How Sound Travels on Mars and Why the Acoustics of the Red Planet Are So Unique

The Physics of Waves: Constant Light and Capricious Sound

On Earth, as in the rest of the universe, certain physical laws seem immutable. The speed of light in a vacuum is one of the most reliable benchmarks in the cosmos, traveling at exactly 299,792,458 meters per second. Even when it passes through an atmosphere and slows down very slightly as it interacts with air molecules, its speed remains virtually the same, whether you’re on our planet or on the Red Planet.

The situation is different for sound, as highlighted by an analysis of acoustic propagation throughout the Solar System published by IFLScience. Sound is a vibration that propagates as an acoustic wave through a given medium, whether liquid, solid, or gaseous. Its speed therefore depends closely on the physical characteristics of the medium it travels through.

By way of comparison, on Earth, sound travels at about 1,500 meters per second in water and around 340 meters per second in air. In solid media, these waves can travel significantly faster, although this maximum speed of sound depends on the type of solid being studied.

A groundbreaking experiment conducted by the Perseverance rover

For a long time, our understanding of Martian acoustics relied on theoretical models. Today, researchers have access to direct recordings transmitted by the various vehicles deployed on the surface, which have notably captured the whistling sound of dust devils sweeping across the Martian regolith.

In 2022, an international team of scientists set out to systematically analyze sound propagation on Mars using NASA’s Perseverance rover. This study made it possible to measure the speed of sound on a planet other than Earth for the very first time, revealing particularly unusual acoustic behavior, as reported by IFLScience.

To take these measurements in Jezero Crater, the scientists used a direct method. They fired a laser at rocks located at known distances, then measured the time it took for the shock wave to reach the rover’s microphones. The experiment established an average speed of sound of 240 meters per second, or about 864 kilometers per hour.

Marked diurnal temperature variations

Measurements taken on Mars also revealed a fluctuation in the speed of sound of about 10% between day and night. This phenomenon is explained by the large temperature variations observed on the planet’s surface—a property also observed on Earth under extreme weather conditions.

As illustrated by an incident in Canada where residents could hear each other speaking from kilometers away on a particularly cold day, air temperature greatly influences the range and speed of sound waves.

If advanced life forms existed on Mars, these daily variations would pose a major acoustic challenge. Any sound produced at night would take much longer to reach its destination than during the day, profoundly altering auditory perception.

A Unique Phenomenon: Two Speeds of Sound in the Audible Spectrum

The most puzzling aspect of Martian acoustics lies in the fact that the speed of sound varies even within the range audible to the human ear, which spans from 20 Hz to 20 kHz. This is a characteristic unique to the Martian atmosphere, which consists primarily of carbon dioxide at low pressure, as confirmed by a study exploring the speed of sound on the Red Planet.

According to the explanations provided in the study presented at the 53rd Lunar and Planetary Science Conference: “Due to the unique properties of carbon dioxide molecules at low pressure, Mars is the only terrestrial planet in the Solar System whose atmosphere experiences a change in the speed of sound right in the middle of the audible frequency range (20 Hz–20 kHz).”

The researchers note that “for an acoustic wave with a frequency higher than about 240 Hz [just below middle C on a piano], the vibration modes of CO₂ activated by collisions do not have time to release their energy.” It turns out that, on Mars, frequencies above 240 Hz travel more than 10 meters per second faster than lower frequencies. High-pitched sounds travel at 250 meters per second, compared to 240 meters per second for low-pitched sounds, which means that high-pitched sounds reach the listener before low-pitched ones.

Extreme sound attenuation and a hostile environment

In addition to this time lag between high and low frequencies, sound propagation on Mars is subject to an extremely rapid drop in intensity. While on Earth sound can easily travel long distances, the Martian atmosphere absorbs acoustic energy very quickly.

An official statement from NASA’s Jet Propulsion Laboratory explains this difference: “On Earth, sound may fade after about 65 meters (213 feet); on Mars, it fades as early as 8 meters (26 feet), with high-pitched sounds being completely lost at that distance.”

This combination of factors would make any concert or musical gathering completely impractical on the Red Planet—not to mention the crowds capable of triggering seismic sensors during massive concerts held on Earth. Between the freezing cold, the thin atmosphere, and significant acoustic distortion, music on Mars is decidedly impossible.

Source: iflscience.com

How Sound Travels on Mars and Why the Acoustics of the Red Planet Are So Unique