TP4

The NASA InSight Lander on Mars includes the Heat Flow and Physical Properties Package HP³ (see Spohn et al. (2018) for a description of the package) to measure the surface heat flow of the planet. The package uses temperature sensors that would have been brought to the target depth of 3–5 m by a small penetrator, nicknamed the mole. The mole requiring friction on its hull to balance remaining recoil from its hammer mechanism did not penetrate to the targeted depth. Instead, it reached a depth of 40 cm, bringing the mole body 1–2 cm below the surface. A discussion of the lessons learned from the penetration failure and suggestions for an improved mole have been given by Spohn et al. (2022). The root cause of the failure - as was determined through an extensive almost two years long campaign - was a lack of friction in an unexpectedly thick cohesive duricrust. (compare Figure 1)

Figure 1. The HP³ mole before complete burial and the properties of the hole that the mole had punched in the duricrust

During the campaign the mole penetrated further aided by friction applied using the scoop at the end of the robotic Instrument Deployment Arm and direct support by the latter. The mole reversed its downward motion twice during attempts to provide friction through pressure on the regolith instead of directly with the scoop to the hull. The penetration record of the mole and its thermal sensors were used to measure thermal and mechanical soil parameters such as the penetration resistance of the duricrust. These parameter values are summarized in Table 1 below. The combined data suggest a model of the regolith that has an about 20 cm thick duricrust underneath a 1 cm thick sand layer and above another 10 cm of sand. Underneath the latter, a layer more resistant to penetration and possibly consisting of debris from a small impact crater was found. The thermal conductivity increases from 14 mW/m K in the 1 cm sand layer to 34 mW/m K in the duricrust and the sand layer underneath the duricrust to 64 mW/m K in the gravel layer below. Applying cone penetration theory, the resistance of the duricrust was used to estimate a cohesion of the latter of 4 - 25 kPa depending on the friction angle of the crust. Pushing the scoop with its blade into the surface and chopping of a piece of crust provided another estimate of the cohesion of 5.8 kPa.

The hammerings of the mole were recorded by the seismometer SEIS and the signals could be used to derive a P-wave velocity and an S-wave as listed (see also Brinkman et al., 2022) representative of the topmost tens of cm of the regolith. Together with a density provided by a thermal conductivity and diffusivity measurement using the mole thermal sensors of  about 1211 (Grott et al., 2021), the elastic moduli could be calculated from the seismic velocities.

Table 1. Model of the InSight landing site regolith

After burial, the mole was used to measure the thermal conductivity of the regolith as a function of the solar longitude (the seasons on Mars). The variations of the thermal conductivity are consequences of the variations in atmosphere pressure with the seasons and the contribution of atmosphere gas in the porous regolith contributing to the thermal conductivity.   

Figure 2 Thermal conductivity in the regolith top 40 cm as measured by sensors on the HP³ mole as a function of the solar longitude (seasons on Mars).

Brinkmann et al. (2022), submitted to J. Geophys. Res. Planets

Grott et al. (2021), Planet and Space Sci, DOI: 10.1029/2019EA000670

Spohn et al. (2018), Space Sci Rev, DOI:10.1007/s11214-018-0531-4   

Spohn et al. (2022), Advances in Space Research, DOI: 10.1016/j.asr.2022.02.009

How to cite: Spohn, T., Grott, M., Müller, N., and Hudson, T. and the HP-cubed team: Using the HP3 mole on InSight to probe the thermal and mechanical properties of the Martian regolith, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-408, https://doi.org/10.5194/epsc2022-408, 2022.

Analyses of the InSight seismic data indicate that there are three major seismic discontinuities beneath the lander where the seismic velocity abruptly increases. In addition to the crust-mantle interface at a depth of about 39 km, two major intracrustal discontinuities are observed at depths near 8 and 20 km (Lognonné et al. 2020, Knapmeyer-Endrun et al. 2021, Kim et al. 2021, Duran et al. 2022). There are many possible explanations for the existence of large-scale layering within the crust, and most of these involve a change in either chemical composition or porosity (see Figure 1). Here, we will assess these hypotheses using improved models of the crust that have been made possible by the InSight mission.

Figure 1. Interpretations of crustal layering beneath the InSight landing site. In the first two schematics, the crustal layering is a result either of stepwise changes in porosity (left) or composition (center). Our preferred interpretation combines elements of both of these end-member models. The depth of each seismic interface below the surface is denoted on the left schematic.

As summarized in Wieczorek et al. (2022), there are a large number of hypotheses for the origin of the three-layered nature of the Martian crust. One or more layers could be composed of volcanic or sedimentary deposits. One of the discontinuities could represent the removal of pore space either by viscous deformation of the host rock or by the precipitation of cements in an ancient aquifer. One layer could represent thick impact basin ejecta deposits, whereas another could represent thick sequences of magmatic intrusions. One of the discontinuities could represent a change in crystallinity, such as is observed in the oceanic crust of Earth. Lastly, one or more discontinuities could be generated by the fractional crystallization of a giant impact melt pool associated with the Borealis impact. Importantly, each of these hypotheses has different implications for the expected thickness of the crustal layer, its composition, and its associated seismic velocity.

Based on the currently available information, we have constructed a plausible model for the observed crustal layering beneath the landing site. As shown in Figure 1, we interpret the uppermost layer as being a result of thick sequences of volcanic materials that were deposited in the early Hesperian, Noachian, and pre-Noachian periods. To account for the low seismic velocities of this layer, these materials would need to be heavily fractured, perhaps being similar in nature to the pyroclastic deposits that make up the nearby Medusae Fossae formation. Given the long duration over which these materials were emplaced, intercalated sedimentary deposits could be common and these materials might also have undergone substantial aqueous alteration at a later date. Ancient impact ejecta deposits from the Utopia basin are likely to be found below the layer of volcanic and sedimentary deposits, potentially in the middle layer between 8 and 20 km depth. The increase in velocity at 20 km depth is likely to be a consequence of the complete viscous closure of all remaining pore space at about 4 Ga when the crustal temperatures were elevated. The deepest layer, from depths of 20 to 39 km, likely corresponds to the initial crust that formed during the differentiation of the Borealis impact melt sheet.

The expected stratigraphy of the southern highlands is less certain. Nevertheless, we speculate that a 20 km seismic discontinuity would be found there as well that represents the transitions from porous to non-porous materials. Another major discontinuity that is likely to be present in the southern highlands would be the base of thick ejecta deposits derived from the ancient Borealis impact event.

It is important to recognize that the InSight landing site is located in the northern lowlands of Mars, and that the layering that is observed beneath the lander might only be indicative of local geologic structure. Future observations of surface waves, as well as analyses of crustal structure at the bounce point of PP waves, will allow us to assess how the thickness of the crustal layers varies across the planet.

References:

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, doi:10.1016/j.pepi.2022.106851

Kim, D. et al. (2021). Improving constraints on planetary interiors with PPs receiver functions. J. Geophys. Res. Planets, 126, e2021JE006983, doi:172810.1029/2021JE006983

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

Lognonné, P., et al. (2020). Constraints on the shallow elastic and anelastic structure of Mars from InSight seismic data. Nature Geosci., 13, 213-220, doi:175910.1038/s41561-020-0536-y

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

How to cite: Wieczorek, M. A. and the InSight Crust Working Group: Origins of crustal layering beneath the InSight landing site (and elsewhere), Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-400, https://doi.org/10.5194/epsc2022-400, 2022.

InSight landed on Mars in November 2018¹ and carries the InSight FluxGate Magnetometer, IFG² which has provided the first surface magnetic field measurements on Mars^1,3. Previous magnetic field measurements taken at orbital altitudes have provided global coverage, with limited spatial resolution. Laboratory analyses of meteorites provide information on magnetic properties of martian rocks, but without detailed local context for their provenances⁴. Advances from the IFG are thus unique and complementary science, specifically characterizing the crustal ambient static and external time-varying fields at a single location on Mars. External fields provide information on the planet’s interaction with the interplanetary magnetic field and the ionosphere. Crustal magnetic fields carry information about the ancient dynamo and crustal conditions at the time at which magnetization was acquired, and on how the crust has been modified by subsequent exogenic and endogenic processes⁴. IFG data for sols 14-736 were collected almost continuously, with some data gaps from electronics anomalies. After sol 736, the magnetometer was operational for shorter periods due to power constraints (Fig. 1) ⁵. A range of studies have been enabled by IFG data, supported by results from other instruments such as the seismometer, and we summarize those.

Strong crustal fields provide evidence for an ancient dynamo. The IFG measured a surface magnetic field strength of ~2000 nT, ~10x stronger than predicted from satellite data^3,6 and consistent with an ancient Earth-like dynamo³. The strong surface field indicates that magnetization at wavelengths shorter than those resolvable from current satellite data (~150 km) contribute substantially to the overall magnetic field. Characterization of the crust through seismic measurements⁷ and geologic inferences³ of subsurface layering allow assessment of magnetization of the crust (Fig. 2). Depending on the depth at which the magnetization is carried, specifically whether it is in the seismically-determined deep layer of Noachian origin or also in the shallow Hesperian-aged crust, the minimum magnetization required to explain the surface field is ~2 A/m or ~0.4 A/m. Seismic characterization of crustal structure⁸ indicates a deep subsurface layer (> 20 km, Fig. 2) of no porosity, while the upper crust (<20 km, Fig. 2) is less porous⁸. Magnetization of these layers require an early active dynamo (>~4 Ga).  Fractured, less porous material could have provided pathways for hydrothermal circulation and chemical remanent magnetization^4,8,10. Magnetization of the most surficial layer of Hesperian age would be consistent with a long-lasting (up to ~3.7 Ga) dynamo⁹.  

