The Convective Electric Field Influence on the Cold Plasma and Diamagnetic Cavity of Comet 67P

Edberg, Niklas J. T.; Eriksson, Anders; Vigren, Erik; Johansson, Folke; Goetz, Charlotte; Nilsson, Hans; Gilet, Nicolas; Henri, Pierre

doi:10.3847/1538-3881/ab2d28

Cited by 10 publications

(12 citation statements)

References 37 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The physics of the region is still under debate but Odelstad et al (2018) showed that cold electrons were almost always observed in large amounts inside the diamagnetic cavity. Edberg et al (2019) found that the observations of cold electrons in the diamagnetic cavity were organized by the direction of the solar wind convective electric field. More cold electrons were observed in the −E conv hemisphere that was the main direction inside the diamagnetic cavity.…”

Section: Observations Of Cold Cometary Electrons Inside Diamagnetic Cmentioning

confidence: 99%

See 1 more Smart Citation

Observations of a mix of cold and warm electrons by RPC-MIP at 67P/Churyumov-Gerasimenko

Gilet

Henri

Wattieaux

et al. 2020

A&A

View full text Add to dashboard Cite

Context. The Mutual Impedance Probe (MIP) of the Rosetta Plasma Consortium (RPC) onboard the Rosetta orbiter which was in operation for more than two years, between August 2014 and September 2016 to monitor the electron density in the cometary ionosphere of 67P/Churyumov-Gerasimenko. Based on the resonance principle of the plasma eigenmodes, recent models of the mutual impedance experiment have shown that in a two-electron temperature plasma, such an instrument is able to separate the two isotropic electron populations and retrieve their properties. Aims. The goal of this paper is to identify and characterize regions of the cometary ionized environment filled with a mix of cold and warm electron populations, which was observed by Rosetta during the cometary operation phase. Methods. To reach this goal, this study identifies and investigates the in situ mutual impedance spectra dataset of the RPC-MIP instrument that contains the characteristics of a mix of cold and warm electrons, with a special focus on instrumental signatures typical of large cold-to-total electron density ratio (from 60 to 90%), that is, regions strongly dominated by the cold electron component. Results. We show from the observational signatures that the mix of cold and warm cometary electrons strongly depends on the cometary latitude. Indeed, in the southern hemisphere of 67P, where the neutral outgassing activity was higher than in northern hemisphere during post-perihelion, the cold electrons were more abundant, confirming the role of electron-neutral collisions in the cooling of cometary electrons. We also show that the cold electrons are mainly observed outside the nominal electron-neutral collision-dominated region (exobase), where electrons are expected to have cooled down. This which indicates that the cold electrons have been transported outward. Finally, RPC-MIP detected cold electrons far from the perihelion, where the neutral outgassing activity is lower, in regions where no electron exobase was expected to have formed. This suggests that the cometary neutrals provide a more frequent or efficient cooling of the electrons than expected for a radially expanding ionosphere.

show abstract

Section: Observations Of Cold Cometary Electrons Inside Diamagnetic Cmentioning

confidence: 99%

“…Fifth panel: Rosetta latitude (green line) expressed in degrees and the heliocentric distance (yellow line). Edberg et al 2019). The cold electrons observed by RPC-MIP inside the diamagnetic cavity are discussed in Sect.…”

Section: Overview Of the Detection And The Location Of Cold Cometary mentioning

confidence: 99%

Observations of a mix of cold and warm electrons by RPC-MIP at 67P/Churyumov-Gerasimenko

Gilet

Henri

Wattieaux

et al. 2020

A&A

View full text Add to dashboard Cite

show abstract

“…To convert the positions from the CSEQ frame into the CSE frame, we used the average local magnetic field outside the cavity in each cavity crossing. No solar wind ions were recorded locally because Rosetta was inside the SWIC (Behar et al 2017), but because the clock angle of the magnetic field in the upstream solar wind tended to remain the same in the inner coma (Edberg et al 2019), we can assume a general anti-sunward motion of the magnetic field (bulk plasma) and thus the motional electric field would point upward (+Z CSE ). Nevertheless, we do not see any asymmetry in the spatial distribution of the accelerated ions in either of the two coordinate systems.…”

Section: Subperiod P1 P2 P3mentioning

confidence: 99%

Flow pattern of accelerated cometary ions inside and outside the diamagnetic cavity of comet 67P/Churyumov-Gerasimenko

