The sound of the Martian winds of Elysium Planitia (more or less)

The sound of the Martian winds of Elysium Planitia (more or less) https://danielmarin.naukas.com/files/2018/12/mars.nasa_.gov_insight-raw-images_surface_sol_0010_idc_D004L0010_597413863EDR_F0002_0080M_.png

How does the wind on Mars sound? This is a question that humanity has been asking since we knew that our neighboring world has an atmosphere. And, finally, we have the answer. So, without further ado, let's satisfy our curiosity:

Yes, it resembles the terrestrial wind to which we are accustomed. What did you expect? It's wind, after all. Of course, the matter has "trick". And the sounds of the Martian wind captured by the NASA InSight probe have had to be processed so that we can perceive them. That is, a microphone has not been used to listen to the sound of the wind, but other instruments. On the one hand, a pressure sensor was used and, on the other, the French seismometer SEIS. Once placed on the Martian surface, SIX will not be able to capture the vibrations of the probe, but now it is located on the cover of the probe. That is why SEIS has been able to detect the vibrations caused by the wind on the large circular panels of InSight. For these vibrations captured by the seismometer SIX sound like the wind have had to be modified making them more acute (two octaves above), so that's why we say that this sound of the Martian wind has a trick. However, it is possible to directly hear the raw vibrations, without the need to increase their frequency, as a very serious noise.

Panorama of the InSight landing zone taken at Sun 10 (NASA / JPL-Caltech / Damia Bouic).

SIX consists of several sensors. The vibrations of the ship have been picked up by the three SP sensors of short period, which are sensitive to frequencies of 0.05 to 50 Hz, that is, a range that overlaps the lower limit of the capacity of the human ear (SIX it has three other VBB sensors, located inside a vacuum titanium sphere, sensitive to frequencies of 0.005 and 1 0 Hz). SIX is sensitive enough to determine the direction of the wind that has caused these vibrations and it turns out that it coincides with the traces of dust devils that are seen in the images from orbit. These data will serve to calibrate the operation of SEIS and, in the future, to create wind models that help filter the wind noise of the data from the interior of Mars. The wind picked up by SIX moved through the Elysium plain at a speed between 16 and 24 km / h and was blowing northwest to southeast. The Viking probes also carried seismometers, but were sensitive to much lower frequencies than the InSight SP sensors. There are also recordings of the "sound" of Titan and Venus captured by sensors aboard the Huygens and Venera probes, respectively, but they are rather "sonograms" and their transformation into sound is still a bit "tricky" (many data can be transformed into sound, but that does not mean that the information is more relevant in that format).

The SIX instrument, in the foreground, seen by the IDC camera of the InSight robor arm (NASA / JPL-Caltech).

One of the British-made SP sensors of the French Seismometer SEIS of InSight (NASA).

Direction of the vibrations detected by SEIS (NASA).

Vibrations detected by one of the SP sensors of SEIS due to the Martian wind (NASA).

InSight instruments (CNES).

The other InSight instrument that has detected the Martian wind is the ASPSS (Auxiliary Payload Sensor Subsystem), a sensor that measures the differences in air pressure. That is, sound of truth. The downside is that ASPSS is sensitive to infrasound with a frequency of 10 Hz, or what is the same, sounds outside the sensitivity range of the human ear (ranging from 20 Hz to 20 kHz, approximately). For the sound collected by the ASPSS to be audible it has been necessary to increase its frequency one hundred times. The ASPSS sensor is located in the center of the InSight cover and is currently covered by the WTS cover (Wind and Thermal Shield) that must precisely protect the SEIS instrument from the wind and temperature changes once it is on the ground. Once the WTS cover is removed, the ASPSS sensor will be able to pick up other weaker sounds, such as those generated by meteorites, by fragmenting in the Martian atmosphere during the entrance (!).

Of course, if we were on Mars we would have trouble hearing the muffled sound of the wind through the walls of our spaceship or scuba. The surface pressure on Mars is around 7 millibars, which for our bodies is practically empty. Only the fastest winds that occur on Mars, with speeds above 100 km / h, would generate a decent noise level (although they would be unable to move an astronaut in a space suit that was walking on the surface ). But, interestingly, infrasound propagates practically the same in the Martian atmosphere as in the terrestrial one.

Location (in blue) of the ASPSS sensor by InSight (NASA).

The infrasound data of the ASPSS sensor (NASA).

Therefore, the sounds of the Martian wind captured by InSight are actually infrasound sounds that have been manipulated so that they can be heard clearly by human beings. That does not mean they are less spectacular, but it is always good to know what we are talking about exactly. So, can we ever hear the Martian wind one day without playing with the frequencies? Yes, and before a person walks the red planet. The future rover of NASA Mars 2020 will be equipped with two microphones that, this time, will directly capture, without "tricks", the sound in the frequencies of the human ear. One of the microphones of the Mars 2020 will also be able to record the sound of the landing of the probe, while the other will be used to listen to the sound of the laser of the SuperCam instrument.

The solar panel of InSight and one of the masts of the Spanish weather station TWINS seen by the IDC camera of InSight (NASA / JPL-Caltech).

One of the InSight legs seen by the IDC camera of the InSight robot arm (NASA / JPL-Caltech).

But they will not be the first microphones that humanity sends to Mars. That honor corresponds to the microphone that traveled aboard the Mars Polar Lander, a probe that was launched towards the red planet in 1999 and that crashed during the descent phase. This microphone was a contribution of the organization The Planetary Society and it was the first instrument developed with private funds that traveled to Mars. It had been installed in a LIDAR of Russian construction, but could never hear the sounds of the Martian wind. This same microphone had to travel in the European Netlander probes, a project that was canceled. The Planetary Society succeeded in incorporating another microphone into the descent chamber of the Phoenix probe that traveled to Mars in 2008, but it could never be activated because the mission managers considered that there was a risk of electrical failure if they turned on the camera. And so the paradox occurred that the first microphone that humanity put on the surface of another world with atmosphere was never ignited.

Therefore, after so many efforts and years to put a microphone on the surface of Mars, these InSight sounds may not be "real", but that does not mean they are less impressive.

References:

https://mars.nasa.gov/resources/22205/nasas-insight-hears-the-sound-of-mars/

https://spacegate.cnes.fr/fr/insight-historique-seis-enregistre-le-bruit-du-vent-sur-mars