SB8

Introduction: Knowledge of the physical and surface properties of most NEAs lags far behind the current rate of their discoveries. Still, asteroid surfaces and internal structures are very diverse, and knowledge derived from a limited number of asteroids typically could not be safely extrapolated to a large number of objects. The situation calls for an alternative approach that permits estimating asteroids' properties for a much larger number of NEAs.

The Demystifying Near-Earth Asteroids (D-NEAs) is the Planetary Society STEP Grant 2021 project aiming to develop a novel method that directly characterises asteroids primarily from ground-based data. In particular, the project's objective is to develop a model to characterise surface thermal properties.

Methodology: The idea is based on the Yarkovsky effect, a non-gravitational phenomenon that causes objects to undergo orbital semi-major axis drift as a function of their size, orbit, and material properties. The effect joins together the asteroid's orbital dynamics, composition, and physical properties. Our idea to derive the surface thermal properties of near-Earth objects is built around these facts.

Theoretical models of the Yarkovsky effect allow predicting the semi-major axis drift, assuming a set of input parameters is available. On the other hand, astrometric observations and orbit determination procedures allow detecting the semi-major axis drift in motion of an asteroid. Therefore, at least one asteroid's property that determines the drift rate could be estimated by comparing the model’s predicted (da/dt) and measured (da/dt)_m magnitude of the effect, as given by Equation 1:

Especially critical are the thermal conductivity uncertainties that span a range of about four orders of magnitude (Delbo et al. 2015). It is also a key to proper estimation of the thermal inertia, which could be diagnostic of surface porosity and cohesion, and, therefore, for the possible presence of the regolith layer at the surfaces.

Results: The first results obtained by Fenucci et al. (2021) are encouraging but also intriguing at the same time. We found that a small super-fast rotator, near-Earth asteroid 2011 PT, should have low thermal inertia (Γ < 100 J m^-1 K^-1 s^-1/2) to maintain the high Yarkovsky drift detected from astrometry.

Future prospect: This exciting result opens the possibility for further studies. There are, however, several essential features that are not included in the preliminary model. To fully exploit the potential of our approach, it is necessary to extend the model by including, for instance, Yarkovsky correction for eccentric orbits, heterogeneity in object’s density, or variable thermal inertia along the orbit (Rozitis et al. 2018). The D-NEAs project will address these issues and develop a robust model which will apply to a much larger number of asteroids.

References

• Delbo, M., Mueller, M., Emery, J.P., Rozitis, B., Capria, M.T.: Asteroid Thermophysical Modeling. Asteroids IV, p.107-128, University of Arizona Press, Tucson, 2015.

• Fenucci, M., Novakovic, B., Vokrouhlicky, D., Weryk, R.J.: Low thermal conductivity of the super-fast rotator (499998) 2011 PT. Astronomy and Astrophysics, id 647, 2021.

• Rozitis, B., Green, S.F., MacLennan, E., Emery, J.P: Observing the variation of asteroid thermal inertia with heliocentric distance. MNRAS, 477, 1782, 2018.

How to cite: Novakovic, B., Fenucci, M., Marceta, D., and Pavela, D.: Demystifying Near-Earth Asteroids, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-159, https://doi.org/10.5194/epsc2022-159, 2022.

Introduction:

To understand the long-term history and age of a planetary surface, it is important to analyze the distribution of impact craters, including the case of fast-spinning asteroids. Two of such asteroids have recently been visited by space probes such as the Hayabusa2 and the OSIRIS-REx spacecraft that targeted the C-type and B-type asteroids (162173) Ryugu and (101955) Bennu, respectively. These NEAs have been found to share similar physical and morphological characteristics, including low bulk density, surface characterized by large blocks and boulders, and top-shape profiles [1, 2]. Moreover, on the surface of both small bodies, several geological features can be identified in detail, such as crater-like features, boulders, linear features, fossae, etc [e.g., 1, 3]. Many crater-like depressions can be identified over the surface strongly skewed towards low equatorial latitudes. This uneven global distribution suggests that different evolutionary and impact history took place at the equatorial ridge with respect to the rest of the body.

Such bodies likely aggregated gravitationally right after the catastrophic collision that originated them [4]. In addition, collisions in the main belt and lately the YORP effect may have contributed to modify their spin rate. For instance, they have been found to be currently slowly spinning up (Bennu) and down (Ryugu) by YORP [5, 6]. The past spinning history of such bodies is unknown, however they may have had spin rates fast enough to cause the detachment of boulders from their surface eventually falling back onto them. Under such conditions, the formation of currently observed crater-like depressions may not be necessarily related to impact events and may rather be the outcome of repeated boulder landing and taking off cycles.

Here, we focus on checking the potential correlation between the formation of depressions and crater-like features with the dynamical behaviour of boulders on Ryugu and Bennu like-asteroids. 

Methodology:

We use the global mosaic of images available for Ryugu and Bennu asteroids created by using data collected from OCAMS and ONCs cameras suites overlapped to shape models [2, 7] to identify and map the characteristic features which we are interested in.

To check our hypothesis on the origin of crater-like features, we developed a two-stage model research, based on: (1) dynamical study of lifted particles due to fast spin, and (2) modelling the movement of big boulders using a N-body Discrete Element Method (PKDGRAV. [8,9]). In the first stage, we analyze the dynamics of particles that can detach from the surface of Ryugu and Bennu at a time they were spinning fast enough so that apparent centrifugal acceleration is sufficient to overcome local gravity. We therefore integrate the equation of motion of sample particles in a non-inertial rotating reference frame [10]. Sample particles -representing blocks and boulders- are initially placed at the center of the triangular facets in the shape model of each asteroid [2, 7]. Their dynamical evolution in time is followed and their trajectory and behaviour is tracked. Particle detachment from the surface at the critical spin state, and the landing latitude on the asteroid surface is also analyzed. In the second stage, we use PKDGRAV to place boulders on the asteroid surface and follow their dynamical evolution at an increasing spin rate.

Summary:

Our model of boulder motion on asteroids Bennu and Ryugu under fast spin conditions shows the formation of depressions and crater-like features due to boulder detaching, landing and/or bouncing off their surface is possible. Also, final landing of boulders at high latitudes is found. This model suggests a potential explanation for the crater abundance observed around the equatorial region in Ryugu and Bennu. In near future, the DART (NASA, 2022) and Hera (ESA, 2026) space missions are scheduled to approach the NEA binary system (65803) Didymos. The primary of such system is also a top-shape fast-spinning asteroid for which we may expect similar features as those studied in Bennu and Ryugu.

Acknowledgements:

LMP, NET and ACB acknowledge funding from the NEO-MAPP project (H2020-EU-2-1-6/870377). LMP acknowledges support from the Margarita Salas UCM postdoctoral grants funded by the Spanish Ministry of Universities with European Union funds - NextGenerationEU.

References:

[1] Lauretta, D. S., et al. (2019). Nature 568, 55–60. [2] Watanabe, S., et al. (2019). Science 364, 268–272. [3] Sugita, S., et al. (2019). Science, 364(6437), 252. [4] Campo Bagatin, A., et al. (2018). Icarus 302, 343–359. [5] Kanamaru, M., et al. (2021). JGR: Planets 126. [6] Hergenrother, C.W. et al. (2019). Nat. Commun. 10, 1291. [7] Barnouin, O.S. et al. (2019). Nature Geoscience 12, 247-252. [8] Richardson, D. C. (2000). Icarus, 143, 45. [9] Schwartz, S. (2012). Granular Matter 14, 263. [10] Trógolo N., et al., (2021). EPSC2021-676.

How to cite: Parro, L. M., Trógolo, N., and Campo Bagatin, A.: Non-impact origin of crater-like features on top-shape near-Earth asteroids, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-726, https://doi.org/10.5194/epsc2022-726, 2022.

Thermal properties of C-type asteroid Ryugu have been investigated through remote sensing using the Thermal Infrared Imager (TIR), on the surface using the radiometer MARA on MASCOT lander, and the analysis of return sample. The global average and the local distribution of thermal inertia were mapped by TIR observations, with the lower thermal inertia than that of typical chabonaceous chondrite meteorites. surface boulders and their surroudings have almost the same thermal inertia of 200 to 400 J m^-2 kg^-1 s-^0.5 (tiu, hereafter), indicating that most of boulders are relatively porous and not completely consolidated and the surroundings are covered with boulders and rocks (not sandy regolith) [Okada et al., 2020), which was confirmed during the descent operations for sampling. Boulders have a variety of thermal inertia, with more than 80 % of boulders with 200 to 400 tiu, while some portions have very low or very high thermal inertias. They are identified as Hot Spots and Cold Spors, because they are exceptionally hot or cold compared with their surroundings (Sakatani et al., 2021). The surface experiment by MARA indicated the simiar thermal inertia for a single boulder (Grott et al., 2019), so that the rough boulders should be the representative material on the asdteroid. The thermal properties of return sample do not seem to be the same, although they are not always representative regaring the physical properties since fragile sample might have been broken during the impact sampling process, during the severe shock and shaking in the return capsule when entry to the Earth surface. The return sample dseem to be more consolidated and flatter surface feature, instead of fragile and porous features. The return sample are more like CI chondrite meteorites with darker, more porous and fragile characteristics (Tada et al., 2021).  The difference of thermal inertia between la arger scale (> 1mm)  and a small scale (<0.1ｍｍ）might attribute to the existing cracks and pores inside of boulder materials. A formation scenario of Ryugu will be shown to explain the history of Ryugu formation or planetary formation. 

