Possible observation of charged nanodust from comet 67P/Churyumov–Gerasimenko: An analysis for the ROSETTA mission

Abstract

Nanodust particles are ubiquitous in the solar system; we may expect that comet 67P/Churyumov–Gerasimenko, the target of the upcoming ROSETTA mission, is also a source of nanodust, that is dust particles of nanometer size. Due to their small size and mass, the dust detectors cannot observe them directly neither on the orbiter nor on the Philae lander. However, if nanodust grains get charged, the ion and electron sensors on board of the orbiter might detect them.In this study we investigate whether this is a realistic option. We show that when the comet activity is low between 3.25 and 2.7AU, the cometary surface and a part of the dust particles get charged due to the charging currents of the solar wind and photoionization as a result of solar radiation. The nucleus׳ surface potential depends on the solar wind density, and it is higher than +4V for solar zenith angle between 0° and 50° for solar wind density n(d=1AU)=4×10−6m−3, and nano-size dust gets immediately accelerated when it collected Q=+1e positive charge due to photoelectron emission. The energy of this charged nanodust is higher than 4eV and it could be detected not far from the subsolar region by the ion and electron sensor (IES) of the Rosetta Plasma Package. In this paper we examine this process in detail.