Mechanics of multi-component asteroid systems

Multi-component asteroid systems can be defined as collections of several distinct components, each of which may be a rubble pile body itself. There are a number of clear examples of these systems that have been observed, including binary and triple asteroids, contact binaries, asteroid pairs and clusters, and any asteroid system that has distinct components which may themselves be rubble piles. Current observations indicate that almost 50% of small, rubble pile asteroids are multi-component systems, thus these form an essential aspect of the asteroid population and their formation circumstances and evolution remain a largely open question. Of specific interest is how the different components interact with each other and form the observed asteroid population. It can be shown that for kilometric-scale and smaller bodies that such separated components can rest on each other without undergoing large-scale shape failure (Meyer & Scheeres, ApJL 963:L14, 2024), thus indicating that the components of contact binaries can themselves be rubble piles. This opens up the analysis of these bodies as few-component systems where these components can orbit each other, rest on each other, and even undergo slow collisions while still maintaining their distinct components. 

In this work we leverage these observations to analyze how the formation and evolution of such multi-component systems can be viewed in a consistent framework. To do this we leverage recent theoretical advances and analysis tools reported in (Scheeres, CMDA 135:35, 2023) and (Scheeres, Icarus  436:116563, 2025) to present a unified approach to modeling and constraining the formation and evolution of multi-component systems. These models enable us to evaluate the conditions for a system to form a contact binary or orbital binary at formation, conditions under which a system can eject a component to become an asteroid pair or cluster, pathways for a system to collapse into a contact binary, implications of exogenous forces, and the overall pathways that these systems can follow. 

These mechanical analyses are based on modeling the components as semi-rigid bodies and tracking the total angular momentum and energy of the system, both orbital and rotational, and the relative mass distributions between the components. Both analytical and numerical simulation approaches can be used. Based on fundamental celestial mechanics constraints, we can delineate the different energetically stable configurations that a multi-component system can have as a function of its total angular momentum. Thus, if a system is spun up or down due to YORP, the possible configurations of the system will change with the changing angular momentum. If a multi-component system reaches a fission spin limit, which generally occurs before surface shedding of material, its subsequent evolution will be largely dictated by the relative masses of the different components, and can lead to the creation of an asteroid pair and a slowly rotating primary, settle into a binary system, or can reconfigure its components and evolve further. The theory can provide a clear overarching approach to the analysis of outcomes, which can help inform our interpretation of the asteroidal bodies that we observe from Earth or Space-based observing platforms.  

This talk will apply this methodology to illustrate the possible evolution of several different example systems, and also address the limitations of this modeling approach.