Displays

One of the main goals of the magnetometer experiment MPO-MAG on board of the Magnetospheric Planetary Orbiter (MPO) during the BepiColombo mission is the determination of the Mercury main magnetic field, epecially in constraining the characteristics of the magnetic dipole offset.
In April 2020 BepiColombo had its Earth Gravity Assist manoeuvre on its way to planet Mercury.
The topocentric distance was lower than three Earth radii and offered a unique opportunity to compare the magnetometer measurements to a multitude of simultaneous measurements of the magnetospheric environment of the Earth performed by several other spacecraft like THEMIS and MMS.
Using a great number of probing points to constrain models of the Earh magnetosphere and compare models to actual measurements of the MPO-MAG sensors enables us to determine the absolute sensor attitude to an accuracy of only a few arc minutes.
Knowing the absolute attitude of a magnetometer sensor in planetary orbiter missions is a key component for the magnetic main field determination.
We present the modelling approach to compare to measurements from MPO-MAG and a study showing the dependence of a mainfield determination on the accuracy of the sensor orientation.

How to cite: Mieth, J. Z. D., Heyner, D., and Glassmeier, K.-H.: Absolute Magnetometer Attitude Reconstruction using Magnetospheric Modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8271, https://doi.org/10.5194/egusphere-egu2020-8271, 2020.

The Mercurian Gamma-ray and Neutron Spectrometer (MGNS) is a scientific instrument developed to study the elementary composition of the Mercury’s sub-surface by measurements of neutron and gamma-rays emission of the planet. MGNS measures neutron fluxes in a wide energy range from thermal energy up to 10 MeV and gamma-rays in the energy range of 300 keV up to 10 MeV with the energy resolution of 5% FWHM at 662 keV and of 2% at 8 MeV. The innovative crystal of CeBr₃ is used for getting such a good energy resolution for a scintillation detector of gamma-rays.

During the BepiColombo long cruise to Mercury, it is planned that the MGNS instrument will operate practically continuously to perform measurements of neutrons and gamma-rays fluxes for achieving two main goals of investigations: monitoring of the local radiation background of the prompt spacecraft emission due to bombardment by energetic particles of Galactic Cosmic Rays and the participation in the Inter Planetary Network (IPN) program for the localization of sources of Gamma-Ray Bursts in the sky.

The MGNS instrument will also perform special sessions of measurements during flybys of Earth, Venus and Mercury with the objective to measure neutron and gamma-rays albedo of the upper atmosphere of Earth and Venus and of the surface of Mercury. Another objective is to test the computational model of the local background of the spacecraft using the data measured at different orbital phases of flyby trajectories. The low altitude flybys (such as the 700 km flyby for Venus and three 200 km flybys for Mercury) would be the most useful for such tests being BC maximally shadowed for cosmic radiation by the actual planet. Neutron and gamma-rays measurements during Earth flybys enable investigation of interaction between solar wind and Earth environments as well as studies of spacecraft neutron and gamma-rays background upon its passage through the Earth's radiation belts.

How to cite: Kozyrev, A., Litvak, M., Malakhov, A., Mitrofanov, I., Mokrousov, M., Sanin, A., Tretiyakov, V., Owens, A., Schulz, R., and Quarati, F.: Spectroscopy of gamma-rays of Earth, Venus and Mercury: MGNS instrument onboard BepiColombo mission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9657, https://doi.org/10.5194/egusphere-egu2020-9657, 2020.

Mercury has been extensively resurfaced by large, effusive lava plains [1–2]. Similar lava plains on the Moon, the maria, are known to contain volatiles [3–4] and are estimated to have outgassed ~10¹⁶ kg of CO and S and ~10¹⁴ kg of H₂O, with the bulk of volatiles being released during peak mare emplacement ~3.5 Ga ago [5]. If volcanic activity released substantial volatiles on the Moon [6–7], then it is possible that substantial volatiles were also volcanically released on Mercury, albeit with different chemical species [6–9]. Here we seek to understand the potential contribution of outgassing to volatile deposits, specifically for Mercury’s volatile species (S, CH₄, Cl, and N-H).

We analyze the production function of volcanic plains deposits on Mercury and find that the volume of outgassed basalts on Mercury is 2 to 3 orders of magnitude larger than that predicted for the Moon [8]. We use a variety of experimental petrology studies [10–12] to predict the dominant species and their abundances associated with these eruptions on Mercury, providing estimates for both low-gas and high-gas scenarios for different oxygen fugacities (IW-3 and IW-7). The most prevalent volatile species predicted for Mercury (S, CH₄, and Cl) are 1 to 4 orders of magnitude more abundant than what is predicted for the most abundant volatiles outgassed on the Moon (CO, S, and H₂O) [5].

On the Moon, it has been predicted that volatiles outgassed from the formation of the maria may have been present in sufficient volumes to produce a transient atmosphere capable of aiding in the transport of H₂O to cold-trapping regions [5]. At mantle pressures and Mercury’s extremely reducing conditions, H₂O is not predicted to be present in the magma [e.g., 6–12]. Therefore, Mercury’s outgassed volatiles are of a different composition from the H₂O ice observed at Mercury’s poles today [e.g., 13], and the polar H₂O-ice deposits are better explained by some external delivery mechanism (likely cometary impacts). But the fate of large volumes of volatiles other than H₂O is an important unanswered question for Mercury.

The large volumes of outgassed volatiles calculated here suggest that volcanism on Mercury may have resulted in the transient production of anomalously high atmospheric pressures of short lifetime due to solar proximity. If Mercury’s atmospheric loss rate was insufficient to lose all of the erupted gases, then it is possible that ancient, outgassed volatiles remain trapped in the planet’s subsurface today. The fate of Mercury’s outgassed volatiles is an important open question that we discuss in this work.

References: [1] Head et al. (2011). [2] Denevi et al. (2013). [3] Boyce et al. (2010). [4] McCubbin et al. (2010). [5] Needham and Kring (2017). [6] Nittler et al. (2011). [7] Zolotov et al. (2013). [8] Peplowski et al. (2016). [9] Greenwood et al. (2018). [10] Anzures et al. (2017). [11] Armstrong et al. (2015). [12] Libourel et al. (2003). [13] Lawrence et al. (2013).

How to cite: Deutsch, A., Head, J., Parman, S., Wilson, L., Neumann, G., and Lowden, F.: The mass flux of volatiles from volcanic eruptions on Mercury, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3742, https://doi.org/10.5194/egusphere-egu2020-3742, 2020.

Mercury and the Moon are examples of terrestrial bodies which lack an atmosphere and therefore have surfaces which interact directly with the space environment. Thus the surfaces can be reprocessed by plasma impact, and in the process can emit X-rays via the Particle Induced X-ray Emission (PIXE) process. We will present and review existing measurements, particularly from SMART-1 and Chandrayaan at the Moon, and Messenger and Mercury, in order to predict opportunities for new science at Mercury by BepiColumbo. We will present predictions of PIXE signals from different regions of the Mercury surface, and examine the possibility of using the signal for direct diagnosis of particle interactions with the surface. These include the auroral signatures of substorm like behaviour, and interactions with coronal mass ejections.

How to cite: Grande, M. and Cooper, R.: Particle Induced X-ray Emission at Mercury and the Moon., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18423, https://doi.org/10.5194/egusphere-egu2020-18423, 2020.

The surfaces of Mercury and Moon are thought to be similar in terms of being rocky, regolith covered planetary bodies, dominated by pyroxene and plagioclase (Taylor et al. 1991, McCoy et al. 2018). Contrary to the Moon, Mercury possesses a global dipole magnetic field, resulting in a highly dynamic magnetosphere that varies surface exposure to solar wind ions and energetic electrons (Winslow et al. 2017, Gershman et al. 2015). The energy of these particles is thereby transferred and material is sputtered from the surface (Sigmund 2012), providing the main contributions to the exospheres of the Moon and Mercury. Parametrizing the underlying sputtering processes is of great interest for successfully linking exosphere observations with surface compositions (e.g. Wurz et al. 2010, Merkel et al. 2018).

