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The University of Cologne.
There is a small impact crater in the artist's impression. The hemisphere on the ground in front of the lander is the light-colored one on the seismometer SEIS. There is a sandy regolith layer on top of alternate layers of basaltic rocks. Credit: Géraldine Zenhusern.
The second largest volcanic region on Mars, Elysium Planitia, has been shown to have a shallow sedimentary layer sandwiched between lava flows. The University of Cologne collaborated with several international research partners in the framework of NASA's InSight mission. The paper 'The shallow structure of Mars at the InSight landing site from insturment vibrations' will be published in Nature Communications.
The earthquake specialists Dr. Brigitte Knapmeyer-Endrun and Sebastian Carrasco used the data to analyze the composition. The authors looked at the shallow sub to around 200 meters. They found a regolith layer that was three meters thick above a 15 meter surface.
Rocks that were ejected after a meteorite impact fell back to the surface.
They found around 150 meters of basaltic rocks, which were mostly consistent with the expected structure, below the top layers. The authors found an additional layer 30 to 40 meters thick with low seismic velocity, which may be weak sedimentary materials, relative to the stronger basalt layers.
The authors used crater counts from literature to date the lava flows. Rocks with many impact craters from meteorites are older than rocks with fewer impact craters. Smaller craters allow scientists to date the deeper rock layers, while larger craters allow them to date the shallow rock layers.
They found that the shallow lava flows are 1.7 billion years old and formed during the time when there were low rates of meteorite and asteroid impacts. The Hesperian period was characterized by widespread volcanic activity and the deeper basalt layer formed 3.6 billion years ago.
The authors propose that the intermediate layer with low volcanic velocities could be composed of deposits sandwiched between the Hesperian and Amazonian basalts. The first chance to compare ground-truth measurements of the shallow subsurface to previous predictions is provided by these results. Dr. Knapmeyer-Endrun had already developed models of the shallow subsurface at the InSight landing site. More porous rocks are now indicated by the actual measurements.
The results help to better understand the geological processes in Elysium Planitia, but it's also useful for future landed missions since it can help to refine predictions. Load-bearing capacity and trafficability for rovers are assessed using knowledge of the shallow subsurface's properties. The information on the layers in the shallow subsurface helps to understand where the ground water or ice might still be. The effect of the shallow structure of Elysium Planitia on marsquake recordings is being analyzed by Sebastian Carrasco.
The InSight lander touched down in the Elysium Planitia region on Mars. Mars has been the target of many planetary science missions, but the InSight mission is the first to specifically measure the subsurface using seismic methods.
The shallow structure of Mars at the InSight landing site is explained by the insturment of ambient vibrations.
Nature Communications is a journal.
The analysis of Mars's wind-induced vibrations sheds light on the planet's underlying properties.
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