Displays

Mass-independent isotopic anomalies in planets and meteorites define two cosmochemically distinct regions: the carbonaceous and non-carbonaceous meteorites, implying that the non-carbonaceous (terrestrial) and carbonaceous (jovian) reservoirs were kept separate during and after planet formation. The iron meteorites show a similar dichotomy.

The formation of Jupiter is widely invoked to explain this compositional dichotomy by acting as an effective barrier between the two reservoirs. Jupiter’s solid kernel possibly grew to ~20 Mearth in ~1 Myr from the accretion of sub meter-sized objects (termed “pebbles”), followed by slower accretion via planetesimals. Subsequent gas envelope contraction is thought to have led to Jupiter’s formation as a gas giant.

We show using dynamical simulations that the growth of Jupiter from pebble accretion is not fast enough to be responsible for the inferred separation of the terrestrial and jovian reservoirs. We propose instead that the dichotomy was caused by a pressure maximum in the disk near Jupiter’s location, which created a ringed structure such as those detected by the Atacama Large Millimeter/submillimeter Array(ALMA). One or multiple such long-lived pressure maxima almost completely prevented pebbles from the jovian region reaching the terrestrial zone, maintaining a compositional partition between the two regions. We thus suggest that our young solar system’s protoplanetary disk developed at least one and likely multiple rings, which potentially triggered the formation of the giant planets [1].

[1] Brasser, R. and Mojzsis, S.J. (2020) Nature Astronomy doi: 10.1038/s41550-019-0978-6

How to cite: Brasser, R. and Mojzsis, S.: The partitioning of the inner and outer solar system by a structured protoplanetary disk, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3685, https://doi.org/10.5194/egusphere-egu2020-3685, 2020.

We give calculations for the excess variance, excess skewness and excess kurtosis with formulas that combine the effects of cylindrical shadows, along with gaps, ghosts and clumps (all calculated for the granola bar model for rectangular clumps and gaps). Wherever the rings have significant gaps or clumps, those will dominate the statistics over the individual ring particles contribution. We have refined an overlap correction for multiple shadows, which is important for larger optical depth. This correction results from summing a geometric series, and is similar to the empirical formula, eq. (22) in Colwell et al (2018). The comparison to Monte Carlo calculations is improved for large particle size by including the edge effects when large particles cross the edges of the viewing area A in Cassini UVIS occultations. As a check, we can explain the upward curvature of the dependence of normalized excess variance for Saturn’s background C ring by the observation of Jerousek etal (2018) that the increased optical depth is directly correlated with effective particle size. Assuming a linear dependence R_eff = 12 * (tau – 0.08) + 1.8m, we match both the curvature of excess variance E and the skewness Gamma in the region between 78,000 and 84,600km from Saturn. This explanation requires no gaps or ghosts (Baillie etal 2013) in this region of Saturn’s C ring.

How to cite: Esposito, L. W., Sremcevic, M., Colwell, J. E., and Eckert, S.: Statistics of Saturn Ring occultations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9973, https://doi.org/10.5194/egusphere-egu2020-9973, 2020.

The inner structure of icy moons comprises ices, liquid water, a silicate rocky core and sometimes an inner metallic core depending on thermal evolution and differentiation. Mineralogy and density models for the silicate part of the icy satellites cores were assessed assuming a carbonaceous chondritic (CI) bulk composition and using a free-energy minimization code and experiments [1]. Densities of other components, solid and liquid sulfides, carbonaceous matter, were evaluated from available equations of state. Model densities for silicates are larger than assessed from magnesian terrestrial minerals, by 200 to 600 kg/m³ for the hydrated silicates, and 300 to 500 kg/m³ for the dry silicates, due to the lower iron bulk concentration in terrestrial silicates as a lot of iron is segregated in the core.

We find that CI density models of icy satellite cores taking into account only the silicate and metal/sulfide fraction cannot account for the observed densities and reduced moment of inertia of Titan and Ganymede without adding a lower density component. We propose that this low-density component is carbonaceous matter derived from insoluble organic matter, in proportion of ~30-40% in volume and 15-20% in mass. This proportion is compatible with contributions from CI and comets, making these primitive bodies including their carbonaceous matter component likely precursors of icy moons, and potentially of most of the objects formed behind the snow line of the solar system. Similar conclusions are reached for 1-Ceres when applying this compositional model, with even higher carbon content of the order of 25±5wt% in line with independent estimates [2]. It suggests that the building materials are similar for asteroid 1-Ceres and the icy moons of giant planets.

[1]Neri et al., Earth Planet Sci Letters, 530 (2020) 115920

[2]Zolotov, Icarus, 335 (2020) 113404

How to cite: Reynard, B., Neri, A., Guyot, F., and Sotin, C.: Carbon-rich composition of the icy moons of Jupiter and Saturn, and asteroid 1-Ceres, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6899, https://doi.org/10.5194/egusphere-egu2020-6899, 2020.

We report direct measurements of thermal diffusivity and conductivity at room temperature for 38 meteorite samples of 36 different meteorites including mostly chondrites, and thus almost triple the number of meteorites for which thermal conductivity is directly measured. Additionally, we measured porosity for 34 of these samples. Thermal properties were measured using optical infrared scanning method on samples of cm-sizes with a flat, sawn surface.

    A database compiled from our measurements and literature data suggests that thermal diffusivities and conductivities at room temperature vary largely among samples even of the same petrologic and chemical type and overlap among e.g. different ordinary chondrite classes. Measured conductivities of ordinary chondrites vary from 0.4 to 5.1 W/m/K. On average, enstatite chondrites show much higher values (2.33 – 5.51 W/m/K) and carbonaceous chondrites lower values (0.5 – 2.55 W/m/K).

    Mineral composition (silicates vs. iron-nickel) and porosity control conductivity. Porosity shows (linear) negative correlation with conductivity. Variable conductivity is attributed to heterogeneity in mineral composition and porosity by intragranular and intergranular voids and cracks, which are important in the scale of typical meteorite samples. The effect of porosity may be even more significant for thermal properties than that of the metal content in chondrites.

Reference

Soini A.-J., Kukkonen I. T., Kohout T., and Luttinen A. (accepted for publication). Thermal and porosity properties of meteorites: A compilation of published data and new measurements. Meteoritics & Planetary Science.

How to cite: Soini, A.-J., Kukkonen, I., Kohout, T., and Luttinen, A.: Thermal and porosity properties of meteorites: A compilation of published data and new measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4679, https://doi.org/10.5194/egusphere-egu2020-4679, 2020.

The ESA’s Rosetta spacecraft had the unique opportunity to follow comet 67P/Churyumov-Gerasimenko (hereafter 67P) for about 2.5 years – from January 2014 to September 2016 – observing how the comet evolved while approaching the Sun, passing through perihelion and then moving back into the outer solar system. Remote sensing and in-situ instruments onboard Rosetta acquired data to study the comet’s dust environment during the entire duration of the mission, while telescopes followed the large-scale coma and tails from Earth. Here we report the latest advances of the ongoing multi-instrument approach that the Rosetta dust working group has been following in the recent years. Individual instrument data analyses have been carried on providing a first characterization of 67P dust environment. Timely, multi-instruments data analyses are now progressing a step forward in understanding how comet works and are providing critical results for a more comprehensive and unified knowledge of cometary dust environments. We will illustrate the progress we have made and the results we have reached following this constructive and collaborative approach.

We also discuss the latest achievements on the cometary dust modelling using the multi-instrument Rosetta data. In particular, what additional information these calibrated dust models provide and what we are still missing in cometary dust characterization.

How to cite: Ivanovski, S. L.: The Latest (Dusty) Pieces in the Rosetta Story, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15089, https://doi.org/10.5194/egusphere-egu2020-15089, 2020.