How to cite: Okada, T., Tanaka, S., Sakatani, N., Shimaki, Y., Arai, T., Senshu, H., Demura, H., Sekiguchi, T., Kouyama, T., Kanamaru, M., and Ishizaki, T.: Thermal properties of asteroid Ryugu from global, local, and micro-scale and its formation scenario, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1187, https://doi.org/10.5194/epsc2022-1187, 2022.

• ¹Instituto Universitario de Física Aplicada a las Ciencias y a las Tecnologías, Universidad de Alicante. Alicante, Spain (nair.trogolo@ua.es)
• ²Observtorio Astronómico de Córdoba, Universidad Nacional de Córdoba. Córdoba, Argentina.
• ³Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante. Alicante, Spain.
• ⁴Instituto de Astrofísica de Andalucía, CSIC. Granada, Spain.

1. Introduction

(65803) Didymos is a binary near-Earth asteroid (NEA) system and is the target of the  upcoming DART (NASA) and Hera (ESA) space missions. Physical parameters of the system have been determined through radar and optical observations. A shape model for the primary, Didymos, is available, showing a top−shape appearance (see Fig. 1). Didymos is a 780 m asteroid with a satellite, Dimorphos, of 160 m in diameter [1]. Also, the main body is estimated to be an S-type asteroid with a density of 2170 ± 350 kg/m³ [2] and a fast rotation period of 2.2600 ± 0.001 h [3]. Given its spectral type, and considering that its meteorite analogs are ordinary chondrites, with a typical density greater than 3 000 kg/m³, Didymos is probably a gravitational aggregate (rubble-pile) [4]. In the equatorial region of such asteroids, the apparent non-inertial centrifugal force acting on surface particles can overcome the gravitational attraction of the asteroid, resulting in a local net outward acceleration, allowing them to leave the surface at zero speed and dynamically evolve in the system [5][6]. 

In this work we analyze conditions for regolith ejection and following dynamical evolution. In addition, we provide an estimation of the amount of material present in the system environment. The model predictions may be tested with data from the DART and Hera missions, making Didymos a particularly interesting system to study.

Figure 1: Surface gravity in the polyhedral shape model used for Didymos made by 1996 faces and 1000 vertices.

2. Methodology

In order to study the detachment process of particles on asteroid Didymos, we developed a numerical code that integrates the equation of motion of a test particle initially at rest at any position on the surface. We have taken into account the central gravitational field generated by the primary, both gravitational perturbation of the secondary and the Sun, and solar radiation pressure (SRP). Furthermore, since that is a rotating, non--inertial  frame, it is necessary to consider the centripetal and coriolis forces. Initially, sample particles are located at the center of the triangular facets of the asteroid shape model, made by 1996 faces and 1,000 vertices. At each integration step, the detachment condition is studied (that is, the sum of the mentioned forces must be directed outwards). A 3D grid is set outside the asteroid  in latitude, longitude and radial distance. Such a grid identifies 3D cells, where cumulative particle mass density is calculated. Based on particle trajectories, we defined four possible final states: ES1) particles that take off from the surface and land again, ES2) particles that remain in orbit, ES3) particles that are accreted into the secondary, and ES4) particles that escape from the system.

3. Numerical simulations and results

The sample particle differential size distribution follows a power law with a -3.5 slope and particles in the range [5 μm-2 mm] are considered. We analyzed the behaviour of particles during 30 days about  perihelion and aphelion epoch and during a complete heliocentric orbit, equivalent to 2.11 Earth years. We find that orbiting particle mass density at the end of integration time (ES2) depends on the position of the asteroid in its orbit around the Sun, especially at small particle size. The system has a high eccentricity (e=0.38), leading to a 4/9 relationship between total mass around perihelion vs. aphelion (See Fig. 2). This is due to smaller particles being strongly influenced by the SRP during passage at perihelion. That circumstance leads them to either leave the system (ES4) or, after taking off, return quickly to the surface (ES1). In general, about 96% of particles that take off land back onto the surface of Didymos, sometimes even at relatively high latitudes (See Fig. 3). Those landing near the equatorial plane can be ejected again, triggering repeated regolith landing and taking off cycles.

 

Fig. 2. Orbiting mass density versus radial distance after 30 days near perihelion and aphelion epoch. R = 0 m corresponds to the Didymos center, R ∼ 430 m to the surface.	Fig. 3. Projection of particle landing positions on the Didymos surface in the Z-Y plane. Each light blue dot corresponds to a particle, the size of the dot does not represent the real size. This is the simulation result over a complete orbit around the Sun (2.1 years).

 

A crucial parameter in the problem we are analyzing is Didymos bulk density, which is currently known with a wide margin of uncertainty. We studied the relationship between the total mass in orbit after 30 days of evolution and the density of the asteroid, varying both the mass of Didymos and its volume. A lack of particles in the system environment is found only in 6% of simulation runs. This shows an optimistic scenario about observing particles in orbit around the asteroid, which perhaps can be estimated by measurement carried out by the Hera space mission.

References:

[1] Benner, L. A. et al. (2010) Bull. Am. Astron. Soc. 42, 1056.

[2] Fang J., Margot J.L., 2012, AJ, 143, 24

[3] Pravec P., et al., 2006, Icarus, 181, 63

[4] Campo Bagatin, A. et al. (2018) Icarus 302, 343–359. 

[5] Campo Bagatin, A. (2013) LPSC. 

[6] Yu, Y., et al. (2019) MNRAS 484, 1057–1071.

How to cite: Trógolo, N., Campo Bagatin, A., Moreno, F., and Pérez Molina, M.: Lifted particles from (65803) Didymos surface due to its fast rotation, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1044, https://doi.org/10.5194/epsc2022-1044, 2022.

The km-scale near-Earth object (1566) Icarus has an extremely eccentric orbit with a perihelion of q = 0.187 au and is classified as a potentially hazardous asteroid (PHA). It has been suspected to be the larger component of an asteroid pair, with the smaller object 2007 MK₆, that is dynamically adjacent to the Taurid-Perseid meteor shower (Ohsutka et al., 2007; Kasuga & Jewitt, 2019). The low radar albedo of ~2% and photometric behavior at high phase angles together suggest a high-porosity surface with a  high macroscopic roughness (Greenberg, et al. 2017; Ishiguro, et al., 2017). Delay-Doppler and visible lightcurve observations indicate a retrograde spin with a rapid rotation period of ~2.26 hr (Greenberg, et al. 2017; Warner et al., 2009).

Combining visible spectrophotometry from the 24-Color Asteroid Survey (Chapman et al., 2020) and MITHNEOS near-infrared reflectance spectra (Binzel et al., 2019), we classify Icarus (Figure 1) as a slightly space weathered LL chondrite via a band parameter analysis routine (MacLennan, et al. in prep.). Using archived lightcurve observations of Icarus collected in 1968 and 2015 (Lagerkvist et al., 1993; Warner et al., 2009), and informed by spin axis constraints, we implement a Bayesian lightcurve inversion approach (Muinonen, et al. 2020) to construct a convex shape model of Icarus (Figure 2).

Figure 1. Combined visible spectrophotometry and near-infrared reflectance spectra of Icarus and reflectance spectrum of the LL4 ordinary chondrite Hamlet from the RELAB database.

Figure 2. Convex shape model of Icarus from inversion of lightcurve photometry.

We incorporate thermal infrared data from the Spitzer Space Telescope (IRAC photometry and IRS spectra) and the NEOWISE survey in order to characterize Icarus’s thermophysical properties. We estimate the effective diameter and thermal inertia to be 1.4 ± 0.2 km and 60 ± 40 J K^-1 m^-2 s^-1/2, respectively, with moderate surface roughness. The relatively low thermal inertia is consistent with a high porosity surface and/or a fine-grained lunar like surface. The latter interpretation is in contradiction to the polarization-phase relationship that suggests larger regolith grains (Ishiguro et al., 2007). We attempt to reconcile these different measurement results in our presentation.

The physical characteristics of this extreme object are important for informing various resurfacing processes that have been proposed to be relevant for rapidly rotating objects, near-Sun asteroids, and spectrally-fresh Q-type asteroids (Graves et al., 2018, 2019). We thus consider our results in the context of these resurfacing processes.

References:

Binzel, R.P., et al. (2019) “Compositional distributions and evolutionary processes for the near-Earth object population: Results from the MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS)” Icarus, 324, 41–76.

Chapman, C.R., Gaffey, M., and McFadden, L. (2020) 24-color Asteroid Survey V1.0. urn:nasa:pds:gbo.ast.24-color-survey::1.0. NASA Planetary Data System.

Greenberg, A., et al. (2017) “Asteroid 1566 Icarus’s Size, Shape, Orbit, and Yarkovsky Drift from Radar Observations” AJ, 153:108.

Graves, et al. (2018) “Resurfacing asteroids from YORP spin-up and failure”, Icarus, 304 (2018) 162–171.

Graves, et al. (2019) “Resurfacing asteroids from thermally induced surface degradation”, Icarus, 322 (2019) 1–12.

Ishiguro, M., et al. (2017) “Polarimetric Study of Near-Earth Asteroid (1566) Icarus”, AJ, 154:180.

