Ionospheric total electron content of comet 67P/Churyumov-Gerasimenko

Hajra, Rajkumar; Henri, Pierre; Vallières, Xavier; Galand, M.; Rubin, Martin; Tsurutani, B. T.; Gilet, Nicolas; Németh, Zoltán

doi:10.1051/0004-6361/201937022

Cited by 3 publications

(1 citation statement)

References 69 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“… 2019 ; Hajra et al. 2020 ). Multiple reasons for this discrepancy have been suggested and it is likely that it comes down to some combination of attenuation of the ionising UV radiation (Johansson et al.…”

Section: Plasmamentioning

confidence: 99%

The Plasma Environment of Comet 67P/Churyumov-Gerasimenko

et al. 2022

Self Cite

View full text Add to dashboard Cite

The environment of a comet is a fascinating and unique laboratory to study plasma processes and the formation of structures such as shocks and discontinuities from electron scales to ion scales and above. The European Space Agency’s Rosetta mission collected data for more than two years, from the rendezvous with comet 67P/Churyumov-Gerasimenko in August 2014 until the final touch-down of the spacecraft end of September 2016. This escort phase spanned a large arc of the comet’s orbit around the Sun, including its perihelion and corresponding to heliocentric distances between 3.8 AU and 1.24 AU. The length of the active mission together with this span in heliocentric and cometocentric distances make the Rosetta data set unique and much richer than sets obtained with previous cometary probes. Here, we review the results from the Rosetta mission that pertain to the plasma environment. We detail all known sources and losses of the plasma and typical processes within it. The findings from in-situ plasma measurements are complemented by remote observations of emissions from the plasma. Overviews of the methods and instruments used in the study are given as well as a short review of the Rosetta mission. The long duration of the Rosetta mission provides the opportunity to better understand how the importance of these processes changes depending on parameters like the outgassing rate and the solar wind conditions. We discuss how the shape and existence of large scale structures depend on these parameters and how the plasma within different regions of the plasma environment can be characterised. We end with a non-exhaustive list of still open questions, as well as suggestions on how to answer them in the future.

show abstract

Section: Plasmamentioning

confidence: 99%

The Plasma Environment of Comet 67P/Churyumov-Gerasimenko

et al. 2022

Self Cite

View full text Add to dashboard Cite

show abstract

A collisional test-particle model of electrons at a comet

Stephenson

Galand

Deca

et al. 2022

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

We have developed the first three-dimensional collisional model of electrons at a comet, which we use to examine the impact of electron-neutral collisions in the weakly outgassing regime. The test particle Monte Carlo model uses electric and magnetic fields from a fully kinetic Particle-in-Cell (PiC) model as an input. In our model, electrons originate from the solar wind or from ionisation of the neutral coma, either by electron-impact or absorption of an extreme ultraviolet photon. All relevant electron-neutral collision processes are included in the model including elastic scattering, excitation and ionisation. Trajectories of electrons are validated against analytically known drifts and the stochastic energy degradation used in the model is compared to the continuous slowing down approximation. Macroscopic properties of the solar wind and cometary electron populations, such as density and temperature, are validated with simple known cases and via comparison with the collisionless PiC model. We demonstrate that electrons are trapped close to the nucleus by the ambipolar electric field, causing an increase in the efficiency of electron-neutral collisions. Even at a low outgassing rate (Q = 1026 s−1), electron-neutral collisions are shown to cause significant cooling in the coma. The model also provides a multi-step numerical framework that is used to assess the influence of the electron-to-ion mass ratio, enabling access to electron dynamics with a physical electron mass.

show abstract

On positively charged dust in the coma of comet 67P

Vigren

Eriksson

Bergman

2022

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

Moment analysis of ion spectrograms measured by the Ion Composition Analyzer (ICA) in the coma of comet 67P typically produces an ion number density estimate markedly lower than the number density of free electrons as measured by the Mutual Impedance Probe (MIP) and the dual Langmuir Probe (LAP). While there are good reasons to distrust the ion density moment estimate in these circumstances, the issue cannot yet be considered fully understood and it is of interest to see if any natural non-instrumental cause is possible. An obvious such cause would be if a significant fraction of the positive charge density resides in positively charged dust grains that are not measured by the ICA. Here we show that this scenario is highly unlikely, even near perihelion where photoemission is the strongest. In our semi-analytical grain charging-model we balance the current contributions to grains of photoelectron emission and electron attachment as to find the expected charge state for a grain of a given radius. The charge state is affected by the ambient electron number density, the electron temperature and the heliocentric distance. While at times the bulk of the dust population around comet 67P could be charged positive, dust charging, including photoelectron emission, should have a negligible influence on the overall ionization balance in the cometary coma simply because the dust particles are not ubiquitous enough.

show abstract

Ionospheric total electron content of comet 67P/Churyumov-Gerasimenko

Cited by 3 publications

References 69 publications

The Plasma Environment of Comet 67P/Churyumov-Gerasimenko

The Plasma Environment of Comet 67P/Churyumov-Gerasimenko

A collisional test-particle model of electrons at a comet

On positively charged dust in the coma of comet 67P

Contact Info

Product

Resources

About