IFG data also reveal time-varying fields at the planetary surface that include contributions with different periods and origins. External fields have been observed and characterized from orbit^11–13. However, the degree to which external fields penetrate to and interact with the surface could not be studied prior to the InSight landing. Static and long-duration observations from a surface magnetometer are advantageous because, unlike satellite measurements, temporal variability in the field is not mixed with spatial variability. Here, we summarize different external magnetic field phenomena, transient and periodic that have been observed in IFG data (Fig. 3). Periodic variations include short period waves (100s-1000s^3,14), diurnal variations¹⁵, the ~26 sol Carrington period associated with solar rotation¹⁶,  and seasonal^15,17 fluctuations. Transient events are observed in response to space weather¹⁸ and dust movement^19,20.

The inclusion of the magnetometer on InSight has provided unique and substantial scientific contributions to the overall mission results, as well as a starting point for future planetary surface magnetic field investigations. To overcome limitations of current data sets, we look forward to Mars sample return, as well as possible near-surface investigations. Including magnetometers on future missions at a variety of surface locations for long duration observations will be of great value in understanding a range of external field phenomena, including the influence of crustal magnetic fields on ionospheric currents and the effects of space weather during different phases of a solar cycle. We further advocate for regional investigations for example via a helicopter²⁰ that can provide local magnetic field measurements at a spatial scale commensurate with detailed geological knowledge, to further constrain evolution of Mars’ ancient dynamo and explore the magnetic properties of the crust.

Figure 1: a) Martian years 1 (blue) and 2 (red) of the magnetic field amplitude, B, versus solar longitude (l_s). All data up to sol 1106 of InSight operations are included (PDS release 13). The blue vertical dashed line marks the beginning of the mission. (b) Corresponding sol numbers.

Figure 2: The minimum magnetization required by B=2013 nT (within its 99% confidence intervals)²¹ for the crust below InSight⁸. Burial depth describes the depth extent of the unmagnetized layers above the top of the magnetized layer. A burial depth of 200 m (blue), corresponds to burial beneath the young (H: Hesperian, HNt: Hesperian-Noachian transition) near-surface lava flow³ and magnetizations are at least ~0.4 A/m if the entire underlying crust is magnetized. A burial depth of 10 km (blue) requires magnetizations >1 A/m, hosted by Noachian units. The velocity profiles show the seismically-determined interface depths⁷.

Figure 3: A composite power spectral density (PSD) plot for the surface magnetic field strength at the InSight landing site. Estimates for longer periods are derived using a Lomb-Scargle algorithm (black), shorter periods (purple) show a Welch spectrum.

[1] Banerdt, W. et al. Nat. Geosci. (2020).[2] Banfield, D. et al. SSR (2019). [3] Johnson, C. L. et al.  Nat. Geosci.(2020). [4]Mitteholz, A. & Johnson, C. L. Frontiers (2022). [5] Joy, S. et. al. (2019). [6] Smrekar, S. et al. SSR (2018). [7] Knapmeyer-Endrun, B. et al. Science (2021). [8] Wieczorek, M. et al. JGR (2022). [9] Mittelholz, A. et al. Sci. Adv. (2020). [10] Gyalay, S. et al. GRL (2020). [11] Mittelholz, A. et al. JGR (2017). [12] Ramstad, R. et al. Nat. Astron. (2020).  [13] Brain, D. et al. JGR (2003). [14] Chi, P. et al. LPSC (2019). [15] Mittelholz, A. et al. JGR (2020). [16] Luo, H. et al. JGR (2022). [17] Mittelholz, A. et al. LPSC (2021). [18] Mittelholz, A. et al. GRL (2021). [19] Thorne, S. et al. PSS (2022).  [20] Bapst, J. et al. AAS (2021). [21] Parker, R. JGR (2003). 

How to cite: Mittelholz, A., Johnson, C. L., Fillingim, M. O., Joy, S., Langlais, B., Thorne, S. N., Wieczorek, M., Smrekar, S., and Banerdt, W. B.: The surface magnetic field environment from InSight, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-988, https://doi.org/10.5194/epsc2022-988, 2022.

The Martian dichotomy is the most conspicuous feature of the surface of the planet. The difference in elevation between the Northern and Southern hemispheres of Mars likely originates from a difference in crustal thickness. Inversion of topography and gravity data constrained by seismic data from the InSight NASA mission suggests that the southern crust is on average thicker by 18 to 28 km than the northern one if one assumes a uniform crustal density of 2900 kg m^-3 (Knapmeyer-Endrun et al., 2021 - Wieczorek et al, 2022).

Several explanations have been proposed for the origin of this crustal dichotomy, involving external processes, such as a large impact (Marinova et al., 2008), or internal ones, such as a degree-one mantle convection (Yoshida and Kageyama, 2006). Here we show that a positive feedback mechanism between crustal growth and partial melting in the mantle could have created this dichotomy. Indeed, because the crust is enriched in heat-producing elements (HPE), the lithosphere of a one-plate planet is thinner where the crust is thicker, inducing a lower pressure at the base of the lithosphere. Because of the pressure-dependence of the mantle solidus, partial melting is more important below a thinner lithosphere, causing a larger rate of melt extraction and crustal growth where the crust is thicker. Larger wavelength perturbations in crustal thickness and extraction, and thus hemispherical perturbations, grow faster because thermal diffusion dampens smaller wavelengths faster.

To model this effect, we use a parametric bi-hemispherical thermal evolution model where a well-mixed convective mantle is topped by two types of lithospheres (North and South) characterized by two potentially different thermal structures (Thiriet et al. 2018). The enrichment in HPE of the crust evolves during crust extraction as the enrichment of the newly formed crustal material depends on mantle melt fraction below the lithosphere, mantle enrichment and partition coefficient. In order to study the growth of a hemispherical perturbation, we impose a small initial difference in lithosphere or crust thickness in between the North and South. We then follow the thermal evolution, mantle melting, crustal growth and crustal enrichment in HPE in both hemispheres over 4.5 Gyr (Fig.1). Our model mainly depends on the mantle reference viscosity, that controls the cooling rate of the convective mantle, on and mantle permeability, that controls crustal extraction from the mantle.

Our results show that this positive feedback mechanism can indeed create a significant crustal dichotomy. The range of North-South crustal thickness differences that we obtain by varying the different model parameters largely encompasses that predicted by inversion of topography and gravity data, assuming different crustal densities. In particular, two types of thermal history allow to reproduce the crustal thickness difference predicted by InSight. The first one is obtained for a rather low viscosity and high mantle permeability; it shows a rapid and early extraction of the crust (Fig1. Solid line) and results in a cold potential temperature at the present-day. The second one is for a higher viscosity and lower mantle permeability; it leads to a late and prolonged extraction of the crust (Fig1. dashed line) and results in a warmer mantle potential temperature and a thicker lid at the present-day. In both cases, the crust is extracted during the first Gyr. The enrichment in HPE of the crust predicted by our model is in agreement with GRS data. 

Figure 1 : Evolution of the (a) lid thickness (b) Crust thickness, (c) average melt fraction in the partially melted zone below the lid. (d) Crustal HPE enrichment relatively to the Bulk Silicate Mars as a function of time for the Northern (blue lines) and Southern (orange lines) hemispheres for 2 different simulations that allow to reproduce the difference in crustal thickness deduced from the InSight mission. One evolution (shown in dashed lines) is for a rather high permeability k₀ = 9.1.10⁻¹⁰ m² and low reference viscosity η₀ = 4.5x10²⁰ Pa.s, while the second evolution (shown in solid lines) has a lower permeability k₀ = 3.72.10⁻¹¹ m² and a higher viscosity η₀ = 2.02x10²¹ Pa.s.

Acknowledgment :

This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 101001689) and from the ANR (grant MAGIS, ANR-19-CE31-0008-08).

Bibliography :

Knapmeyer-Endrun, B., Panning, M. P., Bissig, F., Joshi, R., Khan, A., Kim, D., Leki ́c, V.,
Tauzin, B., Tharimena, S., Plasman, M., et al. (2021). Thickness and structure of the martian crust
from insight seismic data. Science, 373(6553):438–443.

Wieczorek, M. A., Broquet, A., McLennan, S. M., Rivoldini, A., Golombek, M.,
Antonangeli, D., Beghein, C., Giardini, D., Gudkova, T., Gyalay, S., et al. Insight constraints
on the global character of the martian crust. Journal of Geophysical Research: Planets, page
e2022JE007298.

Marinova, M. M., Aharonson, O., and Asphaug, E. (2008). Mega-impact formation of the mars
hemispheric dichotomy. Nature, 453(7199):1216–1219.

Yoshida, M. and Kageyama, A. (2006). Low-degree mantle convection with strongly temperature-
and depth-dependent viscosity in a three-dimensional spherical shell. Journal of Geophysical Re-
search: Solid Earth, 111(B3).

Thiriet, M., Michaut, C., Breuer, D., and Plesa, A.-C. (2018). Hemispheric dichotomy in litho-
sphere thickness on mars caused by differences in crustal structure and composition. Journal of
Geophysical Research: Planets, 123(4):823–848.

How to cite: Bonnet Gibet, V., Michaut, C., and Wieczorek, M.: A new mechanism for the formation of the Martian dichotomy, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-255, https://doi.org/10.5194/epsc2022-255, 2022.

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.

How to cite: Stähler, S. C., Mittelholz, A., Perrin, C., Kawamura, T., Kim, D., Knapmeyer, M., Zenhäusern, G., Clinton, J., Giardini, D., Logonné, P., and Banerdt, W. B.: Seismicity unveils tectonics in Cerberus Fossae, Mars, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1126, https://doi.org/10.5194/epsc2022-1126, 2022.

In August 2021, the first seismological determination of the core radius of Mars was published by the InSight team (Stähler et al., 2021). We take this opportunity to take a mental step backwards and assume a historical perspective on the scientific investigation of planetary cores, and how our knowledge about them, especially in terms of their size, evolved.

