NASA’s Mars Insight Lander Uses Wind-Induced Vibrations To Reveal the Red Planet’s

InSight Lander on Mars

An artist illustration of the InSight lander on Mars. InSight, short for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport, is designed to give the Red Planet its first thorough check up since it formed 4.5 billion years ago. The mission is looking for tectonic activity and meteorite impacts, studying how much heat is still flowing through the planet, and tracking Mars’ wobble as it orbits the sun. Credit: ​​NASA/JPL-Caltech

Seismic data collected in Elysium Planitia, the second largest volcanic region on Subsurface Layering Beneath the InSight Lander

Artist’s impression: The InSight lander is located in Homestead Hollow, a small impact crater. The seismometer SEIS that was used in this study is the light-colored hemisphere on the ground in front of the lander. The ground beneath it consists of a sandy regolith layer on top of alternate layers of sediments (yellow-orange colors) and basaltic rocks, i.e. former lava flows (brown colors). Credit: Géraldine Zenhäusern / ETH Zürich

Below these top layers, they identified around 150 meters of basaltic rocks, i.e., cooled and solidified lava flows, which was largely consistent with the expected subsurface structure. However, between these lava flows, starting at a depth of about 30 meters, the authors identified an additional layer 30 to 40 meters thick with low seismic velocity, suggesting it contains weak sedimentary materials relative to the stronger basalt layers. 

To date the shallower lava flows, the authors used crater counts from existing literature. Established knowledge about the impact rate of meteorites allows geologists to date rocks: surfaces with many impact craters from meteorites are older than ones with fewer craters. Also, craters with larger diameters extend into the lower layer, allowing the scientists to date the deep rock, while smaller ones allow them to date the shallower rock layers.

They found that the shallower lava flows are approximately 1.7 billion years old, forming during the Amazonian period – a geological era on Mars characterized by low rates of meteorite and asteroid impacts and by cold, hyper-arid conditions, which began approximately 3 billion years ago. In contrast, the deeper basalt layer below the sediments formed much earlier, approximately 3.6 billion years ago during the Hesperian period, which was characterized by widespread volcanic activity. 

The authors propose that the intermediate layer with low volcanic velocities could be composed of sedimentary deposits sandwiched between the Hesperian and Amazonian basalts, or within the Amazonian basalts themselves. These results provide the first opportunity to compare seismic ground-truth measurements of the shallow subsurface to prior predictions based on orbital geological mapping. Prior to the landing, Dr. Knapmeyer-Endrun had already developed models of the velocity structure of the shallow subsurface at the InSight landing site based on terrestrial analogs. The actual measurements now indicate additional layering as well as more porous rocks in general. 

‘While the results help to better understand the geological processes in Elysium Planitia, comparison with pre-landing models is also valuable for future landed missions, since it can help to refine predictions,’ Knapmeyer-Endrun remarked. Knowledge of the properties of the shallow subsurface is required to assess, for example, its load-bearing capacity and trafficability for rovers. Besides, details on the layering in the shallow subsurface help to understand where it might still contain ground water or ice. Within the framework of his doctoral research at the University of Cologne, Sebastian Carrasco will continue to analyze the effect of the shallow structure of Elysium Planitia on marsquake recordings.

The InSight lander arrived on Mars on November 26, 2018, touching down in the Elysium Planitia region. Mars has been the target of numerous planetary science missions, but the InSight mission is the first to specifically measure the subsurface using seismic methods. 

Reference: “The shallow structure of Mars at the InSight landing site from inversion of ambient vibrations” by M. Hobiger, M. Hallo, C. Schmelzbach, S. C. Stähler, D. Fäh, D. Giardini, M. Golombek, J. Clinton, N. Dahmen, G. Zenhäusern, B. Knapmeyer-Endrun, S. Carrasco, C. Charalambous, K. Hurst, S. Kedar and W. B. Banerdt, 23 November 2021, Nature Communications.
DOI: 10.1038/s41467-021-26957-7

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