On positively charged dust in the coma of comet 67P

Vigren, Erik; Eriksson, Anders; Bergman, Sofia

doi:10.1093/mnras/stac869

Cited by 4 publications

(3 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Photoelectron emission counteracts the negative charge and may even (depending on the electron temperature) charge grains predominantly positively, but a follow-up study showed that positive grains also cannot carry a significant amount of the total charge in the plasma Vigren et al. ( 2022 ).…”

Section: Plasmamentioning

confidence: 99%

See 1 more Smart Citation

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%

“…From the theoretical models applied to dust observations as described above (Vigren et al. 2021 , 2022 ), the likely answer is no. This contrasts to the strong electron depletion inferred for the Enceladus plume (Morooka 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

show abstract

“…where ν is the total ionisation frequency, r 0 (<< r) is the radius of the comet, and u i is the ion expansion velocity assumed constant and equal to the neutral velocity such that u n = u i = u. In this paper, we assume that the ion density is equal to the electron density, and no charged dust is present (Vigren et al 2021(Vigren et al , 2022. Further assumptions are needed to reach these expressions including equal ionisation frequency at all distances and stability on timescales of weeks.…”

Section: Introductionmentioning

confidence: 99%

Radial distribution of plasma at comet 67P

Edberg

Johansson

Eriksson

et al. 2022

A&A

Self Cite

View full text Add to dashboard Cite

Context. The Rosetta spacecraft followed comet 67P/Churyumov-Gerasimenko (67P) for more than two years at a slow walking pace (∼ 1 m/s) within 1500 km from the nucleus. During one of the radial movements of the spacecraft in the early phase of the mission, the radial distribution of the plasma density could be estimated, and the ionospheric density was found to be inversely proportional to the cometocentric distance r from the nucleus (a 1/r distribution).Aims. This study aims to further characterise the radial distribution of plasma around 67P throughout the mission and to expand on the initial results. We also aim to investigate how a 1/r distribution would be observed during a flyby with a fast (∼ 10's km/s) spacecraft, such as the upcoming Comet Interceptor mission, when there is also an asymmetry introduced to the outgassing over the comet surface. Methods. To determine the radial distribution of the plasma, we used data from the Langmuir probe (LAP) and Mutual Impedance (MIP) instruments from the Rosetta Plasma Consortium (RPC) during six intervals throughout the mission, for which the motion of Rosetta was approximately radial with respect to the comet. We then simulated what distribution a fast flyby mission would actually observe during its passage through a coma when there is a 1/r plasma density distribution as well as a sinusoidal variation with a phase angle (and then a sawtooth variation) multiplied to the outgassing rate.Results. The plasma density around comet 67P is found to roughly follow a 1/r dependence, although significant deviations occur in some intervals. If we normalise all data to a common outgassing rate (or heliocentric distance) and combine the intervals to a radial range of 10-1500 km, we find a 1/r 1.19 average distribution. The simulated observed density from a fast spacecraft flying through a coma with a 1/r distribution and an asymmetric outgassing can, in fact, appear anywhere in the range from a 1/r distribution to a 1/r 2 distribution, or even slightly outside of this range. Conclusions. The plasma density is distributed in such a way that it approximately decreases in a manner that is inversely proportional to the cometocentric distance. This is to be expected from the photoionisation of a collision-less, expanding neutral gas at a constant ionisation rate and expansion speed. The deviation from a pure 1/r distribution is in many cases caused by asymmetric outgassing over the surface, additional ionisation sources being present, electric fields accelerating plasma, and changing upstream solar wind conditions. A fast flyby mission can observe a radial distribution that deviates significantly from a 1/r trend if the outgassing is not symmetric over the surface. The altitude profile that will be observed depends very much on the level of outgassing asymmetry, the flyby velocity, the comet rotation rate, and the rotation phase. It is therefore essential to include data from both the inbound and outbound legs, as well as to compare plasma density to neutral density to get a more ...

show abstract