SEISMICALLY DETECTED CRATERING ON MARS: AN INDEPENDENT MEASURE OF THE RECENT IMPACT FLUX

The NASA InSight mission seismically detected a number of meteoroid impacts on the surface of Mars. Four newly detected impact events were the first recorded seismically on another planet [1], and then two relatively large (~130-150 m diameter) distant impacts were detected [2-4]. Recently, two additional impacts have been verified, for a total of eight seismically detected impact events on Mars [5]. All six VF seismic events with seismic-acoustic chirps have now been positively associated with fresh craters on Mars.

We use Area-Time Factor (ATF) scalings to derive annualized impact rates from these seismic detections and from a recently updated catalog of orbital observations of new impacts [6]. InSight detected a cratering rate several times higher than that found using orbital detections alone. The measured rates differ between a factor of two to ten, depending on diameter. Several tens of VF events without chirps may also be confirmed as impacts in the future; if all VF events were impacts, the impact rate is very similar to that derived from confirmed impacts, and statistically more robust [7-8]. The impact rate measured by InSight is remarkably close to that predicted for Mars by lunar-based chronology models [9]. Those models include field secondaries, however, so the primary impact rate of meter- to decameter-scale craters is likely higher than previously estimated.

The two largest impacts to occur on Mars in the last few decades occurred only 97 Earth days apart. This close timing is an extremely low-probability temporal coincidence, the cause of which is unclear.

InSight has demonstrated that a seismometer can identify and locate impacts on Mars within a few hundred km through the presence of a seismic-acoustic chirp, and that rare large teleseismic impacts on Mars can be detected globally. Seismic methods of measuring the current impact rate offer a more complete dataset than orbital imaging, although the sample size is small.

Acknowledgments: IJD was funded by NASA InSight PSP grant 80NSSC20K0971.

References: [1] Garcia R F et al., Nat. Geosci., 2022. [4] Posiolova L V et al., Science, 2022. [3] Kim D et al., Science, 2022. [4] Dundas C M et al., GRL, 2022. [5] Daubar I J et al., accepted. [6] Daubar I J et al., Icarus, 2013. [7] Zenhäusern G et al., AGU, 2022. [8] Zenhäusern G, et al., in review. [9] Hartmann W K, Icarus, 2005.