Solar wind interaction with comet 67P: impacts of corotating interaction regions

TL;DR

This study uses Rosetta data to analyze how corotating interaction regions (CIRs) from the solar wind impact the plasma environment of comet 67P, revealing significant plasma and magnetic field responses during these solar wind disturbances.

Contribution

First detailed analysis of CIR impacts on comet 67P's plasma environment using multi-spacecraft observations, highlighting plasma density, potential, and magnetic field changes.

Findings

CIRs cause plasma density increases by over 2 times at comet 67P.

Magnetic field strength in the coma increases by a factor of 2-5 during CIR impacts.

Electron fluxes and energies significantly increase, indicating solar wind energy coupling.

Abstract

We present observations from the Rosetta Plasma Consortium of the effects of stormy solar wind on comet 67P/Churyumov-Gerasimenko. Four corotating interaction regions (CIRs), where the first event has possibly merged with a CME, are traced from Earth via Mars (using Mars Express and MAVEN) and to comet 67P from October to December 2014. When the comet is 3.1-2.7 AU from the Sun and the neutral outgassing rate $\sim10^{25}-10^{26}$ s$^{-1}$ the CIRs significantly influence the cometary plasma environment at altitudes down to 10-30 km. The ionospheric low-energy \textcolor{black}{($\sim$5 eV) plasma density increases significantly in all events, by a factor $>2$ in events 1-2 but less in events 3-4. The spacecraft potential drops below -20V upon impact when the flux of electrons increases}. The increased density is \textcolor{black}{likely} caused by compression of the plasma environment, increased particle impact ionisation, and possibly charge exchange processes and acceleration of mass loaded plasma back to the comet ionosphere. During all events, the fluxes of suprathermal ($\sim$10-100 eV) electrons increase significantly, suggesting that the heating mechanism of these electrons is coupled to the solar wind energy input. At impact the magnetic field strength in the coma increases by a factor of ~2-5 as more interplanetary magnetic field piles up around of the comet. During two CIR impact events, we observe possible plasma boundaries forming, or moving past Rosetta, as the strong solar wind compresses the cometary plasma environment. \textcolor{black}{We also discuss the possibility of seeing some signatures of the ionospheric response to tail disconnection events