Poster presentations and abstracts

Introduction

Asteroid (65803) Didymos is an S-type [1] Apollo binary system characterized by a 780±30 m size primary, called Didymos, and a 164±18 m size secondary, called Dimorphos, orbiting at a distance of ~1.19 km [2]. The primary rotation period is 2.26 h [2], close to the 2.2 h disruption spin barrier [3], while the period of revolution of Dimorphos around the primary is 11.9217+0.0002 h [4]. This asteroid has been selected as the target of the Double Asteroid Redirection Test (DART, [5]), whose main goal is to impact Dimorphos at a speed of 6.6 km/s on September 30, 2022, thereby demonstrating the kinetic impactor technique and evaluating the resulting impulsive deflection.

The scientific camera onboard DART is called DRACO, i.e. the Didymos Reconnaissance and Asteroid Camera for Op-nav [6]: its main goals are to image Didymos for optical navigation, to resolve the two bodies and support the spacecraft autonomous navigation to the target, and to locate the impact site precisely and characterize its local surface features. To complement such observations, the Light Italian Cubesat for Imaging of Asteroids (LICIACube, [7]) will be released from DART ten days before the impact, and autonomously guided through a flyby with closest approach distance of ~55 km from the target. LICIACube cameras LEIA (LICIACube Explorer Imaging for Asteroid - narrow angle camera) and LUKE (LICIACube Unit Key Explorer – wide angle camera) will then safely witness the redirection test in-situ, while its crater, as well as the ejecta and plume are being formed.

Boulders SFD on Didymos system

Boulders/large blocks on asteroids are mainly interpreted as produced by target fragmentation and excavation due to high-velocity impact processes. They are the largest fragments excavated during an impact and are typically found within the crater or in its proximity, because they have not reached the escape velocity [8]. Instead, on rubble-pile asteroids boulders (typically the largest ones) are products of the reaccumulation process that formed the minor body itself, and may not be correlated to the observed craters [9]. For both cases, these blocks provide information on impact cratering processes occurring on low gravity bodies or on their parent body disruption event: their size-frequency distribution (SFD) fitting indices are therefore pivotal to provide hints on the fragment/boulder formation and/or degradation processes.

Deriving boulder SFD and the corresponding power/exponential-law indices has been an important scientific topic addressed in several fly-by and orbital missions to minor bodies [e.g. 10-12]: it will be accomplished on the Didymos system as well.

Four minutes before the impact the last image that contains all of Didymos will be taken by DRACO, with an expected spatial scale of 7 m/pixel. 120 seconds before impact, the last DRACO image containing any part of Dydimos will be taken, with a maximum resolution of 3.5 m [13]. DRACO will image all of Dimorphos ~50 cm/pixel ~17 seconds before impact and plans to return at least one higher-resolution image before impact. These final image(s) will have pixel scales <15 cm/pixel [14]. Such images will provide the possibility to identify the boulders SFD located on the illuminated imaged side of the primary down to sizes of ~11 to 21 m and compare it with previously observed SFD of other asteroids [9,15]. Instead, boulders with sizes larger than 0.6-1.5 m will be identified on Dimorphos, hence returning the pre-impacted SFD context of the impact location.

At closest approach (CA), LICIACube/LEIA will image the surface of Dimorphos at 1.4 m/px [7]. If the DART crater will be observed through LEIA (it may be close to the limb during CA, hence the challenging imaging condition), we will be able to identify all boulders larger than 4.0-7.0 m located on the impacted side of Dimorphos, discerning those that have been generated/fragmented/moved after the DART impact from the ones previously imaged through DRACO. In addition, LEIA will image the non-impacted side of Dimorphos (not observed by DRACO) with resolutions ranging from 1.5 to 5 m: this will enable the characterization of the boulders SFD of the secondary down to 4.5 m.

By comparing both the pre-, post- and non-impacted surface areas we will have the unique opportunity to witness how the boulders SFDs and densities/m² will change as a result of a well characterized, hypervelocity impact. We will therefore test if the generation of a crater results in a different power-law distribution of boulders than the one observed on other S-type asteroids, such as (433) Eros and (25143) Itokawa [8,9], as well as recently observed carbonaceous asteroids, (101955) Bennu [12] and (162173) Ryugu [15].

