What do Insight’s latest results tell us?

The first results provided by the Seis seismometer during its first year of operations on Mars were released today. They show that the planet Mars is seismically active but with a seismicity very different from that of Earth. Explanations from Philippe Lognonné, architect of the Seis seismometer, scientific manager and principal investigator of the mission, of Ludovic Margerin, planetary seismologist, and of Philippe Labrot, spokesperson at the Institut de physique du globe de Paris for the InSight mission.

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The first scientific results from Seis, the French seismometer broadband Martian who listens daily and patiently to the activity of the red planet, were published today. Forty-four years after the first probe attempt Viking, Seis (Seismic Experiment for Interior Structure) has just enabled a new planetary discipline, the seismology Martian, to finally see the light of day.

This discipline, which makes it possible to study the internal structure of the planet, is fundamental to better understand the history and the fate of Mars by explaining how the planet was formed, cooled and how it will evolve in the future. Like on Earth, where the tectonic plates probably played an important role in the emergence of life, this study can also provide information on the history of Martian life, although this planet is, according to our current knowledge, mono plate.

Technically, the instrument works very well. Installed on the soil of the planet since December 2018 and put into service in February 2019, the instrument has detected since that date ” more than 300 events and provided many results to planetologists “Explains Philippe Labrot, spokesperson at the Institut de physical from the mission Paris globe InSight. Among these events is a ” ten earthquakes of magnitude 3 to 4 “. If the majority of the events are indeed of seismic nature, then the number of tremors, particularly important, is comparable to that “ observed on terrestrial areas not affected by plate tectonics (unlike Earth and its multiple plates, Mars would consist of a single plate), or associated with hot spots “. Current data suggests that the ” Pthe red hornet would have an activity two to three times weaker than the seismic activity intra-plate terrestrial, and 10 to 20 times higher than that of the Moon “.

Night work pays off!

On March, the best time of day to listen to your tremors is from 5 p.m. to 6 p.m. until midnight. During this period, the noise level collapses, reaching a value 500 to 1,000 lower than that of the Earth – the noise measured by Seis becomes even lower than that recorded on the Moon by seismometers Apollo ! The rest of the time, the activity of theatmosphere Martian becomes more and more turbulent, so much so that the level of the intensity of the disturbances (for the signals of less than one second of period) joins that of the Earth. Surprisingly, the number of earthquakes and seismic events has been increasing steadily since the commissioning of Seis. To explain this phenomenon, scientists, excluding any interference of the instrument, put forward the hypothesis ” an increase of natural origin “Which could, for example, be” due to a periodic phenomenon, implying seasonal warming or the position occupied by Mars in its orbit “.

These high earthquakes frequency, ” which are by far the most numerous, and whose magnitude is low Would be more superficial. Their signals, very tenuous and poor in information, prevent any positioning of their epicenter, even partial, on the map of Mars. The first of them ” at was detected in April 2019 during sol 128 “. He saw himself ” assign a magnitude of only 2.1 “. If the origin of this event remains unknown for the moment, the ” depth of home seismic, from where the waves emanated, would be greater than 5 kilometers “. The earthquake would have originated in the crust, on a circle at a distance of 530 kilometers from the InSight undercarriage. ” On Earth, this type of seismic event would have been imperceptible. “

Cerberus Fossae : the first active seismic zone ever discovered on Mars

As for low frequency earthquakes, ” ten to twenty were recorded with magnitudes of 3 or 4, two of which were particularly interesting “. Detected during soil 173 and 235 (the latter being accompanied by a replica), their epicenter was located some 1,600 kilometers from InSight. The waves arrived from the east, from an area called Cerberus Fossae, on which seismologists have the eyes riveted for a long time already. This is a huge system of flaws located east of the plain of Elysium where InSight landed, and which probably formed during the establishment of Elysium Mons, the second volcanic complex of Mars, for the size, after the dome of Tharsis and his volcano giant Olympus Mons.

Former seat of volcanic, river and wind turbine (the most recent evidence of which dates back only 10 to 2 million years), the Cerberus fracture field has apparently accumulated in its history numerous constraints, some of which are not yet released. Thanks to the images provided by the satellites orbiting Mars, everything indicates that the faults in Cerberus Fossae would still be active, and would continue to play today.

Probe the internal structure of the planet

Thanks to the largest earthquakes detected so far, scientists have been able to start studying the upper crust of the planet and if we rely on the data recorded by the Seis seismometer, the hypothesis ” more likely is that Mars is covered with a regolith porous and fairly thick fractured, probably about ten kilometers “, Underlines Ludovic Margerin, director of research and also co-investigator of the mission. The data shows a stratum 8 to 11 km thick, made of highly altered or fractured volcanic materials who ” might suggest prolonged contact with water “.

Deeper, there would be a more homogeneous and coherent layer which ” could descend to the limit of Mohorovičic, a discontinuity marking the beginning of the coat which has not yet been detected “. If the Martian crust begins to reveal its secrets, the ultimate goal of InSight is to lift the veil on the internal structure of the entire planet. As Ludovic Margerin explains, there are very big efforts “ qwhich are used in the exploitation of recorded seismic signals “. The depth of the crust-mantle discontinuity (Moho) under InSight should ” to be determined in the coming weeks “. In addition, several events recorded remotely from earthquake have ” presumably sampled the Martian mantle so that the structure of the latter should therefore be clarified in the coming months “.

In conclusion, the vast majority of tremors that shake the Martian surface are of very low intensity, while significant earthquakes, with a magnitude greater than 4, are obviously rarer than expected. From this point of view, if the planet Mars is seismically active, even if one has for the moment no precise indication on the depth or the nature of the sources, its seismicity is very different from that of the Earth. The determination of the internal Martian structure could therefore be longer and more delicate than expected.

Three questions to Philippe Lognonné, architect of the SEIS seismometer, scientific manager and principal investigator of the mission. He is also responsible for the planetology and space sciences team atParis physics institute.

What can we learn from these knowledge of the planet except that it is an active planet?

Philippe Lognonné: The main result is effectively the discovery of seismic activity but even more the fact that the largest earthquakes detected are in the Cerberus region. Cerberus was thought to have had activity in the last few tens of millions of years, but still having earthquakes of magnitude 3.5 suggests that this local activity continues.

The second discovery is the discovery of 10 km of altered crust, above a more consolidated crust. This alteration does not only result from impacts of meteorites, but also from the past of Mars activity, including when there were several thousand years ago, there was a circulation of water in the crust and water on the surface. It is the first time that the volume of the altered crust, and we will now have to understand what this volume means in terms of the alteration process.

Finally, third result, the fact that the deep crust is seen by the seismic waves like the earth’s crystalline crust.

What result surprised you the most?

Philippe Lognonné: The most surprising is surely the concentration of earthquakes in Cerberus.

Another year of activity for the seismometer. What do you expect from the next data?

Philippe Lognonné: Statistically, we expect with one more year, doubling the duration, to some earthquakes with signals at least twice as large. We therefore now expect stronger earthquakes, one that will graze or exceed magnitude 4.5, or a first impact of localized meteorite, which will allow us to measure the thickness of the crust and go even deeper.

We are also working on the extended mission, for a new Martian year, 687 days.