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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 ∼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.
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This content will become publicly available on May 1, 2026
Activity-induced Near-infrared Spectral Variability at 29P/Schwassmann–Wachmann 1, 2017–2022
Abstract 29P/Schwassmann–Wachmann 1 (SW1) is both the first-discovered active Centaur and the most outburst-prone comet known. The nature of SW1’s many outbursts, which regularly brighten the comet by 5 mag or more, and what processes power them has been of particular interest since SW1’s discovery in the 1920s. In this paper, we present and model four epochs of low-resolution near-infrared spectroscopy of SW1 taken with the NASA Infrared Telescope Facility and Lowell Discovery Telescope between 2017 and 2022. This data set includes one large outburst, two periods of low activity (“quiescence” or “quiescent activity”), and one midsized outburst a few days after one of the quiescent observations. The two quiescent epochs appear similar in both spectral slope and modeled grain size distributions, but the two outbursts are significantly different. We propose that the two can be reconciled if smaller dust grains are accelerated more than larger ones, such that observations closer to the onset of an outburst are more sensitive to the finer-grained dust on the outside of the expanding cloud of material. These outbursts can thus appear very rapid, but there is still a period where the dust and gas are well coupled. We find no strong evidence of water-ice absorption features in any of our spectra, suggesting that the areal abundance of ice-dominated grains is less than 1%. We conclude with a discussion of future modeling and monitoring efforts that might be able to further advance our understanding of this object’s complicated activity patterns.
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- Award ID(s):
- 1950901
- PAR ID:
- 10610723
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- The Planetary Science Journal
- Volume:
- 6
- Issue:
- 5
- ISSN:
- 2632-3338
- Page Range / eLocation ID:
- 119
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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