Boundaries in the plasma around comet 67P separate regions with different properties. Many have been identified, including a new boundary called an infant bow shock. Here, we investigate how the plasma and fields behave at this boundary and where it can be found. The main result is that the infant bow shock occurs at intermediate activity and intermediate distances to the comet. Most plasma parameters behave as expected; however, some inconsistencies indicate that the boundary is non-stationary.

When the magnetised solar wind meets the plasma surrounding a comet, the magnetic field is enhanced in front of the comet, and the field lines are draped around it. This happens because electric currents are induced in the plasma. When these currents flow through the plasma, they can generate waves. In this article we present observations of ion acoustic waves, which is a kind of sound wave in the plasma, detected by instruments on the Rosetta spacecraft near comet 67P/Churyumov–Gerasimenko.

The Earth's atmosphere is constantly losing molecules and charged particles, amongst them oxygen ions or O⁺. Quantifying this loss provides information about the evolution of the atmosphere on geological timescales. In this study, we investigate the final destination of O⁺ observed with Cluster satellites in a high-altitude magnetospheric region (plasma mantle) by tracing the particles forward in time using simulations. We find that approximately 98 % of O⁺ escapes the Earth's magnetosphere.

In a simulation study of the downward current region of the aurora, i.e. where electrons are accelerated upward, double layers are seen to form at low altitude and move upward until they are disrupted at altitudes of ten thousand kilometres or thereabouts. When one double layer is disrupted a new one forms below, and the process repeats itself. The repeated demise and reformation allows ions to flow upward without passing through the double layers that otherwise would have kept them down.

In this paper, we simulate the plasma on a magnetic field line above the aurora. Initially, about half of the acceleration voltage is concentrated in a thin double layer at a few thousand km altitude. When the voltage is lowered, electrons trapped between the double layer and the magnetic mirror are released. In the process we see formation of electron beams and phase space holes. A temporary reversal of the polarity of the double layer is also seen as well as hysteresis effects in its position.