NASA has released audio clips of marsquake recordings taken by its InSight lander currently resident about on the Red Planet.
The seismometer, known as the Seismic Experiment for Interior Structure or SEIS for short, sniffs out marsquakes and uses the rumblings to reveal the planet’s inner structure. InSight has detected over 100 of these quakes so far and scientists believe 21 of them are marsquakes, with the rest being wind noise, asteroid strikes and other as-yet unidentified causes.
The first grumble was detected in April, earlier this year. Its unexpected high frequency has classified as an “odd duck”. Most of the recordings taken after have much lower frequencies. You can listen to two of them - one taken on the 22 May and the other on 25 July - here. Make sure to turn the volume up fairly high, since the clips are pretty quiet.
If you listen pretty closely, the signals are a low constant ringing. These last for about a minute or so unlike the earthquakes which are normally over in seconds. The ringing is a sign that Mars’ crust is drier than here on Earth.
“The Martian crust is like a mix of the Earth's crust and the Moon's,” according to NASA. The cracks in Earth’s crust get repaired over time as water carrying new minerals floods the gaps, but Mars is a much drier environment, like the Moon. Earth’s smoother texture means sound waves from seismic activity can propagate through the rock, whereas on Mars they are more likely to scatter, making the signal ring.
SEIS is sensitive enough to pick out the quietest quakes, making it difficult for scientists to discern if a signal is real or just noise. Wind blowing through the Martian atmosphere is sometimes logged by the SEIS, so the best time to hunt for marsquakes is twilight. This is down to the Sun’s rays being strongest during the day and the temperature warms the air to create gusts of wind.
At night, the instrument cools down and its components expand and shrink to produce a series of weird sounds that scientists have called "dinks and donks".
"It's been exciting, especially in the beginning, hearing the first vibrations from the lander," said Constantinos Charalambous, an InSight science team member working at Imperial College London. "You're imagining what's really happening on Mars as InSight sits on the open landscape." ®