How NASA recorded the eerie Martian wind without a microphone

Cold winds constantly blow across the wide Martian plains of Elysium Planitia, and NASA unexpectedly recorded the sound of these extraterrestrial gusts. 

Although NASA sent the InSight lander to Mars to study Mars’ earthquakes and geology, the robot’s scientists discovered that one of InSight’s instruments picked up audio of wind gusting against the machine’s metal exterior, and they released the sounds on Friday.

“It’s what it’s like to be there,” Don Banfield, an InSight scientist, said in an interview.

Beginning at the 1:10 mark in the video below, you can hear the Martian wind.

The specific instrument that picked up the sound of wind blowing against the lander is an air pressure sensor, more formally called the Auxiliary Payload Sensor Subsystem. It’s a weather-monitoring device. It’s not a microphone. But it can act like one. 

“It’s much like what a normal microphone does,” said Banfield.

When any noise is made or emanated, perhaps from an amplified Fender Telecaster guitar, this produces pressure changes in the air. These pressure changes are then picked up by a microphone and then turned into an electrical signal. 

The pressure sensor, which Banfield described as a low-frequency microphone, is designed to also take in changes in the air pressure, and then transmit these into electrical signals — which eventually get sent millions of miles back to Earth. 

“Wind or someone hitting a drum or a meteorite exploding in the atmosphere — all these make pressure changes in the air,” explained Banfield.

In the case of the wind, the pressure sensor picked up the wind blowing, but there’s a catch. This specialized instrument was never meant to actually record sound, just air pressure in the natural Martian environs. So it recorded the wind at a very low frequency — outside the range of limited human hearing. 

However, other animals that evolved to hear low-frequency sounds, like whales, would be able to hear the raw tracks from the pressure sensor. “We can record the stuff that elephants and whales can hear if they could survive on Mars,” said Banfield.

But to make it audible to humans, NASA sped up about 2,000 seconds of recorded wind into 20 seconds, which increased the pitch of the sounds 100-fold. Now, we can hear it. 

NASA also released the low-drone sounds derived from InSight’s seismometer, which is intended to measure Martian earthquakes. These can be heard in the above NASA video, starting at around the 50-second mark. 

But the seismometer measured vibrations as the wind blew against the robot’s solar panels. The vibrations, sent back to Earth, are more similar to putting your ear next to a train track and listening to the vibrations of a distant train (you’re not actually hearing the train). It’s a much more indirect way of picking up or interpreting sound. 

In 2020, NASA will send its latest advanced rover to Mars with two actual microphones, specifically intended to record sound. 

The microphones will even record the sound of the rover descending through the Martian atmosphere — and if all goes smoothly — pick up the sound of the robot settling down in the Jezero Crater, an ancient, dried-up lakebed.