The understanding of sputtering from the kinetic energy transfer is sufficient to predict sputter yields of singly charged impinging ions on conducting surfaces (e.g., Stadlmayr et al. 2018). Hijazi et al. (2017) and Szabo et al. (2018) have also made advancements on potential sputtering, investigating the interaction of multiply charged ions with glassy thin films. We expand on their studies and use mineral powder pellets as analogues for sputtering experiments relevant to the surfaces of the Moon and Mercury. The powder pellets include plagioclase, pyroxene, and wollastonite. The latter is a pyroxene-like Ca-rich mineral with Fe contents below detection limits, which allows investigating the effect on reflectivity during sputtering of Fe-free minerals. With these analogues, we strive to supply infrared spectra with a focus on the robust mid infrared (MIR) range for Mercury and sputter yields for both the Moon and Mercury. 

First results of irradiated mineral pellets include MIR spectra of the minerals before and after irradiation as well as sputtering yields and visual alteration effects. So far, no relevant changes in the MIR spectra were observed nor any visual alteration of wollastonite. The first irradiation with 4 keV ⁴He⁺ reached a fluence of about 29 E+20 ions per m² at an angle of 30°. Presumably, the lack of visual alteration is due to the absence of Fe in wollastonite. Further results are expected to bring clarity in the reaction of pellets to irradiation and if their sputtering characteristics differ from those of glassy thin films.

Gershman, D. J., et al. (2015). J. Geophys. Res.-Space, 120(10).

Hiesinger, H., & Helbert, J. (2010). Planet. Space Sci., 58(1–2).

Hijazi, H., et al. (2017). J. Geophys. Res.-Planet, 122(7).

McCoy, T. J., et al. (2018). Mercury: The View after MESSENGER.

Sigmund, P. (2012). Thin Solid Films, 520(19).

Stadlmayr, R., et al. (2018). Nucl. Instrum. Meth. B, 430.

Szabo, P. S., et al. (2018). Icarus, 314.

Taylor, G. J., et al. (1991). Lunar sourcebook-A user’s guide to the moon.

Winslow, R. M., et al. (2017). J. Geophys. Res.-Space, 122(5).

How to cite: Jäggi, N., Galli, A., Wurz, P., Biber, H., Szabo, P. S., Aumayr, F., and Mezger, K.: Mineral powder samples for solar wind ion sputtering experiments relevant for Moon and Mercury, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3303, https://doi.org/10.5194/egusphere-egu2020-3303, 2020.

The large anomalies in the lunar gravity field are in most cases the result of large impacts that occurred more than 3 billion years ago.  Today those anomalies provide the stability of the lunar rotation and if removed would cause a change in the position of the intersection of the spin pole with the lithosphere. Thus, extracting a gravity anomaly from today’s gravity field can provide the approximate location of the pole of rotation prior to the impact that caused the anomaly.  By removing the gravity field of each anomaly in order of age, youngest first, we can estimate the path of the lunar pole back 3 to 4 billion years, to the beginning of the time of heavy bombardment.

Starting from the GRAIL gravity model we selectively remove large gravity anomalies by first determining the center and dimensions of the anomaly from the Bouguer gravity and then deriving the average free air gravity for the Bouguer location and dimensions. The anomaly field is expanded into spherical harmonics and the degree 2 terms used to derive the change in pole position caused by the anomaly. Removing each anomaly in order of increasing age provides an estimate of the pole path from before the time of the first anomaly, SP-A.  Since the pole path depends on the order of the gravity anomalies being created it is important to know when each impact induced anomaly occurred.  The results suggest the re-constructed motion of the lunar pole of rotation is within approximately 10 dgerees of the present pole.

How to cite: Smith, D. E., Zuber, M. T., Goossens, S. J., Neumann, G. A., and Mazarico, E.: Deriving the ancient lunar pole path from impact induced gravity anomalies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6112, https://doi.org/10.5194/egusphere-egu2020-6112, 2020.

Planetary impact events eject large volumes of surface material.  Crater excavation processes are difficult to study, and in particular the details of individual ejecta fragments are not well understood.  A related, enduring issue in planetary mapping is whether a given crater resulted from a primary impact (asteroid or comet) or instead is a secondary crater created by an ejecta fragment.  With mapping and statistical analyses of six lunar secondary crater fields we provide three new constraints on these issues: 1) definition of the maximum secondary crater size as a function of distance from a primary crater on the Moon, 2) estimation of the size and velocity of ejecta fragments that formed these secondaries, and 3) estimation of the fragment size ejected at escape velocity. 

We mapped secondary craters around primary craters ranging in size from ~0.83–660 km in diameter using Lunar Reconnaissance Orbiter Camera (LROC) Narrow and Wide Angle Camera images.  Identification of secondary craters was based on expected secondary crater morphologies (e.g., v-shaped ejecta, clusters or chains, and elongation in the direction radial to the primary, similarity in degradation state across the secondary field) and secondaries were assigned a confidence level (as to whether they were likely a secondary crater) based on the number of expected morphologies they displayed.  Only the most confident features were utilized in this work, as there is no way to capture all secondary craters within a given lunar secondary field.  Scaling from secondary crater sizes to ejecta fragment sizes was carried out using the Housen-Holsapple-Schmidt formulations.                                                                                                                          

The largest secondaries and those made by the highest velocity fragments (up to ~1.4 km/s) were mapped around the Orientale basin.  The estimated size of fragments that could reach the lunar Hill-sphere escape velocity of 2.34 km/s varies by the size of the impact event, but could be as large as ~850 m for Orientale.  Note that these are not necessarily expected to be coherent fragments, they could also be loosely bound collections of smaller fragments.  However, the fragments/clumps mapped here remained in a form that resembles a single fragment in order to form the distinct secondary craters observed.  For low velocity secondaries, surprisingly, we found features that appear to be secondary craters formed from fragments with velocities as small as 50 m/s around the smallest primary.  

Through this analysis, we confirmed and extended a suspected scale-dependent trend in ejecta size-velocity distributions.  Maximum ejecta fragment sizes fall off much more steeply with increasing ejection velocity for larger primary impacts (compared to smaller primary impacts).  Specifically, we characterize the maximum ejecta sizes for a given ejection velocity with a power law, and find the velocity exponent varies between approximately -0.3 and -3 for the range of primary craters investigated here.  Data for the jovian moons Europa and Ganymede confirm similar trends for icy surfaces.  This result is not predicted by analytical theories of formation of Grady-Kipp fragments or spalls during impacts, and suggests that further modeling investigations are warranted to explain this scale-dependent effect.

How to cite: Singer, K., McKinnon, W., and Jolliff, B.: Lunar secondary craters: Results for secondary sizes across the Moon, and size-velocity distributions of ejected blocks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1851, https://doi.org/10.5194/egusphere-egu2020-1851, 2020.

Constraining the duration of magmatic activity on the Moon is essential to understand how the lunar mantle evolved chemically through time. Determining age and initial isotopic compositions of mafic lunar meteorites is a critical step in defining the periods of magmatic activity that occurred during the history of the Moon and to constrain the chemical characteristics of mantle components involved in the sources of the magmas.

We have used the in-situ Pb–Pb SIMS technique to investigate lunar gabbros and basalts, including meteorites from the Northwest Africa (NWA) 773 clan (NWA 2727, NWA 3333, NWA 2977, NWA 773 and NWA 3170), LAP 02224, NWA 4734 and Dhofar 287A. These samples have been selected as they all belong to the dominant chemical group of low-titanium mare basalts and there is no clear agreement on their age. We have obtained ages of 2978 ± 13 Ma for LAP02224, 2981 ± 12 Ma for NWA 4734 and 3208 ± 22 Ma for Dhofar 287. For the NWA 773 clan, four samples (NWA 2727, NWA 773, NWA 2977, NWA 3170) yielded isochron-calculated ages that are identical within uncertainties with an average age of 3086.1 ± 4.8 Ma. The gabbroic sample NWA 3333 yielded an age of 3038 ± 20 Ma suggesting that two distinct magmatic events are recorded in the meteorites of the NWA 773 clan.

