What is sound on Mars like?
JB: This is Earth and Sky for Tuesday, September 9. A listener writes, “If you could be on Mars while a spacecraft was landing nearby, what would you hear? Would the sound be different than on Earth because of differences in atmospheric pressure?”
DB: It’s true that Mars has an atmosphere, and that its atmosphere is much thinner than Earth’s. So suppose you were on Mars, waiting for your fellow astronauts from Earth to join you in a second spacecraft. If you were standing on the Martian surface, you’d have to be in a space suit – maybe one with an external microphone. Even so, as their spacecraft landed, you wouldn’t hear much of anything.
JB: To hear a sound, you need two things – vibrations and a medium, such as air or water, through which those vibrations can move. Sound results from a pressure change that displaces molecules in the medium. Like a pile–up on the freeway, each molecule’s displacement is relayed to the one next to it . . . But Mars’ atmosphere is too thin to carry sound very well. If you were on the Martian surface, and a spacecraft landed nearby, it’s possible you’d sense its landing as a thump – rather than hear it.
DB: That’s because the planet’s surface is so much denser than its atmosphere – it’d be better at transmitting vibrations. By the way, Mars recently passed close to Earth, and it’s still very bright in our sky. You can easily see it tonight – the closest bright object to the nearly full moon. With thanks to the National Science Foundation, we’re Block and Byrd for Earth and Sky.
Our thanks to the following individuals and institutions who assisted in the preparation of this script:
Dr. William Hartmann
Planetary Science Institute
Tucson, Arizona
If you enjoyed this show, the following books and articles may be of further interest to you:
Scientific Encyclopedia (Van Nostrand Reinhold), “Acoustics,” p. 20
The Dorling Kindersley Science Encyclopedia, “Sound,” p. 178
Author’s notes:
The closer together the molecules are in a medium, the faster the sound waves move and the farther they travel before dying away. In water, sounds travels nearly five times faster than it does in the air and many times further. Some whale songs, for example, are known to carry hundreds of miles under water.