Spacecraft imaging of the inner comae of 1P/Halley (Giotto/HMC) and 19P/Borrelly (DS1/MICAS) indicated unexpectedly low ratios for the dust brightness above the dayside hemisphere to that above the nightside. Neither ratio was consistent with dust emission being directly proportional to sublimation loss of H2O using purely insolation-driven models. The near-terminator observations of 67P/Churyumov-Gerasimenko from Rosetta allow very precise separation of the dayside and nightside hemispheres and confirm low dayside to nightside dust brightness ratios. In the case of 67P values of ~3.3:1 were observed and an interesting trend towards increased ratios with decreasing heliocentric distance. Detailed modelling using insolation-driven models do not fit the data by factors of several. Dust from the dayside may contribute to the brightness on the nightside if particles are not escaping and therefore gravitationally bound. However, the radial distribution of brightness on the nightside is inconsistent with this interpretation as can be demonstrated with a simple model. The source is also not in the form of single nightside (e.g. “sunset”) jets. Furthermore, shadowing of emitted dust by the nucleus itself indicates that much of the observed brightness on the nightside is very close to the nucleus and distributed roughly uniformly around in the nightside hemisphere (Gerig et al., submitted).

Gas emission from the nightside has been a consistent element of source distributions (e.g. Bieler et al., 2015) required to model ROSINA/COPS data. However, the composition is frequently not specified. We have been investigating self-consistent, physically generated, numerical models of combined H2O and CO2 emission (see also Herny et al., submitted). Dust emission has been incorporated into the model chain allowing modelling of the observation of the gas composition, the gas density, and the dust brightness distribution in the vicinity of the nucleus for specific times. The results of investigation will be presented.

How to cite: Thomas, N., Gerig, S.-B., Pinzon, O., Marschall, R., Wu, J.-S., and Herny, C.: The spatial distribution of dust in the inner comae of comets: Evidence for and modelling of nightside emission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8393, https://doi.org/10.5194/egusphere-egu2020-8393, 2020.

The origin of cyano (CN) radicals in comets presents a long-standing riddle to the science community. Remote observations, e.g. reviewed by Fray et al. [1], show that for some comets the scale lengths, production rates, and spatial distributions of hydrogen cyanide (HCN) and CN using a Haser-based model are not consistent. Consequently, a process additional to photolysis of HCN seems to be required to explain the observed CN densities. Possible scenarios include (1) degradation of CN-producing refractories (e.g. HCN-polymers, tholins, or ammonium salts [2-3]) and (2) photolysis of other gaseous CN-bearing parent species (e.g. HC₃N or C₂N₂).

The CN/HCN ratio observed in the inner coma of comet 67P/Churyumov-Gerasimenko with the Double Focusing Mass Spectrometer DFMS, part of the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) sensor package [4] onboard ESA’s Rosetta spacecraft, is not compatible with fragmentation of HCN under electron impact ionization. Even though from fragmentation a constant CN/HCN ratio of about 0.15 [5-7] is expected, the observed values range from almost 0.4 at the beginning of the mission (August 2014) to about 0.15 shortly after perihelion passage (August 2015). Towards the end of the mission (September 2016), CN/HCN ratios increase again. This presentation will discuss the data from ROSINA/DFMS in detail and present laboratory-based indications that direct production of CN from sublimating ammonium cyanide (NH₄CN) occurs, leading to increased CN/HCN ratios. Could this be the process generating a surplus of CN radicals with respect to photolysis of HCN in certain comets?

[1] N. Fray et al. The origin oft he CN radical in comets: A review from observations and models Planetary and Space Science 53 (2005) 1243-1262.

[2] N. Hänni et al. Ammonium Salts as a Source of Small Molecules Observed with High-Resolution Electron-Impact Ionization Mass Spectrometry. J. Phys. Chem. A 123 (2019) 27, 5805-5814.

[3] K. Altwegg et al. Evidence of ammonium salts in comet 67P as explanation for the nitrogen depletion in cometary comae. Nat. Astron. (2019) in print.

[4] H. Balsiger et al. Rosina - Rosetta Orbiter Spectrometer for Ion and Neutral Analysis. Space Science Reviews 128 (2007) 745-801.

[5] S.E. Steins in NIST Chemistry WebBook, NIST Standard Reference Database Number 69, Eds. P.J. Linstrom and W.G. Mallard, National Institute of Standards and Technology, (2018).

[6] P. Kusch et al. The Dissociation of HCN, C₂H₂, C₂N₂, and C₂H₄ by Electron Impact. Phys. Rev. 52 (1937) 843-854.

[7] D. P. Stevenson. Ionization and Dissociation by Electron Impact: Cyanogen, Hydrogen Cyanide, and Cyanogen Chloride and the Dissociation Energy of Cyanogen. J. Chem. Phys. 18 (1950) 1347-1351.

How to cite: Hänni, N., Altwegg, K., and Rubin, M.: The ROSINA Perspective on the CN/HCN Ratio at Comet 67P/Churyumov-Gerasimenko, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2617, https://doi.org/10.5194/egusphere-egu2020-2617, 2020.

Our current understanding of the solar system’s micrometeoroid environment relies to a substantial extent on in-situ data acquired by impact ionization dust detectors such as Ulysses’ and Galileo’s DDS or Cassini’s CDA. Such detectors derive the mass and speed of striking dust particles from the properties and evolution of the plasma created upon impact. In particular, empirical evidence suggests that the impact speed is a function of the duration of impact charge delivery onto the target - the so-called plasma rise time. Often, this dependence has been attributed to secondary impacts of target and projectile ejecta. 

During recent years the capabilities of laboratory impact detectors have been significantly improved. In particular we now have ample evidence that secondary ejecta impacts are not responsible for the rise-time dependence. In fact the plasma rise-time is rather related to the ionization of target contaminants in the vicinity of the impact site. 

In this talk we present new experimental data obtained with state-of-the-art impact ionization mass spectrometers, which shed new light on what is really going on during a hypervelocity dust impact. We further discuss the implications for the interpretation of dust data obtained with previous generations of impact ionization detectors.

How to cite: Kempf, S., Goode, W., Srama, R., and Postberg, F.: What does really happen in a dust impact?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20089, https://doi.org/10.5194/egusphere-egu2020-20089, 2020.

Antenna instruments on space missions have been used to detect dust particles and characterize dust populations. The antennas register the transient electric signal generated by the expansion of the impact plasma from the dust impact on the spacecraft body or the antenna. Given the large effective sensitive area, antenna instruments offer an advantage over dedicated dust detectors for dust populations with low fluxes. The dust accelerator facility operated at the University of Colorado has been employed to investigate the physical mechanisms of antenna signal generation. The dominant mechanism is related to the charging of the spacecraft (or antenna) by collecting some fraction of electrons and ions from the impact plasma. We have carried out a number of experimental campaigns in order to characterize the dust impact charge yields from relevant materials, the effective temperatures of dust impact plasmas, and variations of the antenna signals with spacecraft potential, or magnetic field. Here we report on a physical model that provides a good qualitative and quantitative description of the antenna waveforms recorded in laboratory conditions. The model is based on the separation of the electrons from the ions in the impact plasma and their different timescales of expansion. The escaping and collected fractions of charges are driven by the spacecraft potential. Fitting the model to the laboratory data revealed that the electrons in the impact plasma have an isotropic distribution, while ions are dominantly moving away from the dust impact location. Identifying the fine details in the antenna signals requires a relatively high sampling rate and thus not commonly resolved for past instruments. The high-rate mode of the FIELDS instrument on the Parker Solar Probe, however, can be used to verify the proposed model.

How to cite: Sternovsky, Z., Shen, M.-H., DeLuca, M., Fredriksen, Å., Horányi, M., Hsu, S., Kočiščák, S., Malaspina, D., Nouzák, L., and Ye, S.: Dust detection by antenna instruments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1805, https://doi.org/10.5194/egusphere-egu2020-1805, 2020.

