2023-07-14 04:00:15
Four new articles by seismologists from the Institut de physique du globe de Paris and UniversitĂ© Paris CitĂ©, in collaboration with teams from several French and foreign laboratories, detail these results in the special edition of the journal “Geophysical Research Letter from the American Geophysical Association (AGU).
Six months following the end of the InSight mission, the scientific teams continue to analyze the different types of data recorded by the lander (A lander in the field of astronautics means a machine… ) and its SEIS seismometer during their four years of activity on the surface of Mars. Thanks, in particular, to the data of the largest Martian earthquake (Martian is a generic name which designates several types of creatures…), of magnitude 4.7 and detected on May 4, 2022, several studies are refining our knowledge of the internal structure (In France , this name designates a doctor, a pharmacist or a dental surgeon, at the…) of Mars
Three of these articles confirm the complexity of the Martian crust. The surface waves generated by the 1222 earthquake revealed a strong anisotropy (Anisotropy (opposite of isotropy) is the property of being dependent on the direction….), which allows waves with movements of horizontal shear to propagate faster than those having vertical shear (The vertical (rare), or vertical style, is a style of musical writing consisting of…). The study, conducted by Zongbo Xu and collaboratorsshows that this anisotropy comes a priori from a stack of layers in the Martian crust, some of which may correspond to lava flows and the others associated with deposits of lower seismic velocities.
The study led by Jing Shi and collaborators has, for its part, highlighted the presence of a layer of very low seismic speed (We distinguish:) in the first kilometer (The meter (symbol m, from the Greek metron, measure) is the basic unit of length of the System…) just under the InSight station, a priori linked to very porous and altered materials. Finally, Sabrina Menina, Ludovic Margerin (IRAP) and Taichi Kawamura and their collaborators show that the diffraction (Diffraction is the behavior of waves when they encounter an obstacle that is not theirs…) of seismic waves on Mars, which sometimes made the analysis of seismic signals very complex, takes place within 20 first kilometers of the crust. This complexity of the crust, a kind of cracked yarrow, also confirms the complexity of the geological history of the planet (A planet is a celestial body orbiting around the Sun or another star of…)!
In the fourth publication, Philippe LognonnĂ©, Martin Schimmel (Barcelona Geoscience Laboratory, Spain), ElĂ©onore Stutzmann and collaborators, have identified and used the vibrations of the planet following the 1222 earthquake. The planets (and even the stars), can indeed vibrate like musical instruments and are thus characterized by their own modes. Each eigenmode has a particular geometry (Geometry is the part of mathematics that studies the shapes of space…) and generates a vibration with a frequency (In physics, frequency generally designates the measurement of the number of times that ‘un…) pure, as the different strings of a piano can do.
The first notes of Mars identified have frequencies starting around 3 thousandths of Hz, a sound 10,000 times lower than the lowest C of a piano. They are, on Mars as on Earth, inaudible but can be detected by seismometers, becoming, for seismologists, valuable data allowing them to go back more precisely to the characteristics of the deep structure of the planet.
Finally, a fifth study, also published recently, provides new information on the composition of Martian sand. This study was carried out on Mars by the SEIS team when the seismometer cable was buried. Indeed, to minimize external disturbances, the cable connecting SEIS to the lander had been buried under a few cm of sand thanks to the lander’s shovel.
By analyzing the images taken during this operation, Nicolas Verdier (CNES), VĂ©ronique Ansan (LPG) and their colleagues observed that some grains were transported up to 2 meters downwind, even if they fell from the shovel located 50 centimeters above the ground, while others fell much closer. This field experiment, published in the “Journal of Geophysical Research”, enabled them to determine the size distribution of Martian sand grains.
With already more than one hundred scientific articles published, the scientific harvest of InSight and SEIS therefore covers a wide range, from the core of the planet, at a depth of more than 1600 km, to the wind depot on which SEIS has been deployed.
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