Abstract
We have investigated through simulation the electrostatic charging of the nucleus of Comet 67P/Churyumov–Gerasimenko during periods of weak outgassing activity. Specifically, we have modeled the surface potential and electric field at the surface of the nucleus during the initial Rosetta rendezvous at 3.5AU and the release of the Philae lander at 3AU. We have also investigated the possibility of dust acceleration and ejection above the nucleus due to electrostatic forces. Finally, we discuss these modeling results in the context of possible observations by instruments on both the Rosetta orbiter and the Philae lander.
Highlights
Comets are constantly exposed to incoming solar wind plasma, which in the rest frame of the comet is supersonic
We have presented the results of a self-similar model of the cometary plasma wake, showing that significantly enhanced electron temperatures may be expected at the nightside nucleus, leading to strongly negative surface potentials on the order of À300 to À 400 V in certain regions
We have explored the consequences of a lunar-like, reduced secondary emission yield, which allows the nightside nucleus to reach very large negative potentials, in the range of À 600 V to $ À 2 kV near the wake center
Summary
Comets are constantly exposed to incoming solar wind plasma, which in the rest frame of the comet is supersonic. Cometary volatiles at the surface and within the subsurface may sublimate and be expelled from the nucleus. As outgassing rates increase, the solar wind may be sufficiently decelerated (“mass loaded”) for several plasma structures to form, including a weak bow shock (Biermann et al, 1967) and a diamagnetic cavity where the plasma is purely cometary in origin (Ip and Axford, 1987). As cometary gas production rates typically vary by several orders of magnitude depending on the comet–Sun distance, the interaction between the comet and the solar wind will change substantially depending on its activity phase In the case of a comet that is weakly outgassing, either intrinsically so, or when a productive n Corresponding author at: Mullard Space Science Laboratory, University College London, Dorking, UK.
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