The increased interest in crewed and robotic lunar exploration results in a need for high-quality testbeds for instruments, experiments-including seismological ones-and procedures, and for operations training. The LUNA analog facility is a new large-scale testbed on the DLR campus in Cologne, Germany, i.e. located in an urban environment that includes traffic, heavy machinery, and a neighboring international airport. We perform the first characterization of the site and its ambient wavefield, with a focus on anthropogenic signals, as relevant background information for future users of LUNA. Combining active and passive seismic measurements, we derive velocity models for the site down to the bedrock at 152 ± 13 m depth. We provide a preliminary characterization of the ambient noise on campus and discuss and interpret examples of common anthropogenic signals in detail, demonstrating their use e.g. for traffic monitoring with a single station, or as a repeating seismic source. This study showcases how relevant information for future seismological users of a planetary analog facility can be derived with comparatively limited means, the potential of single-station seismology for monitoring airborne and ground traffic, and hints at possible uses of the future permanent seismometer in LUNA.

The composition and layering of the Martian crust provide important constraints on planetary crustal evolution as well as on present-day conditions, e.g., with regard to the presence of liquid water or ice. The seismic data of the InSight mission yielded new and critical information on crustal structure at several locations on Mars. Here, we use rock physical models to investigate the range of lithologies, porosities and alteration scenarios compatible with seismic P- and S-wave velocities as well as vP/vS ratios from InSight. We find that present-day crustal porosity extends to 20-25 km depth at all sampled locations, with large Noachian impacts as main drivers for the creation of porosity, and viscous pore closure as likely agent of removal of porosity at depth, resulting in a discontinuous increase in seismic velocities. Spatially heterogeneous seismic velocities can be related to differences in porosity that could be caused by subsequent localized magmatic activity. At the InSight landing site, where seismic data indicate a four-layered crust, hydrated minerals as traces of aqueous alteration are present throughout the crust, though the water within these minerals could be fairly limited at 0.3 wt% or less. The most likely types of hydrated minerals are also consistent with a post-depositional environment that was limited in water. The velocity increase at about 10 km depth beneath InSight can either be attributed to a change in composition from felsic to basaltic, or to a change in porosity by the deposition of Utopia ejecta. A felsic component to the crust, e.g. due to impact-generated buoyant partial melts, can accordingly not be excluded, but would not be present globally. Seismic and geological constraints for the layer at approximately 200 m to 2000 m depth beneath the lander strongly favor basaltic Noachian sediments saturated with a mixture of up to 10 % ice and brine. However, the lateral extent of this present day aquifer is not constrained by the available data.

The number density of impact craters on a planetary surface is used to determine its age, which requires a model for the production rate of craters of different sizes. On Mars, however, estimates of the production rate of small craters (<60 m) from orbital imagery and from extrapolation of lunar impact data do not match. Here we provide a new independent estimate of the impact rate by analysing the seismic events recorded by the seismometer onboard NASA's InSight lander. Some previously confirmed seismically detected impacts are part of a larger class of marsquakes (very high frequency, VF). Although a non-impact origin cannot be definitively excluded for each VF event, we show that the VF class as a whole is plausibly caused by meteorite impacts. We use an empirical scaling relationship to convert between seismic moment and crater diameter. Applying area and time corrections to derive a global impact rate, we find that 280-360 craters >8 m diameter are formed globally per year, consistent with previously published chronology model rates and above the rates derived from freshly imaged craters. Our work shows that seismology is an effective tool for determining meteoroid impact rates and complements other methods such as orbital imaging.

&lt;p&gt;As international efforts to return humans to the Moon are increasing, ESA&#039;s European Astronaut Center (EAC) and the German Aerospace Center (DLR) are expanding their facilities by the LUNA habitat providing a 700m&amp;#178;-wide testbed covered by 60cm lunar regolith simulant (EAC-1) for astronaut training, including deploying and operating geological and seismic regolith characterization experiments, In Site Resource Utilization technologies (ISRU), biological and chemical experiments by both telerobotic and human activity. The LUNA facility will be operated as collaboration between ESA and DLR&#039;s Microgravity User Support Center (MUSC, see also the presentation by Knapmeyer et al. at this conference).&lt;/p&gt;&lt;p&gt;Geophysical experiments have proven useful to investigate the subsurface structure at the landing sites of e.g. Apollo and Chang&#039;e missions on the Moon, but also at the InSight landing site on Mars, and a seismometer experiment to the lunar far side is already scheduled (Far Side Seismic suite, in 2025). To support future geophysical investigations on the Moon, a first seismic experiment was conducted in June, 2018 at the previously envisioned site of the LUNA facility between the :envihab, a research facility of the Institute for Aerospace Medicine and the European Astronaut Center (EAC) at Cologne-Porz. This passive seismic experiment consisted of a four-element, Y-shaped array of short period seismometers, based on the layout of the Apollo 17 seismic experiment. It recorded regional seismicity as well as urban noise. These measurements will be repeated and expanded by an active seismic refraction experiment at the new construction site just south of the EAC - before, during and after the construction of the facility, before and after the installment of the regolith cover to investigate the impact of the LUNA facility on the data quality and coupling to the ground.&lt;/p&gt;&lt;p&gt;We present details of the 2018 experiment as well as preliminary results, analyzing ambient noise to map the dominant sources of urban noise such as car traffic and airplane traffic at the nearby CGN international airport, the operational noises of the :envihab centrifuge and the wind tunnel as well as nearby construction and drilling.&lt;/p&gt;