Kasuga, T. & Jewitt, D. (2019) “Asteroid-Meteorite Complexes”, In Meteoroids: Sources of Meteors on Earth and Beyond (Ed. G. Ryabova, D. Asher, & M. Campbell-Brown).

Lagerkvist, C.-I. and Magnusson, P., Eds., (2011) Asteroid Photometric Catalog V1.1. EAR-A-3-DDR-APC-LIGHTCURVE-V1.1. NASA Planetary Data System.

MacLennan, E.M., et al. (in prep) “Empirical characterization of space weathering on ordinary chondrite-like asteroids”.

Muinonen , J. Torppa , X.-B. Wang , A. Cellino , and A. Penttilä (2020) “Asteroid lightcurve inversion with Bayesian inference”, A&A, 642, A138.

Ohtsuka, K. “Apollo asteroids 1566 Icarus and 2007 MK6: Icarus Family Members?” AJ, 668: L71–L74.

Warner, B.D., Harris, A.W., Pravec, P. (2009). “The Asteroid Lightcurve Database”, Icarus 202, 134-146.

How to cite: MacLennan, E., Muinonen, K., Uvarova, E., Granvik, M., Wilawer, E., Oszkiewicz, D., and Emery, J.: Shape, Compositional, and Thermophysical Properties of (1566) Icarus, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-893, https://doi.org/10.5194/epsc2022-893, 2022.

We only have indirect information on the internal material properties and structure of small icy bodies in the Solar System, coming from the analysis of meteorites and observations of near-Earth comets. Examination of comets can provide information on the composition of trans-Neptunian objects as they originate primarily in the Kuiper Belt and the Oort Cloud. 

In order to infer the internal structure we need to know the dominant heat sources in the small icy bodies to determine the extent of heat production at each stage of their evolution, and their internal transformations they may have come through. The dominant internal heat sources of small icy bodies during their evolution are:

• accretion heat from the formation process;
• radioactive heating in the silicate component due to the decay of the short-lived radiogenic isotope ²⁶Al (in our Solar system);
• exothermic chemical reactions such as serpentinization;
• differentiation energy released when the nucleus is formed;
• tidal heating by large moons or in binary systems.

In this work, we focused on the early evolution, and our heat evolution model is based on the serpentinization reaction (Farkas-Takács et al. 2022). It takes into account the accretion energy as the initial temperature and the radiogenic decay of ²⁶Al as the internal heat source during the process.

The serpentinization processes require the existence of Mg-pyroxenes (enstatite, MgSiO₃), Mg-rich olivine (forsterite, Mg₂SiO₄), and liquid water in the interior of the planetesimal. The following reaction shows the stoichiometric equation of the formation of serpentinite (Mg₃Si₂O₅(OH)₄):

Mg₂SiO₄ + MgSiO₃ + 2H₂O -> Mg₃Si₂O₅(OH)₄

We examined what changes occur when the initial temperature distribution is inhomogeneous and the surface is warmer (Fig. 1) compared to the homogeneous initial temperature distribution. The serpentinization process is faster in the core independently of the initial conditions due to the higher lithospheric pressure.

Figure 1: Thermal evolution of a planetesimal of R=240km with an outward temperature gradient at the start, represented by curves with 'normal' colors.  The 'pale' colors correspond to the same object/layer, but assuming a homogeneous temperature distribution at the start of the calculations.

We studied another case when the initial temperature distribution was inhomogeneous and the formation occurred in two steps (Fig. 2). In this test, an object formed with a radius of 160km, and τ_f=10,000yr later the formation was completed and the object reached a final radius of 320km. During the time between the two formation/accretion events, the object may have warmed up both from radiogenic decay and serpentinization. We assumed the first formation even t_s=0, the maximum ²⁶Al heat production date, and three ²⁶Al half-life later. The final object is built on the warm core in the second accretion event.

Figure 2: The temperature evolution obtained in models with a two-phase formation scenario. The first formation/accretion event is followed by another event in τ_f=10,000 yr, and the first formation event occurs early, at the maximum of the radiogenic heat production of ²⁶Al (t_s=0, left side) and on the right the first formation event occurs three ²⁶Al half-life later (t_s=3).

We also examined what the critical temperature is which is needed to effectively start the serpentinization reaction with 10 different olivine-to-water ratios. The test object had 400 km radius and the process started when the radiogenic heat production of ²⁶Al was at its maximum (t_s=0). The critical temperature is strongly dependent on the pressure as expected (Fig. 3 left panel), and this dependence can also be seen in serpentinization time (Fig. 3 right panel). The reaction time at a given pressure is also strongly dependent on the composition.

Figure 3: The critical temperature (left panel) and the serpentinzation time (right panel) as a function of the pressure in case of 10 different olivine to water ratio (the colors show the different compositions).

In the case of a high olivine-to-water ratio, the reaction is fast because the water runs out quickly, thus it can achieve only a little temperature increase during the process (Fig. 4). We would expect the fastest reaction with the highest temperature rise at the stoichiometric rate but since a significant part of the process takes place below the freezing point of water, which has yet to melt, and the amount of interfacial liquid water involved in the reaction depends on the amount of rock and the temperature.

Figure 4: Temperature increase (ΔT) during the serpentinization process as a function of the olivine to water ratio under the same pressure.

Our results show that the serpentinization process can proceed under a wide range of initial conditions in the planetesimals in the early Solar System and can efficiently reform the interior of these bodies.

How to cite: Farkas-Takacs, A. and Kiss, C.: Dependence of serpentinization efficiency on the initial conditions of planetesimal formation in the early Solar System, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-977, https://doi.org/10.5194/epsc2022-977, 2022.

Accretion processes in protoplanetary disks produce a diversity of small bodies. In our solar system, such bodies played a crucial role in potentially multiple reshuffling events and in both early and late accretion of planets. Application of thermo-chronometers to meteorites provides precise dating of the formation or cooling ages of various mineralogical components. Nucleosynthetic isotopic anomalies that indicate a dichotomy between non-carbonaceous (NC) and carbonaceous (C) meteorites and precise parent body (PB) chronology can be combined with planetesimal thermal evolution models to constrain the timescale of accretion and dynamical processes in the early solar system.

Achondrite parent bodies are considered to have accreted early and mostly in the NC region. By contrast, late accretion in the C region produced mostly undifferentiated objects, such as the parent body of CR1-3 chondrites that could have formed as late as 4 Ma after solar system formation (Schrader et al., 2011). However, presence of more evolved CR-like meteorites suggests also an earlier accretion timing. Observations of C-type NEA and laboratory investigations of CC meteorites indicate a high porosity of C-type asteroids. The boulder microporosity derived for Ryugu (Grott et al., 2019) is substantially higher than for water-rich carbonaceous chondrites, such as CI and CM meteorites, and could indicate distinct thermal evolution paths. Aqueous alteration of Ryugu’s and CI and CM samples suggests accretion times not dramatically different from that of the aqueously altered CR parent body.

In a previous study, we constrained size and accretion time of Ryugu’s parent body using a numerical model for the evolution of the temperature and porosity (Neumann et al., 2021). These calculations indicate a size of only a few km in radius and an early accretion within ≲2-3 Ma after CAIs. By contrast, calculated properties for CI and CM parent bodies obtained by fitting carbonate formation ages indicate radii of ≈20-25 km and accretion times of ≈3.75 Ma after CAIs. In the present study, we fitted thermo-chronological data available for the C chondrite Flensburg and for CR-related meteorites (CR1-3, NWA011, NWA 6704, and Tafassites, see Ma et al., 2021) that range from altered chondrites to basaltic achondrites to constrain the accretion times of their respective parent bodies. We present modeling evidence for a temporally distributed accretion of parent bodies of CR-like meteorite groups that originate from a C reservoir and range from aqueously altered chondrites to highly equilibrated chondrites and partially differentiated primitive achondrites. The parent body formation times derived range from <1 Ma to ≈4 Ma after solar system formation, with ≈3.7 Ma, ≈1.5-2.75 Ma, ≲0.6 Ma, and ≲0.7 Ma for CR1-3, Flensburg, NWA 6704, and NWA 011, respectively. This implies that accretion processes in the C reservoir started as early as in the NC reservoir and produced differentiated parent bodies with carbonaceous compositions in addition to undifferentiated C chondrite parent bodies. The accretion times correlate inversely with the degree of the meteorites' alteration, metamorphism, or differentiation. The accretion times for the CI/CM, Ryugu, and Tafassites parent bodies of ≈3.75 Ma, ≈1-3 Ma, and ≈1.1 Ma, respectively (Ma et al., 2022, Neumann et al., 2021), fit well into this correlation in agreement with the thermal and alteration conditions suggested by the meteorites (Fig. 1).

Figure 1: Parent body accretion times (colored patches) and meteorite metamorphic ages (data points) for the C reservoir modeled incl. Tafassites, Ryugu, and CI/CM PB (Ma et al., 2021, Neumann et al., 2021). Younger Mn-Cr carbonate ages (circles) of CR1-3 (blue) and CI/CM (yellow) than for Flensburg (grey) result in moderately younger accretion age for the CR1-3 and CI/CM PBs. NWA 6704 (cyan) and NWA 011 (green) have older Pb-Pb whole-rock ages (squares) than Tafassites (light blue), resulting in earlier accretion than the Tafassite PB. The NWA 011 and NWA 6704 Al-Mg (triangles) and Mn-Cr (circles) data support an early PB formation. While Tafassites also include a very late, i.e., young, phosphate Pb-Pb age, their older iron-silicate Hf-W (light blue triangle) and Mn-Cr ages cause a shift to an intermediate PB formation time between NWA 011 and NWA 6704 on one hand, and Flensburg, CR1-3, and CI/CM PBs on the other. The youngest Pb-Pb age has its major effect on the large Tafassites PB size. Younger CR1-3 chondrule formation age (blue diamond) supports the PB accretion at ≈3.7 Ma. All accretion times correlate inversely with the meteorite petrologic type and the degree of metamorphism or melting.

