Image provided by ETH Zurich (Doyeon Kim, Martin van Driel & Christian Boehm)

Following two large meteorite impacts on Mars, an international research team has observed seismic waves propagating along the surface of a planet other than Earth for the first time. Martin Schimmel, a researcher at Geosciences Barcelona (GEO3BCN-CSIC), has collaborated on a new publication which provides new insights into the structure of the Martian crust.

On 24 December 2021, a meteorite impact on Mars gave the researchers the surface waves they had been long anticipating. Until that day, the only seismic waves detected were ones that propagated from the respective quake’s focus, or hypocentre, through the depths of Mars. This data from the marsquakes, recorded by NASA’s InSight lander and analysed at ETH Zurich in collaboration with the InSight Science Team, are now detailed in two papers published today in the journal Science.

“Until now, our knowledge of the Martian crust has been based on only a single point measurement under the InSight lander,” explains Doyeon Kim, a geophysicist and senior research scientist at ETH Zurich’s Institute of Geophysics and the lead author of the study on surface waves on Mars.

The results show that the Martian crust between the meteor impact sites and InSight’s seismometer has a very uniform structure and high density. “The surface wave observations permitted us to expand our current understanding of the crustal structure away from the lander site,” points out Martin Schimmel, GEO3BCN-CSIC researcher. Together with other researchers from Institut De Physique Du Globe De Paris (IPGP), Schimmel did software coding and data analysis to evidence the presence of surface waves.

Seismic waves are key to the mission, which aims to study the planet’s deep interior – its crust, mantle, and core – which can teach scientists about the formation of all rocky worlds, including Earth and the Moon. “The different waves, classified into surface and body waves, travel through the same planet on different paths. And even if their paths are similar, they also sample the same propagation medium differently. Thus using different wave types is essential to better constrain any structure”, explains the Geosciences Barcelona researcher.

Since landing in November 2018, the NASA InSight seismometer has detected 1,318 marsquakes, including several caused by much smaller meteoroid impacts. Nevertheless, this is the very first time that scientists have direct seismic measurements from the crust not only below the seismic sensor. “We now see that the Martian crust at the lander site is likely not representative of the general Martian crust structure,” Schimmel says.

Concretely, crustal seismic velocities and density have been estimated to be higher away from the lander site, suggesting that either the composition is different or the porosity is reduced. “A higher density and lower porosity can be explained by volcanic resurfacing processes. And indeed, a large portion of the surface wave path traverses volcanic provinces”, suggests the GEO3BCN-CSIC seismologist.

Epic Meteoroid Impact on Mars

The superficial waves were detected due to a magnitude four marsquake provoked by a massive meteoroid strike estimated to be one of the biggest seen on Mars since NASA began exploring the red planet. The agency’s InSight lander felt the ground shake during the impact, while cameras aboard the Mars Reconnaissance Orbiter spotted the massive new crater from space.

More About the Missions

Jet Propulsion Laboratory (JPL) manages InSight and the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate. InSight is part of NASA's Discovery Program, managed by the agency's Marshall Space Flight Center in Huntsville, Alabama. Lockheed Martin Space in Denver built the Mars Reconnaissance Orbiter, InSight spacecraft (including its cruise stage and lander) and supports spacecraft operations for both missions.

A number of European partners, including France's Centre National d'Études Spatiales (CNES) and the German Aerospace Center (DLR), are supporting the InSight mission. CNES provided the Seismic Experiment for Interior Structure (SEIS) instrument to NASA, with the principal investigator at IPGP (Institut de Physique du Globe de Paris). Significant contributions for SEIS came from IPGP; the Max Planck Institute for Solar System Research (MPS) in Germany; the Swiss Federal Institute of Technology (ETH Zurich) in Switzerland; Imperial College London and Oxford University in the United Kingdom; and JPL. DLR provided the Heat Flow and Physical Properties Package (HP3) instrument, with significant contributions from the Space Research Center (CBK) of the Polish Academy of Sciences and Astronika in Poland. Spain's Centro de Astrobiología (CAB) supplied the temperature and wind sensors.

Press release elaborated with information provided by JPL & ETH Zurich

Reference article

Kim et al.: Surface Waves and Crustal Structure on Mars, Science. https://doi.org/10.1126/science.abq7157

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