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General Science => Question of the Week => Topic started by: thedoc on 27/11/2012 16:22:59

Title: QotW - 12.11.25 - Would things sound different on Mars?
Post by: thedoc on 27/11/2012 16:22:59

Hi Naked Scientists!

I have a question about Mars: I know the atmosphere is a lot thinner than here on Earth so does that mean sound would travel slower there?

I was thinking about Curiosity wanting to talk with one of his rover buddies & how they could communicate over long distances.

Thanks guys, love the show, keep up the good work!

Jodie Rio
Asked by Jodie


                                        Find out more on our podcast page (http://www.thenakedscientists.com/HTML/podcasts/show/20121125/)

 

Title: QotW - 12.11.25 - Would things sound different on Mars?
Post by: thedoc on 27/11/2012 16:22:59

We answered this question on the show...

Hannah -   Is it true that on Mars, no one can hear you scream?
 First up, we crack into some calculations.  In general, the speed of sound is proportional to the square root to the substance’s stiffness divided by its density.  Since Mars’s atmosphere has a lower density than here on Earth, you'd expect the speed of sound to be faster than here on Earth.  But if you reduce the pressure of a gas, the stiffness also reduces.  So, the speed of sound should stay about the same on Mars as it is on Earth.  But there's another factor to consider.  Mars is further away from the sun.  How does this affect the speed of sound?  Over to an expert…
[img float=left]/forum/copies/RTEmagicC_Mars_Hubble_03.jpg.jpg[/img]Catharine[/b] -   My name is Catharine Conley and I'm the NASA Planetary Protection Officer.  The difference is temperature.  If you reduce the temperature of the atmosphere, the speed of sound does get slower.  In fact, the speed of sound on Mars is about 2/3 of the speed of sound on Earth.
Hannah -   So, say two humans were to land on Mars, given the slightly lower speed of sound there, could they still speak to each other?  A listener got in touch with his thoughts.
Evan -   Hello.  This is Evan Stanbury from Sydney, Australia.  The speed of sound on Mars is around 240 meters a second.  A bit lower than the 340 meters a second on Earth.  By itself, that wouldn’t make sound communication harder.  However, the atmospheric density of Mars is less than 1% of Earth, almost a vacuum by our standards.  This means that sound attenuation is much greater and so, speech wouldn’t carry very far.  Human mouths and ears would not be able to couple sound efficiently into or out of the thin Martian atmosphere, so humans would be effectively deaf.
Hannah -   So, yes.  The speed of sound is slower on Mars.  Largely, due to the cold temperature there.
And the atmosphere’s lower density isn’t suited to human speech and hearing systems which have evolved for life on Earth.  Instead, radio waves, a form of light travels fine through low densities and so, can be used as a method of communication up there which is how exploratory rovers on Mars like Curiosity, communicate, not with each other but with us on Earth using radio wave messages traveling at the speed of light and taking about 15 minutes to be received here on Earth.

Title: Re: QotW - 12.11.25 - Would things sound different on Mars?
Post by: evan_au on 19/11/2012 10:38:30

The speed of sound at the surface of Mars is about 244 meters/second, a bit lower than the 340 meters/second on Earth, making your voice deeper - this by itself would not make sound communication difficult (http://www.aerospaceweb.org/question/atmosphere/q0249.shtml).

However, because the atmospheric density of Mars is <1% of Earth, the attenuation is much higher, so speech would not be a very good medium. http://en.wikipedia.org/wiki/Stokes%27_law_(sound_attenuation) (http://en.wikipedia.org/wiki/Stokes%27_law_(sound_attenuation))  Human mouths and ears would have trouble coupling much sound power into the Mars atmosphere, so humans would be deaf (as well as dead).

The Mars rovers are robots, and despite their sophisitication, they spend most of their time communicating results back to Earth and waiting for commands, rather than chatting to each other about the weather.

The rovers are well spread out over the surface of Mars (http://en.wikipedia.org/wiki/Mars_rover#Interactive_map_of_Mars_landings), so they can't communicate directly with each other - but future generations of robots or human settlements could in principle communicate with each other via satellite relays in high Martian orbit.

Quote

Curiosity can communicate with Earth directly at speeds up to 32 kbit/s, but the bulk of the data transfer should be relayed through the Mars Reconnaissance Orbiter and Odyssey orbiter. Data transfer speeds between Curiosity and each orbiter may reach 2 Mbit/s and 256 kbit/s, respectively, but each orbiter is only able to communicate with Curiosity for about eight minutes per day. http://en.wikipedia.org/wiki/Curiosity_rover#Specifications

For about half of the day, Curiosity can communicate with Earth at the speed of an old-style diallup modem - only the response time is minutes, rather than the seconds possible on a terrestrial connection. Curiosity only has a "broadband" connection for a few minutes per day, as the orbiting satellites have a larger antenna than the rover, and can act as a relay station.

Title: Re: QotW - 12.11.25 - Would things sound different on Mars?
Post by: CliffordK on 19/11/2012 11:20:50

With the Martian atmospheric pressure at about 0.006 ATM, it would be hard to talk, or hear anything without a spacesuit in the middle.

However, I would think that in an enclosed pressurized capsule, the sounds would be more or less the same on Earth and Mars.