Grott M. et al. (2019) Nature Astronomy, 3, 971-976.

Ma N. et al. (2021) Goldschmidt 2021, https://doi.org/10.7185/gold2021.3852.

Neumann W. et al. (2021) Icarus, 358, 114166.

Schrader D. L. et al. (2011) GCA, 75, 308-325.

How to cite: Neumann, W., Trieloff, M., Ma, N., and Bouvier, A.: Temporally distributed accretion of chondritic and differentiated meteorite parent bodies in the C reservoir of the early solar system, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-176, https://doi.org/10.5194/epsc2022-176, 2022.

The project “Deciphering compositional processes in inner airless bodies of our Solar System”, selected in the framework of the ISSI-Call for proposal 2019, set out  to answer two scientific questions. First, why do chemical changes induced by space weathering in the surface regolith appear to be different on Vesta, Mercury and the Moon, and what is the role and importance of mineralogy and composition? Second, bearing in mind that olivine has been identified on the Moon and on the large asteroid Vesta, whereas it has not yet been found on Mercury: what are the implications for all of these three planetary bodies?

Vesta is the parent body of the howardite, eucrite and diogenite (HED) clan of meteorites [1]. Its surface is characterized by the presence of orthopyroxenes [2], and several geological features such as impact craters, grooves, troughs, and some tholi [3]. VIR revealed that all the Vesta spectra show the typical pyroxene bands centered at 0.9 µm and 1.9 µm [4], and allowed for determining the distribution of the HED lithologies across its surface. Like Vesta, the Moon spectra also display pyroxene spectral signatures, but suggest a composition more compatible with low-Ca pyroxenes rather than orthopyroxenes, with shallower band depths and surfaces characterized by “redder” spectral slopes (reflectance increasing with the wavelengths) [5]. Conversely, unlike Vesta and the Moon, Mercury spectra appear featureless and with a steep positive spectral slope, significantly different from the other two bodies [6].

For the spectral and geological analysis of Vesta, we processed data acquired by two instruments onboard the Dawn spacecraft: the Visible and Infrared mapping spectrometer (VIR) [7] and the Framing Camera (FC) [7]. All these datasets are publicly available on the Planetary Data System [8]. We calibrated and removed the artifacts, such as in [9] and [10], then we applied the Akimov photometric correction [11] and a log-linear phase function correction to obtain the reflectance spectra. For the Moon, we used data obtained by Chandrayaan-1/Moon Mineralogy Mapper (M3) and available at [12], then we calibrated and photometrically corrected the data following standard procedures [13, 14]. Regarding Mercury, we used the MESSENGER/Mercury Dual Imaging System (MDIS), publicly available high level products [15], and the MESSENGER/Mercury Atmospheric and Surface Composition Spectrometer instrument - Visible and InfraRed Spectrometer data [16].

To simulate space weathering effects on Vesta’s surface, we performed several irradiation experiments on HED samples at the Institut d'Astrophysique Spatiale (Orsay, France). The HED analogues are provided by the Museo di Storia Naturale dell’Università degli Studi di Firenze (Florence, Italy) and Museo di Scienze Planetarie di Prato (Prato, Italy). In particular, we have 4 HED samples, the olivine-diogenite NWA6232, and the eucrites NWA4968, NWA7234, and NWA6909 (Figs. 1 and 2). The samples are chips and powders with a grain size up to 75 µm to simulate Vesta regolith. The HEDs were put in the INGMAR vacuum chamber and bombarded with He+ atoms with a 40 keV energy, to emulate space weathering conditions.

Space weathering effects are linked to several factors, such as impacts (shock, vaporization, fragmentation, heating, melting, and ejecta formation), radiation damage, and sputtering (due to cosmic rays or solar wind), diurnal thermal cycling, and ion implantation [17, 18]. These phenomena cause the formation of nanophase iron particles (npFe0) in both the agglutinates and in the accreted rims on individual grains [17, 18], inducing spectral reddening and the reduction of band depths [18]. On the Moon, all these effects are evident in the spectra. Mercury has featureless spectra with steep, positive spectral slopes, varying with the terrain type, while on Vesta the band depth reduction is mainly due to the presence of opaque mineralogical phases, and the redder surfaces are observed in the so-called “orange material” units, corresponding to the Oppia and Octavia crater regions. The application of multivariate statistical methods to the Vesta global spectral maps, shows no evidence of diffuse olivine regions, in agreement with previous results [19, 20, 21]. A detailed analysis of  Vesta, the Moon and Mercury is the key for understanding how the space weathering processes influence planetary bodies located in different regions of the Solar System, while the olivine distribution has deep implications for their origin and evolution.

Figure 1: Close up of the HED analogues considered for our study.

Figure 2: Reflectance spectra of the HED samples considered for this project.

Acknowledgements: This work is supported by the International Space Science Institute (ISSI) - Bern (Switzerland), project n°485, “Deciphering compositional processes in inner airless bodies of our Solar System” selected in the framework of the ISSI-call for proposal 2019.

References: [1] Feierberg, M.A., Drake, M.J., 1980, Science 209. [2] McCord, T. B., et al., 1970, Science 168.  [3] Special Issue: The Geology of Vesta, Icarus 244. [4] De Sanctis et al., 2012, Science. [5] Sivakumar, V., 2017. Geoscience Frontiers 8. [6] Izenberg, N., et al., 2014, Icarus 228. [7] Sierks, M. et al., 2011, Space Sci. Rev. 163. [8] De Sanctis et al., 2011, Space Sci. Rev. 163. [9] https://pds-smallbodies.astro.umd.edu/data_sb/target_asteroids.shtml#4_Vesta. [10] Carrozzo, F. G., et al., 2016, Rev. of Sci. Instr. 87. [11] Rousseau, B. et al., 2020, Rev. of Sci. Instr. 91. [12] Schröder, S. E., et al., 2013, Planetary and Space Science 85. [13] https://ode.rsl.wustl.edu/moon/. [14] https://pds-imaging.jpl.nasa.gov/documentation/Isaacson_M3_Workshop_Final.pdf. [21] Besse, S. et al., 2013, Icarus, 222. [15] https://messenger.jhuapl.edu/Explore/Images.html#global-mosaics. [16] https://pds-geosciences.wustl.edu/missions/messenger/mascs.htm. [17] S. Noble et al., 2005, MAPS, [18] C.M. Pieters and S.K. Noble, 2016. JGR. [19] Ammannito, E., et al., 2013, Nature, [20] Ruesch, O., et al., 2014, JGR 119, [21] Palomba, E. et al., 2015, Icarus 258.

How to cite: Zambon, F., Brunetto, R., Combe, J.-P., Klima, R., Rubino, S., Stephan, K., Tosi, F., Besse, S., Barraud, O., Carli, C., Donaldson-Hanna, K., Krohn, K., Nava, J., Pratesi, G., and Rothery, D.: New updates from ISSI project n° 485, Deciphering compositional processes in inner airless bodies of our Solar System, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-666, https://doi.org/10.5194/epsc2022-666, 2022.

Introduction: Linking a meteorite type to a specific parent asteroid allows us to gain insight into the composition of the latter as well as the time, and indirectly the heliocentric distance of its formation. Up to now there have been established solid links between the HEDs and the inner main belt asteroid family of (4) Vesta [1] as well as between the ordinary chondrites and asteroids belonging to the so-called spectroscopic S-complex [2]. Here we report on our search for the enstatite chondrites parent body. We base our analysis on two facts: that (i) inner main belt asteroid collisional families are the most favoured to deliver meteorites to Earth, and (ii) enstatite chondrites (divided in EH and EL groups) have reflectance spectra that are within the broad asteroid spectroscopic X-complex [3]. The newly discovered asteroid families of Athor and Zita [4] are the only two families of the inner main belt that belong to the spectroscopic X-complex and thus are promising candidates. 

Methods and Results: In order to investigate the potential link between the enstatite chondrite meteorites and the aforementioned X-complex asteroid families, we performed near-infrared observations of a statistically significant number of members of Athor and Zita. These were combined with the visible data from the literature and finally each asteroid spectrum was classified using the most common asteroid spectral taxonomy. We showed that the Athor and Zita families are spectroscopically distinct from each other and homogenous among their respective members. Moreover, both families have distinct geometric albedo values, with Athor family being brighter. Focusing on the Athor family, we performed curve matching and absolute reflectance comparison with all the available laboratory meteorite spectra in NASA Reflectance Experiment Laboratory and Planetary Spectrophotometer Facility databases. We will report on our matching and provide a number of further evidence that inner main belt families could indeed deliver enstatite chondrites to Earth. 

