Seismic Constraints on the Thickness and Structure of the Martian Crust from InSight

NASA¿s InSight mission [1] has for the first time placed a very broad-band seismometer on the surface of Mars. The Seismic Experiment for Interior Structure (SEIS) [2] has been collecting continuous data since early February 2019. The main focus of InSight is to enhance our understanding of the internal structure and dynamics of Mars, which includes the goal to better constrain the crustal thickness of the planet [3]. Knowing the present-day crustal thickness of Mars has important implications for its thermal evolution [4] as well as for the partitioning of silicates and heat-producing elements between the different layers of Mars. Current estimates for the crustal thickness of Mars are based on modeling the relationship between topography and gravity [5,6], but these studies rely on different assumptions, e.g. on the density of the crust and upper mantle, or the bulk silicate composition of the planet and the crust. The resulting values for the average crustal thickness differ by more than 100%, from 30 km to more than 100 km [7]. New independent constraints from InSight will be based on seismically determining the crustal thickness at the landing site. This single firm measurement of crustal thickness at one point on the planet will allow to constrain both the average crustal thickness of Mars as well as thickness variations across the planet when combined with constraints from gravity and topography [8]. Here we describe the determination of the crustal structure and thickness at the InSight landing site based on seismic receiver functions for three marsquakes compared with autocorrelations of InSight data [9].We acknowledge NASA, CNES, partner agencies and institutions (UKSA, SSO,DLR, JPL, IPGP-CNRS, ETHZ, IC, MPS-MPG) and the operators of JPL, SISMOC, MSDS, IRIS-DMC and PDS for providing SEED SEIS data. InSight data is archived in the PDS, and a full list of archives in the Geosciences, Atmospheres, and Imaging nodes is at https://pds-geosciences.wustl.edu/missions/insight/. This work was partially carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. ©2021, California Institute of Technology. Government sponsorship acknowledge

The interior of Mars as seen by InSight (Invited)

InSight is the first planetary mission dedicated to exploring the whole interior of a planet using geophysical methods, specifically seismology and geodesy. To this end, we observed seismic waves of distant marsquakes and inverted for interior models using differential travel times of phases reflected at the surface (PP, SS...) or the core mantle-boundary (ScS), as well as those converted at crustal interfaces. Compared to previous orbital observations1-3, the seismic data added decisive new insights with consequences for the formation of Mars: The global average crustal thickness of 24-75 km is at the low end of pre-mission estimates5. Together with the the thick lithosphere of 450-600 km5, this requires an enrichment of heat-producing elements in the crust by a factor of 13-20, compared to the primitive mantle. The iron-rich liquid core is 1790-1870 km in radius6, which rules out the existence of an insulating bridgmanite-dominated lower mantle on Mars. The large, and therefore low-density core needs a high amount of light elements. Given the geochemical boundary conditions, Sulfur alone cannot explain the estimated density of ~6 g/cm3 and volatile elements, such as oxygen, carbon or hydrogen are needed in significant amounts. This observation is difficult to reconcile with classical models of late formation from the same material as Earth. We also give an overview of open questions after three years of InSight operation on the surface of Mars, such as the potential existence of an inner core or compositional layers above the CM

An Autonomous Lunar Geophysical Experiment Package (ALGEP) for future space missions

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

Timing of the martian dynamo: New constraints for a core field 4.5 and 3.7 Ga ago

International audienceThe absence of crustal magnetic fields above the martian basins Hellas, Argyre, and Isidis is often interpreted as proof of an early, before 4.1 billion years (Ga) ago, or late, after 3.9 Ga ago, dynamo. We revisit these interpretations using new MAVEN magnetic field data. Weak fields are present over the 4.5-Ga old Borealis basin, with the transition to strong fields correlated with the basin edge. Magnetic fields, confined to a near-surface layer, are also detected above the 3.7-Ga old Lucus Planum. We conclude that a dynamo was present both before and after the formation of the basins Hellas, Utopia, Argyre, and Isidis. A long-lived, Earth-like dynamo is consistent with the absence of magnetization within large basins if the impacts excavated large portions of strongly magnetic crust and exposed deeper material with lower concentrations of magnetic minerals

