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Comet Outbursts: Linking Gas Composition Changes to Trigger Mechanisms

Presentation #408.05 in the session Comets: Nucleus (Oral Presentation)

Published onOct 23, 2023
Comet Outbursts: Linking Gas Composition Changes to Trigger Mechanisms

Dust outbursts observed during the Rosetta mission on comet 67P/Churyumov-Gerasimenko have produced spectacular images described as fireworks in the literature (Vincent et al., 2016). Nevertheless, little has been published about the in-situ composition of the gas released during these outbursts, as well as the underlying mechanisms that trigger such events. Previous studies suggested potential mechanisms, including cliff collapse (e.g., Pajola et al., 2017), pressure pockets (e.g., Bockelée-Morvan et al., 2022), and the amorphous-to-crystalline phase transition of water (e.g., Agarwal et al., 2017).

Our study presents, for the first time, the long-term evolution of the gas composition in a comet’s coma during outburst events. The mass spectrometer Rosetta/ROSINA DFMS analyzed the gas composition in 67P’s coma for over two years. With this extensive dataset, we were able to match DFMS measurements with published outburst events and hence investigate the origins of these outburst events on comet 67P. Our findings reveal distinct gas composition patterns associated with different trigger mechanisms. Cliff collapses expose fresh ice, resulting in significant water enhancements. These water-dominated events are relatively short-lived and in contrast to long-lasting CO2-driven events. These latter events mostly occur near the comet’s perihelion and coincide with substantial increases of CO2 and other highly volatile species. These species already increased in the gas measurements before the dust events have been observed with Rosetta’s cameras and only declined after a few days. This indicates a much slower triggering process compared to the cliff collapses. We propose that these CO2-driven events originate from sub-surface gas cavities where pressure builds up, similar to a pressure cooker. Enhanced solar flux associated with a smaller distance from the Sun induces the sublimation of highly volatile species, which leads to a gradual pressure increase inside such gas cavities until the bursting event occurs.

By grouping specific changes in the gas composition during cometary outbursts into two distinct categories – rapid water-dominated events and slower, prolonged CO2-driven events – we advance the understanding of cometary activity associated to outbursts.

References: Agarwal, J. et al., 2017, https://doi.org/10.1093/mnras/stx2386 Bockelée-Morvan, https://doi.org/10.1051/0004-6361/202243241 Pajola, M. et al., 2017, ttps://doi.org/10.1038/s41550-017-0092 Vincent, J.-B. et al., 2016, https://doi.org/10.1093/mnras/stw2409

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