Acknowledgments: This research was supported by the Italian Space Agency (ASI) within the LICIACube project (ASI-INAF agreement AC n. 2019-31-HH.0).

References: [1] de León, J. et al. (2010) Astron. Astrophys, 517, A23. [2] Naidu,  S.P. et al. (2020) Icarus, 348, 113777. [3] Pravec P. and Harris A.W. (2000) Icarus, 148, 12-20. [4] Pravec, P. et al. (2006) Icarus, 181, 63. [5] Cheng A. F. et al. (2016) Planet. Space Sci., 121, 27-35. [6] Fletcher, Z.J. et al. (2016) 3^rd Inst. Planetary Missions, 4043. [7] Dotto, E. et al., (submitted), Planet. Space Sci. [8] Thomas, P.C., et al. (2001) Nature 413, 394. [9] Michikami, T. et al. (2008), Earth Planets Space, 60, 13-20. [10] Lee, S.W., et al. (1986) Icarus 68, 77. [10] Geissler, P., et al. (1996) Icarus 120, 140. [11] Pajola, M. et al. (2015), Astron. Astrophys. 583, A37. [12] DellaGiustina, D. et al. (2019), Nat.Astron. 3, 341-351. [13] Cheng, A. F. et al. (2018) Planet. Space Sci., 157, 104-115. [14] Barnouin, O. et al. (2019). LPSC 50 abst. 2448. [15] Watanabe, S. et al. (2019), Science, 364, 6437, 268-272.

How to cite: Pajola, M., Lucchetti, A., Ivanovski, S., Poggiali, G., Ieva, S., Perna, D., Dotto, E., Della Corte, V., Cremonese, G., Amoroso, M., Pirrotta, S., Cheng, A., Chabot, N., Rivkin, A., Barnouin, O., Ernst, C., Daly, T., Hirabayashi, M., Asphaug, E., and Schwartz, S. and the DART & LICIACube Team: Boulders Size-Frequency Distribution on binary asteroid (65803) Didymos: Expected results from LICIACube/LEIA and DART/DRACO cameras, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-117, https://doi.org/10.5194/epsc2020-117, 2020.

Introduction

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 Dimorphos the secondary element of the (65803) Didymos binary asteroid system, and the impact is expected in late September – early October, 2022 [1] The DART S/C will carry a 6U cubesat called LICIACube (Light Italian Cubesat for Imaging of Asteroid) [2], provided by the Italian Space Agency, with the aim to collect pictures of the impact’s effects. On board LICIAcube will be hosted 2 camera payloads: LEIA a panchromatic (400-900nm Filter, 2.9x2.9° FOV) Narrow Angle Camera and  LUKE a RGB (Bayer color filter, 4.8 x 9.15° FOV).  LICIACube will be able to acquire the structure and evolution of the DART impact ejecta plume and will obtain high-resolution images and 2 colours data (B-G, G-R) of the surfaces of both bodies and the plume.

In order to check the imaging capability and to optimize the fast scientific phase of LICIACube, the LICIACube team performed 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. Since the study of the plume and its evolution is one of the main scientific goal of the mission we performed a scattering modelling of the ejecta in order to invert the future photometric data deriving hints on the intimate nature of the dust particles released by the impact.

Plume simulated Images and column density

With the two-fold aim of set the operative parameters for the Payloads and to understand the information retrievable by the images of the evolving plume we started an imaging simulation activities taking into account:

• LICIAcube mission design [3] (Trajectory, Speed, illumination conditions)
• Payloads optical characteristics

The plume evolution was simplified assuming:

• Non colliding particles during the plume evolution;
• A speed distribution in the plume given by eq:

Where x is the distance on Dimorphos surface from the DART impact point and the other parameters used, considering as main material of asteroid system the cemented basalt, are reported in table:

We considered the most representative 3 size bins for what concerns the ejected mass, the expected total number of particles are reported in table:

In Figure 1 is reported the simulated image obtained considering the LICIACube trajectory 50s before the close approach (about 110 s after the DART impact).

