RPC-IES observations of the development and variability of plasma interaction regions near 67P/Churyumov-Gerasimenko

Spacecraft flybys of comets have provided observations of different solar wind-cometary plasma interaction regions separated by boundaries. Past observations were limited to a few high-velocity flybys, so some regions remain poorly understood. Various modeling techniques provide important insight, but do not answer all questions. One unusual region that is difficult to explain with models is called the "Mystery" region. This region was observed on a few flybys on the sunward side beginning well after the bow shock and terminating with a "Mystery" boundary located halfway between the bow shock and the comet. Within this region there is a significant increase in "hot" electrons (> 800 eV) and solar wind He++. The "Mystery" boundary is characterized by a rapid decrease in hot electrons, solar wind He++, and total ion mass flux, along with an increase in cometary ions. The magnetic field did not vary within this region or across the boundary. Rosetta is uniquely placed to improve understanding of plasma interaction regions because the spacecraft remains close (< 1500 km) to comet 67P for an extended period of time. Recent observations by the Rosetta Plasma Consortium (RPC) Ion Electron Spectrometer (IES) suggest that the spacecraft frequently crosses a boundary between two interaction regions that bears some resemblance to the "Mystery" boundary. The timing and location of these boundary crossings appear to correlate with solar wind activity extrapolated to the Rosetta location, suggesting a complex and dynamic plasma interaction environment.