Modelling dust distribution in the ejecta plume from nonspherical dust dynamics perspectives in support of the LICIACube and DART missions

EPSC Abstracts
Vol.14, EPSC2020-1096, 2020
Europlanet Science Congress 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Modelling dust distribution in the ejecta plume from nonspherical
dust dynamics perspectives in support of the LICIACube and DART
missions
Stavro L. Ivanovski1, Alice Lucchetti2, Maurizio Pajola2, Ivano Bertini3, Giovanni Zanotti4, Davide
Perna5, Elisabetta Dotto5, Vincenzo Della Corte6, Marilena Amoroso7, Simone Pirrotta7, Andrea
Capannolo4, Michele Lavagna4, Alessandro Rossi8, Eugene G. Fahnestock9, Masatoshi Hirabayashi10,
Sabina D. Raducan11, Andrea Meneghin12, Giovanni Poggiali12,13, John R. Brucato12, Gabriele
Cremonese2, and the and the LICIACube team*
1
National Institute for Astrophysics, Italy, Osservatorio Astronomico di Trieste, Trieste, Italy (stavro.ivanovski@inaf.it)
2
INAF-Astronomical Observatory of Padova, Padova, Italy
3
Università degli Studi di Napoli "Parthenope", Napoli, Italy
4
Politecnico di Milano - Bovisa Campus, Dipartimento di Scienze e Tecnologie Aerospaziali, Milano, Italy
5
INAF Osservatorio Astronomico di Roma, Monte Porzio Catone (Roma), Italy
6
INAF Istituto di Astrofisica e Planetologia Spaziali, Roma, Italy
7
Agenzia Spaziale Italiana, via del Politecnico, 00133 Roma, Italy;
8
CNR Istituto di Fisica Applicata “Nello Carrara”, Sesto Fiorentino (Firenze), Italy
9
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
10
    Auburn University, Auburn, AL-USA
11
    Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Impe-rial College London, United
Kingdom
12
    INAF Osservatorio Astrofisico di Arcetri, Firenze, Italy
13
    Università di Firenze, Dipartimento di Fisica e Astronomia, Sesto Fiorentino (Firenze), Italy
*
A full list of authors appears at the end of the abstract

Introduction

On September 30, 2022, NASA’s Double Asteroid Redirection Test (DART, [1]) mission will be the
first space mission demonstrating the kinetic impactor method for planetary defense. DART will
impact Didymos B (a 164±18 m secondary of asteroid (65803) Didymos [2]) with its mass of 650 kg
and at a speed of 6.6 km/s. Such impact is expected to change the secondary orbital period by
about 10 minutes. DART will carry as a piggyback the Light Italian Cubesat for Imaging of Asteroids
(LICIACube, [3]) which will be released from DART ten days before the impact. LICIACube will
provide evidence of the impact and will take multiple images of the target up to a distance of ~55
km from the target. The LICIACube narrow and wide angle cameras - LEIA (LICIACube Explorer
Imaging for Asteroid) and LUKE (LICIACube Unit Key Explorer), respectively – will capture the post-
impact processes coming from in situ events, such as the newly formed crater, the expanding ejecta
and the dynamics of its plume. In particular, the measurement of the motion of the slow (

the initial velocity and mass of ejecta. As input we used the ejecta impact properties (ejecta mass,
velocity, launch position distribution, orientation) constrained with iSALE numerical simulations [5].
We discuss the influence of the non-sphericity of the particles on the dynamical properties of the
plume, such as the velocity and dust spatial distribution, and address the optical thickness not only
in terms of particle size distribution but also as a function of particle shape and orientation.

Dust plume model

We use a 3D+t non-spherical dust model that solves the Euler dynamical and kinetic equations.
Considering free-collisional dust regime we study the effects on the particle dynamics provided with
different shapes, initial particle orientation and velocities as well as torque. Torque is computed from
the law of variation of the angular momentum by using the Euler dynamic equations. The particles
are assumed to be homogeneous, isothermal convex bodies, having the same physical properties of
the target. The dust motion is governed by solar radiation pressure force, initial dynamical
parameters (speed, orientation and torque) and gravity of the asteroid binary system. To compute
the gravity we take into account that Didymos B is orbiting at distance of ~1.18 km the Didymos
primary (780±80 m in size) [6].

As input we use the physical parameters obtained via numerically simulated impact into low-gravity
and strength- dominated asteroid surface done with the iSALE numerical code [5]. A detailed
description of the parameters set used in the impact modelling are reported in Table 1. As an
example, in Fig.1, we show the iSALE simulation of the spatial distribution of tracer particles for 50
ms after the impact.

Table 1: Paremeters used for iSAle simulation. A detailed description can be found in [5].

Fig. 1: A snapshot of the formation of the crater resulting from the iSALE modelling performed with
parameters reported in Table 1. The colorbar represent the peak pressure of the ejecta tracer
particles.

Non-spherical dust motion in the plume

We have studied the motion of non-spherical particles after the impact assuming various set of
initial parameters coming from the iSALE simulations, such as particle mass, shape, initial
orientation, launch position and computed velocity. The Didymos system physical parameters and
particle temperature were taken from [7]. Here, in Fig. 2, we show the velocity and the distance
from the surface where it has been reached for a prolate spheroid (aspect ratio = 2 [4]) with
assumed density 2600 kg/m3. The particle mass is 7.45 x10-2 kg, the initial velocity 0.94 m/s, the
launch position is 11 m from the center of the crater and the initial tilt of the initial velocity vector
away from local surface normal is 46 degrees. We plotted the results for two cases: 1) only the
Didymos B gravity field is considered and 2) the gravity of the whole binary is used. Our results
show that the particle dynamics is sensitive to parameters such as orientation and ejection velocity.

Fig. 2: Velocity and distance at which it has been achieved for a prolate particle (aspect ratio a/b =
2). The complete set of parameters is given in the text. The solid line indicates the case when only
gravity of Didymos B was considered and the dashed line when the gravity of the whole binary was
used (binary was approximated as a mass point).

This study of dust dynamics in expanding ejecta together with LICIACube plume evolution images
can further constrain the momentum transfer efficiency estimation as well as the ejecta velocity and
dust size distribution in the “far-field” expanding plume.

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] Cheng A. F. et al. (2016) Planet. Space Sci., 121, 27-35. [2] de León, J. et al. (2010) Astron.
Astrophys, 517, A23. [3] Dotto, E. et al., (submitted), Planet. Space Sci. [4] Ivanovski S. et al.
(2017), Icarus 282, p. 333 - 350. [5] Raducan, S. D. et al. (2019), Icarus, 329, p. 282 - 295. [6]
Michel, P. et al. (2016) Adv. Space Sci. 57, p. 2529 - 2547. [7] Yu Y. et al. (2017), Icarus 282,
p.313 - 325

and the LICIACube team:
S. Ieva 5, E.Mazzotta Epifani 5, B. Cotugno 14, V. Di Tana 14, I. Gai 15, G. Impresario 14, F.
Miglioretti 14, D. Modenini 2, P. Palumbo 3,6, E. Simioni 2, S. Simonetti 14, P. Tortora 15, M.

Zannoni 15, A. Zinzi 16,7.

                                   and the LICIACube team: S. Ieva 5, E.Mazzotta Epifani 5, B. Cotugno 14, V. Di Tana 14, I. Gai
                                   15, G. Impresario 14, F. Miglioretti 14, D. Modenini 2, P. Palumbo 3,6, E. Simioni 2, S. Simonetti 14,
                                   P. Tortora 15, M. Zannoni 15, A. Zinzi 16,7.

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