Secondary gas in debris discs released following the decay of long-lived radioactive nuclides, catastrophic or resurfacing collisions

TL;DR

This paper models gas release in debris belts from comet-like bodies, emphasizing the roles of radioactive decay and collisions, and highlights how these processes affect the interpretation of observed gas and dust emissions.

Contribution

It introduces models for gas release from planetesimals considering radioactive decay and collisions, revealing non-proportional relationships between gas and dust emissions.

Findings

Gas release rate is not proportional to dust release rate when non-catastrophic processes dominate.

Non-catastrophic collisions are the main source of gas at earlier times in planetesimal evolution.

Radioactive decay significantly contributes to CO gas around young planetary systems.

Abstract

Kuiper-like belts of planetesimals orbiting stars other than the Sun are most commonly detected from the thermal emission of small dust produced in collisions. Emission from gas, most notably CO, highlights the cometary nature of these planetesimals. Here we present models for the release of gas from comet-like bodies in these belts, both due to their thermophysical evolution, most notably the decay of long-lived radioactive nuclides and collisional evolution, including catastrophic and gentler resurfacing collisions. We show that the rate of gas release is not proportional to the rate of dust release, if non-catastrophic collisions or thermal evolution dominate the release of CO gas. In this case, care must be taken when inferring the composition of comets. Non-catastrophic collisions dominate the gas production at earlier times than catastrophic collisions, depending on the properties of the planetesimal belt. We highlight the importance of the thermal evolution of comets, including crucially the decay of long-lived radioactive nuclides, as a source of CO gas around young (<50Myr) planetary systems, if large (10-100s kms) planetesimals are present.