Cometary Activity Beyond The Planets

TL;DR

This paper models the sublimation of super-volatile ices in comets at large heliocentric distances, predicting observable activity beyond the planetary region due to heat transport transitions in the nucleus.

Contribution

It introduces a detailed model of gas transport and sublimation in comets, explaining activity at large distances and predicting future observable activity beyond the planets.

Findings

Localized CO sublimation increase near 150 AU

Transition in heat transport regimes affects sublimation

Predicted activity in inbound and interstellar comets at large distances

Abstract

Recent observations show activity in long-period comet C/2017 K2 at heliocentric distances beyond the orbit of Uranus. With this as motivation, we constructed a simple model that takes a detailed account of gas transport modes and simulates the time-dependent sublimation of super-volatile ice from beneath a porous mantle on an incoming cometary nucleus. The model reveals a localized increase in carbon monoxide (CO) sublimation close to heliocentric distance rH = 150 AU (local blackbody temperature around 23 K), followed by a plateau and then a slow increase in activity towards smaller distances. This localized increase occurs as heat transport in the nucleus transitions between two regimes characterized by the rising temperature of the CO front at larger distances and nearly isothermal CO at smaller distances. As this transition is a general property of sublimation through a porous mantle, we predict that future observations of sufficient sensitivity will show that inbound comets (and interstellar interlopers) will exhibit activity at distances far beyond the planetary region of the solar system.