The entire age dataset from lunar mafic meteorites was screened to identify data that are problematic from an analytical viewpoint and/or show evidence of resetting and terrestrial contamination. This refined dataset combines the ages of mafic lunar meteorites and Apollo samples and suggests pulses in magmatic activity, with two main phases between 3350 and 3100 Ma and between 3900 and 3550 Ma followed by a minor phase at ~3000 Ma.

The evolution of the Pb initial ratios of the low-Ti mare basalts between 3400 Ma and 3100 Ma suggests that these rocks were progressively contaminated by a KREEP-like component. Nevertheless, the ~3000 Ma mafic rocks (NWA4734 and LAP02224) show significant differences in terms of initial ²⁰⁴Pb/²⁰⁶Pb ratios that illustrates that the lunar mantle is probably more heterogeneous than has previously been assumed.

How to cite: Merle, R., Nemchin, A., Whitehouse, M., Snape, J., Kenny, G., Bellucci, J., Connelly, J., and Bizzarro, M.: Pb-Pb ages and Pb initial isotopic composition of lunar meteorites: new constrains on the timing of lunar magmatism and its mantle sources, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17704, https://doi.org/10.5194/egusphere-egu2020-17704, 2020.

The Moon is one of the best characterized objects in space science, yet its origin still actively researched. Available orbital, geophysical, and geochemical information imposes clear restrictions on the origin and evolution of the Earth-Moon system (e.g., Canup 2008, 2012; Ćuk and Stewart 2012; Young et al. 2016). In regard to geochemical constraints, one of the most puzzling conundrums is posed by the similar isotopic fingerprints of the Earth and the Moon (e.g., Wiechert et al. 2001; Armytage et al. 2012; Zhang et al. 2012; Young et al. 2016; Schiller et al. 2018), together with the apparent lunar depletion in volatile elements (e.g., Ringwood and Kesson 1977; Wanke et al. 1977; Albarède et al. 2015; Taylor 2014). This apparent lunar volatile depletion is most notable in the low K content in comparison to U, a finding based on chemical analyses of samples collected from the lunar surface and lunar meteorites, and on spectroscopic observations of the lunar near-surface, despite both having been heavily processed in the past ~ 4.4 billion years.

In the past 4.4 billion years, space has been a harsh environment for our Moon, especially in the beginning, when the young Sun was still very active and the young Moon was continuously bombarded by meteorites of varying sizes. Solar wind and micro-meteoritic interactions with the lunar surface led to rapid and intensive processing of the lunar crust. Hence, the K/U depletion trend observable on today's lunar surface does not necessarily reflect a K/U ratio valid for the Moon in its entirety. We model the evolution of the abundances of the major elements over the past 4.3 to 4.4 billion years to derive the composition of the original lunar crust. Accounting for this processing, our model results show that the original crust is much less depleted in volatiles than the surface observable today, exhibiting a K/U ratio compatible with Earth and the other terrestrial planets, which strengthens the theory of a terrestrial origin for the Moon.

How to cite: Vorburger, A., Wurz, P., Scherf, M., Lammer, H., Galli, A., and Assis Fernandes, V.: Chemical composition of the Moon's 'primary' crust – a clue at a terrestrial origin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4495, https://doi.org/10.5194/egusphere-egu2020-4495, 2020.

It is well known that methods of nuclear physics allow one to study distribution of hydrogen-bearing compounds in the upper 1–2 m subsurface soil layer of atmosphereless celestial bodies or planets with thin atmospheres like Mars by measuring neutron spectra leak from the surface. For this study one needs not only to measure neutron spectra but to perform also a set of numerical simulations of the neutron production by the Galactic Cosmic Rays (GCRs) in subsurface soil, leakage of these neutrons from the surface, their transport to the neutron spectrometer on the orbit and processes of neutron interactions with the instrument’s detectors. These simulations make possible a model dependent deconvolution of the measured data to obtain the hydrogen concentration and/or other soil properties at a particular region of the planet.

Currently a number of numerical codes are being used for simulations of the neutron production and transport in planetary applications. All these codes provide a reasonable precision both in modeling of laboratory experiments and nuclear planetology tasks. However, the gravitational field description appropriate for simulation of a neutron propagation on planetary scales is not well addressed. For the planetary scales, it is not just enough to implement a uniform gravitational field (this option is available in some numerical codes). The planetary gravity should be described as a full-scale central force field with its potential depending from the distance from the center of planet.

We have developed a method of accounting effects of lunar gravity force and finite neutron lifetime on the spectral and angular distributions of neutron flux at different altitudes above Moon surface. This method was implemented to reprocess the data gathered by the collimated detectors of LEND instrument operated onboard NASA LRO spacecraft. The gravitational field description appropriate for simulation of a neutron propagation on planetary scales was not well addressed earlier.

As the result of the updated LEND data reprocessing with the discussed method, we obtained a new estimations of Water Equivalent Hydrogen (WEH) abundance in the lunar regolith and new maps of WEH distribution in the lunar polar regions. It is shown that difference of new derived values of WEH is about 0.08 wt% larger in comparison with the previously estimated value. The updated polar maps shows slightly different WEH distribution over the polar regions in comparison to the early published. The new polar maps will be used to select the landing sites of future landers.

How to cite: Sanin, A., Mitrofanov, I., Bakhtin, B., and Litvak, M.: Updated Mapping of the Hydrogen Distribution in the Lunar Polar Regions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8685, https://doi.org/10.5194/egusphere-egu2020-8685, 2020.

The fact that the Moon could have a transient secondary atmosphere due to volcanic outgassing has been known for some time, though typically such an atmosphere was believed to be extremely thin (~10^-8 bar) [1]. But recent research by Needham and Kring (NK) [2] suggests that during the peak of volcanic activity ~3.5 Ga such a volcanically-outgassed atmosphere could reach ~10^-2 bar of surface pressure. In similar research Wilson et al. [3] proposed a more conservative estimate, arguing that the thickness of such an atmosphere would depend on the intervals between major eruptions and may not exceed microbar densities. In either case a collisional atmosphere could be present, which would control transport of outgassed volatiles (such as H₂O) and their deposition in polar regions, where they could be preserved until modern day frozen in permanently shadowed regions (PSR) or buried beneath the regolith.

Here we study such a hypothetical atmosphere to investigate its stability, meteorological properties and the effect on transport of volatiles. We use the ROCKE-3D planetary 3-D General Circulation Model (GCM)[4]. The insolation and orbital parameters were set to conditions 3.5 Ga. The atmospheric composition, based on the list of outgassed species presented by NK in combination with our estimates for atmospheric escape, condensation and the results from our 1-D chemistry model, was chosen to be either CO-dominated or CO₂-dominated (depending on atmospheric temperature). In this study we restricted ourselves to relatively "thick" lunar atmospheres of 1-10 mb, though we believe that our results will scale to thinner atmospheres as well.

We present the results for ground and atmospheric temperature for modeled atmospheres over a wide parameter space. In particular we consider  different atmospheric compositions (CO or CO₂ dominated), a set of atmospheric pressures from 1 mb to 10 mb and a set of obliquities from 0^o to 40^o. We also present an experiment of a single major eruption [5] and show that in just 3 years ~80% of the outgassed water is deposited in polar regions. This demonstrates the efficiency of such an atmosphere in delivering volatiles. We argue that a secondary lunar atmosphere could play a significant role in forming volatile deposits currently observed in the polar regions of the Moon. 

References:
[1] Stern S. A. (1999) Rev. of Geophysics, 37, 453-492.
[2] Needham D. H. and Kring D. A. (2017) Earth and Planetary Sci. Lett., 478, 175-178.
[3] Wilson L. et al. (2019) LPSC 50, Abstract 1343. 
[4] Way M. J. et al. (2017) ApJS, 231, 12.
[5] Wilson L. and Head J. W. (2018) GRL, 45, 5852-5859.

