This animation shows a simulated view of ESA’s Rosetta spacecraft at its target, Comet 67P/Churyumov-Gerasimenko, on 24 February 2016.
The comet is represented in grey in the left-hand frame, while the small cyan satellite represents the simulated Rosetta spacecraft. The simulation reconstructs the plasma conditions when Rosetta spotted an infant bow shock in the process of ‘unforming’: this infant bow shock can be seen as the sweeping red-yellow curve. The colours show the proton density for the region – the number of protons found within a cubic cm – as indicated in the bar at the top, with red-yellow being a high and black-blue a low density. In this frame, the Sun is on the right-hand side, meaning that the solar wind flows from right to left.
As Rosetta circles around the comet in this simulation, crossing the bow shock twice, the associated patterns observed in proton and water ion abundances and energies can be seen in the upper and central panels on the right, with the moving cyan line representing Rosetta’s location. This demonstrates how the major types of charged particles in the vicinity of the forming bow shock change along with Rosetta’s simulated location, and how the distribution of protons becomes wider in the region of the shock than in the surrounding solar wind (shown in the two vertical stripes of red in the top right panel). The bars to the right indicate the differential particle flux to the instrument – the number of particles passing through a given area per unit time and solid angle (a measure of the instrument’s field of view) – with red being high and black being low. The scales to the left indicate particle energies.
The magnetic field strength around the comet can be seen in the bottom-right panel. As the simulated Rosetta crosses the shock, two spikes appear in the field strength, which also correlate with the shock-related effects seen in the upper two right-hand panels.
Credit: ESA/Rosetta/RPC; H. Gunell et al (2018).