The first thoughts about the Earth's interior that we would place into the history of science or rather into that of religion originate in the 17th century. Descartes suggested that the Earth is a former star which produced so many sunspots that it became encrusted in them, and that later processing of sunspot-material resulted in the surface we have today. The innermost part of the Earth, however, is still unaltered solar matter.

Isaac Newton, in the posthumously published "System of the World", suggested that the gravity of a single, isolated mountain could be used to determine the density ratio between the surface and the interior of the Earth. Respective experiments were conducted by Bouguer and, later, by Maskelyne and Hutton - the latter concluded from the result, that the presence of a heavy, metallic core could explain the overall mass of the Earth as well as the density contrast resulting from Newton's experiment. A metallic core was also suggested by Wiechert, by the end of the 19th century. When Oldham demonstrated the S wave core shadow in 1906, he did not make any suggestions about the nature of the central region.

In the early 20th century, it was however doubted that any material could withstand the conditions of the deep interior, or that a segregation of metals could take place. One alternative approach was indeed solar matter, another one a metallic high pressure state of silicate rock: The possibility that the core mantle boundary is a phase boundary like the 410 and 660 km discontinuities was long supported by some.

The consequence of the phase boundary model was that neither the Moon nor Mars could have cores, for the simple reasons that they are too small to provide the necessary internal pressures. This claim fit well with the moment of inertia factors as they were observed back then: Until the mid-1960s it was assumed that the MoIF of the Moon exceeds 0.4, and that of Mars is too close to 0.4 to indicate much differentiation.

In both cases, the space age led to a revision: Having spacecraft near or at the respective bodies turned out to be crucial for a sufficiently precise determination of the MoIF.

In the case of Mars, the Mariner IV mission greatly improved the knowledge of radius, mass, and moment of inertia factor of the planet (because of the atmosphere, even the radius was rather uncertain and observational results depended on the optical wavelength used in photography). After Mariner IV, an iron core suddenly became feasible, if not necessary, again. Mariner VI and VII showed that Mars is neither a small Earth nor a big Moon, but something different - and the global photographic map resulting from the Mariner IX mission showed all the now familiar surface structures for the first time. With Mariner IX it also became possible to map the surface gravity, and the gravity anomaly of Tharsis was discovered - which is so enormous that it biases the J₂ gravity coefficient, and invalidates the previously used hypothesis of hydrostatic equilibrium. Several methods to compensate for this were suggested in the following. A replacement for the hydrostatic assumption became available with precession measurements using Viking radio signals, later augmented by Pathfinder and other missions. It became finally possible to determine the MoIF, which turned out to be significantly below that of the homogeneous sphere. The most significant progress in terms of the estimation of the core radius was however Mariner IX: After this mission, core radii below 1000 km were no longer discussed.

The Viking missions produced important clues for the identification of the SNC meteorites as of martian origin, and thus for improved models of the chemical composition of Mars. This provided better contraints for the densities of core and mantle. A comparison of the core radii discussed in the literature after Viking however shows that none of these models could constrain the core radius with a sufficient precision. Different models were developed, but in the long run, the range of uncertainty of the core radius proved rather stable for more than 40 years.

The results obtained by InSight still build upon the knowledge of geodetic and gravity measurements as well as on geochemistry, but they add seismic data as constraints that are more sensitive to the sought-after structural parameters than to density.

References

Listing all references relevant for the above text would require much more space than is available here. The discussion of the abstract is a condensate from Knapmeyer & Walterová (2022), where all the references can be found.

Knapmeyer, M., Walterová, M. (2022), Planetary Core Radii: From Plato towards PLATO, under review at Advances in Geophysics.

Stähler et al., (2021). Seismic detection of the martian core, Science, vol. 373, 443-448, DOI: 10.1126/science.abi7730

How to cite: Knapmeyer, M. and Walterová, M.: The core radius of Mars: a historical perspective, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-803, https://doi.org/10.5194/epsc2022-803, 2022.

Introduction

Wrinkle ridges are significant landforms on planetary bodies, and most of them occur in flood basalt units of large igneous provinces, [1]-[2]. On Mars, the circum-Tharsis wrinkle ridge system developed under compressional stresses associated with the response of the lithosphere due to the Tharsis volcanic load [1]. The morphology of ridges shows large variations and may reflect subsurface fault patterns [3]–[5]. Numerous studies on their physical dimensions [6]–[10], their accommodated horizontal strain (e.g., [11]–[12]), as well as a variety of conceptual formation models (e.g., [13]–[17]) have been performed to better understand the morphologies and geodynamic significance of wrinkle ridges. A variety of tectonic models including buckling, thrust/reverse faulting, fault-bend folding,  and fault propagation folding have been proposed to explain the formation of wrinkle ridges(e.g., [9]–[19]).

Even though there are many studies on wrinkle ridges, it is still uncertain what the subsurface of these structures looks like. To get insights into the subsurface we selected sites, where deep morphological incisions provide such exposures. Hence, we used steep escarpments formed by impact craters, collapse pits, and valleys. A prerequisite for this study is the availability of high-resolution remote sensing data and digital elevation models to investigate the fault patterns that exist in the subsurface of wrinkle ridges.  

Methodology

We used High-Resolution Imaging Science Experiment (HiRISE) (~0.25 m/px) [20], and Context Camera (CTX) (~6–7 m/px) [21] satellite imageries to generate high-resolution digital elevation models (DEMs) by using the Ames Stereo Pipeline [22] in combination with the Integrated System for Imagers and Spectrometers (ISIS) software [23]. CTX and HiRISE DEMs with the digital raster graphic (DRG) files were used to analyze and measure topographic offsets. We have selected twelve different study areas (with multiple outcrops from A to D) that all belong to the system of circum-Tharsis wrinkle ridges. Our area of interest includes regions at Solis Planum, at the borders of Nilus Dorsa, at the Coprates Chasma, at the south of Lunae Planum, and the Thaumasia Planum that shares significantly akin structures with a south of the Mela's Fossae (Fig. 1).

To measure the strike and dip of fault planes we used two methods: (i) we applied the LayerTools [24]  add-in for ArcGIS Software and (ii) we constructed manually the strike of faults by connecting points along the fault trace that have of the same elevation. The dip angle is determined perpendicular to the strike direction by recording intersection points of the fault trace with different elevation levels. We mapped all fault intersection lineations (red lines) on wrinkle ridges.

Results

Here, we present only two of twelve case study results. Fig. 2 (study area 1) shows that folding and faulting are intimately linked to each other. The outcrop sections show that the slopes of the wrinkle ridge are formed by the limbs of a vergent anticline. The dip of two subordinate thrust faults with NNW-SSE strike directions could be determined (38° and 46°). In Fig. 3 (study area 2), the western part of the flat crater floor is elevated by ~100 m with respect to the eastern crater floor. Along with this occurs a change in polarity of the fault with a dip direction to the east in the northern crater section and a westward dip in the southern crater section. The wrinkle ridge shows complex fault pattern north and south of the crater, where faults cut obliquely through the wrinkle ridge.

Discussion and Conclusion

Both reverse (>45°) and thrust (<45°) faults are frequent in the subsurface of wrinkle ridges and along with the anticlinal folding document that horizontal compression is the driver for their formation. A multitude of subsidiary and splay faults exist. Symmetric wrinkle ridges contain a conjugate system of thrusts or reverse faults. Asymmetric wrinkle ridges have one dominant reverse/thrust that reaches the surface at the base of the steeper slope. In such cases, additional antithetic faults are subordinate and merge into the main fault. A polarity change of wrinkle ridges can take place along strike and is associated with a change in the amount of displacement that is accommodated along the faults. The fault with the largest amount of slip is situated beneath the ridge crest and steeper slope. Several wrinkle ridges display the main thrust fault whose dip angle abruptly gets shallower at a depth of 500-1000 m beneath the surface. The application of fault-propagation fold models to wrinkle ridges [14]-[19] show conditionally the best match to observations.

References: [1] Scott D. H. and Tanaka K. L. (1986) USGS,1802. [2] Strom R. G. et al. (1975) JGR, 80, 2478–2507. [3] V.L. Sharpton and J. W. Head (1988) LPSC XVIII, Abstract#307.[4] Plescia J. B.  and Golombek M. P (1986) Bull. Geol. Soc. Am., 97, 1289–1299. [5] Strom R. G.  (1972), Dordrecht: Springer Netherlands, 187–215. [6] Mueller K. and Golombek M. (2004) Annu. Rev. Earth Planet. Sci., 32, 435–464. [7] Watters T. R. and Robinson M. S. (1997) JGR Planets, 102,10889–10903. [8] Golombek M. P. and Phillips R. J (2010) Eds. Cambridge University Press,183–232. [9] Golombek, M. P. et al. (1991) LPS XXI, Abstract#679. [10] Mangold N. et al. (1998) Planet. Space Sci., 46, 345–356. [11] Plescia J. B. (1991) Geophys. Res. Lett., 18, 913–916. [12] Montési L. G. J.  and Zuber M. T. (2003) JGR Solid Earth, 108,1–16. [13] Allemand P. and Thomas P. G. (1995) JGR, 100, 3251. [14] Schultz R. A. (2000) JGR Planets, 105, 12035–12052. [15] Watters T. R. (2004), Icarus, 171, 284–294. [16] Karagoz O. et al. (2022) Icarus, 374,114808. [17] Chester, J., and Chester, F., (1990) Struct. Geol. 12, 903–910 [18] Suppe J. and Medwedeff D. A. (1990) Eclogae Geol. Helv., 83, 409–454. [19] Suppe J. and Medwedeff D. A. (1984) GSA 16, Abstract#670. [20] McEwen et al., (2007) JGR, 112, E05S02. [21] Malin et al., (2007) JGR, 112, E05S04. [22] Moratto Z. M. et al. (2010) LPSC XLI, Abstract#2364. [23] Becker, K. J.  et al. (2013) LPSC XLIV, Abstract#2829. [24] Kneissl et al., (2010) LPSC XLI, Abstract#1640.

