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Geological constraints on the crustal structure at InSight landing site, Elysium Planitia, Mars

Periodic Reporting for period 1 - GeoInSight (Geological constraints on the crustal structure at InSight landing site, Elysium Planitia, Mars)

Reporting period: 2017-07-10 to 2019-07-09

InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) is a robotic lander mission aimed at characterizing the interior of Mars using a suite of geophysical instruments. This mission has important implications since it may allow us to understand the formation and evolution of the Red Planet and learn more about rocky exoplanet for future explorations. This mission (InSight) has been an international collaborative project with the contribution from both NASA and ESA. Project GeoInSight targets these important questions: What is the geologic background of InSight landing site? What subsurface structures are there near the lander? These questions are crucial to the analysis and interpretation of geophysical obtained by the lander and will contribute to an integrated view of the structure of the Martian crust. By studying a combination of satellite images, this project aims at constraining the subsurface structure of the Martian crust near the InSight lander and maximize the scientific return of the InSight mission. To investigate the crust structure that seismic waves interacted and contribute toward a better understanding of the crustal structure of Mars. The goal of this project is to organize a comprehensive study using a suite of datasets acquired by previous orbital missions and place important constraints on the subsurface structure of InSight landing site.
In summary, we applied a novel approach of probing the subsurface using impact craters to understand the subsurface structure, and for the first time provide prior knowledge about the subsurface using remote sensing datasets to a seismometer which is investigating the interior structure of another planet. As a bonus, our proposed name for the 51-km impact crater has been approved by the International Astronomical Union (IAU) Working Group for Planetary System Nomenclature and it is officially named “Kalpin” crater. Here we explain the work we carried out in this project in each work package:
First (WP1), to characterize the geological and geophysical background of the landing site, we organized previous geological maps of this region and investigated the morphological features of the landing site. We identified local geologic history background based on previous studies and geological mapping works in the InSight science team. It has been shown that InSight landing ellipse is located near the dichotomy of Mars with complicated geologic history. We also delineate a region within ~500 km from the landing site that is relevant to the upper several kilometers of the crustal structure of the landing site for further study.
Second (WP2), we performed orbital spectral data analysis on 89 shortwave-infrared spectral images using a custom algorithm to investigate outcrops near the InSight landing site. We have identified numerous locations where olivine and pyroxene are exposed in small impact craters near the landing site. We also identify Fe/Mg phyllosilicates in the transition unit and in Kalpin crater north of the lander. (We proposed the name of the crater to IAU and it is subsequently accepted). Mapping products are investigated but due to the coarse resolution, no spectral detections are identified associated with rocky outcrops. Out of our expectation, we discovered meter-scale layered, yardang-forming sedimentary units in Kalpin crater. As a consequence, we extended the image survey to higher resolution images to cover the morphology. We then identified a suite of impact craters (6) that expose the same layered sedimentary unit. The detailed morphological study is performed, including HiRISE digital elevation model process and measurements of layer orientations and dip angle; mapping and analysis of fractures within the sedimentary unit. The findings suggest that they are likely excavated materials from the subsurface.
Lastly (WP3), we used several different methods to calculate the possible burial depth before excavation for the craters that expose layered sediments and phyllosilicates. We then compile seismic wave velocities and densities of materials on Earth that are relevant to Mars in a dataset. Combining the wave velocities and densities and depths from geological observations, we made a set of possible crustal models for seismologists to test their forward models and for comparison with InSight seismology data.
During the project, the results are continuously presented in several InSight science team meetings and in international conferences. One publication regarding the geology of the landing site has been submitted and is now under revision. Several other publications stemmed from collaborations with researchers within and outside the host institution have been published or are being prepared. We also disseminate the results to the general public through news interview (Euronews) and outreach activities (in the form of outreach talks to more than 200 school children).
We have fully investigated the complex structure near the dichotomy of Mars and proposed that the layered sediments we identified in impact craters are a buried extension of Medusae Fossae Formation which is buried by younger lava flows. These identifications may indicate physically weaker materials beneath the lava flows at the insight landing site. These heterogeneities in the Martian crust may increase the scattering of the seismic waves, alter the seismic waveforms and complicate the interpretation of the seismic data. These constraints on the crust structure of the first several kilometers have important impacts on the analysis and discussion of geophysical data acquired by the InSight lander. The different crust models derived from this work and other constraints have been constructed and shared with the InSight team, which have potential impacts on the incoming efforts to constrain the interior structure of Mars.
Geological and geophysical background of the InSight landing site
Mineralogy survey of the landing site region (from analysis of CRISM targeted data)
Examples of seismic profiles proposed based on geological constraints