Evolution of the magnetic field at comet 67P/Churyumov-Gerasimenko

Abstract

The magnetic field at a comet is significantly influenced by the solar wind on one side and the outgassing rate on the other. There are no simple spatial models for the magnetic field direction, neither at a comet with low outgassing rates (∼10²⁵ s^-1) where ion gyroradius effects are non-negligible, nor at high outgassing rates (∼10²⁷ s^-1) where plasma boundaries form. However, the long duration of the European Space Agency Rosetta mission has made it possible to track the evolution of the magnetic field while comet 67P/Churyumov-Gerasimenko approaches the Sun. Herein we present a simple model that fits the data quite well, depending on input parameters. The study also includes the influence of the comet's gas production rate and the solar wind conditions, which both have complex effects on the magnetic field, but are clearly recognizable. The evolution of the magnetic field direction related to draping is more complex than previously suggested. Classical draping only exists at the comet for high outgassing rates, for lower rates, the magnetic field roughly follows the Parker angle. It is shown that the interaction of the solar wind with the comet can be roughly divided into three main classes.