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).
