Scientists listening to recordings made by NASA’s Mars InSight lander have discovered a rich haul – although many of the sounds captured turn out to made by the machine itself.
The lander, which touched down in November 2018, is equipped with an ultra-sensitive listening device called the Seismic Experiment for Interior Structures (SEIS), which was designed primarily to detect shifts in the interior of the planet, dubbed marsquakes.
After an initial and worrying period of silence, the device picked up the noise of its first quake in April this year. Since then, researchers have heard at least 21 and perhaps as many as 100 more.
Marsquakes, says NASA, vary in tone and magnitude, but can generally be described as “subtle rumbles”. The emphasis here, however, is on the word “subtle”: for seismologists back on Earth to actually make them out, InSight’s recordings need to be filtered and played back at accelerated speed.
But being a bit on the quiet side is by no means the only acoustic problem the researchers have encountered. Often, the chance of detecting a quake is obscured by several other, rather louder sounds.
One of these is the noise of the wind, which can easily swamp the SEIS microphones as it blows across the ground. For this reason, the InSight team now concentrate their quake hunts in the early evenings, when temperatures drop and the breeze, in consequence, dies down a bit.
However, the cooling air brings its own audio challenges. In a recent release, NASA reports that on most evenings the recorders pick up a series of noises described as “dinks and donks”.
Readers of an imaginative bent should immediately discard any hopeful thoughts of aliens just out of sight of the InSight cameras, perhaps playing a spirited Martian version of mah-jong. The sounds, the researchers say, are produced by the lander itself, the result of its components gently expanding and contracting in response to the changing temperature.
And then there are the piercing screams that were recorded by the SEIS gear on March 6 this year. Initially disquieting, these too turned out to have a prosaic explanation: they were the sounds of InSight’s robotic arm changing its position.
All these extraneous, self-generated sounds might seem problematic, but, in fact, they are welcomed by the researchers as reassuring signs of robotic life.
“It’s been exciting, especially in the beginning, hearing the first vibrations from the lander,” say Constantinos Charalambous, an InSight science team member at Imperial College London.
“You’re imagining what’s really happening on Mars as InSight sits on the open landscape.”
Listen to the sounds of Mars (headphones recommended)