Acknowledgments: We acknowledge support from the ANR ORIGINS (ANR-18-CE31-13-0014). CA was supported by the project “Investissements d’Avenir” UCA-JEDI (ANR-15-IDEX-01) and the European Space Agency, AM acknowledges support from the ERC advanced grant HolyEarth N. 101019380. KJW acknowledges support from the Project ESPRESSO, a NASA SSERVI program at SwRI. This work is based on data provided by the Minor Planet Physical Properties Catalogue (MP3C, mp3c.oca.eu) of the Observatoire de la Côte d'Azur. This research utilises spectra acquired at the NASA RELAB facility at Brown University and at Planetary Spectrophotometer Facility (PSF) at University of Winnipeg.

References: 

[1] Russell C.T. et al. 2012, Science 336, 6082, 684.

[2] Reddy V. et al. 2015, Asteroids IV, University of Arizona Press, Tucson, 895, 43-63

[3] Vernazza P. et al. 2009. Icarus 202, 2, 477-486.

[4] Delbo M. et al. 2019. Astronomy & Astrophysics 624, A69.

How to cite: Avdellidou, C., Delbo, M., Morbidelli, A., Walsh, K., Munaibari, E., Bourdelle de Micas, J., Devogele, M., Fornasier, S., Gounelle, M., and van Belle, G.: On the discovery of the main belt source of the enstatite chondrites., Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-422, https://doi.org/10.5194/epsc2022-422, 2022.

Triton, the largest satellite of Neptune, represents a unique body in our Solar System. One of the few satellites in Solar System with ongoing geological activity, Triton,  which likely originated in the Kuiper’s Belt [1], underwent a troubling evolution, passing through Neptune’s capture [2], subsequent prolonged orbit circularization, which was followed by an enhanced thermal heating and internal differentiation. The predicted differentiated interior includes an outer ice shell, a possible internal ocean, a rocky deep interior, and a putative metallic core [3].

We model the mineral assemblages of the deep interior of Triton, considering a chondritic-like bulk composition. We describe three different evolutionary scenarios and their related mineral assemblages: anhydrous, completely hydrated, and dehydrated. Finally, we show that further investigations of Triton’s gravity field may provide new insights into the present mineral assemblage of its deep interior.

Methods

We used Perple_X software [4] to model three mineral assemblages for Triton’s deep interior at thermodynamical equilibrium, as a function of pressure (P) and temperature (T). We choose as a precursor material a chondritic bulk composition (CM, Mighei group), following a largely adopted approach in literature [5].

Discussion and conclusions

Our modelling provides three distinct mineral assemblages for Triton’s deep interior. Figure 1 shows the anhydrous mineral assemblage, which is dominated by common mantle-forming silicates (olivine, pyroxenes, and accessory phases). Figure 2 shows the hydrated mineral assemblage, formed by completely hydrated silicates (antigorite, amphiboles, chlorite, talc) which results from the water-alteration of rocks, as frequently revealed by chondritic samples [6].

Finally, we describe a dehydrated scenario (Figure 2, orange shaded area), which occurs when the hydration of a silicate shell, composed of amphiboles, olivine, pyroxenes, and accessory phases has been followed by a thermal event.

Therefore, we suggest an internal layering of the rocky core of Triton, which may imply a density-dependent distribution of minerals with increasing lithostatic pressure, with relevant implications for the global internal structure of Triton and its geological processes. The measurement of the degree two of the gravity field would constrain the present mineral assemblages of the deep interior of Triton to a higher degree of certainty.

Acknowledgments

G.M.  and C.C. acknowledge support from the Italian Space Agency (2020-13-HH.0).

References: [1] McKinnon, W. B. (1984). Nature, 311(5984), 355-358. [2] Agnor, C. B., & Hamilton, D. P. (2006). Nature, 441(7090), 192-194. [3] McKinnon, W. B. and Kirk R.L. (2014), Chapter 40, Triton, Encyclopedia of the solar system, Third Edition, Elsevier, 861-881.  [4] Connolly, J.A.D.(2005). Earth Planet Sci Lett, 236.1-2.524-541. [5] Néri, A., et al., (2020). Earth Planet Sci Lett, 530, 115920. [6]  Brearley, A. J. (2006). Meteorites and the early solar system II, 943, 587-624.

How to cite: Cioria, C. and Mitri, G.: Model of the mineralogy of the deep interior of Triton, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-492, https://doi.org/10.5194/epsc2022-492, 2022.

Internal structure models of dwarf planets and giant planets’ moons previously assumed essentially Earth-like silicate-metal cores surrounded by ice. Inner density models of the rocky cores of differentiated Ganymede and Titan, the largest icy moons in the solar system indicate the presence of a low-density component in addition to silicates and metal sulfide. Carbonaceous matter akin to coal formed from abundant organic matter in the outer solar system is a likely low-density component. Progressive gas release from coal may sustain up to present-day the replenishment of ice-oceanic layers in organics and volatiles. This accounts for widespread observation of nitrogen as well as light hydrocarbons to complex organic molecules at the surface, in the atmospheres, or in plumes emanating from moons and dwarf planets. Analysis of available density of rocky cores of other icy moons and dwarf planets also suggests the presence of a low-density carbonaceous component. We tested this hypothesis and found that rocky core densities in dwarf planets and icy moons are consistent with a mixture of chondritic silicate-sulfide rocks and a rock-free precursor composed of ices and carbonaceous matter in near-solar proportions. Thermal models taking into account the presence of carbonaceous matter is performed to evaluate its effects on the present-day structure of icy moons and dwarf planets.

How to cite: Reynard, B. and Sotin, C.: Carbon-rich icy moons and dwarf planets, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-11, https://doi.org/10.5194/epsc2022-11, 2022.

Context – Cybele asteroids constitute an appealing reservoir of primitive material genetically linked to the outer Solar system. The physical properties (size, shape) of the largest members can be directly measured with high-angular resolution imagers mounted on large (8-m class) telescopes.

Aim – We took advantage of the bright apparition of the most iconic member of the Cybele population, (65) Cybele, in July and August 2021 to acquire high angular resolution images and optical light curves of the asteroid that were used to analyze its shape, topography and bulk properties (volume, density).

Methods – Eight series of images were acquired with SPHERE+ZIMPOL on the Very Large Telescope (ESO Program ID 107.22QN.001; PI: Marsset) and combined with optical light curves to reconstruct the shape of the asteroid using the ADAM (Viikinkoski et al. 2015), MPCD (Capanna et al. 2013) and SAGE (Bartczak & Dudziński 2018) algorithms.

Results – We will present Cybele’s bulk properties, including its volume-equivalent diameter and average density, in the context of other low-albedo P-type asteroids. We will show that Cybele’s shape and rotation state are entirely compatible to those of a Maclaurin equilibrium figure, opening up the possibility that D≥260 km (M≥1.4x10^19 kg) small bodies from the outer Solar System formed at equilibrium. We will further present the results of N-body simulations used to explore whether the equilibrium shape of Cybele is the result of a large resetting impact (similarly to the case of Hygiea; Vernazza et al. 2020), or if it is primordial (i.e., the result of early internal heating due to the radioactive decay of short- and long-lived radionuclides).

How to cite: Marsset, M., Brož, M., Vermersch, J., Rambaux, N., Ferrais, M., Viikinkoski, M., Hanuš, J., Jehin, E., Podlewska-Gaca, E., Bartczak, P., Dudziński, G., Carry, B., and Vernazza, P.: (65) Cybele is the smallest asteroid at hydrostatic equilibrium, why?, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-242, https://doi.org/10.5194/epsc2022-242, 2022.

An asteroid family is a group of asteroids with similar orbital proper elements (e.g., Nesvorný et al. 2005), which could be fragments formed by large impact events. The heating temperature in primordial bodies is important to form various mineralogies observed in asteroids and meteorites. The short-lived radiogenic heat of ²⁶Al is the plausible heat source for the early stages of planetesimal formation. After 5 Myr of CAIs, ²⁶Al decreases by <1%. Heating temperatures caused by ²⁶Al highly depend on the water-to-rock ratio (W/R) and accretion timing in the planetesimal. W/R can be a good indicator of the formation distance from the Sun. However, it should be noted that W/R can be changed by the differentiation process (Wakita et al. 2011, Neumann et al. 2020, Kurokawa et al. 2022). The taxonomic composition of a family can be a witness to the internal structure of a primordial body, before disruption to become a collisional family. The near-ultraviolet wavelengths (NUV; 0.3-0.5 µm) and 0.7-µm absorption band are sensitive to the presence of phyllosilicates (Feierberg et al. 1985, Vilas and Gaffey 1989). The presence or absence of the 0.7-µm band and the NUV absorption suggest a possible differentiation process.

Methods: In this study, in order to cover the NUV to visible wavelength range, using two spectrophotometric surveys, we used SDSS MOC4 (Ivezić et al. 2001) and ECAS (Zellner et al. 1985), for evaluation of the taxonomic configuration of family members. The asteroid family members were classified based on Tholen’s taxonomy (Tholen 1984). Furthermore, the 0.7-µm band (HYD) was evaluated as the slope change between  the SDSS r-i filters to i-z filters: HYD=[r-i-(r-i)_sun]-[i-z-(i-z)_sun].

