Sound Waves and Audio Recorders Could Be The Real Keys to Discovering Alien Life Forms

The Perseverance rover on Mars is searching for chemical and biological signs of life on the Red Planet by digging into the soil to both analyze it and store it in canisters for pick-up by a future mission to be further studied back on Earth. It is also searching for visible signs of life by launching the Ingenuity helicopter, which has flown at least 50 times at high and low altitudes looking for tracks, fossils, river beds, unusual rocks and any other signs of Martian life. The Perseverance Rover is also listening for signs of life – it has two microphones which have captured the sound of Martian winds, the crunching of the rover’s own wheels and other noises. It is that last method which interested Timothy G. Leighton, a professor of ultrasonics and underwater acoustics at the University of Southampton in the U.K.. Leighton is studying future sounds – he’s developed a software program which simulates how the human voice will sound on other planets and moons … a good thing to know if an astronaut needs to call for help. Leighton is now convinced that his program will also help us listen for alien life forms and thinks it is a more efficient way to find them.

“For decades, we have sent cameras to other planets in our solar system and learned a great deal from them. However, we never really heard what another planet sounded like until the very recent Mars Perseverance mission.”

It turns out the movie “Alien” was wrong – in space, someone CAN hear you scream … but they may not necessarily hear the same sound one would hear on Earth. Leighton wondered exactly what the differences might be, especially after hearing the sounds recorded by the Perseverance Rover on Mars. While we know what a tire moving on dirt and rocks should sound like, we know less about what noises a Martian wind blowing across the ground might make. And we know nothing about how a human voice would sound.

In the press release announcing Leighton’s demonstration of his software program at the recent 184th Meeting of the Acoustical Society of America, a reference is made to the very first sound recording from another planetary body. That event happened in 2005 when the Huygens atmospheric entry robotic space probe landed successfully on Saturn's moon Titan – making it the first to land on a moon other than our own and the farthest landing from Earth a spacecraft has ever made. The sounder instrument was activated near the end of the lander’s descent and measured the speed of sound in order to determine the distance to the surface, rate of descent and the surface roughness. Those ‘speed of sound’ measurements also gave an indication of the composition of Titan’s atmosphere.

The next big sound advance in space came from the Mars InSight Lander which touched down on November 26, 2018. Just a few days later, on December 7, 2018, InSight recorded the sounds of Martian winds with the Seismic Experiment for Interior Structure (SEIS) instrument – the vibrations of the wind were within human hearing range at about the level of the sounds emitted by a subwoofer, and were sent back to Earth for analysis. These also provided data for Leighton’s software program. The acoustic recordings the Huygens lander’s descent, the Mars InSight wind recordings and Perseverance Rover’s audio pick-ups of wind and the movements of the rover itself were then combined with data from other active and passive acoustic sensors which operated over a wide spectrum of sounds from very low frequency infrasounds below the human hearing threshold to ultrasounds above human hearing.

The end results of Leighton’s other world sound experiments are twofold. First, they will help develop precise sound equipment for various planets and moons. The recording from InSight and Perseverance show that the thin, carbon dioxide-rich Martian atmosphere absorbs more sound than Earth’s, so distant noises appear fainter. Thicker atmospheres will have a different impact on sound speed and absorption. Now, lander engineers can use that data to design and calibrate microphones and speakers for each planet and moon’s special conditions so they – and future astronauts – can discern exactly what they are hearing no matter the location or conditions.

“The idea of sending a probe on a seven-year trip through space, then drilling or melting to the seabed, poses mind-boggling challenges in terms of finance and technology. The ocean on Europa is 100 times deeper than Earth’s Arctic Ocean, and the ice cap is roughly 1,000 times thicker.”

The second benefit of the sound simulation software will help in the search for extraterrestrial life on planets and moons more hostile than Mars. Jupiter’s moon Europa is a target for future missions but its thick layer of surface ice will be difficult to physically penetrate the ice to reach Europa’s ocean and the life forms that might be swimming in it with the limited instruments which can be packaged into a small lander.

“However, instead of sending a physical probe, we could let sound waves travel to the seabed and back and do our exploring for us.”

It’s not like yelling “Is anybody home?” and hoping to pick up a response or an echo (shades of Captain Kirk and the Enterprise landing parties?), but designing sound instrument for the conditions on Europa – and other  planets and moons – is obviously a much better idea with a greater chance of success. Finally, Leighton’s software could make for more realistic Star Trek movies and other science fiction films, which can now show how voices and vehicles might really sound on other planets. In fact, entertainment is the first area where Leighton’s software will be used. Demonstrations, which will include both simulations plus actual sounds recorded on Titan and Mars by both NASA and China’s Zhurong mission, are being scheduled to be played at planetariums and museums around the world. 

In space, new instruments CAN hear you scream, and now we have the software to figure out if you need help, are screaming for joy, or  are yelling out the lyrics of a song with your new extraterrestrial friend.