After ~4 years of deployment on the martian surface monitoring the planet’s ground motion, the InSight seismometer is now retired. Here, we review the procedures and methods the Marsquake Service (MQS) used to curate the seismic event catalog and describe the content of the catalog. The marsquake catalogue is different from normal catalogues on Earth as it aims to provide the authoritative catalog for the mission, covering the entire planet, using only a single station. As of January 1st, 2023, the MQS catalog contains 1319 seismic events of which 6 are known meteorite impacts. We have also identified 1383 superhigh frequency events that are interpreted as thermal cracking nearby the InSight lander. Late in the project large distant events occurred that allowed MQS to detect surface waves. Multiple events have been associated as impacts using orbital imaging, confirming the MQS single station location procedures. All of these new seismic phases have contributed to advance our understanding of the internal structure of Mars. The marsquake S1222a, the largest event recorded during the mission (MW 4.7) occurred in March 2022 and is also documented in our latest MQS catalog, V13, with many associated seismic phases including both Rayleigh and Love waves, their first-order overtones, and multi-orbiting surface waves that have not been identified in other marsquake records from our previous catalogues. The InSight mission is now closed but the MQS operation continues to analyze the ~4 years of seismic recordings on Mars and a final catalog, including event-specific products such as filter banks, and spectra, is in preparation. This final catalog will inform capabilities and field strategies in geophysical explorations for future martian science missions.

The crater density on planetary surfaces is used to determine their ages throughout the solar system, which requires a model for the rate of meteorite impacts of different sizes. For craters smaller than 30 meters, this rate has been observed from the generation of new craters in repeated orbital images. For larger craters, the rate was extrapolated from the lunar surface ages, taking into account the atmospheric removal of small craters. It has been observed that both estimates do not match for crater diameters smaller than 30 meters. The NASA InSight seismometer SEIS provided a new independent constraint, when it recorded seismic signals of several impacts during its mission. These confirmed impacts are part of a larger class of marsquakes (Very High Frequency, VF), all of which have characteristics consistent with an impact origin. We show that these VFs are plausibly caused by meteorite impacts and derive the impact rate required to explain their numbers. An empirical scaling relationship is used to convert between seismic moment and crater diameter. We apply area and time corrections to derive a global impact rate and find that the derived rate is 210--290 craters >8m globally per year, consistent with previously published chronology model rates and above the rates derived from freshly imaged craters.

&lt;p&gt;Recently, NASA&amp;#8217;s InSight mission has shown the value of geophysical landers by greatly increasing our knowledge of the interior of Mars. Correspondingly, geophysical experiments are also of great relevance to lunar exploration: a number of geophysical experiments were proposed in response to the ESA&#039;s 2020 call for ideas for a scientific utilization of the large logistics lander (Argonaut). Geophysical payloads are already planned for the Moon, e.g. the Farside Seismic Suite will land a broad-band seismometer in 2025. We here present how the &lt;em&gt;LUNA Habitat&lt;/em&gt; training facility under construction in Cologne, Germany, can contribute to the development and testing of lunar geophysical instrumentation.&lt;/p&gt; &lt;p&gt;The about 700 square meters of the &lt;em&gt;LUNA Habitat&lt;/em&gt; will be covered by 60 cm of EAC-1 regolith simulant on most of the area. On an area of 140 square meters, regolith depth increases to 3 m along a sloping bottom (25&amp;#176; and 40&amp;#176;). This part of &lt;em&gt;LUNA&lt;/em&gt; provides an invisible, but explorable underground structure suitable for seismic profiling, ground penetrating radar, geoelectrics, geomagnetics and other techniques, as well as sufficient depth for drilling, subsurface sampling, and deployment of heat flow probes. Sculpting craters and even caves in the regolith, as well as cooling small portions of it, is envisioned. Support by the facility will include personnel with experience in geophysical measurements and data analysis, an end-to-end operational environment including a remote control center with standard communication technology, and, last but not least, training of astronauts in co-operation with robotic units to operate the equipment in lunar surface suits and under gravity offloading.&lt;/p&gt; &lt;p&gt;A four-element, Y-shaped array of short period seismometers, based on the layout of the Apollo 17 seismic experiment, will be deployed on the &lt;em&gt;LUNA&lt;/em&gt; construction site before erecting the building to record seismic noise sources (car traffic on the DLR campus, the &lt;em&gt;ENVIHAB&lt;/em&gt; short arm centrifuge, wind tunnel discharges, air traffic on the nearby CGN international airport etc.). It will also allow for ambient noise analysis aimed at the underground structure, which is expected to consist of Rhine sediments. An active refraction seismic experiment and the deployment of 12 nodal sensors will further aid in site characterization. &lt;em&gt;LUNA&lt;/em&gt; will have a concrete floor of up to 60 cm thickness, but with a structured underside for static reasons. The array will be re-deployed on the concrete once the hall is erected to characterize in how far the new high-velocity layer hides the underlying sediments from seismic observation. After completion of &lt;em&gt;LUNA&lt;/em&gt;, the effect of the regolith cover on seismic recordings will be characterized by a third array deployment. Documentation of construction details, especially steel enforcing in the concrete, is foreseen. &amp;#160;A broad-band seismometer will be installed in the &lt;em&gt;LUNA Habitat&lt;/em&gt; permanently, once construction is finished, to support the identification of artificial noise sources and local seismicity in the recordings of customer instruments, and monitor possible changes in the background e.g. due to new buildings or other large-scale research facilities on the DLR campus.&lt;/p&gt;