Figure 1 Plume simulated image relative values for irradiance

Once the simulated column density image was obtained, we added a scattering simulation considering spherical dust particles and using a Mie code well suited for large particles approaching the geometric optics regime [4]. In this way we were able to translate column densities in luminous fluxes measured by the instrument using a methodology described in the next section.

Plume colours scattering modelling

RGB data of the ejecta plume can be used to derive hints on the physical properties of the ejected particles through scattering modelling of the measured two colours (B-G, G-R) and the phase function versus the phase angle of observation α.

Given the intensity of solar light incident on the plume’s single particle I_inc,, considering the incident solar light as unpolarized, the intensity of light scattered by the particle at α, I_sca is given by [5]:

where S₁₁(α) is the first element of the 4X4 scattering Müller matrix, k=2π/λ is the wave number, and r is the distance between the particle and the observer. In this case: 

being F_Sun the solar flux at 1 AU, r_h the heliocentric distance of the dust particle, and a its radius.

The Mie code provides the complete scattering matrix once the dimension of the particle and its composition in terms of the complex refractive index of the material at the considered wavelength are given as input. We used largely referenced laboratory data on basaltic materials to obtain the optical properties of the dust particles [6]. This composition is used to model the dust particles residing on the asteroid surface [1], [2].

Then, in order to find the intensity due to the scattering of a single particle measured by the instrument at phase angle α, we convolved I_sca with the photometric response of the instrument. For a generic filter, such measured intensity is  where Resp is the photometric response of the instrument extended throughout the bandpass of the filter. This response is a known product of several factors as the entrance pupil of the system, the reflectivity of the optics, the transmission curve of the filter, the quantum efficiency of the detector, and the exposure time.

Synthetic colours of the dust particles can therefore being computed being the generic color A-B = -2.5log(I_A/I_B). We performed sample scattering colour calculations varying the particle size from 0.1 micron to 1 cm.

Small particles provide extremely variable colours due to the strong influence of scattering resonances being the incident wavelength comparable with the size of the particles themselves. Colours get stable for a larger interval of phase angle proportionally to the increase of the size. Observations of stable colours in the plume during LICIACube flyby will be indicative of particles larger than 100 micron. At the same time, large basalt particles provide a flatter phase function at intermediate and small phase angles than smaller particles.

Combined observations of the plume phase function and colour will therefore effectively constrain the size of the ejected particles providing theoretical inputs to the dynamical models.

Acknowledgements: The LICIACube team acknowledges financial support from Agenzia Spaziale Italiana (ASI, contract No. 2019-31-HH.0 CUP F84I190012600).

References

[1] Cheng et al. P&SS 121 (2016).

[2] Dotto et al. 2020, " LICIACube - the Light Italian Cubesat for Imaging of Asteroids In support of the NASA DART mission towards asteroid (65803) Didymos” P&SS, submitted.

[3] Capannolo et al. 70th IAC Conference Paper (2019).

[4] Wolf and Voshchinnikov. Computer Physics Communications 162 (2004).

[5] Bohren & Huffman. Absorption and Scattering of Light by Small Particles. Wiley (1983).

[6] Pollack et al. Icarus 19 (1973).

How to cite: Bertini, I., Della Corte, V., Ivanovski, S., Dotto, E., Mazzotta Epifani, E., Amoroso, M., and Pirrotta, S. and the LICIACube Team: Synthetic Images and Colours of the Dimorphos Asteroid Ejecta Plume as seen from the LICIACube spacecraft, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1030, https://doi.org/10.5194/epsc2020-1030, 2020.

