# What would sounds on Mars be like?

Figure there was a microphone on the surface of Mars, exposed to the atmosphere. If it recorded stuff, how would it sound? E.g. walking through sand, stuff falling down onto rock, a rocket engine, the wind, etc.

Can one transform sounds happening here on Earth to what they would be like on Mars? If so, are there any examples?

This question is not about that we wouldn't be able to listen directly since we'd have a pressurized helmet on. Just how would a microphone record stuff. A sensitive one, capturing all of the usual human hearing frequencies.

Do the mars rovers have any mics?

• Not sure where I read that, but the Mars 2020 Rover is supposed to record martian sounds. Maybe you can find something out with that info. – DaGroove Jul 31 '18 at 12:13
• They've tried, twice, one on a probe that crashed, the other wasn't turned on due to electrical concerns. I can't help but think that with the atmosphere as thin as it is the results are going to be disappointing. – GdD Jul 31 '18 at 12:24

This is a fantastic question!

There are some sounds recorded by a GoPro camera high in Earth's atmosphere in the video linked in the question How did the tangential thrusters for the 2014 LDSD test spin-up then spin-down so nicely? also shown below.

The sound starts at 120,000 feet (36.4 km) and then is heard at about 180,000 feet (54.5 km). Using NASA's U.S. Standard Atmosphere 1976 (in the vicinity of page 60-ish) these translate to about 0.5% and 0.05% of Earth's standard (i.e. sea level) atmosphere, which is already Mars's surface pressure (at a high altitude) and much lower than that, respectively.

The sounds is fainter, as can be expected, since fewer air molecules with the same excitation will transmit less power, and answers to What is the relation of sound propagation to air pressure? confirm it's roughly proportional.

As long as the mean free path is much shorter than the wavelength of sound, which it will be on the surface of Mars, there will not be much of a frequency dependent attenuation. So you can assume that the sounds will be 1% as loud as they would be on Earth, but sound very similar.

For scalar sound waves, 10 dB in amplitude is 10 dB in power, so this will be a roughly 20 dB reduction in level, but otherwise sound similar.

This contrasts with vector electromagnetic waves where 10 dB in amplitude is 20 dB in power.

• @Fred the speed of sound in a gas changes very little with density. It's primarily a function of the average speed of molecules, and therefore scales with the square root of temperature. It will be about 4% slower in the triatomic gas CO2 than a diatomic gas like nitrogen. So the speed of sound will be slower on Mars than Earth but that won't change the recorded qualities of sound other than a slightly longer delay (subtle effects if multi-path?). I don't see how the Doppler effect applies at all. Feel free to add a new answer! – uhoh Aug 1 '18 at 1:21
• the speed of sound in a gas changes very little with density afaik, it does well depend on density, and additionally on temperature and pressure. Since all of them are lower on Mars, speed of sound is definitely lower too. – Everyday Astronaut Aug 1 '18 at 8:23
• @derwodamaso post an answer, show your source. You'll find my statements are accurate once you research it though. – uhoh Aug 1 '18 at 9:02
• I think you guys are mixing two different measures of "density": number density, the number of molecules per unit volume; and mass density, the mass per unit volume. Sound speed does not depend greatly on number density, but indeed does depend on mass density (and thus on the average molecular mass). It also depends on the gas's specific heat ratio, which is different for molecules of different numbers of atoms. The wikipedia article on the speed of sound covers this in detail. – Tom Spilker Dec 18 '18 at 21:53
• @TomSpilker yes you are right and I was wrong. Speed of sound reflects average thermal velocity, so yes the speed of sound scales as $\frac{1}{\sqrt{m_{mol}}}$. CO2 is not nitrogen. 40 vs 28 so it's a 20% difference. Thank you for pointing that out! – uhoh Dec 19 '18 at 0:58

Finally, my favorite Youtube educator did a comprehensive video covering exactly this topic. There are some edited "sound" recordings of Insight's seismometer and it's air pressure sensor, but they are rather disappointing.

Past missions were planned to bring microphones to the surface of Mars but in all cases something went wrong so that we still don't have any actual ambient sound recordings. Fortunately, the Mars 2020 rover will carry microphones.

I'm thinking about leaving this question open until we get the sounds. Fly safe, Mars 2020!