Numerical modelling of recent impacts on Mars and contribution to InSight mission science
Authors: Miljkovic Katarina , Rajsic Andrea , Neidhart Tanja , Sansom Eleanor , Wojcicka Natalia , Collins Gareth , Daubar Ingrid 
Published: July 2021

The crust on Mars has been structurally affected by various geologic processes such as impacts, volcanism, mantle flow and erosion. Previous observations and modelling point to a dynamically active interior in early Martian history, that for some reason was followed by a rapid drop in heat transport. Such a change has significantly influenced the geological, geophysical and geochemical evolution of the planet, including the history of water and climate. Impact-induced seismic signature is dependent on the target properties (conditions in the planetary crust and interior) at the time of crater formation; Thus, we can use simulations of impact cratering mechanics as a tool to probe the interior properties of a planet.Contrary to large impacts happening in Mars&#8217; early geologic history, the present-day impact bombardment is limited to small meter-size crater-forming impacts (in the atmosphere and on the ground), which are also natural seismic sources (Daubar et al., 2018, 2020; Neidhart et al., 2020). Impact simulations, in tandem with NASA InSight seismic observations (Benerdt et al., 2020, Giardini et al., 2020), can help understand the crustal properties over the course of Mars&#8217; evolution, including the state of Mars&#8217; crust today. Our most recent numerical investigations include: estimating the seismic efficiency and moment from small meter-size impact events, tracking pressure propagation from the impact point into far field, transfer of impact energy into seismic energy, etc (Rajsic et al., 2020, Wojcicka et al., 2020). Understanding coupling between impact crater formation process with the generation and progression of seismic energy can help identify small impact everts in seismic data on Mars. We also looked at the same process on the Earth (Neidhart et al., 2020) and the Moon (Rajsic, et al., this issue).Since the landing of the NASA InSight mission on Mars, there was a dozen known new impacts (Miljkovic et al., 2021). However, all but one impact occurred much too far away (3000 to 8400 km distance from the InSight lander) to be within the detectability threshold estimates (Teanby et al., 2015; Wojcicka et al., 2020). About 50% of the observed craters were likely single impacts and the other 50% were evidently cluster craters with less than 40 individual craters in the largest cluster. The largest single crater was ~14 m in diameter, and the largest crater in a cluster was ~13 m (Neidhart et al., this issue), consistent with crater cluster observations (Daubar et al., 2013). The one impact that had a possibility of being detected by SEIS was 1.5 m in diameter at 37 km distance (Daubar et al. 2020).Considering that orbital imaging is limited in space and time, these known new impacts represent only a fraction of the total number of impacts that have occurred on Mars in the last ~2 years. According to impact flux calculations (Teanby and Wookey, 2011), there should have been ~3000 detectable craters, larger than 1 m in diameter, formed on Mars since InSight landed. If any of these unobserved impacts have been large enough and close enough to InSight to detect seismically, we have not yet discerned them in the seismic data.References:Banerdt, W.B. et al. (2020) Nature Geosci. 13, 183-189.Giardini, D. et al. (2020) Nature Geosci. 13, 205-212.Daubar, I.J. et al. (2020) J. Geophys. Res. Planets, 125: e2020JE006382.W&#243;jcicka, N. et al. (2020) J. Geophys. Res. Planets, 125, e2020JE006540.Raj&#353;i&#263; et al. (2021) J. Geophys. Res. Planets, 126, e2020JE006662.Daubar et al. (2013) Icarus 225, 506-516.Teanby, N.A. &amp; Wookey, J. (2011) PEPI 186, 70-80.Neidhart, T. et al. (2020) PASA, 38, E016.Teanby, N.A. et al. (2015) Icarus 256, 46-62.Miljkovic, K. et al. (2021) LPSC, LPI Contribution No. 1758.