The Near-Earth Object Surveillance Mission (NEOSM) is a planned space-based infrared mission that will nominally launch in 2025 and librate at the Earth-Sun L1 Lagrange point.  The NEOSM Project was formulated to address the need to detect, catalog, and characterize near-Earth objects (NEOs) to support informed decision making for any potential mitigation activity. NEOSM detects NEOs, obtains high quality orbits for them, provides physical characterization of the NEOs and their source populations, and provides more detailed physical characterization for individual targets with significant impact probabilities.  Specifically, NEOSM will detect, track, and characterize 2/3 of potentially hazardous asteroids (PHAs) larger than 140m - large enough to cause potentially significant regional damage.  NEOSM is expected to detect thousands of comets, hundreds of thousands of NEOs and millions of main belt asteroids. Since moving objects, in particular NEOs, are the main focus of the NEOSM project, the survey can be optimized for maximum discovery rate by adjusting the survey cadence to ensure efficient and reliable linking observations into tracklets, which are position-time sets of a minor planet. It is also important for the survey cadence to provide self-followup that yields orbits with quality similar to that of the known NEOs today. The NEOSM Investigation Software Suite (NISS) is a set of tools being developed to support the efforts to optimize the survey and verify the ability of the designed mission to meet its scientific objectives. The NISS consists of a comprehensive representation of the mission performance, including the flight system hardware, mission operations, and ground data system processing. The NSS takes as its input a reference population of solar system bodies, the NEOSM Reference Small Body Population Model (RSBPM), and performs a frame-by-frame simulation of the survey over the course of its entire operational lifetime. Note that the RSBPM allows for performance to be evaluated as a function of diameter, rather than the traditional method of equating absolute magnitude H = 22 mag as a proxy for 140m. It has been shown that a completeness of 90% of objects with H < 23 mag is needed in order to ensure that 90% of objects larger than 140 m are found. We present here our ongoing work on mission architecture trades and the optimization of the survey cadence for NEO discovery and tracking. We will present the latest NEOSM survey cadence and its expected performance.  We will present the completeness rate after the baseline 5-year mission and a possible extended mission.  Studies have previously shown that the 90% goal can be achieved by a combination of a space mission like NEOCam and a ground based survey like LSST. We will also present how the survey cadence provides self-followup of the NEOs population and ensures orbital quality on par with the current NEO population.

How to cite: Sonnett, S., Mainzer, A., Grav, T., Spahr, T., Lilly, E., and Masiero, J.: NEOSM Survey Cadence and Simulation, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-503, https://doi.org/10.5194/epsc2020-503, 2020.

Abstract

The Near-Earth Object Surveillance Mission (NEOSM) will provide unprecedented detection, tracking and characterization of Near-Earth Objects (NEOs) using high-cadence imaging from a space-based infrared telescope. Planning for the NEOSM requires an accurate model of the solar system’s small body populations in order to develop efficient operational survey strategies and to assess survey performance once in-flight operations have commenced. The NEOSM Investigation Team is currently developing the Reference Small Body Population Model (RSBPM; [1]) that will contain the current best estimates of the dynamical and physical properties of the solar system’s small body populations. Development of the RSBPM will be completed before the NEOSM launch, and the finished product will be peer-reviewed to ensure accuracy. Once the survey begins, we will compare predictions based on the RSBPM to actual observational measurements to calculate the efficiency of the survey, and thus de-bias the survey to properly characterize each population in order to assess Earth impact risks. We present here an update to the methods of incorporating comets into the RSBPM, with particular focus on accurately incorporating dust and CO+CO₂ gas comae activity behaviors. A better understanding of these physical characteristics are relevant for planetary defense (e.g., determining nuclei diameters).

The high abundance of volatile ices (e.g., H₂O, CO, CO₂) present in comet nuclei drives outgassing and dust lofting when the surface material is exposed to the Sun, generating comae and tails. While high-cadence and long-baseline observational campaigns producing physical characterization of nuclei and comae exist for a few comets (e.g. 1P/Halley, 9P/Tempel, 67P/Churyumov-Gerasimenko, C/1995 O1 (Hale-Bopp), C/2012 S1 (ISON)) and have allowed determination of single-apparition secular light curves, predictions for the behaviors of an individual comet are notoriously difficult due to the possibility of outbursts, fragmentation events, complete nucleus disintegration and seasonal effects. This high degree of uncertainty for cometary behaviors introduces complications for modeling the brightening trends for individual comets as compared to those for the asteroid populations. Fortunately, characterizing the behaviors of comets in the infrared as an ensemble population is a somewhat more tractable problem. Previous (e.g., COBE [2], AKARI [3], Spitzer [4]) and ongoing surveys (e.g, Pan-STARRS [5], Zwicky Transient Facility [6], ATLAS [7], WISE/NEOWISE [8]) detecting large numbers of comets in the infrared are allowing a framework through which an individual comet’s activity behaviors can be estimated based on behavior trends in infrared emission of the larger ensemble. We are utilizing derived ensemble properties from these observational campaigns to develop a recipe for best simulating the morphological and photometric behaviors for the solar system’s comet populations.

