Europlanet Science Congress 2022
Palacio de Congresos de Granada, Spain
18 – 23 September 2022
Europlanet Science Congress 2022
Palacio de Congresos de Granada, Spain
18 September – 23 September 2022

TP12

Planetary Seismology and Geophysics

The investigations of planet's interior are key to understand the origin and evolution of the planet. Seismology has proven to be a very powerful tool for determining the internal structure of Earth, leading to the direct measurement of the thickness of crust, mantle and core, as well as obtaining detailed 3-dimensional structure models.

The first successful extraterrestrial seismic experiment was carried out by the Apollo missions from 1969 to 1972, when a network of seismometers was deployed along with other in situ geophysical instruments. A renaissance of planetary seismology occurred almost 50 years later, when the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander deployed successfully a seismometer on the surface of Mars. Since its landing, on November 26, 2018, data from this mission have shown that Mars is a seismically active planet, and have placed key constraints on the thickness of the crust, core radius, and the presence of a low velocity zone in the upper mantle. Improved constraints for the interior structure of both the Moon and Mars have since been obtained through the joint analysis of seismic datasets with other geophysical observables, such as gravity, surface topography, magnetic field measurements, and heat flow.

This session invites abstracts concerning the following topics:
- Studies based on the analysis of existing extraterrestrial seismic datasets.
- Analyses of geophysical data that rely on seismic constraints or that offer information for the design of future seismic experiments.
- Works that propose new methodologies and mission concepts for future extraterrestrial seismic experiments.

Co-organized by MITM
Convener: Philippe Lognonné | Co-conveners: Melanie Drilleau, Foivos Karakostas, Mark Panning, Simon C. Stähler, Mark Wieczorek
Orals
| Tue, 20 Sep, 15:30–17:00 (CEST)|Room Machado, Wed, 21 Sep, 10:00–11:30 (CEST)|Room Machado
Posters
| Attendance Mon, 19 Sep, 18:45–20:15 (CEST)|Poster area Level 1

Orals: Tue, 20 Sep | Room Machado

Chairpersons: Philippe Lognonné, Mark Panning, Mark Wieczorek
15:30–15:45
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EPSC2022-773
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solicited
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MI
Bruce Banerdt and the InSight Science Team

After an auspicious beginning, with the Ranger, Apollo and Viking missions carrying multiple seismometers into space, planetary seismology lay dormant for 40 years, save for a cruelly-extinguished hope on the Mars’96 mission. InSight put an end to this seismological drought with its landing on Mars in November, 2018, and subsequent deployment of the SEIS instrument two months later (Banerdt et al., 2020; Lognonné et al., 2019, 2020).

After a slow start (uncannily, no seismic events were detected for the first two months after deployment), the subsequent three-plus years  have been an unqualified triumph for planetary seismology. Roughly 2700 seismic events have been detected and cataloged (Clinton et al., 2021; Ceylan et al., 2022), ranging from more than a thousand tiny SF events, thought to be locally-sourced thermal events, to a massive magnitude 5 marsquake more than 2000 km away, but still with a signal-to-noise ratio over 160,000. This catalog includes more than 30 Low Frequency and Broad-Band marsquake signals of quality A or B, meaning they have clear body-wave phase arrivals and, in the case of quality A, identifiable polarization. These have been clearly identified as teleseismic events, which taken together describe a set of ray paths that have probed the interior of the planet from the surface down to its core.

The analysis of this seismic data set has already transformed our knowledge of the interior structure of Mars. We have for the first time been able to directly measure the thickness of the crust beneath InSight (Knapmeyer-Endrun, et al., 2021; Kim et al., 2021; Durán et al., 2022; Drilleau et al., 2022) and the size of the martian core (Stähler et al., 2021). Analysis of the data has further allowed us to place tight constraints on the density of the core and crust, and the thermal profile of the mantle (Stähler et al., 2021; Khan et al., 2021, 2022; Wieczorek et al., 2022). In addition, SEIS’s observations have proved invaluable for studying the near-surface structure beneath InSight on scales from tens of centimeters to hundreds of meters (e.g., Lognonné et al., 2020; Banerdt et al., 2020; Kenda et al., 2020; Hobiger et al., 2021; Murdoch et al., 2021; Compaire et al., 2021, 2022).