Results: Some of these families had been studied spectroscopically and the fraction of members with 0.7-µm band absorption can be obtained from the literature (Mothé-Diniz et al. 2005, Morate et al. 2016, 2018, 2019, de León et al. 2016, De Prá et al. 2020). Families with negative HYD values have a majority of members with the 0.7-µm band absorption from the spectroscopic studies. Thus, we found the HYD is a good proxy for the 0.7-µm band absorptions, even though the SDSS filters are not optimized for characterizing the 0.7-µm band. Furthermore, a strong correlation (correlation coefficient of -0.69) exists between HYD and the NUV absorption, suggesting that the NUV absorption can be also used for evaluating the presence of Fe-bearing phyllosilicates. The NUV absorption strength decreases from G > C/B > F/CP > P > D, which is in good agreement with the percentage of objects showing 0.7-µm band found by Vilas (1994) and Fornasier et al. (2014). Thus, G types might be dominated by Fe-bearing phyllosilicates in composition, while F types might be dominated by Fe-poor phyllosilicates. The figure shows the taxonomic compositions for primitive asteroid families that have greater than 30 asteroid members. We found several families consist of relatively homogeneous taxonomic types. The collisional families with majority of G type (the highest NUV absorption) are composed of Fe-rich phyllosilicates, and those with majority of F type (the lowest NUV absorption) are composed of Mg-rich phyllosilicates or dehydrated phyllosilicates. There are also intermediate families which consist of variety of taxonomic classes, which may inhere compositional heterogeneity. This heterogeneous families are larger than 200 km, indicating the size of primordial bodies may play a great role to differentiate or produce different lithologies inside the bodies.

Figure. Taxonomic structure of primitive asteroid families.

References: Nesvorný et al. (2005) Icarus 173, 132-152. Wakita et al. (2011) EPS 63, 1193-1206. Neumann et al. (2020) A&A 633, A117. Kurokawa et al. (2022) AGU Acvances 3, e2021AV000568. Feierberg et al. (1985) Icarus 63, 183-191. Vilas and Gaffey (1989) Science 246, 790-792. Ivezić et al. (2001) Astron. J 122, 2749-2784. Zellner et al. (1985) Icarus 61, 355-416. Tholen (1984) PhD thesis from University of Arizona. Mothé-Diniz et al. (2005) Icarus 174, 54-80. Morate et al. (2016) A&A 586, A129. Morate et al. (2018) A&A 610, A25. Morate et al. (2019) 630, A141. De Prá et al. (2020) A&A 643, A102. Vilas (1994) Icarus 111, 456-467.

How to cite: Tatsumi, E., de León, J., Vilas, F., Popescu, M., Hiroi, T., Hasegawa, S., Morate, D., Tinaut-Ruano, F., and Licandro, J.: Internal compositional structure of large primitive asteroids based on the photometric surveys, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-175, https://doi.org/10.5194/epsc2022-175, 2022.

The desorption of volatiles from comets detains many pieces of information on cometary interiors, as well as the morphology of the ices hidden under the dust. The aim of this work is to study the sublimation and desorption of CH4 through amorphous solid water (ASW), and a layer of indene (C9H8, as a proxy for dust grains), during thermal processing, in order to simulate temperature changes occurring in cometary environments. Sublimation and diffusion experiments are performed for pure CH4, as well as CH4 layered or mixed with H2O. At about 30 K and with 1% of CH4 abundance ratio, the ices are deposited and the temperature is increased until (maximum) 200 K with a heating ramp of either 1 or 5 K/min. Mass and Infrared (IR) Spectroscopy are used to analyze the results through a Quadrupole Mass Spectrometer (QMS) and Fourier Transform Infrared (FTIR) spectrometry.

It has been noticed that depending on the heating ramp and type of deposition (layered or co-deposited ices), the desorption of methane varies, both in intensity and in desorption temperature. In the case of mixed ices, desorption is lower in intensity and occurs at higher temperatures compared to layered ices. Moreover, more methane desorbs due to the crystallization of water, rather than at its pure ice sublimation temperature. When the heating ramp is faster, instead, the desorption of methane occurs at higher temperatures, for both types of ice deposition.

In a second set of experiments, temperature cycles are applied, meaning that temperatures are increased up to 140 K, decreased down to 30 K, and then increased and decreased again. The desorption process of methane and water crystallization are slower for mixed ices than for layered ones, thus meaning that if comets present a mixed structure, they will undergo more cycles to lose the same quantity of volatiles. During the first temperature cycle performed, water is observed to perform the change of phase from amorphous to crystalline and then, during the second cycle, to a “better” crystalline cold. By reaching only 140 K and not 200 K still some methane is retained after one cycle, while water does not sublimate much.

Finally, a layer of indene is placed on top of a layered/mixed ice structure. The thicker the indene layer the higher the temperature at which methane desorbs since it is more difficult at colder temperatures to diffuse through the indene crust. However, the thicker the crust layer, the larger the quantity of methane that is observed to go out.

The desorption of methane that happens, even if slightly, during the entire process of warming up, is linked to the presence of the coma around the comet and its evolution. Moreover, the shift due to different ramps used experimentally allows extrapolating the desorption temperature shifts experienced by comets along their orbit. The temperature cycles performed give us high hopes for astrophysical results regarding comets since by noticing that the sub-layers retain material, it is understood the evolution of comets during their lives. The crust experiments can give insight into the behavior of cometary nuclei and their layer of crust on top. The more the dust surrounding the nucleus and thus the thicker its layer, the more difficult it will be for molecules trapped in the nucleus to desorb. Therefore, higher temperatures and thus multiple orbital cycles are needed in order for these lower layers to desorb.  

How to cite: Tamai, C., Maté, B., Cazaux, S., and Satorre Aznar, M. Á.: Laboratory experiments on diffusion and sublimation of methane through ice dust layers to mimic cometary nucleus activity., Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-107, https://doi.org/10.5194/epsc2022-107, 2022.

 Methanol ice structural changes due to thermal processing

Miguel Ángel Satorre, Carmina Santonja, Ramón Luna, Manuel Domingo, Carlos Millán

Escola Politècnica Superior d’Alcoi, Centro de Tecnologías Físicas, Universitat Politècnica de València, Placeta Ferrándiz-Carbonell, s/n, 03801 Alcoi, Spain

  Abstract

Methanol is one of the complex organic molecules of interest in astrophysics. This molecule is formed at low temperatures (< 20 K) by CO hydrogenation and survives the thermal processing during some solar system formation. The temperature changes modify the initial methanol structure. The final structure achieved after heating the ice remains virtually unchanged in small body objects in the outer Solar System. If one of these small bodies becomes a comet, the Sun reprocesses the methanol thermally during its perihelion. Our experiments study the structural changes, such as the ice compaction, of methanol deposited at different temperatures and warmed up at different rates. We also monitor the ice crystallization and the interaction ice-substrate, and observe that the ice monolayers interacting with the substrate behave differently from the rest of the ice. This fact could be relevant for the molecule survivor during the Solar System formation.

1.    Introduction

Methanol is an exciting molecule as it is the simplest complex organic molecule (COM). That species has awakened interest because they are the link between the simplest ice molecules (H₂O, CO, CH₄…) and more complex ones such as amino acids. Many Solar System bodies present shreds of evidence of solid methanol, such as KBOs[1] and TNOs[2], and it is also detected in comets[3]. This molecule can survive the star formation period as it has been detected in a warm environment such as HD 100546 (A-type star)[4]. Because of the high temperatures, CO ice is not present in this system, then CH3OH had to be formed in the mother molecular cloud. Then in our Solar System, methanol maybe appears from the priest ice formed during the molecular cloud phase. Depending on the thermal history (and radiation processing), the structure of the ice changes among different amorphous and crystalline structures[5]. As the structure changes, the density of the material does so. Density is a crucial parameter for ion irradiation experiments[6], cause the penetration depth of ions depends on it, and in determining abundances[7], because the integrated band strength also depends on the density. In this communication, we warm up methanol ice at low temperatures and follow its morphological changes by laser interferometry. We relate structure with the minimum density, corresponding with amorphous methanol from low temperatures, and the maximum density, associated with compact amorphous and crystalline methanol ice.

2.    Experimental methods

We deposit pure methanol on the cold surface of a gold-coated quartz crystal microbalance (QCMB). During deposition, a double laser interferometric method allows us to control and measure the actual refractive index of the ice and determine the density of the material by knowing the mass deposited on the QCMB. After that, a temperature controller warms the ice at a constant rate. The system records laser signal variations due to structural changes in the ice during the temperature increase.

3.    Preliminary results

The amorphous structure evolves without crystallizing up to temperatures almost above 100 K. The effect of compaction does not seem to imply the collapse of the structure, as suggested by Isokoski et al.[8], at least not in all of our experiments. Probably it depends on the conditions of ice formation and warming up of the sample. To study the compaction process of the ice, we deposit methanol at different temperatures and follow the warming-up variation, showing that the compaction depends on the initial amorphous structure. The laser signals drop abruptly when the ice crystallizes at around 110 K, probably because of a strong interaction between the substrate and the monolayers of the ice interacting with the substrate. The drop in the laser signals remains until the ice monolayers closer to the substrate sublimate. Laser signals show a variation just before sublimation, likely because of the crystalline phase change.

4.    Conclusions

The amorphous structure of the methanol ice deposited below 20 K, evolves with temperature and becomes more compact at 100 K before it becomes crystalline. The methanol ice structure breaks during crystallization, causing a sudden drop in the laser signals at about 110 K.  This drop probably indicates an interaction between methanol-substrate stronger than between methanol-methanol. The laser signals also reveal possible changes in the crystalline methanol structure at about 130 K. The reorganization of the structure after the maximum compaction at about 100 K does not seem to imply denser structures as it is almost constant for those high temperatures, as shown by Luna et al.[9].