NEOSM will utilize a space-based 50-cm aperture infrared-optimized telescope located at the Sun-Earth L1 Lagrange position. It will contain a single instrument with a dual-channel infrared imaging camera that will survey the sky in bandpasses at 4-5.2 microns (denoted NC1) and 6-10 microns (denoted NC2). NC1 images of comets will mostly contain thermal emission (for comets within ~3 au of the Sun) from the nucleus and any dust coma/tail/trail. Additionally, the bandpass of NC1 covers the CO₂ gas ν₃ vibrational mode emission band centered at 4.26 microns and the CO gas vibrational mode emission band centered at 4.67 microns, which will allow detection of a comet’s combined CO+CO₂ gas coma. This method of detecting such cometary volatiles via broadband imaging has had much success in the past with Spitzer (e.g. [4, 9]) and WISE/NEOWISE (e.g. [10, 11]). The longer wavelength NC2 images of comets will measure thermal emission from nuclei and dust. Because of the particular bandpasses of NC1 and NC2 we are currently focusing on developing methods of modeling cometary activity behaviors utilizing derived (1) nuclei cumulative size distributions, (2) dust activity behaviors as characterized by empirical trends of the εfρ parameter and (3) CO and CO₂ gas comae trends based on the previously mentioned past and ongoing surveys. Future efforts by the NEOSM Investigation Team will focus on incorporation of other characteristic cometary phenomena (e.g., dust tails and trails) to help refine expected detection efficiencies and coma and/or tail flux removal for robust nucleus size estimation.

Acknowledgements

NEOSM is a project sponsored by NASA’s Planetary Defense Coordination Office, a division of NASA’s Planetary Science Directorate.

References

[1] Lilly (Schunova) et al., 2020, AAS Meeting Abstracts, 385.04.

[2] Lisse et al., 2002, IAU Colloq. 181, Vol. 15, 259.

[3] Ootsubo et al., 2012, ApJ, 752:15.

[4] Fernandez et al., 2013, Icarus, 226, Issue 1.

[5] Denneau et al., 2013, PASP, 125:926.

[6] Masci et al., 2019, PASP, 131:995.

[7] Tonry et al., 2018, PASP, 130:988.

[8] Mainzer et al., 2011, ApJ, 731:53.

[9] Kelley et al., 2013, Icarus, 225:475.

[10] Bauer et al., 2015, ApJ, 814:85.

[11] Bauer et al., 2017, AJ, 154:53.

How to cite: Schambeau, C., Mainzer, A., Kramer, E., Fernandez, Y., Bauer, J., Harrington-Pinto, O., Lilly (Schunova), E., Grav, T., Surace, J., Abell, P., Buratti, B., and NEO Surveillance Mission Team, T.: Methods for Simulating Comet Populations in Preparation for the Near-Earth Object Surveillance Mission, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-460, https://doi.org/10.5194/epsc2020-460, 2020.

Abstract

This work presents the results from a set of low-velocity impact simulations that were performed using the soft-sphere Discrete Element Method and two different codes: pkdgrav and Chrono. In these tests, a spherical projectile is dropped onto a bed of glass beads, where the size of the container, the size of the beads, the impact velocity of the projectile, and the gravity-level are varied. First, the simulation results are compared against experimental data and theoretical collision behaviors. Then, the results from pkdgrav and Chrono are examined in more detail and are compared in terms of output and performance differences.

Introduction

The robotic exploration of small-body surfaces often involves the direct interaction between a slow-moving mechanism and a bed of loose regolith. Take, for instance, the two most recent missions to near-Earth asteroids. In 2018 and 2019, the Hayabusa2 spacecraft deployed several landers to the surface of the asteroid Ryugu [9]. In October of this year, the OSIRIS-REx mission will collect a sample from the surface of the asteroid Bennu using a ‘touch-and-go’ mechanism [2]. One way to develop our understanding of lander-surface interactions is to study low-velocity collisions dynamics for penetrators of diverse shapes and sizes.

