Exocometary physics: material release and tails

TL;DR

This paper reviews the physical mechanisms of mass loss from exocomets and their observable signatures across diverse stellar environments, providing a framework to interpret exocometary activity and its dependence on stellar properties.

Contribution

It offers a comprehensive comparison of gas and dust production mechanisms in exocomets and examines how these processes vary with different stellar conditions, including case studies of four systems.

Findings

Mass loss mechanisms vary significantly with stellar environment.

Stellar luminosity and activity influence ejecta composition and dynamics.

Exocomet behavior helps explain the prevalence around A-type stars.

Abstract

Despite decades of observations, the physical processes governing mass loss from small bodies beyond our Solar System remain poorly constrained. These exocomets are often treated as analogs of Solar System comet, yet the stellar environments they inhabit spans a wide range in terms of luminosity, stellar winds, and evolutionary stage, leading to potentially very diverse physical behaviors. Within our Solar System, small bodies lose material through a range of mechanisms, including sublimation, desorption, impacts, and/or sputtering. Once released, the composition and dynamics of the ejecta are then altered by additional processes, such as dust sublimation, ionization, and radiation pressure. In extrasolar systems, these mechanisms unfold under vastly different radiative and plasma conditions, leading to a rich diversity of mass-loss pathways and observable signatures. This work reviews our understanding of the mechanisms driving mass loss from small bodies and the subsequent evolution of ejecta in diverse stellar environments. We compare the physical and chemical mechanisms that drive gas and dust production, and investigate how they scale with stellar luminosity, temperature, and activity. We then examine the processes that modify the composition of the ejecta (e.g., dust sublimation, dissociation, or ionisation) and its dynamics (e.g., radiation pressure or stellar winds). To illustrate how these processes vary across different stellar environments, we use four well-studied planetary systems as case studies: the Sun, $\beta$ Pictoris, AU Microscopii, and WD 1145+017. By exploring how cometary tails behave under such diverse conditions, this work provides a physical framework for interpreting exocometary activity and sheds light on why A-type stars, such as the famous $\beta$ Pictoris, are over-represented in the population of exocomet-hosting stars.