How to cite: Aleinov, I., Way, M., Tsigaridis, K., Wolf, E., Harman, C., Gronoff, G., and Hamilton, C.: Secondary Volcanically-Induced Lunar Atmosphere and Lunar Volatiles: 3-D Modeling and Analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11545, https://doi.org/10.5194/egusphere-egu2020-11545, 2020.

Research on propagation of ELF waves in the ground-ionosphere waveguide has been conducted in order to develop methods for solving inverse problem, which enable measurement of physical parameters of the Marsian ground [1]. It was assumed that the Marsian ground has multi-layer structure with layers characterized by low conductivity. The ELF field penetrates the soil to the depth of several dozen kilometers, that is much more that at Earth. This has a strong impact on dispersive properties of group velocities and attenuation in the waveguide. It is assumed that dust storms and dust devils generate short impulses of ELF field that can propagate over long distances, on the order of megameters. They can be recorded by ELF observation station located on the Marsian surface. The waveforms of these impulses are closely connected with the propagation parameters of the waveguide and should enable identification of ground structure and its components.

Ground contribution to the parameters of the waveguide was examined using analytical solutions in [2]. Its contribution to the propagation of impulses and Schumann resonances on Mars was further studied in [3,4]. Studies presented here show impact of local ground structure on vertical electric dipole radiation in the ground-ionosphere waveguide. Modeling of impulse propagation in the time domain was performed using cylindrical coordinates. Solutions for large distances were corrected using the focusing factor. As approximation of the conductivity profile of ionosphere, a “double-knee” model [5] was used. Computation was performed with space steps dr = 10km, dz = 1 km and time step 1 us. Two examples of two-layer ground with different depth of the first layer (10km and 40km) were implemented. Impact of highly and weakly conducting plate on the radiation of the source was also studied. Validation of the model was based on a well studied analytical solution [3].

This work has been supported by the National Science Center under grant 2015/19/B/ST9/01710.

[1] A. Kułak, et al. (2015), Tomography of the Martian ground using inverse solutions for ELF waves generated by dust storms in the ground-ionosphere waveguide, National Science Center, Poland, under grant 2015/19/B/ST9/01710.

[2] A. Kulak, and J. Mlynarczyk (2013), ELF Propagation Parameters for the Ground-Ionosphere Waveguide With Finite Ground Conductivity, IEEE Transactions on Antennas and Propagations, 61, 4, doi: 10.1109/TAP.2012.2227445.

[3] A. Kulak, J. Mlynarczyk, J. Kozakiewicz (2013), An Analytical Model of ELF Radiowave Propagation in Ground-Ionosphere Waveguides With a Multilayered Ground, IEEE Transactions on Antennas and Propagations, 61, 9, 10.1109/TAP.2013.2268244.

[4] J. Kozakiewicz, A. Kułak, J. Młynarczyk (2015), Analytical modeling of Schumann resonance and ELF propagation parameters on Mars with a multi-layered Ground, Planetary and Space Science, 117, 127–135.

[5] O. Pechony, and C. Price (2004), Schumann resonance parameters calculated with a partially uniform knee model on Earth, Venus, Mars, and Titan, Radio Sci., 39, RS5007, doi:10.1029/2004RS003056.

How to cite: Rzonca, P., Kulak, A., and Mlynarczyk, J.: Studying the propagation of ELF waves in the Marsian ground-ionosphere waveguide using an FDTD method with application to the ground tomography, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20696, https://doi.org/10.5194/egusphere-egu2020-20696, 2020.

Knowledge of collision rates through time and space is essential because meteoritic impact crater counting is the only way to determine the ages of surface geological units and processes on the solid bodies of our Solar System. All chronology models assume a constant size distribution of impactors and an exponential decay of the impact flux between 4 Ga and 2.5 Ga before the present followed by a constant rate over the last 2.5 Ga. These two assumptions are challenged by recent evidence for an increase of the impact flux on the Moon and the Earth and probably on Mars associated with a decoupling between the flux of small and large impactors over the last billion years. Here, using the results of an automatic crater detection algorithm, we investigate the evolution of the rate of formation of large impact craters (Dc ≥ 20km) on Mars and thus infer the evolution of the flux of large impactors (Di > 5km) from the size-frequency distribution of small craters superposed to the ejecta blankets of large ones.

The dating of large impact craters on Mars is limited by several factors such as the degradation of ejecta blankets and the retention rate of small craters superposed to their ejecta. We therefore focused on craters ≥20km in diameter exhibiting an ejecta blanket according to the crater database and located on a latitudinal band between ±35°. We then selected those whom their ejecta are not affected by volcanic/tectonic processes or by the formation of another large nearby impact crater. The final set includes 590 impact craters.

If one can argue the impact flux cannot be fully recorded for the last 4Ga due to resurfacing processes erasing progressively the ejecta blanket and large craters themselves, Hesperian and Noachian terrains within the 35° latitudinal band should nevertheless have retained all D≥20km craters over a portion of the Amazonian period. The CSFD of craters younger than 600Ma (113 craters) superposed to these terrains is consistent with the 600Ma isochron, supporting the fact that the entire population of craters ≥20km formed over the last 600 million years on this portion of the Martian surface has been counted completely. We therefore focused on the analysis of the impact rate evolution over this range of time from this crater sub-sample.

The formation of large impact craters is not homogeneously distributed over the time range investigated here. Our data suggest an inconsistency between the flux used to date each crater and the rate inferred from these datings, thus implying that the small and large body impact fluxes are decoupled from one another. We note also sharp peaks centered around 480, 280 and 100Ma. Preliminary statistical test show that 280Ma peak is marginally significant whereas the two others are too small to be statistically significant. This pattern would be consistent with other independent arguments for increased rate with similar intensity and timing on the Moon and Mars for which the causes are probably collisions and potentially formation of asteroid families within the main asteroid belt.

How to cite: Lagain, A., Kreslavsky, M., Benedix, G., Baratoux, D., Bland, P., Towner, M., Paxman, J., Bouley, S., Norman, C., Anderson, S., Servis, K., Samson, E., Chai, K., and Meka, S.: Fluctuation of recent large impact craters rate on Mars from automatic crater detection, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5003, https://doi.org/10.5194/egusphere-egu2020-5003, 2020.

The idea of visualizing shock wave passage along a dusty (sooty) surface was first proposed and tested by Ernst Mach. High resolution HiRISE images of new impact craters on dusty areas of Mars gave in many cases revealed dark “fresh” halos around craters. In ~7% of cases they have low albedo/color contrasting curved strips near craters referred to as “parabolas” and “scimitars”. We analyze these albedo details as the possible surface footprints of atmospheric shock waves generated during atmospheric passage and shocks from impact cratering by small meteoroids and their fragments. In this approach “parabolas” are the trace of two colliding air shocks propagated from a pair of neighboring craters formed after a meteoroid fragmented during the atmosphere passage. The mechanism of the “scimitar’s” formation is more enigmatic and tentatively could be related to the interaction of the ballistic cone wave and a spherical wave from the point of impact. The study of images is accompanied by numerical modeling of impact of small projectiles at the atmosphere/rock boundary. This modeling constrains the minimum efficiency of an impact to generate the air shock wave in the rarified Martian atmosphere below of 0.1% of the kinetic energy for non-volatile targets. Targets with near surface volatiles could amplificated the air blast (if volatiles are presented in the shocked zone). The study is intended to estimate the air-shock wave parameters along the visible surface traces around impact craters. By constraining shock wave parameters opens new possibilities for investigating the mechanical properties of the Martian surface.
The work is supported by RAS program 12 “Universe Origin and Evolution from Earth-based Observations and Space Missions” (BAI), and a grant from the NASA Mars Data Analysis Program, number 80NSSC18K1368.

How to cite: Ivanov, B., Barnes, G., Daubar, I., Dundas, C., McEwen, A., and Melosh, J.: New craters on Mars: Air shock wave traces, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4212, https://doi.org/10.5194/egusphere-egu2020-4212, 2020.