How to cite: Karagoz, O., Kenkmann, T., and Wulf, G.: Clues to the subsurface fault pattern of circum-Tharsis wrinkle ridges, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-59, https://doi.org/10.5194/epsc2022-59, 2022.

Introduction:  The edge of the pre-Noachian Borealis impact basin, thought to be the cause of the planetary dichotomy boundary [1-2], crosses the northern Valles Marineris troughs [1-3]. Intense deformation is exposed in the deepest parts of the Ophir and Hebes Chasmata, the northernmost troughs. Structural geology and mineralogical analyses motivate the tentative identification of brittle and brittle-ductile shear zones and hydrothermal activity in the Valles Marineris basement. Implications for the Borealis basin and the proto-Valles Marineris crust are examined.

Structural analysis:  Crustal right-lateral shear zones are identified in the pre-Noachian basement of Ophir and Hebes Chasmata (Figure 1). In Ophir Chasma, S-C-C' structures, indicate deformation in the brittle-ductile domain. In Hebes Chasma, megabreccia indicates brittle deformation. From scaling relationships [4-5], the shear zones are inferred to be at least hundreds of kilometers long. They do not extend to the surface nor even up into the interior layered deposits (ILD), and are therefore interpreted to affect the Valles Marineris basement only, which at this depth, is interpreted to be of pre-Noachian age.

Mineralogy: A new method of non-linear spectral unmixing derived from the LinMin algorithm [6] is implemented and applied to three pre-Noachian basement exposures in a CRISM cube in Ophir Chasma. After gas absorption removal, two groups of minerals are robustly detected (Figure 2): primary minerals of mafic rocks (olivine, hypersthene, augite, anorthite, albite), and sulfates, most of them likely of hydrothermal origin (copiapite, jarosite, szomolnokite). Anhydrite (ROI3) is not diagnostic of any particular environment. Kieserite is interpreted as transported by wind from the neighboring ILDs. S-C-C' structures constrain the granulometry of the sheared rock which, under the assumption that all the primary minerals are detected, would be olivine-gabbronorite (ROI1) or troctolite (ROI2-3). Combined structural and mineralogical analyses point to hydrothermal alteration of a mafic intrusive basement, or contamination of this basement by hydrothermal activity in the ILDs.

Relationships with the Borealis basin: The general trend of the shear zones follows the edge of the Borealis as inferred from gravity and topography [4], also of pre-Noachian age, suggesting that they may have initiated as basin ring faults and were reactivated as crustal shears. North of Valles Marineris, the radial component of the remanent magnetic field at the surface [7] shows elongated anomalies that follow the trend of the shear zones and more generally, the expected curved edge of the Borealis basin. The existence of a magnetic field (or dynamo) was coeval with formation of the planetary dichotomy boundary [8]. Two anomalies also correspond to Noachian or pre-Noachian crustal ridges in Ophir Planum, of igneous [9] or tectonic [10] origin. Mapping reveals that the ridges are fractured parallel to the magnetic anomalies, and that their topography guided a hydrologic system (Figure 3). Moreover, these fractures are parallel to a dyke swarm exposed in eastern Candor Chasma [11]. Therefore, the ridges have a volcanotectonic origin within an active hydrologic context.

Figure 1. Ophir shear zone (OSZ) and Hebes shear zone (HSZ): (a) location map showing trace of the Borealis impact basin with ±5° uncertainty (dashed area) [5]; (b) zoom on S-C-C' structures in the OSZ, and illustration of shear orientations; (c) zoom on fault megabreccia in the HSZ. HiRISE images ESP_017754_1755 and ESP_040211_1790.

Figure 2. Results of nonlinear spectral unmixing applied to basement exposures in Ophir Chasma: (a) CRISM cube location (frt00018b55_07_if165l_trr3); (b) the cube (bands R: 233, G: 78, B: 13); (c) mineral relative abundances, after aerosol contribution removal; (d)  best fit plots and HiRISE images of the basement exposures: ESP_051999_1755, ESP_039525_1755, ESP_039525_1755.

Figure 3. Features related to hydrothermal activity possibly resulting from the Borealis impact and suggested to explain magnetic banding north of Coprates Chasma. Dykes are located thanks to HiRISE images. The rose diagram was established from 26 representative dykes observed on the eastern Candor Chasma wall; the indicated strike refers to the mean resultant dyke orientation. Magnetic anomalies are from [7]. Topographic contours (spacing 500 m) are from HRSC (ESA/DLR/Freie Univ. Berlin).

Circumferential magnetic anomalies are observed at some terrestrial impact craters (e.g.[12]) as well as the Chicxulub impact basin [13] and are due to crystallization of magnetic minerals in an impact-related hydrothermal system [14]. We suggest, therefore, that the magnetic anomalies measured above the Valles Marineris plateau similarly result from hydrothermal activity in response to the Borealis impact, and follow basin ring structures. This hydrothermal activity might be the surface counterpart of deep hydrothermal activity in the basement detected using spectral unmixing [15].

Conclusions:  Analysis of northeastern Valles Marineris supports the interpretation of a pre-Noachian Borealis impact basin that would have underlain the later northern troughs of Valles Marineris in the presence of an active dynamo. Large shear zones in the Valles Marineris basement would be reactivated ring faults. Borealis basin formation may have triggered a huge hydrothermal system, identified along these structures and also producing magnetic minerals that generated the observed magnetic anomalies. Primary deposits of base and rare metals likely formed as well. Other evidence of hydrothermal activity at the edge of the Borealis basin would confirm these interpretations.

References: [1] Andrews-Hanna J. et al. (2008) Nature, 453, 1212–1215. [2] Marinova M. M. et al. (2008) Nature, 453, 1216–1219. [3] Andrews-Hanna J. (2012) J. Geophys. Res., 117, E03006. [4] Schultz R. A. and Fossen H. (2002) J. Struct. Geol. 24, 1389–1411. [5] Fossen H. (2010) Structural Geology, Cambridge Univ. Press. [6] Schmidt F. et al. (2014) Icarus, 237, 61–74. [7] Langlais B. et al. (2019) J. Geophys Res., 109, E02008. [8] Mittelholz et al. (2020) Sci. Adv., eaba0513. [9] Tanaka K. L. et al. (2014) USGS Sci. Inv. Map 3292. [10] Viviano-Beck et al. (2017) Icarus, 284, 43–58. [11] Mège D. and Gurgurewicz J. (2017) 48th LPSC, Abstract #1087. [12] Hawke P. J. et al. (2006) Explor. Geophys., 37, 191–196. [13] Abramov O. and Kring D. A. Meteor. Planet. Sci., 42, 93–112. [14] Osinski G. R. et al. (2011) Meteor. Planet. Sci., 36, 731–745. [15] Gurgurewicz J. et al., submitted to Commun. Earth Environ.

How to cite: Mège, D., Gurgurewicz, J., Schmidt, F., Schultz, R. A., Douté, S., and Langlais, B.: Tectonic and hydrothermal activity at the edge of the Borealis impact basin in Valles Marineris, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-116, https://doi.org/10.5194/epsc2022-116, 2022.

We use DEM and orthoimages from HRSC [10] to obtain information on the displacement distribution along fault traces. This also enabled determining the maximum displacement. We compare our results to previous measurements of faults on Mars, Earth, and beyond. Based on these analyses, we discuss the implications of fault segmentation and linkage for further interpretation. HRSC data offer high-resolution topography and spatially contiguous coverage, which are required to analyze detailed topographic characteristics of large fault systems. For structural interpretation of key locations (e.g., relay ramps), CTX images (~5-6 m px^-1) have been inspected. Fault length was digitized along the fault line, and multiple topographic cross-sections across the fault were drawn with a spacing of ~1 km. Fault throw (a proxy for true displacement) was visually determined in the digitized cross-sections.

Results

At the time of writing, 16 images out of 75 available images/DEM from the Memnonia Fossae region exhibiting normal faults have been investigated. In this preliminary stage, a total number of 83 faults in Memnonia Fossae were studied. We find an average D_max/L ratio of 0.007, consistent with our previous findings for other regions on Mars, where this ratio had an average value of 0.006 [4].

References

[1] Schultz, R.A. et al. (2010) J. Struct. Geol., 32, 855-875. [2] Golombek, M.P. et al. (1992) Science 258, 979-981. [3] ] Kim, Y., Sanderson, D. J. (2005) Earth Sci. Reviews, 68, 317-334. [4] Hauber, E. et al. (2014) Lunar Planet. Sci. Conf. 45, #1981. [5] Cartwright, J. A., et al., J. Struct. Geol. 17, 1319-1326, 1995. [6] Cowie, P.A. and Scholz, C.H., J. Struct. Geol. 14, 1133-1148, 1992. [7] Wells, D.L. and Coppersmith, K.J. (1994) Bull. Seismol. Soc. Amer., 84, 974-1002. [8] Knapmeyer, M. et al. (2006) J. Geophys. Res., 111, E11006. [9]  Schultz, R.A. et al. (2006) J. Struct. Geol., 28, 2182-2193. [10] Lognonné, P., et al., (2019) Space Science Reviews, 215(1), 1-70. [11] Drilleau, M., et al., (2021) EGU General Assembly. Conf. 14998. [12] Gwinner et al., Planetary and Space Science 126 (2016) 93–138.

How to cite: Yazici, I., Hauber, E., and Tirsch, D.: Fault scaling at Memnonia Fossae, Mars: Displacement-length relationship derived from HRSC data, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1105, https://doi.org/10.5194/epsc2022-1105, 2022.