The current Martian cratering rate has been determined either from repeated orbital imaging (e.g.[1][2]), or using lunar rates extended to Mars in combination with crater counting [3]. Eight seismic events detected by the NASA InSight seismometer have been confirmed as impacts by orbital imaging [4]. Six of those events are part of the Very High Frequency (VF) group of marsquakes, which consists of 70 events in total. The impact signals are very similar to other VF events, suggesting that more or all VF events could be impact related. The unique characteristics of VF events, such as a long seismic coda interpreted as a result of shallow source in a strongly scattering near-surface layer [5] and their temporal and spatial distributions, are consistent with impact origin.Assuming all high quality VF events are impacts allows us to place a novel constraint on the impact rate on Mars, independent of the formation of easy-to-spot large blast zones, necessary to identify fresh craters in orbital images. We test the compatibility with the existing cratering rate estimates by using two approaches to derive a first seismically constrained impact rate for Mars. First, we use the Gutenberg-Richter law to determine the slope of the VF event magnitude-frequency distribution. The impact rate is derived by applying a relationship between seismic moment and crater diameter [6]. We refine our estimates by extrapolating the detectability of each event using a semi-empirical relationship between crater size and seismic amplitude [6]. We find that both approaches give similar rates, varying slightly depending on the detectability conditions assumed by each method. The cumulative rates N(D≥8m) = 1-4x10-6 /km2/yr are higher than those from previous imaging studies, but consistent with isochron rates [3].The discrepancy with imaging-based rates could indicate that there are impacts which are missed in imagery due to absent blast zones or that are located in unfavourable terrain, unaccounted for in the imaging-based area correction. References:[1] Daubar et al. (2013). doi: 10.1016/j.icarus.2013.04.009[2] Daubar et al. (2022). doi: 10.1029/2021JE007145[3] Hartmann (2005). doi: 10.1016/j.icarus.2004.11.023[4] Daubar et al. (2023). InSight Seismic Events Confirmed as Impacts Thus Far. Lunar and Planetary Science Conference 2023 abstract.[5] van Driel et al. (2021). doi: 10.1029/2020JE006670[6] Wójcicka et al. (2023). Impact Rate on Mars Implied by Seismic Observations. Lunar and Planetary Science Conference 2023 abstract.

The seismic activity of a planet can be described by the corner magnitude, events larger than which are extremely unlikely, and the seismic moment rate, the long-term average of annual seismic moment release. Marsquake S1222a proves large enough to be representative of the global activity of Mars and places observational constraints on the moment rate. The magnitude-frequency distribution of relevant Marsquakes indicates a b $b$-value of 1.06. The moment rate is likely between 1.55x1015Nm/a $1.55\times {10}<^>{15}\mathrm{N}\mathrm{m}/\mathrm{a}$ and 1.97x1018Nm/a $1.97\times {10}<^>{18}\mathrm{N}\mathrm{m}/\mathrm{a}$, with a marginal distribution peaking at 4.9x1016Nm/a $4.9\times {10}<^>{16}\mathrm{N}\mathrm{m}/\mathrm{a}$. Comparing this with pre-InSight estimations shows that these tended to overestimate the moment rate, and that 30% or more of the tectonic deformation may occur silently, whereas the seismicity is probably restricted to localized centers rather than spread over the entire planet.