Acknowledgements

The PID2020-118974GB-C22 grant of the Spanish Ministerio de Ciencia e Innovación funds this work.

References

[1] Stern, A., Weaver, H. A., Spencer, J. R. et al., Science 364, eaaw9771, 2019.

[2]  Barucci, M. A., Merlin, F., Perna, D. et al., A&A 539, A152, 2012.

[3]  Bergman, P., Lerner, M. S., Olofsson, A. O. H. et al, A&A 660, A118, 2022.

[4]  Booth, A. S., Walsh, C., van Scheltinga, J. T. et al., Nature Astronomy 5, 684-690, 2021.

[5] Torrie, B. H., Binbrek, O. S., Strauss, M., Swainson, I. P., Journal of Solid State Chemistry 166, 415-420, 2002.

[6] Urso, R. G., Baklouti, D., Djouadi, Z., Brunetto, R., EPSC Abstracts 13, EPSC-DPS2019-594-1, 2019.

[7] Fernández-Valenzuela, E., Pinilla-Alonso, N., Stansberry, J., et al., EPSC Abstracts 13, EPSC-DPS2019-1849-1, 2019.

[8] Isokoski, K., Bossa, J. B., Triemstra, T., Linnartz, H., Phys. Chem. Chem. Phys. 16, 3456-3465, 2014.

[9] Luna, R., Molpeceres, G., Ortigoso, J. et al., A&A 617, A116, 2018.

How to cite: Satorre, M. A., Santonja, C., Luna, R., Domingo, M., and Millán, C.: Methanol ice structural changes due to thermal processing, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1065, https://doi.org/10.5194/epsc2022-1065, 2022.

Introduction

To accurately describe the variable surface and subsurface temperatures of regolithcovered small Solar System bodies, thermal models describing the heat transport in granular media need to be applied. The thermal models require as an input parameter the thermal conductivity of the granular material, but this property has yet to accurately be derived for arbitrary volume filling factors. With simulations of packings of spheres, we examine the relation between volume filling factor and thermal conductivity.

Thermal conductivity

Our work is based on the thermal conductivity model of sphere packings derived by Chan and Tien (1973) with augmentations for cohesive particles by Gundlach & Blum (2012). Input parameters for the analytical approximation of the thermal conductivity are the particle radius, the local temperature, and the local volume filling factor, the thermal conductivity of the solid grain material, the specific surface energy and the Young’s modulus of the grain material as well as an empirical factor describing the details of the packing structure. However, the latter is quite uncertain, because this factor depends on the details of the generation, homogeneity and isotropy of the sphere packing. For a broad application of the thermal conductivity model that allows for a wide range of (local) volume filling factors and different packing morphologies, we conduct a series of numerical simulations and derive their heat conductivities. We also examine packings with identical porosities but different packing structures to assess more subtle influences on the heat conductivity. 

Heat Transfer in LIGGGHTS

With the open-source discrete-element particle-simulation software LIGGGHTS, which is optimized for general granular and granular heat-transfer simulations, packings of spherical grains and their physical properties can be simulated and analyzed. To determine the thermal conductivity of such a packing, we sandwich the spheres between two simulated mesh walls of different temperatures T1 and T2 and distance L. After sufficient time steps, the constant heat flux through a unit area of the packing can be derived through

with λ being the heat conductivity of the granular packing. All other particle properties that determine, e.g., the contact radius between the spheres and the flow of heat among them, are set within the simulation. With this method, the thermal conductivity of any box-shaped or cylindric spherical package can be determined, making it possible to investigate the changes in thermal conductivities with changing volume filling factors.

Perspectives

An improved understanding of heat flow through granular packings will lead to better thermal models for the sub-surface of small bodies in the Solar System. With accurate knowledge of their thermal conductivity, we will get a better insight into their heat distribution and temperature evolution, the evaporation rates of volatiles in comets, and overall a better idea of the thermal evolution of young planetesimals regarding sintering and melting. 

References

Gundlach & Blum (2012), Icarus, 219, 2
Chan & Tien (1973), J. Heat Transfer, 95, 302-308

How to cite: Lammers, K., Gundlach, B., and Blum, J.: Thermal Conductivity of Granular Media and its Dependence on Volume Filling Factor, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-376, https://doi.org/10.5194/epsc2022-376, 2022.

We have developed a high-irradiance space simulator,  SHINeS which can be used to replicate the thermal environment in the immediate neighborhood of the Sun down to a heliocentric distance of about 0.06 au.

Our motivation for building this experimental system was to study the effect of intense solar radiation on the surfaces of asteroids when their perihelion distances become smaller than the semi-major axis of the orbit of Mercury.   The most recent population models (Granvik et al. 2016, 2017,2018) for NEAs predict far more objects with small perihelion distances than those observed. The discrepancy of a factor of almost 9 disappears when a hypothesized mechanism of total disruption of these objects is introduced in the model, with an average disruption distance of 0.076 au.

Previous experimental studies on the processes on asteroid surfaces include the thermal crack growth experiments of Delbo et al. 2014, optical mining technology demonstrations by Dreyer et al. 2016, and the volatility of Sodium as the primary mechanism for Phaethon’s activity by Masiero et al.2021.

SHINeS was developed to directly mimic the conditions an asteroid’s surface experiences at various heliocentric distance in terms of Solar irradiance, rather than trying to match the predicted temperature in a more conventional heating experiment. Thus, SHINeS consists of a powerful Solar simulator and a large vacuum chamber, complemented by an assortment of measuring and monitoring devices to closely record the processes on the surface and interiors of illuminated samples.

Our preliminary studies are focused on samples of CI asteroid simulants to find the correlation between the rate of disruption and the heliocentric distance of an object. 

How to cite: Tsirvoulis, G., Granvik, M., and Toliou, A.: Space and High-Irradiance Near-Sun Simulator (SHINeS), Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1005, https://doi.org/10.5194/epsc2022-1005, 2022.

1. Introduction

The Yarkovsky–O'Keefe–Radzievskii–Paddack effect, or YORP effect, has influence on the rotational state and evolution of asteroids [1]. Depending on several parameters, it can either increase or decrease the spin rate as well as change the spin obliquity of an asteroid, on timescales that also depend on the physical and dynamical properties of the considered asteroid. 

The current YORP model reads

T_YORP = T_NYORP + T_TYORP,

where T_NYORP stands for the YORP effect on the whole asteroid and T_TYORP stands for the tangential YORP effect, which is related to the presence of boulders and surface roughness. 

Figure 1. The components on asteroids that contribute to the YORP effect.

The current model still faces difficulties calculating the YORP torque because of the extreme sensitivity of the YORP effect to the surface topology. Here, we consider the YORP effect of the crater, which has not been considered so far. We show that the crater-induced YORP (called CYORP hereafter) might contribute the total YORP torque as well, which adds a "CYORP" term into the Equation (1):

T_YORP = T_NYORP + T_TYORP + T_CYORP

with

T_CYORP = Σ_iT_CYORP,I

as a summation for a whole set of craters or concave structures on the asteroid (see Figure 1). The CYORP torque is the difference of the torque caused by the presence of the crater and the torque by the ground before the birth of the crater (dashed curves in Figure 1)

T_CYORP = T_crater - T_ground.

Using these calculations, we find that a single crater with a size equal to one-third of the asteroid size would produce a torque that is comparable to the normal YORP torque. The smaller craters also contribute to the total torque due to their large amount. Therefore, the CYORP should be considered in the future study of the YORP. The derived CYORP torque can be applied both for craters and for any concave structures on the surface of an asteroid, although a modification accounting for the geometry is needed. Since craters arise from collisions, this study builds a link between the rotational evolution and collisional history of asteroids.

2. Heat model

As a first step, we simply assume a non-thermal conductivity regime, which leads to a recoil thermal force on the surface element dS

f = -(2Φα/3c)dS.

where Φ and c are solar flux and light speed, respectively. Here α is the cosine of the angle between the surface normal vector and the light ray. 

3. Shape model for the crater

Figure 2. The shape model for the crater.

We consider a simple crater shape model, which is represented by a full or a portion of a semi-sphere with crater radius R₁ and depth h (see Figure 2). The widely used parameter depth d-diameter D₀ ratio expresses:

h/D₀ = (1-sinγ₀)/2.

Space mission data from real asteroids show that the average h/D₀ for fresh craters covers a range that goes from 0.11 (for Ceres) to 0.19 (for Eros), depending on many parameters and the considered crater diameter range [2].

4. Calculation of the torque

For a concave geometry such as a crater, the self-shadowing has a significant influence on the YORP effect. There are two major effects of self-shadowing. (1) During the rotational cycle, only a fraction of the crater is illuminated, depending on where it lies on the asteroid. (2) The effective recoil force is not normal due to the shelter. Considering non-zero thermal inertia and a given asteroid shape requires a numerical model and will be the topic of the next study.

The recoil force must be integrated over the whole illuminated area of the crater

F = ∫fdS.

The total torque of the crater is

T = ∫r×fdS ≈r₀×F.

Here r and r₀ are the position vector of the surface element on the crater and the sphere center of the crater, respectively. To understand this effect on the secular spin evolution of the asteroid, we need to average the torque over the orbital and spin motion.

In general, T_CYORP takes the form of the following scaling rule with the radius of the crater R₀ and of the asteroid R:
T_CYORP = gΦR₀² R/c,

where g is a function of the properties of the crater and asteroid, Φ is the solar flux and c is light speed.

