STUDYING IMPACT PROCESSES WITH THE INSIGHT MISSION (Invited Presentation)

InSight is studying the interior of Mars using seismic signals emanating from quakes and also from meteoroid impacts. A new impact observed in both orbital images and seismic data would have a known formation time and exact location, allowing for determination of seismic ray paths and calibrating interior structure models, seismic velocity, attenuation, source parameters, moment, frequency cutoff, and seismic efficiency (the ratio of impact energy to radiated seismic energy). High resolution images would characterize crater sizes, eventually leading to an independent measurement of the current impact rate.

With real measurements of the ambient seismic noise, we can now update our pre-landing predictions of detectable impacts. We expect impact events near the detection limit at a rate of 0.1-200/year on the broadband seismometers and 0.2-20 per year on the short period seismometers. We predict ~3 detected impact events per year with signal/noise ~3. Significant daily variation in event detection capability makes weak signals less likely to be detected during the noisier daytime.

Half of the current impacts on Mars occur as clusters when the impactor fragments in the atmosphere. We expect these clusters to be detectable at greater epicentral distances than single impacts, and that fragmentation in the atmosphere may also cause an atmospheric pressure signal. Numerical modeling indicates that the smallest, most frequent impacts that produce ~meter-scale craters are formed by highly decelerated impactors, ~1-3 km/s.

Though discriminating between seismic sources and other transient sources (i.e. wind, dust devils, or mechanical noise) requires care, the number of detected seismic events is growing. It is challenging to locate events and identify discriminating features suggestive of an impact source. Thus we are also pursuing this investigation in reverse: analyzing orbital images for new albedo features associated with craters formed since InSight landed. If such features are observed, the seismic and pressure data during the time period constrained by before/after images could be further investigated using a known distance, azimuth, and impact size.