On Mars, prominent thick-layered sulfate-bearing deposits are observed at a number of late Noachian to late Hesperian locations (~3.5 Ga) [1]. Their apparent absence in older strata has led to the hypothesis that they represent ancient evaporites related to the global aridification [2]. In Gale crater, the Curiosity rover is now exploring the Layered Sulfate-bearing unit (LSu), which is a hundreds of meters thick regional package of yet unknown origin within the Mt Sharp group (Fig. 1). Curiosity investigations can test whether its formation processes are similar to the Burns fm., another major sulfate-bearing strata documented by the Opportunity rover, or distinct such as a form of primary evaporites, syndiagenetic or later stage diagenetic precipitations with different aqueous conditions.

After exploring the mudstone-rich strata of the Murray and Carolyn Shoemaker fm. for about seven years, the Curiosity rover entered the LSu in 2021. Bedrock in the basal section is marked by diverse diagenetic overprints where sedimentary structures are less visible. In some places, laminated mudstones or siltsontes associated with concretions and with mm-scale nodular features may present similarities to evaporitic textures previously observed in the Murray formation [3]. Further up, the rover imaged butte-forming outcrops (Fig. 1) and revealed a ~100-m-thick interval with a transition into large-scale trough cross-bedded structures, the lithology, scale and thickness of which has never been observed before by the rover at such close range [4].

The base of the LSu succession is marked by a sharp increase in density of bedrock nodular textures. The rover analyzed the composition of two bedrock components: (i) a smooth host bedrock, which was drilled several times, revealing the disappearance of clay minerals in X-ray diffraction [5] – the evolved gas analyses also suggest Mg-sulfates and an isotopic change in sulfur compared to the clay-bearing unit below [6]; (ii) a nodular bedrock, which was not drilled due to its uneven surface, but shows diverse sulfate-enriched compositions as measured by ChemCam. Overall, the bulk bedrock (combining smooth and nodular) shows an increase in sulfate content relative to prior strata, nodular textures being a key component of that change (Fig. 2). Unusual lithologies have been observed in the basal LSu, including a regular pattern of polygonal ridges (Fig. 2), clearly crosscut by later stage fractures, pointing to multiple phases of diagenetic alteration. These sulfate-enriched polygonal ridges may represent the first evidence of a paleosol on Mars formed by sustained wet-dry cycles at the surface [7].

The LSu shows multiple signs of marked changes towards drier paleoenvironments in the sedimentary and geochemical record. Within the large-scale cross-bedded strata of most likely eolian origin sulfates in the LSu differs from the Burns fm. homogeneous enrichments as they occur in the form of diverse heterogeneities mostly related to nodular bedrock. Ongoing exploration could help test whether the drying-upward transition reflects internal basin controls on the evolution of ancient Gale lake or external, possibly global, climatic controls.

References: [1] Ehlmann B. L. and Edwards C. S. (2014) Annu. Rev. Earth Planet. Sci. 42, 291–315. [2] Bibring J.-P. et al. (2006) Science 312, 400–404. [3] Schieber et al. (2022) LPSC #1034. [4] Rapin W. et al. (2021) Geology 49, 842–846. [5] Rampe et al. (2022) LPSC #1532. [6] Clark et al. (2022) LPSC #1160. [7] Goehring L. et al. (2010) Soft Matter 6, 3562–3567.

Figure 1: Context of the Layered Sulfate-bearing unit (LSu) exploration by the Curiosity rover. Top to bottom: map with rover traverse and general stratigraphic column; architecture of deposits observed on Rafael Navarro Mountain outcrop; example RMI close-up (red) showing evidence of large-scale cross-bedded sedimentary structures with possible hierarchy of eolian surfaces.

Figure 2: Top Geochemical transition into the sulfate-bearing unit as recorded by the ChemCam instrument on bedrock with both host and nodular textures. From left to right: Normalized sulfur signal on bedrock targets with elevation within the clay-bearing unit, the LSu, blue line shows bedrock average (host and nodular) highlighting a significant change of bedrock sulfur composition associated with the nodular bedrock (red line average); Sulfur as function of MgO and CaO content highlights the presence of Mg and Ca-sulfates in bedrock.

Figure 3: Remarkable nodular bedrock in the basal LSu highlights the diversity of textures observed within a short stratigraphic range with distinct sulfate-enriched composition. Decimeter-sized concretions (a); dark-toned nodular beds (b); regular pattern of polygonal ridges (c).

How to cite: Rapin, W., Sheppard, R., Dromart, G., Schieber, J., Clark, B., Kah, L., Rubin, D., Ehlmann, B., Gupta, S., Caravaca, G., Mangold, N., Dehouck, E., Le Mouélic, S., Gasnault, O., Clark, J., Bryk, A., Dietrich, W., Lanza, N., and Wiens, R.: The Curiosity rover investigates an aridification sequence in the layered sulfate-bearing unit., Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1112, https://doi.org/10.5194/epsc2022-1112, 2022.

Over the past 10 years, the Mars Science Laboratory (MSL) rover Curiosity has been investigating the plains of Aeolis Palus and the lower reaches of Aeolis Mons (informally known as Mount Sharp), a 5 km tall mound of sedimentary rocks in Gale crater (Figure 1). After traversing 27 km and nearly 600 m of vertical stratigraphy, three lithostratigraphic groups have been identified: Bradbury, Mount Sharp, and Siccar Point (SP). The Bradbury group consists of fluvial, deltaic, and lacustrine sedimentary rocks [1-2]. The Mt. Sharp group mainly consists of laminated mudstones with minor fluvial sandstones, interpreted as evidence of a long-lived lacustrine environment [1]. Locally, exposures of the Mt. Sharp group are unconformably overlain by aeolian cross-bedded sandstones of the SP group, interpreted to have deposited on an aeolian deflation surface [3].

While these three groups show evidence of deposition in specific environmental and climatic conditions, knowledge of their stratigraphic relationships is a key information to understand the evolution of environmental conditions in Gale. Yet, no clear stratigraphic contact has been observed at the boundary between the Bradbury and the Mt. Sharp groups. Because the mean dip of the Bradbury group is approximately horizontal, the MSL team suggested that the Bradbury group might be stratigraphically lower than the Mt. Sharp group, and therefore lower than the SP group [1]. Nonetheless, orbital analyses of the region suggested that capping strata of the Bradbury group could be part of the SP group [4]. Chemical data from the ChemCam and APXS instrument suites of Bradbury and SP group rocks have recently shown that both groups have similar compositions and possibly similar sediment sources [5-8]. In this study, we aim to reappraise the stratigraphic and chemical relationships between the Bradbury and SP groups using Mastcam [9-10] and ChemCam data [11-12] to characterize the evolution of Gale’s ancient environment.

Lithostratigraphy of Zabriskie Plateau

One of the best candidates to assess the potential contact between Bradbury and SP group rocks is located at the Zabriskie Plateau outcrop in the Pahrump Hills area (Figure 1). To better appreciate the facies and 3D geometry of the contacts, this outcrop has been reconstructed as a Digital Outcrop Model (Figure 2, https://skfb.ly/o9ZAq) [13]. In this model, we observe that most of the outcrop is composed of fine to medium-grained sandstones, arranged in dm- to meter-scale cross-stratifications, similar to some of the aeolian facies of the SP group [3]. These sandstones exist as “capping rocks” similar to previously described examples [4], suggesting that they are locally well-cemented on the topmost meter. Near the base of the DOM, we observe a meter-scale, ~30-cm thick, cross-stratified lens-shaped interval of coarser medium to pebble conglomerate. This level represents deposition under energetic aqueous conditions to transport clasts up to the pebble size, more likely to pertain to a fluvial channel. Interestingly, this conglomerate interval is at similar elevation (within one meter) to the surrounding sandstones, with no apparent unconformity, likely evidencing a conformable emplacement of this level within the finer sandstone succession. This would argue that the conglomerate level was deposited synchronously with the finer-grained sandstones during the same depositional event.

Chemical composition of Bradbury and Siccar Point groups

The average compositions of Bradbury and SP group rocks are overall quite similar (Table 1), and clearly distinct from Mount Sharp group rocks (Figures 3 and 4). By analyzing the rock compositions of Bradbury and SP groups, we sorted them into five major chemical groups, which are, in order of increasing average K₂O/Na₂O ratio and average K₂O content for groups 1 to 4: group 1 has a basaltic composition; group 2 has low SiO₂, intermediate TiO₂, high FeO_T and Na₂O contents; group 3 has low CaO, high TiO₂, FeO_T, and K₂O contents; group 4 has low TiO₂ and Al₂O₃, and very high K₂O contents; and group 5 has a composition close to group 1 with higher SiO₂ and alkali contents (Table 1, Figure 3). Overall, the MgO and Al₂O₃ contents are quite variable. The composition of these rocks suggests mixing between mafic minerals and feldspars, including alkali feldspars in various proportions (Figure 4). Interestingly, both Bradbury and SP rocks occur in the first three chemical groups, which suggests similar source rocks for both groups of at least two types: a relatively low-potassium basaltic rock and a potassic-rich rock. The relative abundance of potassic-rich source rock in the mixture is interpreted to increase from group 1 to group 4. Besides, Bradbury and SP group rocks have a low Chemical Index of Alteration (CIA), which is indicative of limited chemical weathering (Figure 4).

Conclusion

3D observations in the Pahrump Hills area suggest that Bradbury and Siccar Point units are intermingled and synchronous in an environment allowing fluvial episodes to occasionally occur among a drier setting, as observed on Earth [14]. This is consistent with the chemical compositions of Bradbury and Siccar Point groups which suggest similar source rocks in different relative abundances. This relationship implies that the Bradbury group could be younger than Mount Sharp group (Figure 5). To summarize, these observations are in favor of a common origin for both Bradbury and Siccar Point as a single clastic group, representing a temporal evolution from clement conditions during the deposition of Mount Sharp group to a colder and drier environment with still transient episodes of fluvial activity during the deposition of Bradbury and Siccar Point groups.

