Ejection and Dynamics of Aggregates in the Coma of Comet 67P/Churyumov-Gerasimenko

TL;DR

This study investigates the ejection mechanisms and properties of large aggregates from comet 67P, using observational data and simulations to map their origins and constrain activity models.

Contribution

It provides the first detailed analysis of large aggregate ejection, combining observational tracking with dynamical simulations to identify source regions on the comet surface.

Findings

Aggregates have an average radius of about 5 cm.

Most aggregates originate near terrain boundaries.

Gas drag has limited influence on large aggregate dynamics.

Abstract

The process of cometary activity continues to pose a challenging question in cometary science. The activity modeling of comet 67P/Churyumov-Gerasimenko, based on data from the Rosetta mission, has significantly enhanced our comprehension of cometary activity. But thermophysical models have difficulties in simultaneously explaining the production rates of various gas species and dust. It has been suggested that different gas species might be responsible for the ejection of refractory material in distinct size ranges. This work focuses on investigating abundance and the ejection mechanisms of large ($\gtrsim$ 1 cm) aggregates from the comet nucleus. We aim to determine their properties and map the distribution of their source regions across the comet surface. This can place constraints on activity models for comets. We examined 189 images acquired at five epochs by the OSIRIS/NAC instrument. Our goal was to identify bright tracks produced by individual aggregates as they traversed the camera field of view. We generated synthetic images based on the output of dynamical simulations involving various types of aggregates. By comparing these synthetic images with the observations, we determine the characteristics of the simulated aggregates that most closely resembled the observations. We identified over 30000 tracks present in the OSIRIS images, derived constraints on the characteristics of the aggregates and mapped their origins on the nucleus surface. The aggregates have an average radius of $\simeq5$ cm, and a bulk density consistent with that of the comet's nucleus. Due to their size, gas drag exerts only a minor influence on their dynamical behavior, so an initial velocity is needed in order to bring them into the camera field of view. The source regions of these aggregates are predominantly located near the boundaries of distinct terrains on the surface.