A semi-analytical approach to modeling the configuration of dust ejected from atmosphereless bodies

Academic Dissertation to be presented with the assent of the Faculty of Science, University of Oulu, for public discussion in the Auditorium L10, on April 25th, 2025, at 12 o’clock noon.

Abstract

The study of dust dynamics is essential for understanding various processes in the Solar System, ranging from the evolution of small bodies to the formation of potentially habitable environments. Over the past decades, numerous space missions have been conducted, providing extensive datasets that offer insights into the dynamics and composition of dust in diverse Solar System environments. A tool for analyzing such data from a dynamical perspective is therefore highly relevant.

This thesis presents a semi-analytical approach to modeling dust dynamics. Using the formulae of the gravitational two-body problem, we derived mathematical expressions for the spatial number density of dust particles ejected from atmosphereless bodies at any given point in the vicinity of the dust source. Our model describes the physical and dynamical properties of dust at ejection statistically with a set of continuous distributions of arbitrary functional forms. This freedom enables the model to accommodate a wide range of dust ejection scenarios. Furthermore, the resulting solution for the dust number density is a continuous function too, offering flexibility in selecting the exact location for evaluation. This contrasts with approaches that rely on integrating individual dust particle trajectories, which typically require averaging the dust number density over grid cells.

Our approach led to the development of two models and their corresponding software implementations in Fortran-95. The first model, implemented as the package DUDI, describes dust ejection from atmosphereless spherical moons, accounting only for the moon’s gravity in dust dynamics. The second model, implemented as the package DUDI-heliocentric, addresses dust ejection from asteroids and comets, where the gravity of the dust parent body is neglected, and particle motion is governed by solar gravity and radiation pressure. Both tools enable efficient computation of dust number density using modest computational resources.

We employed the DUDI package for modeling the Enceladus dust plume. We fitted model parameters by integrating insights from prior research on Enceladus with recent advances in the interpretation of in situ data from the Cassini Cosmic Dust Analyzer, particularly the number density and compositional profiles obtained during Cassini’s plume traversals. Our model is self-consistent and successfully reproduces the observational data. Using this model, we estimated the plume’s dust production rate as at least 28 kg/s and determined the proportions of different types of dust particles in the plume, finding that salt-rich dust contributes less than 1% to the plume’s mass.

We used DUDI-heliocentric to investigate the dust environment of the near-Earth asteroid 3200 Phaethon and the role of the dust grains’ dynamical characteristics at ejection in shaping this environment. Specifically, we analyzed how the dust cloud around the asteroid changes with varying ejection speed distribution. Additionally, we demonstrated the capability of DUDI-heliocentric to reconstruct a comet tail image, using comet C/1996 B2 Hyakutake near its perihelion as a case study.