Mercury is a mysterious planet in many ways very different from what scientist were expecting. BepiColombo was launched on 20 October 2018 the BepiColombo from the European spaceport in French Guyana and is now on route to Mercury to unveil Mercury’s secrets. BepiColombo with its state of the art and very comprehensive payload will perform measurements to increase our knowledge on the fundamental questions about Mercury’s evolution, composition, interior, magnetosphere, and exosphere. BepiColombo is a joint project between the European Space Agency (ESA) and the Japanese Aerospace Exploration Agency (JAXA) and consists of two orbiters, the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (Mio). 

The BepiColombo spacecraft is during its 7-year long journey to the innermost terrestrial planet in a so-called ‘stacked’ configuration: The Mio and the MPO are connected to each other, and stacked on-top of the Mercury Transfer Module (MTM). Only in late 2025, the ‘stack’ configuration is abandoned and the individual elements spacecraft are brought in to their final Mercury orbit: 480x1500km for MPO, and 590x11640km for Mio. The foreseen orbits of the MPO and Mio will allow close encounters of the two spacecraft throughout the mission. The mission has been named in honor of Giuseppe (Bepi) Colombo (1920–1984), who was a brilliant Italian mathematician, who made many significant contributions to planetary research and celestial mechanics.

On its way BepiColombo has several opportunities for scientific observations - during the cruise into the inner solar system and during nine flybys (one at Earth, two at Venus and six at Mercury). However, since the spacecraft is in a stacked configuration during the flybys only some of the   instruments on both spacecraft will perform scientific observations. In early April of 2020 BepiColombo will flyby Earth and later in October the first Venus flyby will follow.

A status of the mission and instruments and first results of measurements taken during the Earth flyby and the first year in cruise will be given.

How to cite: Benkhoff, J., Zender, J., and Murakami, G.: BepiColombo – Status and first Results from Activities during Cruise and the Earth flyby , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11528, https://doi.org/10.5194/egusphere-egu2020-11528, 2020.

The ESA-JAXA joint mission BepiColombo is now on the track to Mercury. Two spacecraft for BepiColombo, "Mio" (Mercury Magnetospheric Orbiter: MMO) and "Bepi" (Mercury Planetary Orbiter: MPO), were successfully launched by Ariane-5 launch vehicle from Kourou in French Guiana on 20 October 2018. Mio is fully dedicated to investigating Mercury’s environment with a complete package of plasma instruments (particles, electric fields, and magnetic fields), a spectral imager of sodium exosphere, and a dust monitor. During the cruise to Mercury, in addition to two spacecraft MMO Sunshield and Interface Structure (MOSIF) and Mercury Transfer Module (MTM) are all integrated together. After the commissioning operations of spacecraft, we are focusing on preparing science operations for interplanetary cruise and planetary flybys. Some science instruments can be used even in the composite spacecraft configuration. The first and second flybys will happen at the Earth in April 2019 and at Venus in October 2019, respectively. In addition, during the interplanetary cruise BepiColombo can contribute to inner heliospheric science by measuring the solar wind and solar energetic particles. Thanks to NASA’s Parker Solar Probe and ESA’s Solar Orbiter, multi-spacecraft observations of the inner heliosphere will soon be possible and provide us deeper knowledge of this region. Here we report the updated status of BepiColombo mission, initial results of the commissioning operations, and the future plans for interplanetary cruise and planetary flybys.

How to cite: Murakami, G., Benkhoff, J., and Hayakawa, H.: Current status, initial results, and updated plans of BepiColombo/Mio: interplanetary cruise and planetary flybys, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12235, https://doi.org/10.5194/egusphere-egu2020-12235, 2020.

BepiColombo is en-route to Mercury. The boom carrying the planetary magnetometers (MPO-MAG instrument) was deployed in space on 25th of October in 2018. After the deployment, the magnetic disturbances arising from the spacecraft have been greatly decreased. Since the deployment, the fluxgate sensors have been monitoring the magnetic field continuously except for the solar electric propulsion phase. Extensive calibration and data processing activities have since enabled us to greatly decrease spacecraft-generated
disturbances in the magnetic field observations; these activities constitute a key step towards making the data
suitable for scientific analysis. We present a few cases of identified magnetic disturbances, discuss the challenges
they pose, and compare methods to clean the data. We also compare MPO-MAG measurements to observations by the
Advanced Composition Explorer (ACE) solar wind monitor, thereby highlighting the small-scale nature and rapid
evolution of interplanetary magnetic field (IMF) variations. We conclude with an overview of the scientific
goals of the instrument team for the in-orbit mission phase.

How to cite: Heyner, D., Richter, I., Plaschke, F., Fischer, D., Mieth, J., Auster, H.-U., and Glassmeier, K.-H.: Solar Wind Measurements from the Planetary Magnetometer Onboard the BepiColombo Spacecraft, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10707, https://doi.org/10.5194/egusphere-egu2020-10707, 2020.

Recently ESA and JAXXA launched the two-spacecraft mission BepiColombo to explore the plasma and magnetic field environment of Mercury. Both spacecraft, the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO, also referred to as Mio), are equipped with fluxgate magnetometers, to provide in-situ data for the characterization of the internal magnetic field origin as well as its dynamic interaction with the solar wind. To achieve this goal, accurate magnetic field measurements are thus of crucial importance, which require proper in-flight calibration. In particular the magnetometer offset, which relates relative fluxgate readings into an absolute value, needs to be determined with high accuracy. Usually, the magnetometer offsets are evaluated from Alfvénic fluctuations observed in the pristine solar wind. However, while Mio's orbit will indeed partially reside in the solar wind, MPO will remain within the magnetosphere at most times during the main mission phase. Therefore, we examine an alternative offset determination method, based on the observation of highly compressional fluctuations, the so-called Mirror Mode Method. To evaluate the method performance in the Hermean environment, we analyze four years of MESSENGER magnetometer data, which are calibrated by the Alfvénic fluctuation method, and compare it with the accuracy and error of the offsets determined by the Mirror Mode Method in different plasma environments around Mercury. We show that the Mirror Mode Method yields the same offset estimates and thereby confirms its applicability. Furthermore, we also evaluate the spacecraft observation time within different regions necessary to obtain reliable offset estimates. Although the lowest percentage of strong compressional fluctuations are observed in the solar wind, this region is most suitable for an accurate offset determination with the Mirror Mode Method. 132 hours of solar wind data are sufficient to determine the offset to within 0.5nT, while thousands of hours are necessary to reach this accuracy in the magnetosheath or within the magnetosphere. We conclude that in the solar wind the Mirror Mode Method might be a good complementary approach to the Alfvénic fluctuation method to determine the (spin-axis) offset of the Mio magnetometer. However, although the Mirror Mode Method requires considerably more data within the magnetosphere, it might also be for the MPO magnetometer one of the most valuable tools to determine the offsets accurately.

How to cite: Schmid, D., Plaschke, F., Heyner, D., Mieth, J. Z. D., Anderson, B. J., Baumjohann, W., Matsuoka, A., and Narita, Y.: Magnetometer in-flight offset accuracy for the BepiColombo spacecraft, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13932, https://doi.org/10.5194/egusphere-egu2020-13932, 2020.

In the 1970’s the flybys of NASA’s Mariner 10 spacecraft confirmed the existence of an internally generated magnetic field at Mercury. The measurements taken during its flybys already revealed, that Mercury‘s magnetic field is unique along other planetary magnetic fields, since the magnetic dipole moment of ~190 nT ∙ R_M³ is very weak, e.g. compared to Earth’s magnetic dipole moment. The following MESSENGER mission from NASA investigated Mercury and its magnetic field more precisely and exposed additional interesting properties about the planet’s magnetic field. The tilt of its dipole component is less than 1°, which indicates a strong alignment of the field along the planet’s rotation axis. Additionally the measurement showed that the magnetic field equator is shifted roughly 0.2 ∙ R_M towards north compared to Mercury‘s actual geographic equator.

