Seismic constraints from a Mars impact experiment using InSight and Perseverance

NASA’s InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission has operated a sophisticated suite of seismology and geophysics instruments on the surface of Mars since its arrival in 2018. On 18 February 2021, we attempted to detect the seismic and acoustic waves produced by the entry, descent and landing of the Perseverance rover using the sensors onboard the InSight lander. Similar observations have been made on Earth using data from both crewed1,2 and uncrewed3,4 spacecraft, and on the Moon during the Apollo era5, but never before on Mars or another planet. This was the only seismic event to occur on Mars since InSight began operations that had an a priori known and independently constrained timing and location. It therefore had the potential to be used as a calibration for other marsquakes recorded by InSight. Here we report that no signal from Perseverance’s entry, descent and landing is identifiable in the InSight data. Nonetheless, measurements made during the landing window enable us to place constraints on the distance–amplitude relationships used to predict the amplitude of seismic waves produced by planetary impacts and place in situ constraints on Martian impact seismic efficiency (the fraction of the impactor kinetic energy converted into seismic energy)

Seismic constraints from a Mars impact experiment using InSight and Perseverance

NASA’s InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission has operated a sophisticated suite of seismology and geophysics instruments on the surface of Mars since its arrival in 2018. On 18 February 2021, we attempted to detect the seismic and acoustic waves produced by the entry, descent and landing of the Perseverance rover using the sensors onboard the InSight lander. Similar observations have been made on Earth using data from both crewed1,2 and uncrewed3,4 spacecraft, and on the Moon during the Apollo era5, but never before on Mars or another planet. This was the only seismic event to occur on Mars since InSight began operations that had an a priori known and independently constrained timing and location. It therefore had the potential to be used as a calibration for other marsquakes recorded by InSight. Here we report that no signal from Perseverance’s entry, descent and landing is identifiable in the InSight data. Nonetheless, measurements made during the landing window enable us to place constraints on the distance–amplitude relationships used to predict the amplitude of seismic waves produced by planetary impacts and place in situ constraints on Martian impact seismic efficiency (the fraction of the impactor kinetic energy converted into seismic energy)

Impacts de météorites sur Mars - Observations sismiques, théorie de la source et modélisation.

