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InSight picks up strange sounds on Mars

Put your ear to the ground on Mars and you'll be rewarded with a veritable symphony. Sure, you'll need superhuman hearing, but NASA's InSight lander is equipped with an exceptional ear: SEIS.

InSight picks up strange sounds on Mars

Publication date: 04/10/2019

General public, Observatories, Press, Research

Related observatories : InSight Observatory

The probe’s extremely sensitive seismometer, called SEIS for Seismic Experiment for Interior Structure, is capable of picking up vibrations as subtle as a breeze. It was designed to shed light on the deep internal structure of Mars by recording the seismic waves that travel through the Red Planet’s interior.

However, following the installation of the seismometer on December 19th 2018, Mars proved to be somewhat tentative. The planet didn’t produce a rumble until last April, when it emitted a seismic signal of surprisingly high frequency compared with what the scientific team had been able to hear until now. Of the more than 100 events detected to date, around 21 are considered with a high probability to be seismic tremors.

Astonishment and trembling

The two largest tremors detected by SEIS occurred on May 22nd 2019 (Sol 173, magnitude around 3.7) and July 25th 2019 (Sol 235, magnitude around 3.3). They were recorded by SEIS’s very wide-band VBB sensors, developed in France by the technical and scientific teams at the Institut de Physique du Globe de Paris (IPGP) – University of Paris, CNES, the Paris Diderot University space campus and the industrial company SODERN. The VBBs are capable of detecting much lower frequencies than short-period seismic sensors. These vibrations, which are not perceptible to the human ear, have been accelerated and lightly processed to make them audible. Each tremor is a subtle rumble. That of G 235 is particularly rich in bass at the end of the event.

These two tremors suggest that the Martian crust is a mixture of Earth and lunar crusts. Cracks in the Earth’s crust close up as water fills them with new minerals, allowing sound waves to continue on their way uninterrupted even as they pass through old fractures. Drier crusts, like those on the Moon or the first few kilometres of Mars near the equator, remain fractured after impacts, scattering sound waves for long minutes instead of allowing them to travel in a straight line. With its cratered surface, Mars is more like the Moon, with waves that resonate for about a minute, whereas tremors on Earth come and go in a matter of seconds.

Mechanical sounds and gusts of wind

SEIS has no trouble perceiving very weak vibrations, but such a sensitive ear means that the scientists also have a lot of extraneous noise to filter out. Over time, the team learned to distinguish between the different sounds. “It was very exhilarating, especially at first, to hear the first vibrations from the probe. You can really imagine what is happening on Mars thanks to InSight”, reports Constantinos Charalambous, who worked on the SP short-period sensors at Imperial College London. He and Nobuaki Fuji, from the IPGP, are behind these audio recordings, including the next one, which captures the working environment of the lander on March 6th 2019:

Every movement of the robotic arm represents a piercing noise for SEIS. Gusts of wind can also create ‘noise’, which is why the team probes for tremors at dusk. During the day, sunlight warms the air and creates more interference with the wind.

The evening is also a good time to listen to the strange sounds that the InSight team has nicknamed “dinks and donks” (onomatopoeia to imitate these sounds). These come from the seismometer, parts of which are rubbing gently against each other, probably as they cool down, in the same way that an engine makes clicking noises as it starts to cool down.

In the following sequence, the strange hissing sounds recorded just after sunset on July 16th 2019 (Sol 226) may have been caused by interference in the electronic systems:

The InSight team, through the IPGP’s PhiloGaïa orchestra, is currently working on a symphonic composition project using the sounds recorded by SEIS.

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