NASA has released a recording that captures the "sound" of the Martian winds for the first time ever. Collected on December 1 by the InSight mission, the low rumble was unexpectedly detected by the unmanned lander's seismographs and other sensors when they detected vibrations in the spacecraft generated by a northwest wind blowing at 10 to 15 mph (16 to 24 km/h).
The InSight lander was not specifically equipped to detect sounds, but it does have a pair of highly sensitive sensor packages presently sitting atop its deck awaiting deployment. These are an air pressure sensor from the Auxiliary Payload Sensor Subsystem (APSS) that collects meteorological data, and the Seismic Experiment for Interior Structure (SEIS) for detecting marsquakes and therefore learn more about the interior of the Red Planet.
The sounds sent back by InSight isn't of the Martian winds itself, but of vibrations from the lander's two 7-ft (2.2-m) wide circular solar panels, which act a bit like a pair of wings when the winds hit them, turning them into huge, crude microphones. The SEIS seismometers normally wouldn't be able to detect these vibrations, but they can when the experiment is still stowed aboard the spacecraft.
The SEIS consists of two sets of seismometers. One is a pair built by the French Space Agency CNES, and the others are the short period (SP) silicon sensors made by Imperial College London with electronics from Oxford University. The latter can detect vibrations up to 50 Hz, which is at the lower edge of human hearing.
"The InSight lander acts like a giant ear," says Tom Pike, InSight science team member and sensor designer at Imperial College London. "The solar panels on the lander's sides respond to pressure fluctuations of the wind. It's like InSight is cupping its ears and hearing the Mars wind beating on it. When we looked at the direction of the lander vibrations coming from the solar panels, it matches the expected wind direction at our landing site."
The audio recording released by NASA includes an unaltered version, which can just be heard, though it usually requires headphones or a good subwoofer, and a second from the APSS that's been sped up a hundred times to cause a shift in frequency.
But NASA says that such recording can only come for a limited time. In a few months, the SEIS will be placed on the surface of Mars and then sealed by a hemispherical cover to protect it from outside noise. However, when the space agency's Mars 2020 rover touches down in 2021, it will have a pair of microphones aboard to record the sounds of the landing and to collect the audio of the rover's laser zapping sample to help in analysis.
"Capturing this audio was an unplanned treat," says Bruce Banerdt, InSight principal investigator at NASA's Jet Propulsion Laboratory in Pasadena, California. "But one of the things our mission is dedicated to is measuring motion on Mars, and naturally that includes motion caused by sound waves."
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