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Gravitation of Rubble-pile Asteroid with Internal N-body Structure

Periodic Reporting for period 2 - GRAINS (Gravitation of Rubble-pile Asteroid with Internal N-body Structure)

Reporting period: 2019-06-01 to 2020-05-31

"In the last decades, both remote and in-situ observations have brought evidence to support the idea that small and medium-size (up to few hundreds of km) asteroids are made of loosely consolidated material, namely ""rubble piles"". The idea behind GRAINS is to study these peculiar celestial object by means of numerical simulations of gravitational aggregation and granular dynamics. The goal is to gain insights on the properties, dynamics and evolution of these objects. In particular, their internal structure is largely unknown, due to the lack of data caused by technological limitations in assessing them through remote observations and by the limited number of in-situ measurement opportunities.
Asteroids are of crucial importance for our society. They offer a unique and low-cost opportunity for deep-space technological development and represent the natural pathway for the human and robotic exploration of our Solar System. They have been identified worldwide by the major Space Angencies as the next step in the path towards the human exploration of Mars. In the last few years, asteroids have been identified as potential resources and asteroid mining has become a focus topic in the worldwide industrial community. Mining and harvesting resources from asteroids would be important not only for returing these materials to Earth, but also to provide low-cost and in-orbit fuel to support the exploration of our Solar System. Finally, asteroids represent a singular threat for humanity. In the past years, all major Space Angencies have started planetary defense offices, to monitor the trajectory of these objects and to help mitigating the risk of impacts.
The knowledge of asteroids and their interior is crucial to plan effective planetary defense mitigation actions, to exploit their resources and to fully leverage the opportunities they offer."
"The first year of the project has been devoted to the development of the numerical code to be used for the study of ""rubble pile"" scenarios and its validation. The code has been developed and tested to deal with a large number of bodies, mutually interacting through gravity and contact/collisions. The code has been implemented with a parallelized architecture to run on GPU and CPU clusters, to improve performance and to enable the simulation of a large number of bodies (up to millions).
Test cases implemented include the study of rubble pile reshape dynamics and the study of the close-proximity environment near these bodies, modelled as granular systems. Mission and science scenarios to be studied have also been identified and proof-tested using the newly implemented code. Science scenarios include:
- formation of rubble piles after disruption event
- evolution of rubble piles after spin-up
- equilibrium shapes of rubble-pile objects
- interaction of rubble piles with external actions (e.g. tidal forces induced by close encounters)
Mission scenarios include:
- modeling granular soil features
- interaction between lander and soil
During the second year of the project the code implemented has been exploited to study selected science and mission scenarios. Novel results on the dynamics and properties of rubble pile objects have been found, thanks to the capability of the code to deal with more realistic particles, compared to existing state-of-the-art implementations.
Relevant results have been reported in journal papers and presented at technical conferences."
Currently, the gravitational-granular problem is studied using N-body solvers, whose typical capabilities are limited to the handling of contact and collision interactions between spherical particles. The code developed within GRAINS is capable to deal with non-spherical particles, which might be chosen to have any given or random irregular shape. This represent a major step forward, towards a more realistic representation of the physical phenomenon. It is known from terrestrial applications and experimental data that, while dealing with granular media, a very relevant difference exists when comparing spheres vs real irregular fragments. This was never done before because of limitations in the capability of the numerical codes in use. GRAINS makes use of a cutting edge methodology and brings together numerical methods from different disciplines (engineering and astrophysics) into a single implementation that is capable of dealing with irregular fragments, while considering both gravity and contact/collisions.
The project has the potential to study the dynamics and internal properties of rubble pile asteroids with a new numerical tool, more realistic compared to current capabilities.
force distribution inside the asteroid
rubble pile model of asteroid Bennu
terrain features
lander interaction with soil