5. Results and implications

We find that a single crater with a size equal to one-third of the asteroid size would produce a torque that is comparable to the normal YORP torque. This torque decreases with the crater as R₀². Since the cumulative size distribution of craters typically follows a power law of the form N(R ≥ R₀) ∝ R₀^-b, the larger number of smaller craters contributes also to the total YORP torque, although each of them causes a small torque. Moreover, since an asteroid experiences a lot of impacts leading to a crater during its evolution, the resulting CYORP torques may cause a random walk of the spin rate and obliquity of the asteroid, which may either slow down or even prevent the YORP spin up to occur. This can have strong implications on the formation of top shapes and binary systems based on this process [3], and on the resulting timescale, which will be assessed in future work.

Acknowledgment

We acknowledge support from the Universite Cote d'Azur. W.Z. and X.Y. acknowledge funding support from Chinese Scholarship Council. W.Z. acknowledge funding support from Origin Space Company. P.M. acknowledges funding support from the French space agency CNES and from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 870377 (project NEO-MAPP). 

[1] Rubincam, D (2000) Icarus 148, 2;

[2] Noguchi, R et al (2021) Icarus 354, 114016;

[3] Walsh, K and Jacobson, S (2015), in Asteroids IV (Michel et al., eds), UAP, 375.

How to cite: Zhou, W.-H., Zhang, Y., Yan, X.-R., and Michel, P.: The crater-induced YORP effect, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-795, https://doi.org/10.5194/epsc2022-795, 2022.

Rubble pile asteroids such as Itokawa, Ryugu, and Bennu are covered by regolith of various sizes. In some instances like on Itokawa the regolith is not distributed evenly but large boulders congregate in some areas whereas other are dominated by finer material [1].  Several mechanisms have been proposed to explain this size sorting, among them the so called ballistic sorting effect (BSE) [2]. The BSE depends on impacting particles rebounding more elastically from large targets (boulders) than when hitting a bed of fine grains. This mechanism of course not only applies to the primary impactor hitting an asteroid surface but also to secondary impacts from material ejected by the primary impact. In order to fully understand the BSE on asteroids, it is therefore important to quantify the mass- and velocity distribution of ejecta generated by impacts into asteroid surfaces. In particular from impacts with low velocities that will then generate ejecta that is slower than the escape velocity of the asteroid.

To conduct realistic experiments under asteroid conditions we use the ERICA (Experiments on Rebounding Impacts and Charging on Asteroids) platform [3] under the microgravity provided by the ZARM Bremen drop tower and the new GTB-Pro, also at ZARM. To provide a low but directed gravity level, i.e. asteroid gravity, ERICA consists of a vacuum chamber that contains the sample material which is mounted to a linear stage that - once the whole setup is in microgravity - provides a linear acceleration to simulate asteroid-level gravity. Using the linear stage eliminates any Coriolis forces a centrifuge would create. Due to the low g-jitter and the long microgravity time of 9.2 s in the drop tower and 2.5 s in the GTB-Pro these experiments are able to focus on ultra low velocity impacts in the cm/s rage, complementing earlier experiments by Brisset et al. [4].

In the sample chamber we place granular beds (regolith analog) of various sizes and a launcher mechanism that impacts a basaltic projectile at the simulated asteroid surface. Using a stereo pair of cameras, as well as a high speed camera we then record the ejecta plume created by the impact. From the resulting image data we extract ejecta velocities using particle tracking (for larger ejecta particles) and digital image correlation (for smaller ejecta). 

Fig.1. Ejecta Plume generated by impacting a basaltic projectile (v = 65 cm/s)  in a bed of 0-300 μm sized particles at a gravity level of 2 • 10^-4 m/s^2

[1] A. Fujiwara, J. Kawaguchi, D.K. Yeomans, M. Abe, T. Mukai, T. Okada, J. Saito, H. Yano, M. Yoshikawa, D.J. Scheeres et al., Science 312,1330 (2006) 

[2] T. Shinbrot, T. Sabuwala, T. Siu, M.V. Lazo,P. Chakraborty, Phys. Rev. Lett.118 (2017) 

[3] K. Joeris, L. Schönau, L. Schmidt, M. Keulen, V. De-sai, P. Born, J. Kollmer, EPJ Web of Conferences 249, 13003 (2021)

[4] J. Brisset, C. Cox, S. Anderson, J. Hatchitt, A. Madison, M. Mendonca, A. Partida, D. Remie, Astron. Astrophys (2020)

How to cite: Joeris, K., Keulen, M., Schönau, L., and Kollmer, J. E.: Ejecta Generated by Ultra Slow Impacts on Regolith Surfaces in Low Gravity, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-913, https://doi.org/10.5194/epsc2022-913, 2022.

Past, present and future small body missions include onboard accelerometers that are used either by main spacecraft during surface interactions such as sampling or touching the surface [1-2],  or by lander packages deployed to the surface [3-6].  All surface interactions provide a wealth of information about the behaviour and the properties of surface materials but accelerometer data is particularly valuable. However, particular care must be taken to correctly account for the low gravity environment when interpreting the measurements. As long as the proper (Froude number) scaling is applied, the collision duration and penetration depth derived from the acceleration data can be used to infer surface properties such as the internal friction angle or the bulk density of the material [7].

Previous work has demonstrated the link between collision velocity and peak acceleration in both terrestrial and low-gravity experimental trials [8-9]. Here we will present recent experimental results investigating the link between accelerometer data and the surface properties.  The collision velocity is adjusted by modifying the drop height of the projectile and impacts are performed into several different surface materials (Fig. 1). 

Figure 1. The  granular materials used in the experimental trials

To obtain the in-situ acceleration profile during the collision, we use a projectile that contains an accelerometer.  We apply the same data processing for the accelerometer measurements as used in previous work [8-9] to extract the drop height (z_drop), the collision velocity (v_c), the collision duration (t_stop) and the peak acceleration (a_peak). In addition, we also extract the time between the instant the projectile makes contact with the ground and the moment when the projectile is at its peak acceleration (t_peak), the mean amplitude of acceleration fluctuations after the peak acceleration, and the frequency of these fluctuations (Fig. 2). As noted in previous work [10,11], the acceleration profiles have a clear dependence on particle size (Fig. 3). In this talk we will present new experimental results and discuss the information that can be extracted from accelerometers about the surface properties during .

Figure 2: Typical profile measured by an in-situ accelerometer in a spherical projectile during an impact into granular material. See text for description of the variables indicated.

Figure 3: Acceleration profile during the impacts with different granular materials, and different collision velocities: 0.5 m/s (blue), 0.8 m/s (red), 1.2 m/s (yellow).

Acknowledgements

The authors acknowledge funding support from the European Commission's Horizon 2020 research and innovation programme under grant agreement No 870377 (NEO-MAPP project). This project also received funding from the Centre National d'Etudes Spatiales (CNES) and CS acknowledges PhD research grant funding from ISAE-SUPAERO.

References:

[1] Lauretta, D.S. and the OSIRIS-REx Team, 2021, March. The OSIRIS-REx Touch-and-Go Sample Acquisition Event and Implications for the Nature of the Returned Sample. In Lunar and Planetary Science Conference (No. 2548, p. 2097).

[2] DellaGiustina D., et al. 2022, OSIRIS-APEX: A PROPOSED OSIRIS-REX EXTENDED MISSION TO APOPHIS, Apophis T-7 Years 2022 (LPI Contrib. No. 2681)

[3] Lorenz, R.D., et al. 2009. Titan surface mechanical properties from the SSP ACC–I record of the impact deceleration of the Huygens probe.

[4] Biele, J., Ulamec, S., Maibaum, M., Roll, R., Witte, L., Jurado, E., Muñoz, P., Arnold, W., Auster, H.U., Casas, C., Faber, C., and others, 2015. The landing (s) of Philae and inferences about comet surface mechanical properties. Science, 349(6247), p.aaa9816.

[5] Michel et al., 2022, The ESA Hera mission: Detailed characterisation of the DART impact outcome and of the binary asteroid (65803) Didymos, The Planetary Science Journal (accepted)

[6] Michel, P., et al. 2022, The MMX rover: performing in situ surface investigations on Phobos. Earth Planets Space 74, 2

[7] Sunday, C., et al. 2022. The influence of gravity on granular impacts-II. A gravity-scaled collision model for slow interactions. Astronomy & Astrophysics, 658, p.A118.

[8] Murdoch, N., et al. 2017. An experimental study of low-velocity impacts into granular material in reduced gravity. Monthly Notices of the Royal Astronomical Society, 468(2), pp.1259-1272.

[9] Murdoch, N., et al. 2021. Low-velocity impacts into granular material: application to small-body landing. Monthly Notices of the Royal Astronomical Society, 503(3), pp.3460-3471.

[10] Clark et al., 2013, Granular impact dynamics: Fluctuations at short time-scales, AIP Conference Proceedings 1542, 445-448

[11] Duchêne, A., et al. 2022, A Machine Learning Approach For Estimating Asteroid Surface Properties from Accelerometer Measurements, Lunar and Planetary Science Conference 2022, no. 1563

How to cite: Murdoch, N., Duchêne, A., Segovia-Otera, J., Drilleau, M., Stott, A., and Sunday, C.: What can we learn from an in-situ accelerometer during surface interactions?, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-910, https://doi.org/10.5194/epsc2022-910, 2022.