Meteorite impacts are important actors in the evolution of the solar system and planetary surfaces. With the first seismic exploration of the Moon during the Apollo missions, it was revealed that meteorite impacts can also be a significant source of seismic signal. The interest in this type of source has been renewed since the landing of the InSight mission on Mars in November 2018, which brought a short-period and a very broadband seismometer on the surface. Eight signals of impact origin were detected by InSight seismometers during the four-year mission. As on the Moon, these signals differ from those of more classical tectonic quakes. Today, no model can fully explain, the impact signal spectrum and magnitude, the P- and S- wave relative amplitudes and the seismic source mechanism.In addition to seismic waves, the fall and final impact of the meteor produces a shock wave in the Martian atmosphere. On Mars, such shock can be trapped in a low-altitude atmospheric waveguide, and can thus propagate over long distances as a guided infrasound wave. Such infrasound was recorded by InSight seismometer after coupling to the ground surface. These seismo-acoustic signals carry information about their propagation medium, the Martian atmosphere, and their coupling medium, the subsurface below InSight. Hence, they can help understand the structure of Mars.In this work, we propose to investigate both types of seismic signals. First, we model the seismic source related to the impact cratering process. We design a new analytical model of the impact seismic source using the seismic Representation Theorem and the notion of stress glut. The impact can be seen as an extended field of equivalent forces, or as a point source, combining a seismic moment tensor and a vector force. We develop a numerical method to compute the stress glut associated to a hypervelocity impact using numerical simulations based on the Finite-Discrete Element Method (FDEM). We test this numerical model thanks to a coupling method: at some distance from the crater, the signal produced by the stress glut model is compared to the FDEM signal, prolongated by coupling. Our model succeeds in representing the low-frequency amplitude of impact generated signals, but additional terms are needed to explain the signal cutoff-frequency and high-frequency energy content. We show that this model of the impact seismic source brings insight into the difference in source mechanism of vertical and oblique impacts, and reproduces key properties of Lunar and Martian recordings.In parallel, we investigate Martian impact-generated seismo-acoustic signals. Thanks to a 1D model of the propagation and coupling of guided infrasound, we show that the group velocity of these signals depends on the effective sound speed profile in the Martian atmosphere. On the other hand, the amplitude ratio of horizontal to vertical displacement is shown to depend on the shear wave velocity structure below InSight. With a Bayesian inversion and using three impact-generated seismo-acoustic signals, we infer the Martian atmospheric and subsurface structure. The obtained sound speed profiles are in agreement with simulations of the Martian Climate Database. However, the inversion of the subsurface is shown to be dependent on the choice of inversion priors. Two models are possible: one with high seismic velocities in the first ∼20m below InSight, and the other with a single interface at ∼40m depth. These solutions are consistent with those obtained by previous near-subsurface studies. Hence, a better discrimination between models can be achieved in the future by combining multiple datasets.Les impacts de météorite sont des acteurs majeurs de l’évolution du système solaire et des planètes telluriques. Les expériences de sismologie menées sur la Lune durant les missions Apollo ont permis de découvrir que ces impacts sont également une source importante de signal sismique. L’intérêt pour ce type de source s’est accru avec l’atterrissage de la sonde InSight sur Mars en novembre 2018, qui y a placé deux sismomètres large-bande et courtes périodes. Durant les quatre ans de la mission, ces instruments ont détecté huit impacts de météorites. Comme sur la Lune, les signaux d’impacts diffèrent de ceux, plus classiques, d’origine tectonique. Aucun modèle ne permet encore d’expliquer tout à la fois leur spectre en fréquence, leur magnitude, l’amplitude relative de leurs ondes P et S, ainsi que le mécanisme de la source sismique.La chute et l’impact final des météores produit également des ondes de choc dans l’atmosphère martienne. Sur Mars, ces chocs peuvent être piégés dans un guide d’onde atmosphérique à basse altitude, et se propager ainsi sur de longues distances sous forme d’infrasons. Ces infrasons ont pu être détectés par les sismomètres d’InSight après s’être couplés à la surface. De tels signaux sismo-acoustiques contiennent des informations sur leur milieu de propagation, l’atmosphère martienne, ainsi que sur le milieu de couplage, le sous-sol d’InSight, et peuvent donc permettre d’interroger la structure de Mars.A travers cette thèse, nous proposons d’analyser ces deux types de signaux. Premièrement, nous modélisons la source sismique liée à la formation d’un cratère d’impact. Nous élaborons un modèle analytique de la source d’un impact à l’aide du Théorème de Représentation sismique et de la notion de "stress glut". L’impact peut ainsi être vu comme un champ étendu de force équivalentes, ou comme une source ponctuelle, combinant un tenseur de moment sismique et une force vectorielle. Nous développons une méthode numérique pour calculer le stress glut d’un impact à grande vitesse à partir de simulations numériques basées sur la méthode des éléments finis-discrets (FDEM). Ce modèle est testé via un système de couplage logiciel : à une certaine distance du cratère, le signal produit par le modèle de stress glut est comparé au "vrai" signal prolongé de la simulation FDEM. Notre modèle parvient ainsi à expliquer le contenu basse- fréquence des signaux d’impacts, mais des termes de source supplémentaires sont nécessaires pour modéliser leur énergie à haute-fréquence. Nous montrons que ce modèle éclaire les différences de mécanisme sismique entre les impacts obliques et verticaux, et reproduit certaines caractéristiques clefs des signaux martiens et lunaires.En parallèle, nous examinons les signaux sismo-acoustiques liés aux impacts martiens. Grâce à un model 1D de la propagation et du couplage des infrasons guidés, nous montrons que la vitesse de groupe de ces signaux dépend du profile de vitesse sonore dans l’atmosphère martienne. De même, le ratio des amplitudes sismiques radiales et verticales dépend principalement du profil de vitesse des ondes S sous InSight. Nous dérivons la structure de l’atmosphère et du sous-sol mar- tien via une inversion bayésienne à partir de trois des signaux sismo-acoustiques d’impacts. Les profils de vitesse sonore obtenus sont en accord avec ceux prédits par les simulations climatiques du Mars Climate Database. En revanche, la structure souterraine est dépendante des paramètres de l’inversion. Deux modèles sont ainsi possibles, l’un ayant de fortes vitesses sismiques dans les premiers ∼20 m sous InSight, l’autre ayant une simple interface vers ∼40 m de profondeur. Ces solutions s’approchent de celles obtenues par de précédentes études. Ainsi, combiner les signaux d’infrasons à d’autres données pourra permettre de trancher entre différents modèles