The zodiacal cloud in the inner solar system undergoes continual evolution, as its dust grains are collisionally ground and sublimated into smaller and smaller sizes. Sufficiently small (~<500 nm) grains known as beta-meteoroids are ejected from the inner solar system on hyperbolic orbits under the influence of solar radiation pressure. These small grains can reach significantly larger speeds than those in the nominal zodiacal cloud and impact the surfaces of airless bodies. Since the discovery of the Moon's asymmetric ejecta cloud, the origin of its sunward-canted density enhancement has not been well understood. We propose impact ejecta from beta-meteoroids that hit the Moon's sunward side could explain this unresolved asymmetry. The proposed hypothesis rests on the fact that beta-meteoroids are one of the few truly asymmetric meteoroid sources in the solar system, as unbound grains always travel away from the Sun and lack a symmetric inbound counterpart. This finding suggests beta-meteoroids may also contribute to the evolution of other airless surfaces in the inner solar system as well as within other exo-zodiacal disks. We will also highlight recent observations from the Parker Solar Probe (PSP) spacecraft, which suggest it is being bombarded by the very same beta-meteoroids. We discuss how observations by PSP, which lacks a dedicated dust detector, can be used to inform the structure and variability of beta-meteoroids in the inner solar system closer to the Sun than ever before.

How to cite: Szalay, J., Pokorny, P., Horanyi, M., Bale, S., Christian, E., Goetz, K., Goodrich, K., Hill, M., Kuchner, M., Larsen, R., Malaspina, D., McComas, D., Mitchell, D., Page, B., and Schwadron, N.: The Effects of Hyperbolic Meteoroids from Parker Solar Probe to the Moon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4160, https://doi.org/10.5194/egusphere-egu2020-4160, 2020.

We present details on the first white-light detection of a dust trail following the orbit of asteroid 3200 Phaethon, seen in images recorded by the Wide-field Imager for Parker Solar Probe (WISPR) instrument on the NASA Parker Solar Probe (PSP) mission. In this talk we will present a brief introduction to the PSP mission and the WISPR instrument. We will then show observations returned by WISPR in multiple perihelion 'encounters' that clearly show a diffuse dust trail perfectly aligned with the perihelion portion of the orbit of 3200 Phaethon, recorded while the asteroid itself was near aphelion. We will discuss the physical parameters that we have derived for the dust trail, including its visual magnitude, surface brightness and mass. We also speculate on the relationship of this trail to the Geminid meteor shower, of which Phaethon is assumed to be the parent, and demonstrate why the trail has not been detected visually until now, despite a number of dedicated observing campaigns. We also hope to present initial analyses of the most recent set of WISPR observations (January 2020), where we anticipate the trail should again be visible in the WISPR observations.

How to cite: Battams, K., Stenborg, G., Howard, R., Gallagher, B., Knight, M., and Kelley, M.: Parker Solar Probe Observations of a Dust Trail in the Orbit of 3200 Phaethon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20056, https://doi.org/10.5194/egusphere-egu2020-20056, 2020.

The Parker Solar Probe (PSP) mission has completed four solar encounters, observing the solar corona from distances significantly closer to the Sun than from previous missions (to 36 solar radii during the first three perihelia and to 28 solar radii during the fourth). During these encounters, the Wide-field Imager for Solar Probe (WISPR) onboard PSP has been observing the F-corona/Zodiacal light - probing the dust environment in the solar corona as PSP moves through the corona. This allowed WISPR to find 1) a gradual decrease of the expected brightness of the F-corona for distances shorter than about 0.1 AU, 2) dust trails of short-period asteroid/cometary objects (e.g., 3200 Pheathon and 2P/Encke) and 3) a changing rate of dust impacts on the S/C throughout the encounter period. In this presentation, we will present these findings, discuss their nature, and elaborate on the novelty of these results. The authors acknowledge support from the NASA Parker Solar Probe program.

How to cite: Howard, R., Stenborg, G., Hess, P., Gallagher, B., and Battams, K.: White-light observations of features in the Zodiacal dust cloud from within the solar corona, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20135, https://doi.org/10.5194/egusphere-egu2020-20135, 2020.

Hera is ESA’s contribution to an international effort supported by ESA and NASA named Asteroid Impact and Deflection Assessment (AIDA). NASA’s DART mission will first perform a kinetic impact on Didymos secondary, nicknamed Didymoon, then Hera will follow-up with a detailed post-impact survey, to fully characterize this planetary defense technique. Two CubeSats will be deployed by the Hera spacecraft once the Early Characterization Phase has completed.

The Hera spacecraft communicates with the ground station on the Earth by means of a standard two-way X-band system. The microwave signal is sent to the S/C from a ground antenna and coherently retransmitted back to Earth, where Doppler (the key observable for gravity science) and range measurements are obtained. In addition, Hera will track the two CubeSats by means of a space-to-space inter-satellite link (ISL). This represents a very nice add-on to the gravity investigation carried out by means of Hera tracking observables as the Doppler effect that affects the inter-satellite link contains the information on the dynamics of the system, i.e. masses and gravity field of Didymos primary and secondary.

We describe here the mission scenario for the gravity science experiments to be jointly carried out by the three mission elements, i.e. Hera, CubeSat#1 (named Juventas) and CubeSat#2, via Ground-based and Satellite-to-Satellite Doppler Tracking. Also, our results and achievable accuracy for the estimation of the mass and gravity field of Didymos primary and secondary are presented.

How to cite: Tortora, P., Gai, I., Lombardo, M., Zannoni, M., Carnelli, I., Kueppers, M., Martino, P., and Michel, P.: Didymos Gravity Science through Ground-based and Satellite-to-Satellite Doppler Tracking, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12800, https://doi.org/10.5194/egusphere-egu2020-12800, 2020.

NASA and its partners maintain a watch for near-Earth objects (NEOs), asteroids and comets that pass within Earth’s vicinity, as part of an ongoing effort to discover, catalog, and characterize these bodies and to determine if any pose an impact threat. NASA’s Planetary Defense Coordination Office (PDCO) is responsible for:

• Ensuring the early detection of potentially hazardous objects (PHOs) – asteroids and comets whose orbits are predicted to bring them within 0.05 astronomical units of Earth's orbit; and of a size large enough to reach Earth’s surface – that is, greater than perhaps 30 to 50 meters;
• Tracking and characterizing PHOs and issuing warnings about potential impacts;
• Providing timely and accurate communications about PHOs; and
• Performing as a lead coordination node in U.S. Government planning for response to an actual impact threat.

NASA’s current congressionally-mandated objective is to detect, track, and catalogue at least 90 percent of NEOs equal to or greater than 140 meters in size by 2020, and characterize the physical properties of a subset representative of the entire population. This mandate will likely not be met given current resources dedicated to the task; however significant progress is being made.

In this paper, we will report on the status of our program and the missions working to support our planetary defense coordination office. In addition, we will provide the latest detections and characterizations results. Our office continues to work diligently with our international partners to achieve our goals and continue to safeguard Earth with the latest technologies available.

How to cite: Daou, D. and Johnson, L.: A Summary and Update on NASA’s Planetary Defense Program., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22173, https://doi.org/10.5194/egusphere-egu2020-22173, 2020.

The target of the ESA’s HERA mission is asteroid 65803 Didymos (1996 GT), an Apollo-type near-Earth object (NEO). Didymos is a binary asteroid; the primary body has a diameter of around 775 m and a rotation period of 2.26 hours, whereas the secondary body (informally called Didymoon) has a diameter of around 165 m and rotates around the primary at a distance of around 1.2 km in around 12 hours.

