Modified ion-Weibel instability as a possible source of wave activity at Comet 67P/Churyumov-Gerasimenko

Meier, Patrick; Glaßmeier, Karl‐Heinz; Motschmann, U.

doi:10.5194/angeo-34-691-2016

Cited by 32 publications

(56 citation statements)

References 42 publications

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“…Prominent features are the increase in Bo and the rotation in the field direction. Detailed analyses of the magnetic field indicate the disappearance of low-frequency waves (tens of mHz), usually observed in the close plasma environment of the comet (Richter et al 2015(Richter et al , 2016Koenders et al 2016;Meier et al 2016), at the time of the outburst (see Sects. 2.3 and 2.4).…”

Section: Observationsmentioning

confidence: 99%

“…7. Small yellow and green regions within the frequency range of ∼10-100 mHz in the frequency spectrum indicate magnetic "singing comet waves" (Richter et al 2015(Richter et al , 2016Koenders et al 2016;Meier et al 2016). These singing comet waves disappear or become weakened between ∼1000 and 1300 UT, as shown by the reduced wave amplitudes shown in the right panels.…”

Section: Wave Characteristics During the Cometary Outburstmentioning

confidence: 99%

“…A modified ion-Weibel instability (Chang et al 1990) associated with newborn cometary ion current under low cometary activity was proposed as a possible source mechanism for this new type of waves at 67P (Meier et al 2016). Accordingly, under the low cometary activity conditions, when 67P was at ∼2.0 AU from the Sun or beyond, newborn ions moving transversely to the ambient magnetic field and the solar wind flowing in the direction of the electric field constitute a cross-field current that can trigger the ion-Weibel instability.…”

Section: Disappearance Of the Singing Comet Wavesmentioning

confidence: 99%

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Impact of a cometary outburst on its ionosphere

Hajra¹,

Henri²,

Vallières³

et al. 2017

A&A

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We present a detailed study of the cometary ionospheric response to a cometary brightness outburst using in situ measurements for the first time. The comet 67P/Churyumov-Gerasimenko (67P) at a heliocentric distance of 2.4 AU from the Sun, exhibited an outburst at ∼1000 UT on 19 February 2016, characterized by an increase in the coma surface brightness of two orders of magnitude. The Rosetta spacecraft monitored the plasma environment of 67P from a distance of 30 km, orbiting with a relative speed of ∼0.2 m s −1 . The onset of the outburst was preceded by pre-outburst decreases in neutral gas density at Rosetta, in local plasma density, and in negative spacecraft potential at ∼0950 UT. In response to the outburst, the neutral density increased by a factor of ∼1.8 and the local plasma density increased by a factor of ∼3, driving the spacecraft potential more negative. The energetic electrons (tens of eV) exhibited decreases in the flux of factors of ∼2 to 9, depending on the energy of the electrons. The local magnetic field exhibited a slight increase in amplitude (∼5 nT) and an abrupt rotation (∼36.4• ) in response to the outburst. A weakening of 10-100 mHz magnetic field fluctuations was also noted during the outburst, suggesting alteration of the origin of the wave activity by the outburst. The plasma and magnetic field effects lasted for about 4 h, from ∼1000 UT to 1400 UT. The plasma densities are compared with an ionospheric model. This shows that while photoionization is the main source of electrons, electron-impact ionization and a reduction in the ion outflow velocity need to be accounted for in order to explain the plasma density enhancement near the outburst peak.

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Section: Observationsmentioning

confidence: 99%

Section: Wave Characteristics During the Cometary Outburstmentioning

confidence: 99%

Section: Disappearance Of the Singing Comet Wavesmentioning

confidence: 99%

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Impact of a cometary outburst on its ionosphere

Hajra¹,

Henri²,

Vallières³

et al. 2017

A&A

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“…A survey of the plasma environment of 67P/Churyumov-Gerasimenko was performed by Odelstad et al (2015), who reported electron temperatures around 5 eV. Low frequency wave activity -the peak of the spectrum at approximately 40 mHz -was discovered by Richter et al (2015), observed simultaneously at two points by Rosetta and the Philae lander , and has been interpreted in terms of a modified ion-Weibel instability (Meier et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Ion acoustic waves at comet 67P/Churyumov-Gerasimenko

Gunell

Nilsson

Hamrin

et al. 2017

A&A

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Context. On 20 January 2015 the Rosetta spacecraft was at a heliocentric distance of 2.5 AU, accompanying comet 67P/ChuryumovGerasimenko on its journey toward the Sun. The Ion Composition Analyser (RPC-ICA), other instruments of the Rosetta Plasma Consortium, and the ROSINA instrument made observations relevant to the generation of plasma waves in the cometary environment. Aims. Observations of plasma waves by the Rosetta Plasma Consortium Langmuir probe (RPC-LAP) can be explained by dispersion relations calculated based on measurements of ions by the Rosetta Plasma Consortium Ion Composition Analyser (RPC-ICA), and this gives insight into the relationship between plasma phenomena and the neutral coma, which is observed by the Comet Pressure Sensor of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis instrument (ROSINA-COPS). Methods. We use the simple pole expansion technique to compute dispersion relations for waves on ion timescales based on the observed ion distribution functions. These dispersion relations are then compared to the waves that are observed. Data from the instruments RPC-LAP, RPC-ICA and the mutual impedance probe (RPC-MIP) are compared to find the best estimate of the plasma density. Results. We find that ion acoustic waves are present in the plasma at comet 67P/Churyumov-Gerasimenko, where the major ion species is H 2 O + . The bulk of the ion distribution is cold, k B T i = 0.01 eV when the ion acoustic waves are observed. At times when the neutral density is high, ions are heated through acceleration by the solar wind electric field and scattered in collisions with the neutrals. This process heats the ions to about 1 eV, which leads to significant damping of the ion acoustic waves. Conclusions. In conclusion, we show that ion acoustic waves appear in the H 2 O + plasmas at comet 67P/Churyumov-Gerasimenko and how the interaction between the neutral and ion populations affects the wave properties.

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“…Two mechanisms have been discussed in literature thus far: (i) heating of electrons through wave particle interactions, such as the singing comet waves (understood as an ion Weibel instability [43,52]) or lower hybrid waves [45], and (ii) the acceleration of electrons along the ambipolar electric field [29]. In the second scenario, solar wind electrons traveling toward the comet fall into the potential well that is generated by the gradient in electron number density [53,54].…”

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confidence: 99%

3D View of a Comet’s Neighborhood

DeForest

2017

Physics

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Using a 3D fully kinetic approach, we disentangle and explain the ion and electron dynamics of the solar wind interaction with a weakly outgassing comet. We show that, to first order, the dynamical interaction is representative of a four-fluid coupled system. We self-consistently simulate and identify the origin of the warm and suprathermal electron distributions observed by ESA's Rosetta mission to comet 67P/Churyumov-Gerasimenko and conclude that a detailed kinetic treatment of the electron dynamics is critical to fully capture the complex physics of mass-loading plasmas.

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Modified ion-Weibel instability as a possible source of wave activity at Comet 67P/Churyumov-Gerasimenko

Cited by 32 publications

References 42 publications

Impact of a cometary outburst on its ionosphere

Impact of a cometary outburst on its ionosphere

Ion acoustic waves at comet 67P/Churyumov-Gerasimenko

3D View of a Comet’s Neighborhood

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