Since its discovery Mercury‘s magnetic field has puzzled the community and modelling the dynamo process inside the planet’s interior is still a challenging task. Adapting the typical control parameters and the geometry in the models of the geodynamo for Mercury does not lead to the observed field morphology and strength. Therefore new non-Earth-like models were developed over the past decades trying to match Mercury’s peculiar magnetic field. One promising model suggests a stably stratified layer on the upper part of Mercury’s core. Such a layer divides the fluid core in a convecting part and a non-convecting part, where the magnetic field generation is mainly inhibited. As a consequence the magnetic field inside the outer core is damped very efficiently passing through the stably stratified layer by a so-called skin effect. Additionally, the non-axisymmetric parts of the magnetic field are vanishing, too, such that a dipole dominated magnetic is left at the planet’s surface.

In this study we present new direct numerical simulations of the magnetohydrodynamical dynamo problem which include a stably stratified layer on top of the outer core. We explore a wide parameter range, varying mainly the Rayleigh and Ekman number in the model under the aspect of a strong stratification of the stable layer. We show which conditions are necessary to produce a Mercury-like magnetic field and give a inside about the planets interior structure.

How to cite: Kolhey, P., Heyner, D., Wicht, J., and Glassmeier, K.-H.: The effect of a strongly stratified layer in the upper part of Mercury’s core on its magnetic field, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13847, https://doi.org/10.5194/egusphere-egu2020-13847, 2020.

In the last months of its mission, MESSENGER was able to obtain measurements at low altitude (< 120 km). This has made it possible to measure small magnetic field signals, probably of crustal origin (Johnson et al, 2015). Maps of the crust signatures at 40 km altitude were produced by Hood (2016) and Hood et al. (2018), showing that the strongest anomalies are about 14 nT in the Caloris basin. Some of the anomalies are associated with impact craters, and it has been demonstrated that this is not a coincidence (Hood et al., 2018). It is believed that these anomalies are the result of impactor materials rich in magnetic carriers (e.g., metallic iron) that were incorporated on the surface acquiring remanent magnetic fields during the cooling of the material. We intend to analyze whether the anomalies of the crustal field are related to geological characteristics by examining two Hermean craters in order to test this impactor hypothesis. Anomalies associated with Rustaveli and Stieglitz craters are slightly or totally asymmetric with respect to the crater center. The morphology and geological setting of these two fresh impact craters that still maintain a well-preserved ejecta blanket and visible secondary crater chains are investigated to constrain the overall impact dynamics. Both impact angles were likely > 40°. In both cases, slight asymmetries in the morphology and ejecta distribution show that the magnetic anomalies correlate well with the location of impact melt. For the large basin Rustaveli, the melt emplaced SE in the downrange direction, whereas in the case of the smaller crater Stieglitz, downrange direction remains uncertain; in one scenario the melt naturally migrated to the northern topographic lows away from a SW downrange direction, while in the other the downrange direction corresponds to the location of the melt to the north. Rustaveli is associated with a ~5 nT crustal magnetic anomaly centered close to the crater’s midpoint, although offset ~20 km east-southeast. This offset is somewhat consistent with the downrange direction implied by Rustaveli’s impact melt and crater chains distribution. For Stieglitz, all anomalies are offset from the crater’s center. An anomaly larger than 3 nT includes most of the ejecta melt locations towards southwest. The ejecta melt cluster to the north of the crater corresponds to an anomaly of ~5 nT, while the largest anomaly of ~7 nT is found further north and closely corresponds to the crater’s deepest chain, making the second scenario of a N downrange direction more realistic. For both craters, the melt likely recorded the prevailing magnetic field of Mercury after quenching. For Stieglitz, also some solid impactor fragments likely contribute to the anomaly. Hence, both impactors brought magnetic carriers to the surface that could record the past magnetic field of Mercury.

Acknowledgements: The authors gratefully acknowledge funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2017-47-H.0.

References: Hood, J. Geophys. Res. Planets 121, 2016; Hood et al., J. Geophys. Res. Planets 123, 2018; Johnson et al., Science 348, 2015.

How to cite: Galluzzi, V., Oliveira, J. S., Wright, J., Hood, L. L., and Rothery, D. A.: Asymmetric magnetic anomalies over two young impact craters on Mercury, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18513, https://doi.org/10.5194/egusphere-egu2020-18513, 2020.

Celestial bodies with surface-bound exosphere are valuable because we can directly see the interaction between the bodies and space environment to which they are exposed. This interaction is especially expected to be clearly observed around Mercury. This research aims to clarify the generation process of neutral sodium exosphere, through the comparison between the data from MASCS onboard MESSENGER spacecraft and 3-D model calculation considering generation, transportation and dissipation processes.

First, seasonal variability of the amount of sodium exosphere is analyzed for each local time (LT) using MASCS data. Previous research has shown that the amount of sodium above LT12 reaches a maximum at aphelion, and it is found that this maximum is seen only above LT12. In addition, two hypotheses proposed by the research: the increase in the surface sodium density of the dayside due to fast rotation of terminator, and the expansion of exosphere owing to weaker radiation pressure, were turned out to be inconsistent with seasonal variability above LT06 and the results of test particle calculations.

Following these results, in order to understand the key process of the seasonal variation of the amount of sodium especially around LT12, 3-D sodium exosphere model including release from the surface, transport due to gravity and solar radiation pressure, and dissipation due to ionization caused by solar radiation is constructed. The results from numerical calculation is consistent with the observations by MASCS in terms of the vertical profile and the seasonal variability above LT06 and LT18, but the maximum at aphelion above LT12 could not be reproduced. Then, when the existence of the impact of comet dust stream is assumed as a local and short-term sodium source, the model with impact of 10⁸kg comets per Mercury year could reproduce observations.

Using the model constructed in this study, the sodium distribution which would be observed by MSASI onboard MIO spacecraft is predicted. The comparison between the calculation and observation by MSASI will provide us new insights into the interaction between the celestial bodies and space environment.

In this presentation, we will summarize the results of comparison between observations by MASCS and 3-D Monte Carlo simulation about the seasonal variability of Mercury’s sodium exosphere.

How to cite: Suzuki, Y., Yoshioka, K., Murakami, G., and Yoshikawa, I.: Seasonal variation of Mercury's exosphere deduced from MESSENGER data and simulation study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6542, https://doi.org/10.5194/egusphere-egu2020-6542, 2020.

Navigation of deep space probes is most commonly operated using the spacecraft Doppler
tracking technique. Orbital parameters are determined from a series of repeated measurements of the frequency shift of a microwave carrier over a given integration time. This study addresses the work that is done on Doppler orbit determination of MPO - one of the two spacecraft of the European Space Agency’s BepiColombo mission- using Bernese software.

For modelling the orbit of MPO around Mercury, we use a full force model, including Mercury gravity field GGMES-100V07 (up to degree and order 50), solid tides and third body perturbations. We also have an extensive modelling of non-gravitational forces that act on the orbit of spacecraft. This modelling includes the solar radiation pressure and planetary IR and albedo radiation together with a 33-plates macromodel of MPO. We propagate the orbit using this force model. Our simulations of Doppler tracking measurements include 2-way X-band and K-band Doppler measurements, station and planetary eclipses and the relativistic corrections. 

The imperfect knowledge of the non-gravitational forces due to the proximity of Mercury to the Sun, together with the effect of desaturation maneuvers uncertainties, makes the use of the accelerometer necessary. Therefore, in our modelling of the orbit recovery, the models for the non-conservative forces were replaced by the noisy simulated accelerometer measurements. We find out that the modelling of the accelerometer noise has a huge impact on the results of the POD.

We perform several orbit reconstruction tests using daily arcs with noise modulated Doppler data with different settings on the arc lengths, arcs initial conditions, dynamical model, observation mode and orbit determination process and we solve for the initial state vector of each arc. We also run sensitivity analysis with respect to the different accelerometer model. The final goal of this study is to provide an independent solution for the precise orbit determination of Mercury planetary orbiter (MPO) using the planetary extension of the Bernese GNSS software. We present out latest results and then compare our results with the existing ones from the MORE team.

