Friday Seminar (28 July 2023) Philippe Lognonné (IPGP)

Title: SEIS on Mars: First legacy after 4 years of seismic monitoring of Mars


SEIS, the international seismometer of NASA’s InSight mission, has operated on Mars from February 2019 until mid-December 2022. For the first time, a robotic seismometer installation was made on the ground followed by wind shield deployment. This allowed the Very-Broad-Band sensors of SEIS to reach ultra-low noise during the much of the night. This lowered the detection threshold to M<3 in the InSight hemisphere and to M~4 in the antipodal one. Noise was much larger during the rest of each day, exceeding the noise recorded on the Moon but still 10 times less than the quietest sites on Earth in the 0.1-1H bandwidth.
     More than 1300 events were detected during two Martian years, including a Mw=4.7 marsquake with Surface waves and Normal modes observations, 34 teleseismic events with determined distances (and azimuths, giving locations, for half of them), 6 impacts confirmed by orbital crater imaging, two with very large craters and a thousand regional crustal high frequency quakes. During the windy period, SEIS also detected several thousand pressure drops associated with atmospheric vortices, and during sunset thousands of very shallow local thermal cracks. Even Phobos eclipses were detected.
     We present a summary of the achievements and successes of the SEIS/InSight science team and services. These include the first models for the subsurface, for the crust below InSight and between InSight and several epicenters, and for the mantle as well as the determination of the core radius and first constraints on the outer liquid core and core-mantle boundary. We present also results in term of anisotropy, attenuation and scattering. Seismic source analyses have determined magnitude, depth and centroid moment tensors for the largest marsquakes and provided better understanding of impact processes, including partitioning of blast energy in the subsurface and atmosphere.
     Finally, the success of InSight contributed to the return of seismology in planetary science, and as of today 4 missions in development have seismometers with hopefully many more to come in the future. We therefore conclude with perspectives for the future of planetary seismology, including on the Moon.
For a review of SEIS results: Mars seismology, Lognonné et al., 2023, Annual Review.doi: 10.1146/annurev-earth-031621-073318. (open access)