Thermophysical properties of the uppermost surface govern the exchange of radiative energy between the asteroid and its environment, hence determine surface and subsurface temperatures.  These thermophysical properties are characterized by grain size, porosity, or packing of the surface materials.  Diurnal change in surface temperature show large variations in fine soils like sand and highly porous rock with low thermal inertia, and much smaller variations in in dense rock with high thermal inertia. Here we present a thermophysical model of Didymoon based on known, assumed and derived range of physical properties.  A parameter study has been carried out for surface temperatures assuming possible thermal inertia ranges.  

Results from this study are used to investigate performance for Thermal Infrared instrument TIRA onboard HERA spacecraft. Hera is the European contribution to an international double-spacecraft collaboration. Due to launch in 2024, Hera would travel to the binary asteroid system. TIRA onboard HERA will be operating in the 8-14 µm wavelength range. It will be used for scientific analysis and to demonstrate the feasibility of using a TIR camera for GNC (Guidance, navigation and control). The main scientific output for TIRA is to determine the thermal inertia and thus the properties of the surface material.

How to cite: Karatekin, Ö., Henry, G., Gloesener, E., and van Hove, B.: Thermal modeling of the binary asteroid Didymos, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20885, https://doi.org/10.5194/egusphere-egu2020-20885, 2020.

The Low Frequency Radar (LFR) on the JUVENTAS CubeSat for HERA / ESA mission to Didymos Binary Asteroid is a unique opportunity to perform direct measurements of its internal structure and regolith. LFR has been developed to fathom asteroid from a small platform. This instrument is inherited from CONSERT/Rosetta and has been redesigned in the frame of the AIDA and HERA ESA mission.

Onboard JUVENTAS, LFR is operating in monostatic mode to probe down to the first hundreds of meters into the subsurface and to achieve a full tomography of the Didymos' moonlet. Direct observations of the internal structure of asteroids can solve still open basic questions like: Is the body a monolithic piece of rock or a rubble-pile? How high is the porosity? What is the typical size of the constituent blocks? Are these blocks homogeneous or heterogeneous? How is the regolith covering its surface constituted?

The low frequency aboard the Juventas CubeSat will contribute to the solution of these open and for planetary defense crucial questions.
- The first LRF objective is the characterization of the moonlet interior, to identify internal structure and to analyze the size distribution and heterogeneity of constitutive blocks from sub metric to global
- The second objective is the estimation of average permittivity and mapping of its spatial variation especially in the crater area.
- The same characterization applied to the main of the binary system is among secondary objectives.
- Supporting shape modeling and determination of the dynamical state by radar ranging is a further secondary objective.

This paper will present the instrument concept and measurement strategy, its performances and the expected science return.

How to cite: Herique, A., Plettemeier, D., Kofman, W., Rogez, Y., and Goldberg, H.: Low Frequency Radar (LFR) on the JUVENTAS CubeSat for HERA / ESA mission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19957, https://doi.org/10.5194/egusphere-egu2020-19957, 2020.

Over the last decades, the exploration of our Solar System carried out by automatic probes allowed a huge leap in our understanding of the planets, their main satellites and minor bodies such as asteroids and comets. However, despite the large number of diverse datasets available nowadays, comparative studies of different bodies are still poorly addressed in several cases, in particular for airless bodies.

The primary goal of our two-year project, selected in the framework of the “ISSI/ISSI-BJ Joint Call for Proposals 2019 for International Teams in Space and Earth Sciences”, is to quantify similarities and differences in the surface mineralogy of Vesta, Mercury and the Moon, substantially enhancing the scientific return of individual instrumental datasets and/or individual space missions. Here, we give an overview of our project, we clarify what is the status after the first team meeting held in March 2020.

Our project focuses on two specific questions:

Our overall approach is to apply various techniques of analysis on hyper- and multispectral data sets that are publicly available, such as those on acquired by the Dawn mission at Vesta, MESSENGER datasets obtained at Mercury and Chandrayaan-1 data for the Moon.

This work is supported by the International Space Science Institute (ISSI) and by INAF-IAPS.

How to cite: Zambon, F., Tosi, F., Besse, S., Brunetto, R., Carli, C., Combe, J.-P., Forni, O., Klima, R., Krohn, K., Rothery, D., Stephan, K., Donaldson-Hanna, K., Barraud, O., and Nava, J.: Deciphering compositional processes in inner airless bodies of our Solar System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18758, https://doi.org/10.5194/egusphere-egu2020-18758, 2020.

Meteorites, especially the undifferentiated ones like primitive chondrites, provide information about the origin and initial conditions of the solar system since they contain presolar and solar nebula materials (Scott, 2007). Differentiated meteorites like iron meteorites play a distinct role in constraining the early phases of planetary accretion (Yang et al. 2007). They also provide the possibility to receive information about core properties and planetary bodies. In addition to the gain in such fundamental scientific knowledge both types are of interest for the exploration of critical and precious elements (CRMs).

In the future, the tremendous increase of the consumption of these elements from terrestrial deposits and the subsequent shortage could lead to an exploitation of extra-terrestrial deposits. Therefore, “space-mining” of near Earth objects could be used as alternative source of raw materials (Ross, 2001).

While improving the characterization and classification of the Santa Rosa de Viterbo Iron Meteorite, we found notable concentrations of Au and Ge alongside major elements such as Fe, Ni and Co in the bulk composition of that meteorite. Major and rock-forming minerals such as kamacite and taenite incorporate hundreds of ppm of Ge whereas schreibersite, itself a minor component in that particular meteorite, is a source for Au. In kamacite and taenite also Ir and Ga were found in minor amounts.

Scott, E. R. (2007). Chondrites and the protoplanetary disk. Annu. Rev. Earth Planet. Sci., 35, 577-620.

Ross, S. D. (2001). Near-earth asteroid mining. Space, 1-24.

Yang, J., Goldstein, J. I., & Scott, E. R. (2007). Iron meteorite evidence for early formation and catastrophic disruption of protoplanets. Nature, 446(7138), 888.

How to cite: Wilke, F. D. H., Bsdok, B., Altenberger, U., and Concha, A. E.: The Santa Rosa Meteorite from Colombia: An example of critical raw materials in a meteorite, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8598, https://doi.org/10.5194/egusphere-egu2020-8598, 2020.

In the early solar system radiogenic heating by ²⁶Al and collisions are the two prominent ways expected to modify the internal composition of cometesimals, building blocks of comets, by removing highly volatile compounds like CO, CO₂ and NH₃. However, observations indicate that even large comets like Hale-Bopp (R ≈ 70 km) can be rich in these highly volatile compounds [1].

Here we constrain under which conditions cometesimals experiencing both internal heating and collisions can retain pristine interiors. For this purpose, we employ both the state-of-the-art finite-difference marker-in-cell code I2ELVIS [2] to model the thermal evolution in 2D infinite cylinder geometry and a 3D SPH code [3] to study the interior heating caused by collisions among cometesimals. For simplicity we assume circular porous cometesimals with a low density ( ≈ 470 kg/m³) based on measurements for comet 67P/Churyumov-Gerasimenko [4].

For the parameter study of the thermal history we vary (i) cometesimal radii, (ii) formation time and the (iii) the silicate/ice ratio. For the latter we keep the mean density fixed and change the porosity of the cometesimal. For the impact models we use porous, low-strength objects and vary (i) target and (ii) projectile radii, (iii) impact velocity as well as (iv) impact angle. Potential losses of volatile compounds from their interiors are calculated based on their critical temperatures taken from literature [5]. Our combined results indicate that only small or late-formed cometesimals remain mostly pristine, while early formed objects can even reach temperatures high enough to melt the water ice.

REFERENCES

[1] Biver et al., Nature 380, 137-139 (1996).

[2] Gerya & Yuen, Phys. Earth Planet. Int. 163, 83-105 (2007).

[3] Jutzi, Planet. Space Sci. 107, 3–9 (2015).

[4] Sierks et al. Science 347, 1044 (2015).

[5] Davidsson et al. Astronomy & Astrophysics 592, A63 (2016).

