Within hours of the Mars Polar Landers arrival at the Red Planet on December 3, a tiny microphone stowed aboard the NASA spacecraft will begin to pick up the sounds of the distant world.
But what will the microphone hear?
Initially, it will record the grinding of the robotic spacecraft itself as it busies itself for a three-month mission probing its surroundings near Mars south pole. But after that, during scheduled quiet periods when the Polar Lander will be inactive and only Mars will speak to the microphone, no one is certain what the tiny instrument -- about the size of a block of sticky notes -- will pick up.
"It really is an instrument of discovery. We dont know what we will hear," said Lou Friedman, executive director of the Planetary Society.
The Pasadena, California-based space exploration advocacy group funded the full cost of the $50,000 microphone, which piggybacks to Mars on a Russian-built atmospheric sounding experiment.
During laboratory tests here on Earth, engineers have already recorded the sounds of the spacecrafts robotic arm as well as the whir of various motors. The real surprise on Mars will come when those instruments fall silent.
Scientists hypothesize the microphone will be privy to the whistle of Mars winds, the crackle of charged dust particles in its thin, cold atmosphere and the low-frequency moan of approaching spring storm systems.
"The challenge we expect will be not in picking up sounds, but in distinguishing sounds," Friedman said.
In the age of the sound bite, the microphone will fit in nicely, recording just 10 seconds of the loudest noises it hears each day.
However, it will also chart the average of the sound signals it receives throughout the day, allowing scientists to see how the acoustic "picture" changes with each passing hour.
Should, for example, a loud but unexplained noise be heard -- but not recorded -- each day at dusk, the microphone can be told to turn on at precisely that time, said Janet Luhmann, a University of California,
Berkeley scientist and member of the microphone team.
Since Mars is a very different place from Earth, with a very different atmosphere, things sound differently that they do here.
Mars thin, cold and carbon dioxide-rich atmosphere mutes loud noises to a quiet whisper. And since sound travels just two-thirds as fast as it does on Earth, sounds are lower pitched. (The Planetary Societys website,
, uses a "Marsinator," or Mars voice simulator, to give listeners examples of what a variety of peoples voices would sound like on Mars.)Mission members may eventually match Martian recordings made during the Polar Lander mission with images of what is being heard, creating in effect the first "talkies" made on another planet.
Luhmann said she hopes microphones will become a fixture on future planetary missions, adding depth and richness to the exploratory process.
"I always tell people to imagine going through life and not being able to hear, how that would change your life experience," Luhmann said.
The Mars microphone could well become the first ever to hear the sounds of another planet -- but it wont be the last.
A Russian mission to Venus carried a microphone, but it is unclear whether it ever successfully recorded any sound. And the Huygens probe aboard the Cassini spacecraft carries a microphone to record the sounds of thunder and turbulence as it parachutes down onto Saturns moon Titan in 2004.
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