The analysis of dust and gas emission at 67P/Churyumov-Gerasimenko sheds light on cometary activity

The primary goal of this work is to investigate the properties of the inner coma of comets and establish connections between the processes occurring within it and specific locations on the surface and subsurface of the comet. The analysis of gas and dust in the inner coma and their connection with the surface of comets is crucial to understand the context of cometary activity and represents an important reference for the ESA and JAXA missions as Comet Interceptor and for small bodies showing ‘’cometary activity’’. Additionally,  future Vera C. Rubin Observatory observations, the James Webb Space Telescope (JWST), and the Extremely Large Telescope (ELT) will increase the need for understand comet activity as they rapidly discover and characterize new objects. Those efforts rely on the capability to model and forecast the activity of comets, which in turn relies on connecting observed activity to surface properties and regions.

The work is developed in two parts:

1-  Our first focus is the analysis of the dust and gas coma of comet 67P using data acquired by the ESA Rosetta mission during the period between July and November 2015, when activity was near its peak postperihelion.

2-  The second focus is the development of a Lagrangian code based on the Smoothed Particle Hydrodynamics (SPH) method to investigate transient phenomena, such as volatile and refractory emissions from the surface (M. Teodori et al. 2024, 2025).

The Visible InfraRed the Thermal Imaging Spectrometer (VIRTIS) and the ALICE ultraviolet spectrograph, observed and detected a series of outbursts and jets (Rinaldi et al. 2018, Noonan et al. 2021). H2O, CO2, and O2 were all indirectly observed by ALICE within outbursts via emission fingerprints of dissociative electron impact from the daughter products H, C, and O, identified in the spectra as the first two members of the H I Lyman series, OI multiplets at 1152, 1304, and 1356 Å, and weak multiplets of C I at 1561 and 1657 Å . VIRTIS detected and characterized the dust properties of the jets and outburst in terms of radial profile, light curve, color, and dust mass loss in the VIS and IR wavelength range. The outburst observations show that mixed gas and dust outbursts can have different spectral signatures representative of their initiating mechanisms, with outburst showing indicators of a cliff collapse origin or showing fresh volatiles being exposed via a deepening fracture. Preliminary analysis shows the cometary activity observed after some outburst events has a moderate CO2/H2O ratio, while others show only a large increase in reflected light due to dust. When connected to specific surface regions and provided with the proper spectral signal, this analysis opens up the possibility of remote spectral classification of cometary activities with future work.

The second focus of this work is to consider the physical processes driving the comet activity. We aim at simulating gas and dust emission from a surface fracture, by introducing an advanced numerical model that adopts the Smoothed Particle Hydrodynamics (SPH) approach. The code accounts for multiple components and incorporates several physical mechanisms. Among them, phase transitions (mainly sublimation and deposition), viscous dynamical interaction between gas and solid components (dust and eventually icy grains), solar radiation, and volatile-surface dynamical and thermal interactions. Preliminary results will be presented during this session.