The Spatial Architecture of the Main Asteroid Belt: Size, Composition, and Dynamical Gradients

Abstract: The asteroid belt's structure provides a window into its formation and long-term evolution. To understand how dynamical processes have shaped this population, we mapped the joint distribution of asteroid size and composition with orbital elements (semimajor axis, eccentricity, inclination). Using a dataset of 35,623 main-belt asteroids with measured properties, we applied a suite of statistical and machine learning techniques, including one- and two-dimensional binning, Kernel Density Estimation, unsupervised clustering (DBSCAN, Gaussian Mixture Models), and predictive modeling (regression and classification). Our analysis reveals profound structural gradients: asteroid size systematically increases with increasing semimajor axis, and a stark compositional zoning transitions from S-type dominated populations in the inner belt to C-type dominated populations in the outer belt. Kernel Density Estimation highlights the fine-scale density variations in orbital space, while clustering successfully identifies distinct dynamical groups, many corresponding to known asteroid families, each exhibiting characteristic size and compositional distributions. Predictive modeling demonstrates that while orbital location predicts population-level trends, it provides limited predictive power for the properties of individual asteroids, emphasizing the role of stochastic processes like collisions. Furthermore, analysis of mean-motion resonance regions reveals they act as dynamic filters, preferentially depleting smaller asteroids and altering the local compositional mix, consistent with the influence of size-dependent non-gravitational forces such as the Yarkovsky effect. This comprehensive mapping provides a detailed view of the asteroid belt's architecture, illustrating how primordial conditions, collisional evolution, and dynamical sculpting have jointly shaped its present-day configuration.

Subjects:	astro-ph.EP; physics.space-ph
Cite as:	PX:2508.00057