Cometary Electron Heating Driven by Solar Wind Interaction with the Coma

Rosetta's observations of 67P/Churyumov-Gerasimenko have highlighted the dynamic nature of a comet's plasma environment. In this work, we study the suprathermal electrons excited in the coma using observations from the Ion and Electron Sensor (IES) and other instruments onboard the Rosetta spacecraft. We fit the IES electron observations with the summation of 2 kappa distributions, which are characterized as a dense, warm population and a rarefied, hot population. The parameters of our fitting technique determine the populations' density, temperature, and invariant kappa index. It was previously determined that the hot population is likely solar wind halo electrons, but the warm population remains a mystery. Consequently, we focus our analysis on the warm population to determine its origin by comparing the density and temperature to the neutral density and magnetic field strength. We find that the warm electron temperature above 100,000 K is strongly correlated with the neutral density, which is in contrast to previous results that found cometary electron temperature to be anti-correlated with neutral density. Additionally, we found that the warm electron temperature is closely related to the electrostatic wave power near the lower hybrid frequency. We conclude that the warm electron population is being heated by lower hybrid waves driven by the two-stream instability of solar wind protons and newly-formed, cometary ions created in localized, dense neutral streams.