InSight’s seismometer has also been able to study the current tectonics of Mars, providing a measure of the size distribution of seismic events (and thus a window into the rate of moment release) and a map of their geographic distribution (in particular, the strong concentration of Eastern hemisphere activity around Cerberus Fossae; Giardini et al., 2020; Stähler et al., 2022) and even revealing the source mechanisms responsible for some marsquakes, from which the orientation of stresses in the lithosphere can be inferred (Brinkman et al., 2021).

InSight and SEIS have proven conclusively the value of planetary seismology in general, and a single high-quality seismometer in particular, in understanding the solid planets of our solar system. The results described in this talk are only a subset of the work that has been done, and was derived from just the first round of analysis of SEIS data. As the seismic community becomes more familiar with the data set and it becomes more widely used, we can expect new insights into the geophysics of Mars for decades to come.

 

References:

Banerdt, W. B., and Smrekar, S. E., et al., 2020. Initial results from the InSight mission on Mars. Nat. Geosci. 13, 183–189. https://doi.org/10.1038/s41561-020-0544-y

Brinkman, N., et al., 2021. First focal mechanisms of marsquakes, J. Geophys. Res. Planets, e2020JE006546. https://doi.org/10.1029/2020JE006546

Ceylan, S., et al., 2022. The marsquake catalogue from InSight, sols 0-1011, Phys. Earth Planet. Int., in press.

Clinton, J., et al., 2021. The Marsquake Catalogue from InSight, Sols 0-478, Phys. Earth Planet. Int. 310, 106597. https://doi.org/10.1016/j.pepi.2020.106597

Compaire, N., et al., 2021. Autocorrelation of the ground vibrations recorded by the SEIS-InSight seismometer on Mars, J. Geophys. Res. Planets 126, e2020JE006498. https://doi.org/10.1029/2020JE006498

Compaire, N., et al., 2022. Seasonal variations of subsurface seismic velocities monitored by the SEIS-InSight seismometer on Mars, Geophys. J. Int. 229:2, 776–799. https://doi.org/10.1093/gji/ggab499

Drilleau, M., et al., 2022. Marsquake location and 1-D seismic models for Mars from InSight data, J. Geophys. Res. Planets, in press.

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. Int., in press.

Hobiger, M., et al., 2021. The shallow structure of Mars from inversion of high-frequency ambient seismic vibrations Rayleigh wave ellipticity at the InSight landing site, Nat. Comm. 12, 6756,. https://doi.org/10.1038/s41467-021-26957-7

Kenda, B., et al., 2020. Subsurface structure at the InSight landing site from compliance measurements by seismic and meteorological experiments, J. Geophys. Res. Planets 125, 6, e2020JE006387. https://doi.org/10.1029/2020JE006387

Khan, A., et al., 2021. Upper mantle structure of Mars from InSight seismic data, Science, 373, 434-438. https://doi.org/10.1126/science.abf2966

Khan, A., et al., 2022. Geophysical and cosmochemical constraints on the bulk composition of Mars , Earth Planet. Sci. Lett. 578. https://doi.org/10.1016/j.epsl.2021.117330

Kim, D., et al., 2021. Improving constraints on planetary interiors with PPs receiver functions, J. Geophys. Res. Planets 126, e2021JE006983. https://doi.org/10.1029/2021JE006983

Knapmeyer-Endrun, B., et al., 2021. Thickness and structure of the martian crust from InSight seismic data, Science, 373, 438-443. https://doi.org/10.1126/science.abf8966

Lognonné, P., et al., 2020. Constraints on the shallow elastic and anelastic structure of Mars from InSight seismic data. Nat. Geosci. 13, 213–220. https://doi.org/10.1038/s41561-020-0536-y

Murdoch, N., et al., 2021. Constraining Martian regolith and vortex parameters from combined seismic and meteorological measurements, J. Geophys. Res. Planets 126, e2020JE006410. https://doi.org/10.1029/2020JE006410

Stähler, S. C., et al., 2021. Seismic detection of the martian core, Science, 373, 443-448. https://doi.org/10.1126/science.abi7730

Stähler, S., et al., 2022. Marsquakes indicate dike-induced tectonics in Cerberus Fossae, Mars, Nature Geoscience, in press.

Wieczorek, M., et al., 2022. InSight constraints on the global character of the Martian crust, J. Geophys. Res. Planets, e2022JE007298. https://doi.org/10.1029/2022JE007298

How to cite: Banerdt, B. and the InSight Science Team: InSight’s Contributions to Planetary Seismology and Geophysics, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-773, 2022.