We present the first observations of seismic waves propagating through the core of Mars. These observations, made using seismic data collected by the InSight geophysical mission, have allowed us to construct the first seismically constrained models for the elastic properties of Mars' core. We observe core-transiting seismic phase SKS from two farside seismic events detected on Mars and measure the travel times of SKS relative to mantle traversing body waves. SKS travels through the core as a compressional wave, providing information about bulk modulus and density. We perform probabilistic inversions using the core-sensitive relative travel times together with gross geophysical data and travel times from other, more proximal, seismic events to seek the equation of state parameters that best describe the liquid iron-alloy core. Our inversions provide constraints on the velocities in Mars' core and are used to develop the first seismically based estimates of its composition. We show that models informed by our SKS data favor a somewhat smaller (median core radius = 1,780 to 1,810 km) and denser (core density = 6.2 to 6.3 g/cm3) core compared to previous estimates, with a P-wave velocity of 4.9 to 5.0 km/s at the core-mantle boundary, with the composition and structure of the mantle as a dominant source of uncertainty. We infer from our models that Mars' core contains a median of 20 to 22 wt% light alloying elements when we consider sulfur, oxygen, carbon, and hydrogen. These data can be used to inform models of planetary accretion, composition, and evolution.

The InSight mission collected an astounding seismic dataset from Mars during more than four years (1450 sols) of operation until it was retired on 21 December 2022.The Marsquake Service MQS detected more than 1300 events of seismic origins. Two of these events (S1000a and S1094b) were later confirmed as distant impacts (Figure 1), with magnitudes of MWMa=4.0 and 4.2 and crater diameters of 130 and 150 m, respectively. Finally, the largest marsquake (S1222a, MWMa=4.6) that occurred during InSight's lifetime was recorded on May 4, 2022.Here, we present the current understanding of the Martian seismicity and the different types of events we observed on Mars, based on the data collected over the whole mission.Low-frequency (LF) and broadband (BB)The LF family of events include energy predominantly below 1 Hz. They are similar to teleseismic events observed on Earth, and clear P and S waves are often identified. The hypocenter is known for about half of the recorded LF-BB events, owing to the difficulty of determining back-azimuth and in some cases also distance for the smaller events. The following elements are now understood:Seismicity appears to be located only in few spots around Mars (Figure 2) and no tectonic events were located within 25° from the InSight station. A large number of LF-BB events are located 26–30° from the station, interpreted to be associated with the active dynamics of the volcanic Cerberus Fossae area. A group of events show only a weak S-wave energy and are aligned using the P-wave and length of its coda to around 46°. Their tectonic origin is yet unknown. A few events are located around 60° with relatively emergent P- and S-wave energy. Two large events (S0976a and S1000a) lie beyond the core shadow and have PP and SS phases; S0976a in the Valles Marineris region 146° away from InSight, and S1000a as the result of a meteoritic impact. A number of events of uncertain location are clustered in the same distance, around 100-120° distance. LF events have the largest magnitudes with S1222a reaching MWMa=4.6 and a few others at or above MWMa=3.5. High-frequency (HF) The HF family of events are predominantly at and above the 2.4 Hz, local subsurface resonance. The HF events have magnitudes below MWMa 2.5 and originate from a distance range of 25–30°, likely a single area in the central Cerberus Fossae region, as very shallow events associated to active volcanic dykes. Very high frequency (VF):A small number of HF events are characterized by higher frequency content, up to 20–30 Hz with a notable amplification on the horizontal components at very high frequency, and are termed VF events. The amplification is plausibly explained by the local subsurface structure. These events are observed only close to the lander. Remote imaging of recent craters and the presence of a distinctive acoustic signal confirmed that the closest events were produced by meteoric impacts. Investigations are being conducted to understand if other VF events can be confirmed as impacts, too.