How to cite: HosseiniArani, A., Bertone, S., Arnold, D., Jäggi, A., and Thomas, N.: An independent solution for the precise orbit determination of Mercury planetary orbiter (MPO), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18363, https://doi.org/10.5194/egusphere-egu2020-18363, 2020.

How to cite: Travnicek, P. M., Schriver, D., Orlando, T., and Slavin, J. A.: Effects of the Solar Wind Conditions on Mercury's Exosphere: Hybrid Simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13020, https://doi.org/10.5194/egusphere-egu2020-13020, 2020.

The imaging spectrometer MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) is part of the payload of ESA/JAXA’s BepiColombo mission, launched in 2018 [1,2]. The instrument consists of an IR-spectrometer and radiometer, which will observe the surface in the wavelength range of 7–14µm and 7–40μm, respectively. In preparation of the mission, we are investigating Mercury analog minerals at the IRIS (Infrared and Raman for Interplanetary Spectroscopy) laboratory of the Institut für Planetologie at the Westfälische Wilhelms-Universität Münster. We study typical rock-forming minerals, e.g., pyroxenes, olivines, and feldspars, as well as mineral mixtures.

Here we present results of a deconvolution model used to quantify mineral specific abundances of mineral mixtures [4,5]. Planetary surfaces are composed of a variety of different minerals, therefore the obtained spectral data reflects a mixture of these minerals. In order to quantify the mineral abundances a non-linear unmixing model is necessary. Our model is based on the Hapke reflectance theory [6-8] and is applied to data obtained at the IRIS laboratory [9]. Results of olivine and pyroxene mixtures, as well as grain size mixtures, will be presented at the meeting.

We used olivine (Fo₉₁) from Dreiser Weiher, Germany, and pyroxene (En₈₇) from Bamble, Norway and a range of mineral mixtures for IR measurements. Samples are sieved in grain size fractions of <25µm, 25-63µm, 63-125µm, and 125-250µm. For the mineral mixing analysis presented here, we focus on the 63-125µm fraction, which was also used by [10,11] for further investigations. Samples are analyzed by a Bruker Vertex 70v spectrometer with an A513 variable mirror reflectance stage for various incidence/emergence angles. A total of 512 single channel scans of the sample and the background (diffuse gold standard INFRAGOLD™) were accumulated to ensure a high signal-to-noise ratio.

The pure pyroxene and olivine spectra clearly show characteristic Christiansen features and Reststrahlen bands for all applied geometries and increasing phase angles result in decreased intensities. The reflectance increases from pyroxene and pyroxene-rich mixtures to olivine and olivine-rich mixtures. Moreover, the olivine-rich mixtures exhibit more olivine reflectance features, compared to pyroxene-rich mixtures [11].

Our studies of pyroxene grain size analysis focus on pyroxene mixtures of 50%fine/50%coarse and 30%fine/70%coarse material. Generally, the intensities increase with increasing grain sizes. The transparency feature is evident for small grain sizes and the 50%fine/50%coarse mixture.

At IRIS laboratory, we will further investigate planetary analog material and their mineral mixtures applying various analytical techniques. With these data we are establishing a database that will enable the correct interpretation of MERTIS results.

This work has been funded by DLR grant 50 QW 1701 in the framework of the BepiColombo mission.

[1] Hiesinger H. et al. (2010) PSS58, 144-165. [2] Benkhoff J. et al. (2010) PSS58, 2-20. [3] Grumpe A. et al (2017) Icarus299, 1-14. [4] Rommel D. et al. (2017) Icarus284, 126-149. [5] Hapke B. (1981), JGR86(B4), 3039-3054. [6] Hapke B. (2002), Icarus157, 523-534. [7] Hapke B. (2012), 2^ndCambr. Univ. Press., NY. [8] Bauch, K.E. et al. (2019) LPSC L, Abstract#2521. [9] Weber I. et al. (2019) LPSC L, Abstract#2326. [10] Weber, I. et al. (2020) LPSC LI, Abstract#1889.

How to cite: Bauch, K. E., Weber, I., Reitze, M. P., Morlok, A., Hiesinger, H., Stojic, A. N., and Helbert, J.: Deconvolution of Laboratory IR Spectral Reflectance Measurements of Olivine-Pyroxene Mineral Mixtures., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13099, https://doi.org/10.5194/egusphere-egu2020-13099, 2020.

Tsiolkovskiy is a 180 km diameter late Imbrian crater located at 20.4° S, 129.1° E on the far side of the Moon [Whitford-Stark & Hawke, 1982].

Compared to the extensive mare deposits present of the lunar side facing the Earth, Tsiolkovskiy crater represents one of the few basaltic exposures on the far side [Pieters & Tompkins, 1999]. Along with its particularly dark and smooth crater floor, the impact crater is also characterized by a morphologically well-shaped central peak on which has been detected both olivine [Corley et al., 2018] and PAN [Ohtake et al., 2009; Lemelin et al., 2015].

The area represents thus a potential scientific site of interest for a safe landing. The production of geological maps aiming at characterize Tsiolkovskiy crater will allow the definition of interesting locations for rover exploration.

A geomorphological mapping of the crater has been performed using the ~100m/pixel LRO-WAC [Robinson et al., 2010] global mosaic along with the ~59m/pixel LRO-LOLA and Kaguya TC DEM merge which has a vertical resolution of 3-4m [Barker et al., 2016]. The mapping defined six units corresponding to the well-recognizable central peak and the texturally different smooth and hummocky materials constituting the crater floor units, and by scarps with slopes >40°, isolated ponds of smooth material discernible from the rough material constituting the crater rim and constituting the crater walls units.

The geomorphological mapping has then been coupled with a spectral characterization of Tsiolkovskiy crater performed on the basis of the ~200m/pixel Clementine UVVIS false color composite (Red 750/415nm; Green 750/1000nm; Blue 415/740nm) [Lucey et al., 2000]. The spectral mapping allowed to discriminate different units characterized by different origin and composition. In particular, the morphologically smooth crater floor unit is composed by fresher basalts and basaltic soils, the steep scarps and the central peak units are mostly composed by norites, troctolites and anorthosites, while the remaining smooth ponds, crater rim and the hummocky crater floor units are generally composed by mature highland soils.

In order to define landing ellipses and broad traverses for a rover exploration of the site, the geological mapping is also been supported by an ongoing high-resolution mapping of a quarter of Tsiolkovskiy crater by means of a mosaic of ~0.5m/pixel LRO-NAC [Robinson et al., 2010] images here scaled to 3m/pixel.

Finally, a radar investigation for the presence of deep structures will be performed to possibly detect lava pile emplacements and voids in the crater subsoil.

Acknowledgments

This research was supported by the European Union’s Horizon 2020 under grant agreement No 776276-PLANMAP.

References

Whitford-Stark, J.L. & Hawke, B.R., XXXIII LPSC, pp. 861-862, 1982Barker, M.K. et al., Icarus, Vol. 273, pp. 346-355, 2016

Pieters, C.M. & Tompkins, S., JGR, Vol. 104, pp. 21935-21949, 1999

Corley, L.M. et al., Icarus, Vol. 300, pp. 287-304, 2018

Ohtake, M. et al., Nature, Vol. 461, pp. 236-241, 2009

Lemelin, M. et al., JGR: Planets, Vol. 120, pp. 869-8878, 2015

Robinson, M.S. et al., Space Sci. Rev., Vol. 150, pp. 81–124, 2010

Barker, M.K., et al., Icarus, Vol. 273, pp. 346-355, 2016

Lucey, P.G. et al., JGR, Vol. 105, pp. 20377-20386, 2000

How to cite: Tognon, G., Pozzobon, R., and Massironi, M.: Geological mapping of an interesting lunar site: Tsiolkovskiy crater, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-733, https://doi.org/10.5194/egusphere-egu2020-733, 2020.