15:45–16:00
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EPSC2022-1101
Attilio Rivoldini, Sébastien Le Maistre, Alfonso Caldiero, Marie Yseboodt, Rose-Marie Baland, Mikael Beuthe, Tim Van Hoolst, Veronique Dehant, William Folkner, Dustin Buccino, Daniel Kahan, Jean-Charles Marty, Daniele Antonangeli, James Badro, Melanie Drilleau, Alex Konopliv, Marie-Julie Peters, Ana-Catalina Plesa, Henri Samuel, and Nicola Tosi and the InSight/RISE team

We report the results of more than 2 years of monitoring the rotation of Mars with the RISE instrument on InSight. Small periodic variations of the spin axis orientation, called nutations, can be extracted from the Doppler data with enough precision to identify the influence of the Martian fluid core. For the first time for a planetary body other than the Earth, we can measure the period of the Free Core Nutation (FCN), which is a rotational normal mode arising from the misalignment of the rotation axes of the core and mantle. In this way, we confirm the liquid state of the core and estimate its moment of inertia as well as its size. 

The FCN period depends on the dynamical flattening of the core and on its ability to deform. Since the shape and gravity field of Mars deviate significantly from those of a uniformly rotating fluid body, deviations from that state can also be expected for the core. Models accounting for the dynamical shape of Mars can thus be tested by comparing core shape predictions to nutation constraints. The observed FCN period can be accounted for by interior models having a very thick lithosphere loaded by degree-two mass anomalies at the bottom. 

The combination of nutation data and interior structure modeling allows us to deduce the radius of the core and to constrain its density, and thus, to address the nature and abundance of light elements alloyed to iron. The inferred core radius agrees with previous estimates based on geodesy and seismic data. The large fraction of light elements required to match the core density implies that its liquidus is significantly lower than the expected core temperature, making the presence of an inner core highly unlikely. Besides, the existence of an inner core would lead to an additional rotational normal mode the signature of which has not been detected in the RISE data. 

How to cite: Rivoldini, A., Le Maistre, S., Caldiero, A., Yseboodt, M., Baland, R.-M., Beuthe, M., Van Hoolst, T., Dehant, V., Folkner, W., Buccino, D., Kahan, D., Marty, J.-C., Antonangeli, D., Badro, J., Drilleau, M., Konopliv, A., Peters, M.-J., Plesa, A.-C., Samuel, H., and Tosi, N. and the InSight/RISE team: A view into the deep interior of Mars from nutation measured by InSight RISE, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1101, 2022.

16:00–16:15
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EPSC2022-880
Anna Horleston, John Clinton, Savas Ceylan, Taichi Kawamura, Simon C. Stähler, Constantinos Charalambous, Nikolaj L. Dahmen, Cecilia Duran, Doyeon Kim, Matthieu Plasman, Géraldine Zenhäusern, Fabian Euchner, Martin Knapmeyer, Domenico Giardini, Philippe Lognonné, William T. Pike, Mark Panning, Suzanne Smrekar, and William B. Banerdt

Introduction: NASA’s InSight lander has been operating on the surface of Mars for over 1200 Martian solar days (sols). Despite decreasing power, the lander has acquired near continuous seismic data throughout the mission to date. The Marsquake Service (MQS) performs daily analysis of the data and catalogues the seismicity. The catalogue currently contains over 1300 local, regional and teleseismic marsquakes and more than 1300 events that are likely associated with thermal cracking close to the lander (Table 1). Here we will present the latest update on the marsquake catalogue.


Martian Seismic Data: The Martian seismic dataset is often heavily contaminated by atmospheric effects, especially during the daytime and in the Northern hemisphere autumn and winter (Figure 1)[1,2]. This environmental noise can obscure the seismicity which is often at low amplitudes. During spring and summer, the atmospheric conditions are much more favourable from shortly before sunset until approximately sunrise and much of the MQS catalogue is detected during these hours. Other transient effects on the data that can interfere with event detection are discussed in [3]. One notable feature of the seismic noise on Mars is a resonance at 2.4 Hz which is observed during quiet periods and is also excited by seismic events that contain energy at that frequency. This resonance is likely caused by sub-surface structure [4] and greatly enhances the detection rate of higher frequency events.