The motion of spherical, cylindrical, and conical penetrators through different granular media has been extensively studied for the terrestrial gravity environment [1] but much less so for low-gravity levels. [3] and [4] conducted low-velocity impact experiments under both Earth and reduced-gravity conditions using two different projectile shapes (spherical and cubic) and four different granular surface materials (quartz sand and 1.5 mm, 5 mm, and 10 mm glass beads). The Earth-gravity tests were completed using a static laboratory set-up, while the reduced-gravity tests were performed using an Atwood-type drop-tower [7]. In both configurations, in-situ accelerometers were used to monitor the projectile’s motion.

[4] discuss the dependency of certain collision parameters, like collision duration and collision depth, on gravity-level. However, the work examines a limited range of collision cases. Due to internal friction and sizing constraints, the ISAE-Supaéro drop-tower can only reach gravity levels spanning from 0.2 to 1.5 m/s^2. The easiest way to compliment the experimental study is through numerical modeling. This work replicates and expands upon a sub-set of the impact experiments performed by [3] and [4].

Simulations

The numerical simulations presented in this study are conducted using two different codes. The first code, pkdgrav, is frequently used for small-body related studies [5]. The second code, Chrono, is presented as an open-source alternative to pkdgrav [7, 8]. One objective of this work is to validate the Chrono code by comparing the simulation results against observations from pkdgrav, collision theory, and laboratory experiments. A second objective is to compare Chrono and pkdgrav in terms of input parameters, results, and overall computational performance.

At this time, simulations are restricted to the “static” (1g) set-up with the spherical projectile and the glass-bead surface material. In the static experiments, a 1 kg, 10 cm diameter sphere is dropped into an aluminum bucket with a base diameter of 31.5 cm and a rim diameter of 35 cm (Fig. 1). The fill height of the bucket ranges from 1 to 17 cm, and the impact velocity of the projectile varies from approximately 0 to 1.2 m/s.

For simplicity, the simulations assume that the bucket has a constant diameter and that the container is filled with either 5 mm or 10 mm diameter glass beads (Fig 2). In order to investigate the influence of the container size on the collision behavior of the projectile, the diameter and fill height of the bucket are varied from 31.5 and 40 cm and from 2 to 18 cm respectively. Though experimental data for this set-up only exists for the 1g case (g = 9.81 m/s²), simulations are conducted for gravity levels ranging from 0.2 to 9.81 m/s².

Results

The simulations are in general agreement with trends observed in the 1g impact experiments from [4]. The results are discussed within the context of existing collision models and theories and are used to identify the optimal material properties for the simulated glass beads. The coefficients of friction differ between pkdgrav and Chrono. This is to be expected, since the two codes implement different friction models. Similarly, the computation times vary due to differences in the codes’ architectures and parallelization methods.

Both the experiments and simulations show that the container fill height does not influence collision behavior as long as the particle bed is at least 8 cm deep, at least for the test cases where g = 9.81 m/s^2. Chrono is used to determine if the same conclusion applies for test cases where g = 0.2 m/s^2, or the lowest gravity-level obtained by the drop-tower set-up.

Acknowledgements

We would like to thank ISAE-Supaéro and the Centre National d’Études Spatiales (CNES) for financially supporting this research effort.

References

[1] Clark, Abram H., and Robert P. Behringer. "Granular impact model as an energy-depth relation." EPL (Europhysics Letters) 101.6 (2013): 64001.

[2] Lauretta, D. S., et al. "OSIRIS-REx: sample return from asteroid (101955) Bennu." Space Science Reviews 212.1-2 (2017): 925-984.

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

[4] Murdoch, N., et al. “Low-velocity and shallow impacts into granular material: application to small-body landing.” (2020) [in preparation].

[5] Schwartz, S. R., et al. “An implementation of the soft-sphere discrete element method in a high-performance parallel gravity tree-code.” Granular Matter, 14(3) (2012): 363-380.

[6] Sunday, Cecily, et al. "A novel facility for reduced-gravity testing: A setup for studying low-velocity collisions into granular surfaces." Review of Scientific Instruments 87.8 (2016): 084504.

