First seismo-acoustic location and orbital imaging of recent impacts on Mars: constraints on atmosphere and interior structure and impact processes

The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander is providing an unprecedented set of high frequency records of ground deformations, pressure and wind at the surface of Mars. Seismic and acoustic waves from impacts have been observed by SEIS seismometer through the ground movements that they generate, and their sources as impacts have been confirmed with orbital images of newly appearing craters. Three impacts have been identified and located, and one additional seismic event is consistent with a date-constrained new impact. Several other events are currently being investigated as well. Arrival times and polarization of seismic and acoustic waves were used to estimate impact locations. These estimated locations were subsequently confirmed by orbital imaging of associated craters and temporal matches to the events times, with previous orbital images showing no craters. Crater dimensions and estimates of meteoroid trajectories from images allow us to understand and model the recorded seismograms. The precise source locations provided by impacts as compared to tectonic sources provide direct constraints on the structure of the martian interior. First arrival seismic waves confirm the previously determined crustal models, and the dispersion of trapped acoustic waves confirms the current models of sound speed and wind in the atmosphere. In addition, these observations provide the first ground-truth for distance-amplitude scaling relationships between impacts and the mechanical waves for Mars. They confirm the relationship between the seismic moment of impacts and the vertical impactor momentum, and demonstrate the capability of planetary seismology to constrain impact rates and internal structure of terrestrial planetary objects throughout the solar system.