Masunaga

Nilsson

Béhar

et al. 2019

A&A

View full text Add to dashboard Cite

Analyzing data from the Ion Composition Analyzer on board the Rosetta spacecraft, we studied a flow pattern of accelerated cometary ions (40–80 eV) inside and outside the diamagnetic cavity of comet 67P/Churyumov-Gerasimenko (67P). We found that the accelerated ions are intermittently observed and are ten times more frequently observed outside the cavity than inside, and they mainly flow tailward with an aberration (~20–40°). We suggest that they are accelerated by the tailward polarization electric field upstream of the comet. Because their occurrence frequency becomes lowest near perihelion where the water production rate is highest at 67P, ion-neutral collisions and/or charge exchange may play a role in controlling the occurrence frequency. The aberration pattern is different inside and outside the cavity in the cometocentric solar equatorial (CSEQ) frame but it is consistent in the comet-Sun electric (CSE) frame; the latter is rotated from the CSEQ frame about the comet-Sun line so that the Z-axis is aligned with the local motional electric field. Because the flow pattern of the accelerated ions inside the cavity in the CSE frame is the same as outside, we suggest that the flow pattern inside is determined by the flow outside, depending on the local plasma and magnetic field. Near the CSE polar plane the aberration is in the opposite direction of the motional electric field, while it is in the anti-cometward direction near the CSE equator plane. The aberration in the anti-electric-field direction near the CSE polar plane suggests that the accelerated ions are mass-loaded by local cold cometary ions, just like the mass-loading of the solar wind by cold cometary ions. The cause of the anti-cometward aberration near the CSE equator plane is still unknown, but this may indicate that the tailward-flowing cometary ions are deflected across the upstream boundaries or by an outward-pointing ambipolar electric field.

show abstract

“…For this comparison, the solar wind direction is simply assumed as the direction away from the Sun. This has been shown to be a good estimator for the CSE system (Edberg et al, 2019). The local solar wind velocity at this stage in the cometary development is not representative of the upstream solar wind direction, because of deflection (Nilsson et al, 2017).…”

Section: Location Of the Eventsmentioning

confidence: 99%

“…In this regime the cometary ions are accelerated by the convective electric field far upstream of the comet and a polarisation and ambipolar electric field closer to the nucleus (Nilsson et al, 2018;Gunell et al, 2019). The presence of the convective electric field induces an asymmetry in the interaction region that has consequences for all plasma parameters (Koenders et al, 2016a, b;Edberg et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Warm protons at comet 67P/Churyumov-Gerasimenko – Implications for the infant bow shock

Goetz¹,

Gunell²,

Johansson³

et al. 2020

Preprint

Self Cite

View full text Add to dashboard Cite

Abstract. Multiple plasma boundaries have been observed at comet 67P/Churyumov-Gerasimenko. Among them was an infant bow shock, an asymmetric structure in the plasma environment that separates the less disturbed solar wind from a plasma with warmer, slower protons. Rosetta crossings of the infant bow shock have so far only been reported for two days. Here, we aim to investigate this phenomenon further by focusing on the proton behaviour and surveying all of the Rosetta comet phase data. We find over 300 events that match the proton signatures at the infant bow shock. We investigate the properties of the plasma and magnetic field at this boundary and the location where it can be found. We find that the protons are preferentially detected at intermediate gas production rates with a slight trend towards larger cometocentric distances for higher gas production rates. The events can mostly be found in the positive convective electric field hemisphere. Both results agree well with simulations of the infant bow shock. The properties of the plasma are harder to constrain, but there is a trend towards higher electron flux, lower magnetic field, higher magnetic field power spectral density, and higher density in the region that contains the warm protons. This is in partial agreement with the previous IBS definitions, however it also indicates that the plasma and this structure are highly non-stationary. For future research, Comet Interceptor, with its multi-point measurements, can help to disentangle the spatial and temporal effects and give more clarity on the influence of changing upstream conditions on the movement of boundaries in this unusual environment.

show abstract

The Convective Electric Field Influence on the Cold Plasma and Diamagnetic Cavity of Comet 67P

Cited by 10 publications

References 37 publications

Observations of a mix of cold and warm electrons by RPC-MIP at 67P/Churyumov-Gerasimenko

Observations of a mix of cold and warm electrons by RPC-MIP at 67P/Churyumov-Gerasimenko

Flow pattern of accelerated cometary ions inside and outside the diamagnetic cavity of comet 67P/Churyumov-Gerasimenko

Warm protons at comet 67P/Churyumov-Gerasimenko – Implications for the infant bow shock

Contact Info

Product

Resources

About