[7] Sunday, C., et al. “Validation of Chrono for granular DEM simulations in reduced-gravity environments.” (2020) [submitted].

[8] Tasora, Alessandro, et al. “Chrono: An open source multi-physics dynamics engine.” International Conference on High Performance Computing in Science and Engineering, Springer, Cham , 2015.

[9] Watanabe, Sei-ichiro, et al. "Hayabusa2 mission overview." Space Science Reviews 208.1-4 (2017): 3-16.

How to cite: Sunday, C., Thuillet, F., Murdoch, N., Yp-Tcha, A., Drilleau, M., and Michel, P.: Low velocity impact simulations with pkdgrav and Chrono, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-246, https://doi.org/10.5194/epsc2020-246, 2020.

Abstract

The present work aims to study the use of a kinetic impact technique as a way to deflect asteroids that may present some risk of collision with the Earth at a given time. This is a very current topic of research and it is related to planetary defense. It has been receiving the attention of researchers worldwide. In the work to be developed here, intend to evaluate in more detail the possibility of deflecting the orbit of asteroid 101955 Bennu, taking into account specific aspects.

Asteroids are the smallest bodies in the solar system, usually with diameters on the order of a few hundred’s, or even only tens of kilometers. The total mass of all asteroids in the solar system must be less than the mass of the Earth’s Moon. Despite this fact, they are objects of great importance. They must contain information about the formation of the solar system, since its chemical and physical compositions remain practically constant over time. These bodies also pose a danger to Earth, as many of these bodies are on a trajectory that passes close to Earth. There is also the possibility of mining on asteroids, in order to extract precious metals and other natural resources.

Asteroids have a very irregular shape, which makes their study difficult. In addition, they have rotational movement, in general very complex, due to their irregular shape. Asteroids are classified into groups: NEA (Near-Earth Asteroid), Trojans, Kuiper Belt, etc. NEAs are the most dangerous from the point of view of collision with Earth, since their trajectories are close to Earth’s orbit. There is even a mission, AIDA (Asteroid Impact and Deflection Assessment), in which ESA aims to achieve a binary system (65803 Didymos). There is also the American Asteroid Redirect Mission (ARM), which plans to collected item over a long period of time to deflect the asteroid’s orbit. Within this context, the present work intends to focus on the application aimed at the deflection an asteroid on a hazardous course with Earth, utilizing the technique of kinetic impact.

For this project we are using the numerical integrator package Mercury N-bodies, designed to simulate the orbit of bodies of different sizes around a central body. The different numerical integrators present in Mercury allow the user to obtain a good relationship between the computational cost and the resolution of the simulations. Mercury also allows the user to add forces from sources other than gravity, as well as to modify algorithms such as collisions that, by default, result in the perfect fusion of two bodies with mass conservations and linear momentum.

For the input data for integration, the components of position and velocity of the bodies were used, taken from the JPL Horizons website, for the same date used in this work. The mass of (7,329 ± 0.009) × 10¹⁰kg and density of 1190 ± 13 kg.m^-3 were considered for the asteroid Bennu (Kováčová et al.2020, Lauretta et al.2019a, Scheeres et al. 2019). We are not considering the composition and dimensions of the asteroid, as well as its rotation properties and minor disturbances that may occur due to its non-linear dynamics.

For this work, we used velocity variations simulating an impact opposite to the direction of the asteroid's movement (Δv negative) and also in the same direction of movement of the asteroid (Δv positive). The variations used here were from 10 mm/s to 50 mm/s. We also divided the impact point into 16 parts of the asteroid's orbital period, approximately 27 days to achieve greater precision in the results and also to reach the perihelion and aphelion points.

We are also monitoring the influence of all planets in the solar system, applying the technique of deflecting the asteroid considering all the planets of the solar system, a system of 4 bodies (Sun, Earth, Moon and asteroid) and a system of 5 bodies (Sun, Earth, Moon, Jupiter and asteroid), to determine Jupiter's influence on the results.

Acknowledgements

This work is funded by Fapesp (Proc. 2018/17864-1 ).

References

[1] J.E.Chambers (1999) “A Hybrid Symplectic Integrator that Permits Close Encounters between Massive Bodies”. Monthly Notices of the Royal Astronomical Society, vol 304, pp793-799..