The InSight (Interior exploration using Seismic Investigations, Geodesy and Heat Transport) lander provides the unique opportunity to explore the seismicity and the present-day seismic structure of Mars (Banerdt et al., 2020; Lognone et al., 2020; Giardini et al. 2020). Since the deployment of the seismometer SEIS, hundreds of seismic events have been recorded, and information about these events is available in the seismic catalogs produced by the Mars Quake Service (MQS) (Clinton et al., 2021; MQS Catalog V9). Fig. 1: Computational framework used in this study to incorporate thermal models in numerical wave simulations: Spherical harmonic Vp, Vs, and density models based on thermal simulations (e.g., Plesa et al., 2021, top-left) are expanded on a spectral-element mesh (Ciardelli et al. 2022, bottom-left) at desired resolutions. Sample synthetic 3D and 1D seismograms at 0, 90, 180, and 270-degree azimuths and 29 and 74-degree epicentral distances computed for the thermal model Case65-TAY (Plesa et al. 2021) with crustal thickness model 3200_1_DWTh2Ref1 (Wieczorek & Zuber 2004) and its average, respectively, shown on the right. Topography, rotation, ellipticity, gravity, and PREM attenuation are all taken into account during simulations with the SPECFEM3D_GLOBE package (Komatitsch & Tromp 2002). The source is the moment tensor solution of event S0235b located at the InSight lander with a higher scalar moment. The seismograms are bandpass filtered between 10-100 s. InSight’s seismic recordings have been used to constrain the thickness of the crust (Knapmeyer-Endrun et al., 2021), the upper mantle structure (Khan et al., 2021) and the size of the martian core (Stähler et al., 2021), which has recently been updated by Duran et al. (2022). The latest largest moment magnitude ~5 event provides an unprecedented opportunity to investigate the interior of Mars, and to constrain its seismic structure using both body and surface waves. Seismic wavespeeds can present substantial variations in particular in the lithosphere where they follow the same pattern as the crustal thickness (Plesa et al., 2021). These variations can extend to 400 km or deeper for models with a thick thermal lithosphere as suggested by the analysis of seismic events. In this study, we investigate the 3D structural effects on the seismic body and surface waveforms, such as surface topography, crustal thickness variations, etc., and combine them with thermal evolution models using 3D seismic wave simulations (Fig. 1). We quantify the difference between 1D radially symmetric seismic models, radially symmetric models with 3D crustal thickness variations and topography, and full 3D seismic wavespeeds caused by the variations of crust-mantle interface and mantle thermal anomalies (i.e., mantle plumes) derived from thermal simulations. In our simulations, we include the latest crustal thickness models of Mars (Wieczorek et al., 2022) derived from gravity and topography data and constrained by seismic measurements from InSight. In a first step, we use the radially symmetric structure constrained by the InSight data and similar to the study of Bozdag et al. (2017), and investigate the effect of surface topography, 3D crustal thickness variations, attenuation, and moment tensor solutions constrained by Insight data on body and surface waves. As expected, surface waveforms are most affected by the crustal dichotomy, which also highlights the importance of anelasticity in explaining multi-orbit Rayleigh and Love waves. In a second step, we explore the effect of a 3D mantle derived from thermal evolution models on body and surface waves. We use seismic models that are representative of various thermal conditions obtained by 3D geodynamical models. Similar to Plesa et al. (2021), we use the present-day thermal state and associated temperature variations to calculate P and S wavespeeds that are then used to simulate the seismic wave propagation. We use the 3D global wave propagation solver SPECFEM3D_GLOBE package (Komatitsch & Tromp 2002) for numerical simulations, freely available from CIG (Computational Infrastructure for Geodynamics), and compare synthetics to the prominent marsquakes, including the latest largest moment magnitude ~5 event. References Banerdt et al., 2020. Initial results from the InSight mission on Mars. Nature Geoscience, 13, 183– 189. Bozdağ et al., 2017. Simulations of seismic wave propagation on Mars, Space Science Reviews, doi: 10.1007/s11214-017-0350-z. Ciardelli et al., 2022. SphGLLTools: A toolbox for visualization of large seismic model files based on 3D spectral-element meshes, Computers & Geosciences, 159, 105007, https://doi.org/10.1016/j.cageo.2021.105007. Clinton et al. (2021). The Marsquake catalogue from InSight, sols 0-478. Physics of the Earth and Planetary Interiors, 310, 106595. https://doi.org/10.1016/j.pepi.2020.106595 Durán et al., “Seismology on Mars: An analysis of direct, reflected, and converted seismic body waves with implications for interior structure,” Physics of the Earth and Planetary Interiors, vol. 325, p. 106 851, 2022, issn: 0031-9201. doi: 10.1016/j.pepi.2022.106851. Giardini et al. (2020). The seismicity of Mars. Nature Geoscience, 13(3), 205– 212. Khan et al., “Upper mantle structure of Mars from InSight seismic data,” Science, vol. 373, no. 6553, pp. 434–438, 2021, issn: 0036-8075. doi: 10.1126/science.abf2966. Knapmeyer-Endrun et al., 2021. Thickness and structure of the Martian crust from InSight seismic data, Science, 6553(373), 438-443, DOI: 10.1126/science.abf8966. Komatitsch & Tromp, 2002. Spectral-element simulations of global seismic wave propagation – I. Validation, Geophysical Journal International, 149(2), 390–412. Lognonné et al., 2019. SEIS: Insight's seismic experiment for internal structure of Mars. Space Science Reviews, 215(1), 12. Plesa et al., 2021. Seismic Velocities Distribution in a 3D Mantle: Implications for InSight Measurements, Journal of Geophysical Research-Planets, https://doi.org/10.1029/2020JE006755. Stähler et al., 2021 “Seismic detection of the martian core,” Science, vol. 373, no. 6553, pp. 443–448, 2021, issn: 0036- 8075. doi: 10.1126/science.abi7730. Wieczorek & Zuber, 2004. Thickness of the martian crust: Improved constraints from geoid-to-topography ratios. J. Geophys. Res., Planets 109(E1), E01009. doi:10.1029/2003JE002153 Wieczorek et al., 2022. InSight constraints on the global character of the Martian crust. Journal of Geophysical Research: Planets, e2022JE007298.

When NASA's InSight lander touched down in Elysium Planitia, Mars, in November 2018 and deployed its seismometer SEIS, it ushered in a new age for planetary seismology - more than 40 years after the first attempt to record marsquakes with the Viking missions. SEIS, an extremely sensitive instrument, has by now provided near continuous seismic records for more than 3 years. Its rich dataset shows Mars to be seismically active, with over 1,300 marsquakes detected so far, mostly with magnitudes below 4. Despite their small size, these quakes provide important and unprecedented constraints on the interior structure of the planet, from the shallow subsurface via the crust, the lithosphere, and the mantle transition zone down to the core, and allow to study Martian tectonics and thermo-chemical evolution. Single-station seismology has answered some of the big questions about the interior of our planetary neighbour, and this contribution gives an overview of results and surprises so far.

