InSight Surface Operations, 26 Nov 2018- 21 Dec 2022 Options

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Congratulations to the InSight team on a successful landing! We'll discuss the remainder of the mission here.

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Hello everyone, special thanks to Steve and Paul,

Recent interview given by Philippe Lognonné, Principal Investigator, Instrument SEIS sur InSight (NASA) and Responsable-adjoint de l'Equipe Planétologie et Sciences Spatiales de l'Institut de Physique du Globe de Paris, entre autres.

I deliver a translation (machine)

Original link : https://lejournal.cnrs.fr/articles/insight-...ous-sol-martien

Arriving on Mars more than a year ago to study the earthquakes, the Insight mission has just delivered its first results. Geophysicist Philippe Lognonné explains the stakes.
You are a geophysicist at the Institut de physique du globe de Paris1 (IPGP), a professor at the University of Paris and the principal investigator of the seismeter. What are the objectives of the Insight mission?

Philippe Lognonné : Launched in May 2018 and arriving at its destination in November of the same year, Insight is a NASA mission that is equipped with the seismometer SEIS. This instrument was developed between the Centre national d'études spatiales (Cnes) and the IPGP, with the help of European industrial and academic partners, and with Nasa’s Jet Propulsion Laboratory (JPL). It aims to study seismology and the depths of Mars, still very little known. The operations on Mars are done by the Cnes and the IPGP, which distributes the data to the international community via its datacentre.

What were the main challenges?

P. L. : It all started with the Viking mission, launched in 1975, which had seismometers on both landers. The first one never worked, while the other provided skewed data. Indeed, all the vibrations reported were due to the Martian winds shaking the aircraft. For Insight, Seis was deployed on the ground by a robotic arm and then covered with a dome that protects it as much as possible from atmospheric disturbances. The wind still has an impact, but it has no impact with Viking. Atmospheric currents still cause major disturbances during the day, but this background noise drops drastically, by a factor of 100, between 17 and midnight, solar time. Thanks to this, we were able to measure signals ten times weaker which rewards the efforts of the IPGP technical team that designed this sensitive sensor. Even if this noise will surely evolve according to the seasons and will probably increase during storms, Insight is today the least noisy seismic station in the solar system! This very low level of noise allows it to detect Martian earthquakes: if the Earth knows very strong earthquakes of magnitude of seismic moment 5, 6, 7 or even 8, on Mars, we were expecting earthquakes around a magnitude 4. There is indeed no more tectonics of the plates on the red planet. But when you go from magnitude 7 to magnitude 4, you divide the wave amplitude by a factor of 30,000.

How did the first seismic scan go ?

P. L : We started acquiring data in February 2019, but we only detected very small events in the first two months. We finally had a high-frequency, high-amplitude event on April 7. We were of course very surprised and excited, even though the magnitude was only 2.1. It was also by chance that this earthquake occurred just before the 130th anniversary of the very first earthly seismological measurement, carried out by Ernst von Rebeur-Pacshwitz in Postdam on 17 April 1889. At the end of September 2019, eight of the detected low frequency earthquakes had primary (P) and secondary (S) seismic wave phases, and three of them had measurable wave polarization. These two waves are essential for measuring the distance of the epicentre of an earthquake when only one seismometer is available. The polarization of these waves gives us their direction of arrival, which ultimately allows the localization of the event. These polarized waves also allowed us to discover the presence of a discontinuity in the crust, at a depth of about ten kilometres. In mid-February 2020, the number of detected events is 460. Most are high frequency signals and their origin is not yet clear: small very superficial earthquakes, landslides or collapses of cliff areas are candidates for their origin. But the number of earthquakes with signals below 1 hertz (Hz) is now close to quarantine.

When you took off from Insight, you hoped to measure about 50 earthquakes per year, of which about 10 magnitude are up to 5.5. What is the balance sheet ?

P. L. : As said earlier, the low background noise at night has allowed us to detect earthquakes much weaker than expected, and therefore more numerous. However, the most powerful reached a maximum magnitude of 3.8 or we hoped to see with magnitudes of at least 4.5. A tremor of such intensity indeed generates surface waves, which would inform us about the depths of Mars, such as the thickness of its crust and the structure of its superior mantle, and would allow us much better constraints.So we are still hungry, waiting for these bigger earthquakes, but we also had some good surprises. So we came up with the idea of doing seismology without seismic activity, using instead the interactions between the soil and the atmosphere. Whirlwinds of dust, called dust devils, form on Mars. They cause a depression at ground level that Seis and the Insight weather station were able to detect when they passed close enough. We deduced the properties of stiffness and elasticity of the soil up to a depth of about ten meters. It’s a new form of seismology !

How is the first results revealed ?

P. L. : Six publications are synchronized: five in Nature Geoscience and one in Nature Communications. They are not all associated with seismological experiments, since two deal with atmospheric and magnetic measurements and one with the geological context. In addition to a general article, two focus on Seis and present our main results. The first discovery is, of course, in the measure of a shock large enough to be sure that it is indeed an earthquake. Then, the three largest earthquakes, two of magnitude of about 3.6 and one of magnitude 3.1, all come from the same region: Cerberus Fossae. This huge volcanic fault system extends 1,600 kilometres from the Elysium Plain, where Insight landed. We knew that the area had been geologically active over the last few tens of millions of years, but we did not expect to detect our three largest earthquakes. It’s a nice surprise. Finally, a third major result is the confirmation of a priori: the Martian seismic activity lies between that of the Earth and that of the Moon. It is ten to twenty times more important than on the Moon, but two to three times weaker than on our planet, if we exclude earthquakes due to plate tectonics. With other comparative analyses between the Moon and Mars, such as on wave attenuation and diffraction, we can now initiate planetary seismology compared. In addition to these publications in Nature Geoscience, we are expecting a special edition of the American Geophysical Union, and by the summer we should reach a dozen or even twenty articles.

What’s next for Insight ?

The nominal mission will last another year, but we will extend it by at least another two years. We hope that a stronger earthquake will occur in the meantime, in order to improve our models of the structure of Mars. It’s like a French seismological station is trying to detect a magnitude 5 event in Europe. We have to wait, because Mars is much less active than Earth. In any case, we have already collected high quality data and these first articles are the result of the work of the French, European and American teams of Insight, with a strong collaboration with the ETH of Zurich in Switzerland and the JPL. In France, Aymeric Spiga of the Laboratoire de météorologie dynamique co-hosted the analysis of atmospheric data and several supplements of seismological analyses were co-hosted by French researchers, such as Naomi Murdoch of the Higher Institute of Aeronautics and Space for Dust Modelling, Clément Perrin of the IPGP for seismotectonic analyses of Cerberus, Ludovic Margerin of the Institut de recherche en astrophysique and Benoît Tauzin of the Laboratoire de géologie de Lyon: Earth, planets, environment for seismological analysis, among other things.
Much work remains to be done to better understand and analyze Martian seismology. As is often the case in science, the first publications present fascinating discoveries, but these interpretations and results can evolve with the arrival of new data.


PS : This kind of long text is not very common on UMSF. If I hurt, please tell me.
I do not process images and my contributions would be reduced to providing information.