Inner coma of comet 67P/Churyumov-Gerasimenko during increased activity at perihelion on 2015 August 22-23

Kleshchonok V.; Sierks H.; Güttler C.

Abstract

The study presents observations of the coma of comet 67P/Churyumov-Gerasimenko using the Wide Angle Camera of the OSIRIS instrument aboard the Rosetta spacecraft on 22-23 August 2015. An outburst occurred on August 22, resulting in the release of a significant amount of icy particles. The spatial distribution of CN, OH, NH, NH, and O i emissions was analysed. The brightness of CN emission exhibits weak dependence on position angle and distance from the nucleus, unlike other emissions, which peak strongly in the solar direction. The ability to determine the bulk density of dust particles through photometry of the shadow cast by the nucleus has been demonstrated. The distribution of the bulk density of dust particles reveals the existence of two components, each characterized by different rates of density decrease with distance from the nucleus: larger particles are located closer to the nucleus, while smaller particles dominate in the region of free expansion. In the free expansion region, the power-law index describing the decrease in volumetric density of dust particles with distance is significantly greater than -2. This is attributed to the rapid fragmentation of dust resulting from the evaporation of volatile components in the free expansion area.