What does Mars sound like? For almost 25 years, The Planetary Society has been trying to find out. In 1996, our co-founder Carl Sagan wrote a letter to NASA, urging the space agency to include a microphone on a Mars lander. "Even if only a few minutes of Martian sounds are recorded from this first experiment, the public interest will be high and the opportunity for scientific exploration real," he wrote.
Planetary Society members and supporters funded the world's first Mars microphone on NASA's Mars Polar Lander, which launched in 1999. It was the first citizen-funded science experiment to fly to another world. Sadly, the spacecraft crashed on Mars later that year. We were scheduled to refly the microphone experiment on a French Mars mission called Netlander that was ultimately canceled in 2004. NASA's Mars Phoenix lander had a microphone aboard, but it had to be turned off before launch due to last-minute technical difficulties.
This image shows the flight spare of The Planetary Society's Mars Microphone, which flew to Mars aboard Mars Polar Lander in 1999.
In 2016, NASA announced it would include 2 microphones on its Perseverance rover mission. One will record the sounds of Perseverance plummeting through the Martian atmosphere and landing on the surface, and another is attached to Supercam—a science instrument that zaps rocks with a laser and records the resulting light spectra to determine the rocks’ compositions. If all goes well, we'll soon hear the very first real sounds from Mars, adding a second human sense to our robotic exploration of the solar system.
The original Mars microphone
The Planetary Society’s original Mars microphone, which flew on NASA’s Mars Polar Lander, was built with a team at the Space Sciences Laboratory at the University of California, Berkeley. It cost less than $100,000, took up just 25 cubic centimeters of space, and weighed less than 50 grams.
What are we hoping to hear?
Given that sound waves need an atmospheric medium through which to travel, many people are surprised to learn that any sounds at all can be heard on Mars. The atmospheric pressure on the Red Planet’s surface is small, amounting to less than 1 percent of Earth's sea level pressure. But even at Mars' low pressure, acoustic signals within the frequency range of the human ear can be detected.
The descent microphone will record and transmit audio as Perseverance executes its complicated landing procedure, giving engineers back on Earth a second set of data to analyze how things went—and in a worst-case scenario, help them troubleshoot what went wrong. The microphone is based on inexpensive, store-bought hardware, and is unlikely to work long after landing. If it does survive, it may be able to hear the Martian wind or even the rover’s wheels crunching on the soil as it drives.
This video shows the SuperCam laser on NASA's Perseverance rover zapping a test target. Credit: IRAP/CNES
Amazingly, the sound a rock makes when Perserverance’s laser strikes it can help scientists infer its mass and relative hardness. The latter is helpful for figuring out whether the rock formed in a lake or from wind erosion.
There is weather on Mars, including winds, sandstorms, and dust devils, which are little tornadoes caused by local weather patterns. The SuperCam microphone may be able to hear these phenomena, as well as Perseverance itself using its arm and drill. By recording how the rover sounds over time, the mission team may be able to diagnose the health of the rover’s science instruments and internal mechanisms.
The most exciting sounds may be ones that we don't even know about yet. Experience has demonstrated that whenever a new instrument is developed and flown in space, we learn something new about extraterrestrial environments, and therein lies the true spirit of the Mars microphone concept.
What would a human sound like on Mars?
Suppose you found yourself on Mars without a spacesuit. What would you say? Probably "Help!" because the air is more than 100 times thinner than Earth's, and contains very little oxygen.
Your understandably poignant plea wouldn't go far in the Martian air, which will mute even the loudest screams to near whispers. Stranger still, your voice would be lower-pitched than on Earth because of the lower sound speed. But suppose, suspending disbelief for a short while, that you really could speak on Mars. How would you sound?
Back when we were first pioneering the concept of a Mars microphone, we recorded some sample audio to show how human voices would sound on Mars:
The European Space Agency’s Huygens probe had a microphone running when it landed on Saturn’s moon Titan in 2004. University of California Berkeley scientist Greg Delory, who worked with The Planetary Society on the Mars microphone project, helped ESA quickly process the audio data after Hugyens’ landing so members of the public could hear what it would sound like to plunge through Titan’s haze.
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