NASA's InSight lander comes with an extremely sensitive seismometer called the Seismic Experiment for Interior Structure (SEIS) which can pick up vibrations as subtle as a breeze. SEIS was created to listen for marsquakes for the study of Mars' deep inner structure.
However, SEIS' sensitive ear means scientists have lots of other noises to filter out. Luckily, over time, the team has learned to recognize the different sounds and identify which are marsquakes and which are not.
"It's been exciting, especially in the beginning, hearing the first vibrations from the lander," said Constantinos Charalambous, an InSight science team member at Imperial College London who works with the SP sensors. "You're imagining what's really happening on Mars as InSight sits on the open landscape."
Charalambous and Nobuaki Fuji of Institut de Physique du Globe de Paris provided the following audio samples.
The samples above reveal the noises of two marsquakes. The Sol 173 quake is about a magnitude 3.7; the Sol 235 quake is about a magnitude 3.3. They occurred on May 22, 2019, and July 25, 2019 (Sol 235).
The noises are not just fun to listen to. They also serve to understand Mars' composition. The two sounds together suggest that the Martian crust is like a combination of the Earth's crust and the Moon's.
Cracks in Earth's crust enable sound waves to continue uninterrupted as they pass through old fractures that seal over time as water fills them with new minerals. Quakes on Earth can come and go in seconds. Meanwhile, drier crusts like the Moon's remain fractured after impacts. This generates scattered sound waves that last for tens of minutes.
According to the researchers, the sounds reveal that Mars is slightly more Moon-like, with seismic waves ringing for a minute.
What do you think of these rumbles? How exciting is it to actually hear such a far-away planet?