Changes in the physical environment of the inner coma of 67P/Churyumov-Gerasimenko with decreasing heliocentric distance

TL;DR

This study uses OSIRIS camera data to analyze how the gas emissions and physical environment of comet 67P's inner coma change with decreasing heliocentric distance, revealing variations in gas sources and electron impact effects.

Contribution

It provides new insights into the spatial distribution and sources of gas emissions in 67P's coma, highlighting the role of CO2 and electron impact excitation.

Findings

CO2 is a significant source of [OI] emission, more than H2O.

A persistent plume indicates local CO2/H2O ratio enhancement.

Electron temperatures decrease after March 2015, affecting emission intensities.

Abstract

The Wide Angle Camera of the OSIRIS instrument on board the Rosetta spacecraft is equipped with several narrowband filters that are centered on the emission lines and bands of various fragment species. These are used to determine the evolution of the production and spatial distribution of the gas in the inner coma of comet 67P with time and heliocentric distance, here between 2.6 - 1.3 AU pre-perihelion. Our observations indicate that the emission observed in the OH, OI, CN, NH, and NH2 filters is mostly produced by dissociative electron impact excitation of different parent species. We conclude that CO2 rather than H2O is a significant source of the [OI] 630 nm emission. A strong plume-like feature observed in the in CN and [OI] filters is present throughout our observations. This plume is not present in OH emission and indicates a local enhancement of the CO2/H2O ratio by as much as a factor of 3. We observed a sudden decrease in intensity levels after March 2015, which we attribute to decreased electron temperatures in the first kilometers above the nucleus surface.