. Despite the extreme conditions, this microphone survived and continues to record ambient noise and the sounds of the rover’s movement. Both microphones required extreme sensitivity to detect the heavily attenuated, faint sounds in the cold, low-pressure CO2 atmosphere. Their successful operation has provided the ground truth for modeling acoustic processes in rich CO2 atmospheres, a first for planetary science.