Impacts de météorites sur Mars : observations sismiques, théorie de la source et modélisation

Meteorite impacts are important actors in the evolution of the solar system and of planetary surfaces. With the first seismic exploration of the Moon during the Apollo missions, it was revealed that meteorite impacts can also be a significant source of seismic signal. The interest in this type of source has been renewed since the landing of the InSight mission on Mars in November 2018, which brought a short-period and a very broadband seismometer on the surface. Eight signals of impact origin were detected by InSight seismometers during the four-year mission. As on the Moon, these signals differ from those of more classical tectonic origin. Today, no model is able to explain the signal spectrum, its P- and S- wave amplitudes and the seismic source mechanism. In addition to seismic waves, the fall and impact of the meteor produces a shock wave in the Martian atmosphere. On Mars, such shock can be trapped in a low-altitude atmospheric waveguide, and can thus propagate over long distances as a guided infrasound wave. Such infrasound was recorded by InSight seismometers after coupling to the ground surface. These seismo-acoustic signals carry information about their propagation medium, the Martian atmosphere, and their coupling medium, the subsurface below InSight. Hence, they can help understand the structure of Mars. In this work, we propose to investigate both types of seismic signals. First, we model the seismic source related to the impact cratering process. We design a new analytical model of the impact seismic source using the seismic Representation Theorem and the notion of stress glut. The impact can be seen as an extended field of equivalent forces, or as a point source, combining a seismic moment tensor and a vector force. We develop a numerical method to compute the stress glut associated to a hypervelocity impact using numerical simulations based on the Finite-Discrete Element Method (FDEM). We test this numerical model thanks to a coupling method: at some distance from the crater, the signal produced by the stress glut model is compared to the prolongated FDEM signal. Our model succeeds in representing the low-frequency amplitude of impact generated signals, but additional terms are needed to explain the signal cutoff-frequency and high-frequency energy content. We show that this model of the impact seismic source brings insight into the difference in source mechanism of vertical and oblique impacts, and reproduces key properties of Lunar and Martian recordings. In parallel, we investigate Martian impact-generated seismo-acoustic signals. Thanks to a 1D model of the propagation and coupling of guided infrasound, we show that the group velocity of these signals depend on the effective sound speed profile in the Martian atmosphere. On the other hand, the amplitude ratio of horizontal to vertical displacement is shown to depend on the shear wave velocity structure below InSight. With a Bayesian inversion and using three impact-generated seismo-acoustic signals, we infer the Martian atmospheric and subsurface structure. The obtained sound speed profiles are in agreement with simulations of the Martian Climate Database. However, the inversion of the subsurface is shown to be dependent on the choice of inversion priors. Two models are possible: one with high seismic velocities in the first 20 m below InSight, and the other with a single interface at 40 m depth. These solutions are consistent with those obtained by previous near-subsurface studies. Hence, a better discrimination between models can be achieved in the future by combining multiple datasets.Les impacts de météorite sont des acteurs majeurs de l'évolution du système solaire et des planètes telluriques. Les expériences de sismologie menées sur la Lune durant les missions Apollo ont permis de découvrir que les impacts sont également une source importante de signal sismique. L'intérêt pour ce type de source s'est accru avec l'atterrissage de la sonde InSight sur Mars en novembre 2018, qui y a placé deux sismomètres large-bande et courtes périodes. Huit impacts de météorites ont été détectés