How to cite: Jutzi, M. and Golabek, G.: Modification of cometesimal interiors by early thermal evolution and collisions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5144, https://doi.org/10.5194/egusphere-egu2020-5144, 2020.

On 30 September 2016, Rosetta completed its mission by landing on comet 67P/Churyumov-Gerasimenko. Although this marked an end to the spacecraft’s operations, intensive work has continued for several years, with the instrument teams updating their data in response to scientific reviews and delivering them to ESA’s Planetary Science Archive (PSA). ESA has also been working with the instrument teams to produce new and enhanced data, and to improve documentation, aiming to provide the best long-term archive possible for the Rosetta mission.

All teams have now completed their nominal science data deliveries from the comet phase, and samples of final data from the enhanced archiving activities went through a last science review in September 2019. The aim is to to complete any updates requested and deliver final products in the first half of 2020.

As soon as Rosetta’s operational mission ended, ESA established a number of activities with the Rosetta instrument teams to allow them to continue working on enhancing their archive content. The updates were focused on key aspects of an instrument’s calibration or the production of higher level data / information, and were therefore specific to each instrument. Most activities are now complete, but a few are still in the process of being closed in early 2020.

Almost all instrument teams have now provided a Science User Guide for their data, which have been highly appreciated by the scientists in the recent reviews. Many teams have also updated their calibrations to deliver higher level and/or derived products. For example, OSIRIS have delivered data with improved calibrations, as well as straylight corrected, I/F corrected, and three-dimensional georeferenced products. These are all already available in the archive. They now also provide their data additionally in FITS format, and have added quicklook (browse) versions of their products to allow an end-user to more easily identify the images they may be interested in. Internal straylight data and boresight corrected / full frame data are currently in preparation and will be added to the archive early this year.

Similarly, the VIRTIS team will update both their spectral and geometrical calibrations, and deliver mapping products to the final archive. The Rosetta Plasma Consortium instruments completed several cross-calibrations and a number of activities individual to each instrument, as well as producing illumination maps of the comet. The MIDAS team have produced a dust particle catalog from the comet coma. GIADA have produced dust environment maps with omni-directional products. COSIMA has delivered laboratory data to help understand their inflight measurements. An activity is also ongoing to produce data set(s) containing supporting ground-based observations of the comet.

The Rosetta ESA archiving team are also producing calibrated data for the NAVCAM instrument, and will include the latest shape models from the comet in the final Rosetta archive. Work is also underway to incorporate the radiation monitor (SREM) and spacecraft housekeeping (MUST) data into the archive.

This presentation will outline the current status of the Rosetta archive, and highlight the work being done this year to close out the archive and prepare it for legacy use.

How to cite: Heather, D., Fraga, D., O'Rourke, L., and Taylor, M.: The Rosetta Science Archive: Closing Out the Science Content, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5711, https://doi.org/10.5194/egusphere-egu2020-5711, 2020.

Determining the ion bulk velocity is essential to understand the physics of the inner magnetosphere of comets. This velocity controls the strength of the ion-neutral drag force, which plays a very important role in the energy and momentum transfer processes of that region. Unfortunately there are no direct measurements of this quantity available. The energy thresholds of the ion instruments on board the Rosetta orbiter would prevent the direct detection of the bulk ion content of the plasma as long as the plasma is relatively slow and cold. The picture is further complicated by the spacecraft potential, which accelerates the thermal ions to energies higher than the measurement threshold, but effectively screens the magnitude and direction of their original velocity. That distortion effect is not arbitrary however; it is possible to recover the original ion velocity distribution from IES measurements by simulating the effects of the spacecraft potential on the ion motion. We performed these simulations for several bulk and thermal velocity as well as spacecraft potential values, and compared the results with IES measurements. From this we could determine the most probable values of the bulk and thermal speeds of the plasma ions in the inner magnetosphere of comet 67P/ Churyumov–Gerasimenko.

How to cite: Nemeth, Z., Szego, K., Timar, A., Foldy, L., Burch, J., and Goldstein, R.: Determining the ion velocity in the inner magnetosphere of comet 67P/Churyumov–Gerasimenko using Rosetta IES measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3347, https://doi.org/10.5194/egusphere-egu2020-3347, 2020.

Dhooghe et al. (2017) studied halogen-bearing compounds in the coma of 67P/C-G with the Double Focusing Mass Spectrometer (DFMS) of Rosetta’s ROSINA instrument during a few time periods from first encounter up to perihelion (August 2014-August 2015). The main halogen-bearing compounds identified in the comet atmosphere were the hydrogen halides HF (hydrogen fluoride), HCl (hydrogen chloride) and HBr (hydrogen bromide). The halogen to oxygen ratios were found to vary between ~10^-4 (Cl/O and F/O) to ~10^-6 (Br/O), which shows these compounds have a very low abundance. In a follow-up article, De Keyser et al. (2017) observed an increase in the halogen-to-oxygen ratio as a function of distance, which suggests a distributed source for HF and HCl, probably through progressive release of these compounds from grains. Fayolle et al. 2017 and recent work by Altwegg et al. 2020 show that also CH₃Cl and NH₄Cl, respectively are present in the coma.

To further our knowledge on halogen containing species, we have applied recent improvements in DFMS data analysis techniques (De Keyser et al. 2019) to obtain a high quality time series for the complete mission duration. These data analysis techniques improve the retrieval of the abundances for overlapping mass peaks (¹⁸OH⁺ for F⁺, H₂¹⁸O⁺ for HF⁺, H³⁴S⁺ for ³⁵Cl⁺, and ³⁶Ar⁺ and H₂³⁴S⁺ for H³⁵Cl⁺). The contribution of CS₂⁺⁺ to the signal of H³⁷Cl⁺ has been determined from data for CS₂⁺.

Based on the full mission data, and focusing on chlorine, we determine the ³⁷Cl/³⁵Cl isotopic ratio. An interesting finding is that the ³⁵Cl⁺/H³⁵Cl⁺ and ³⁷Cl⁺/H³⁷Cl⁺ ratios in the DFMS mass spectrometer do not match the NIST ones for the H³⁵Cl and H³⁷Cl parents. This indicates that at least one additional chlorine source must be present. The variability of halogen-containing species as a function of time is discussed, as well as the possible role of distributed sources.

Altwegg, K. et al. (2020): Evidence of ammonium salts in comet 67P as explanation for the nitrogen depletion in cometary comae. Nature Astronomy, in press

Dhooghe, F. et al (2017): Halogens as tracers of protosolar nebula material in comet 67P/Churyumov-Gerasimenko, MNRAS, 472, Issue 2, 1336, doi 10.1093/mnras/stx1911.

De Keyser, J. et al (2017): Evidence for distributed gas sources of hydrogen halides in the coma of comet 67P/Churyumov–Gerasimenko, MNRAS, 469, Issue Suppl_2, S695, doi 10.1093/mnras/stx2725.

De Keyser, J. et al. (2019): Position-dependent microchannel plate gain correction in Rosetta's ROSINA/DFMS mass spectrometer. IJMS, 446, 116232, doi 10.1016/j.ijms.2019.116232.

Fayolle et al. (2017): Protostellar and cometary detections of organohalogens. Nature Astronomy 1, 703, doi.org/10.1038/s41550-017-0237-7

How to cite: Dhooghe, F., De Keyser, J., Altwegg, K., Hänni, N., Rubin, M., Berthelier, J.-J., Cessateur, G., Combi, M., Fuselier, S., Maggiolo, R., and Wurz, P.: Halogen-containing species at Comet 67P/Churyumov-Gerasimenko: Full mission results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13051, https://doi.org/10.5194/egusphere-egu2020-13051, 2020.

Following its arrival at comet 67P/Churyumov-Gerasimenko in August 2014, the Rosetta spacecraft successfully navigated in its proximity for two years, using a combination of Earth-based astrometric and radiometric tracking data as well as space-based optical navigation data. 