[1] Grotzinger et al., Science 2015. [2] Mangold et al., JGR 2016. [3] Banham et al., Sedimentology 2018. [4] Williams et al., Icarus 2018. [5] Bedford et al., Icarus 2020. [6] Bedford et al., JGR 2022. [7] Thompson et al., LPSC 2022. [8] Thompson et al., this conference. [9] Malin et al., LPSC 2010. [10] Bell et al., Earth and Space Science 2017. [11] Wiens et al., Space Sci Rev. 2012. [12] Maurice et al., Space Sci. Rev. 2012. [13] Caravaca et al., PSS 2020. [14] Newell, Marine and Petroleum Geology 2001.

How to cite: Le Deit, L., Caravaca, G., Mangold, N., Le Mouélic, S., Dehouck, E., Bedford, C. C., Wiens, R. C., Johnson, J. R., Gasnault, O., Forni, O., and Lanza, N.: Investigation of the stratigraphic and chemical relationships between Bradbury and Siccar Point lithostratigraphic groups in Gale crater, Mars, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-508, https://doi.org/10.5194/epsc2022-508, 2022.

Introduction:

Curiosity has encountered eolian Stimson formation, Siccar Point group sandstones [1-3] at several locations during ascent of Mount Sharp, Gale crater, at: 1) the Emerson and Naukluft plateaus; 2) on the northern Greenheugh pediment (GP); and most recently 3) on the eastern GP (Figure 1). The Siccar Point group unconformably overlies [4] the predominantly lacustrine, Mount Sharp group, which itself is considered to overlie the Bradbury group (Figure 2). Alpha Particle X-ray spectrometer(APXS) analyses acquired during recent investigations of the eastern GP have expanded the range of eolian Stimson formation compositions and provide further evidence for a relationship with Bradbury group sandstones and cap rocks encountered early in the mission. The Bradbury group includes alkaline composition sandstones, clasts within breccio-conglomerates, and float rocks interpreted to represent primary igneous and volcaniclastic rocks derived from mixing of multiple igneous source rocks [5-12]. We report the results of APXS analyses of the Stimson formation and discuss implications for provenance and timing of events within Gale crater.

APXS results:

Basaltic composition sandstones, related to average Mars sand and soil, were identified at all three Stimson locations (Figures 1,2). All compositions are discussed here, relative to typical basaltic Stimson chemistry. Sandstones with 3xK₂O and >MnO concentrations are identified on the northern GP overlying basaltic composition sandstones (Figures 1,2) [13-14]. Most recently, on the eastern GP, APXS analyses have revealed sandstones with even >K₂O concentrations that fall into two groups (Figures 1,2): 1) with ~4xK₂O, trending to >Na₂O concentrations, and 2) with ~5xK₂O, trending to <Na₂O, Al₂O₃, and Ni, ≫Zn and Ge, and ≈MgO concentrations. The eastern GP, high-K sandstones also overlie more typical basaltic chemistry sandstones.

Compositional relationship to Bradbury group and other targets previously encountered on the mission:

The higher-K, Stimson sandstones share many compositional characteristics with Bradbury group rocks as well as several float rocks encountered along the Mount Sharp group traverse [13-14] (Figures 3,4). The CCAM instrument has also detected similar relationships [15]. The Bradbury group targets include sandstones near the landing site, high-K Bathurst and Kimberley formation sandstones, and capping sandstones situated just prior to driving on to the Mount Sharp group. Related composition float rocks analyzed along the Mount Sharp traverse are typically associated with Stimson outcrops.

The higher-K Stimson sandstones do not plot on the sorting trend defined by the varying grainsize, modern Gale crater sands, and the basaltic Stimson sandstones on an A-CN-K diagram (Figure 4b). Instead, they are offset parallel to the plagioclase–potassium feldspar join. Thus, we do not attribute the compositional differences between the basaltic and high-K pediment Stimson to be the result of eolian sorting. Instead, based on sedimentology [3], mineralogy [16], and composition [13-14], we invoke a change in provenance, with input of a more potassium feldspar-rich source. Given the compositional relationship to Bradbury group sandstones, we suggest that the high-K Stimson sandstones are also derived from the mixing of multiple, igneous source rocks including basaltic and more alkaline compositions [13-14].

Many of the Bradbury group sandstones, Mount Sharp float and higher-K, pediment sandstones are also texturally alike. They are all relatively smooth, resistant, and blockier in appearance than typical basaltic Stimson sandstone (Figure 5). The high-K pediment and Bradbury sandstones also share similar orbital characteristics; both are manifest as crater-retaining units.

Timing Implications:

The more alkaline composition Bradbury group sandstones near the landing site are >9 km lateral distance and 400 m of elevation from the high-K pediment sandstones. Therefore, we have found evidence along the entire traverse for the presence of alkaline igneous source rocks. These source rocks have provided sediment input to both fluvial (Bradbury) and eolian (Siccar Point) sandstones [13-14]. Based on the compositional and textural relationships between the Bradbury and Siccar Point groups we revisit the timing of events at Gale.

The Bradbury group is generally considered to be older than both the Mount Sharp and Siccar Pt groups (Figure 1). This work raises the possibility that they could instead be contemporaneous, with both being younger than the Mount Sharp group. In this scenario, the Mount Sharp group represents relatively old lacustrine/fluvial deposits, which were buried, lithified, and eroded, before deposition of the Bradbury and Siccar Point groups onto that erosional surface, thus explaining differences in elevation between the two groups (Figure 6a). Alternatively, the Bradbury group alkaline sedimentary rocks are the oldest unit and would have been deposited prior to the Mount Sharp group. The Siccar Point group eolian sandstones (basaltic and alkaline) would then have been deposited on to the Mount Sharp group (Figure 6b). In this case, a more alkaline source area in the vicinity of, or within, Gale crater has been eroded by both water and wind at different times during the history of the evolution of the crater and its infill [13-14]. Both scenarios are consistent with widespread evidence at Gale crater for the presence of multiple igneous source rocks.

Acknowledgements:

MSL APXS is managed and financed by the Canadian Space Agency (CSA). Thanks to the JPL engineers and MSL science team. 

References:

[1] Banham, S.G., et al. (2018) Sedimentology, 65, 993–1042. doi.org/10.1111/sed.12469

[2] Banham, S.G., et al. (2021) JGR: Planets, 126 (4): e2020JE006554

[3] Banham, S.G., et al. (submitted) JGR: Planets

[4] Watkins, J.A., et al. (2016) 47th LPSC, Abstract #2939

[5] Stolper, E.M., et al. (2013) Science 341 (6153), 1239463. doi:10.1126/science.1239463

[6] Schmidt, M.E., et al. (2014) JGR Planets, 119(1):64-81, doi:10.1002/2013JE004481

[7] Sautter, V., et al. (2015) Geoscience, 8(8), 605.

[8] Thompson, L.M., et al. (2016) JGR Planets, 121(10):1981-2003, doi:10.1002/2016JE005055

[9] Treiman, A.H., et al. (2016) JGR Planets, 121(1), p.75 – 106. doi:10.1002/2015JE004932

[10] Cousin, A., et al. (2017) Icarus 288, 265-283. doi:10.1016/j.icarus.2017.01.014

[11] Edwards, P.H., et al. (2017) MAPS, 52 2931-2410. doi.org/10.1111/maps.12953

[12] Bedford, C.C., et al., (2019) Geochimica et Cosmochimica Acta, 246, 234-266. doi.org/10.1016/j.gca.2018.11.031

[13] Thompson, L.M., et al., (submitted) JGR Planets 2021JE007178

[14] Thompson, L.M., et al., (2022) 53rd LPSC, 1475.pdf

[15] LeDeit, L., et al. (this conference)

[16] Thorpe, M.T., et al. (Submitted) JGR Planets 2021JE00709

How to cite: Thompson, L., Spray, J., Gellert, R., Williams, R., Berger, J., O'Connell-Cooper, C., Yen, A., McCraig, M., VanBommel, S., and Boyd, N.: APXS-determined compositional diversity of eolian Siccar Point group sandstones, Gale crater Mars: Implications for provenance and timing of events, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1184, https://doi.org/10.5194/epsc2022-1184, 2022.

A Mastcam-Z mosaic of basal delta strata acquired on sol 411 in the vicinity of Three Forks and at an approximate distance of 250 m from the scarp provides a spectacular view of a prominent embayment in the delta scarp that has been informally named Hawksbill Gap. Hawksbill Gap is the proposed ascent route for Perseverance in her investigation and sampling of delta front strata. Prominent cliffs that make up the eastern and western margin of Hawksbill Gap show stratal patterns similar to those observed at Kodiak. The mid-sections of the scarps are characterized by decametre-scale inclined strata interpreted as foreset strata of a Gilbert-type delta succession. Internally these comprise stacked tabular beds that are locally conglomeratic but predominantly comprise finer-than-conglomerate lithologies, likely pebbly sandstones. Units with variable dips are present, together with some evidence of over-steepened dips suggestive of possible slumping or synsedimentary deformation. On the eastern side of Hawksbill Gap, the inclined strata are overlain across a sharp truncation surface by generally planar parallel thin-bedded horizontal strata that we interpret as topset beds deposited by fluvial processes in a delta top environment. The prominent erosion surface separating the foresets from the topsets indicates that these are oblique prograding clinoforms, which suggests delta progradation here during lake level fall based on Earth field examples and experimental studies. Conglomerate beds containing boulders are observed within the topset strata indicating sediment-transport on the delta top by episodic high-discharge floods. Their relationship to the delta-capping boulder conglomerates described by Mangold et al.  2021 that were interpreted as evidence for major post-delta flood episodes remains to be determined. Foreset beds capped by sub-horizontal topsets are also observed on the western flank of Hawksbill Gap. Observations of the western flank of Hawksbill Gap, interpreted to be a promontory of a preserved channel body show complex bivergent inclined stratification indicative of a complex delta geometry, possibly a very narrow (~200 m wide) lobe distinct from other lobes of the delta. Detailed analysis of such stratigraphic patterns will permit reconstruction of fine-scale depositional processes and preservation here.