par ces sismomètres durant les quatre ans de la mission. Comme sur la Lune, leurs signaux diffèrent de ceux d'origine tectonique. Aucun modèle ne permet encore d'expliquer leur spectre en fréquence, l'amplitude de leurs ondes P et S, ainsi que le mécanisme de la source sismique. La chute et l'impact des météores produit également des ondes de choc dans l'atmosphère martienne. Sur Mars, elles peuvent être piégée dans un guide d'onde atmosphérique à basse altitude, et se propager ainsi sur de longues distances sous forme d'infrasons. Ces infrasons ont pu être détectés par les sismomètres d'InSight après s'être couplés à la surface. De tels signaux sismo-acoustiques contiennent des informations sur leur milieu de propagation, l'atmosphère martienne, ainsi que sur le milieu de couplage, le sous-sol d'InSight, et peuvent donc permettre d'interroger la structure de Mars. A travers cette thèse, nous proposons d'analyser ces deux types de signaux. Premièrement, nous modélisons la source sismique liée à la formation d'un cratère d'impact. Nous élaborons un modèle analytique de la source d'un impact à l'aide du Théorème de Représentation sismique et de la notion de "stress glut". L'impact peut ainsi être vu comme un champ étendu de force équivalentes, ou comme une source ponctuelle, combinant un tenseur de moment sismique et une force vectorielle. Nous développons une méthode numérique pour calculer le stress glut d'un impact à grande vitesse à partir de simulations numériques basées sur la méthode des éléments finis-discrets (FDEM). Ce modèle est testé via un système de couplage logiciel : à une certaine distance du cratère, le signal produit par le modèle de stress glut est comparé au "vrai" signal prolongé de la simulation FDEM. Notre modèle parvient ainsi à expliquer le contenu basse-fréquence des signaux d'impacts, mais des termes de source supplémentaires sont nécessaires pour modéliser leur énergie à haute-fréquence. Nous montrons que ce modèle éclaire les différences de mécanisme sismique entre les impacts obliques et verticaux, et reproduit certaines caractéristiques clefs des signaux martiens et lunaires. En parallèle, nous examinons les signaux sismo-acoustiques liés aux impacts martiens. Grâce à un model 1D de la propagation et du couplage des infrasons guidés, nous montrons que la vitesse de groupe de ces signaux dépend du profile de vitesse sonore dans l'atmosphère martienne. De même, le ratio des amplitudes sismiques radiales et verticales dépend principalement du profil de vitesse des ondes S sous InSight. Par une inversion bayésienne, nous dérivons la structure de l'atmosphère et du sous-sol martien à partir de trois des signaux sismo-acoustiques d'impacts. Les profils de vitesse sonore obtenus sont en accord avec ceux prédits par les simulations climatiques du Mars Climate Database. En revanche, la structure souterraine est dépendante des paramètres de l'inversion. Deux modèles sont ainsi possibles, l'un ayant de fortes vitesses sismiques dans les premiers 20 m sous InSight, l'autre ayant une simple interface vers 40 m de profondeur. Ces solutions s'approchent de celles obtenues par de précédentes études. Ainsi, combiner les signaux d'infrasons à d'autres données pourra permettre de trancher entre différents modèles

Modeling Seismic Recordings of High‐Frequency Guided Infrasound on Mars

International audienceNASA’s InSight mission records several high-frequency (>0.5 Hz) dispersive seismic signals on Mars. These signals are due to the acoustic-to-seismic coupling of infrasound generated by the entry and impact of meteorites. This dispersion property is due to infrasound propagating in a structured atmosphere, and we refer to this dispersive infrasound as guided infrasound. We propose to model the propagation of guided infrasound and the seismic coupling to the ground analytically; we use a 1D layered atmosphere on a three-layer solid subsurface medium. The synthetic ground movements fit the observed dispersive seismic signals well and the fitting indicates the regolith beneath InSight is about 40-m in thickness. We also examine and validate the previously-published subsurface models derived from InSight ambient seismic vibration data

