Put an ear to the ground on Mars and you’ll be rewarded with a symphony of sounds. Granted, you’ll need superhuman hearing, but NASA’s InSight lander comes equipped with a very special “ear.”
The spacecraft’s exquisitely sensitive seismometer, called the Seismic Experiment for Interior Structure (SEIS), can pick up vibrations as subtle as a breeze. The instrument was provided by the French space agency, Centre National d’Études Spatiales (CNES), and its partners.
SEIS was designed to listen for marsquakes. Scientists want to study how the seismic waves of these quakes move through the planet’s interior, revealing the deep inner structure of Mars for the first time.
But after the seismometer was set down by InSight’s robotic arm, Mars seemed shy. It didn’t produce its first rumbling until this past April, and this first quake turned out to be an odd duck. It had a surprisingly high-frequency seismic signal compared to what the science team has heard since then. Out of more than 100 events detected to date, about 21 are strongly considered to be quakes. The remainder could be quakes as well, but the science team hasn’t ruled out other causes.
Put on headphones to listen to two of the more representative quakes SEIS has detected. These occurred on May 22, 2019 (the 173rd Martian day, or sol, of the mission) and July 25, 2019 (Sol 235). Far below the human range of hearing, these sonifications from SEIS had to be speeded up and slightly processed to be audible through headphones. Both were recorded by the “very broad band sensors” on SEIS, which are more sensitive at lower frequencies than its short period sensors.
The Sol 173 quake is about a magnitude 3.7; the Sol 235 quake is about a magnitude 3.3.
Each quake is a subtle rumble. The Sol 235 quake becomes particularly bass-heavy toward the end of the event. Both suggest that the Martian crust is like a mix of the Earth’s crust and the Moon’s. Cracks in Earth’s crust seal over time as water fills them with new minerals. This enables sound waves to continue uninterrupted as they pass through old fractures. Drier crusts like the Moon’s remain fractured after impacts, scattering sound waves for tens of minutes rather than allowing them to travel in a straight line. Mars, with its cratered surface, is slightly more Moon-like, with seismic waves ringing for a minute or so, whereas quakes on Earth can come and go in seconds.
Source & further reading: https://www.nasa.gov/feature/jpl/nasas-insight-hears-peculiar-sounds-on-mars