[2]Holsapple, K.A., Housen, K.R. 2016. Momentum transfer in asteroid impacts. I. Theory and scaling. Icarus 221, 875-887.

[3] Brophy, J.R., AND Muirhead, B., Near-Earth Asteroid Retrieval Mission (ARM) Study. IEPC-2013-82, Presented at the 33rd International Electric Propulsion Conference, Washington, DC, October 6-10, 2013.

[4] Cheng, A. F. et al. Asteroid Impact Deflection Assessment mission: Kinetic impactor. AIDA TEAM. Avances in Space Research. Vol. 121, pages 27-35. 2016. http://dx.doi.org/10.1016/j.pss.2015.12.004.

[5] DART. Dart mission: Double Asteroid Redirection Test. http://dart.jhuapl.edu/Mission/index.php. Accessed in February, 2017.

[6] Falcone, G. et al. Attitude Control of the Asteroid Redirect Robotic Mission Spacecraft with a Captured Boulder. AIAA/AAS Astrodynamics Specialist Conference, AIAA SPACE Forum, (AIAA 2016-5645), 2016. HTTP://DX.DOI.ORG/10.2514/6.2016-5645.

[7] M. Kováčová, R. Nagy, et al. 101955 Bennu and 162173 Ryugu:dynamical modelling of ejected particles to the Earth. Planetary and Space Science. 2020. https://doi.org/10.1016/j.pss.2020.104897

[8] Jutzi, M., Michel, P. 2014. Hypervelocity impacts on asteroids and momentum transfer. I. Numerical simulations using porous targets. Icarus 229, 247-253.

[9] Kerslake, T.W. et al..”Structural Design Considerations for a 50 kW-Class Solar Array for NASAs Asteroid Redirect Mission”, 3rd AIAA Spacecraft Structures Conference, AIAA SciTech Forum, (AIAA 2016-1701). 2016. http://dx.doi.org/10.2514/6.2016-1701.

[10] Lauretta, D. S., DellaGiustina, D. N., Bennett, C. A. et al.: The unexpected surface of asteroid (101955) Bennu, Nature 568, 55-60, 2019a.

[11] Scheeres, D. J., McMahon, J. W., French, A. S. et al.: The dynamic geophysical environment of (101955) Bennu based on OSIRIS-REx measurements, Nature Astronomy 3, 352-361, 2019.

How to cite: Chagas, B., Prado, A., and Winter, O.: Deflect an hazardous asteroid through Kinetic Impact: Aplication in 101955 Bennu , Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-449, https://doi.org/10.5194/epsc2020-449, 2020.

Most close-in planetary satellites are in synchronous rotation, which is usully the stable end-point of tidal despinning. Saturn's moon Hyperion is a notable exception by having a chaotic rotation. Hyperion's dynamical state is a consequence of its high eccentricity and its highly prolate shape (Wisdom et al. 1984). As many binary asteroids also have elongated secondaries, chaotic rotation is expected for moons in eccentric binaries (Cuk & Nesvorny 2010), and a minority of asteroidal secondaries may be in that state (Pravec et al. 2016). The question of the secondary's rotation is importrant for the action of the BYORP effect, which can quickly evolve orbits of synchrnous (but not non-synchronous) secondaries (Cuk & Burns 2005). Here we report preliminary numerical simulations which indicate that in binary systems with a large secondary and significant spin-orbit coupling a different kind of non-synchronous rotation may arise. In this "barrel instability" the secondary slowly rolls along its long axis, while the longest diameter is staying largelly aligned with the primary-secondary line. This behavior  may be more difficult to detect through lightcurves than a fully chaotic rotation, but would likewise shut down BYORP. Unlike fully chaotic rotation, barrel instability can happen even at low eccentricties. In our presentation we will discuss our theoretical results and their implications for the evolution of binary asteroids, such as the Didymos-Dimorphos pair.

How to cite: Cuk, M., Jacobson, S., and Walsh, K.: "Barrel Instability" for Elongated Secondaries in Binary Asteroids, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-983, https://doi.org/10.5194/epsc2020-983, 2020.