Peter Wurz

Dust and gas outbursts are recurrent cometary phenomena, playing a crucial role in shaping the coma. Proposed outburst trigger mechanisms include cliff collapse, pressure pockets, and amorphous-to-crystalline phase transition of water ice; however, the underlying processes remain inadequately understood. In this study, we analyse Rosetta/ROSINA data from multiple outbursts on comet 67P/Churyumov-Gerasimenko and present the evolution of the gas composition in the comet’s coma during outburst events. We distinguish two distinct categories of cometary outbursts on the comet: water-driven events characterized by rapid (minutes to hours) changes in coma composition, and CO2-driven events displaying a slow, prolonged (hours to days) increase in highly volatile species. We tentatively associate these different gas composition patterns with different trigger mechanisms. Exposure of fresh ice due to cliff collapse leads to a notable water enhancement, while most perihelion outbursts coincide with substantial density increases of CO2. We propose that these CO2-driven events originate from subsurface gas-filled cavities, whose walls are suggested to have been sealed by earlier refreezing of CO2 migrating from warmer spots, hence increasing the cavity pressure required to burst.

The Mars Ion and Neutral Particle Analyzer (MINPA) onboard Tianwen-1 aims to study the interaction between Mars and the solar wind via in situ ion measurement and energetic neutral atom imaging. Despite the efforts for Ultra-Violet suppression in MINPA design, 0.48% of ion observations from November 2021 to July 2022 were identified as UV-contaminated. The UV emissions primarily penetrate into the instrument through the ENA entrance. Statistically, the distribution of the UV contamination in phase space typically spans 3 to 4 azimuth sectors. The contamination is uniformly distributed across the polar dimension while, in the energy and mass dimensions, it is proportional to the time-of-flight duration. Comparisons between the in-flight performance and ground calibration suggest that azimuthal broadening and intensity variations of the contamination may result from differing responses across the azimuthal sectors. Based on the characteristics of the UV impact on MINPA ion observations, a removal algorithm is proposed to reduce contamination while preserving valid signals, which improves the data quality effectively and benefits the interpretation of MINPA’s ion measurements in the Martian space environment. The cause, effect, and distribution of the UV contamination obtained by this study may serve as a reference for other space ion observations.