Suprathermal electrons near the nucleus of comet 67P/Churyumov‐Gerasimenko at 3 AU: Model comparisons with Rosetta data

Madanian, Hadi; Cravens, T. E.; Rahmati, Ali; Goldstein, R.; Burch, J. L.; Eriksson, Anders; Edberg, Niklas J. T.; Henri, Pierre; Mandt, K.; Clark, G.; Rubin, Martin; Broiles, T. W.; Reedy, N. L.

doi:10.1002/2016ja022610

Cited by 54 publications

(91 citation statements)

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“…The data set presented here has not been corrected for the spacecraft potential, though for the quantitative analysis we have carried out, the electron flux density has been corrected (see Section 3.4.3). The hot electron population detected by RPC-IES includes various sources, such as photoelectrons -produced by solar EUV radiation in the coma -and solar wind electrons, all which may have been affected by different acceleration mechanisms (Clark et al 2015;Broiles et al 2016b;Madanian et al 2016). The RPC-IES electron count rates are found to be primarily anti-correlated with the ROSINA-COPS neutral density (including during period T1).…”

Section: Overview Of the Selected Daysmentioning

confidence: 98%

“…The electron-impact ionization frequency at the location of Rosetta is derived from the hot electron intensity I IES e measured by RPC-IES electron spectrometer (Burch et al 2007;Broiles et al 2016a;Madanian et al 2016). For a given neutral species, it is calculated as follows:…”

Section: Rpc-ies Electron-impact Ionization Frequencymentioning

confidence: 99%

“…They concluded that the electron population had been heated by lower hybrid waves, though it remains unclear what population -solar wind or cometary -it is heated from. Madanian et al (2016) also proposed the effect of ambipolar electric field with inward acceleration of electrons and, for more extreme cases, the compression of solar wind electrons associated with interplanetary shocks, as other energization processes of the electron population. The origin of the hot electrons is still under debate, but may be further constrained by the analysis of additional cases under different outgassing activities, seasons and conditions in the space environment of comet 67P.…”

Section: O N C L U S I O Nmentioning

confidence: 99%

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Ionospheric plasma of comet 67P probed byRosettaat 3 au from the Sun

Galand

Héritier

Odelstad

et al. 2016

Mon. Not. R. Astron. Soc.

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170

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We propose to identify the main sources of ionization of the plasma in the coma of comet 67P/Churyumov-Gerasimenko at different locations in the coma and to quantify their relative importance, for the first time, for close cometocentric distances (<20 km) and large heliocentric distances (>3 au). The ionospheric model proposed is used as an organizing element of a multi-instrument data set from the Rosetta Plasma Consortium (RPC) plasma and particle sensors, from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis and from the Microwave Instrument on the Rosetta Orbiter, all on board the ESA/Rosetta spacecraft. The calculated ionospheric density driven by Rosetta observations is compared to the RPC-Langmuir Probe and RPC-Mutual Impedance Probe electron density. The main cometary plasma sources identified are photoionization of solar extreme ultraviolet (EUV) radiation and energetic electron-impact ionization. Over the northern, summer hemisphere, the solar EUV radiation is found to drive the electron density -with occasional periods when energetic electrons are also significant. Over the southern, winter hemisphere, photoionization alone cannot explain the observed electron density, which reaches sometimes higher values than over the summer hemisphere; electron-impact ionization has to be taken into account. The bulk of the electron population is warm with temperature of the order of 7-10 eV. For increased neutral densities, we show evidence of partial energy degradation of the hot electron energy tail and cooling of the full electron population.

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Section: Overview Of the Selected Daysmentioning

confidence: 98%

Section: Rpc-ies Electron-impact Ionization Frequencymentioning

confidence: 99%

Section: O N C L U S I O Nmentioning

confidence: 99%

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Ionospheric plasma of comet 67P probed byRosettaat 3 au from the Sun

Galand

Héritier

Odelstad

et al. 2016

Mon. Not. R. Astron. Soc.

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170

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“…It is possible that a fraction of the electrons belong to a hotter -suprathermal -distribution. Such suprathermal electrons, with kinetic energies of approximately 100 eV and densities at a level of 10% of the thermal densities, were observed at comet 67P/ChuryumovGerasimenko by Madanian et al (2016). While the presence of suprathermal electrons can support electron acoustic waves, a suprathermal to thermal density ratio of above 0.2 would be required (Mace & Hellberg 1990).…”

Section: Measured the Ratio Of The H 3 Omentioning

confidence: 99%

Ion acoustic waves at comet 67P/Churyumov-Gerasimenko

Gunell

Nilsson

Hamrin

et al. 2017

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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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“…2. Since the electron flux energy distribution is known to be variable, both in time and with distance to the nucleus (Madanian et al 2016), and not all cross sections have measured energy dependence, adjustments of up to 25%s are made to match the synthetic spectrum to the observed Alice spectrum.…”

Section: January 30mentioning

confidence: 99%

FUV Spectral Signatures of Molecules and the Evolution of the Gaseous Coma of Comet 67P/Churyumov–Gerasimenko

Feldman

A’Hearn

Bertaux

et al. 2017

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The Alice far-ultraviolet imaging spectrograph onboard Rosetta observed emissions from atomic and molecular species from within the coma of comet 67P/Churyumov-Gerasimenko during the entire escort phase of the mission from 2014 August to 2016 September. The initial observations showed that emissions of atomic hydrogen and oxygen close to the surface were produced by energetic electron impact dissociation of H 2 O. Following delivery of the lander, Philae, on 2014 November 12, the trajectory of Rosetta shifted to near-terminator orbits that allowed for these emissions to be observed against the shadowed nucleus that, together with the compositional heterogeneity, enabled us to identify unique spectral signatures of dissociative electron impact excitation of H 2 O, CO 2 , and O 2 . CO emissions were found to be due to both electron and photoexcitation processes. Thus we are able, from far-ultraviolet spectroscopy, to qualitatively study the evolution of the primary molecular constituents of the gaseous coma from start to finish of the escort phase. Our results show asymmetric outgassing of H 2 O and CO 2 about perihelion, H 2 O dominant before and CO 2 dominant after, consistent with the results from both the in situ and other remote sensing instruments on Rosetta.

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Suprathermal electrons near the nucleus of comet 67P/Churyumov‐Gerasimenko at 3 AU: Model comparisons with Rosetta data

Cited by 54 publications

References 60 publications

Ionospheric plasma of comet 67P probed byRosettaat 3 au from the Sun

Ionospheric plasma of comet 67P probed byRosettaat 3 au from the Sun

Ion acoustic waves at comet 67P/Churyumov-Gerasimenko

FUV Spectral Signatures of Molecules and the Evolution of the Gaseous Coma of Comet 67P/Churyumov–Gerasimenko

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