Full sphere dynamo models for Mars' ancient magnetic field

The ancient martian dynamo is mysterious in both spatial and temporal features. First, strong crustal magnetic fields are concentrated in the southern hemisphere, whereas the crustal magnetic fields in the northern hemisphere are mostly weak. Second, the ancient martian dynamo appears to have been active both before and after the Late Heavy Bombardment, with a shut down in between. These suggest that Mars’ ancient dynamo might be quite different from the conventional geodynamo. Recent seismic measurements from the NASA Mars InSight mission revealed that Mars’ core has a relatively low density, implying that it contains a larger fraction of lighter elements than previously thought. This could possibly prevent Mars from forming a solid inner core during Mars’ early history when the dynamo was active. Here we perform full sphere dynamo simulations to eliminate the influence of an inner core on dynamo behaviors. Furthermore, we investigate the effects of various heat flux perturbations at the core mantle boundary on the morphology of the resulting field and compare to models with small inner cores. These studies provide insight into Mars’ interior, thermal history and core evolution

Seismicity and volcanism on Mars

No active volcanism has been ever observed on Mars, but the planet has many recent traces of volcanic activity and significant parts are covered by volcanic units (1). The InSight seismic dataset localizes more than half of the observed seismic activity in Cerberus Fossae (2), a young (<10 Ma (3)) graben structure in Elysium Planitia, previously interpreted as a result of dyke intrusion (4) or large-scale tectonic stress (3). While initial reports of volcanic tremor (5) could not be confirmed, spectral analysis of marsquakes observed in this region show a warm, elastically weakened source region (6), e.g. due to partial melting at lithospheric depths (7) or deformation due to a mantle plume (8). The significant contribution of this small region to Mars’ global seismic budget (9) means that volcanism shapes the planet’s surface at a higher rate than contraction. We discuss the mechanisms of Martian seismicity as they are currently understood and their relation to orbitally observed tectonics. 1. K. L. Tanaka et al., USGS Geol. Investig., 3292–3292 (2014). 2. S. Ceylan et al. Phys. Earth Planet Inter. 333, 106943 (2022). 3. J. Vetterlein, G. P. Roberts, J. Struct. Geol.32, 394–406 (2010). 4. R. Ernst, et al., Annu. Rev. Earth Planet. Sci.29, 489–534 (2001). 5. S. Kedar et al., JGR Planets, 126 (4) (2021). 6. S. C. Stähler et al., Nat. Astron.6, 1376–1386 (2022). 7. A.-C. Plesa et al., Adv. Geophysics. 63, 179–230 (2022). 8. A. Broquet, J. C. Andrews-Hanna, Nat. Astron., 7, 160–169 (2023). 9. M. Knapmeyer et al., Geophys. Res. Lett., (2023

The Origin of Observed Magnetic Variability for a Sol on Mars From InSight

International audienc

Exploring Martian Magnetic Fields with a Helicopter

The era of helicopter-based surveys on Mars has already begun, creating opportunities for future aerial science investigations with a range of instruments. We argue that magnetometer-based studies can make use of aerial technology to answer some of the key questions regarding early Mars evolution. As such, we discuss mission concepts for a helicopter equipped with a magnetometer on Mars, measurements it would provide, and survey designs that could be implemented. For a range of scenarios, we build magnetization models and test how well structures can be resolved using a range of different inversion approaches. With this work, we provide modeling ground work and recommendations to plan the future of aerial Mars exploration

Seismicity of Elysium Planitia, Mars

At first glance the single tectonic plate setting of Mars implies that most of its deformation is characterized by an intraplate seismicity. Before the InSight mission, it was proposed that Martian seismicity could be driven by contraction of the lithosphere, due to secular cooling of the planet, leading to wide-spread seismicity of thrust style. Orbital images indeed show ubiquitous wrinkle ridges and lobate scarps, which are interpreted as buried thrust faults. However, over the last 3 years, InSight observed a large number of marsquakes and have shown rather a very localized distribution of the seismicity, mainly governed by normal faulting, centered around a relatively young graben system called Cerberus Fossae. We present a working model of seismicity in Cerberus Fossae that addresses the spatial distribution of hypocenters, as well as stress drop inferred from body wave spectra. One class of events, the stronger low frequency marsquakes, are located at 20-40 km depth, near the brittle-ductile transition zone. Associated low stress drops and low corner frequencies are consistent with a heated setting, possibly due to recent or possibly ongoing volcanic activity at depth. A second class of events with higher corner frequencies can plausibly be located at the graben flanks near the surface, possibly related to long-term release of residual stress from the initial opening