The Persistent Activity of Jupiter-Family Comets at 3 to 7 AU

TL;DR

This study analyzes the activity of Jupiter-family comets at 3-7 AU using Spitzer data, revealing that a significant fraction show ongoing activity, especially post-perihelion, with dust production rates influenced by orbital history.

Contribution

It introduces the epsilon-f-rho parameter as a thermal emission measure and provides new insights into the activity patterns and dust production of Jupiter-family comets at large heliocentric distances.

Findings

37% of targets showed dust detection

24% exhibited signs of ongoing or recent activity

Comets with larger perihelion distances may produce more dust

Abstract

We present an analysis of comet activity based on the Spitzer Space Telescope component of the Survey of the Ensemble Physical Properties of Cometary Nuclei. We show that the survey is well suited to measuring the activity of Jupiter-family comets at 3-7 AU from the Sun. Dust was detected in 33 of 89 targets (37 +/- 6%), and we conclude that 21 comets (24 +/- 5%) have morphologies that suggest ongoing or recent cometary activity. Our dust detections are sensitivity limited, therefore our measured activity rate is necessarily a lower limit. All comets with small perihelion distances (q < 1.8 AU) are inactive in our survey, and the active comets in our sample are strongly biased to post-perihelion epochs. We introduce the quantity epsilon-f-rho, intended to be a thermal emission counterpart to the often reported A-f-rho, and find that the comets with large perihelion distances likely have greater dust production rates than other comets in our survey at 3-7 AU from the Sun, indicating a bias in the discovered Jupiter-family comet population. By examining the orbital history of our survey sample, we suggest that comets perturbed to smaller perihelion distances in the past 150 yr are more likely to be active, but more study on this effect is needed.