NASA’s Mars InSight lander has had its ear to the ground since it arrived on the planet in November 2018. The spacecraft’s “ear” is an exquisitely sensitive seismometer, called SEIS (Seismic Experiment for Interior Structure), that can pick up vibrations as subtle as a breeze.
SEIS was designed to listen for marsquakes, quakes which, much like earthquakes, are the shaking of Mars’ surface or interior as a result of the sudden release of energy inside the planet. But after the seismometer was set down by InSight’s robotic arm on December 19, 2018, Mars didn’t produce a rumbling until April 2019, and this first quake turned out to be an “odd duck,” said NASA. That’s because it turned out to have a surprisingly high-frequency seismic signal, compared to what the science team has heard since. 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.
To really hear what’s happening in the recordings below, it’s best to wear headphones. They are recordings of two of the more representative quakes SEIS has detected. These occurred on May 22 and July 25, 2019. Because they’re far below the human range of hearing, these sonifications from SEIS had to be speeded up and slightly processed to be audible through headphones.
The May 22 quake is about a magnitude 3.7 and the July 25 quake is about a magnitude 3.3. Each quake is a subtle rumble. The July 25 quake becomes particularly bass-heavy toward the end of the event.
May 22, 2019
July 25, 2019
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.
SEIS has no trouble identifying quiet quakes, but its sensitive ear means scientists have lots of other noises to filter out. Over time, the team has learned to recognize the different sounds. Some are trickier than others to spot. The recording below, also best heard with headphones, captures the array of sounds the science team is hearing.
On March 6, 2019, a camera on InSight’s robotic arm was scanning the surface in front of the lander. Each movement of the arm produces what to SEIS is a piercing noise.
Wind gusts can also create noise. The team is always on the hunt for quakes, but they’ve found the twilight hours are one of the best times to listen for marsquakes. Thaat’s because during the day, sunlight warms the air and creates more wind interference than at night.
Evening is also when peculiar sounds that the InSight team has nicknamed “dinks and donks” become more prevalent. The team knows they’re coming from delicate parts within the seismometer expanding and contracting against one another and thinks heat loss may be the factor, similar to how a car engine “ticks” after it’s turned off and begins cooling.
Listen for these dinks and donks in the set of sounds, below, recorded just after sundown on July 16, 2019. If you listen carefully, you can also pick out an eerie whistling that the team thinks may be caused by interference in the seismometer’s electronics.
The SEIS instrument was provided by the French space agency, Centre National d’Études Spatiales (CNES), and its partners. Insight team members Constantinos Charalambous of Imperial College London and Nobuaki Fuji of Institut de Physique du Globe de Paris provided the audio samples for this story.
Bottom line: Listen to recordings of sounds detected on Mars by the Insight lander.
Eleanor Imster has helped write and edit EarthSky since 1995. She was an integral part of the award-winning EarthSky radio series almost since it began until it ended in 2013. Today, as Lead Editor at EarthSky.org, she helps present the science and nature stories and photos you enjoy. She also serves as one of the voices of EarthSky on social media platforms including Facebook, Twitter and G+. She and her husband live in Tennessee and have two grown sons.