The Sol 411 Mastcam-Z mosaic from Three Forks also revealed the basal stratigraphy of the Jezero western delta for the first time showing low relief, recessive strata separated by laterally continuous at 100 m scale, thin tabular resistant beds that provide useful local marker horizons to sub-divide the stratigraphy. On a ledge at the top of lowermost strata, a distinct very light-toned layer that is laterally continuous for tens of metres is observed in the Mastcam-Z mosaic (and also in HiRISE imagery). This distinct unit has been informally named at two locations as Hogwallow Flats and White Rocks.  Above Hogwallow Flats a prominent resistant planar unit that forms a distinct planar unit named Rocky Top is visible in Mastcam-Z and HiRISE imagery. This unit in vertical section has thin-bedded strata in its lower part and more thickly bedded at its top which may represent a thickening-up succession typical of lobe progradation in delta toe settings.  This unit is laterally discontinuous clearly pinching out to the east and disappearing within less resistant beds.

In the light of the occurrence of horizontally bedded strata at the base of the delta scarp and also located below, the horizontally bedded basal strata below the large-scale inclined strata interpreted as foreset beds may represent bottomset and delta toeset beds. In this scenario, the more resistant beds may represent coarser-grained turbidite flow deposits, with the less resistant strata perhaps representing finer-grained rocks that weather more recessively. The latter may have formed from either fine-grained turbidity currents or decantation processes in a prodelta environment. Close range observations are required to test these hypotheses.

Interrogation of the stratal geometry and sedimentary facies of the western delta succession will provide constraints on the character, relative timing and persistence of ancient aqueous activity at Jezero. Such analyses inform interpretations of Martian climate evolution, potential habitability, and search strategies for rocks that might contain potential biosignatures and organic matter.

References: [1] Goudge et al. (20170 EPSL doi:10.1016/j.epsl.2016.10.056

[2] N. Mangold, et al., (2021) Science, 10.1126/science.abl4051.  

[3] Caravaca et al, (2022) EPSC this meeting.

How to cite: Gupta, S. and the NASA Mars2020 science team: Sedimentary and stratigraphic observations at the Jezero western delta front using Perseverance cameras: initial constraints on palaeoenvironments, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1098, https://doi.org/10.5194/epsc2022-1098, 2022.

Introduction:

The Perseverance rover landed at Jezero crater in 2021, close to the delta of an ancient river (1). This crater once hosted a paleolake (2). Previous studies of this system have concluded that the current fan-delta units were formed during the last phase of the Jezero fluvial activity, which postdates the formation of the olivine-rich unit and predates the formation of the current floor unit. From crater counts, the formation of the delta unit is assigned to an Early or Late Hesperian age (3.5 + 0.1/-0.3 Gy) (3). However, little is known about the processes that happened before and the plausible fluvial and igneous history that determined the evolution of the fresh impact crater. A comparative analysis with craters of similar size suggests that Jezero crater has experienced approximately 1 km of infilling compared to the morphologically fresh crater(4,5). The crater floor depth d can be calculated with the power-law scaling d = 0.372D^0.375 + 0.072D^0.62  (6) , which is valid for craters wider than 7 km. For Jezero D=49 km and the crater floor base should be at a depth of 2,404 m.

The purpose of this work is to investigate the plausible existence of preserved radar reflectors  (7–12) that may indicate the geometry of crater filling layers. Recent research by other authors (7) have confirmed the usefulness of this approach to detect preserved layers in other craters. Here we shall apply a similar methodology to investigate it on Jezero crater.

Materials and methods:

SHARAD is a sounding radar experiment aboard the MRO mission designed to reveal the shallow structures of the Martian subsurface.(9). We visualize SHARAD radargrams using JMARS software. When a potential echo is detected as a bright feature, these signals have to be compared with the simulated cluttergrams, that are produced using the current surface topography, (MOLA-HRSC with 200m/pix. and MOLA with 463m/pix) in order to discriminate ghost signals.  The protocol followed to investigate the plausible existence of buried reflectors on MARS using SHARAD data is the following one:

• Interpret visually the radargrams looking for subsurface reflectors in JMARS.
• Download the geometry data for each radargram under investigation and crop only the area of study, to reduce the computational time.
• Build the clutter simulation using the sets of topography data mentioned above. The data were downloaded from astrogeology. The DTM was selected only for the area of interest to reduce the overall computational resources. The clutter simulator estimates the reflected echoes from the topography based on the directivity pattern of the antenna, the distance from the source, and the orientation of the slope with respect to the angle of incidence (13)
• Compare the off-nadir reflections with the apparent bright reflectors.
• If a true reflector is detected, the wave travel times can be transformed to depth using Δh=c Δt/√ε where ε is the assumed permittivity of the materials above the reflector.

In order to test our methodology we validate it in a previously described case, in a crater near Mangala Fossa region (7). A confirmed  reflector, which is distinguished in the radargram underneath the subsurface (Fig1-b) is not seen in the cluttergram (Fig1-a) confirming it as a true buried reflector. Any other bright feature that appears in both images is an artifact produced by the radar echo of the surface.

Next we apply this methodology to Jezero crater. We observe in Figure 2-b an example of a potential reflector. To confirm or discard the nature of this reflector we compare with the cluttergrams at different resolution scales, in Figure 2-a and 2-c. The reflectors from SHARAD data are observed on the radagrams at both resolution scales and therefore they are interpreted as artifacts produced by surface topographic echoes. Similar examples are shown in Figures 3 and 4.

Conclusions:

Our preliminary analysis, can discard the existence of true recognizable reflectors at Jezero. Assuming ε= 6  (14)  and a crater filling depth of about 1 km, a crater-base reflector should have given an echo at a single travel time less or equal than 8165 ns. This distance is covered in our investigation and therefore this analysis suggests that SHARAD measurements can neither detect any reflector within the crater filling nor distinguish the crater floor. This may be due to the presence of strong off nadir reflections produced by the surface topography that may overwrite true reflectors. Moreover, gradual variations between layers can reduce their reflection coefficients making them transparent to radar. Future studies will investigate the existence of subsurface reflectors in environments with higher signal to clutter ratio, such as paleolake environments with smoother surfaces.

Acknowledgments: We are grateful to the PDS, SHARAD and HRSC for the materials and JMARS and QGIS for the software. The work of F. Mansilla is supported by the grant PRE2020-09170 founded by MCIN/AEI/10.13039/501100011033. Spanish State Research Agency (AEI) Project No. MDM‐2017‐0737 Unidad de Excelencia “María de Maeztu”‐ Centro de Astrobiología (INTA‐CSIC) and the Spanish Ministry of Science and Innovation (PID2019‐104205GB‐C21).

References:

• N. Mangold et al., Science. 374, 711–717 (2021).
• C. I. Fassett, J. W. Head, Geophys. Res. Lett.32, 14, (2005)
• N. Mangold et al., Astrobiology. 20, 994–1013 (2020).
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How to cite: Mansilla, F., Zorzano, M. P., Giannakis, I., and Ruiz, J.: No evidence of reflectors on Jezero radargrams, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-460, https://doi.org/10.5194/epsc2022-460, 2022.

Introduction: Mars is a primary destination to search for signs of life and probing the subsurface is a key element in this search. Access to the Martian subsurface, under most altered layers, is needed to understand the nature, timing and duration of alteration and sedimentation processes on Mars, as well as habitability conditions. For such a reason, ExoMars rover mission includes a drill to collect subsurface samples and has a complex payload able to conduct detailed investigations of composition, search for organics, and recognize indicators of past or extant life[1]. The drill is a critical element of the mission which will explore and collect samples down to 2 m of depth. An essential part of the payload is Ma_MISS (Mars Multispectral Imager for Subsurface Studies) experiment hosted by the drill system[2,3]. Ma_MISS is a Visible and Near Infrared  miniaturized spectrometer with an optical head inside the drill tip capable of observing the borehole from where samples are collected.

Ma_MISS instrument description: Ma_MISS miniaturized spectrometer is hosted inside the drill system of the ExoMars rover and will characterize the mineralogy and stratigraphy of the excavated borehole wall at different depths (up to 2 m).

Ma_MISS is a modular instrument, and it consists of two main parts: (i) the spectrometer with the PE located outside of the drilling tool, and (ii) the Optical Head (OH) and fibers located inside the drill itself (Fig.1). The Drill consists of a main rod and three additional rods  to reach a maximum depth of 2 m. The drill tip also has the Ma_MISS OH with a sapphire window to observe the borehole wall. All the rods are equipped with optical fibers to transmit light and signal. Ma_MISS is equipped with a light source of 5W and the illumination spot is about 1 mm at a focal distance of about 0.6 mm. The reflected light is collected through a 120 μm spot. The spectrometer observes a single point on the borehole wall and, using the drill movements, can build up  images of the target. By combining several column and ring observations, Ma_MISS allows the reconstruction of a complete image of the borehole wall (Fig.2). Ma_MISS spectral characteristics and fine spatial resolution enable the in situ investigation of rocks, prior the sample collection, that will be manipulated and crushed for  further analysis by the analytical laboratory. Thus, Ma_MISS is the instrument that will closely investigate the mineralogical characteristics of Mars subsurface material in its original geologic context.

What mineralogy is expected in the subsurface ? Ma_MISS will investigate deeper into the subsurface than prior rover missions. Viking and Phoenix landers scooped materials from the upper few centimeters for compositional analysis. The MER  excavated trenches up to 11 cm deep[4] and collected data with the alpha-particle x-ray spectrometer and Mossbauer instruments. The MERs [5]  grounded up to 9 mm deep and revealed coatings enriched in S, Cl, Zn and Ni and iron oxides on outer rock surfaces. The MER data from the subsurface show that those soils had high ferric sulfate contents or silica contents, likely signaling an influence from volcanic or hydrothermal processes[6,7]. Mars Science Laboratory (MSL)  drilled several holes into the Martian surface demostraing differences between the surface and the subsurface, as shown in the colors of the excavated fines, mainly linked with the oxidation state of the materials[8]. Most interesting is the fact that well preserved organic material was discovered at Pahrump Hills , even with the very harsh surface conditions, suggesting even better preservation may be possible farther beneath the Martian surface[9].

