By: Yeeyao Wong

Chatting on Mars will be hard. That’s because it’s really cold. It’s also because Mars’ small atmosphere, made of mainly carbon dioxide, doesn’t transport sound very well. A person chatting to you will sound as quiet as if they were talking really far away, 200 feet to be exact.

“It’s a pretty drastic difference from Earth,” Baptiste Chide says. “You don’t want to do it.” It’s way better to use some microphones and headphones, even when you’re really close, he says. He’s a planetary scientist at the Los Alamos National Lab in New Mexico. He and his teammates shared these discoveries about the sound on Mars in the May 26 issue of Nature.

Chide and his team analyzed some of the first recorded sounds ever made on Mars. The videos had been collected by a microphone on the Perseverance robot, made by NASA. It has been explored since February 2021.

The videos that were taken weren’t caused naturally on Mars. They were sounds made when Perseverance fired a laser at some small rocks on the planet. The zap made a sound wave, like thunder, but on a smaller scale. Chide and his team studied about five hours total of sounds this way.

This data opened the door for scientists to measure the speed of sound on Mars, and showed a surprise: on Mars, there is more than one speed of sound. In the range of human hearing frequencies, high-pitched sounds move at about 560 mph. Low-pitched sounds, however, travel at about only 535 mph. These low-pitched sound waves will disappear after they have traveled only a few meters before becoming inaudible. The higher-pitched sounds distinguish after less than the distance of the lower-pitched sounds.

“For an Earthling, this may be surprising. But it makes sense,” Andy Piacsek says. He is a physicist who works at Central Washington University. He wasn’t involved in Chide’s discovery team, but he does observe how sound waves travel through different materials.

When a wave of sound travels through air or a liquid it gives energy to the molecules surrounding it. Air currents will slowly move that energy around. This is the relaxation effect.

For sound waves going through the air (the thing that you can’t see in front of you), the relaxation effect depends on the frequency of the sound and the kind of molecules around it. On Mars, the relaxation after a higher-pitched noise happens quicker than after a lower-pitched noise. That is because that Mars’ atmosphere is mostly made up of carbon dioxide.

“This doesn’t happen on Earth because the pressure of our atmosphere is so much higher than on Mars,” says Piacsek. Also, Earth’s atmosphere is mainly made up of nitrogen. In these conditions, the relaxation effect is about the same thing for low and high-pitched sounds. On Earth, sounds usually travel at 767 mph.

With Perseverance sending more and more sounds back to Earth, it will be possible for scientists to study how sounds works on Mars, says Chide. “We’re very excited to see how sound behaves during winter and autumn—during every season on Mars.”