The InSight mission has measured the seismicity of Mars since February 2019 and has enabled the investigation of tectonics on the surface of another planet for the first time. Its dataset shows that most of the widely distributed surface faults are not seismically active, and that seismicity is mostly originating from a single population of tectonic structures, the Cerberus Fossae. We show that the spectral character of deeper low-frequency marsquakes suggests a structurally weak, potentially warm source region consistent with recent magmatic activity at depths of 30–50 km. We further show that high-frequency marsquakes occur distributed along the Cerberus Fossae, in the brittle, shallow part, potentially in fault planes associated with the graben flanks. Together, these quakes release an annual seismic moment of 1.4–5.6 × 10 15 N m yr −1 or at least half the seismicity of the entire planet. Our findings confirm that the Cerberus Fossae represents a unique tectonic setting shaped by current day magmatic processes and locally elevated heat flow.

For over three Earth years the Marsquake Service has been analyzing the data sent back from the Seismic Experiment for Interior Structure—the seismometer placed on the surface of Mars by NASA’s InSight lander. Although by October 2021, the Mars seismic catalog included 951 events, until recently all these events have been assessed as lying within a radius of 100° of InSight. Here we report two distant events that occurred within days of each other, located on the far side of Mars, giving us our first glimpse into Mars’ core shadow zone. The first event, recorded on 25 August 2021 (InSight sol 976), shows clear polarized arrivals that we interpret to be PP and SS phases at low frequencies and locates to Valles Marineris, 146° ± 7° from InSight. The second event, occurring on 18 September 2021 (sol 1000), has significantly more broadband energy with emergent PP and SS arrivals, and a weak phase arriving before PP that we interpret as Pdiff. Considering uncertain pick times and poorly constrained travel times for Pdiff, we estimate this event is at a distance between 107° and 147° from InSight. With magnitudes of MwMa 4.2 and 4.1, respectively, these are the largest seismic events recorded so far on Mars.

Geophysical observations will provide key information about the inner structure of the planets and satellites and understanding the internal structure is a strong constraint on the bulk composition and thermal evolution of these bodies. Thus, geophysical observations are a key to uncovering the origin and evolution of the Moon. In this article, we propose the development of an autonomous lunar geophysical experiment package, composed of a suite of instruments and a central station with standardized interface, which can be installed on various future lunar missions. By fixing the interface between instruments and the central station, it would be possible to easily configure an appropriate experiment package for different missions. We describe here a series of geophysical instruments that may be included as part of the geophysical package: a seismometer, a magnetometer, a heat flow probe, and a laser reflector. These instruments will provide mechanical, thermal, and geodetic parameters of the Moon that are strongly related to the internal structure. We discuss the functionality required for future geophysical observations of the Moon, including the development of the central station that will be used commonly by different payloads.

