THE SEISMOMETER DELIVERS THE FIRST SEISMIC AND ACOUSTIC WAVES FROM A METEORITE IMPACT ON MARS
To date, the seismometer on InSight has identified and located four impacts that have occurred on the surface of Mars. For this, the sound waves emitted by the impacts were detected by the minute deformations of the ground produced when they pass over the seismometer. Then, the arrival times and polarization of the seismic and acoustic waves were used to estimate the locations of the impacts.
These observations, which are the first ever on a planet other than Earth, have been confirmed by orbital imaging of the associated craters. The dimensions of the craters and the estimates of the trajectories of the meteorites make it possible to understand and model the recorded seismograms. By knowing the location of these sources, the impacts detected enable the Martian interior to be imaged. The first arrivals of the seismic waves confirm the previously determined models of the crust.
“Knowing the structure of the Mars crust and its level of heterogeneity enables us to learn more about how it has evolved over the years. It must be understood that it is in the core of this crust that the radioactive elements that make the thermics of the planet fluctuate are concentrated. Its fracturing level also tells us about the capacity of Mars to renew its surface,” explained Raphael F. Garcia, professor of planetary geophysics at ISAE-SUPAERO and who coordinated this study.
These observations provide the first ground evidence of distance-amplitude scale relationships of seismic waves generated by impacts on Mars. They confirm the link between the seismic moment of the impacts and the vertical moment of the impactor. This development demonstrates the ability of planetary seismology to estimate impact rates and to image the internal structure of planetary objects in the solar system.
These scientific analyses, the result of international collaboration between researchers from different laboratories, have been published in the journal Nature Geoscience.
“As part of the InSight mission, obtaining impact recordings was the last scientific goal we had not yet achieved. These results prove that with a single seismometer, we are able to feel Mars “vibrate”, but also hear the noise of explosions and therefore locate the impacts. This instrument can be deployed on other planets to study their internal structure. As such, one of the sensors of SEIS’ replacement model will fly to the hidden side of the Moon in the Farside Seismic Suite (FSS) instrument in 2025,” concluded Raphael F. Garcia.
RECORDING MARSQUAKES MAKES IT POSSIBLE TO CARRY OUT ULTRASONIC SCANS OF THE INTERIOR OF MARS
The work carried out by seismologist Mélanie Drilleau and numerous scientific experts on the data collected from some twenty marsquakes detected by the French seismometer, has increased our knowledge about the interior of the red planet. Thanks to the SEIS seismometer recordings, scientists were able to set up the most complete Martian seismic database published to date.
Thus, most of the marsquakes recorded come from an area called Cerberus Fossae, where there are many seismic faults that are most likely the source of these marsquakes. The analysis of the seismic waves that propagate inside the planet, in a manner similar to that of an ultrasonograph, has made it possible to establish a more precise structure model of the interior of Mars.
“In particular, we estimated that the Martian crust is compatible with a gabbro type rock, a magmatic rock that is the main constituent of the oceanic crust on Earth,” explained Mélanie Drilleau, CNRS research engineer at ISAE-SUPAERO. “This new work also confirms the discoveries made last year and published in the journal Science, in particular that the interior of Mars is warmer now than it was in the past,” explained Mélanie Drilleau, CNRS research engineer at ISAE-SUPAERO.
This study, the result of a strong international collaboration involving five French laboratories (ISAE-SUPAERO, Institut de Physique du Globe (CNRS/IPGP/Université Paris Cité), Laboratoire de Planétologie et Géosciences (CNRS/Nantes University/Angers University), Lyon Laboratoire de Géologie: Terre, Planètes, Environnement (Lyon CNRS/ENS/Claude Bernard University Lyon 1), J-L Lagrange laboratory (CNRS/Observatoire de la Cote d’Azur), as well as the Royal Observatory of Belgium, ETH Zurich and the Jet Propulsion Laboratory, has just been published in the American Journal of Geophysical Research – Planets. It is a further step toward understanding the formation and thermal evolution of Mars.
PORTRAITS OF RESEARCHERS
RAPHAËL F. GARCIA: PROBE THE HEARTS OF THE PLANETS
Raphael F. Garcia got a taste very early for "concrete, applied physics". His PhD at the Midi-Pyrénées Observatory on the seismology of the Earth’s core testifies to this. Seismic waves are indeed a powerful tool for probing the internal structure of planets. Based on the data from the Apollo missions, the young researcher proposed a model of the Moon’s core. Moreover, he specialized in land-atmosphere coupling, a fundamental parameter to be taken into account in order to distinguish real seismic signals from noise. Raphael F. Garcia is involved in a major international project: InSight, the first geophysics mission to Mars. Its main instrument, the SEIS seismometer, benefits from our expertise. “We have developed new land-atmosphere coupling tools, which are now the state of the art,” said Raphael F. Garcia. His work has enabled him to be among the co-signatories of major articles published in the journal Science in 2021, which reveal the internal structure of Mars.
How do we produce scientific results on an international mission with the collaboration of several international laboratories?
Raphaël F. Garcia : The principle is to pool the scientific analyses of the different members of the team.
The results we publish are the result of combined work in particular with the "Mars Quake Service" which detects and establishes an initial analysis of seismic events and the imager (CTX, HiRISE) specialists who get the views of the craters.
The most thrilling thing for you in this research?
Raphaël F. Garcia : The moment when the teams running the imagers in orbit confirm the location of the crater that you gave and when we get the image of the crater that created the signals that you analyzed! An intense joy that only happens a few times in a scientific career. Like scoring in a basketball or rugby game in the last minute of the final.
Mélanie Drilleau: journey of a simologist researcher
Mélanie Drilleau completed her PhD in Geophysics at the University of Nantes on the temperature and mineralogy of the Earth’s mantle. A subject that then led her to explore and develop an expertise to estimate the physical properties of the interiors of planetary bodies from geophysical and especially seismological data.
The researcher has been involved in the Insight mission since 2014. She holds a key role in the "Mars Structure Service" which brings together a team of international researchers working on the evolution of knowledge of Mars thanks to the SEIS seismometer.
"The most exciting part is being among the first scientists who were able to image the interior of Mars, much like scientists did for Earth in the early 20ᵉ with the first seismological stations. It is exciting to compare the data provided by the seismometer with our scientific hypotheses before the InSight mission."
INSIGHT: ISAE-SUPAERO, AN INTERNATIONALLY RECOGNIZED SPACE LABORATORY
SEIS DETECTS FIRST MARTIAN EARTHQUAKE
FIRST YEAR OF THE INSIGHT MARS MISSION, SURPRISING SCIENTIFIC RESULTS
INSIGHT MISSION: ISAE-SUPAERO REVEALS RESULTS OF ITS RESEARCH ON THE PLANET MARS
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