Six outbursts of comet 46P/Wirtanen
Support for this work was provided by the NASA Solar System Observations program (80NSSC20K0673), the Space Telescope Science Institute (HST-GO-15372), the National Science Foundation (PHY-2010970), the National Research Foundation (NRF; No. 2019R1I1A1A01059609), the MINEDUC-UA project ESR1795, the European Union H2020-MSCA-ITN-2019 under Grant no. 860470 (CHAMELEON), and by the Novo Nordisk Foundation Interdisciplinary Synergy Program (NNF19OC0057374). ; Cometary activity is a manifestation of sublimation-driven processes atthe 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 ∼104 to 106 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 (∼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. ; Publisher PDF ; Peer reviewed