On the 1222nd sol of the InSight mission (or May the Fourth of 2022), a seismic event was detected that turned out to be the largest marsquake recorded so far. At a moment magnitude of 4.7, event S1222a released as much seismic moment as all seismic events previously catalogued by InSight together, and greatly surpasses the second largest event, S0976a.The frequency of occurrence of earthquakes follows a power law with an exponent (the b value) close to 1 over a wide range of magnitudes. The class of Low Frequency marsquakes, to which S1222a belongs, shows a similar behaviour. At low magnitudes, the slope of the cumulative distribution suggests that the InSight marsquake catalog for Low Frequency events is representative for events with moment magnitude exceeding 3 (Figure 1). Up to and including the occurrence of event S0976a one could however guess that events larger than magnitude approx. 3.6 might be less frequent than predicted by this power law. Event S1222a mends this apparent decrease, and the b value derived from all events is 1 within the formal uncertainty. Hence the resulting distribution follows a power law for events exceeding magnitude 3.Figure 1 Size frequency distribution of Low Frequency and Broadband events. Red: status before occurrence of S1222a, blue: afterwards. The dashed lines represent the Maximum Likelihood solutions for fitting a Power Law distribution, with b-values as indicated in the legend.Since S0976a occurred at an epicentral distance of about 140° (Horleston et al., 2022) at night time(02:26 LMST), but was recorded with amplitudes high enough to be visible during typical day time noise, we can infer that the catalog is complete for events the size of S0976a or larger. Since the slope of the distribution appears to be stable over the entire magnitude range from 3 up to that of S1222a, we conclude that the catalogue of Low Frequency events is not only representative, but complete for events larger than 3.The magnitude of S1222a is slightly to the right of the value predicted by the power law, but, compared to other deviations, not excessively so. Also, the distribution does not show an indication of increasing slope any more. With about 30 events of magnitude 3 during the 3.3 years of InSight observations so far, this suggests that events larger than S1222a can be expected with respective recurrence rates: A magnitude 5 event appears likely about once in 11 years, i.e. on a decadal scale.We use the approach of Knapmeyer et al. (2018) to estimate the seismic moment rate of Mars, and also the corner magnitude above which the size-frequency distribution becomes much steeper and events larger than the corner magnitude extremely unlikely (our analysis uses the Tapered Gutenberg-Richter distribution with an exponential roll-off above the corner frequency). The simple idea of Knapmeyer et al. (2018) was that, since a few large events release most of the seismic moment, the moment of the largest event ever observed, scaled with the duration covered by the catalog and a factor depending on b value and corner moment, provides a good estimation of the moment rate. Including not only the one largest, but the n largest events (with n between 1 and 10 or so) provides an even better estimation. In the 2018 study we have shown that the approach yields a surprisingly good estimation of the Earth's moment rate after a few months of registration, rather than after the many decades necessary to witness a magnitude 9 event.We employ here an estimation based on the 5 largest events in the catalog. Knapmeyer et al. (2018) have shown that this low number may already provide a reasonable rate estimate. At the same time we attempt to avoid using events too small to be globally detectable. Future analyses will show if the use of 5 events is actually the best choice. The inclusion of event S1222a shifts the estimated moment rate slightly upwards, as well as the estimated corner moment. Figure 2 shows that both parameters are slightly below those of the WeakMany model of Knapmeyer et al., (2006). Compared to the catalog from before its occurrence, the parameter modifications due to S1222a are hardly significant (and not shown here). At least as important is the reduction of the uncertainty region in the moment-rate / corner-moment parameter space. We cannot yet exclude that the moment rate of Mars is as low as that of the Moon, but if it were, it would be rather unlikely to observe the event sequence that InSight observed.Figure 2 Estimation of Moment Rate and Corner Moment. For each Pixel, 10000 synthetic catalogs were evaluated to compare their parameters with the five largest events from the InSight catalog (KS5 estimation). Colour indicates the probability that the five largest events drawn from a tapered Gutenberg Richter distribution in 3.3 years reproduce the KS5 estimation obtained from the observed events, to within an 80 % interdecile around the median. The vertical line indicates the moment rate for the Moon (observed, from Shallow Moonquakes), markers indicate the WeakMany and Medium models of Knapmeyer et al. (2006). The moment rate of the Earth corresponds to an equivalent magnitude of about 8.5 (Knapmeyer et al., 2018). Horizontal lines indicate the magnitude of the largest event and its uncertainty. The maximum of the distribution is marked by a small white circle.ReferencesHorleston, A. C., et al. (2022). The Far Side of Mars: Two Distant Marsquakes Detected by InSight, The Seismic Record. 2(2), 88–99, doi: 10.1785/0320220007Knapmeyer, M., Oberst, J., Hauber, E., Wählisch, M., Deuchler, C., Wagner, R. (2006). Working models for spatial distribution and level of Mars' seismicity. Journal of Geophysical Research, vol. 111, E11006, doi:10.1029/2006JE002708Knapmeyer, M., et al. (2018). Estimation of the Seismic Moment Rate from an Incomplete Seismicity Catalog, in the Context of the InSight Mission to Mars, Bull. Seis. Soc. Am., vol. 109, No. 3, 1125-1147, doi: 10.1785/0120180258Taylor et al., (2013). Estimates of seismic activity on the Cerberus Fossae region of Mars, Journal of Geophysical Research, vol. 118, 2570-2581, doi:10.1002/2013JE004469

The boundary between rocky mantle and iron core constitutes the most significant discontinuity within the terrestrial planets, the core itself is one of the largest, if not the largest, structural features of these planets with consequences for the entire geodynamical evolution of the planet: It contains a significant amount of the planets iron inventory, and planetary magnetic fields are generated within the core. We take the occasion of the first seismic determination of the core size of Mars to look back into the development of theories about planetary interiors and cores, starting with early mythological narrations. The renaissance produced the first geologically and physically motivated inferences about the Earth's core, which were extended to the Moon, Mars and other planets in the 19th century. Theories based on telescopic observations soon found their limits, and spacecraft missions to the Moon and to Mars provided the necessary precision of radius, mass, and moment of inertia determinations, and finally seismic data, to determine the core radius precisely. Meanwhile, interest extended to beyond the solar system, and we discuss the observational foundations on which models for the core size of exoplanets are based.

The NASA InSight mission has helped to measure the deep interior of Mars using observations of seismic waves excited by marsquakes. Currently, installation of seismometers on the moon is foreseen. We review the case for seismic experiments on all major planetary bodies of the solar system. We discuss scientific goals in accordance with the Decadal survey for planetary science and astrobiology and the ESA Voyage 2050 program as well as technical challenges and potential mission concepts, to answer the question: Where could we do seismology on other planets and why should we do it?

