Investigating the physical properties of outbursts on comet 67P/Churyumov–Gerasimenko

Abstract : Cometary outbursts on several comets have been observed both by ground-based telescopesand byin situinstruments on spacecraft. However, the mechanism behind these phenomenaand their physical properties are still unclear. The optical, spectrocopic and infrared remoteimaging system (OSIRIS) onboard theRosettaspacecraft provided first-hand informationon the outbursts from comet 67P/Churyumov–Gerasimenko during its perihelion passage in2015. The physical properties of the outbursts can be investigated by examining the timeseries of these high-resolution images. An analysis is made of the wide- and narrow-angleimages obtained during the monitoring of the outburst sequences, which occurred between Julyand September in 2015. A ring-masking technique is used to calculate the excess brightnessof the outbursts. The ejected mass and expansion velocity of the outbursts is estimated fromdifferences in images made with the same filter (orange filter). The calculated excess brightnessfrom these outburst plumes ranges from a few per cent to 28 per cent. In some major outbursts,the brightness contribution from the outburst plume can be one or two times higher than thatof the typical coma jet activities. The strongest event was the perihelion outburst detected justa few hours before perihelion. The mass ejection rate during a generic outburst could reacha few per cent of the steady-state value of the dust coma. Transient events are detected bystudying the brightness slope of the outburst plume with continuous streams of outflowinggas and dust triggered by driving mechanisms, as yet not understood, which remain active forseveral minutes to less than a few hours.