Depending on the mission phase, the orbital navigation system was tasked with the simultaneous estimation of both spacecraft and comet state, in addition to several other physical parameters including amongst others the comet rotational state, its gravitational field and the body-fixed coordinates of surface landmarks.

Estimating the heliocentric trajectory of 67P has proven to be challenging, due to the lack of reliable models to take into account the non-gravitational accelerations acting on the comet (particularly close to perihelion) and to occasional degradations of the ranging observables caused by geometrical constraints (solar conjunctions).

The accuracy of the resulting comet heliocentric trajectories, which show discontinuities in the order of tens of kilometers between consecutive short-arc solutions, was sufficient for spacecraft proximity operations, where navigators are mostly concerned by the relative comet/spacecraft position. However, a continuous and more accurate orbital solution is strictly coupled with the development of analytical models for non-gravitational accelerations and comet outgassing for which the Rosetta mission represents an ideal test case.

The work presented here represents a joint effort between academic institutions and ESA’s Flight Dynamics team to improve the accuracy of 67P’s orbit, by re-analyzing the radiometric data over long time scales for the whole duration of Rosetta proximity operations at comet 67P.

Details on the orbit determination process and filter implementation will be presented, together with a discussion on the achieved formal uncertainties and on the observables’ residuals.

How to cite: Lasagni Manghi, R., Zannoni, M., Tortora, P., Küppers, M., O'Rourke, L., Martin, P., Mottola, S., Keller, U., Budnik, F., Taylor, M., Jorda, L., Groussin, O., and Thomas, N.: Accurate reconstruction of comet 67P orbit through re-analysis of Rosetta ranging data acquired during proximity operations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19173, https://doi.org/10.5194/egusphere-egu2020-19173, 2020.

Interplanetary Field Enhancements are phenomena in the interplanetary magnetic field, first discovered near Venus, during an extremely long duration (12 hours) and large size (about 0.1 AU) passage across the Pioneer Venus spacecraft. Three and a half hours later and 21 x 10⁶ km farther from the Sun, this structure, somewhat weaker and off to the side of the expected radial path of any solar initiated disturbance, was seen by first Venera 13 and then Venera 14, trailing behind V13. Since this discovery, many smaller such disturbances have been observed and attributed to collisions of small rocks in space at speeds of about 20 km/s at 1 AU and faster, closer to the Sun. All sightings with magnetometers and other space plasma instruments give very precise measurements of the radial structure (of usually the magnetic field), but the scale transverse to the solar radius is poorly defined, as is the temporal evolution of the structure from single spacecraft data.

On January 16, 2018, near Earth, 12 spacecraft equipped with plasma spectrometers and magnetometers observed the passage of a single Interplanetary Field Enhancement. The magnetic field profiles at the four 1 AU spacecraft were very similar. The profiles were obtained at different times appropriate to their locations. The 4 Cluster spacecraft were closer to the Earth and in a region in which the solar wind had slowed down because of the Earth’s bow wave (shock) in the solar wind. The disturbance in the shocked solar wind occurred at the time expected if the IFE structure had not been slowed by the plasma, but rather had proceeded with the momentum it had prior to the shock crossing. If the disturbance causing particles are small bits of rock (not protons), then they should have kept most of their momentum in crossing the bow shock. We view this as a complete test of the dust producing collisional origin of these Interplanetary Field Enhancements, and a clear demonstration of how the solar wind clears out the dust in the inner solar system produced by the continuing destructive collisional process.

How to cite: Lai, H., Jia, Y., Connors, M., and Russell, C.: Nanoscale Dust Production at 1 Au; Identification and Tracking with 12 Spacecraft, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2476, https://doi.org/10.5194/egusphere-egu2020-2476, 2020.

A fraction of the dust that is contained in the local interstellar medium around the Sun can enter the heliosphere and be observed in the solar system. The exception is the small size component of the interstellar dust spectrum, which can be directly observed only beyond the heliopause. 

The charge-to-mass ratio of the interstellar dust grains of nanometer size can be high enough to make their dynamics highly sensitive to the magnetic field and plasma flow. Based on numerical simulations and analytical models, we show how the small interstellar grains entering the transition region between the undisturbed interstellar medium and the outer boundary of the heliosphere respond to plasma and magnetic field structures (in particular the heliospheric bow shock and the heliopause) expected in this region. We also point out which dust impact measurements from a spacecraft in the interstellar space would be most desirable for imaging the structure of the transition region by means of interstellar dust.

How to cite: Czechowski, A. and Mann, I.: What can we learn from observations of small dust grains in the interstellar space?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9599, https://doi.org/10.5194/egusphere-egu2020-9599, 2020.

The white-light Fraunhofer corona (F-corona) and inner Zodiacal light are generated by interplanetary (Zodiacal) dust particles that are located between Sun and observer. At visible wavelength the brightness comes from sunlight scattered at the dust particles. F-corona and inner Zodiacal light were recently observed from STEREO (Stenborg et al. 2018) and Parker Solar Probe (Howard et al. 2019) spacecraft which motivates our model calculations. We investigate the brightness by integration of scattered light along the line of sight of observations. We include a three-dimensional distribution of the Zodiacal dust that describes well the brightness of the Zodiacal light at larger elongations, a dust size distribution derived from observations at 1AU and assume Mie scattering at silicate particles to describe the scattered light over a large size distribution from 1 nm to 100 µm. From our simulations, we calculate the flattening index of the F-corona, which is the ratio of the minor axis to the major axis found for isophotes at different distances from the Sun, respectively elongations of the line of sight. Our results agree well with results from STEREO/SECCHI observational data where the flattening index varies from 0.45° and 0.65° at elongations between 5° and 24°. To compare with Parker Solar Probe observations, we investigate how the brightness changes when the observer moves closer to the Sun. This brightness change is influenced by the dust number density along the line of sight and by the changing scattering geometry.

-Stenborg G., Howard R. A., and Stauffer J. R., 2018: Characterization of the White-light Brightness of the F-corona between 5° and 24° Elongation, Astrophys. J. 862: 168 (21pp).

-Howard, R.A. and 25 co-authors, 2019: Near-Sun observations of an F-corona decrease and K-corona fine structure, Nature 576, 232–236.

How to cite: Eren, S. and Mann, I.: Model Calculations of the F-Corona and inner Zodiacal Light , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7486, https://doi.org/10.5194/egusphere-egu2020-7486, 2020.

This work addresses the generation of charge during impacts of nano- to microscale projectiles on metal surfaces at speeds from 0.1 to 10 km/s. These speeds are well above the range of elastic deformation and well below speeds where volume ionization occures. Earlier models have utilized impurity diffusion through molten grains together with a Saha-equation to model impact ionization at these speeds. In this work we employ a model of capacitive contact charging in which we allow for projectile fragmentation upon impact. We show that this model well describes laboratory measurements of metal projectiles impacting metal targets. It also can describe in-situ measurements of dust in the Earth’s atmosphere made from rockets. We also address limitations of the currently most used model for impact ionization.

How to cite: Antonsen, T., Mann, I., Vaverka, J., and Nouzak, L.: A fragmentation model approach for low velocity impact charging, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18932, https://doi.org/10.5194/egusphere-egu2020-18932, 2020.

Over the last few decades, our picture of comets has been continuously changing and growing due to several successful space missions, as well as cometary simulation projects in the laboratory (e.g. KOSI 1987-1992, CoPhyLab 2018 - 2021). This work aims for a better understanding of the gas transport through a porous cometary surface layer. Therefore, gas flow measurements have been performed in our laboratory to investigate the permeability of several analogue materials, which have been chosen to mimic cometary surface properties.

