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

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 coronal mass ejection, are traced from Earth via Mars (using Mars Express and Mars Atmosphere and Volatile EvolutioN mission) 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 ∼1025–1026 s−1, the CIRs significantly influence the cometary plasma environment at altitudes down to 10–30 km. The ionospheric low‐energy (∼5 eV) plasma density increases significantly in all events, by a factor of >2 in events 1 and 2 but less in events 3 and 4. The spacecraft potential drops below −20 V upon impact when the flux of electrons increases. The increased density is likely caused by compression of the plasma environment, increased particle impact ionization, and possibly charge exchange processes and acceleration of mass‐loaded plasma back to the comet ionosphere. During all events, the fluxes of suprathermal (∼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 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. We also discuss the possibility of seeing some signatures of the ionospheric response to tail disconnection events.

Solar wind‐ and EUV‐dependent models for the shapes of the Martian plasma boundaries based on Mars Express measurements

“…The expansion of the IMB with increasing EUV also explains part of the trend in the BS distance as the stand-off distance of the obstacle is increasing; however, the trend is stronger for the BS implying that another mechanism is also in effect. Increased photoion production in the sheath, as suggested by Edberg et al [2009], could indeed be responsible for this mechanism, particularly as observations of pickup hydrogen by Yamauchi et al [2015] suggested that photoion production in the hydrogen corona is strongly dependent on EUV intensity.…”

The Convective Electric Field Influence on the Cold Plasma and Diamagnetic Cavity of Comet 67P

“…Photoionization creates free electrons with an energy of about 10 eV, and electrons from impact ionization have similar "warm" energy. At 67P, a significant amount of hot electrons, i.e., an energy of ∼100 eV, was present, believed to be heated through wave-particle interaction André et al 2017;Karlsson et al 2017) or through the interaction with the solar wind (Broiles et al 2015Edberg et al 2016aEdberg et al , 2016b. Cold electrons with an energy <1 eV were also observed, believed to have been cooled through collisions with neutrals before they reached Rosetta, and possibly also affected by ambipolar electric fields (Madanian et al 2016;Eriksson et al 2017;Gilet et al 2017;Vigren et al 2017;Engelhardt et al 2018;Vigren & Eriksson 2019).…”

CME impact on comet 67P/Churyumov-Gerasimenko

“…Besides the continuous growth and decay of the coma as the heliocentric distance decreases and increases, respectively, the plasma environment of the comet also exhibits large variations due to the changing solar wind. Edberg et al (2016) studied four cases of impacting corotating interaction regions on the comet from October to December 2014, as the comet activity grew stronger, and McKenna-Lawlor et al (2016) observed two CMEs arriving at 67P in September 2014, i.e. soon after Rosetta's arrival at the comet when the outgassing was relatively low.…”