Two Seismic Events from InSight Confirmed as New Impacts on Mars

We report confirmed impact sources for two seismic events on Mars detected by the NASA InSight mission. These events have been positively associated with fresh impact craters identified from orbital images, which match predicted locations and sizes to within a factor of 3, and have formation time constraints consistent with the seismic event dates. They are both of the very high frequency family of seismic events and are present with chirps (dispersed infrasound/acoustic waves). This brings the total number of confirmed Martian impact-related seismic events to eight thus far. All seismic events with chirp signals have now been confirmed as having been caused by impact cratering events. This includes all seismic activity within 100 km of the lander and two out of the four events with source locations between 100 and 300 km distance.ISSN:2632-333

Two seismic events from InSight confirmed as new impacts on Mars

We report confirmed impact sources for two seismic events on Mars detected by the NASA InSight mission. These events have been positively associated with fresh impact craters identified from orbital images, which match predicted locations and sizes to within a factor of three, and have formation time constraints consistent with the seismic event dates. They are both of the Very High Frequency family of seismic events and present with chirps (dispersed infrasound/acoustic waves). This brings the total number of confirmed martian impact-related seismic events to eight thus far. All seismic events with chirp signals have now been confirmed as having been caused by impact cratering events. This includes all seismic activity within 100 km of the lander, and two out of the four events with source locations between 100-300 km distance

Seismic constraints from a Mars impact experiment using InSight and Perseverance

NASA's InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission has operated a sophisticated suite of seismology and geophysics instruments on the surface of Mars since its arrival in 2018. On 18 February 2021, we attempted to detect the seismic and acoustic waves produced by the entry, descent and landing of the Perseverance rover using the sensors onboard the InSight lander. Similar observations have been made on Earth using data from both crewed(1,2) and uncrewed(3,4) spacecraft, and on the Moon during the Apollo eras(5), but never before on Mars or another planet. This was the only seismic event to occur on Mars since InSight began operations that had an a priori known and independently constrained timing and location. It therefore had the potential to be used as a calibration for other marsquakes recorded by InSight. Here we report that no signal from Perseverance's entry, descent and landing is identifiable in the InSight data. Nonetheless, measurements made during the landing window enable us to place constraints on the distance-amplitude relationships used to predict the amplitude of seismic waves produced by planetary impacts and place in situ constraints on Martian impact seismic efficiency (the fraction of the impactor kinetic energy converted into seismic energy).ISSN:2397-336

Questions to Heaven: InSight's attempted detection of Zhurong's arrival at Mars

Benjamin Fernando and colleagues report on the international cooperation involved InSight's attempt to gather seismic data from the arrival at Mars of China's Zhurong rover

Newly formed craters on Mars located using seismic and acoustic wave data from InSight

International audienceMeteoroid impacts shape planetary surfaces by forming new craters and alter atmospheric composition. During atmospheric entry and impact on the ground, meteoroids excite transient acoustic and seismic waves. However, new crater formation and the associated impact-induced mechanical waves have yet to be observed jointly beyond Earth. Here we report observations of seismic and acoustic waves from the NASA InSight lander’s seismometer that we link to four meteoroid impact events on Mars observed in spacecraft imagery. We analysed arrival times and polarization of seismic and acoustic waves to estimate impact locations, which were subsequently confirmed by orbital imaging of the associated craters. Crater dimensions and estimates of meteoroid trajectories are consistent with waveform modelling of the recorded seismograms. With identified seismic sources, the seismic waves can be used to constrain the structure of the Martian interior, corroborating previous crustal structure models, and constrain scaling relationships between the distance and amplitude of impact-generated seismic waves on Mars, supporting a link between the seismic moment of impacts and the vertical impactor momentum. Our findings demonstrate the capability of planetary seismology to identify impact-generated seismic sources and constrain both impact processes and planetary interiors