Rosetta’s plasma shock takes a bow

Comets can have very different size and shape bow shocks, plasma and magnetispheres. Rosetta's scientists could not find a bow shock far away from the active asteroid 67P and finally found weird things much closer to comet 67P/Churyumov–Gerasimenko.

Did they observe the formation of a cometary bow shock? Was it already there?

Significant changes to the electromagnetic, electrochemical nature of the comets interaction with the Electric Sun and its solar plasma wind seem to have happened to then either create the new bow shock or increase its structure in different ways.

A new study reveals that, contrary to first impressions, Rosetta did detect signs of an infant bow shock at the comet it explored for two years – the first ever seen forming anywhere in the solar system... Rosetta looked for signs of such a feature over its two-year mission, and ventured over 1500 km away from 67P's centre on the hunt for large-scale boundaries around the comet – but apparently found nothing...

However, it seems that the spacecraft actually did find a bow shock, but that it was in its infancy. In a new analysis of the data, we eventually spotted it around 50 times closer to the comet's nucleus than anticipated in the case of 67P. It also moved in ways we didn't expect, which is why we initially missed it.
Rosetta witnesses birth of baby bow shock around comet | phys.org

Rosetta comet bow shock plasma

The bow shock is the first boundary the solar wind encounters as it approaches planets or comets. The Rosetta spacecraft was able to observe the formation of a bow shock by following comet 67P/Churyumov–Gerasimenko toward the Sun, through perihelion, and back outward again. The spacecraft crossed the newly formed bow shock several times during two periods a few months before and after perihelion; it observed an increase in magnetic field magnitude and oscillation amplitude, electron and proton heating at the shock, and the diminution of the solar wind further downstream. Rosetta observed a cometary bow shock in its infancy, a stage in its development not previously accessible to in situ measurements at comets and planets...

Ion dynamics, as described by single-particle models of solar wind protons gyrating in the magnetic field of the coma (Behar et al. 2017), may influence the shape of the infant bow shock. However, our observations of ion and electron heating together with magnetic field enhancements and oscillations at infant bow shocks show that the physics goes beyond a single-particle description. When the comet was closer to the Sun – with respect to the events reported here – the ion production rate increased, causing the bow shock to move further upstream, and it could not be observed in situ by the Rosetta spacecraft. Observations of cometary water group ions from the upstream regions have indicated the presence of a boundary 4000 km upstream of the nucleus for a heliocentric distance of 1.4 AU (Nilsson et al. 2007).
The infant bow shock: a new frontier at a weak activity comet

Rosetta bow shock plasma

Rosetta's plasma bow shocks

The research is still based on mathematical models but using observed data.

Are comet bow shocks, cometopause, magnetospheres, ionopause, variations of electromagnetic plasma spheres, plasma layers, double layers, filaments etc?

Rosetta bow shocks

Comets offer scientists an extraordinary way to study the plasma in the solar system. Plasma is a hot, gaseous state of matter comprising charged particles, and is found in the solar system in the form of the solar wind: a constant stream of particles flooding out from our star into space... Bow shocks have been found around comets, too – Halley's comet being a good example. Plasma phenomena vary as the medium interacts with the surrounding environment, changing the size, shape, and nature of structures such as bow shocks over time...

explored data from the Rosetta Plasma Consortium, a suite of instruments comprising five different sensors to study the plasma surrounding Comet 67P. They combined the data with a plasma model to simulate the comet's interactions with the solar wind and determine the properties of the bow shock.

The scientists found that, when the forming bow shock washed over Rosetta, the comet's magnetic field became stronger and more turbulent, with bursts of highly energetic charged particles being produced and heated in the region of the shock itself. Beforehand, particles had been slower-moving, and the solar wind had been generally weaker – indicating that Rosetta had been 'upstream' of a bow shock.
Rosetta witnesses birth of baby bow shock around comet | phys.org

comets ionopause cometopause

Early observations of Earth’s bow shock showed a sharp increase in the magnetic field as the solar wind passes the shock, followed by a number of oscillations in the downstream region (Heppner et al. 1967). At comets, bow shocks were observed during the flybys of 21P/Giacobini– Zinner (Jones et al. 1986), 1P/Halley (Gringauz et al. 1986a), and 26P/Grigg–Skjellerup (Neubauer et al. 1993). These bow shocks were found to be wider and more gradual than the sharp shocks seen at planets due to solar wind mass loading, and in some instances they have been called “bow waves” instead (Neubauer et al. 1993). These observations were made when the comets were close to perihelion and their bow shocks were fully developed. At comet 1P/Halley additional boundaries were found: a cometopause, which separates the solar wind from the cometary ion environment (Gringauz et al. 1986b), and a diamagnetic cavity (Neubauer et al. 1986).
The infant bow shock: a new frontier at a weak activity comet