In December 2021, a meteorite hit the surface of Mars, generating powerful seismic waves on the surface of the planet. It was enough for the InSight mission’s seismometer. Analysis of these seismic waves made it possible to establish the structure of the Martian crust for the first time on a large scale.
On December 24, 2021, Major EarthquakeEarthquake It was shaking the surface of Mars, an event that was instantly detected and recorded by Seismometer for the InSight missionplaced on the surface. And quickly, the origin of this earthquake is of interest to scientists, because the Red Planet does not have it tectonic platestectonic platesAnd the Very rarely large earthquakes occur. Indeed, the earthquake had nothing to do with a fundamental geological event of the planet. It could have been caused by a meteorite impact on the surface, a hypothesis confirmed by the probe MROMRO In orbit around the planet reveals the presence of a new crater 150 meters in diameter!
For scientists, this kind of event was simply unexpected. Because the force of the impact generated a very special kind of wave, which spread over the surface. The properties of these waves, which were not detected on Mars at that time, made it possible to study the structure of the Martian crust as a whole.
Hear the meteor impact on Mars recorded by the InSight lander. © NASA, JPL-Caltech, Cnes, Imperial College London
Very special waves make it possible to examine the crust of Mars
surface waves They are really very special waves that are produced on Earth during strong earthquakes. For this reason, they have not been observed before on Mars, which produces only low-magnitude earthquakes. Although these waves only propagate along the surface, it is they that transmit most of the earthquake’s energy. On Earth, these are especially feared because they are the ones who do the most damage.
Unlike waves SizesSizes (P and S), and SpeedSpeed Surface waves depend on repeatrepeat. However, lower frequencies are more sensitive to greater depths. This is a particularly interesting property for studying the crust of Mars. For the first time, measuring the scattering of these waves made it possible to directly observe changes in velocity as a function of depth and create a complete picture. The cortical structure of Mars.
The impact of the meteorite excavated ice blocks the size of rocks from the subsurface of Mars. The presence of ice so close to the surface has raised eyebrows and questioned scientists. Overview of the affected region created from images captured from space by the MRO probe. © NASA, JPL-Caltech, University of Arizona
The cortical structure of Mars, for the first time on a large scale
Like the CrustalCrustalMars’ crust shows important differences in topography, thickness, and age, but is also affected in a variable way by craters, erosion, and volcanoesvolcanoes. The crust of Mars also represents an important difference betweenNorthern HemisphereNorthern Hemisphere and theSouthern HemisphereSouthern Hemisphere, whose origin is still much debated. A binary characterized by a topographical difference of about five kilometers. The southern part, higher, shows a cratered surface compared to the northern one, and is characterized by vast plains.
The seismometerseismometer From InSight so far it has made it possible to better constrain the thickness of the shell in the area in which it is located (Elysium Planetia) i.e. 39 +/- 8 km. As important as this result is, it is just a point and the crust of Mars, as a whole, remains largely unknown. However, the impact of the meteorite made it possible to build a universal model. Thus, the analysis of surface waves has made it possible for scientists to study the structure of the crust to depths of up to 30 kilometers below the surface.
A priori uniform crust between north and south
The results are published in the journal Science, indicating that the Martian crust exhibits a relatively uniform structure between the meteor impact site and the InSight site. In general, the crust is also characterized by a high density, contrary to what was suggested by observations at the seismometer level. The crust just below InSight appears to be low-density and could have been formed by a large meteorite impact 3 billion years ago. In any case, it seems that this part of the crust of Mars does not represent General cortical structure of Mars.
Regarding the origin of the Martian dichotomy, the study indicates that, contrary to the previous theory, the crusts in the north and south are likely to be relatively similar, both in texture and composition. Differences in density could explain this impression of a difference in crust thickness. However, the origin of the split is still debated and can be linked to either important meteorite impacts, or abnormalityabnormality In the pregnancypregnancy The CoatCoator a combination of the two.