For the first measurements, which we are reporting here, only dry materials, free of volatiles have been selected, to isolate the gas transport from gas production inside the materials. They include glass beads made of soda lime glass, which are sieved into separate fractions to obtain distinct grain size ranges from 45 µm up to 4.3 mm. The Mars simulant JSC-Mars 1 is used in the experiments, as well as JSC-1 as a lunar soil simulant. Furthermore, an Asteroid analogue material named UCF/DSI-CI-2 from the Exolith Lab in Florida is also used. A quartz sand called UK4 mined at a local quarry in Graz is investigated as well. In a further step, a sample is created by mixing different grain size fractions of the glass beads replicating the grain size distribution of the Asteroid simulant.

The materials are also treated on a shaking table in order to obtain the packing properties of the samples. For the gas flow experiments a cylindrical sample container, with 4 cm diameter, is filled with the sample (30 mm in height) and placed inside of the vacuum chamber at the interface of two separate volumes. Four pressure sensors covering different pressure ranges monitor the gas pressure in the two volumes. A vacuum pump in the lower volume removes the gas from the chamber and through a gas inlet a defined flow of the test gas (compressed air) is inserted into the upper volume. Due to this set-up, the gas flow can only pass through the sample material. To avoid particle fluidisation and thus a texture change in the sample the gas flow is intentionally directed downwards through the sample. The gas flow is controlled by regulators from 0.15 mg/s up to 19.2 mg/s. Via the measured pressure difference between the upper and lower volume, in equilibrium flow, the gas permeability and the Knudsen diffusion coefficient of the sample material are obtained. The gas flow experiments show that the grain size distribution and the packing density of the sample play a major role for the permeability of the sample. From the analysis of the permeability measurements it is clearly visible that the larger the grains the bigger the permeability. The measured permeability values range from 10^-13 to 10^-8 m². This work is part of the CoPhyLab project funded by the D-A-CH programme (DFG GU1620/3-1 and BL 298/26-1 / SNF 200021E 177964 / FWF I 3730-N36).

How to cite: Schweighart, M., Kargl, G., Tiefenbacher, P., and Team, C.: Gas flow through porous cometary media, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5268, https://doi.org/10.5194/egusphere-egu2020-5268, 2020.

Presolar silicon carbide, identified by anomalous ¹²C/¹³C, have long been the only direct physical sampling of asymptotic giant branch stars and Type-II supernovae (SNII) ejecta. The bulk of non-novae grains form in the dust clouds of 1-3M_☉ carbon stars in the thermally pulsing asymptotic giant branch (AGB) phase of their life. While these grains have been extensively studied for their unique isotopic signature characteristic of their exotic origin and trace gasses carrying the s-process and r-process nucleosynthetic signature, to date studies on their structures of presolar grains have been limited to electron diffraction surveys using transmission electron microscopy. We present high-resolution single-crystal structural refinement of presolar silicon carbides determined using data synchrotron x-ray diffraction data collected at Advanced Photon Source. Preservation and resolvability of the circumstellar pressure/temperature regime was determined with an examination of nanostrain states in several grains of presolar silicon carbide. By accounting for the environment present at (1) circumstellar formation, (2) interstellar transport, and (3) asteroidal and meteoritic storage and shock environments we hope to open a new opportunity to directly study the limits of our theoretical understanding of stellar structures.

How to cite: McKenzie, W. and Dera, P.: Single-Crystal Structure Refinement of Presolar Silicon Carbide, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12541, https://doi.org/10.5194/egusphere-egu2020-12541, 2020.

Cassini spacecraft spent at Saturn almost half of the Saturn year. During these 13 years in the Saturn magnetosphere, the RPWS (Radio Plasma Wave Science) instrument recorded more than half a million of waveforms with signatures that can be interpreted as dust impact signals. The RPWS antennas in both dipole and monopole configurations operated with 10 kHz or 80 kHz sampling rates during the mission.
We qualitatively and quantitatively analyze the registered waveforms taking into account the spacecraft potential, density of the ambient plasma, magnitude of the Saturn’s magnetic field and its orientation with respect to the spacecraft. The magnetic field orientation is also used for distinguishing between signals resulting from dust impacts and signals produced by solitary waves, which can exhibit similar shapes. The results of analysis are compared with a prediction of the dust impact model that was recently developed on a base of laboratory simulations. The simulations used the reduced model of Cassini that was bombarded with submicron-sized iron grains in the velocity range of 1–40 km/s at the 3 MV dust accelerator operated at the LASP facility of University of Colorado. The model predicts generation of impact signals due to different fractions of collected and escaped electron and ion charges from the impact plasma plume and different timescales of their expansion. The core of the paper is devoted to a discussion of differences between model predictions and observations.

How to cite: Nouzak, L., Pavlů, J., Vaverka, J., Šafránková, J., Němeček, Z., Píša, D., Shen, M., Sternovsky, Z., and Ye, S.: Dust impact signals detected by Cassini RPWS instrument at Saturn, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3698, https://doi.org/10.5194/egusphere-egu2020-3698, 2020.

Impact ionization is a process of plasma generation upon hypervelocity impact of a small body (e.g., interplanetary dust grain) onto a solid surface.  Such process may play an important role in astrochemistry. Understanding the plasma generation, we can clarify the interpretation of proclaimed dust impact detections onto antenna-equipped space experiments, which have become widely popular in the recent years.

We present the data gained in charge generation and collection experiments conducted at the University of Colorado IMPACT hypervelocity dust accelerator facility. The impacts are of sub-micrometer cosmic dust simulants onto a metal target in the range of velocities between 1 and 50 km/s. We discuss measured charge collection on a microsecond scale as well as aggregated results of electron and ion drift velocities and temperatures and specifically their dependence on the velocity of the impactor.

How to cite: Kočiščák, S., Fredriksen, Å., DeLuca, M., Pavlů, J., and Sternovsky, Z.: Components of Impact Plasma: Velocity and Temperature, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3095, https://doi.org/10.5194/egusphere-egu2020-3095, 2020.

Dust grains in space frequently face energetic particles, e.g., ions, electrons, X-ray, positrons, etc. Such a broad variety of particle–dust interactions plays a significant role in dust charging and surface modification. The combination of high energy of particles together with a limited size of objects (dust) comprises interesting mesoscopic structure with non-obvious behavior. While in situ experiments are difficult and rare, we observed particular interactions experimentally in an electrodynamic trap. It allows us to study of a single dust grain temporal evolution under well defined conditions, i.e., to somewhat separate aforementioned processes and to investigate them individually. We present a summary of laboratory simulations and their
comparison with simple theoretical models. We discuss dust charging by different elementary particles and its importance for various space regions.

How to cite: Pavlů, J., Nouzák, L., Wild, J., Vaverka, J., Richterova, I., Šafránková, J., and Němeček, Z.: Dust Interaction with Energetic Particles — A Laboratory Simulation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3085, https://doi.org/10.5194/egusphere-egu2020-3085, 2020.

The Bright Monitor of the Solar Wind (BMSW) for the Luna-Resurs-1 mission is an instrument designed for high-time (30 ms) resolution measurements of moments of the ion energy distribution by Faraday cups in the solar wind and in a plasma environment at altitudes between 65 and 150 km above the lunar surface. Previous studies performed by a similar instrument located on-board the Spektr-R spacecraft demonstrated a possibility to detect hypervelocity impacts of dust grains by such instruments Our analysis shows that the main problem of the reliable detection of dust impacts using such types of instruments is their sampling rate. In the paper, we present a novel design of a set of FCs that improves the ability of the dust detection using a simple identification algorithm that can store data with a higher sampling rate around the impact pulse. Moreover, we discuss a calibration of the detectors and their front-end electronics using the dust accelerator in order to find a relation between impact parameters and pulse heights.

How to cite: Kononov, O., Pavlů, J., Nouzák, L., Šafránková, J., Němeček, Z., and Přech, L.: Dust impact detections by a set of Faraday cups in the lunar environments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3082, https://doi.org/10.5194/egusphere-egu2020-3082, 2020.

