Post-Impact Ejecta Dynamics in Binary Asteroids



Studying the fate of asteroids ejecta is of scientific interest to understand the dynamics around minor bodies. Indeed, particles orbiting around asteroids can serve as a way to understand their gravitational strength and internal structure. It is also relevant to study natural orbits around asteroids where ejecta particles can potentially be trapped. This would provide with evidence of possible stable orbits around asteroids that can be useful for artificial satellites as CubeSats. Moreover, natural ejecta (i.e. Bennu/NASA’s Osiris-REx mission) and artificial impact ejecta (i.e. Ryugu/JAXA’s Hayabusa2 mission) can pose a risk to a spacecraft operating in close proximity with an asteroid [1]. Previous work in our group have carried out analysis for the fate of asteroid ejecta for Ryugu adopting both semi-analytical methods [2], shooting methods and direct integration of the N-Body planetary dynamical equations [3-4]. All these methods have been developed and validated in real time during the Hayabusa2 operations for a single asteroid model (a python code called goNAER tool was developed [3-4]). The complexity of a binary asteroid system will require to develop a rigorous approach to conduct those analysis for binary asteroids [5]. Dr Soldini is PI of a UKRI project named REMORA - REndezvous Mission for Orbital Reconstruction of Asteroids: a fleet of self-driven CubeSats for tracking and characterising asteroids and it is in partnership with Citadel Space Systems. The REMORA project will lay the foundation for the development of a “space-based early warning system” of a swarm of micro satellites each to individually tag asteroids that could hit the Earth. You will have the opportunity to be involved in the REMORA project activities.

AIM and SCOPE: The scope of the thesis is to investigate the fate of the ejecta after NASA’s DART impact on dimorphos (Didymos’s moonlet). While it is expected that high velocity ejecta particles of mm size will leave the system, natural impact phenomena on asteroids observed from Rosetta spacecraft suggest that dust particles of 1 cm size in diameter can be captured for several months in orbit around the asteroid. This condition can pose a risk to ESA/HERA spacecraft and CubeSats. A collision with small particles can severely damage the spacecraft structure and compromise its functionality. The computation of stable orbits (i.e. terminator orbits) for binary asteroid systems for different size of particles is the major subject of this work. This project shares synergies with the European Space Agency’s HERA and NASA’s DART missions to the binary asteroid Didymos. Dr Soldini is core member of the HERA’s dynamics working group and DART’s Ejecta working group. The candidate will also be expected to be actively involved in the HERA/DART activities.

RESEARCH ENVIRONMENT: You will work within a vibrant and rapidly growing community of space researchers in the Aerospace Division of the School of Engineering at the University of Liverpool. This includes participation in NASA’s DART, ESA’s HERA and JAXA’s Haybusa2 missions.  In addition, you will have the opportunity to collaborate with colleagues from the School of engineering’s robotic lab, Department of Electrical Engineering and Electronics and the computer science group.

REQUIRED SKILLS: We are seeking candidates with a minimum of 2:1 (or equivalent) first degree in Astrophysics, Applied Mathematics, Aerospace Engineering, Computer Science or any other related subject. Experience in one of more of the following areas is required: A strong background in applied math, modeling and simulation, and a good understanding of optimization methods. Excellent coding skills in one computing language e.g., Python or MATLAB or C++. Strong communication and team working skills are essential as well.

HOW TO APPLY: Please apply through the University of Liverpool’s online system How to apply for a PhD - University of Liverpool for a PhD in Aerospace Engineering with a full Curriculum Vitae, covering letter, a two A4 side research proposal, and contact details for at least two academic references. We will only consider serious candidates who are applying for a full-time postgraduate position after conducting an online interview.



Open to UK applicants

Funding information

Funded studentship

FUNDING: The Faculty will fund one PhD studentship granted on current UKRI levels of support: Home fee rate, a Research Training Support Grant (RTSG) and annual stipend granted for 3.5 years for full-time study. Currently, the home fee rate is £4,500, the stipend is £15,609, and the Faculty cover a RTSG of £5000 over the duration of study. The fee rate and stipend will change according to UKRI levels at the time of student registration.





[1] D. Villegas-Pinto, S. Soldini et al, “Temporary Capture of Asteroid Ejecta into Periodic

    Orbits: Application to JAXA’s Hayabusa2 Impact Event”, 30th AIAA/AAS, January,2020.
[2] Soldini et al A generalised methodology for analytic construction of 1:1 resonances

    around irregular bodies: Application to the asteroid Ryugu’s ejecta dynamics, Planetary

    and Space Science, 2019.
[3] S. Soldini et al, “Hayabusa2’s Superior Solar Conjunction Mission Operation: Planning

    and Post-operation Results”, Special Issue of Hayabusa2 – Sample Return Mission to

    the Asteroid Ryugu, Astrodyn, (2020) DOI: 10.1007/s42064-020-0076-7.

[4] S. Soldini et al, “Hayabusa2's Superior Solar Conjunction Phase for Hovering Satellite:

    Trajectory Design, Guidance and Navigation”, Space Sci Rev 216, 108 (2020).

    DOI: 10.1007/s11214-020-00731-5.

[5] F. Ferrari, S. D. Raducan, S. Soldini and M. Jutzi, “Ejecta Formation, Early Collisional

     Processes, and Dynamical Evolution after the DART Impact on Dimorphos”, Planet.

  1. J., 3, 177 (2022).

Example of ejecta simulation for Ryugu

Example of ejecta simulation for Dimorphos