Differently from the previous missions, the drill and Ma_MISS measurements will be the deepest compositional measurements made on Mars. Ma_MISS is able to detect compositional gradients with depth, changes in type and abundance of minerals, weathering fronts or rinds, and diagenetic veins or nodules. The spectral range of Ma_MISS is optimal to detect changes in the occurrence and crystal chemistry of olivines and pyroxenes as well as Fe(II)/Fe(III) in silicates, oxides, and salts. There may be changes in these redox sensitive minerals with depth that record different environments. Furthermore, changes in the hydration state of materials can be also detected.  For Oxia, the study of the subsurface could provide information on depositional regimes in zones not too far from the delta deposits, using the granulometric variation with dept.This will help to reconstruct the paleoenvironments that have characterized Oxia Planum.

In addition, at sufficient concentrations, organic molecules will also be detectable [10]: depending on the kind of organic, Ma_MISSis capable to detect their presence even when a 1 wt.% in the mixture, as verified by specific tests in the laboratory using the Ma_MISS breadboard. Spectroscopic measurements on these mineral/organic mixtures are useful to understand how the Ma_MISS instrument can detect traces of organic intimately mixed with minerals.

Conclusion: Ma_MISS will reconstruct the 3-D images of the borehole excavated by the ExoMars drill and will acquire spectra of the subsurface layers from which the sample will be collected. The calibration and tests performed with the flight model demonstrate the ability of the instrument in detecting most of the spectral signatures expected in Martian subsurface, including those due to the presence of possible salts and organics.

Acknowledgments. This work is fully funded and supported by the Italian Space Agency (ASI) [Grant ASI-INAF n. 2017-48-H.0].

References. [1] Vago et al. (2017) Astrobiology 17, 471–510. [2] De Sanctis, M. C. et al. (2017) Astrobiology, 17(6–7). [3] De Sanctis et al. (2022) PSJ in press. [4] Sullivan, R., et al.. (2011), J. Geophys. Res., 116, E02006; [5] Gorevan et al., (2003), J. Geophys. Res., 108, 8068; [6] Gellert, R and Yen, A.S, (2019) Remote Compositional Analysis, 10.1017/9781316888872, (555-572); [7] Morris et al., (2019), Remote Compositional Analysis, 10.1017/9781316888872, (538-554); [8] Abbey et al., (2020), Icarus,  /doi.org/10.1016/j.icarus.2020.113885. [9] Eigenbrode et al., 2018, Science, doi/10.1126/science.aas9185, [10] Ferrari et al., 2022. In preparation.

How to cite: De Sanctis, M. C., Altieri, F., De Angelis, S., Ferrari, M., Frigeri, A., Fonte, S., Ammannito, E., Brossier, J., Giardino, M., Apuzzo, A., costa, N., and rossi, L.: Ma_MISS: a powerful tool for exploring the Martian subsurface, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-104, https://doi.org/10.5194/epsc2022-104, 2022.

CLUPI, the high-performance colour close-up imager, on board the 2020 ExoMars Rover plays an important role in attaining the mission objectives: it is the equivalent of the hand lens that no geologist is without when undertaking field work. CLUPI is a powerful, highly integrated miniaturized (<900g) low-power robust imaging system, able to sustain very low temperatures (–120°C). CLUPI has a focus mechanism allowing a working distance from 11.5cm to infinite providing outstanding pictures with a color detector of 2652x1768x3. At 11.5cm, the spatial resolution is 8 micrometer/pixel in color (Josset et al, 2017). The concept benefits from well-proven heritage: Proba-1, Rosetta, MarsExpress and Smart-1 missions…The CLUPI payload accommodation on the drill box of the rover allows to perform several key science operations configuration thanks to the two degrees of freedom movement of the drill, height and rotation. (Fig. 1).

In a typical field scenario, the geologist will use his/her eyes to make an overview of an area and the outcrops within it to determine sites of particular interest for more detailed study. In the ExoMars scenario, after having made a preliminary general evaluation, the geologist will approach a particular outcrop for closer observation of structures at the decimetre to subdecimeter scale before finally getting very close up to the surface with a hand lens (CLUPI), and/or taking a hand specimen, for detailed observation of textures and minerals. Using structural, textural and preliminary compositional analysis, the geologist identifies the materials and makes a decision as to whether they are of sufficient interest to be subsampled for laboratory analysis (using the ExoMars drill and laboratory instruments).

Given the time and energy expense necessary for drilling and analysing samples in the rover laboratory, preliminary screening of the materials to choose those most likely to be of interest is essential. ExoMars will be choosing the samples exactly as a field geologist does – by observation (backed up by years and years of field experience in rock interpretation in the field). Because the main science objective of ExoMars concerns the search for life, whose traces on Mars are likely to be cryptic, close up observation of the rocks and granular regolith will be critical to the decision as whether to drill and sample the nearby underlying materials.  Thus, CLUPI is the essential final step in the choice of drill site. But not only are CLUPI’s observations of the rock outcrops important, but they also serve other purposes. CLUPI, could observe the placement of the drill head. It will also be able to observe the fines that come out of the drill hole, including any colour stratification linked to lithological changes with depth. Finally, CLUPI will provide detailed observation of the surface of the core drilled materials when they are in the sample drawer at a spatial resolution of about 17 micrometer/pixel in color. All of these investigations are summarized in the figure 1 describing the CLUPI science operational configurations.

After a brief description of these science observation configurations of CLUPI, the first promising results of the operations preparations and simulations in order to optimize the science return will be detailed. Indeed, the science operation simulations are performed by using a CLUPI flight model representative together with a drill/rover simulator, all inside a dedicated laboratory of the Space Exploration Institute based in Microcity, Neuchatel in Switzerland. The relevant results are of prime importance for the future science exploitation of CLUPI. It demonstrates the CLUPI capabilities to provide information significantly contributing to the understanding of the geological environment and could identify outstanding potential biofabrics of past life on Mars.

Figure 1: CLUPI science operational configurations. (a) On the platform, (b) geological environment survey, (c) Close-up outcrops observation, (d) drilling area observation, (e) drilling operation observation, (f) Drill hole and fines observation, (g) drilled core sample observation and (h) calibration: calibration target imaging. Images credit: ESA/SEI-TJ

Figure 2: SEI CLUPI Science Operations Laboratory based in Microcity Neuchatel. Simulations using a CLUPI flight model representative. Images Credit: Space Exploration Institute (SEI)

Figure 3: Left: CLUPI on the drill/rover simulator, sample observation configuration. Right: CLUPI output data, mosaic of three images. Images Credit: Space Exploration Institute (SEI). CLUPI Science Operations Laboratory based in Microcity Neuchatel. Simulations using a CLUPI flight model representative

How to cite: Josset, J.-L. and the CLUPI Team: CLUPI, Close-UP Imager on the ExoMars rover mission, Status and Science Operations Preparations/Simulations First Results, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1256, https://doi.org/10.5194/epsc2022-1256, 2022.

The WISDOM (Water Ice Subsurface Deposits On Mars) ground penetrating radar (GPR) (2)(3) has been specifically designed for the ExoMars (ESA/ROSCOSMOS) Rosalind Franklin rover to investigate the first meters below the surface of Oxia Planum in order to understand the geological context of the landing site and to provide guidance for sample collection by the drill.

The detection of clear buried interfaces or resolvable large reflecting structures might be the most rewarding features a GPR can reveal. Nevertheless, the shallow subsurface of some locations in Oxia Planum may be such as WISDOM radargrams would be difficult to interpret because of the lack of clearly identifiable structures. In particular, this will be the case if the subsurface consists in a heteregenous medium including a large density of scattering  structures of dimension commensurate with WISDOM wavelengths of operation. Such scattering structures could be indicative of local changes in porosity or composition ; their characterisation is of interest as it provides information about the geological history and processes in the investigated area. This work proposes and tests a method to statistically estimate the typical size and, possibly shape, of buried scatterers and to retrieve their permittivity contrast with the surrounding material from WISDOM radargrams.

• WISDOM, GPR of the ExoMars mission 

The WISDOM instrument is a step-frequency radar operating in a broad frequency bandwidth (0.5-3 GHz) corresponding to wavelength values ranging from 5 cm to 27 cm (for a relative permittivity value of 5), that ensures a vertical resolution better than 3 cm in the subsurface (1). WISDOM is also a polarimetric GPR. Thanks to its antenna system, it can acquire data in four polarization configurations (6) which allows an in-depth analysis of the received echoes for a better characterization of the shape and orientation of any buried reflector. These characteristics make WISDOM an instrument very well suited to the quantitative analysis of small-scale heterogeneities in the subsurface. 

• Method

For this study,  we have conducted numerical simulations with the code TEMSI-FD (4), which solves Maxwell equation using the Finite-Difference Time-Domain (FDTD) method. TEMSI-FD can simulate the propagation of WISDOM electromagnetic waves in  realistic environments. 

For the purpose of our study, we have considered subsurfaces embedding heterogeneities of fractal properties. These latters were generated by the diamond-square splitting technique implemented in the TEMSI-FD code. The resulting medium is characterized by 3 parameters : its mean relative permittivity mean, the standard deviation of its permittivity and the typical size of the heterogeneities L.

For a given set of these parameters, a number of subsurface volumes were generated in order to be able to perform meaningful statistical averages. Fig. 1 shows two examples of modeled subsurfaces with different L values and somewhat similar distributions of permittivity (right).