Dust grains impacting with high velocities the spacecraft body can be partly or totally evaporated and create clouds of charged particles. Presence of electrons and ions generated by such hypervelocity impacts can consequently influence the spacecraft potential and/or measurements of on-board scientific instruments. Electric field instruments are able to register signals generated by dust impacts as short pulses in the measured electric field. These signals can be used for detection of dust grains by the spacecraft without dedicated dust detectors. This dust detection method has been successfully used for data collected by many spacecraft as Voyager, Cassini, Wind, STEREO, MAVEN, and MMS. On the other hand, our understanding of this complex process comprising from dust grain evaporation, generation of charged particles, to impact cloud expansion and signal detection is still not complete.

We present a study of events related to dust impacts on the spacecraft body detected by electric field probes operating simultaneously in the monopole (probe-to-spacecraft potential measurement) and dipole (probe-to-probe potential measurement) configurations by the Earth-orbiting MMS spacecraft. The presented study is focused on events when expanding ions affect not only the potential of the spacecraft body but also one or more electric probes on the end of antenna booms. Expanding ions can influence electric probes located far from the spacecraft body only when the spacecraft is located in tenuous ambient plasma as inside of the Earth’s magnetosphere. This analysis can confirm if these events are really connected to dust impacts and gives us some information about ion expansion velocity, and improve our knowledge of dust impact process.

How to cite: Vaverka, J., Pavlů, J., Nouzák, L., Kočiščák, S., Šafránková, J., and Němeček, Z.: Ion cloud expansion after hypervelocity dust impacts detected by the MMS spacecraft , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2743, https://doi.org/10.5194/egusphere-egu2020-2743, 2020.

Electric field data obtained by the Langmuir Probe and Waves (LPW) instrument on board the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft are used to identify signals related to dust impacts on the spacecraft body and/or on the instrument probes. The analyzed waveforms snapshots are 62.5 ms long (4,096 points sampled at 65,536 Hz). An automatic procedure to identify short electric field pulses with signatures corresponding to those expected for the dust impacts has been developed and applied to available data in years 2014–2018, resulting in about 40,000 of events. Each of the identified pulses is characterized by several quantitative parameters (polarity, magnitude, relaxation time, magnitude of a possible pre-spike). The event occurrence and respective quantitative parameters of detected pulses are then analyzed as a function of local plasma conditions in the Martian ionosphere (electron density and temperature), the spacecraft location, and the spacecraft potential. The obtained results are compared with a simple scheme of the signal formation upon a dust impact.

How to cite: Ševčíková, K., Němec, F., Nouzák, L., Vaverka, J., and Andersson, L.: Identification and preliminary analysis of dust impacts on the MAVEN spacecraft, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2438, https://doi.org/10.5194/egusphere-egu2020-2438, 2020.

Dust particles represent an important fraction of the matter composing the interplanetary medium. At 1 A.U. dust mass density is comparable to the one of the solar wind. The large number and broad diversity of dust particles detected by the radio instrument on the STEREO satellites recommend this mission for a closer dust investigation. In situ dust measurements are based on the detection of the charges generated by dust impacts, recorded by the S/WAVES instrument near 1 A.U. since the beginning of the STEREO mission. We study the electric signals produced by these impacts, using the waveform sampler data produced by the TDS subsystem of the radio instrument, connected to three monopole antennas. For this study, we concentrate on macroscopic dust particles (~0.1 microns) whose impact generated nearly simultaneous pulses on the antennas. In particular, we present statistics of typical shapes and features of these signals based on the TDS electric potential time-series and compare the data to a theoretical model of how pulses are generated by charge collection.
These results will have implications on dust detection from Parker Solar Probe and Solar Orbiter missions.

How to cite: Rackovic Babic, K., Issautier, K., and Zaslavsky, A.: In situ dust measurements in the solar wind from S/WAVES TDS instrument on STEREO mission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8793, https://doi.org/10.5194/egusphere-egu2020-8793, 2020.

The NASA Double Asteroid Redirection Test (DART) mission will be the first test to check an asteroid deflection by a kinetic impactor. The target of DART mission is the secondary element of the (65803) Didymos binary asteroid system and the impact is expected in late September – early October, 2022. The DART S/C will carry a 6U cubesat called LICIACube (Light Italian Cubesat for Imaging of Asteroid), provided by the Italian Space Agency, with the aim to collect pictures of the impact’s effects. The impact of the 610 kg DART spacecraft at 6.58 km/s on the 163 m Didymos B will result in a change of the binary orbital period of about 10 minutes assuming momentum transfer efficiency β = 1. Values of β > 1 are expected because the produced ejecta carries momentum, primarily in the direction opposite the DART speed direction. The LICIACube mission profile consists in a flyby of Didymos system with closest approach about 3 minutes after the DART impact. LICIACube will be able to acquire the structure and evolution of the DART impact ejecta plume and will obtain high-resolution images and also in 3 colour of the surfaces of both bodies. The nominal mission foresees also imaging of the Dydymos B non-impact hemisphere. The contributions of LICIACube observations to the DART investigations are important for determination of the momentum transfer efficiency β, that is a crucial result of the planetary defence test. Moreover, captured images can enable scientific investigations about the main features of the asteroid system. 

In order to check the imaging capability and to optimize the fast scientific phase of LICIAcube, the LICIA team performed several simulations of pictures’ acquisition. In these simulations, considering the specifications of the 2 optical payloads and the foreseen mission design, we reconstructed synthetic images mainly of the plume. As the plume evolution remains the most important uncertainty, since it depends on a very high number of impacting phase parameters, we simulated imaging of different expected evolution behaviours, to obtain instrument operative parameters and to prepare the data analysis.  

How to cite: Corte, V., Mazzotta Epifani, E., Dotto, E., Amoroso, M., Pirrotta, S., and Cheng, A. and the LICIAcube TEAM: LICIACube observation capabilities of dust plume evolution after DART impact, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19159, https://doi.org/10.5194/egusphere-egu2020-19159, 2020.

The risk of asteroids impacting the earth is a common space security issue facing human beings. Since the ground-based monitoring network cannot cover the space area comprehensively, there are cases of celestial body out of monitoring. In response to this problem, this report studies the space-based platform's monitoring system, and calculates its performance for orbit determination and monitoring of small celestial bodies. For small celestial bodies that are not in the catalog, the initial orbit determination needs to be performed before the orbit improvement. In addition, this paper proposes a method based on Fibonacci search method to quickly predict the impact location of asteroids.

How to cite: yezhi, S.: Space-based platform asteroid orbit determination and collision warning, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12597, https://doi.org/10.5194/egusphere-egu2020-12597, 2020.

Synthetic tracking technique uses multiple short exposure images to observe moving objects to prevent the objects from streaking in an individual frame. It integrates frames in post-processing, where the tracking of telescope at any desired rate can be simulated by shifting frames accordingly. Such an approach avoids trailing loss, thus improves detection sensitivity, especially for fast moving objects. It also yields accurate astrometry for moving objects independent of rate of motion with precision comparable to stellar astrometry. Using the Gaia DR2 catalog, we are able to demonstrate 10 mas level near-Earth-object (NEO) astrometry with the synthetic tracking technique. Accurate NEO astrometry allows us to determine NEO orbit more precisely. We discuss applications such as cataloging newly discovered NEOs with less measurements and/or from observation time windows covering shorter orbit arcs, better predicting the chance for a potentially hazardous asteroid to impact the Earth, measuring non-gravitational acceleration to infer physical properties of minor planets, and optical navigation for future spacecraft carrying optical communication lasers.

How to cite: Zhai, C., Shao, M., Saini, N., Trahan, R., Choi, P., Nazli, K., Evans, N., and Owen, W.: Accurate Near-Earth-Object Astrometry using Synthetic Tracking and Applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12729, https://doi.org/10.5194/egusphere-egu2020-12729, 2020.