Six Outbursts of Comet 46P/Wirtanen

TL;DR

This study investigates six mini-outbursts of comet 46P/Wirtanen during its 2018 perihelion, analyzing their characteristics, frequency, and possible surface roughness implications, with no evidence of large ejecta observed post-outburst.

Contribution

The paper provides the first detailed analysis of mini-outbursts of comet 46P/Wirtanen, comparing their properties and frequency with other comets, and suggests surface roughness characteristics based on outburst data.

Findings

Mini-outbursts range from -0.2 to -1.6 mag in brightness.

Dust masses are estimated between 10^4 and 10^6 kg.

No macroscopic ejecta was detected in HST images post-outburst.

Abstract

Cometary activity is a manifestation of sublimation-driven processes at the surface of nuclei. However, cometary outbursts may arise from other processes that are not necessarily driven by volatiles. In order to fully understand nuclear surfaces and their evolution, we must identify the causes of cometary outbursts. In that context, we present a study of mini-outbursts of comet 46P/Wirtanen. Six events are found in our long-term lightcurve of the comet around its perihelion passage in 2018. The apparent strengths range from $-0.2$ to $-1.6$ mag in a 5" radius aperture, and correspond to dust masses between $\sim10^4$ to $10^6$ kg, but with large uncertainties due to the unknown grain size distributions. However, the nominal mass estimates are the same order of magnitude as the mini-outbursts at comet 9P/Tempel 1 and 67P/Churyumov-Gerasimenko, events which were notably lacking at comet 103P/Hartley 2. We compare the frequency of outbursts at the four comets, and suggest that the surface of 46P has large-scale ($\sim$10-100 m) roughness that is intermediate to that of 67P and 103P, if not similar to the latter. The strength of the outbursts appear to be correlated with time since the last event, but a physical interpretation with respect to solar insolation is lacking. We also examine Hubble Space Telescope images taken about 2 days following a near-perihelion outburst. No evidence for macroscopic ejecta was found in the image, with a limiting radius of about 2-m.