The Wolf crater is an irregularly shaped crater situated within the central part of Mare Nubium in the southern hemisphere on the lunar near side (16.573°W, 22.904°S). With an approximate diameter of about 25 km, this crater has been recently suspected to be a lunar silicic construct, hinting at a felsic composition that is more silicic than pure, immature anorthite. These suspicions have mainly been triggered by the high thorium anomaly in this region, and Christiansen Feature (CF) and Concavity Index (CI) mapping using Diviner multispectral data from the Lunar Reconnaissance Orbiter (LRO) mission. Many areas in the Wolf crater show CF values lower than 7.84 µm (CF for pure, immature anorthite). This study adopts a more holistic approach by studying the mineralogical composition and morphology of this crater complex using Moon Mineralogy Mapper (M³) data for mineralogical analysis and LROC WAC (wide angle camera) and NAC (narrow angle camera) data for morphological analysis. The whole complex can be divided into two parts- highland massif and mare basalt regions. CSFD analyses show that the outer part of the massif is older than the mare basalt, whereas the inner part have relatively younger surfaces. Analysis of the M³ data reveals the presence of pyroxene exposures on the massif as well as the mare basalt. However, their compositions are distinctly different, the massif pyroxenes being low-Ca pyroxene while the mare pyroxenes are High-Ca pyroxenes in composition. It can be inferred that the pyroxene exposures on the massif are not related to any ejecta deposits from the mare basalts. The highly silicic compositions implied by the CF and CI maps are limited to only certain parts of the massif, indicating a compositional heterogeneity in the massif region as well. Morphologically, the highland massif shows an extremely knobby structure which surrounds the mare basalt in a topographically depressed central part. The massif is discontinuous and the mare-highland boundary is very irregular, suggesting that the central depression is not of an impact-related origin. Extensional deformation features near the mare-highland boundaries also support this. In some parts, dome like features can be identified, with fresh rock fragments being visible on the surface. The rock fragments seem to be of two different tones- one very bright tone, and another comparatively darker tone. These rock fragments cannot be related to any nearby cratering activity, and they seem to be embedded in their locations. Pyroclastic deposits can also be identified around some of these domes, by their characteristic low albedo and smooth appearance. Overall, the Wolf crater complex shows signatures of non-mare volcanic activity and can be of non-impact related volcanic origin.

How to cite: Moitra, H., Pathak, S., Chauhan, M., Gupta, S., and Bhattacharya, S.: Mineralogical and morphological characterization of a suspected lunar silicic construct: The Wolf crater, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20201, https://doi.org/10.5194/egusphere-egu2020-20201, 2020.

The formation process of the crustal dichotomy of Mars has remained elusive since its discovery more than three decades ago.  Workers put forward different theories including (i) an endogenic origin, where the dichotomy is formed by degree-1 mantle convection [1, 2]; (ii) an exothermic origin, where the northern crust is excavated by an impact [3]; and (iii) a hybrid origin, where an impact generated large amounts of melt, followed by crust production shaping the crustal dichotomy [4]. 

In this study we focus on the last hypothesis. Our previous results using a parameterized impact show that a dichotomy can be formed in this manner.  In order to confirm whether these results still hold when using a realistic impact, and to consider the most probable impact angles and velocities, a SPH code [5] is used to model both the impact itself and the first 24 hours of post-impact evolution. The result is then transferred into mantle convection code StagYY [6] in order to simulate the long-term evolution of both crust and mantle for 4.5 Gyrs.  Due to the different physical nature and assumptions between the SPH impact models and long-term mantle convection models, care in data treatment is required when coupling the two simulations.  In this study, different setups regarding the transfer of data are tested and explored, including the treatment of temperature profiles, the choice of density and viscosity of materials, and the time of transfer.

Preliminary results from coupled SPH-geodynamics evolution models are presented, involving the crust thickness and topography maps after 4.5 Gyrs of evolution.

[1] Roberts, J., & Zhong, S. (2006). Degree-1 convection in the Martian mantle and the origin of the hemispheric dichotomy. Journal Of Geophysical Research, 111(E6).

[2] Keller, T., & Tackley, P. (2009). Towards self-consistent modeling of the martian dichotomy: The influence of one- ridge convection on crustal thickness distribution. Icarus, 202(2), 429-443.

[3] Andrews-Hanna, J., Zuber, M., & Banerdt, W. (2008). The Borealis basin and the origin of the martian crustal dichotomy. Nature, 453(7199), 1212-1215.

[4] Golabek, G., Keller, T., Gerya, T., Zhu, G., Tackley, P., & Connolly, J. (2011). Origin of the martian dichotomy and Tharsis from a giant impact causing massive magmatism. Icarus, 215(1), 346-357.

[5] Emsenhuber, A., Jutzi, M., Benz, W. (2018). SPH calculations of Mars-scale collisions: The role of the equation of state, material rheologies, and numerical effects. Icarus, 301, 247-257

[6] Tackley, P. (2008). Modelling compressible mantle convection with large viscosity contrasts in a three- dimensional spherical shell using the yin-yang grid. Physics Of The Earth And Planetary Interiors, 171(1-4), 7-18.

How to cite: Cheng, K. W., Rozel, A. B., Ballantyne, H., Jutzi, M., Golabek, G. J., and Tackley, P. J.: Impact-induced crustal dichotomy on Mars: from SPH to long-term mantle convection models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10248, https://doi.org/10.5194/egusphere-egu2020-10248, 2020.

The detailed composition of terrestrial planetary cores is still unknown. The nature of the ‘light element’ alloying with Fe-Ni in planetary cores can affect a large range of properties, such as its melting temperature and the stable crystal structures it exhibits. While geophysical and geodetic parameters of a planet can provide first order information, mineral physics can also be used to investigate the compositional space.

We present ab initio simulations on the [Fe,Ni]₃Si system (at ~7wt% and 14wt% Ni) to determine stable crystal structures and thermoelastic properties at PT conditions relevant to smaller terrestrial planets (central pressure <45 GPa). This will allow for comparisons to be made to any future seismic profile of Mars (from InSight or otherwise), and other research on the [Fe,Ni]₃[Si,S] system. The overall aim to produce a compositional model for the core of Mars and place it in the context of the evolution of planetary cores, including the state and structure of Mars’ core.

How to cite: Jamieson, A., Vočadlo, L., and Wood, I.: Equation of state of the [Fe,Ni]3Si system at conditions relevant to small terrestrial planets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22354, https://doi.org/10.5194/egusphere-egu2020-22354, 2020.

The Martian moons, Phobos and Deimos are exciting new targets for future in-situ, and possibly future human explorations. The mission of JAXA, Martian Moons eXplorer (MMX), is scheduled to launch in 2024 to perform observations of both moons, landing on one of them. How the landing modules should be designed depends greatly on the surface conditions, thus studying the surface of Phobos (the likely candidate for landing) is highly important. The exact composition of the regolith covering the surface of the moon is still under debate; but even with the chemical compositions and size distributions of the grains established, numerous mechanical properties remain problematic to estimate. The thermal inertia of the regolith determines the amount of heat the soil can store, as well as how quickly the heat is reradiated. It is also possible to estimate the particle diameter and porosity of the regolith, if thermal inertia is measured, however, the Hayabusa2 and OSIRIS-REx missions showed that the actual grain sizes can vary greatly. In our study we work with the Tagish Lake-based simulant developed at the University of Tokyo (UTPS-TB). Using a thermostatic chamber and a vacuum chamber at the ISAS/JAXA laboratory in Sagamihara, we measure and calculate the thermal inertia of UTPS-TB samples with different grain sizes and densities. This work was supported by the by Campus Mundi short scientific research programme, and the ÚNKP-19-3 New National Excellence Program of the Ministry for Innovation and Technology. 

How to cite: Pál, B., Miyamoto, H., Niihara, T., Sakatani, N., Takano, A., and Kereszturi, Á.: Determining the Thermal Inertia of the UTPS-TB simulant for different grain sizes and densities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16875, https://doi.org/10.5194/egusphere-egu2020-16875, 2020.