Seismic measurements of the InSight lander confirm tectonic activity in an extraterrestrial geological system for the first time: the large graben system Cerberus Fossae (Giardini et al., 2020). In-depth analysis of available marsquakes thus allows unprecedented geophysical characterization of an active extensional structure on Mars, using the epicenter locations, depths, magnitudes, focal mechanisms and spectral character from marsquake data. In summary, InSight seismic data show: * Both major families of marsquakes, characterized by low and high frequency content, LF and HF events respectively, can be located on central and eastern parts of the graben system (Zenhäusern et al., 2022). This is in agreement with the decrease in structural maturity towards the East as inferred from orbital images (Perrin et al., 2022). Specifically, we find that the distance distribution of the larger LF marsquakes peaks near Zunil crater and the Cerberus Mantling Unit, which has been hypothesized to be of volcanic origin (Horvath et al., 2021). * The two event families correspond to two depth regimes: LF marsquake hypocenters are located at about 15-50 km, based on identification of depth phases (Durán et al., 2022; Stähler et al., 2021), while the HF marsquakes are likely much shallower and at 0-5 km depth (van Driel et al., 2021). * Estimated magnitudes are between 2.8 and 3.8 (Böse et al., 2021; Clinton et al., 2021), resulting in a total seismic moment release within Cerberus Fossae of 1.4-5.6×1015 Nm/yr, or at least half of the observed seismic moment release of the entire planet. * Estimated focal mechanisms of deep marsquakes (Brinkman et al., 2021; Jacob et al., 2022) show primarily extensional normal faulting, compatible with the image-based interpretation as a graben system. * The deeper LF marsquakes are “slow” compared to terrestrial quakes, i.e. lack high frequency energy in the seismic body waves. This can be explained by low stress drop and a weak, potentially warm source region. We propose a geological model that integrates these observations: The deep LF quakes are caused by the large-scale extensional stress pattern, while fractures occur in this specific location only due to the presence of a dike from Elysium Mons. The shallow seismicity is caused in a brittle region near the surface, potentially on the subsurface continuation of the graben flanks. This could potentially explain the seasonality of the HF event rate, which peaks at the times of maximum solar illumination of the bottom in the Cerberus Fossae (Knapmeyer et al., 2021). While a small number of large endogenic marsquakes have been observed in other regions on Mars, specifically Southern Tharsis (Horleston et al., 2022), Cerberus Fossae represents a uniquely active seismic setting. Current day tectonic activity seems to be driven by volcanic processes, and furthermore, we find no trace of seismic activity on compressional thrust faults on Mars, as opposed to the models of seismicity driven by secular cooling and lithospheric contraction. References: Böse, M., et al., 2021. Magnitude Scales for Marsquakes Calibrated from InSight Data. Bull. Seismol. Soc. Am. https://doi.org/10.1785/0120210045 Brinkman, N., et al., 2021. First focal mechanisms of marsquakes. J. Geophys. Res. Planets. https://doi.org/10.1029/2020je006546 Clinton, J.F., et al., 2021. The Marsquake catalogue from InSight, sols 0–478. Phys. Earth Planet. Inter. 310. https://doi.org/10.1016/j.pepi.2020.106595 Durán, C., et al., 2022. Seismology on Mars: An analysis of direct, reflected, and converted seismic body waves with implications for interior structure. Phys. Earth Planet. Inter. 325, 106851. https://doi.org/10.1016/j.pepi.2022.106851 Giardini, D., et al., 2020. The seismicity of Mars. Nat. Geosci. 13, 205–212. https://doi.org/10.1038/s41561-020-0539-8 Horleston, A., et al., 2022. The far side of Mars - two distant marsquakes detected by InSight. Seism. Rec. accepted. Horvath, D.G., et al., 2021. Evidence for geologically recent explosive volcanism in Elysium Planitia, Mars. Icarus 365, 114499. https://doi.org/10.1016/j.icarus.2021.114499 Jacob, A., et al., 2022. Seismic sources of InSight marsquakes and seismotectonic context of Elysium Planitia, Mars. Tectonophysics in revision. Knapmeyer, M., et al., 2021. Seasonal seismic activity on Mars. Earth Planet. Sci. Lett. 576, 117171. https://doi.org/10.1016/j.epsl.2021.117171 Perrin, C., et al., 2022. Geometry and Segmentation of Cerberus Fossae, Mars: Implications for Marsquake Properties. J. Geophys. Res. Planets 127, e2021JE007118. https://doi.org/10.1029/2021JE007118 Stähler, S.C., et al., 2021. Seismic detection of the martian core. Science 373, 443–448. https://doi.org/10.1126/science.abi7730 van Driel, M., et al., 2021. High-Frequency Seismic Events on Mars Observed by InSight. J. Geophys. Res. Planets 126, e2020JE006670. https://doi.org/10.1029/2020JE006670 Zenhäusern, G., et al., 2022. Low Frequency Marsquakes and Where to Find Them: Back Azimuth Determination Using a Polarization Analysis Approach. ArXiv220412959 Phys.